[Federal Register Volume 60, Number 245 (Thursday, December 21, 1995)]
[Proposed Rules]
[Pages 66344-66469]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-29458]
[[Page 66343]]
_______________________________________________________________________
Part II
Environmental Protection Agency
_______________________________________________________________________
40 CFR Parts 260, 261, 266, and 268
_______________________________________________________________________
Hazardous Waste: Identification and Listing; Proposed Rule
Federal Register / Vol. 60, No. 245 / Thursday, December 21, 1995 /
Proposed Rules
[[Page 66344]]
ENVIRONMENTAL PROTECTION AGENCY
40 CFR Parts 260, 261, 266, and 268
[FRL-5337-9]
RIN 2050-AE07
Hazardous Waste Management System: Identification and Listing of
Hazardous Waste: Hazardous Waste Identification Rule (HWIR)
AGENCY: Environmental Protection Agency.
ACTION: Proposed rule, tentative response to Chemical Manufacturers
Association petition and the Hazardous Waste Identification Dialogue
Committee recommendations, and request for comments.
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SUMMARY: The Environmental Protection Agency (EPA) today is proposing
to amend its regulations under the Resource Conservation and Recovery
Act (RCRA) by establishing constituent-specific exit levels for low-
risk solid wastes that are designated as hazardous because they are
listed, or have been mixed with, derived from, or contain listed
hazardous wastes. Under this proposal, generators of listed hazardous
wastes that meet the self-implementing exit levels would no longer be
subject to the hazardous waste management system under Subtitle C of
RCRA as listed hazardous wastes. Today's Notice, commonly referred to
as the Hazardous Waste Identification Rule (HWIR), establishes a risk-
based ``floor'' to hazardous waste listings that will encourage
pollution prevention, waste minimization, and the development of
innovative waste treatment technologies.
Many of the exit levels are established using an innovative risk
assessment which evaluates potential exposure pathways, both direct and
indirect, from a variety of sources, such as waste piles and surface
impoundments. This assessment focuses on both human and environmental
receptors and is presented for comment in today's Notice. The remaining
exit levels are based on an alternative risk analysis.
The Agency is also proposing to modify some of the land disposal
restriction (LDR) numerical treatment standards listed in subpart D of
40 CFR part 268. This notice proposes to cap technology-based treatment
standards with the risk-based exit levels which minimize threats to
human health and the environment. This notice also takes comment on
several general approaches and one specific approach for conditional
exemptions from subtitle C management. Today's notice also contains the
Agency's tentative response to a petition for rulemaking submitted by
the Chemical Manufacturers Association and the Agency's tentative
response to the recommendations made by the Dialogue Committee on
Hazardous Waste Identification. This committee was formally chartered
in July 1993 in accordance with the Federal Advisory Committee Act
(FACA).
DATES: EPA will accept public comments on this proposed rule until
February 20, 1996. Comments postmarked after this date may not be
considered. However, the Agency recognizes that, because of the
complexity of this proposed rulemaking, some commenters may want to
request additional time for comment submittal. In anticipation of these
requests, EPA will be communicating with the litigants and the court
regarding the implications on our rulemaking schedule of a possible
extension of the comment period for this proposal. If the comment
period is extended, the Agency will provide notice of such in the
Federal Register.
Any person may request a public hearing on this amendment by filing
a request with Mr. David Bussard, whose address appears below, by
January 5, 1996.
ADDRESSES: The public must send an original, two copies, and whenever
possible, a 3.5 inch computer disk containing the comments in a common
word processing format such as WordPerfect version 5.1 1. to: EPA
RCRA Docket (5305W), 401 M Street, SW., Washington, DC 20460.
\1\ This will greatly facilitate EPA's preparation of the
comment responses and will significantly reduce the cost associated
with responding to the comments.
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Place ``Docket number F-95-WHWP-FFFFF'' on your comments. The RCRA
docket is located at: EPA's Crystal Gateway Office, 1235 Jefferson
Davis Highway, Arlington, Virginia, and is open from 9 a.m. to 4 p.m.,
Monday through Friday, excluding Federal holidays. The public must make
an appointment to review docket materials by calling (703) 603-9230.
The public may copy material from any regulatory docket at a cost of
$0.15 per page. Copies of the background documents, Integrated Risk
Information System (IRIS) chemical files, and other references (which
are not readily available) are available for viewing and copying only
in the RCRA docket.
Requests for a public hearing should be addressed to Mr. David
Bussard, Director, Characterization and Assessment Division, Office of
Solid Waste (OS-330), U.S. Environmental Protection Agency, 401 M
Street, SW., Washington, DC 20460.
FOR FURTHER INFORMATION CONTACT: The RCRA/Superfund Hotline at (800)
424-9346 or at (703) 412-9810. For technical information contact Mr.
William A. Collins, Jr., Mr. Greg Helms, or Ms. Pamela McMains, Office
of Solid Waste (5304), U.S. Environmental Protection Agency, 401 M
Street, S.W., Washington, DC 20460, (202) 260-4770.
Preamble Outline
I. Authority
II. Background
A. Overview of Hazardous Waste Identification Program
B. The Mixture and Derived-From Rules and the Contained-In
Policy
C. Overview of Expected Impacts of the Exit Rule
III. Scope of Revisions to the Mixture and Derived-From Rules
A. Rationale for Retention of the Mixture and Derived-From Rules
B. Revision to Derived-from Rule for Wastes Listed Because They
Exhibit the Characteristics of Ignitability, Corrosivity, or
Reactivity
IV. Development of Exit Levels and Minimize Threat Levels
A. Need for an Exit
B. Overview of the Exit
C. Selection of Constituents of Concern
1. Development of the Master List
2. Development of the Exit Constituent List
3. Constituents of Ecological Concern
D. Risk-Based Information
1. Human Health Benchmarks
a. Non-carcinogens
b. Carcinogens
c. Consideration of MCLs
2. Ecological Benchmarks
3. Sources of Data
a. Human
b. Ecological
E. Risk Assessment
1. The Risk Analysis
a. Introduction
b. How the Analysis was Structured
c. How Uncertainty is Addressed
d. Linkage of the Risk Analysis to the Groundwater Fate and
Transport
e. Risk Targets Used
2. Detailed Overview of the Non-Groundwater Risk Analysis
a. Waste Management Units
1. Use of Subtitle D Survey
2. Fate and Transport
3. Ash Monofill
i. Particle Size Distribution for Air Dispersion Modeling
ii. Monofill Characterization
iii. Vehicle Traffic
iv. Emission Equations for Ash Blown from Trucks and Spreading
and Compacting
4. Land Application Unit
i. Particle Size Distribution for Air Dispersion Modeling
ii. Area of Land Application Unit Relative to Agricultural Field
iii. Application Rate
iv. Waste Characteristics
[[Page 66345]]
v. Depth of Contamination
vi. Partitioning
5. Waste Pile
i. Waste Pile Height
ii. Particle Size Distribution for Air Dispersion Modeling
iii. Waste Characteristics
iv. Vehicle Traffic
v. Emission Equation for Ash Blown from Trucks
6. Surface Impoundments
i. Two-Phase Sludge Formation Model
ii. Dilution of Waste During a Spill
7. Tank
i. Unit Characterization
ii. Volatilization
8. Combustors
b. Fate and Transport
1. Pathways
2. Equations
3. Specific Issues on Pathways and Equations
i. Chemical Transformation
ii. Biodegradation
iii. Meteorological Data
iv. Soil Data
v. Soil Pathways
vi. Surface Water Pathways
vii. Food-Chain Pathways
c. Receptors
1. Human Receptors
2. Ecological Receptors
3. Groundwater Fate and Transport Modeling
a. Fate and Transport Processes
1. Effects of groundwater mounding
2. Transformation products
3. Fate and transport of metals
b. Enhanced solution algorithms
1. Linkage between unsaturated zone and saturated zone modules
2. Numerical transport solution
3. Solution for metals transport
4. Elimination of biases in determination of receptor well
concentrations
c. Revision of Monte Carlo methodology for nationwide
assessments
1. Data sources
2. Finite-source methodology
3. Site-based regional analysis
d. Implementation of EPACMTP
e. Waste management scenarios
1. Landfills
2. Surface impoundments
3. Waste piles
4. Land application units
f. Determination of regulatory limits
g. Chemical specific fate and transport processes
1. Organic constituents
2. Metals
4. Other Risk Assessment Issues
a. Difference between groundwater and nongroundwater pathways
1. Infiltration
2. Density of waste applied to land application unit
3. Unsaturated zone characteristics
4. Hydrolysis rates
b. Other groundwater pathway analysis issues
1. Use of 1000 years versus 10,000 years exposure time horizon
2. Implementation of parameter bounds in Monte Carlo procedure
3. Hydraulic conductivity of surface impoundment bottom layer
4. Waste pile infiltration rates
5. Land application unit infiltration rates
6. Aggregate effects of alternative groundwater modeling
procedures
F. Additional Eco-Receptor Consideration
G. Background Concentrations in Soils and other Issues Relating
to Results
H. Constituents with Extrapolated Risk-based Levels
I. Analytical Considerations
1. Development of Exemption Quantitation Criteria (EQC)
2. EQCs and LDR Requirements as Exemption Criteria
a. EQCs as exit levels
b. LDR Requirements in combination with EQC Exit Levels
3. Exemption for Constituents Without EQCs
V. Presentation of Exit Levels
A. Constituents with Modeled or Extrapolated Risk-based Exit
Levels
B. Constituents with Quantitation-based Exit Levels
C. How to Read the Exit Level Tables
VI. Minimize Threat Levels
A. Background
1. Summary of the Hazardous and Solid Waste Amendments of 1984
2. EPA's Interpretation of Standard for Treatment Requirements
B. Risk Assessment and Minimize Threat Levels
1. Rationale
2. Public Policy Considerations
C. Minimize threat levels
1. List of Constituents and Minimize Threat Concentrations
2. Constituents for which Exit Levels are not Minimize Threat
Levels
D. Meeting LDR requirements
1. Wastes Below Exit Levels as Generated
2. Wastes Above Exit Levels as Generated
VII. Dilution
VIII. Implementation of Exit
A. Implementation Requirements
1. Testing Requirements
a. Data Evaluation
i. Compliance with the Exit Levels
ii. Wastewater and Nonwastewater Categories
iii. Totals and TCLP Analyses
iv. Oily Wastes
b. Initial Test
2. Notification Requirements
B. Implementation Conditions
1. Records Maintained on Site
2. Testing Conditions
3. Testing Frequency and Process Change
C. Public Participation
IX. Request for Comment on Options for Conditional Exemptions
A. Legal Basis for Conditional Exemptions
B. Improvements in Management of Non-Hazardous Waste and in Risk
Assessment Methodology
C. Overview of Options for Conditional Exemptions
1. National Approach
a. Eliminate Disposal in Land Application Units
b. Unit-Specific Exit Levels for Each Disposal
c. Consideration of Additional Management Unit Design or
Management Practices
2. State Program Approach
3. Establish Exit Levels that Consider Regional or Site-Specific
Factors that might Affect Constituent Fate and Transport
4. Relief from Land Disposal Restrictions
D. Land Disposal Restrictions for Contingent Management Options
E. Contingent Management of Mixed Waste
X. Implementation of Conditional Exemption Option 1
A. Introduction and Overview
B. When Contingent Management Exemptions Become Effective
1. Placement of the waste in a qualifying unit
2. Point of generation
C. Requirements for Obtaining an Exemption
1. Sampling and Testing Requirements for Contingent Management
Exemptions
2. Requirements for Public Participation in contingent
Management Exemptions
3. Notification Requirements for Contingent Management
D. Implementation Conditions
1. Tracking conditions
2. Qualifying Unit
3. Claimant's Duty to Ensure Compliance with all Conditions
E. Retesting and Recordkeeping Conditions for Contingent
Management Exemptions
F. Compliance Monitoring and Enforcement for Contingent
Management Exemptions
1. Compliance Monitoring
2. Enforcement
G. Exports of Wastes Eligible for Contingent Management
Exemptions
H. Land Disposal Restrictions
XI. Relationship to Other RCRA Regulatory Programs
A. Hazardous Waste Determination
B. Characteristic Hazardous Waste
C. Toxicity Characteristic Level for Lead
D. Hazardous Waste Listings
E. Delisting
F. Requirements for Treatment, Storage, and Disposal Facilities
and Interim Status Facilities
G. Closure
H. HWIR-Media Rule/Subtitle C Corrective Action
I. Land Disposal Restriction Program
J. RCRA Air Emission Standards
K. Hazardous Debris
L. Hazardous Wastes Used in a Manner Constituting Disposal
XII. CERCLA Impact
XIII. State Authority
A. Applicability of Rules in Authorized States
B. Effect of State Authorizations
C. Streamlining Issues
XIV. Regulatory Requirements
XV. References
Appendix A: Background Tables for Risk Analysis Receptors and
Pathways
Appendix B: Table Comparing Groundwater Modeling Effects of 1000 vs.
10,000 years
Appendix C: Tables Comparing the Modeled or Extrapolated Risk Levels
vs. the EQCs for Each Constituent
Appendix D: Tables Comparing the Exit Levels and the UTS Levels
Regulatory Language
[[Page 66346]]
I. Authority
These regulations are proposed under the authority of sections
2002(a), 3001, 3002, 3004 and 3006 of the Solid Waste Disposal Act of
1970, as amended by the Resource Conservation and Recovery Act of 1976
(RCRA), as amended by the Hazardous and Solid Waste Amendments of 1984
(HSWA), 42 U.S.C. 6912(a), 6921, 6922, 6924 and 6926.
II. Background
A. Overview of the Hazardous Waste Identification Program
Section 1004(5) of the Resource Conservation and Recovery Act
(RCRA) as amended by the Hazardous and Solid Waste Amendments (HSWA) of
1984, defines ``hazardous waste'' as ``a solid waste, or combination of
solid waste, which because of its quantity, concentration, or physical,
chemical, or infectious characteristics may (A) cause, or significantly
contribute to an increase in the mortality or an increase in serious
irreversible, or incapacitating reversible, illness; or (B) pose a
substantial present or potential hazard to human health or the
environment when improperly treated, stored, transported, or disposed
of, or otherwise managed.''
Section 3001 of RCRA requires EPA to identify those wastes that
should be classified as ``hazardous.'' The Agency's hazardous waste
identification rules designate wastes as hazardous in one of two ways.
First, the Agency has established four hazardous waste characteristics
which identify properties or attributes of wastes which would pose a
potential hazard if the waste is improperly managed. See 40 CFR 261.21-
261.24. Any generator of a solid waste is responsible for determining
whether a solid waste exhibits any of these characteristics. See 40 CFR
262.11. Any solid waste that exhibits any of the characteristics
remains hazardous until it no longer exhibits the characteristics. See
40 CFR 261.4(d)(1).
The other mechanism EPA uses to designate wastes as hazardous is
``listing.'' The Agency has reviewed data on specific waste streams
generated from a number of industrial processes and has determined that
these wastes would pose hazards if mismanaged for one or more reasons,
including the presence of significant levels of hazardous constituents
listed in appendix VIII to 40 CFR part 261, the manifestation of one or
more of the hazardous waste characteristics, or the potential to impose
detrimental effects on the environment. (See generally 40 CFR 261.11).
As discussed in detail in the preambles and in associated dockets
accompanying the listings, EPA has generally determined that these
wastes contain toxic constituents at concentrations which pose risks
which are unacceptable for human or environmental exposure and that
these constituents are mobile and persistent to the degree that they
can reach environmental or human receptors.
On May 19, 1980, as part of the final and interim final regulations
implementing section 3001 of RCRA, EPA published two lists of hazardous
wastes: One composed of wastes generated from non-specific sources
(e.g., spent solvents) and one composed of wastes generated from
specific sources (e.g., distillation bottoms from the production of
benzyl chloride). The Agency also published two lists of discarded
commercial chemical products, off-specification species, container
residues, and spill residues thereof which are hazardous wastes under
specific circumstances. These four lists have been amended several
times, and are currently published in 40 CFR 261.31, 261.32, 261.33(e)
and (f), respectively.
B. The Mixture and Derived-From Rules and the Contained-In Policy
1. Mixture and Derived-From Rules
a. Scope and Purpose of the Rules
In 1980 EPA promulgated its first comprehensive regulatory program
for the management of hazardous waste under RCRA. 45 FR 33066 (May 19,
1980). As part of that rulemaking EPA promulgated several rules to
identify hazardous wastes. Two of these rules clarify the scope of the
hazardous waste listings. Under the mixture rule, a solid waste is a
hazardous waste if it is mixed with one or more listed hazardous
wastes. 40 CFR 261.3(a)(2)(iv). Under the derived-from rule a solid
waste generated from the treatment, storage or disposal of a listed
hazardous waste is also a hazardous waste. 40 CFR 261.3(c)(2)(i).
EPA promulgated the mixture and derived-from rules to close
potentially major loopholes in the subtitle C management system.
Without a ``mixture'' rule, generators of hazardous wastes could
potentially evade regulatory requirements by mixing listed hazardous
wastes with other hazardous wastes or non-hazardous solid wastes to
create a ``new'' waste that arguably no longer met the listing
description, but continued to pose a serious hazard. Such a waste also
might not exhibit any of the hazardous waste characteristics.
Similarly, without a ``derived-from'' rule, hazardous waste generators
and owners and operators of hazardous waste treatment, storage, and
disposal facilities (TSDFs) could potentially evade regulation by
minimally processing or managing a hazardous waste and claiming that
resulting residue was no longer the listed waste, despite the continued
hazards that could be posed by the residue even though it does not
exhibit a characteristic. (See 57 FR 7628).
It is for these reasons that the Agency continues to believe that
the mixture and derived-from rules are extremely important in
regulating hazardous wastes and reducing risk to human health and the
environment. However, EPA acknowledges that the mixture and derived-
from rules apply regardless of the concentrations and mobilities of
hazardous constituents in the waste. The purpose of this rulemaking is
to reduce any overregulation of low-risk wastes captured by the mixture
and derived-from rule.
b. Subsequent History
Numerous industries that generate hazardous wastes challenged the
1980 mixture and derived-from rules in Shell Oil v. EPA, 950 F. 2d 741
(D.C. Cir. 1991). In December 1991 the D.C. circuit vacated the rules
because they had been promulgated without adequate notice and
opportunity to comment. The court, however, suggested that EPA might
want to consider reinstating the rules pending full notice and comment
in order to ensure continued protection of human health and the
environment.
In response to this decision, EPA promulgated an emergency rule
reinstating the mixture and derived-from rules as interim final rules
without providing notice and opportunity to comment. 57 FR 7628 (Mar.3,
1992). EPA also promulgated a ``sunset provision'' which provided that
the mixture and derived-from rules would remain in effect only until
April 28, 1993. Shortly after, EPA published the proposal containing
several options for revising the mixture and derived-from rules. See 57
FR 21450 (May 20, 1992). This proposal also included options for
exempting media contaminated with listed hazardous wastes that are
regulated under the ``contained in'' policy.
The May 1992 proposal and the time pressure created by the ``sunset
provision'' generated significant controversy. In response, Congress
included in EPA's 1992 appropriations bill several provisions
addressing the mixture and derived-from rules. Pub. L. No. 102-389, 106
Stat. 1571. First, Congress nullified the sunset provision by providing
that EPA could not promulgate any revisions to the rules
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before October 1, 1993 and by providing that the reinstated regulations
could not be ``terminated or withdrawn'' until revisions took effect.
However, to ensure that EPA could not postpone the issue of revisions
indefinitely, Congress also established a deadline of October 1, 1994
for the promulgation of revisions to the mixture and derived-from
rules. Congress made this deadline enforceable under RCRA's citizen
suit provision.
On October 30, 1992 EPA published two notices, one removing the
sunset provision, and the other withdrawing the May 1992 proposal. See
57 FR 49278, 49280. EPA had received many comments criticizing the May
1992 proposal. The criticisms were due, in a large part, to the very
short schedule imposed on the regulation development process itself.
Commenters also feared that the proposal would result in a
``patchwork'' of differing State programs because some states might not
adopt the revisions. This fear was based on the belief that States
would react in a negative manner to the proposal and refuse to
incorporate it into their programs. Finally, many commenters also
argued that the risk assessment used to support the proposed exemption
levels failed to provide adequate protection of human health and the
environment because it evaluated only the risks of human consumption of
contaminated groundwater ignoring other pathways that could pose
greater risks. Based on these concerns, and based on the Agency's
desire to work through the individual elements of the proposal more
carefully, the proposal was withdrawn.
Meanwhile, a group of waste generating industries challenged the
March 1992 action that reinstated the mixture and derived-from rules
without change. Mobil Oil Corp. v. EPA, 35 F.3d 579 (D.C. Cir. 1994).
EPA argued that the 1992 appropriations act made the challenge moot
because it prevented both EPA and the courts from terminating or
withdrawing the interim rules before EPA revised them, even if EPA
failed to meet the statutory deadline for the revisions. In September,
1994 the D.C. Circuit issued an opinion that dismissed the challenges
as moot under the rationale that the Agency had offered.
In early October 1994 several groups of waste generating and waste
managing industries filed citizen suits to enforce the October 1
deadline for revising the mixture and derived-from rules. The U.S.
District Court for the District of Columbia Circuit entered a consent
decree resolving the consolidated cases on May 3, 1993. Environmental
Technology Council v. Browner, C.A. No. 94-2119 (TFH) (D.D.C. 1994)
Under this decree the Administrator must sign a proposal to amend the
mixture and derived-from rules by November 13, 1995 and a notice of
final rulemaking by December 15, 1996. The decree also specifies that
the deadlines in the 1992 appropriations act do not apply to any rule
revising the separate regulations that establish jurisdiction over
media contaminated with hazardous wastes.
c. Federal Advisory Committees Act (FACA) and Outreach
After the withdrawal of the HWIR proposal, the Agency initiated a
series of public meetings with invited representatives from industry,
environmental groups, hazardous waste treaters, and States. These
meetings focused on three major issues: --RCRA regulation of low hazard
wastes with a particular interest in addressing issues raised regarding
the mixture and derived-from rules; concerns that full RCRA
requirements for contaminated media may unnecessarily impede clean-ups;
and need to regulate additional high-risk wastes outside the scope of
the current listings and characteristics.
A strong and successful effort was made to encourage all the
interested parties to participate in the public meetings. EPA forged a
solid partnership with the States (both ASTSWMO and Environmental
Commissioners under the National Governors Association) and the state
representatives worked closely with EPA as co-regulators in our
analyses of options.
In July of 1993, EPA chartered this group as an advisory committee
under the Federal Advisory Committee Act (Pub. L. 92-463)(58 FR 36200).
The committee rather quickly formed two sub-committees to allow
separate discussion of the low risk waste problem associated with the
mixture and derived-from rules and the rules for managing contaminated
media and other wastes during remediation.
By September of 1994 the low risk waste group had made significant
progress in identifying options for creating exemptions for low risk
wastes. Despite significant investment of time and effort, however, the
group was unable to reach consensus on many key issues.
With the statutory deadline for revisions to the mixture and
derived-from rules approaching, EPA requested that group to present a
final report in late September of 1994. EPA and representatives from
several state environmental agencies then took up the task of selecting
options for creating an exit rule, crafting regulatory language, and
developing necessary supporting materials. The FACA subcommittee's
final report was taken into consideration during the development of
today's proposal.
2. Contained-In Policy
The Agency also has interpreted its regulatory definition of
hazardous waste to extend to mixtures of hazardous wastes and
environmental media (such as contaminated soil and groundwater).2
See 40 CFR 261.3(c)(1) and (d)(2). Media that are contaminated with
listed or characteristically hazardous waste must be managed as
hazardous wastes until they no longer contain such wastes. To date, the
Agency has not issued any general rules as to when, or at what levels,
environmental media contaminated with hazardous wastes are no longer
considered to ``contain'' those hazardous wastes. Media that contain
hazardous wastes with constituent concentrations below the levels
proposed today will be eligible for exemption under the procedures
proposed today. In addition, in a separate rulemaking, the Agency plans
to propose additional rules reducing regulation of contaminated media
during remediation activities.
\2\ EPA's ``contained in'' policy was upheld as a reasonable
interpretation of 40 CFR 261.3(c)(1) and (d)(2) by the D.C. Circuit
in Chemical Waste Management, Inc v. U.S. EPA, No. 869 F.2d 1526
(D.C. Cir. 1989).
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C. Overview of Expected Impacts of the Exit Rule
1. Listed Wastes
The purpose of this rule is to exempt from hazardous waste
regulation those solid wastes currently designated as hazardous waste
even though they contain constituent concentrations at levels that pose
very low risk to human health and the environment. While facilities
generating such wastes can petition for delisting by rulemaking under
the provisions of 40 CFR Sec. 260.20 and 260.22, EPA believes that the
detailed waste-stream specific review required under delisting is not
necessary for the low risk wastes that are identified by today's
proposal. The alternative, generic exit rule proposed today will be
faster and less resource-intensive for both the Agency and the
regulated community. By providing an opportunity for a more self-
implementing exemption, the Agency intends to create incentives for
effective and innovative waste minimization and waste treatment and to
reduce unnecessary demand for Subtitle C disposal capacity, without
[[Page 66348]]
compromising needed environmental protection.3
\3\ As will be discussed further in this notice, the Agency
believes that the delisting process will continue to be valuable for
certain types of wastes which are not eligible for an exemption
under this proposal. Thus the Agency is not proposing to eliminate
or modify the delisting program as a result of this proposal.
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By proposing a risk-based ``floor'' to listed wastes, today's
proposal should give a very strong incentive to generators of listed
hazardous waste to apply pollution prevention to their processes to
avoid Subtitle C control. This action should also give incentive for
the development of innovative treatment technologies to render wastes
less risky.
Today's proposed rule specifies sampling and analysis requirements,
public participation, reporting and record keeping requirements. Most
of these provisions are alternatives to the safeguard of waste-specific
review provided under the delisting program. The exit levels are risk-
based concentrations at which a human or wildlife species could be
directly or indirectly exposed to the exempted waste, and would be
unlikely to suffer adverse health effects. The exposure scenario used
to develop these levels assume that the exempted waste will no longer
be subject to Subtitle C control, but will be managed as a solid waste
in one of a variety of non-hazardous waste management units regulated
under Subtitle D.
2. Characteristic Wastes
Listed hazardous wastes exempted under today's proposed rule which
exhibit any of the characteristics will continue to be regulated as
hazardous wastes until the characteristic is removed. In a number of
cases, wastes were listed on the basis of containing both toxic
hazardous constituents and exhibiting one or more of the hazardous
waste characteristics that do not relate to chemical toxicity (e.g.,
ignitability, corrosivity, or reactivity). If such a waste still
exhibits any characteristic after complying with the exemption criteria
proposed in today's proposed rule, it must continue to be managed as a
characteristically hazardous waste.
III. Scope of Revisions to the Mixture and Derived-From Rules
The mixture and derived-from rules promulgated in 1980 and
reinstated in 1992 require Subtitle C regulation of all mixtures of
listed hazardous wastes and solid wastes and all residuals from
treatment of hazardous wastes. The rules proposed today, however, allow
rapid exemptions for mixtures and derived-from wastes that present no
significant threats to human health and the environment. Those wastes
that would remain subject to the mixture and derived-from rules
typically will pose risks that warrant regulation under Subtitle C. To
the extent that this is not true for a particular mixture or treatment
residual, the delisting process remains available (at least at the
state level) to exempt wastes with constituents at more site- and
waste-specific levels. Consequently, EPA has tentatively determined
that further revisions of the mixture and derived-from rules, with the
exception of the one minor change to the derived-from rule discussed
later in this section, are not warranted in this rulemaking. However,
EPA requests comment on this conclusion.
A. Rationale for Retention of the Mixture and Derived-From Rules
EPA continues to believe that it had ample statutory and regulatory
authority to promulgate the original rules and that it also has ample
authority to maintain the rules without further revisions. The mixture
and derived-from rules, particularly with the revisions proposed today,
ensure that hazardous wastes that are mixed with other wastes or
treated in some fashion do not escape regulation so long as they are
reasonably likely to continue to pose threats to human health and the
environment. They thus retain jurisdiction over listed hazardous wastes
and clarify that such wastes are not automatically eligible for exit
when they are mixed or treated. Although RCRA sets out criteria for the
identification of hazardous wastes to enter the subtitle C system, it
is silent on the question of how to determine that a waste is eligible
to exit the system. EPA's interpretation of the statute is thus
entitled to deference so long as it is reasonable and consistent with
RCRA's purposes.
EPA believes that its decision to retain jurisdiction over major
portions of the universe of waste mixtures and treatment residues is
consistent with its authorities under sections 3002-3004 of RCRA to
impose requirements on waste handlers until wastes have ``cease[d] to
pose a hazard to the public''. Shell Oil Corp. v. EPA, 959 F.2d 741,
754 (D.C. Cir. 1991). See also Chemical Manufacturers Assoc. v. EPA,
919 F.2d 158, 162-65 (EPA may regulate the disposal of nonhazardous
wastes in a hazardous waste impoundment under section 3004) and
Chemical Waste Management, Inc. v. EPA, 976 F.2d 2, 8, 13-14 (D.C. Cir.
1992) (EPA may require further treatment of wastes under section 3004
even though they cease to exhibit a hazardous characteristic).
The mixture and derived-from rules are also valid exercises of
EPA's authority to list hazardous wastes under section 3001. That
provision gives EPA broad authority to promulgate listing criteria.
EPA's 1980 criteria authorize the listing of classes of hazardous
wastes when it has reason to believe that wastes in the class are
typically or frequently hazardous. See 40 CFR 261.11(b). Such class
listings are permissible even if some members of the class do not
actually pose hazards. Nothing in the section 1004(5) definition of
hazardous waste, in section 3001, or in EPA's listing criteria require
EPA to prove that every member of a class poses a hazard. In fact, many
waste listings describe ``classes'' of hazardous wastes because they
cover a range of materials that are not identical in composition. The
mixture and derived-from rules thus are fully authorized as class
``listings'' under section 3001.
EPA has also made a reasonable factual determination that these
classes of waste warrant regulation under sections 3002-3004 and
section 3001. In 1980 EPA determined that the hazardous constituents
contained in these wastes are not generally eliminated or rendered
nontoxic simply because a waste is mixed with other wastes or managed
in some fashion. In 1992, when EPA repromulgated the mixture and
derived-from rules, it documented numerous instances of mixed and
derived-from wastes that continued to pose hazards. See 57 FR 7629
(March 3, 1992). Today, EPA is proposing that members of this class of
wastes that pose low risks will be eligible for an expedited, self-
implementing exemption from Subtitle C regulation. Accordingly, EPA has
an even better basis for believing that wastes which remain within the
scope of the mixture and derived-from rules pose threats warranting
regulation.
Additionally, EPA continues to believe, as it did in 1980, that it
would be virtually impossible to try to identify all possible waste
mixtures and treated wastes and assess their hazards individually.
EPA's rule reasonably retains jurisdiction over both broad classes and
places the burden of proof on the regulated community to show that a
particular waste has ceased to present a hazard. Today's self-
implementing exit proposal will reduce that burden significantly,
ensuring that the mixture and derived-from rules represent a reasonable
approach to regulating these classes of wastes.
[[Page 66349]]
B. Revision to Derived-from Rule for Wastes Listed Because They Exhibit
the Characteristics of Ignitability, Corrosivity, or Reactivity
In 1981 EPA responded to a number of comments on the scope of the
original 1980 mixture rule by promulgating a number of exemptions for
mixtures of solid wastes and listed hazardous wastes which, according
to information submitted by commenters, posed no significant risk to
human health and the environment. See 46 FR 56582 (Nov. 17, 1981). The
1981 rule included an exemption for mixtures of solid wastes and
hazardous wastes listed solely because they exhibited one or more of
the hazardous waste characteristics, if the resultant mixtures no
longer exhibited a characteristic. The exemption was based on a finding
that such mixtures did not pose threats to human health and the
environment warranting Subtitle C regulation. See 46 FR 56568 and the
current text of the exemption at Sec. 261.3(a)(2)(iii). EPA notes that
it has never promulgated any listings for wastes solely on the basis
that they exhibit either the 1980 EP toxicity characteristic or the
1990 toxicity characteristic; consequently, only mixtures containing
wastes listed because they exhibit the characteristics of ignitability,
corrosivity, or reactivity have been eligible to exit Subtitle C when
they no longer exhibit the characteristic.
The 1981 notice focused exclusively on issues concerning the
mixture rule. Consequently, EPA did not propose any parallel exemption
for such wastes for the separate derived-from rule (codified at
Sec. 261.3(c)(2)(i)), even though the derived-from wastes would appear
to present similarly low risks if they no longer exhibited a
characteristic and were treated to meet LDR standards before land
disposal. Recent inquiries from the public have highlighted the
discrepancy in the scope of the mixture rule and the derived-from rule
for wastes listed solely because they exhibit characteristics. EPA
believes it has no reason to treat derivatives of wastes listed solely
because they exhibit the characteristic of ignitability, corrosivity,
or reactivity any differently from the way it treats mixtures of such
wastes because both present similar low risks to human health and the
environment.
Consequently, EPA is today proposing a revision to the derived-from
rule that will closely resemble the 1981 revision to the mixture rule.
Since no listings to date have been based on the toxicity
characteristic, EPA is proposing to limit the new revision to the
derived-from rule to wastes listed because they exhibit only the
characteristics of ignitability, corrosivity, or reactivity. EPA is
also not proposing to exempt wastes that might in the future be listed
only because of the toxicity characteristic because (as this rule
proposal indicates) there can be risk concerns with the TC constituents
below TC levels. EPA requests comment on this proposal to create a new
exemption to the derived-from rule for this limited category of listed
wastes.
The proposed exemption will also remind the regulated community of
the separate duty to comply with requirements imposed by the part 268
regulations implementing the LDR program. In CWM v. EPA, 976 F.2d 2
(D.C. Cir. 1992), the U.S Court of Appeals for the D.C. Circuit
interpreted RCRA section 3004(m) as requiring treatment of de-
characterized hazardous wastes to meet LDR treatment standards even
after the wastes cease exhibiting a characteristic. EPA believes that
de-characterized derived-from residues from wastes listed because they
exhibit characteristics also must meet LDR requirements, unless they
are either delisted or are exempt at the point of generation pursuant
to other provisions proposed in this rule (e.g., meeting HWIR levels at
the point of generation).
In 1992 EPA amended the 1981 exemption to mixture rule to provide a
similar cross-reference and clarification for mixtures containing de-
characterized listed wastes. See 57 FR 37194, 37210-11 (Aug. 18, 1992).
That 1992 clarification, however, only covers nonwastewater mixtures.
As explained in that mixture rule preamble, EPA then regulated de-
characterized wastewaters much less stringently under the LDR program.
Consequently, EPA did not believe it was necessary to remind the
regulated community to comply with LDR requirements for wastewater
mixtures.
Later in 1992 the CWM v. EPA decision invalidated most of the
distinctions between the LDR rules for wastewaters and nonwastewaters.
EPA is now revising the LDR program to comply with that decision in the
LDR Phase III and Phase IV rulemakings. To reflect the changes in LDR
regulation of wastewaters, the derived-from rule exemption proposed
today reminds the regulated community of the need to comply with part
268 LDR requirements for all types of derived-from residues. EPA
requests comment on this clarifying language. EPA also requests comment
on whether it should revise the LDR clarification for the mixture rule
as well.
IV. Development of Exit Levels and ``Minimize Threat'' Levels
A. Need for the Exit
The primary purpose of this rule is to address listed hazardous
wastes, mixtures of listed hazardous wastes and solid wastes, and
residues derived-from managing listed hazardous waste that, under
current rules, continue to be designated as ``hazardous waste''
although they are either generated with constituent concentrations that
pose low risks or treated in a manner that reduces constituent
concentrations to low levels of risk.
EPA notes that there are currently exemptions, both codified and
contained in policy directives, from the hazardous waste identification
system, particularly the mixture and derived-from rules, for certain
types of wastes or wastes with certain constituent concentrations. See
e.g. 40 CFR 261.3(a)(2)(iv)(A) through (E) and policy memorandums such
as the ``Skinner Memorandum'' dated August 23, 1995. EPA is not
proposing to modify or replace any of these exemptions and policy
statements.
B. Overview of the Exit
For 191 of the 376 constituents of concern, EPA conducted a
detailed human health risk analysis to develop risk-based levels for
either the wastewater or nonwastewater form of a constituent (or both).
To conduct this analysis, EPA identified five types of units actually
and rather frequently used to manage nonhazardous wastes that covered
the full range of environmental releases needing analysis. The May 1992
proposal of exit levels for listed wastes, like many previous RCRA
rules, assessed only risks from releases to groundwater. In response to
complaints that such an assessment would not protect human health and
the environment from other types of releases, EPA also assessed
potential releases to air, surface water and soil in this proposal.
For each category of releases, EPA evaluated both relatively simple
pathways (such direct human ingestion of contaminated groundwater) and
more complex pathways (such as the deposition of windblown waste
particles on agricultural land, followed by crop uptake, consumption of
the crop by cattle, and consumption of contaminated beef or milk by
humans). EPA assessed approximately 8 to 27 release pathways depending
on the type of waste management unit.
Additionally, EPA screened the same group of 191 constituents to
identify the highest priorities for assessment of
[[Page 66350]]
ecological receptors. In addition, EPA considered for its assessment
the toxicological effects of silver on ecological receptors. EPA
conducted a specific assessment of ecological risks for 47 constituents
using the same five units and the same pathways (modified to reflect
ecological exposures) for each unit. This risk assessment is described
in more detail in sections V.B. and C.
Data limitations and resource constraints prevented EPA from
conducting a risk analysis for the remaining constituents of concern.
For each of these constituents, EPA extrapolated exit levels from
levels derived-from the risk assessment for similar chemicals. EPA's
extrapolation methodology is described in section IV.F.
The current capabilities of analytical chemistry constrain EPA's
ability to use some of concentrations as exit levels. For approximately
one-fourth of the constituents, EPA found that available methods could
not routinely measure the constituent at the modeled or extrapolated
risk-based exit level.
C. Selection of Constituents of Concern
1. Development of the Master List
EPA developed an initial ``Master List'' of 506 constituents to be
evaluated for purposes of establishing exit criteria. This master list
was developed by combining the constituents specifically listed in the
following appendices of 40 CFR part 261: Appendix VII, Basis for
Listing Hazardous Waste; Appendix VIII, Hazardous Constituents; and
appendix IX of part 264, the Ground-Water Monitoring List. The master
list includes the full list of constituents referenced in appendix VII,
including the F039 constituents.
Appendix VII to part 261, which was originally promulgated on May
19, 1980 (45 FR 33084) sets out the chemical constituents found to pose
threats to human health and the environment that served as the actual
basis for each of EPA's original hazardous waste listings. Appendix
VIII to Part 261, also promulgated in 1980, is a more general listing
of chemicals found to pose potential threats to human health and the
environment. (45 FR 33084). EPA considers wastes containing appendix
VIII constituents to be candidates for listing determinations. EPA
amends appendix VII from time to time as EPA identifies additional
potentially toxic constituents.
EPA later promulgated appendix IX to part 264 to identify those
appendix VIII constituents which it could routinely expect owners and
operators of permitted hazardous waste treatment, storage and disposal
facilities to monitor in groundwater. EPA also included in this
appendix 17 additional constituents found to pose significant risks
that the Superfund program routinely monitored in groundwater. (52 FR
25942, July 9, 1987).
EPA established in these rulemakings that each of these
constituents had significant potential to threaten human health, and,
by implication, potential to threaten the environment. (Most of the
data EPA utilized predicted toxic effects on humans.) EPA finds it
reasonable to include each of these constituents on the list of
chemicals of concern.
Further, EPA believes that, with the exception of the six chemicals
identified below, the three appendices identify the chemicals of
current concern to EPA that are likely to be found in listed wastes.
The Agency requests comment on whether the master list should also
include six constituents that are not listed in any of the above
sources. These six constituents, which are listed in Table 1, are found
in six ``U'' listed wastes (commercial chemical products that become
hazardous wastes when discarded). See 40 CFR 261.33(f). EPA originally
listed these wastes because they routinely exhibited the characteristic
of ignitability. Since the original listings, however, sufficient
toxicity data have become available for these constituents. (The risk
number for dimethylamine was recently withdrawn; however, EPA
understands that it will shortly be replaced). Because of the toxicity
data associated with these constituents, the Agency is taking comment
on whether exit levels should be established for these six constituents
in today's rulemaking. The Agency also requests comment on whether
these six constituents should be added to Appendix VIII.
Table 1.--Constituents Not on Appendices VII, VIII, or IX
----------------------------------------------------------------------------------------------------------------
Nonwastewater
CAS # Constituent Wastewater -------------------------
Totals Leach
----------------------------------------------------------------------------------------------------------------
75-07-0............................. Acetaldehyde (ethanal)............ ........... ........... ...........
98-82-8............................. Cumene............................ .67 18,000 2.5
124-40-3............................. Dimethylamine..................... ........... ........... ...........
110-00-9............................. Furan............................. .16 1300 .06
79-10-7............................. Acrylic acid...................... (\1\) (\1\) (\1\)
98-01-1............................. 2-Furancarbox- aldehyde (furfural) (\1\) (\1\) (\1\)
----------------------------------------------------------------------------------------------------------------
\1\ No exit levels because no EQC is available for this constituent. The criteria for exit would be to meet LDR
treatment standards in Sec. 268.
Full documentation concerning the selection of constituents of
concern is available in the docket under The Background Document to
Support Development of the Final Constituent List under the Waste Exit
Rule.
2. Development of the Exit Constituent List
The Agency narrowed the list of 506 constituents to consist of 376
constituents that are included in the exemption list. 130 constituents
were deleted from the master list. Criteria for constituent deletions
from the master list include: Reactivity in air, analysis as a
different constituent, reactivity in water, hydrolysis in soil or
water, or is part of a chemical class with a specific constituent
represented on the list. Because different methods and quantitation
limits are necessary for solid and liquid matrices, two separate
analyses were conducted. The Background Document to Support Development
of the Final Constituent List under the Waste Exit Rule in the docket
further justifies deletions of constituents from the master list and
lists the deleted constituents.
Molybdenum is not on the Appendices VII, VIII, or IX, which
provided the scope of today's master list of constituents. In
anticipation of the Petroleum listing, due to a Drinking Water Sewage
Sludge regulatory level, and due to available toxicity information, the
Agency has included molybdenum on the exemption list. Due to modeling
time constraints, Molybdenum was not modeled for groundwater risk. The
groundwater
[[Page 66351]]
leach level was estimated by assuming a DAF of 10 and using the RfD.
The Agency requests comment on whether molybdenum should be on the
list.
Two modeled constituents do not have estimated quantitation
criteria (EQCs--see section IV.G.) and therefore do not have associated
exit levels. These constituents are ethylene thiourea and phenyl
mercuric acetate. The Agency requests comment on how to deal with these
two constituents. The following table represents modeled results for
these constituents for comment.
Table 2.--Modeled Constituents Without EQCs
----------------------------------------------------------------------------------------------------------------
CASNUM Constituent NWW totals NWW leach WW totals
----------------------------------------------------------------------------------------------------------------
96-45-7............................... Ethylene thiourea............. 0.51 0.00017 .00053
62-38-4............................... Phenyl mercuric acetate....... 0.0093 0.0045 0.012
----------------------------------------------------------------------------------------------------------------
EPA modeled chromium VI in the risk assessment. However, totals
chromium appears on the exit tables based on the exit levels calculated
from modeling chromium VI. This approach is consistent with the
Toxicity Characteristic approach to chromium. The Agency asks for
comment on this approach.
The cyanide exit level was extrapolated. It is meant to be totals
cyanide. The Agency requests comment on whether testing for totals
cyanide is appropriate.
The values in the exit tables for silver do not represent results
of human toxicity data for silver, rather they represent ecological
results from the risk assessment. The Agency has determined that the
effect of silver on humans is not a human health problem, rather it is
an aesthetic problem. The groundwater model did not model ecological
exposure, therefore, there is no groundwater risk level for silver.
3. Constituents of Ecological Concern
As explained above, EPA established in previous RCRA rulemakings
that the constituents on the exit list (376) present significant
threats to human health. Numerous comments submitted on EPA's May 1992
proposal to establish exit levels urged EPA to conduct a more specific
and detailed analysis of threats to non-human species. Consequently, in
this rulemaking EPA determined the constituents it believed to also be
reasonably likely to pose risks to ecological receptors.
EPA has not set benchmarks for ecological impacts for a large
number of constituents under any of its programs. Establishing such
benchmarks for this proposal would be a resource-intensive and time-
consuming task. Accordingly, EPA narrowed the list of exit constituents
for which ecological receptors would be evaluated. First, EPA decided
to consider only the 191 constituents which it had already targeted for
analysis to protect human health. Second, the Agency developed a
methodology for screening the 191 constituents to identify those most
likely to pose significant risks to ecological receptors.
Based on an extensive review of available literature, EPA developed
five criteria to indicate the potential for ecological risks:
(1) Constituents that bioaccumulate (and possibly biomagnify) in
the food chain that can present elevated exposures to certain
predators;
(2) Persistent constituents that are likely to increase long-term
multi-generational exposures in wildlife;
(3) Constituents that cause reproductive and developmental effects
that can elicit adverse effects at sensitive life stages;
(4) Constituents that may cause ecological effects that have no
human analog (e.g., eggshell thinning); and
(5) Constituents that may cause effects to ecological receptors
continuously exposed.
EPA also developed operational definitions for each criterion. The
definitions were quantitative where possible. Further details can be
found in appendix B of the Technical Support Document for the Risk
Assessment for Human and Ecological Receptors.
EPA decided to designate as constituents of ecological concern the
47 constituents that exhibited at least two of the five criteria. The
Agency believes these constituents present the highest priorities in
terms of environmental risk. An additional 36 constituents exhibited
only one criterion. EPA, however, chose not to designate them as
constituents of concern because time and resource constraints would
prevent the Agency from completing an analysis with these constituents.
EPA, nevertheless, believes it has identified and analyzed sufficient
constituents of concern to ensure that the exit levels proposed today
provide for reasonable protection of the environment. Only 83 of 191
screened constituents showed any significant potential to pose threats
to the environment at levels protective of human health. Further, as
discussed in more detail below, of the 47 constituents that EPA
actually assessed for ecological impacts, only 6 wastewater
constituents and 18 nonwastewater constituents required exit levels to
protect environmental receptors lower than those necessary to protect
human health under the baseline proposal. Consequently, EPA believes it
is unlikely that all of the remaining constituents will present
significant threats to ecological receptors at levels that would
adequately protect human health.
D. Risk-Based Information
The Agency's proposed option for establishing exit values is based
on risk modeling to a hazard quotient of 1 and a 1 x 10-6 cancer
risk. The Agency chose a hazard quotient of 1 as its toxicity benchmark
value for non-carcinogens because evaluation of these compounds
presumes there is a threshold exposure above which individuals would be
at significant risk of suffering the adverse effects attributable to
the compound. The HQ is the Agency's best attempt to estimate that
level. Therefore, the Agency believes all exposures should remain below
HQ 1. Some Agency programs rely on HQ values less than 1 in standard
setting (the drinking water program uses an HQ of 0.20 to provide a
safety factor which allows for exposure to the constituent from sources
other than drinking water).
The Agency chose a toxicity benchmark of 1 x 10-6 cancer
risk for carcinogens for several reasons. A cancer risk level of 1 x
10-5 risk was used as a clearly hazardous level in establishing
the toxicity characteristic. Second, in the listings program, a 1 x
10-4 cancer risk is used as the presumptive listing risk, and a 1
x 10-6 as the presumptive no-list level. A cancer risk of 1 x
10-5 represents a level of initial concern about risk. Therefore,
in allowing listed hazardous waste to exit the requirements of Subtitle
C, the Agency was targeting waste that is clearly not hazardous. Thus,
the Agency believes the risk level should be at the
[[Page 66352]]
low end of the risk range used to bring waste into the hazardous waste
system.
Similarly, the Agency sought to be protective of public health in
developing its fate and exposure modeling. For the groundwater
evaluation, the Agency used a DAF 10 (which represents an approximate
90th percentile protection level) for infinite source type
constituents. (Constituent-specific DAFs were developed using the same
input assumptions, and different DAFs result from modeling of
degradation or retardation factors in the environment). This is the
generic DAF used in the delisting program for large volume wastes.
Since this is a national program which will largely benefit the largest
volume generators, the DAF 10 assumption is consistent with delisting
practice. Also, the toxicity characteristic used a DAF of 100
(representing an approximate 85th percentile protection level) for
identifying clearly hazardous waste (for infinite source type
constituents; regulation of hydrolysers was deferred). Again the policy
goal of exits was to strive to be well below clearly hazardous levels.
The Agency also modeled exposure at the nearest downgradient well. The
TC rule restricted well placement to within the plume. Today's proposal
attempts to balance the protectiveness level and well placement by
requiring a more protective level than the TC rule, but is less
restrictive in well location, e.g., wells outside of the plume, at
significantly lower risk, are averaged in.
For modeling of the non-groundwater pathways, the Agency used four
high-end parameter values for which the modeling outcome is most
sensitive as inputs to the analysis to be protective of public health
and the environment. These include: Two high-end parameters in the
waste management unit characterization and fate portions and two high-
end parameters in the exposure portions of the model. The remaining
input parameters were evaluated at typical values or central tendency
values. The Agency sought to be protective of a high percentile exposed
population (at least 90th percentile).
1. Human Health Benchmarks
For each constituent on the master list, the Agency evaluated the
existing toxicity information to determine whether there were
sufficient toxicity data to establish a benchmark. For those
constituents with adequate data, the data were evaluated either by the
Agency's CRAVE (Carcinogen Risk Assessment Verification Endeavor)
Workgroup, Reference Dose/Reference Concentration (RfD/RfC) Workgroup,
or the Office of Research and Development. This approach is consistent
with the approach used in the Agency's other risk-based RCRA programs
such as the Toxicity Characteristic, delisting petition evaluations,
listings, as well as the CERCLA program. See Section 4, ``Benchmarks,''
of the Technical Support Document for the Hazardous Waste
Identification Rule: Risk Assessment for Human and Ecological Receptors
for more details.
a. Non-carcinogens
The Agency proposes to use oral reference doses (RfDs) and
inhalation reference concentrations (RfCs) as the basis for developing
the exit criteria for non-carcinogenic constituents. An RfD or RfC is
an estimate (with uncertainty spanning perhaps an order of magnitude)
of a daily exposure to a constituent for the human population
(including sensitive subgroups) that is likely to be without an
appreciable risk of deleterious effects during a lifetime.
The approach used to derive an RfD or RfC is to identify the
highest test dose of a constituent associated with no effects or
effects that are not considered adverse in an appropriate animal
bioassay test. These experimental no-observed-adverse-effect-levels
(NOAELs) or no-observed-effect-levels (NOELs) are considered to be an
estimate of the animal population's physiological threshold for adverse
effects. The RfD or RfC is derived by dividing the NOAEL or other
toxicity benchmark by suitable uncertainty and modifying factors. In
the event that an appropriate NOAEL or NOEL is not available, the
lowest-observed-adverse-effect level (LOAEL) may be used with
additional uncertainty factors.
It is important to note that the contributions of the constituent
from various sources in the environment (e.g., air, food, water) are
not considered in the development of an RfD or RfC. Rather, the RfD or
RfC reflects the estimated total permissible daily human exposure from
all sources of exposure. RfDs and RfCs have been calculated for many,
but not all, of the non-carcinogenic constituents for which the Agency
is establishing exit criteria.
The Agency prefers to use only RfDs and RfCs that have been
evaluated and verified by the RfD/RfC Workgroup as the basis for
setting regulatory levels. However, for some constituents, the Agency
has not yet completed its verification process; thus, RfDs and RfCs
under development are being used for purposes of this proposal for
those constituents. If the final verified RfDs and RfCs differ from the
RfDs and RfCs under development proposed in today's notice, the Agency
will adopt the new (i.e., verified) values for the final rule after
noticing the data in the Federal Register.
b. Carcinogens
The Agency proposes to use the oral cancer slope factor and
inhalation cancer unit risk as the basis for developing exit levels for
carcinogenic constituents unless the non-carcinogenic effects occur at
lower levels. EPA's CRAVE Workgroup and Office of Research and
Development have estimated the carcinogenic slope factor (CSF) (i.e.,
the slope of the ``dose-response'' curve) and inhalation unit risks for
humans exposed to low-dose levels of carcinogens in the environment.
The slope factors indicate the upper-bound confidence limit estimate of
excess cancer risk for individuals experiencing a given exposure over a
70-year lifetime. In practice, a given dose multiplied by the slope
factor gives an upper estimate of the lifetime risk to an individual of
developing cancer. By specifying a level of lifetime risk (no matter
how small), one can also estimate the corresponding dose using the
slope factor.
EPA proposes to quantify on a weight-of-evidence basis, as
described below. EPA promulgated ``Guidelines for Carcinogen Risk
Assessment'' on September 24, 1986 (51 FR 33992), which defined a
scheme to characterize substances based on experimental data and the
kinds of responses induced by a suspect carcinogen. These guidelines
specify the following five classifications:
Group A--Human carcinogen (sufficient evidence from epidemiologic
studies)
Group B--Probable human carcinogen
Group B1--Limited evidence of carcinogenicity in humans
Group B2--A combination of sufficient evidence in animals and
inadequate or no evidence in humans
Group C--Possible human carcinogen (limited evidence of carcinogenicity
in the absence of human data)
Group D--Not classifiable as to human carcinogenicity (inadequate human
and animal evidence of carcinogenicity or no data available)
Group E--Evidence of non-carcinogenicity for humans (no evidence of
carcinogenicity in at least two adequate animal tests in different
species or in both adequate epidemiologic and animal studies).
The weight-of-evidence basis was used to eliminate Group D and E
constituents from further consideration as carcinogens.
[[Page 66353]]
Under each of the regulatory options presented in today's proposal,
the Agency is using the same risk level for Groups A, B, and C
carcinogens. This approach is consistent with the way carcinogens were
treated in the 1990 Toxicity Characteristic rule, hazardous waste
listing determinations, and the delisting program. The rationale for
this approach is that while the classifications indicate the type
(human or animal) and strength of the studies available which reflects
upon the uncertainty about the carcinogenic potential, the severity of
the effect, cancer, warrants equal treatment. It is important to note
that a few Group C carcinogens do not have slope factors or unit risks.
In these cases the Agency used the benchmark developed for the non-
cancer endpoint.
c. Consideration of MCLs
The Agency is proposing two approaches for setting human health-
based levels for carcinogens and non-carcinogens in routes of exposure
involving water ingestion. For the first approach, the Agency is
proposing to use Maximum Contaminant Levels (MCLs) promulgated under
the Safe Drinking Water Act (SDWA) of 1974, as amended in 1986, as the
human health-based levels for the constituents for which they have been
established. In general, MCLs for non-carcinogens are derived from the
Reference Doses (RfDs), while MCLs for most carcinogens are set as
close to zero as technically and economically feasible; this normally
corresponds to risk levels that range from 10-4 to 10-6.
(Note that, although the derivation of MCLs considers feasibility of
treatment, analytic chemistry, and cost factors in addition to health
effects, it also considers other routes of exposure. The Agency's
policy has been to use MCLs, when available, in other similar
concentration-based programs.) For those constituents which do not yet
have MCLs, the Agency is proposing to use oral reference doses (RfDs)
for non-carcinogens and oral slope factors for carcinogens as described
above. However, if new MCLs are finalized under the SDWA prior to the
promulgation of today's rule, the Agency proposes to substitute the new
MCLs for the RfDs and slope factor-derived human health-based levels
for water ingestion presented in today's notice.
For the second approach, the Agency intends to propose to use only
RfDs and slope factors in deriving human health-based levels for water
ingestion. The Agency requests comment on these two approaches.
2. Ecological Benchmarks
Ecological benchmarks were developed for a variety of ecological
receptors based on the availability of data. Benchmarks were needed for
mammals, birds, plants, soil fauna, fish, aquatic invertebrates,
aquatic plants, and benthos (sediment-dwelling organisms). A much
smaller number of constituents have been evaluated by the Agency for
ecological effects than have been for human health effects, as
discussed under V.A. In general, measurement endpoints were selected:
(1) For consistency with the Agency's Framework for Ecological Risk
Assessment (U.S. EPA 1992x), the Great Lakes Initiative, and other
ecological efforts within the Agency, and (2) relevance to the
ecological receptor. As discussed in ``Section D--Risk Assessment'' the
ecological assessment focussed on inferring the sustainability of
populations and communities within ecosystems. Therefore, benchmarks
were derived from measurement endpoints (i.e., reproductive,
developmental, growth, survival, and mortality) from which such
inferences could be made. Reproductive studies (e.g., number of viable
young per female) were preferred over other endpoints. For some
constituents, acute or mortality studies were used, however, this
occurred only for developing benchmarks for fish, aquatic
invertebrates, and benthos where protocol exists (AWQC development) for
using such data. The Agency seeks comment on the measurement endpoints
selected for each ecological receptor.
The toxicological benchmarks were established using the more
conservative no effects level (or concentration) approach for
ecological receptors as compared to a 20% effects level. The 20%
effects level is the lowest level for ecological effects that can be
detected in field population analyses (Suter et al., 1992). Although
the 20% effects level may indeed be the lower limit that could be
reliably confirmed in field studies, this level reflects our current
analytical abilities and not necessarily the ecological significance of
the effects level. The no effects approach was taken because the
ecological analysis infers the sustainability of various populations
under the assumption that if a sufficient number of populations within
an ecosystem is protected, then the likelihood of adverse effects that
are causally related to the chemical stressor will be reduced at the
ecosystem level. The Agency was concerned that if an effects approach
was taken, then the assumption underlying the ecological analysis would
no longer be valid. The Agency seeks comment on the approach taken for
setting toxicological benchmarks.
Given the number and variety of ecological receptors included in
the analysis (predatory birds to soil fauna) as well as the variety of
effects and endpoints considered, the benchmark development process
required an approach that was internally consistent and acknowledged,
at least qualitatively, the uncertainty involved in estimating
ecological benchmarks. The Agency, therefore, developed a benchmark
classification scheme to incorporate both the relationship of the
benchmark to the entire toxicity data set and the adequacy of the
database used to derive the benchmark. Three classifications were
established: Adequate, provisional, and interim. These classifications
were developed on a receptor group-specific basis (i.e., fish and
aquatic invertebrates, benthos, mammals, birds, soil fauna, and
terrestrial plants) and represent a weight-of-evidence designation for
the toxicological benchmark. In many respects, this classification
scheme is similar in meaning to the human carcinogen weight-of-evidence
groups and the difference between ``verified'' values on IRIS and
``unverified'' values in HEAST. The classifications relate to the
certainty assigned to a given ecological benchmark. The benchmarks were
treated the same in the analysis regardless of classification. See
Section 4 in the ``Technical Support Document for the Hazardous Waste
Identification Rule: Risk Assessment for Human and Ecological
Receptors'' for details on each classification and how they were used
for each ecological receptor group. The Agency seeks comment on the
classification developed for the analysis.
Below is a discussion of how benchmarks were developed for each of
the receptor groups. For a detailed discussion of each of their
developments, see Section 4, ``Benchmarks,'' and Appendix B,
``Toxicological Profiles for Ecological Receptors,'' of the ``Technical
Support Document for the Hazardous Waste Identification Rule: Risk
Assessment for Human and Ecological Receptors.'' The Agency seeks
comment on the overall development of each of the ecological benchmarks
generated for this proposed rule.
For populations of birds and mammals, the overall approach used to
establish toxicological benchmarks was similar to the methods used to
establish RfDs for humans as described in IRIS. Each method uses a
hierarchy for the selection of toxicity data (e.g., no effects
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levels are generally preferred to lowest effects levels) and
extrapolates from a toxicity benchmark for the test species to a
toxicity benchmark for the desired species. However, the procedures
used to develop benchmarks (i.e., RfDs) for the protection for human
health establish an acceptable daily dose for all individuals
(including sensitive sub-populations) while the development of
ecological benchmarks for this analysis establish a level that will
sustain the reproductive fitness in a local population. Consequently,
benchmarks for birds and mammals were established using three key
guidelines. First, because the reproducing population was selected as
the assessment endpoint, the benchmarks were developed from measures of
reproductive success or, if unavailable, other effects that could
conceivably impair the maintenance of the population.
Second, the taxon of the test species was matched to the taxon of
the wildlife species to the greatest extent possible. The evolutionary
processes that result in obvious differences in taxa (e.g., morphology)
also result in differences in the physiological processes that govern
chemical response. Moreover, taxonomic similarities are generally
associated with similarities in feeding habits, physiology, and
chemical sensitivity at the family classification and, to a lesser
extent, the order classification. For example, herbivores are generally
more resistant to toxicants than predators because they are exposed to
plant toxins, and the enzymatic system that detoxifies plant toxins
also detoxifies pesticides and other organic chemicals.
Third, a default safety factor of 10 was adopted only for
extrapolating from an lowest-observed-effects level (LOEL) to a no-
effects level (NOEL). A ten-fold safety factor was not applied to sub-
chronic studies since reproductive and developmental toxicity studies
are frequently short-term. Even among target organ toxicity studies,
there are many instances where sub-chronic studies are actually more
sensitive than chronic studies carried out on the same substance. Also,
for mammals and birds, differences in interspecies uncertainty were
indirectly addressed through the use of the species-scaling equation
described in Section 4 of the ``Technical Support Document for the
Hazardous Waste Identification Rule: Risk Assessment for Human and
Ecological Receptors.'' The Agency requests comment on the use a safety
factor of 10 when extrapolating from a LOEL to a NOEL. The Agency also
requests comment on the use of a scaling approach to address
interspecies uncertainty as described above. Furthermore, the Agency
seeks comment on the inability of the Risk Assessment to evaluate the
inhalation and dermal routes of exposure for birds and mammals.
For the terrestrial plants, the approach used to establish
toxicological benchmarks was adapted from the Effects Range Low (ER-L)
approach developed by the National Oceanographic and Atmospheric
Administration (NOAA). The NOAA ER-L approach estimates a percentile of
the distribution of various toxic effects thresholds. The measurement
endpoints were generally limited to growth and yield parameters because
(1) they are the most common class of response reported in
phytotoxicity studies and, therefore, will allow for benchmark
calculations for a large number of constituents, and (2) they are
ecologically significant responses both in terms of plant populations
and, by extension, the ability of producers to support higher trophic
levels. It should be noted that these benchmarks were limited to soil
concentrations and do not explicitly consider the adverse impacts on
plants from ambient contaminant concentrations in the air. Further
details can be found in section 4.3.3 of the ``Technical Support
Document for the Hazardous Waste Identification Rule: Risk Assessment
for Human and Ecological Receptors.'' The Agency solicits comment on
the overall approach taken to develop benchmarks for the terrestrial
plant community.
For the soil fauna, the toxicological benchmarks were established
based on methods developed by the Dutch National Institute of Public
Health and Environmental Protection (RIVM). The RIVM approach estimates
a confidence interval containing the concentration at which the no
observed effects concentration (NOEC) for p percent (95th percentile
was selected) of the species within the community is not exceeded 50%
of the time. A minimum data set was established in which key structural
and functional components of the soil community (e.g., decomposer and
grazing organisms) encompassing different sizes of organisms (i.e.,
microfauna, mesofauna, macrofauna) were represented. As with the
Ambient Water Quality Criteria, measurement endpoints included
reproductive effects as well as measures of growth, survival,
mortality. The Agency requests comment on the use of the RIVM
methodology, and protecting 95 percent of the community 50 percent of
the time. The Agency also requests comment on its inability to fully
quantify the effect of soil characteristics on toxicity of constituents
to soil organisms.
For populations of fish and aquatic invertebrates (represented by
daphnids), a hierarchical approach was taken for use of data sources in
deriving benchmarks. The first choice was final chronic values (FCVs)
from the Sediment Quality Criteria effort by the EPA Office of Water,
followed by values from the Great Lakes Initiative (GLI) effort, and
finally, the Ambient Water Quality Criteria (AWQC). If these benchmarks
were not available, then a benchmark was developed using AWQC
procedures or, if data were inadequate, the GLI Tier II procedures for
establishing chronic values (termed secondary chronic values--SCVs).
The AWQC ranked third since many years have passed since their
establishment and the SQC and GLI efforts re-evaluated the toxicity
data sets of several of these. The Agency solicits comment on the
hierarchical approach described above for deriving toxicity benchmarks.
For aquatic plants, the approach used to establish toxicological
benchmarks was adapted from the ER-L approach developed by NOAA. The
NOAA ER-L approach estimates a percentile of the distribution of
various toxic effects thresholds. However, due to the general lack of
toxicity data, the default ER-L approach was used wherein the lowest
LOEC for either vascular plants or algae was used. The Agency solicits
comment on the overall approach taken to develop benchmarks for aquatic
plants.
For the sediment organisms, the approach used to establish
toxicological benchmarks for non-ionic, hydrophobic organic chemicals
was based on sediment quality criteria methods for non-ionic
constituents. Two key assumptions form the basis for the proposed
sediment quality criteria. First, benthic species, defined as either
epibenthic or infaunal species, have a similar toxicological
sensitivity as water column species. As a result, FCVs (or SCVs)
developed for the fish and aquatic invertebrates can be used for the
benthic community. Second, pore water and sediment carbon are assumed
to be in equilibrium and the concentrations are related by a partition
coefficient, Koc. This assumption, described as equilibrium
partitioning (EqP), provides the rationale for the equality of water-
only and sediment-exposure-effects concentrations on a pore water
basis: The sediment-pore water equilibrium system results in the same
effects as a water-only exposure. The Agency requests comment on the
use of this approach in support of today's proposal. In some cases,
protecting these
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ecological receptors represents the critical pathway that limits the
projected exit level for management of a waste stream outside of the
Subtitle C hazardous waste program. These ecological receptors serve as
the basis for the proposed exit levels for 18 constituents, including 6
metals. To the extent that contaminants from these waste streams reach
off site areas, the Agency based its proposal on modeling the
ecological receptors on a neighboring land area of 500 acres or an
adjacent stream (with a total length of 12 miles). This approach as
currently modeled, may only serve as an indicator of a potential nearby
threat to ecological receptors (e.g., the soil fauna and plant life),
rather than serving as a measure or indicator of a broader threat to
the environment. The Agency solicits comment on the appropriateness and
relevance of these receptors as the basis for exit levels under the
HWIR program.
3. Sources of Data
a. Human
The two primary sources used to identify human health benchmarks
were the Integrated Risk Information System (IRIS) and the Health
Effects Assessment Summary Tables (HEAST). Both of these sources were
developed and are maintained by the USEPA. For a few constituents,
other Agency sources such as Carcinogen Assessment Group (CAG)
profiles, Health Effect Assessments (HEAs), and Health Assessment
Documents (HADs) were used to fill data gaps.
IRIS is the Agency's official repository of Agency-wide consensus
chronic human health risk information. IRIS evaluation are conducted by
the Agency's Work Group review process that leads to internal Agency
scientific consensus regarding risk assessment information on a
chemical. This information is recorded on IRIS and is considered to be
``Work Group Verified.''
The HEAST is prepared by EPA's Office of Research and Development.
They contain risk assessment information on chemicals that have
undergone a more limited review and have the concurrence of individual
Agency program offices; each is supported by an Agency reference. The
information has not, however, had enough review to be recognized as
Agency-wide consensus information.
b. Ecological
A thorough literature review was conducted to identify
toxicological data from laboratory and field studies for each of the
constituents of ecological concern. The review included secondary
sources such as the Synoptic Review Series published by the U.S. Fish
and Wildlife Service, the Ambient Water Quality Criteria documents, and
other Federal compendia of toxicity data (e.g. HEAs, the Derivation of
Proposed Human Health and Wildlife Bioaccumulation Factors for the
Great Lakes Initiative, Agency for Toxic Substances and Disease
Registry documents, PHYTOTOX, GRIN, TERRETOX, and AQUIRE). Toxicity
data on soil organisms were obtained for several constituents from van
de Meent et al. (1990). In addition to AQUIRE, the other primary data
source for toxicity data on aquatic plants were the Toxicological
Benchmarks for Screening Potential Contaminants of Concern for Effects
on Aquatic Biota:1994 Revision (Suter and Mabrey, 1994). On-line
literature searches were conducted to identify primary sources of
toxicity data on constituents lacking sufficient data in the secondary
sources. Additional studies were identified in conventional literature
reviews.
E. Risk Assessment
1. The Non-groundwater Risk Assessment
a. Introduction
The risk assessment underlying today's proposed rule is based upon
a comprehensive approach to evaluating the movement of many different
waste constituents from their waste management units, through different
routes of exposure or pathways, to the points where human and
ecological receptors are potentially exposed to these constituents.
This risk assessment is being used in today's proposed rule to
determine which listed hazardous wastes can be defined as ``low-risk''
wastes, able to exit the Subtitle C system and be managed in non-
Subtitle C units. The previous approach taken in the May 20, 1992,
proposed HWIR rule also addressed the risks associated with the
management of wastes containing hazardous constituents with very
diverse physical and chemical properties; however, only groundwater
ingestion exposures from landfill units were evaluated. That approach
led to a concern by the Agency, as well as commenters on the proposed
rule, that leachate from landfills contaminating groundwater and
subsequent consumption of the contaminated groundwater by humans may
not be the only exposure pathway important to evaluate. Although the
ingestion of contaminated groundwater pathway may be appropriate to
propose exit levels for some wastes and constituents, it may be under-
protective for others, depending on the physical and chemical
properties of each waste constituent. (For example, some constituents
have a high potential to bioaccumulate or bioconcentrate in living
organisms. Pathways in which these constituents come in contact with
fish, grazing livestock, wildlife, or edible plants would be important
to evaluate.) In addition, over the past 14 years of implementing the
RCRA program, the Agency has learned more about potential routes of
release to the environment from various management practices.
Therefore, for today's proposal the Agency undertook an extensive
risk assessment that examines numerous exposure pathways, rather than
just the groundwater ingestion pathway. In selecting the exposure
pathways, previous rulemakings were used as a guide, as well as other
special studies by the Agency that implement analyses examining
numerous pathways. (Tables A-1 and A-2 contain the human and ecological
pathways, respectively, evaluated in the assessment, and are presented
in appendix A to today's preamble.) With regard to waste management
units considered in the assessment, it is important to note that
because today's proposal establishes criteria for waste to exit the
Subtitle C system, the assessment evaluated exposures associated with
managing wastes in non-Subtitle C units. The human and ecological
receptors considered in the assessment were selected to represent a
range of behaviors, activities, dietary habits, and trophic levels that
influence exposure levels.
The risk assessment supporting this proposal is currently
undergoing review by the Science Advisory Board and EPA's Office of
Research and Development. As a result of these reviews, and of comments
received during the public comment period, it is likely that EPA would
make changes to the risk assessment or other parts of the rule. Topics
on which the Agency has received informal comment include the use of
ecological benchmarks for regulation and the overland transport of
waste constituents. The Agency, to the extent consistent with the
schedule negotiated in the consent decree for this rulemaking, would
publish a supplemental notice proposing any significant changes before
finalizing the rule.
b. How the Assessment is Structured
The non-groundwater assessment acknowledges that not all human and
ecological pathways arise from each
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source; for example, movement of particles from an active surface
impoundment is not expected to occur. To account for this, the
assessment matched the environmental transport pathways with both the
releases from various types of waste management units and the various
receptors for the nearly 200 constituents examined. All constituents
were assessed in all pathways deemed plausible for a given waste
management unit, if the data permitted. Tables A-3, A-4, and A-5 of
appendix A show the pathways assessed for each waste management unit,
human receptors assessed for each pathway, and ecological receptors
assessed for each pathway, respectively. The assessment estimated the
constituent-specific concentrations in a waste at the management unit
that could be expected to result in an acceptable exposure for a human
or ecological receptor (determined through using the toxicity
benchmarks discussed in section V.B.), taking into account the various
pathways by which the constituent may move through the environment from
the waste management unit to the receptor.
The waste management units considered in the assessment are not
all-inclusive but were selected to reflect those that might be commonly
associated with the management of exited hazardous wastes (from
wastewaters to nonwastewaters) in non-Subtitle C waste management
units. These units were identified as commonly used in the management
of solid wastes in the 1988 Report to Congress entitled Solid Waste
Disposal in the United States Report. The Agency believes that risks
posed by other types of management of these exited wastes will be no
greater than those from the units assessed.
There is a high degree of variability in the physical and chemical
properties of the approximately 200 constituents evaluated. An
understanding of those properties and how they interact with the
physical and chemical properties that control persistence and mobility
in the environment is an essential element of the assessment. The
management units could potentially be located in the range of
environments that exist across the United States. These environments
have differing characteristics (e.g., meteorological conditions, soil
type) that are more conducive for the movement of certain constituents
in certain pathways than others. For example, an environment with a
high precipitation and high organic soil content may result in
significant exposures to fishers by constituents that readily adsorb to
soils (i.e., have a high log Kow) through erosion of contaminated
soil and uptake in the food chain. For other pathways, however, an
environment with these characteristics may result in relatively low
exposures. The assessment was designed to determine what conditions
would need to exist to cause higher exposures for each pathway rather
than developing a scenario and determining all the types of exposures
and receptors for that scenario. By determining the appropriate
conditions for which higher exposures from a given pathway will occur,
the Agency believes that environments where the conditions are not as
likely for a constituent to move through a pathway are protected.
The assessment was structured using a deterministic approach. A
deterministic approach uses a single, point estimate of the value of
each input or parameter and calculates a single result based on those
point estimates. The assessment used the best data available to select
typical (i.e., approximately 50th percentile) and high-end (i.e.,
approximately 90th percentile) values for each parameter or parameter
group as discussed in Section E.2. below. Sometimes full distributions
were available but, more commonly, ranges of values or point values
were available with no description of distributions or variability. If
there was not a sufficient distribution for the parameter, best
professional judgement was used in determining typical and high-end
values (which sometimes would be the maximum).
The assessment is constructed as a set of calculations that begin
with an acceptable exposure level for a constituent at a receptor, and
back-calculates to a concentration in a waste in a management unit that
corresponds to the acceptable exposure level. For the human receptors,
the assessment was designed to determine constituent concentrations in
waste for each waste management unit that would correspond to
protecting receptors at the high-end of exposure (i.e., above the 90th
percentile of each of the receptor populations and types of exposures
being assessed). The Agency estimated waste concentrations
corresponding to the high-end exposure by identifying four critical or
sensitive parameters in the source/pathway/receptor equations and using
high-end input values for those parameters and using central tendency
values for the remaining parameters. The Agency also estimated central
tendency (approximately the 50th percentile) and bounding estimates
(worst-case) of constituent concentrations in waste for each of the
receptor populations and types of exposures being assessed. For
ecological receptors, the approximate percentile level of protection is
difficult to discern. The Agency believes the ecological analysis is
conservative with respect to the overall assessment endpoint (e.g.,
sustainability of the reproducing populations) because of the way the
source, fate and transport parameters are set, the dietary habits
assumed, and how the toxicity benchmarks are developed. However, the
degree to which this conservativeness transfers to ecosystems is not
known.
The steps of the assessment which provide estimates of acceptable
constituent-specific concentrations in waste include the following:
Step 1--Specify acceptable risk levels for each constituent and
each receptor. See Section V.B. in today's preamble for a discussion of
how benchmarks are set for both human and ecological receptors.
Step 2--Specify the exposure medium. Using the toxicity benchmarks
as a starting point and the exposure equations, the assessment back-
calculates the concentration of contaminant in the medium (e.g., beef,
milk, plant, air, water, soil) that corresponds to the ``acceptable''
exposure level. The exposure equations include a quantitative
description of how a receptor comes into contact with the contaminant
and how much the receptor takes in through specific mechanisms (e.g.,
ingestion, inhalation, dermal adsorption) over some specified period of
time. Thus, for the subsistence farmer eating contaminated beef, the
exposure specifies the amount of beef eaten on a daily basis, the
period of time over which the contaminated beef is eaten, and
descriptions for the individual such as body weight and lifetime. For
this example, the concentration in the beef is what is back-calculated.
Step 3--Calculate the point of release concentration from the
exposure concentration. Based on the back-calculated concentration in
the exposure medium (from Step 2), the concentration in the medium to
which the contaminant is released to the environment (i.e., air, soil,
groundwater) for each pathway/receptor was modeled. The end result of
this calculation is a medium concentration at the point of release from
the waste management unit.
Step 4--Calculate the concentration in the waste that corresponds
to the medium concentration at the point of release. This step depends
on the characteristics (e.g., area, cover practices, waste consistency)
of the waste management unit.
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The output of the assessment is a range of constituent
concentrations, reflecting the range of pathway-receptor combinations
considered for each waste management unit. The lowest concentration
(per constituent) of this range represents the highest exposure
pathway-receptor combination for that waste management unit.
c. How Uncertainty is Addressed
Any analysis of the magnitude used in this rule-making will have
uncertainty associated with the outputs generated. The uncertainty can
be associated with the models or equations used and the data relied on
for the model parameters. In addition, policy assumptions, such as
waste management units assessed and receptors assessed, may also affect
the degree of representativeness of the assessment. In order to be
consistent with Agency policy on the characterization of risk,
stochastic and deterministic approaches were considered. A stochastic
approach, such as Monte Carlo analysis, which produces a distribution
of constituent concentrations, was initially considered due to the
tremendous interest in, and use of, these techniques in risk
assessment. However, after evaluation of the models and data available
for use, the Agency decided to use a deterministic approach for the
non-groundwater assessment.
The Agency's deterministic approach used for this assessment, like
most such approaches, uses point values in all calculations and
produced point estimates of constituent concentrations for waste in
each management unit-exposure pathway-receptor combination. However, in
selecting and developing point values for parameters, EPA considered
all available data. Wherever possible, the Agency developed both a
central-tendency and high-end value for each parameter used in the
assessment. This was not possible in all cases because some parameters
were a property, such as density of water, and because some values were
fixed by Agency-wide policy decisions. (For example, EPA used standard
Agency-wide human toxicity benchmarks and body weights.) EPA then
calculated constituent concentrations based on a mixture of central-
tendency and high-end values.
EPA believes that the deterministic approach described above (based
on identifying critical parameters and using higher-end values only for
those parameters and central-tendency values for the other parameters)
allowed it to derive constituent concentrations in waste for each waste
management unit that are reasonably protective across a range of
conditions and for a range of receptors. EPA also believes that this
approach is consistent with EPA's risk assessment policy.
EPA further believes that the approach chosen allows both the
Agency and the public to determine more easily which parameters played
the most critical roles in determining the constituent concentrations
in waste for each waste management unit. This furthers general
understanding of the assessment and helps commenters effectively target
their resources for reviewing what EPA is proposing. It has also helped
EPA target its own data collection and input selection efforts. It is
often more difficult to identify critical parameters in a stochastic
assessment because of the greater number of iterations and because
results are reported as probability distributions. This is particularly
true for an analysis with a large number of parameters such as the
assessment used for this proposed rule.
EPA notes that stochastic approaches are also consistent with
Agency risk assessment policy. In fact, EPA applied a stochastic
``Monte Carlo'' approach to the separate analysis of dilution and
attenuation of groundwater performed for this proposal. That analysis,
however, has been under development for many years and EPA is more
familiar with the underlying data and the relationships between various
parameters. In addition, the public has had a chance to comment on
aspects of that analysis in previous rule-makings. EPA was more
comfortable applying a stochastic analysis for the groundwater analysis
than a stochastic approach to the non-groundwater analysis.
EPA believes that it is not necessary to resolve all issues
relating to the relative merits of the two approaches or to determine
which approach would be ideal for each of the assessments described
above. Rather, the debate should focus on whether the approaches chosen
allowed EPA to reach reasonable regulatory decisions.
The Agency solicits comment on the use of a deterministic approach
as described above. Specifically, the Agency seeks comment on whether
the approach proposed is a reasonable approach for setting protective
levels across a set of types of management units and exposure pathways.
d. Linkage of the Non-groundwater Risk Assessment to the Groundwater
Risk Assessment
In the non-groundwater risk assessment, the pathways involving
potentially contaminated groundwater (e.g., bathing) are back-
calculated from the receptor to the wellhead (i.e., the assessment
provides constituent concentrations in the groundwater at the well). In
order to determine the concentration of a constituent in leachate
coming from a waste management unit that would result in the estimated
constituent concentration at the water well, the Agency used a separate
groundwater fate and transport risk analysis. That analysis is
described in detail in Section D.8. elsewhere in today's proposal. The
well concentrations estimated from the pathways involving bathing are
used as input to the groundwater fate and transport modeling from which
a leachate concentration is determined.
e. Risk Targets Used
As previously discussed in Section V.B. of today's proposed rule,
the Agency used existing toxicity benchmarks when available. However,
many ecological benchmarks were developed for this rule-making, as
discussed in Section V.B. of today's proposed rule. As described in
that section, the Agency used a cancer risk target of 1 x 10-6,
and a hazard quotient equal to 1 for non-carcinogens. For ecological
benchmarks, a hazard quotient equal to 1 was used. The Agency solicits
comment on the risk targets being used for today's proposed rule.
2. Detailed Overview of the Non-groundwater Risk Analysis
The assessment can be broken down into six components:
Constituents; toxicity benchmarks; receptors; exposure; fate and
transport; and waste management units. Each of these components is
discussed in turn below, except the constituents and toxicity
benchmarks which were discussed earlier in section V.A and V.B. It is
important to recognize that the assessment was not able to evaluate all
constituents in all receptor-pathway-waste management unit combinations
because of data gaps in either toxicity or chemical properties, or
inadequate methodologies. Many of these gaps have been identified in
different sections of the Technical Support Document for the Hazardous
Waste Identification Rule: Risk Assessment for Human and Ecological
Receptors'' (denoted ``Uncertainties and Issues of Concern''). The
Agency requests additional data or other information that would assist
in filling these gaps.
a. Waste Management Units
The manner in which constituents are released to environmental
media and the relative quantity released to each
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medium will affect the pathways of most concern for a particular
constituent. The pathway presenting the highest risk to human or
ecological receptors is not always easily determined because of the
complex interactions of the waste management unit and its types of
releases, the physical and chemical properties of the constituent, and
the properties that control mobility and persistence in a particular
environmental medium. For some constituents, the management practice
will determine which exposure pathway is of most concern. For example,
benzene tends to migrate to both air and groundwater. Upon examining
the risks from exposure to these two media arising from releases from a
quiescent surface impoundment, the groundwater ingestion pathway may
pose the highest risks. But, when examining the risks from these two
media for releases from an aerated tank, the air inhalation pathway may
pose the higher risks. Further, the air inhalation risks may even be
higher than groundwater ingestion risks from the quiescent surface
impoundment.
Therefore, and as stated earlier, the selection of non-Subtitle C
waste management units examined in the assessment attempted to reflect
both the influence of the type of unit on pathways and those that might
be commonly associated with the management of exited hazardous wastes
in non-Subtitle C waste management units. Again, the Agency believes
that risks posed by other types of management of these exited wastes
will be no greater than those from the units assessed. The management
units examined include the following:
Aerated treatment tanks. Relative to all other types of
management, aerated tanks containing wastewaters can potentially have
the most significant releases of volatile organics to air.
Quiescent surface impoundments. This type of unit
containing wastewaters also can potentially result in significant
releases of volatile organic constituents to air. These units also have
a potential to affect surface water bodies if the unit is not well
maintained or constructed. The sludges generated, which may contain
high concentrations of metals and hydrophobic constituents, may impact
groundwater. (As discussed above, the groundwater fate and transport
analysis was conducted in a separate analysis.)
Land application. This type of unit, when used for non-
wastewaters can potentially have significant releases of certain
constituents to nearby land and surface water bodies through erosion
and runoff, particularly if run-on and run-off control measures are not
practiced. In addition, significant releases of volatile organics
constituents to air are possible. Further, after the unit is closed,
significant on-site exposures to some persistent and relatively
immobile constituents may occur as well as continued long-term releases
to the nearby land and surface water bodies. The Agency believes such
units will pose higher exposures relative to landfills in all pathways
except those arising from groundwater. Therefore, the non-groundwater
assessment did not examine landfills, but they were examined in the
groundwater fate and transport analysis.
Ash monofill. This type of unit used for ash disposal can
potentially have significant releases of particulates to air which may
be inhaled or may deposit on land and plants, and result in exposure
through food and soil ingestion.
Wastepiles. This type of unit used for nonwastewaters can
have significant releases of particulates to air as well as significant
releases of particulates through erosion and runoff.
Each of the pathways that evaluates a receptor using contaminated
groundwater other than as a source of drinking water (i.e., bathing)
are back-calculated to a concentration in a drinking water well. The
pathways are applicable to all of the waste management units modeled
(except tanks). All of the waste management unit and chemical-specific
portions of the groundwater fate and transport analysis and subsequent
estimated leachate concentrations are contained in the Agency's
separate groundwater fate and transport analysis (see Section E.3
below).
One exception to the above discussion of the types of waste
management units evaluated involves the combustion of wastes. Although
the Agency attempted to include this type of management in the
assessment, it became clear that the emissions from combustion are not
easily predicted from the waste inputs to the units. The combustion
process both destroys and creates constituents. Although destruction of
constituents can be predicted based on certain operating
characteristics of combustion units, the creation of other
constituents, referred to as products of incomplete combustion (PICs),
is not easy to predict. It may be possible to make such predictions for
a specific waste and a specific combustion unit; however, the extensive
data (e.g., on the variety of combustion units, waste types,
constituent combinations) needed for the assessment used in this
rulemaking relating wastes with emissions are not available. Therefore,
acceptable constituent levels in waste going to a combustion unit could
not be established. However, the Agency is developing emission
standards for various types of combustion units and those emission
standards may be a more appropriate vehicle for addressing combustion.
In addition, the assessment does not address accidental or
catastrophic releases, such as transportation accidents or tank
failures. The Agency determined that, although such releases are
possible, they are of low probability and non-routine and, therefore,
are not appropriate for developing exit criteria that apply to all
wastes.
The Agency has identified several specific areas giving rise to
uncertainty in the characterization of the waste management units and
for which the Agency seeks comment:
(1) Use of Subtitle D Survey.
The Agency relied upon data from a 1987 survey of Subtitle
D facilities to characterize waste management units. That survey, used
in the 1988 Report to Congress on Solid Waste Disposal in the United
States, was designed primarily to collect estimates of the following
parameters:
Number of establishments that manage Subtitle D wastes on
site;
Number of establishments that manage Subtitle D wastes on
site in land application units, wastepiles, surface impoundments, or
landfills;
Number of land application units, wastepiles, surface
impoundments, or landfills used to manage Subtitle D wastes;
Amount of Subtitle D wastes managed on site in land
application units, wastepiles, surface impoundments, or landfills.
In addition to these parameters, data were also collected for some
other parameters, such as the area of the waste management units.
Although the survey was not designed to collect accurate estimates for
these other parameters, it is the most comprehensive date available to
characterize these other parameters. One difficulty encountered in
using these data is that the survey requested information on total area
or waste quantity for all of each type of units at a facility. The
total area or waste quantity was divided by the number of each type of
unit at the facility (number of each unit being one of the primary
parameters the survey was designed to estimate) to estimate average
unit area. Further, it is not certain how well the on-site units (which
are used routinely for wastes generated on-site) reflect the
characteristics of off-site units. Uncertainty related to the
[[Page 66359]]
representativeness of the data is important because exited wastes could
be managed in units off-site as well as on-site. The Agency seeks
comment on the use of the Subtitle D survey to characterize the waste
management units.
In evaluating the waste management unit components of the risk
assessment, the Agency made certain assumptions when data were not
available or were incomplete. A description of the waste management
unit parameters for which there was little to no data is described
below. The rationale behind these assumptions is presented (e.g.,
results of any sensitivity analyses, references to other work, etc.).
The Agency requests comment on the specific issues raised for each
management unit.
(2) Fate and Transport
Fate processes, particularly biodegradation and hydrolysis, were
accounted for only in the land application unit since that unit had
wastes applied intermittently and that unit was being examined for on-
site risks after closure (assuming human occupation of the site begins
10 years after closure occurs). Because waste is continuously applied
to the other waste management units, biodegradation and hydrolysis were
presumed to have minimal influence on the subsequent availability of
constituents to the above ground pathways. The Agency requests comment
on not considering biodegradation and hydrolysis in waste management
units other than the land application unit. The Agency also requests
comment on the appropriateness of the data and methods used to account
for the fate and transport of constituents in waste management units,
with particular emphasis on data and methods of determining
biodegradation and hydrolysis of constituents in land application
units.
(3) Ash Monofill
(i) Particle Size Distribution for Air Dispersion Modeling
A size distribution of ash particles that become airborne from an
ash monofill was not available. Therefore, a sensitivity analysis was
performed to assess the importance of the particle size distribution in
the calculation of air concentrations and deposition rates. Different
distributions were modeled reflecting a variety of assumptions for
particle size distributions between PM10 and PM30 classes. The greatest
deviation among the modeled conditions in the estimated air
concentration of PM10 was 12 percent; for the estimated deposition rate
for PM30 the greatest deviation was 59 percent. Given the uncertainties
and variabilities inherent in the assessment, these variations were
considered minor, therefore, the Agency assumed an equal distribution
of particle sizes between the two size classes used in the assessment.
(ii) Monofill Characterization
Because limited data were available to characterize hazardous waste
ash monofills, data from municipal waste ash monofills were used.
However, because ash generation rates for municipal waste incinerators
ere more than 100 times greater than ash generation rates for hazardous
waste incinerators and reuse-as-fuel combustors resulting in
significantly larger municipal monofills, EPA calculated an ash
monofill volume for this analysis based on generation rates reported in
the 1988 National Survey of Hazardous Waste Treatment, Storage,
Disposal, and Recycling Facilities, assumed bulk density of the ash,
and assumed lifetime of the monofill. The Agency is not certain that
hazardous waste monofills should be sized in the same manner as
municipal waste monofills. The Agency also assumed that each waste
monofill would accept ash from only a single combustor. Accepting
wastes from more than one combustor may underestimate monofill size.
(iii) Vehicle Traffic
The estimates of number of ash trucks per day are dependent on the
size of truck. Limited data were available on the sizes of trucks
hauling ash. These data were used to characterize a range of truck
sizes. The truck sizes may either under- or overestimate the size of
trucks actually used at hazardous waste ash monofills depending on the
representativeness of municipal waste ash truck sizes.
No data were available on other vehicular traffic; therefore, these
values were estimated, introducing additional uncertainty into the
overall amount of traffic at the ash monofill.
(iv) Emission Equations for Ash Blown From Trucks and During Spreading
and Compacting
The emission equation used for ash blown from trucks was developed
for windblown emissions from storage piles. This was adapted to trucks
by using the truck speed to estimate frequency of wind greater than 5.4
m/s. Because this equation was not derived for windblown emissions from
moving trucks, the results of its application to such emissions are
uncertain. It may over- or underestimate actual emissions of
particulates blown from trucks.
Similarly, the emission equation used for spreading and compacting
was developed for agricultural tilling. Agricultural tilling was
thought to approximate the process of spreading and compacting;
however, the use of this equation may under- or overestimate emissions
due to spreading and compacting.
(4) Land Application Unit
(i) Particle Size Distribution for Air Dispersion Modeling
A size distribution of soil particles that become airborne was not
available. The same assumption was made for soil particles as was done
for ash particles when modelling the monofill (see above). As described
above for ash particles, the Agency assumed an equal distribution of
particle sizes between the two size classes.
(ii) Area of Land Application Unit Relative to Agricultural Field
The assessment examined the impact of subsistence farming on the
land application unit beginning 10 years after closure. Based on the
distribution of sizes for land application units and agricultural
fields, the Agency selected a combination of fields such that the
central tendency land application unit (61,000 m2) is smaller in
area than the central tendency agricultural field (2,000,000 m2).
The significantly larger size of the agricultural field suggests that
the model may inappropriately average the constituent concentration
over the agricultural field. However, the Agency does not believe this
to be a significant impact on the analysis because: (1) The area of the
agricultural field is not an explicit input to the model; (2) the size
of the land application unit is large enough to support a subsistence
farmer; and (3) this pathway is driven by the assumptions for the high-
end analysis. The Agency requests comment on the relationship between
the land application unit and the agricultural field.
(iii) Application Rate
The waste application rate is an important parameter in determining
the constituent's soil concentration after application. In practice,
this rate is a function of the characteristics of the waste being
applied, the characteristics of the receiving soil, the environmental
conditions, and the purposes for which the waste is being applied.
Information from the Subtitle D survey was used to calculate the rates,
since those rates
[[Page 66360]]
were not expressly requested in the survey. The rates were calculated
from the area receiving the wastes and the waste quantity applied. This
introduces uncertainty for it combines rates applicable to both
treatment of wastes and rates for specific uses (e.g., farming, mine
reclamation). To account for the potential of having application rates
be much too high for the site they are being applied to, the data on
receiving area and waste quantity applied were linked.
(iv) Waste Characteristics
Limited data were available on the characteristics of wastes being
land applied. As a result, soil values for most parameters (e.g.,
hydraulic conductivity, moisture retention index) were used to
characterize nonwastewaters. It is not known to what extent these soil
values differ from the waste properties.
(v) Depth of Contamination
Depth of contamination affects the amount of constituent available
for exposure. For the non-groundwater pathways, only constituents at
the soil surface were assumed available for each exposure pathway. The
Agency selected tilling depth as the depth of contamination available
to the non-groundwater pathways as over time, the depth of the waste
layer would increase and a portion of the mass of waste would move out
of the zone available for the surface pathways. The model kept the
depth of contaminated soil constant that was available for the surface
pathways. The Agency recognizes that the use of the tilling depth may
underestimate the depth of contamination in some cases and overestimate
it in others. Thus, the Agency requests comment on the use of tilling
depth as a surrogate for depth of contamination.
(vi) Partitioning
Releases from the land application unit were partitioned among
volatilization, evaporative losses, hydrolysis, erosion, runoff, and
leaching. Periodic application of waste was factored into the
partitioning model during the active life of the unit. Biodegradation
was factored in during both the active life and closed period. The
finite source Jury model was used to estimate volatilization emissions.
The Jury model, which models the convection of constituents caused by
the flux of water in soil, was used for evaporative losses. Runoff and
leaching losses were calculated using the soil-water partition
coefficient (Kd) to determine constituent concentration in the
soil water and multiplying that by the land application unit area and
runoff rate for run-off losses or recharge rate for leaching losses.
(See Technical Support Document for the Hazardous Waste Identification
Rule: Risk Assessment for Human and Ecological Receptors, Section 7,
Land Application for full description.)
(5) Waste Pile
(i) Waste Pile Height
No data were available on this parameter; therefore, the value is
an estimate based on heights attainable by a front-end loader. This
parameter is important in the air dispersion modeling, which is
sensitive to the height of the pile. The Agency requests suggestions
for alternatives to determining waste pile height and any data which
would support those determinations.
(ii) Particle Size Distribution for Air Dispersion Modeling
The same sensitivity analysis and assumptions discussed above for
ash monofills were used for waste piles. Given that the air dispersion
analysis is not very sensitive to particle size distribution, the
simple assumption described above was believed to be an adequate
approximation for the assessment.
(iii) Waste Characteristics
Limited data were available on the characteristics of wastes in
waste piles. As a result, soil values for most parameters (e.g.,
hydraulic conductivity, moisture retention index) were used to
characterize the nonwastewaters disposed in piles. It is not known to
what extent these soil values differ from the waste properties. The
soil values, however, were not used for the ash waste pile. The ash
disposed in the piles had the same properties as that disposed of in a
monofill.
(iv) Vehicle Traffic
The estimates of number of trucks per day are dependent on the size
of truck and waste quantity. Limited data were available on truck
sizes. These data were used to characterize a range of truck sizes.
These truck sizes may either under- or overestimate the size of trucks
actually used around waste piles.
(v) Emission Equation for Ash Blown from Trucks
As described in the section above on ash monofills, the emission
equation used for ash blown from trucks was developed for windblown
emissions from waste piles. It may over- or underestimate actual
emissions of particulates blown from trucks.
(6) Surface Impoundment
(i) Two-Phase Sludge Formation Model
The two-phase sludge formation model simplifies the solids
concentration gradient in a surface impoundment into two distinct and
homogeneous layers, a liquid layer with the same average solids content
as the inflow and a sediment or sludge layer with a much higher solids
concentration.
(ii) Dilution of Waste During a Spill
Overflows or breaches associated with surface impoundments are a
waste release examined in the assessment. The algorithm used for spills
does not account for dilution of the wastewater caused by excess run-
on. Such run-on is presumably relatively uncontaminated; thus the spill
volume, consisting partly of contaminated wastewater from the
impoundment and partly of uncontaminated run-on would have a lower
concentration than the wastewater in the impoundment. By using the
concentration in the impoundment, the mass of contaminant released to
surface water is overestimated. This effect could be considerable for
the central tendency impoundment, as the quantity of run-on is
significant compared to the capacity of the central tendency
impoundment. However, to determine the extent of such dilution, the
degree to which such run-on becomes mixed with the wastewater would
need to be estimated. No model has been found to assist in this
estimation.
(7) Tank
(i) Unit characterization
Limited data were available on Subtitle D tanks. The assessment
used the profiles (specifies design and operating parameters) for
uncovered aerated treatment tanks developed in the Hazardous Waste
TSDF--Background Information for Proposed RCRA Air Emission Standards
(TSDF--BID, U.S. EPA, 1991)
(ii) Volatilization
The Agency used the well-mixed flow model. This model assumes that
the contents of the system are well mixed and that the equilibrium
concentration in the system is equal to the effluent concentration. The
equilibrium concentration is the average concentration throughout the
unit and the driving force for volatile emissions.
(8) Combustors
For the reasons stated below, EPA did not modelled a combustion
unit in the risk analysis for this regulation. EPA,
[[Page 66361]]
however, asks for comments on that decision.
In initial analyses (see Multipathway Analysis Background Document
available through the docket), EPA modeled potential risks from several
types of combustion units, using engineering judgment to make a best
estimate for destruction and removal efficiencies for non-hazardous
waste combustors. Early comments suggested that the assumptions might
have overstated or understated the estimated risks by not reflecting
actual practice in industrial boilers or other likely combustion
facilities not regulated by Subtitle C. However, initial comparisons
indicated that the combustion risk estimates back-calculated to the
combustion unit were not often the most significant risk and,
therefore, would not be the basis for the limiting exit criteria.
EPA also recognized that there are many issues related to organics
that are produced during the combustion process, but are not
necessarily originally in the waste. The amount and type of these
``products of incomplete combustion'' are generally believed to be
dependent on a number of aspects of the design and operation of a
facility, and not easily related to the composition of the wastes fed
into the combustion unit. For purposes of this proposal, EPA decided
that because of the high degree of uncertainty associated with
developing waste concentrations from combustion units, it was not
appropriate to use risks from combustion as a factor in deciding what
wastes remain under the hazardous waste regulations. Rather, EPA
believes there are more appropriate ways to regulate emissions from
combustion units through various regulatory authorities, including
regulation of a range of units under the Clean Air Act.
EPA, however, asks comment on the appropriateness of this approach.
In particular, there may be some constituents (e.g., certain metals
that are difficult to capture in pollution control equipment) where a
better correlation exists between waste input and potential risk from
combustor emissions than for organics that are in the waste and also
created as PICs during the combustion process.
b. Fate and Transport
(1) Pathways
In selecting environmental fate and transport pathways to include
in the assessment, EPA used as a guide previous rulemakings and other
special studies by the Agency that examine numerous pathways. For
example, the Agency has used similar risk assessment methodologies in
several recent rules including: Wastes from Wood Surface Protection,
Final Rule (59 FR 458, January 4, 1994); Standards for Use or Disposal
of Sewage Sludge, Final Rule (58 FR 32, February 19, 1993); Corrective
Action Management Units, Final Rule (58 FR 29, February 16, 1993); and
rulemaking efforts on the Pulp and Paper Industry (56 FR 21802, May 10,
1991 and 58 FR 66078, December 17, 1993).
The sewage sludge and pulp and paper rulemakings in particular
examined both human and ecological risk. Other rulemakings under
development within the Office of Solid Waste also use non-groundwater
risk assessment methodologies including various hazardous waste listing
determinations and the dioxin emission rules for hazardous waste
combustion units. Most of these assessments rely on several Agency
guidance documents issued in recent years. In January 1990, the Agency
issued an interim report, Methodology for Assessing Health Risks
Associated with Indirect Exposure to Combustor Emissions (EPA/600/6-90/
003 and referred to as the Indirect Exposure Document). This document
served as the basis for further development of non-groundwater pathway
assessments by the Agency. In November 1993, the Agency issued an
Addendum to the Indirect Exposure Document that updated and revised
portions of the methodology presented in the Indirect Exposure
document. In April 1994, OSW issued a draft implementation guidance
entitled Implementation Guidance for Conducting Indirect Exposure
Analysis at RCRA Combustion Units. In June 1994, the Agency released a
review draft of Estimating Exposure to Dioxin-Like Compounds: Volumes
I-III (EPA/600/6-88/005C), which presents an extensive and expanded
version of the Agency's previous multiple pathway exposure assessments.
Finally on November 16, 1994, the Agency issued Draft Soil Screening
Guidance (59 FR 59225), which presents a multiple pathway assessment
using air, groundwater, and soil pathways for soil screening levels at
Superfund sites. The risk assessment presented relies on the
methodologies presented in these Agency guidance documents to maintain
consistency with previous Agency efforts.
Based on these efforts by the Agency in conducting non-groundwater
pathway assessments, comments by reviewers on previous draft versions
of the risk assessment, and some screening analyses to identify
pathways that are either very similar or unimportant compared to other
pathways, the Agency selected the human and ecological exposure
pathways presented in Table A-1 (human exposure pathways) of appendix A
and Table A-2 (ecological exposure pathway) of appendix A. These
exposure pathways are described in greater detail in the Technical
Support Document for the Hazardous Waste Identification Rule: Risk
Assessment for Human and Ecological Receptors.
Tables A-1 and A-2 presents four columns: column 1 (exposure
media), identifies the medium, such as air or soil, to which the
receptor is exposed; column 2 (route of exposure), identifies the
route, such as inhalation or ingestion, by which a receptor is exposed
to the exposure medium; column 3 (type of fate and transport),
classifies the pathway by the primary mode of fate and transport of the
contaminant to the exposure medium, including direct air, air
deposition, air diffusion, groundwater, overland, and soil; and column
4 (exposure scenario), identifies the compartments in the pathway
(e.g., source to air to humans), and describes the exposure scenario
(e.g., inhalation of volatiles).
The fate and transport pathways examined can be grouped into six
types of initial release and movement away from a waste management
unit, as follows:
Direct air pathways--air emissions of volatiles and
respirable (PM10) particulates;
Air deposition pathways--air emissions of particulates
that deposit on soil or plant surfaces;
Air diffusion pathways--air emissions that, while in the
vapor phase, diffuse directly into surface water or plants;
Groundwater--groundwater releases (These are the pathways
that link to the separate groundwater fate and transport analysis that
then links to the waste management units.);
Overland pathways--overland transport (i.e., surface
runoff and soil erosion) to surface water or transport by soil erosion
to off-site fields;
Soil pathways--on-site soil exposures.
There are three types of pathways not included in the analysis.
Pathways involving the use of contaminated water (groundwater and
surface water) for irrigation were removed due to modeling difficulties
that could not be resolved, however early results indicated these are
not the most significant pathways for any of the waste management
units. Pathways involving the deposition of contaminated particles
directly onto
[[Page 66362]]
surface water bodies were not included because previous efforts by the
Agency have shown these pathways not to be as significant when compared
to particle deposition onto the watershed and subsequent erosion to the
surface water body. Pathways involving wet deposition were not
examined. An air model recently developed evaluates the impact of wet
deposition and was not available to use at the time of this proposed
rule. This new model also was addressing problems with the area
component of earlier models. When the model is available, the Agency
will determine whether its use will have an impact on the proposed exit
criteria. If the Agency determines that there will be an impact, it
will provide an opportunity for public comment on use of the updated
model.
As stated earlier, not all exposure pathways were evaluated for all
waste management units. Constituents may be released from each waste
management unit by a variety of mechanisms. Each release mechanism may
be associated with certain exposure pathways. By examining the release
mechanisms assumed for each waste management unit and identifying the
exposure pathways associated with those release mechanisms, the
appropriate pathways to be modeled for each waste management unit were
identified. The exposure pathways modeled for each waste management
unit are presented in Table A-5 of appendix A.
b. Equations
Since the objective of the assessment was to generate acceptable
levels in waste rather than determining risks posed by waste, the
equations, which are designed to calculate risks, had to be turned
around or run in reverse. The assessment began with a target risk (or
acceptable risk to the receptor) that was used to back-calculate what
constituent concentration in a waste would not exceed the target risk.
Wherever appropriate, the equations used in the back-calculation
were taken from Methodology for Assessing Health Risks Associated with
Indirect Exposure to Combustor Emissions (U.S. EPA, 1990x; hereafter,
the Indirect Exposure document, or IED) as modified by the November 10,
1993, draft of Addendum: Methodology for Assessing Health Risks
Associated with Indirect Exposure to Combustor Emissions, Working Group
Recommendations (U.S. EPA, 1993x; hereafter, the Addendum). The
Addendum is currently being revised based on comments from the Science
Advisory Board and is being combined with the IED to generate a single
methodology guidance document. Therefore, the equations may change
after that revision is completed. If this occurs, the assessment used
for this rule-making will be revised. If such a revision is needed and
occurs, the Agency will provide an opportunity for public comment on
those changes. For convenience, the methodology presented in the IED as
modified by the Addendum will be referred to as the Indirect Exposure
Methodology, or IEM.
The equations presented in the IEM were modified to estimate the
soil concentration for constituents eroding to an off-site field. The
IEM did not address this pathway because it was developed for stack
emissions from combustors rather than releases from land-based units.
However, because soil erosion is a critical release pathway for this
analysis, the Agency applied the Universal Soil Loss Equation (USLE)
and other equations presented in the IEM to calculate soil erosion to
the off-site field. However, the application of these equations
resulted in concentrations greater at the receptor than in the waste
management unit. This phenomenon, first noted in the Dioxin
reassessment, occurred because the equations assumed that the amount of
uncontaminated soil that was eroded into the field was negligible in
comparison to the total mass of soil in the field. Therefore, the
Agency modified these equations to reflect erosion of uncontaminated
soil together with the constituents.
Certain modifications to the equations used in the assessment were
made for dioxin-like compounds to reflect the different behavior of
these constituents in the environment. These modifications were based
on Estimating Exposure to Dioxin-like Compounds, Volume III: Site-
Specific Assessment Procedures (U.S. EPA, 1994x), hereafter referred to
as the Dioxin document. The Dioxin document defines dioxin-like
compounds as ``* * * compounds with nonzero Toxicity Equivalency Factor
(TEF) values as defined in the 1989 International scheme * * * [which]
assigns nonzero values to all chlorinated dibenzodioxins (CDDs) and
chlorinated dibenzofurans (CDFs) with chlorines substituted in the
2,3,7,8 positions. Additionally, the analogous brominated compounds
(BDDs and BDFs) and certain polychlorinated biphenyls (PCBs) have
recently been identified as having dioxin-like toxicity * * * and thus
are also included in the definition of dioxin-like compounds.''
Although the modifications presented in the Dioxin document may be
applicable to other highly lipophilic compounds, in keeping with this
definition, the modifications for dioxin-like compounds were made only
for 2,3,7,8-TCDDioxin Toxicity Equivalents (TEQs), and PCBs. Other
dioxin congeners are addressed through the 2,3,7,8-TCDDioxin TEQ. The
Agency solicits comment on not using these modifications for other
highly lipophilic compounds.
(3) Specific Issues on Pathways and Equations
Below are specific issues of the risk assessment related to the
modeling of the fate and transport pathways on which the Agency is
requesting comment on their use, improvements to them, or alternative
ways to model them. A detailed discussion of these aspects is in
Section 6, Fate and Transport Modeling, of the Technical Support
Document for the Hazardous Waste Identification Rule: Risk Assessment
for Human and Ecological Receptors. (Air emission and dispersion
modeling is discussed in Section 7, Waste Management Units, in the
technical support document. To be consistent, issues related to that
modeling were presented earlier in this preamble in Section D.2.a.)
(i) Hydrolysis
The Agency accounted for fate processes (e.g., biodegradation,
hydrolysis) and transport processes (e.g., volatilization) for
constituents throughout their movement from the point at which the
constituent leaves the waste management unit until it reaches the
location at which contact with the receptor occurs. During an initial
screen, the Agency identified four constituents that were known to
hydrolyze completely or rapidly. These constituents were not included
in the detailed assessment and include: Benzotrichloride (98-07-7);
maleic anhydride (108-31-6); phthalic anhydride (85-44-9); and 1,2-
diphenylhydrazine (122-66-7). In addition, 16 inorganic salts known to
dissociate completely were also not assessed. These included: Calcium
cyanide (592-01-8); copper cyanide (544-92-3); potassium cyanide (151-
50-8); potassium silver cyanide (506-61-6); silver cyanide (506-64-9);
sodium cyanide (143-33-9); thallium (I) carbonate (6533-73-9); thallium
(I) chloride (7791-12-0); thallium (I) nitrate (10102-45-1); thallium
(I) sulfate (7446-18-6); zinc cyanide (557-21-1); zinc phosphide (1314-
84-7); cyanogen bromide (506-68-3); cyanogen chloride (506-77-4);
hydrogen cyanide (74-90-8); and thallium acetate (563-68-8). The Agency
solicits comment on not assessing these constituents.
[[Page 66363]]
Of the 192 constituents evaluated in the non-groundwater analysis,
the Agency directly accounted for chemical hydrolysis for 18
constituents. For the remaining constituents, hydrolysis was not
considered for the following reasons: The constituent has no
hydrolyzable chemical group; hydrolysis is not expected to be important
or significant; the degradation half-life of the chemical, which
includes hydrolysis, is greater than one year; or, there was no data
available for the constituent.
The extent to which fate and transport processes play a role in the
removal of a constituent from a pathway, or its movement from one
environmental compartment to another is determined by site-specific
environmental conditions as well as chemical-specific parameters. To
simplify the analysis, the Agency used fate and transport data based on
one set of environmental conditions to represent all possible spatial
and temporal environments encountered in any given exposure pathway.
The Agency solicits comments on this simplification for modeling fate
and transport processes throughout the exposure pathways considered in
the MPA.
(ii) Other Fate and Transport Processes
Fate and transport processes other than hydrolysis may be important
in determining the concentration of a constituent reaching a receptor.
The Agency's approach to incorporate consideration for these other
processes involved the use of biodegradation and volatilization rates
into the fate and transport pathways, when applicable. The Agency
recognizes that the rate for many chemical-specific fate and transport
processes (in particular, biodegradation) varies with characteristics
of the environment (e.g., temperature, soil type). However, the Agency
simplified the non-groundwater analysis by applying chemical-specific
fate and transport rates generically across environmental settings
found in the various exposure pathways. This simplification may
overestimate the exit level in some instances and underestimate the
exit level in other instances. The Agency solicits comments on this
simplification for modeling fate and transport processes throughout the
exposure pathways considered in the non-groundwater analysis.
(iii) Bioavailability
With regard to the metals examined in the risk assessment, there is
considerable uncertainty about their bioavailability that affects their
fate, transport, and uptake in various media (e.g., plant tissue,
animal tissue) and receptors. Speciation and associated solubility of
metal species in wastes which contain metals are key factors that
influence the bioavailability of metals. The Agency had no information
on the speciation, solubility, or availability of the metals in the
wastes in which they are disposed or how they may transform in the
environment. The Agency assumed that the metals were in a soluble form,
mobile, and available. In the absence of this information, the Agency
assumed that metals are soluble, mobile, and bioavailable. The Agency
seeks comment on this approach, and requests data on the speciation and
solubility of metals in wastes, together with the conditions of the
waste (e.g., pH) that could be disposed by the methods considered in
this rulemaking and methodologies that account for the transformation
of the metals through changing environmental conditions.
(iv) Meteorological Data
The approach for setting central-tendency and high-end
meteorological conditions in the risk assessment was to evaluate sets
of meteorological data from a variety of locations, and then select
locations that reflect central tendency or high-end conditions for a
given exposure pathway.
The Agency used the set of 29 meteorological stations identified
during its efforts to develop soil screening levels for Superfund
sites. These are considered representative of the United States.
Central-tendency and high-end locations were then selected from these
29 locations for the exposure pathways where meteorological conditions
were required as input to the models; these were the air pathways and
overland pathways. The meteorological data were evaluated as location
sets as opposed to individual parameters. Once locations were selected,
the annual average values for those locations were used.
For air pathways, which required data on wind speed, wind
direction, temperature, sunshine, cloud cover, and air mixing height,
selection of meteorological data was waste management unit-specific and
based on extensive sensitivity analysis. EPA considered only the effect
of meteorological data on emissions and dispersion in selecting
locations for air pathways. However, for consistency, once a pair of
high-end and central tendency locations were selected for a pathway,
any meteorological data used in that pathway were selected to
correspond to the locations chosen, even in any overland transport
component of the pathway.
Overland pathways were driven by soil erosion, for which the
critical meteorological input is the Universal Soil Loss Equation
(USLE) rainfall factor (R). Therefore, to select central tendency and
high-end locations for overland pathways, the 29 locations were ranked
based on the rainfall factor, and the 50th and 90th percentile
locations chosen for all overland pathways.
See Section 6.8, Fate and Transport Inputs and Section 7.1.5. Air
Modeling, of the Technical Support Document for the Hazardous waste
Identification Rule: Risk Assessment for Human and Ecological Receptors
for a detailed discussion of how meteorological data were selected and
used. The Agency solicits comment on how meteorological data was
selected and used in the risk assessment.
(v) Soil Data
A variety of soil parameters were required for the modeling. These
parameters are interdependent and vary with the type of soil (e.g.,
loam, clay). However, values for these parameters also vary within a
soil type. Due to the interdependence of the parameter, the Agency
chose to maintain them as a set and determine a central-tendency
property set and a high-end property set.
The Agency used loam type soils to characterize all soils simulated
in the risk assessment because these types of soils are fairly
prevalent in the United States. All soils are composed of varying
percentages of sand, silt, and clay. Loam, by definition, is composed
of equal proportions of sand, silt, and clay; therefore, it represents
a combination of each of the physical properties of the individual soil
textures. Central tendency and high-end values were selected from the
range of values for loam soil so that each individual soil parameter
required by the model is consistent with a loam soil. (Sec Section 6.8,
Fate and Transport Inputs, in the Technical Support Document for the
Hazardous Waste Identification Rule: Risk Assessment for Human and
Ecological Receptors for more detail.) The Agency solicits comments its
approach for characterizing soil in the assessment.
(vi) Soil Pathways
The Agency seeks comment on the following issues related to the
modeling of soil pathways:
Use of the Universal Soil Loss Equation to predict soil
erosion in a generic application - This is a widely-used model intended
for site-specific
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applications where specific input data can be used for relatively small
fields. Its use in a generic application, and for fairly large waste
management units, may overestimate quantities of soil eroded.
Handling of the Soil Loss Constant - This term is the sum
of loss rates for leaching, erosion, runoff, biodegradation,
hydrolysis, and volatilization. Possible uncertainties may arise
because: the assessment assumes that these terms are first-order decay
rates and therefore can be added together; loss processes are
calculated independently, even though they may occur simultaneously.
Use of the Soil Water Content Equation to predict soil
water content in a generic application - The equation is from the
Superfund Exposure Assessment Manual (U.S. EPA, 1988x), and was
developed for site-specific applications.
Area of garden and agricultural field - No data were
available on the size of home gardens, gardens on subsistence farms, or
yards of residential lots (for soil ingestion). Therefore, a single set
of central tendency and high-end values was estimated for these, based
on best professional judgment; this set is referred to as garden area,
even though it might also apply to a yard. Because a larger area leads
to greater dilution of deposited or eroded contaminant, a high-end
garden would be one that was relatively small.
Areas for agricultural fields were estimated from data in
the 1992 Census of Agriculture (U.S. Department of Commerce, 1992). The
Census gives average farm acreage by State for 48 States (the data are
not yet complete for the two missing States). No percentile data were
available. These data do not distinguish between commercial and
subsistence farms.
Mixing Depth--Mixing depth reflects the depth of soil to
which deposited or eroded contaminant is mixed. It is important to
distinguish between soil that is tilled for agricultural purposes and
soil that is untilled in determining appropriate mixing depth values. A
smaller mixing depth results in less dilution of a constituent, and
therefore higher soil concentrations; therefore, a high-end mixing
depth would be smaller than a central tendency mixing depth.
(vii) Surface Water Pathways
Water column as well as benthic sediment concentrations were
estimated. Water column concentrations include dissolved, sorbed to
suspended sediments, and total (sorbed plus dissolved, or total
contaminant divided by total water volume). Benthic sediment
concentrations included: Dissolved in pore water, sorbed to benthic
sediments, and total. The model accounts for three routes of
constituent entry into the water-body were examined: Sorbed to soils
eroding into the water-body; dissolved in runoff water; and diffusion
of vapor phase contaminants into the water-body. Air deposition of
constituents bound to particles into a water-body was not examined
because earlier analysis demonstrated that its contribution would be
negligible when compared to that of eroding particles. Volatilization
of dissolved constituents and removal of constituents through burial in
bed sediments were modeled as loss processes.
Important assumptions made for the surface water modeling included:
Water-body sufficiently large to support certain ecological receptors;
sufficient fish to support a subsistence fisher; uniform mixing within
the water-body (this tends to be more realistic for smaller water-
bodies as compared to large river systems); and equilibrium is
established between constituents within the water column, bed
sediments, and air.
The Agency seeks comment on the following issues related to the
modeling of surface water pathways:
Water-body/Watershed Characterization--The water-body
characterization parameters are another example of a set of parameters
that are interdependent and therefore were used as a group. Watershed
characterization relates to the water-body (in the case of the
assessment, a stream) characterization. Streams are characterized
(flow, water-body area, watershed area, depth, and various other
parameters) by their ``order.'' A first-order stream has no tributary
channels; a second-order stream forms when two first-order streams
converge, and so on through stream order 10. The Agency used a stream
order 4 as the high-end estimate because EPA believes this stream order
would be among the smallest stream orders that would support sufficient
fish or a subsistence fisher and the receptors assessed. A stream order
5 was used as the central-tendency estimate based on the number of
streams within each stream order. (See Section 6.8 in the Technical
Support Document for the Hazardous Waste Identification Rule: Risk
Assessment for Human and Ecological Receptors for more detail.)
Total Suspended Solids--Total suspended solids (TSS) can
range from 1 to 100 mg/L with a typical value being 10 mg/L for streams
and rivers. This value is used as the central tendency value. No data
on frequency of values in actual streams was available to estimate a
90th percentile value. Since 80 mg/L is believed to be the maximum
tolerable value for aquatic life; this value was used as the high-end
value.
Bed Sediment Concentration--The bed sediment concentration
term is analogous to the bulk density for soil in that it describes the
concentration of solids in terms of a mass per unit volume. A single
value of 1 kg/L was used in the assessment given that this is
considered a reasonable value in most situations and the range is quite
narrow, 0.5 to 1.5 kg/L.
Gas-Phase Transfer Coefficient--The gas-phase transfer
coefficient is used to estimate volatile losses from the water-body.
Volatile losses are calculated using a two-layer resistance model that
incorporates a gas-phase transfer coefficient and a liquid-phase
transfer coefficient. Both transfer coefficients are controlled by flow
induced turbulence in flowing systems. The liquid-phase transfer
coefficient is calculated based on chemical-specific properties. A
single value of 36,500 m/yr. was used. There is some uncertainty
related to setting this parameter to a single value that is not
chemical specific. It is reasonable to assume that chemical properties
affecting volatility would have some effect on this value, although it
is not known how large such an effect would be.
Fraction Organic Carbon in Bottom Sediment--The fraction
organic carbon in bottom sediment is derived from the fraction organic
carbon in watershed soils. For a fraction organic carbon of about 0.01
in the watershed, the fraction organic carbon for bottom sediments is
typically 0.03 to 0.05. The midpoint of this range, 0.04, divided by
the fraction organic carbon of the watershed (0.01) derives a
multiplier of 4 for calculating fraction organic carbon in bottom
sediments from fraction organic carbon in watershed soils. The fraction
organic carbon values used of 0.024 and 0.008 correspond to the central
tendency and high-end values for soil fraction organic carbon of 0.006
and 0.002, respectively. The fraction organic carbon in the bottom
sediments was varied with the fraction organic carbon in soil.
(viii) Food-Chain Pathways
The Agency seeks comment on the following issues related to the
modeling of food-chain pathways: (Please note the fish uptake
methodology is described below in Section D.2.c.2), Ecological
Receptors and Exposure; the littoral methodology is used for humans):
[[Page 66365]]
Use of regression equations based on Kow to derive
biotransfer factors for plants--The biotransfer factors are based upon
empirical relationships with Kow defined by studies on relatively few
chemicals.
The lack of accounting for translocation of contaminants
within plants--The plant uptake models do not account for translocation
of contaminants (should such a translocation occur) from one part of a
plant to another. The Agency is considering two models developed by
Stephan Trapp, plantx and plantE, and solicits comment on their use.
Use of regression equations based on Kow to derive
biotransfer factors for beef and milk--The biotransfer factors for beef
and milk are based upon empirical relationships with Kow defined by
studies on relatively few chemicals.
c. Receptors
Both human and ecological receptors are considered in the
assessment. The human receptors evaluated were selected to represent a
range of behaviors and activities that influence exposure levels. The
Agency believes that these represent typical and more exposed types of
behaviors and activities that might exist around waste management units
or media contaminated by releases from waste management units. Each
receptor was evaluated for individual exposure pathways (i.e., exposure
to multiple pathways was not included). For ecological receptors,
populations or communities were selected for the generic terrestrial
and freshwater ecosystems based on behavior patterns such as dietary
habits (plant-eater vs. meat-eater) as well as qualities such as
significance and representativeness with respect to trophic structure
in the ecosystem (bald eagle). The selection of ecological receptors
was limited by the level of characterization available such as food
intake and body weight. Again, the Agency believes that these represent
the types of organisms that might exist around waste management units
or media contaminated by releases from waste management units.
(1) Human Receptors and Exposure
Human receptors assessed in the assessment included the following:
Adult resident living in the vicinity of a management
unit--This individual is representative of the general population in
the United States and is evaluated independently through the following
potential exposure pathways: Inhalation, ingestion of contaminated
soil, ingestion of contaminated drinking water, dermal contact with
contaminated soil, and dermal contact during bathing. In addition, the
analysis evaluates exposures to an adult resident living on-site of a
land application unit begining 10 years after closure of the unit.
Child resident living in the vicinity of a management
unit--Children are a special population considered in certain pathways
because of their low body weight compared to high intake rates or
surface area. A child is evaluated through the following potential
exposure pathways: ingestion of contaminated soil, dermal contact with
contaminated soil, and dermal contact during bathing.
Home Gardener--This individual represents a sub-population
that supplements their fruit and vegetable consumption with fruits and
vegetables they grow on contaminated land.
Subsistence Fisher--This individual represents a sub-
population that subsists on contaminated fish.
General Fish Consumer--This individual represents a sub-
population that consumes contaminated fish and supplements their intake
with other non-contaminated foods.
Subsistence Farmer--This individual represents a sub-
population that grows or raises most of their own food on contaminated
land. This individual is evaluated independently through the following
exposure pathways: beef ingestion, milk ingestion, and fruit and
vegetable ingestion.
On-site Worker--This individual represents the working
population that may be found at the waste management units. This
individual is evaluated during the active phase of the unit for the
following on-site exposures: Inhalation and dermal contact with
contaminated soil.
Each of the receptors has been matched with the most relevant
exposure routes. Table A-3 in appendix A shows the pathways were
modeled for each receptor.
As previously discussed, the assessment begins with a target human
toxicity benchmark and exposure assumptions tailored to each receptor,
and back-calculates to constituent-specific concentrations in each
media. In characterizing the exposure, two exposure parameters are set
to high-end values and the rest of the exposure parameters are set to
central tendency or default values. The two high-end exposure values
were typically exposure duration and a parameter affecting intake of,
or exposure to, a contaminant (e.g., fraction contaminated, consumption
rate, inhalation rate).
The exposure equations used for back-calculating media
concentrations are based on standard risk equations used in most Agency
risk assessments. For all inhalation and ingestion pathways, these
equations were adapted from Risk Assessment Guidance for Superfund
(RAGS): Volume I--Human Health Evaluation Manual (Part B, Development
of Risk-based Preliminary Remediation Goals) (U.S. EPA, 1991x;
hereafter, RAGS Part B) and subsequent modifications. For dermal
pathways, which are not covered in RAGS Part B, the equations presented
in Dermal Exposure Assessment: Principles and Applications, Interim
Report (U.S. EPA 1992x; hereafter, the Dermal document) were used; this
document reflects the current techniques for assessing dermal exposure.
The Agency requests comment on the data sources and assumptions used in
the human exposure portion of the risk assessment, described in detail
in Section 5.0 of the Technical Support Document for the Hazardous
Waste Identification Rule: Risk Assessment for Human and Ecological
Receptors.
The Agency seeks comment on the following types of human exposure
that were not examined:
Ingestion of contaminated water by humans while bathing or
swimming--The ingestion rate of water while swimming or bathing is 30
times smaller than the normal consumption rate of water used in the
drinking water ingestion pathways; therefore, the drinking water
ingestion pathways should be protective of the incidental water
ingestion pathways.
Inhalation of volatiles while bathing--No appropriate,
chemical-specific equations could be found to address this pathway.
Ingestion of airborne particulates--The ingestion rate of
soil used in the soil ingestion pathways is many times larger than the
ingestion rate from airborne particulates; therefore, the soil
ingestion pathways should be protective of the ingestion of airborne
particulates. Also, given the way the soil ingestion rates were
empirically derived, ingestion of airborne particulates should, in
effect, be accounted for in the estimated soil ingestion rates.
Ingestion of contaminated soil by resident on active
site--While the waste management units are active, it is assumed that
access is limited to workers.
(2) Ecological Receptors and Exposure
In addition to the human receptors, ecological receptors were
evaluated in the assessment. Lacking an Agency precedent for the
selection of ecological
[[Page 66366]]
receptors for a generic analysis, a simple framework was developed for
ecological receptor identification based on EPA's Framework for
Ecological Risk Assessment (U.S. EPA, 1992x). During the problem
formulation phase, a suite of ecological receptors was selected to
include species that represent each of the trophic levels or feeding
habits within an ecosystem. At best, one can only infer that an
ecosystem is protected from chemical stressors. In addition, the
toxicological data support the evaluation of individuals, populations,
and occasionally communities, but are inadequate to address the
complexities of an ecosystem in most cases. Thus, the approach taken in
the assessment was to estimate protective levels for the populations
and communities (inferred from the measurement endpoints used) found in
generic ecosystems. The species included in the ecological assessment
encompass a wide range of dietary preferences, sizes, and trophic
levels.
In selecting ecological receptors for the assessment, a number of
ecosystem types (e.g., lakes, streams, estuaries, deserts, forests,
grasslands) were considered because the waste could be disposed
anywhere once it has exited the Subtitle C system. Two generic
ecosystems were designed: A freshwater-based ecosystem and a
terrestrial-based ecosystem. Specific details of these ecosystems are
described in Section 3, Receptors, in the Technical Support Document
for the Hazardous Waste Identification Rule: Risk Assessment of Human
and Ecological Receptors. The Agency solicits comment on both the
adequacy of the design of the ecosystems used in the assessment and the
use of generic ecosystems to assess potential ecological hazards.
Generally, ecological receptors were identified at different
trophic levels as well as at different levels of biological
organization and included species of relatively low ecological
significance but high societal relevance (e.g., American kestrel). The
final selection of receptors was based primarily on the availability of
data with which to assess the risks to that receptor. As suggested in
the Framework for Ecological Risk Assessment (1992x), the process of
selecting appropriate assessment endpoints was iterative, including
information from the other activities included in the assessment
phase--the characterization of ecological effects. The ecological
receptors included in the assessment were:
Mammals--Mammals were evaluated for both generic
ecosystems and include upper trophic level predators such as the mink
or red fox, lower trophic level consumers such as the whitetail deer,
and insectivores such as the meadow mole; species were selected to
represent a variety of body sizes, habitats, and dietary habits for
which data on body weight, food intake, etc., are available. Mammals
may be exposed by eating contaminated prey items (e.g., fish, other
vertebrates, insects) or plants, through incidental ingestion of
contaminated soil while eating or preening, or through lactation or
placental transfer.
Birds--Birds were also evaluated for both generic
ecosystems and include upper trophic level predators such as the red-
tailed hawk and lower trophic level consumers such as the American
robin; species were selected to represent a variety of body sizes,
habitats, and dietary preferences for which input parameters (e.g.,
body weight, diet, ingestion rates) are available. Birds are exposed
through the ingestion of contaminated prey items (e.g., fish, worms),
through incidental ingestion that occurs while eating or preening, or
through maternal transfer to eggs.
Terrestrial Plants--Vascular plants that might be common
in a generic terrestrial ecosystem were evaluated. The species of
plants used to represent plants within the terrestrial ecosystem were
determined by the availability of data and included primarily forage
grasses and food crops. Plants are exposed through soil-to-root uptake,
deposition on the surface of leaves or bark, and during air-to-leaf
transport of volatile or semi-volatile constituents.
Soil Community--Representative species for the soil
community were based on six metrics for measuring ecological function:
(1) Location, (2) size, (3) abundance, (4) taxon richness, (5) trophic
structure, and (6) energy metabolism. Organisms living in or on the
soil are exposed through direct contact (e.g., insects), through the
ingestion of contaminated soil (e.g., earthworms), and through the
ingestion of other soil dwellers (e.g., centipedes). The Agency
solicits comment on the representative species selected to comprise the
soil community.
Fish--Given the small percentage of freshwater species for
which toxicological data are available, all species of freshwater fish
were considered as potential receptors, regardless of size or dietary
habits. Fish are subject to continuous exposure to contaminated water
via gill exchange and may be exposed to bioaccumulative chemicals
through the food chain.
Aquatic Invertebrates (Daphnids)--Aquatic invertebrates
are believed to be among the most sensitive aquatic species (Suter,
1993x), daphnids were selected to represent free living aquatic
invertebrates. Continuous exposure to contaminated water is considered
the primary route of exposure.
Aquatic Plants--Vascular aquatic plants and algae typical
of aquatic ecosystems were evaluated. Aquatic plants are exposed during
sediment-to-root uptake and through water-to-leaf transport.
Benthic Community--Representative species include
organisms that fall within any of the eight taxonomic genera used in
the development of the Ambient Water Quality Criteria for the
protection of aquatic life. Because these organisms spend most (if not
all) of their lives in the sediment, they are exposed through direct
contact and ingestion of contaminated sediments as well as through the
ingestion of other sediment dwellers.
Each of these receptors has been matched with the exposure pathways
and waste management units likely to result in exposure. Table A-4 of
appendix A shows which pathways were modeled for each receptor. The
Agency solicits comment on the use of a single species to represent
major trophic elements.
The development of medium-specific concentrations for the
protection of ecological receptors was based on ingestion of
contaminated vegetation, water, soil, or prey or through continual
contact with a contaminated medium (e.g., aquatic invertebrates with
water or soil fauna with soil).
Numerous studies have demonstrated the capacity of hydrophobic
organic chemicals to bioaccumulate in the food chain that are orders of
magnitude above the concentration in the contaminated medium (e.g.,
Oliver and Niimi, 1988x). However, it is important to recognize that
food-chain pathways may be significant even for constituents that do
not bioaccumulate appreciably. Dietary exposure to constituents that
concentrate weakly in fish tissue (e.g., bioconcentration factor below
10) may be more significant than exposure to contaminated drinking
water simply because a particular animal may ingest relatively more
fish than water.
For constituents that bioaccumulate, particularly those that
biomagnify, benchmarks should account for exposure through the
ingestion of contaminated prey as well as contact with or ingestion of
contaminated media. The majority of toxicological studies examined a
single route of exposure and seldom considered the potential increase
in exposure concentrations through successive
[[Page 66367]]
trophic levels. As a result, toxicity benchmarks for bioaccumulative
constituents cannot be used as acceptable medium exposure
concentrations; exposure estimates must incorporate the bioaccumulation
potential in the food chain. For nonbioaccumulating constituents, where
toxicity benchmarks that are medium specific (i.e., concentration
units--mg/kg or mg/L)) can be used as acceptable medium concentrations
for ecological receptors (e.g., Ambient Water Quality Criteria).
In the aquatic ecosystem, for bioaccumulative chemicals (log
Kow>4), bioaccumulation factors (BAFs) were estimated using models
developed by Thomann (1989x) for the limnetic (or pelagic) food chain
and Thomann et al. (1992x) for the littoral food chain (i.e., sediment-
based). However, for constituents with log Kow above 6.5, only
measured values were used. The Agency is considering using the Gobas
model since it can be used for constituents with log Kow above
6.5. Further, switching to the Gobas model would be consistent with the
Great Lakes Initiative which recently switched to that model. The
results produced by either the Thomann models or the Gobas model are
very similar. The tissue concentration (TC) was estimated for prey
based on the intake, body weight, and dietary preference (i.e., trophic
level of fish consumed) of the representative predator species.
Protective surface water concentration was calculated by dividing the
tissue concentration (TC) by the bioaccumulation factor for the
appropriate trophic level. For nonbioaccumulative chemicals, the
protective surface water concentration for fish and aquatic organisms
was the Final Chronic Value (FCV) or Secondary Chronic Value (SCV) as
described in Section 4 of the Technical Support Document for the
Hazardous Waste Identification Rule: Risk Assessment for Human and
Ecological Receptors. For upper trophic level aquatic wildlife such as
mink and osprey, protective surface water concentrations were
calculated based on the consumption of contaminated fish and water. The
benthic community was included in the littoral ecosystem. Protective
sediment concentrations were estimated using the equilibrium
partitioning (Eqp) methods developed by Di Toro et al. (1991x). As
explained in Section 4 of the Technical Support Document for the
Hazardous Waste Identification Rule: Risk Assessment for Human and
Ecological Receptors, the sediment benchmark was calculated by
multiplying the FCV (or SCV) by the octanol/carbon partition
coefficient (Koc) and adjusting for the fraction organic carbon
(foc) in the sediment. EPA requests comment on the selection of
the bioaccumulation model, the potential switch to the Gobas model,
BAFs used, dietary assumptions, and how tissue concentrations were
calculated.
For receptors in the generic terrestrial ecosystem, methods used
represented a range of dietary habits across trophic levels for
wildlife, including plants and organisms that live in the soil (i.e.,
soil fauna). (See the discussion on the development of soil and plant
benchmarks elsewhere in today's rule.) For higher trophic level
wildlife, dietary preferences, daily intake, and bioconcentration
factors for prey items were identified or estimated to calculate
protective soil concentrations. The key equation used to back-calculate
soil concentrations as a function of dietary exposure (including soil
ingestion), and the exposure inputs (e.g., body weights, daily intake)
for ecological receptors are discussed in Section 5.3 of the Risk
Assessment. The Agency requests comment on the equations and inputs
used in the generic terrestrial ecosystem modeling.
The following types of exposure were not assessed in the
assessment:
Inhalation by ecological receptors--No suitable
methodology was available.
Dermal contact with soil--No suitable methodology or
sufficient toxicity data were available.
Dermal contact with water--No suitable methodology or
sufficient toxicity data were available.
3. Groundwater Fate and Transport Modeling
In the risk analysis previously described in the section, the
pathways involving groundwater are only modeled (back-calculated) to
the wellhead, i.e., to the point of exposure at a water well. For
groundwater modeling from the waste management unit (i.e., surface
impoundment) to the water well, the Agency used a separate fate and
transport analysis. This section describes the groundwater model and
the modeling procedures for the various waste management scenarios for
the groundwater path. The details of the model and the modeling
procedures are presented in the background documents (USEPA, 1995 a-f).
The Agency has developed specialized subsurface fate and transport
modeling for four waste management options: (1) Landfills; (2) surface
impoundments; (3) waste piles; and (4) land application units. All four
waste management scenarios assume that the waste if exempted could be
managed in the respective RCRA Subtitle D units. In deriving the
exemption levels, the Agency needs to evaluate the fate and transport
of constituents from the waste unit to the nearby drinking water wells.
The potential migration of constituents from a waste unit to the
leachate at the bottom of the waste unit can be simulated by the
laboratory test, the Toxicity Leaching Procedure (TCLP), or the
Synthetic Precipitation Leaching Procedure (SPLP), Method 1312.
Although one procedure may be more applicable for some wastes than the
other procedure, as described on page 21483 of the Federal Register
Notice of May 20, 1992 (57 FR 21450), the Agency is soliciting comments
on the applicability and use of one test over the other for this
proposal.
The fate and transport of constituents in leachate from the bottom
of the waste unit through the unsaturated zone and to a drinking water
well in the saturated zone is estimated using a fate and transport
model. The Agency proposes to use EPACMTP (EPA's Composite Model for
leachate migration with Transformation Products) for this purpose. The
EPACMTP considers not only the subsurface fate and transport of
chemical constituents, but also the formation and the fate and
transport of transformation (daughter) products. The Agency also
solicits comments on the technical correctness and applicability of the
model and the data for this proposal.
The Agency proposed the use of a subsurface fate and transport
model (EPASMOD) on June 13,1986 (51 FR 21648) in the Toxicity
Characteristic (TC) Rule. However, after receiving numerous comments,
the Agency revised the model and the data used in the model (53 FR
28692) and the enhanced model (EPACML) was used in the TC Final Rule
(55 FR 11798). The EPACMTP replaces the EPACML for use in this
proposal. The EPACMTP was recently published in a refereed journal
(Kool, Sudicky and Saleem, Journal of Contaminant Hydrology 17(1994)
69-90) and has been reviewed by the EPA's Science Advisory Board (SAB).
The SAB commended the Agency for making for its significant
improvements to the model. They also stated that it represents the
state of the art for such analyses. However, they also recommended
additional testing of the model.
The modeling approach used for this proposed rulemaking includes
three major categories of enhancements over the EPACML and the approach
for the TC rule. The enhancements fall into the
[[Page 66368]]
following categories: (1) Incorporation of additional fate and
transport processes (e.g., degradation of chemical constituents); (2)
Use of enhanced flow and transport solution algorithms and techniques
(e.g., three-dimensional transport); and (3) Revision of the Monte
Carlo methodology (e.g., site-based implementation of available input
data). A discussion of the key enhancements which have been implemented
in the EPACMTP is presented here and the details are provided in the
background documents (USEPA, 1995a-g). The Agency is soliciting
comments on the modeling enhancements and the modeling methodology as
well as on the values derived for individual chemical constituents:
(1) Fate and Transport Processes
Effects of groundwater mounding underneath waste unit.--The EPACML
was limited to conditions of uniform groundwater flow. It could not
handle accurately the conditions of significant groundwater mounding
and non-uniform groundwater flow due to a high rate of infiltration
from the waste units. These conditions increase the transverse
horizontal as well as the vertical spreading of a contaminant plume.
The EPACMTP accounts for these effects directly by simulating
groundwater flow in the vertical as well as horizontal directions
(USEPA, 1995 a).
Transformation products.--The EPACMTP model has capability to
simulate the formation and fate of multiple transformation products (up
to seven) in the unsaturated as well as in the saturated zones. For
constituents which have toxic transformation products, the EPACMTP can
provide an assessment of the groundwater impact of the transformation
products, along with that of the parent constituent. This methodology
has been implemented for hydrolyzing organic constituents included in
this proposal.
Fate and transport of metals.--The EPACMTP can simulate fate and
transport of metals, taking into account geochemical influences on the
mobility of metals. The EPA's MINTEQA2 (USEPA, 1995 f) metals
speciation model is used to generate effective sorption isotherms for
individual metals, corresponding to a range of geochemical conditions.
The transport modules in EPACMTP have been enhanced to incorporate the
nonlinear MINTEQ sorption isotherms. This enhancement provides the
model with capability to simulate, in the unsaturated and in the
saturated zones, the impact of Ph, leachate organic matter, natural
organic matter, iron hydroxide and the presence of other ions in the
groundwater on the mobility of metals.
(2) Enhanced Solution Algorithms and Techniques
Linkage between unsaturated zone and saturated zone modules.--The
saturated zone module implemented in the EPACML was based on a Gaussian
distribution of concentration of a chemical constituent in the
saturated zone. The module also used an approximation to account for
the initial mixing of the contaminant entering at the water table
underneath the waste unit. The approximate nature of this mixing factor
could sometimes lead to unrealistic values of contaminant concentration
in the groundwater close to the waste unit, especially in cases of a
high infiltration rate from the waste unit. The enhanced model
incorporates a direct linkage between the unsaturated zone and
saturated zone modules which overcomes these limitations of the EPACML.
Numerical transport solution modules.--To enable a greater
flexibility and range of conditions that can be modeled, the analytical
saturated zone transport module has been replaced with a numerical
module, based on the highly efficient state-of-the-art Laplace
Transform Galerkin (LTG) technique. The enhanced module can simulate
the anisotropic, non-uniform groundwater flow, and transient, finite
source, conditions. The latter requires the model to calculate a
maximum receptor well concentration over a finite time horizon, rather
than just the steady state concentration which was calculated by the
EPACML. The saturated zone modules have been implemented to provide
either a fully three-dimensional solution, or a highly efficient quasi-
3D solution. The latter has been implemented for Monte Carlo
applications and provides nearly the same accuracy as the fully three-
dimensional option, but is more computationally efficient. Both the
unsaturated zone and the saturated zone transport modules can
accommodate the formation and the transport of parent as well as of the
transformation products.
Solution for nonlinear metals transport.--A highly efficient semi-
analytical unsaturated zone transport module has been incorporated to
handle the transport of metals in the unsaturated zone and can use
MINTEQA2 derived linear or nonlinear sorption isotherms. Conventional
numerical solution techniques are inadequate to handle extremely
nonlinear isotherms. An enhanced method-of-characteristic based
solution has been implemented which overcomes these problems and
thereby enables the simulation of metals transport in the Monte Carlo
framework. Non-linearity in the metals sorption isotherms is primarily
of concern at higher concentration values; for low concentrations, the
isotherms are linear or close to linear. Because of the attenuation in
the unsaturated zone, and the subsequent dilution in the saturated
zone, concentrations in the saturated zone are usually low enough so
that properly linearized isotherms are used by the model in the
saturated zone without significant errors.
Elimination of biases in determination of receptor well location.--
The internal routines in the model which determine placement of the
receptor well relative to the areal extent of the contaminant plume
have been revised and enhanced to eliminate bias which was present in
the implementation in the EPACML. The calculation of the areal extent
of the plume has been revised to take into consideration the dimensions
of the waste unit. The logic for placing a receptor well inside the
plume limits has been improved to eliminate a bias towards larger waste
unit areas and to ensure that the placement of the well inside these
limits, for a given radial distance from the unit, is truly randomly
uniform. However, for this proposal, the closest drinking water well is
located anywhere on the downgradient side of the waste unit and the
Agency is soliciting any comments on this procedure.
(3) Revisions of Monte Carlo methodology for nationwide assessment
Data sources.--The data sources from which parameter distributions
for nationwide Monte Carlo assessments are obtained have been
evaluated, and where appropriate, have been revised to make use of the
latest data available for modeling. Leachate rates for Subtitle D waste
units have been revised using the latest version of the HELP model with
the revised data inputs. Source specific input parameters (e.g., waste
unit area and volume) have been developed for various different types
of industrial waste units besides landfills. Input values for the
groundwater related parameters have been revised to utilize information
from a nationwide industry survey of actual contaminated sites.
Finite-source methodology.--The original version of the model was
implemented for Monte Carlo assessments assuming continuous source
(infinite source) conditions only. This methodology did not take into
account the finite volume and/or operational life of waste units. The
EPACMTP model has been
[[Page 66369]]
implemented for Monte Carlo assessments of either continuous source or
finite source scenarios. In the latter scenario, predicted groundwater
impact is not only based on the concentrations of contaminants in the
leachate, but also on the amount of constituent in the waste unit and/
or the operational life of the unit. The Monte Carlo methodology was
enhanced to allow determination of regulatory threshold levels for
these two waste characteristics USEPA, 1995.
Site-based regional analysis.--The Monte Carlo methodology has been
fundamentally revised and enhanced to account for the interdependency
among the various model input parameters based on regional
distributions. The original methodology simply assumed that a waste
site could be located anywhere in the US, and that the probability
distributions of individual model parameters (e.g., infiltration rate,
depth to groundwater, etc.) at any waste site were mutually independent
and given by their nationwide frequency distributions. The model
therefore only had limited capability to account for correlations and
dependencies among the model parameters. To address this limitation, a
site-based methodology has been implemented, based on the OSW's surveys
of existing waste facilities in the US, and their geographical
locations. The information of geographical location is used in this
enhanced approach to select the other model parameters, such as
infiltration rate and hydrogeological characteristics. A number of
different sources were reviewed for the development of the site-based
approach. Four of these sets were selected to derive the regional
characteristics of the more important parameters for each sampled site:
The OSW's survey of industrial waste management units (EPA, 1986); the
infiltration and recharge analysis performed for U.S. climatic regions;
the U.S. Geological Survey inventory of groundwater resources; and the
API's (American Petroleum Institute) survey of hydrogeologic parameters
for the different groundwater environments in the U.S.
(4) Implementation of EPACMTP
The specific modeling options selected for the modeling analyses
are summarized in Table 3 below. All modeling analyses were conducted
in the finite source, Monte Carlo mode, for four industrial Subtitle D
waste management scenarios. The groundwater fate and transport model
was used to predict the maximum concentration at a receptor well placed
down gradient from the waste unit. A 10,000 years time limit was
imposed on the exposure time period, i.e., the calculated concentration
is the highest exposure concentration occurring within 10,000 years
following the initial release from the waste unit. The Monte Carlo fate
and transport simulation provides a probability distribution of
receptor well exposure concentrations as a function of waste and
leachate concentrations. For this proposal, the groundwater modeling
results were used to derive leachate concentration thresholds. For
carcinogenic constituents, the exposure concentration calculated by the
model corresponds to the maximum 30-year average receptor well
concentration. For non-carcinogenic constituents, the peak receptor
well concentration is used. The regulatory threshold leachate
concentration limits were determined using a back-calculation
procedure, to correspond to an approximate 90th percentile protection
level. This means that the closest downgradient drinking-water wells at
90% of the industrial Subtitle D waste management units would have
water concentrations below the HBN/MCL. The wells further away at 90%
of the sites would be protected at higher protection levels. The wells
at the other 10% of the sites would be protected at lower protection
levels.
The Agency uses a 95th percentile protection level in the RCRA
Delisting program and the 85th percentile for the toxicity
characteristic program. These two programs have slightly different
goals from the exemption proposed today. The recently developed
Superfund soil-screening levels use a 90th percentile protection level
to identify sites at which no additional investigation for possible
remediation is required. The exit proposed today is similar to the
soil-screening levels program. Today's proposed exit is intended to
identify wastes no longer needing Subtitle C management. Finally, the
90th percentile was chosen because it is nearly consistent with the
protectiveness level in the other pathways of the multipath risk
assessment performed for today's proposal as far as could be
identified.
Table 3 provides a summary of the methodology and/or data sources
used to obtain values for the source-specific parameters, chemical-
specific parameters, unsaturated zone parameters, saturated zone
parameters, and receptor well location parameters. Because the
groundwater pathway analysis was performed in Monte Carlo mode, all
parameters are in principle described by their probability
distributions. Details on the actual distributions used are provided in
the background documents (USEPA, 1995a-g). Probability distributions
used for the unsaturated zone parameters, the saturated zone
parameters, and receptor well location parameters were the same for all
waste management scenarios and individual constituents that were
analyzed for today's exit.
(5) Waste Management Scenarios
The waste management unit represents the source term in the fate
and transport model for the waste management scenarios evaluated for
groundwater contamination. In the modeling framework, the source is
defined in terms of four key parameters: (i) Waste unit area, (ii)
Leachate flux (infiltration) rate, (iii) Leachate concentration, and
(iv) Duration of leachate pulse. The first of these parameters, waste
unit area, was determined from the nationwide OSW survey of industrial
Subtitle D waste management facilities (USEPA, 1995 a-b). After
screening out records with unreliable waste site area and/or volume,
the OSW Industrial Subtitle D survey provides data on location, area
and volume of 790 landfills, 1655 surface impoundments, 774 waste
piles, and 311 land application sites nationwide. The weighted
distributions of waste unit characteristics used as input to the model
are based on the results of the survey.
The leachate flux, or infiltration rate, and duration of the
leachate pulse are determined from the design and operational
characteristics of the waste management scenario being modeled.
Consideration of a leachate pulse of finite duration is a fundamental
aspect of the present analysis and distinguishes it from the continuous
source (infinite source) assumption used for the 1990 Toxicity
Characteristic (TC) Rule (55 FR 11798). It should be emphasized though
that the results of the finite source analysis are not necessarily
different from those of the continuous source analysis. If the source
leaching duration is long enough to drive the maximum receptor well
concentration to its steady state value, the finite source and
continuous source analyses are in fact the same. In practice, the
distinction between continuous source and finite source analysis is the
most important for chemicals which are subjects to sorption,
speciation, and/or degradation, including hydrolyzing organics and
metals.
The leachate concentration of specific constituents in the waste
forms the basis for regulating the wastes. The leachate concentration
is not specified a-priori, but rather it is back-calculated at the end
of the Monte Carlo analysis to satisfy the regulatory criterion that
the
[[Page 66370]]
maximum groundwater exposure concentration should be at, or below, the
constituent-specific health-based drinking water standard, in at least
90 % of the cases.
The following sections present background on the determination of
the source parameters for each waste management scenario.
Landfills.--The key characteristic of the landfill scenario is that
the duration of the leachate pulse is independent of the operational
life of the waste management unit, i.e., the period of time required to
fill the landfill. The landfill is taken to be filled to capacity and
covered when leaching begins. The time period during which the landfill
is filled-up, usually on the order of 20 years, is considered to be
small relative to the time required to leach all of the constituent
mass out of the landfill. The model simulation results indicate that
this assumption is not unreasonable; the model calculated leaching
duration (see below) is typically on the order of several hundred
years.
The leachate flux, or infiltration rate, is determined using the
HELP model. The net infiltration rate is calculated using a water
balance approach, which considers precipitation, evapo-transpiration,
and surface run-off. The HELP model was used to calculate landfill
infiltration rates for a representative subtitle D landfill with 2-foot
earthen cover, and no liner or leachate collection system, using
climatic data from 97 climatic stations located throughout the US.
These correspond to the reasonable worst case assumptions as explained
in the Risk Assessment Background Document (USEPA, 1995b). The model
calculates the daily water balance for the total period for which
climatic data are available. For each waste site in the OSW survey, an
infiltration rate was calculated using the data from the closest
climate station (USEPA, 1995b).
In the landfill scenario, the duration of the leaching period is
not prescribed. Instead it is calculated as part of the Monte Carlo
simulation from the total mass of constituent in the landfill, and the
rate of leaching. This relationship is derived from a straight-forward
mass balance principles. The methodology is documented in the
Background Document for the Finite Source Procedure (USEPA, 1995-c);
only the most salient aspects are presented here.
The duration of the leachate pulse, Tp, is determined by the
total mass of constituent that is initially present in the landfill,
and the rate at which the constituent is removed by leaching:
Aw . d . Fh . Phw . CW=Aw . I . CL .
TP
or
TP={d . Fh . Phw} over {I} CW over CL where
Aw=Area of the waste unit (m\2\),
d=Depth of waste unit (m),
Fh=Fraction of waste unit volume occupied by this waste,
Phw=Density of the waste (g/cm\3\),
I=Leachate flux (Infiltration) rate (m/y),
CW=Constituent waste concentration (mg/kg), and
CL=Constituent leachate concentration (mg/L).
The determination of Tp according to (2) tacitly assumes that
the constituent does not degrade inside the waste unit, does not
consider removal by mechanisms other than leaching (e.g.,
volatilization), and assumes that all of the constituent mass will
eventually leach out. The formulation given above also assumes that the
leachate concentration, CL, remains constant until all of the
constituent mass has leached out. The methodology was adapted to handle
a time-varying leachate concentration, e.g., a gradually diminishing
leachate concentration to represent the depletion of the contaminant
mass in the landfill over time. If it is assumed that the leaching of
the constituent from the waste into the water phase is controlled by a
linear equilibrium partitioning process, the reduction of the leachate
concentration with time can be modeled as a first-order decay process
(EPA, 1995c):
CL(t)=CL0e{-t}
where
CL0=Initial leaching concentration (mg/L)
=Apparent decay constant (y-1)
t=Time (y)
The rate at which the leachate concentration is reduced is determined
by the coefficient , which is given by:
={I} over [{d FhwPhw}{CW over CL0}]
Using (3), the leachate concentration will gradually and asymptotically
be reduced to zero. The total amount of constituent that is released
into the subsurface will be the same whether a constant leachate
concentration of finite duration, or a gradually diminishing leachate
concentration is assumed. In the latter case, the duration of the
release period is longer, but the average leachate concentration lower,
as compared to the former case.
It can be seen from either (2) or (4) that the duration of the
leachate pulse, or the rate of depletion, respectively, can be
expressed as a function of the initial leachate concentration, CL.
For the modeling analyses, equation (3) was used for organic
constituents. The underlying assumption that the concentration is
controlled by linear equilibrium partitioning is reasonable for organic
constituents. For metals, the pulse release option (equation 2) with
constant leaching concentration was used.
The calculation of Tp (or ) requires a number of
ancillary source and waste parameters. These are the depth of the waste
unit (d), the fraction of the waste unit occupied by the waste
(Fh), and the waste density (Phw). The waste unit depth is
obtained directly from the OSW waste site survey. The survey provides
data on both landfill areas and volumes, which allows the depth to be
calculated for any landfill selected during the Monte Carlo simulation.
The fraction of waste in the landfill is assigned a uniform
distribution with lower and upper limits of 0.036 and 1.0,
respectively, based on analysis of waste composition in Subtitle D
landfills (EPA, 1995). The lower bound assures that the waste unit will
always contains a minimum amount of the waste of concern. The waste
density is assigned a value based on reported densities of hazardous
waste, and varies between 0.7 and 2.1 g/cm\3\ (EPA, 1995c).
Surface Impoundment.--The surface impoundment waste management
scenario is that of a non-hazardous waste industrial impoundment. The
area of the impoundment is obtained from the OSW Subtitle D Industrial
Survey (USEPA 1995 b). No direct data is available on the rate of
infiltration from surface impoundments. The rate of infiltration from
the impoundment is calculated inside the EPACMTP fate and transport
model. The rate of infiltration is calculated, using Darcy's Law, as a
function of surface impoundment depth, and hydraulic conductivity and
thickness of a low-permeability sediment layer at the base of the
impoundment.
Impoundment depth is obtained from the OSW survey, for each
impoundment site in the survey, in the same way as the landfill depth
is obtained (see above). The sediment layer at the base of the
impoundment is taken to be 2 feet thick, and have an effective
equivalent saturated conductivity of 10-7 cm/s . These values were
selected in recognition of the fact that most non-hazardous waste
surface impoundments do have some kind of liners in place (USEPA,
1995b). During the Monte Carlo fate and transport simulation, the
infiltration rate is calculated using the impoundment depth value for
the specific unit selected for each Monte Carlo realization.
The leachate concentration again is not determined a priori, but is
determined after the analysis, based on
[[Page 66371]]
the desired regulatory protection level (90th percentile). The surface
impoundment is taken to have a 20-year operational life. After this
period, the impoundment may be filled in, or simply abandoned. In the
latter case, the waste in the impoundment will drain and/or evaporate
relatively quickly. In the modeling analysis, the duration of the
leaching period is therefore set equal to 20-years.
Waste Pile.--The waste pile management scenario is conceptually
similar to that of the landfill, but differs in a number of key
aspects. In contrast to landfills which represent a long-term waste
management scenario, waste piles represent a more temporary management
scenario. During the operational life of the waste pile, it may be
regarded as an uncovered landfill. Typically at the end of the active
life of a waste pile, the waste material is either removed for land
filling, or the waste pile is covered and left in place. If the waste
is removed, there is no longer a source of potential contamination. If
a waste pile is covered and left in place, it then becomes equivalent
to a landfill, and consequently is to be regulated as a landfill. For
the analyses, therefore, only the groundwater impacts associated with
the period that the waste pile is active, are considered.
Data on the waste pile area are obtained from the OSW Subtitle D
survey. Infiltration rates for the waste pile are obtained by treating
the waste pile as an uncovered landfill. HELP model derived landfill
infiltration rates assuming a sandy loam soil cover were used to assign
infiltration rates for waste piles. A sandy loam cover represents the
most permeable cover considered for the landfill scenario, and most
closely resembles a situation in which no cover is present. The
methodology for assigning an infiltration rate to any specific waste
pile in the OSW survey follows that used for landfills (see above).
An active life of 20 years is assumed for the waste pile. This also
determines the duration of the leaching period. As with the landfill
and surface impoundment scenario, the leachate concentration is
determined at the end of the analysis, to satisfy the regulatory
protection level.
Land Application Units.--Data on the location, area and waste
application rates at industrial land application sites were obtained
from the OSW survey of industrial Subtitle D sites. Location-specific
infiltration rates were estimated for each land application site by
applying the HELP model, using climatic data from the nearest climate
station. Because wastes applied at land application sites typically
have a high liquid content, this factor was accounted for in the water
balance calculations. An annual waste application rate of six inches of
waste, containing 85% water was assumed. This is typical of sludges
which constitute a large fraction of waste at land application sites.
Therefore, an additional 5.1 inches of water were added to the natural
precipitation for the water balance evaluation at each land application
site.
The leaching duration for the land application unit was set to 40
years, consistent with the release period modeled for the air pathway.
No reliable data were available for the active life of land application
units. Using a longer value than for surface impoundments and waste
piles is warranted because part of the applied waste material may
remain in the soil at the end of the active life of a land application
unit, and may continue as a source of contaminant leaching.
(6) Determination of Regulatory Waste and Leachate Concentration Limits
The objective of the Monte Carlo fate and transport analysis is the
determination of regulatory limits for the concentration of individual
toxic constituents in the leachate, CL. These limits are
determined so as to satisfy the regulatory criterion that disposal of a
waste in a subtitle D waste management unit should not lead to an
exceedance of the health-based value or the drinking water standard, at
a receptor well placed down gradient from the waste unit, in at least
90% of the cases.
The CL limits are specific to each waste management scenario,
and are also constituent specific. CL limits are constituent
specific because of their dependence on constituent specific health-
based standards, as well as on constituent specific fate and transport
characteristics that affect the concentration received at the receptor
well. The latter factors are discussed in the following section; this
section discusses the determination of regulatory CL thresholds.
Using Equation (2) or (3) and (4), the groundwater exposure
concentration calculated by the fate and transport model can be
expressed as a function CL. All other parameters used in the
modeling analysis are obtained from prescribed probability
distributions. Consequently, by comparing the predicted exposure
concentration to the appropriate regulatory standard, e.g., health-
based value or a drinking-water standard, threshold levels of CL,
can be calculated. Wastes for which the leachate concentration exceeds
the CL threshold would not be exempted. Because the Monte Carlo
analysis produces a probability distribution of exposure
concentrations, the back-calculation of CL threshold levels can be
performed for any desired level of protection.
For those constituents that degrade (see next subsection) and
produce toxic degradation products, the development of regulatory
threshold values for CL considers not only the exposure
concentration and toxicity of the parent constituent, but also the
exposure concentration and toxicity of toxic transformation products.
For instance, consider two waste constituents that have similar
toxicity values, i.e., similar health-based levels, as well as similar
fate and transport characteristics, so that they show comparable values
for the model simulated receptor well exposure concentration. However,
if one of the two chemicals produces toxic off-spring, but the other
chemical does not, the chemical which has toxic daughter products will
have more stringent limits for CL.
(7) Chemical--Specific Fate and Transport Processes
The Monte Carlo fate and transport analysis considers chemical-
specific sorption and hydrolysis (degradation) characteristics. These
characteristics directly affect the model-predicted groundwater
exposure concentration. Chemicals which are subject to sorption and/or
hydrolysis will exhibit lower exposure concentration as compared to
non-sorbing, non-degrading chemicals. This translates into higher
regulatory waste and concentration limits. Two broad groups of
chemicals are considered under today's proposal. They are organic
constituents and metals.
Organic Constituents.--Organic constituents account for the largest
group of chemicals addressed under today's proposal. The groundwater
pathway analyses were performed for a total of 222 organic
constituents. The fate and transport analysis accounts for sorption of
organics onto soil and aquifer organic matter, as expressed by a
chemical-specific organic-carbon partition coefficient (Koc), and
degradation due to hydrolysis reactions, as expressed by chemical-
specific hydrolysis constants. Sorption is modeled as a reversible,
linear equilibrium process. Degradation due to hydrolysis is modeled as
a first-order kinetic process. The groundwater pathway analysis
utilizes a comprehensive set of Koc values and hydrolysis rate
constants compiled by the EPA-ORD (Environmental Fate
[[Page 66372]]
Constants for Organic Chemicals Under Consideration for EPA's Hazardous
Waste Identification Projects , EPA/600/R-93/132). Chemicals with
identical Koc values and hydrolysis constants will exhibit the same
fate and transport behavior, and given the same leachate concentration
and leaching period, they will result in the same exposure
concentration. Note, however, that they may still have different
regulatory leachate concentration limits, if they have different
health-based drinking water standards and/or produce toxic
transformation products.
For the groundwater pathway analysis, organic constituents with a
hydrolysis half-life of 6,900 years or less (first-order degradation
rate of 10-4 or greater) were classified as degraders, the
remainder were classified as non-degraders. The EPACMTP can simulate
the formation and subsequent fate and transport of transformation
daughter products, enabling the groundwater exposure concentrations of
any toxic transformation products to be determined and, therefore,
included in the determination of leachate concentration thresholds.
It has been established, by analyzing modeling results for
different constituents with a range of sorption and degradation
characteristics that, after normalizing the results against the
chemical-specific HBN/MCL, the effect of sorption and degradation on
the regulatory values can be expressed as a function of the Koc and
hydrolysis rate coefficients, using a straight-forward scaling
relationship. After these relationships have been established, it is
not actually necessary to conduct the Monte Carlo fate and transport
computer simulations for each individual constituent. Instead, for each
waste management scenario of concern, a set of reference CL values
are generated by running the Monte Carlo model for a selected range of
values of Koc and hydrolysis rate coefficients using a normalized HBN/
MCL of 1 mg/L. Constituent-specific CLMIN values are then
determined in two steps: First, the reference curves are scaled to the
constituent specific Koc value, and (for degraders) hydrolysis rate
coefficients. Secondly, an adjustment is made for the constituent-
specific value of the drinking water standard. The final values of
CLMIN are obtained by multiplying the concentration limits
based on the normalized drinking water standard, by the actual value of
the drinking water standard of that particular constituent. For
constituents with toxic transformation products, this procedure is
repeated for the transformation products, to find the minimum values of
CL (CLMIN) which ensure that the exposure concentrations
of the parent constituent and any daughter products will not be
exceeded. The benefit of this approach is that if additional
constituents are to be regulated, or a different value of the drinking
water standard HBN/MCL, the appropriate CLMIN can be
determined with less effort, because it is not necessary to repeat the
time-consuming complete Monte Carlo simulation.
Metals.--Fate and transport of metals in the subsurface may be
controlled by complex geochemical interactions. To account for these
processes, the OSW has developed and implemented a modeling approach
which utilizes the MINTEQA2 metals speciation model in conjunction with
the EPACMTP subsurface fate and transport model. The MINTEQ model has
been applied to generate effective sorption isotherms reflecting
variations in four geochemical master variables affecting metals fate
and transport. These factors are: Ph, leachate organic matter natural
organic matter in the soil or aquifer, and ironhydroxide content. Each
of these parameters has a range of values, reflecting their nationwide
probability.
Table 3.--EPACMTP Modeling Options
----------------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------
Management Scenarios.......................................................... Industrial Subtitle D: (i)
Landfill; (ii) Surface
Impoundment; (iii) Waste Pile;
and (iv) Land Application Unit.
Modeling Scenario............................................................. Finite Source Monte Carlo.
Regulatory Protection Level................................................... 90% (yields an approximate DAF
of 10 for a continuous source
landfill).
Source Parameters:
Waste Unit Area........................................................... Site based, form OSW Industrial
Subtitle D Survey.
Waste Unit Volume......................................................... Site based, from OSW Industrial
Subtitle D Survey.
Infiltration Rate:
Landfill.............................................................. Site-based, derived from water
balance using HELP model.
Surface Impoundment................................................... Site-based, derived from
impoundment depth using Darcy's
law.
Waste Pile............................................................ Site-based derived from water
balance using HELP model.
Land Application Unit................................................. Site-based, derived from water
balance using HELP model.
Leaching Duration:
Landfill.............................................................. Derived, continues until all
constituent has leached out.
Surface Impoundment................................................... 20 years (operational life of
waste unit).
Waste Pile Land....................................................... 20 years (operational life of
waste unit).
Application Unit...................................................... 40 years.
Chemical Specific Parameters:
Decay Rate:
Organics.............................................................. Hydrolysis rates based on
measurements or based on
appropriate structure-activity
relationships.
Metals................................................................ No decay.
Sorption:
Organics.............................................................. Koc estimated from Kow, which is
based on measurements or based
on appropriate structure-
activity relationships.
Metals................................................................ MINTEQ sorption isotherms (Pb,
Hg, Ni, Cr (III), Ba, Cd).
pH dependent isotherms (As, Cr
(VI), Se (VI), Th)
Unsaturated Zone Parameters:
Depth to groundwater...................................................... Site-based, from API/USGS
hydrogeologic database.
Soil Hydraulic Parameters................................................. National distribution for the
main soil types.
Fraction Organic Carbon................................................... National distribution for the
main soil types.
Bulk Density.............................................................. National distribution for the
main soil types.
Saturated Zone Parameters:
Recharge Rate............................................................. Site-based, derived from
precipitation/evaporation and
soil type.
[[Page 66373]]
Saturated Thickness....................................................... Site-based, from API/USGS
hydrogeologic database.
Hydraulic Conductivity.................................................... Site-based, from API/USGS
hydrogeologic database.
Porosity.................................................................. Effective porosity derived from
national distribution of
aquifer particle diameter.
Bulk Density.............................................................. Derived from porosity.
Dispersivity.............................................................. Derived from a national
distribution and is based on
distance to the receptor well.
Groundwater Temperature................................................... Site-based, from USGS regional
temperature map.
Fraction Organic Carbon................................................... National distribution, from EPA
STORET database.
pH........................................................................ National distribution, from EPA
STORET database.
Receptor Well Location:
Radial Distance........................................................... Nationwide distribution based
the survey.
Angle Off-Center.......................................................... Uniform within 90
deg. from plume centerline.
Depth of Intake Point..................................................... (No restriction to be within
plume) Uniform throughout
saturated thickness of aquifer.
----------------------------------------------------------------------------------------------------------------
4. Other Risk Assessment Issues
a. Differences Between the Groundwater and Non-groundwater Analyses
As mentioned previously, the Agency conducted separate analyses for
the evaluation of risks from groundwater and non-groundwater pathways.
The groundwater pathways relied on a full Monte Carlo analysis; whereas
the non-groundwater pathway analyses were performed using high-end and
central tendency parameters, consistent EPA's risk characterization
guidance (EPA 1995).
Although the approaches to the modeling differed, the Agency used
the same data for parameter inputs (i.e., OSW's Industrial Subtitle D
Survey, U.S. EPA 1986) to describe the waste management units common to
both analyses (i.e, surface impoundments, waste piles, and land
application units). However, even though the same data were used, some
differences exist based on the different modeling approaches. These
differences are discussed below.
(1) Infiltration
For the groundwater pathway analysis, the Agency used the HELP
model to calculate the net infiltration rate for landfills, land
application units and waste piles, as a function of regional climatic
conditions and waste unit design characteristics (see EPACMTP
background Document). The analysis used the meteorological data from 93
meteorological stations located throughout the United States to develop
infiltration rate distributions using the HELP model.
For the non-groundwater analysis, the Agency used rainfall to
calculate the recharge rate. The rainfall was selected from 29
meteorological stations distributed among 9 climate regions. However,
the method for selecting the rainfall factor differed between the air
release pathways and the overland release pathways.
For the air release pathways, the Agency conducted a
sensitivity analysis for each waste management unit type to rank the 29
meteorological stations with respect to several air modeling outputs,
including maximum air concentration of pollutants, average air
concentrations over the agricultural field and water body, and average
deposition over the agricultural field and water body. Based on these
sensitivity analyses, the Agency selected a central tendency location
and high-end location for the air pathway for each of the waste
management units. Thus, locations with meteorologic data, including the
rainfall factor, approaching the central tendency and high-end values
were selected for each waste management unit.
For the overland release pathways, the Agency ranked the
rainfall factors from the 29 meteorological stations and selected the
50th and 90th percentile based on the distribution of the 29
meteorological stations.
(2) Density of Waste Applied to the Land Application Unit
The approach used in the groundwater analysis assumed the bulk
density of the applied waste to be 1 gram per cubic centimeter (g/cc)
because the waste was assumed to be comprised predominantly of water.
However, changes in the density of applied waste do not significantly
affect the results of the groundwater modeling results.
The approach used in the non-groundwater analysis assumed the bulk
density of waste to be analogous to the density of sewage sludge (i.e.,
1.4 g/cc). The waste in the LAU is a mixture of industrial waste and
soil. The central tendency bulk density for soil (i.e., 1.5 g/cc) is
similar to the bulk density assumed for industrial waste. Because the
waste is incorporated into soil, the properties of the waste/soil
mixture are needed. There is little variability in bulk density for the
type of soil used in the analysis (i.e., loam), thus, the same value
was used for central tendency and high-end estimates of the waste/soil
mixture bulk density.
(3) Unsaturated Zone Characteristics
The groundwater pathway analysis used the characteristics (e.g.,
percent organic matter, saturated hydraulic conductivity) of the entire
unsaturated zone as input into the modeling analysis. The non-
groundwater pathway analysis used as input the characteristics of only
the upper portions of the unsaturated zone because these
characteristics were those significant for the surface exposure
pathways.
(4) Hydrolysis Rates
The hydrolysis rate for a chemical constituent is used in the Monte
Carlo groundwater pathway analysis as a function of temperature and pH
of the groundwater at the Monte Carlo realized site. The Agency used
hydrolysis rates for constituents that have been measured through
appropriate structure activity relationships. They have been reviewed
by a panel of experts from the Agency's Office of Research and
Development (USEPA, 1993). The non-groundwater pathway analysis used
hydrolysis rates from the ``Handbook of Environmental Fate and Exposure
Data for Organic Chemicals'' (Howard et. al, 1993).
b. Other Groundwater Pathway Analysis Issues
(1) Use of 1,000 Year Versus 10,000 Year Exposure Time Horizon
The Agency's proposal is based on a 10,000 year time horizon for
the groundwater pathway. This means that the determination of leachate
concentration limits is based on the highest (30-year average)
concentration that occurs within 10,000 years from the start of the
release. Although this longer time horizon has been used in other
programs (U.S. Nuclear Regulatory
[[Page 66374]]
Commission and U.S. Department of Energy), the Agency is considering
using 1,000 years as an alternative time horizon. The Agency requests
comment on this issue which is described in more detail below.
Using this shorter time horizon results in an increase of the
leachate concentration limit for a number of constituents. The
constituents affected are those which are strongly sorbed in the
subsurface, and which therefore tend to migrate slowly. These
constituents include organics with retardation factors (R)
significantly greater than one. The organic carbon partition
coefficient (koc) values for these constituents are about 3,500 g/
cm3 or greater, and certain metals such as lead and chromium(III).
For organic constituents with koc values less than about 3,500 g/
cm3, the highest receptor well exposure concentration is generally
reached in less than 1,000 years. Reducing the modeling time horizon
from 10,000 to 1,000 years therefore does not affect the results of the
pathway analysis for these constituents. The effect of using a 1,000
year versus a 10,000 year time horizon is illustrated in Table 4. The
constituent-specific differences are shown in Table B-1 of appendix B
to the preamble. The table is based on a landfill waste management
scenario, and all constituents are assumed to have identical toxicity
values and not be subject to hydrolysis. For reference, the leachate
concentration limit for constituents with koc=0 (no sorption,
R=1), and a 10,000 year time horizon is equal to 1.0 mg/L. This table
shows that the increase in leachate concentration limit for organic
constituents is affected for a shorter modeling horizon (1,000 years)
only when koc values (or R values) are very large. (About fifteen
percent, out of a total of approximately 200, including eight metals,
fall into this category.) The effect of hydrolysis rate is not
considered in results shown in the table. While hydrolysis influences
the magnitude of the exposure concentration at a receptor well, the
time that it takes for a contaminant to reach the receptor well is
independent from the chemical-specific hydrolysis rate. It is, however,
strongly influenced by chemical-specific sorption characteristics,
which for organics are expressed in terms of koc or R values.
Table 4.--Effect of 1,000 Year Versus 10,000 Year Modeling Time Horizon
on Leachate Concentration Limit
------------------------------------------------------------------------
10,000 1,000
koc (cm3/) years years
------------------------------------------------------------------------
0.0............................................... 1.0 1.0
3,384............................................. 1.0 1.0
(R=10)
37,224............................................ 1.0 60
(R=100)...........................................
------------------------------------------------------------------------
(2) Implementation of Parameter Bounds in Monte Carlo Procedure
The Monte Carlo modeling procedure used in the groundwater pathway
analysis uses data on waste site location from the EPA's Industrial
Subtitle D Survey (USEPA, 1986). These data are combined with other
data sets for climatic and hydrogeological parameters. Auxiliary
parameters for which no direct data is available are calculated
internally in the model. For instance, ground-water velocity is
calculated from hydraulic conductivity, gradient and effective
porosity, and the dispersivity is calculated from the receptor well
distance (See EPACMTP Background Document and User's Manual). Each
parameter furthermore can have specified upper and lower bounds to
guard against the possibility that physically infeasible parameters
and/or parameter combinations are not used. When the latter condition
occurs, the particular Monte Carlo realization is rejected, and another
realization is generated. The Agency is considering an alternative
procedure in which only the offending parameter is regenerated, or, if
necessary, set equal to its upper or lower bound to avoid selection of
values beyond the minimum to the maximum values range. In first case,
the frequency distribution of parameter values generated by the Monte
Carlo module, may be different from its input distribution. The Agency
has determined that the two alternative procedures have little impact
on the overall modeling results in the case of landfills and land
application units, but that the default procedure tends to favor the
selection of sites with larger waste unit area in the case of waste
piles and surface impoundments. Therefore it produces more conservative
(lower) values for the final leachate concentration limits. The
analysis results show that for the two alternative Monte Carlo
procedures for surface impoundments, the default procedure results in a
leachate concentration limit of 1.0 mg/L, the alternative procedure
results in a concentration limit of about 31 mg/L for a chemical with
R=1. The effect of changes in the hydrolysis rate or the R value on the
resultant regulatory leachate concentration do not impact the results
obtained by using the alternative Monte Carlo procedure described in
this subsection. The Agency is also soliciting comments on the Monte
Carlo parameter rejection procedure used for the results presented in
this subsection.
(3) Hydraulic Conductivity of Surface Impoundment Bottom Layer
The surface impoundment scenario modeled in the groundwater pathway
analysis incorporates a 2 feet thick layer at the base of the
impoundment. In the base case for this proposal, the layer is assigned
a hydraulic conductivity of 10-7 cm/sec. The Agency recognizes that
this value may or may not be appropriate value for bottom sediments as
a nationwide typical for industrial Subtitle D surface impoundments. To
evaluate the impact of varying this parameter, the Agency has compared
modeling results obtained using a 10 times higher conductivity of 10-6
cm/sec. A higher conductivity value corresponds to a greater leachate
flux from the impoundment, and generally higher receptor well
concentrations, which translates into a more conservative (lower)
regulatory leachate concentration limit. The regulatory limit
calculated for a conductivity value of 10-7 cm/sec is 1.0 mg/L,
the corresponding value for a conductivity of 10-6 cm/sec would be
0.35 mg/L. The effect of changes in hydraulic conductivity on the
results is believed to be independent of the sorption or the hydrolysis
characteristics of the chemical. The Agency is inviting comments on the
appropriate value for the hydraulic conductivity of the bottom sediment
layer for industrial D surface impoundments. In addition, the Agency
requests the submission of hydraulic conductivity data for industrial
Subtitle D surface impoundment bottom sludges.
(4) Waste Pile Infiltration Rates
The Agency used the HELP model to calculate the net infiltration
rate for landfills, land application units and waste piles, as a
function of regional climatic conditions and waste unit design
characteristics (see EPACMTP background Document). For waste piles, the
Agency considered two alternatives. The procedure used in the base case
considered a waste pile, for the purpose of estimating infiltration
rates, to be similar to an uncovered landfill. The Monte Carlo modeling
analysis therefore used landfill infiltration rates corresponding to
the most permeable (sandy loam) of the three cover types
[[Page 66375]]
used for landfill modeling. As an alternative, the Agency has used the
HELP model to calculate infiltration rates for waste piles directly. In
the initial evaluation, the runoff used in the water balance
calculation was computed by the HELP model as a function of soil
texture and vegetative cover (bare ground).The Agency has evaluated the
impact of representative bare, but unevenly surfaced, waste piles on
simulated runoff using the HELP model. A comparison of the impact of
using this alternative procedure against the values used in this
proposal for the base case, on the regulatory leachate concentration
limit, was conducted. The comparison of regulatory leachate
concentration limits is based on a non-degrading, non-sorbing
constituent, which has a concentration limit of 1.0 mg/L in the
proposal. Using the alternative procedure, the corresponding leachate
concentration level changes to 0.77. The Agency is inviting comments on
the two methods for the waste piles for the estimation of infiltration
rates through them. If you have any data and other information to
support your comment, send it along with your comments to the Docket.
(5) Land Application Unit Infiltration Rates
In the calculation of infiltration rates for land application units
for the base case in the proposal, it was assumed that land application
units receive, on average, 1,295.4 m\3\ha (5.1 inches) of water
annually through the application of the waste. This amount of water was
included in the HELP model water balance calculation, resulting in an
increased net infiltration as compared to ambient conditions. The waste
application rate may or may not represent true field situations. As an
alternative to the modeling procedure used for the base case of this
proposal, the Agency evaluated the effect of using ambient recharge
rates, i.e., the application of waste does not significantly alter the
water balance, on the calculated leachate concentration limits. The
comparison of this alternative with the procedure used for the base
case shows that the regulatory leachate concentration limits for a non-
degrading, non-sorbing constituent in land application units changes to
1.12 mg/L from 1.0 mg/L for the procedure used in the base case.
(6) Aggregate Effects of Alternative Groundwater Modeling
Procedures and Data
The preceding sections have presented the effect of alternative
modeling options and data sources that have been considered by the
Agency. A consequence of the Monte Carlo exposure modeling approach is
that the effects of changes in model parameters are not always linearly
additive; rather the aggregate effect of changing multiple parameters
or options may be to either magnify or reduce the effect of the
individual changes. The Agency, therefore, has conducted modeling
analyses of the aggregate effect of the alternatives discussed above
for each of the four waste management scenarios. In addition to the
alternatives presented in the preceding subsections, a modification was
also made in the procedure for modeling waste sites for which the
corresponding hydrogeological region was initially assigned as ``not
classifiable''. Rather than ignoring the small fraction of sites
involved, they were incorporated into the analysis by assigning them
nationwide average values for the groundwater parameters. Table 5
presents the aggregate effect of all changes for each of the four waste
management scenarios modeled. The modeling results correspond to a non-
degrading, non-sorbing constituent. The leachate concentration limits
are normalized with respect to a value of 1.0 mg/L for the landfill
scenario, under the modeling procedure for the base case of this
proposal. The results are presented for a 1,000 year time horizon;
however for a non-sorbing constituent, these same results also hold for
the 10,000 year time horizon.
Table 5.--Aggregate Effect of Modeling Alternatives on Leachate
Concentration Limits for Non-Degrading, Non-Sorbing Constituents for
Four Waste Management Scenarios
------------------------------------------------------------------------
HWIR Alternative
Waste management scenario proposal Options
------------------------------------------------------------------------
Landfill........................................ 1.0 0.71
Surface Impoundment............................. 0.22 0.27
Waste Pile...................................... 0.29 484
Land Application Unit........................... 0.08 0.22
------------------------------------------------------------------------
Table 5 shows that, except for landfills, the aggregate effect of
the combined alternative options is a less conservative (higher)
leachate concentration limit. For landfills, adoption of the
alternative modeling options would have resulted in a 30 % less
stringent regulatory leachate limit for the groundwater pathway for
non-sorbing and non-degrading constituents. For surface impoundments,
there is little overall impact because the opposing effects of
increasing the impeding layer hydraulic conductivity, and the
alternative Monte Carlo procedure for handling parameter bound
exceedances, nearly cancel out. For waste piles on the other hand, the
procedure used for the base case, results in a significantly more
conservative leachate concentration limit as compared to the
alternative modeling options. This is due to the handling of parameter
exceedances in the Monte Carlo simulation. Because many waste piles
have very small sizes (surface areas), the alternative Monte Carlo
procedure has a large impact. For land application units, the
procedures used in the proposal for the base case also result in a more
conservative regulatory limit as compared to the alternative modeling
options. The contributing factors are much the same as for waste piles,
but the overall impact is much smaller, primarily because there are
only few land application units with very small areas.
F. Additional Eco-Receptor Considerations
EPA considered two different policy goals with respect to
protection of terrestrial ecological receptors (i.e., soil fauna,
birds, mammals, and plants). One goal protected terrestrial ecological
receptors outside the boundaries of the waste management site, thus,
the constituent had to travel off-site before exposures would be
assessed. The alternative goal protected terrestrial ecological
receptors on the closed land application site.
The Agency chose to propose exit levels based on off-site impacts
for several reasons. One reason is that there are many land use
decisions that significantly affect terrestrial ecological receptors on
the property of a party making those decisions (e.g., a decision to
pave a portion of land as a parking lot). EPA does not generally
regulate those sort of decisions. However, many impacts are judged
through local zoning regulations. Congress has typically asked EPA or
other Federal entities to regulate activities on a property when there
are significant off-site impacts, such as a groundwater plume that
migrates, an air release that moves beyond the property, a wetland
(located on the property) that is a significant resource for migratory
birds and has broader ecological significance, or an endangered species
with social values beyond the impact on a specific landowners purview.
EPA asks for comment, however, on the alternative of protecting
terrestrial ecological receptors on-site. The rationale for this
alternative approach would relate to protection from impacts on bird
and mammal populations, and
[[Page 66376]]
other ecological receptors, and to the regulation of certain
constituents that could potentially result in environmental
consequences that go significantly beyond the bounds of a current waste
management unit.
G. Background Concentrations in Soils and Other Issues Relating to
Results
EPA has compared the exit levels for nonwastewaters to data on the
variation in mean background concentrations found in soils. For some
metals, the exit levels calculated based on risks at land application
units are below 4 mean soil concentrations. One reason exit
criteria may be below soil concentrations is that these metals
bioaccumulate, causing greater exposure for higher trophic levels.
Also, the acceptable levels for some of the metals that would be
calculated for practices other than land application are significantly
higher and not below mean soil concentrations.
\4\ When compared with mean soil background levels provided by
the USGS, the exit levels are not more that 1 order of magnitude
more restrictive.
---------------------------------------------------------------------------
If the final exit levels are below typical soil levels, EPA would
consider promulgating levels based on concentrations that are either
typical soil concentrations (national mean levels) or some percentile
or portion of the naturally-occurring range such as the 10th
percentile. If the effect of concern is an ecological impact, the
rationale for using the 10th percentile (or similar figure if the data
available does not allow that precision) would be that in 90 percent of
locations, if the soil already contains those or greater levels, the
ecological receptors existing in the area should already reflect the
toxicity of the waste material; the rational for using the 10th
percentile (or similar value) value is that human behavioral practices
(e.g., treatment of groundwater prior to use) may already reflect
protection from the potential toxicity of concern. EPA asks for comment
on whether these are reasonable arguments.
EPA is concerned, however, that there are also issues of the
chemical and physical form in which compound or chemicals exist, in
both natural conditions and in the waste and that a simple comparison
of total concentrations in soils and in wastes might be misleading
about potential ecological or human impacts. EPA requests comment on
these issues. EPA's first preference will be to reexamine the risk
modeling to identify any inappropriate assumptions or modeling issues
that may explain the low proposed exit level, and to look more
carefully at those constituents where this issue only arises from the
modeling of risks from land application units, to identify potential
contingent management solutions to this problem.
Finally, EPA requests comment on whether these arguments could be
extended to site-specific determinations where information on local
background constituent concentrations and form in soil are available
and have been reviewed by a State regulatory authority. EPA assumes
that such an approach would only apply if the background concentrations
were more than very localized and the concentrations were naturally-
occurring rather than due to past contamination. If a site-specific
determination were adopted, two approaches are available that have been
used in other contexts. One statistical technique for determining
whether background data conform to a normal distribution assumption
includes combining the Student-t difference of means test, presented in
the Permit Guidance Manual on Unsaturated Zone Monitoring for Hazardous
Waste Land Treatment Units, (EPA, 1986) with the normal tolerance
interval approach found in Statistical Analysis of Ground Water at RCRA
Facilities-Interim Final Guidance, (EPA, April 1989). The Student-t
test compares averaged waste/media concentrations to background
concentrations, and is used to determine if the waste/media as a whole
is within a specified criteria. However, even if the waste/media passes
the Student-t test, individual sample concentrations may still exceed
the tolerance interval limit. The normal tolerance interval approach is
used to compare sample concentrations to an upper tolerance value based
on the background mean, standard deviation, and sample size.
If such an approach is incorporated into the final rule, it would
include criteria for defining and collecting adequate background
samples. More specifically, the facility would be required to identify
background locations, sample size, soil depth, etc. for at least four
samples in a ``difference of means'' demonstration, and six to eight
samples for a ``tolerance of means'' demonstration. The facility would
also need to demonstrate the normalcy of the sample distribution. The
Agency would require that this information be included as part of the
facility's sampling and analysis plan and subject to review by the
appropriate overseeing authority.
A more simplified approach would be to establish exit levels at \1/
10\ of the naturally occurring background level. The rationale for
using \1/10\ is that these levels would not appreciably contribute to
the overall risk posed by elevated levels in the environmental media.
EPA requests comment of this approach as well as the rationale.
Alternatively, the rule could defer any background level
demonstrations to an omnibus authority for the overseeing agency. Under
this concept, a claimant could submit information on naturally
occurring background level and a request for modified exit levels to
the agency overseeing the exemption process, which would have
discretion to grant modifications where they are clearly justified.
Comment is requested on the need for this authority.
The Agency solicits comments on other appropriate and generic ways
(1) to identify background levels in soils, and (2) to incorporate the
existing 40 CFR part 264, subpart F standards for establishing
background levels for groundwater. Other suggestions that address the
Agency's intent to promulgate a simplified exemption with little
reliance on site-specific considerations but also allow for
consideration of elevated background levels will be considered.
EPA also observed that some of the exit levels for organic
chemicals appear relatively high (see, for example, the level for
xylene). EPA believes that these results occurred primarily because
these chemicals either are toxic only at relatively high concentrations
or undergo high dilution during transport. EPA, however, requests
comment on whether these chemicals are frequently co-disposed and, if
so, whether they might pose cumulative risks not assessed by the risk
analysis. EPA is interested in information on issues such as whether a
waste containing one or more of these constituents at concentrations
near exit levels would be ignitable or threaten the integrity of
control measures such as liners.
H. Constituents with Extrapolated Risk-based Levels
EPA was unable to conduct the risk assessment for 187 of the 376
constituents on the exit list. In most of these cases, EPA was unable
to find acceptable human health benchmarks to serve as the starting
place for the assessment. In a few cases, EPA could not find values for
critical physical or chemical properties, such as log Kows. Based
on its past experience, EPA believes it would need at least a year to
develop a new human health benchmark value for any constituent. EPA has
less experience with the type of research and peer review needed to
develop values for physical and chemical properties, but it believes
that this process also would be time-consuming.
[[Page 66377]]
Rather than not consider the 187 constituents for which EPA was
unable to conduct the risk assessment as potential candidate
constituents for exit criteria, EPA developed an approach for
establishing exit criteria for these constituents. The Agency grouped
the constituents on the exit list into classes, based on chemical
structure. EPA selected the 50th percentile value from the range of
modeled risk levels for each chemical class. This 50th percentile value
serves as the extrapolated risk-based level for the un-modeled
constituents in the corresponding chemical class. The constituents and
their 50th percentile extrapolated risk-based levels are presented in a
background document Background Document to Support the Methodology used
in Extrapolating Exit Levels to Constituents with no Health-Based
Benchmarks. EPA is proposing the 50th percentile level to avoid adding
another conservative assumption to the derivation of exit levels for
these constituents. EPA believes that the multipathway approach is
already sufficiently conservative to protect human health and the
environment even for these chemicals. EPA, however, requests comment on
the alternative of using the 10th percentile or a different percentile
from the modeled exit levels from each class. Such an approach would
reduce the chances that the actual health benchmark for a particular
level was lower than the extrapolated estimate. However, it would also
increase the odds that the extrapolated level was higher than needed
for many constituents. A complete list of extrapolated constituents and
associated risk levels may be found in appendix C to today's preamble.
EPA recognizes that this approach to generating exit levels is much
less sophisticated and precise than the multipathway analysis.
Nonetheless, EPA prefers it to any of the available alternatives. If
EPA set no exit levels and made wastes containing any of these
constituents ineligible for exit, a significant number of waste streams
would probably be ineligible, even though they may pose no significant
threat to human health and the environment. EPA's RIA data shows that
some of these constituents, such as Cyanide and Anthracene, are fairly
prevalent. Although other constituents, such as those found in the
commercial chemical products on the P and U lists of hazardous wastes,
are not very prevalent, they may be significant for generators that
manage multiple waste streams in centralized wastewater treatment
plants. In the absence of extrapolated exit criteria, a generator would
lose its opportunity to claim an exit for an entire combined stream if
any of these constituents is found in the waste stream. Furthermore, it
would take a long time to complete the work necessary to conduct
exposure pathway assessments for any significant number of these 187
constituents.
Alternatively, EPA could propose to allow wastes to exit without
testing for constituents lacking modeled exit levels. EPA, however,
finds this approach insufficiently protective, especially when it can
at least approximate likely risk levels as described above.
Finally, EPA considered the alternative of basing exit levels for
these constituents on quantitation limits. As explained below, EPA is
proposing to use EQCs as exit levels where they are higher than a
constituent's multipathway or extrapolated exit level. (EPA is also
proposing that wastes with such constituents meet the technology-based
LDR standards for those constituents prior to exit.) EPA considered
using this EQC and LDR approach for constituents lacking multipathway
levels. Such an approach would actually produce more conservative exit
levels, because EPA would not use extrapolated levels that are higher
than EQCs. EQCs (and technology-based LDRs), however, are not based on
risk. EPA prefers the extrapolated approach because it takes into
account the toxicity and fate and transport of structurally similar
chemicals. EPA believes it would be unreasonable to continue to
regulate a chemical because chemistry can detect it, where the
extrapolation described above suggests that the chemical poses no
significant risks at the EQC level.
EPA finds the option of basing exit levels on the extrapolation
procedure described above to strike a reasonable balance between the
goals of protecting human health and the environment and eliminating
regulation of low-risk wastes. EPA, however, requests comment on all of
the alternatives described in this section.
I. Analytical Considerations
Some of the proposed exit levels established by the risk assessment
and the extrapolation methodology are low. In some cases, existing
analytical methods cannot routinely detect the constituents at those
levels. EPA is proposing to cap these potential exit levels with
reasonable analytical quantitation limits. The Agency is proposing
quantitation limits that represent the lowest levels that can be
reliably measured within acceptable limits of precision and accuracy
during routine laboratory operating conditions using appropriate
methods. These concentrations are referred to as ``exemption
quantitation criteria,'' or EQCs. It is necessary to specify EQCs
because a number of the constituents on the exemption list have either
modeled or extrapolated risk-based levels that are not analytically
achievable in all matrices. Appendix C to today's preamble lays out the
comparison between the modeled or extrapolated risk level and the EQC
for every constituent. Approximately one-quarter of the constituents
have proposed modeled or extrapolated risk-based levels lower than EQC.
1. Development of Exemption Quantitation Criteria (EQC)
To develop the EQCs proposed in today's notice, EPA compiled a
master list of the quantitation limits published for the identified
constituents in the Third Edition of Test Methods for Evaluating Solid
Waste, (SW-846), including the first and second updates (both of which
are widely distributed throughout the regulated community). The Agency
believes that the resultant EQCs present achievable quantitation limits
for the proposed exemption constituents in most matrices. The Agency
requests comment on the proposed quantitation limits as well as any
data supporting those comments.
A regulatory action level (e.g., exit levels) must provide a clear
distinction between those wastes subject to the regulation and those
excluded. Action levels based on analytical determinations within a
methods quantitative range can be used to determine regulatory status
with a high degree of confidence. On the other hand, when an analyte is
present at a concentration equal to the detection limit (DL) it will be
detected only half the time. In other words there is a 50% risk of a
false negative result when the analyte is present at the DL
concentration. There is, however, a less than 1% risk of false positive
results at this level. Therefore, regulations set at the detection
limit would not identify non-compliance reliably.
The Agency is in the process of re-evaluating EQCs for some
constituents. Preliminary updated EQCs could not be incorporated into
today's proposed rule, but have been included in the docket for
comment.
2. EQCs and LDR Requirements as Exit Levels
A comparison of the modeled or extrapolated risk-based levels with
the EQCs reveals a number of cases where
[[Page 66378]]
quantitative measurement of analyte concentration at the modeled or
extrapolated risk-based level cannot be reliably achieved, using
standardized analytical methods. In today's proposed rule, for wastes
containing constituents with a modeled or extrapolated risk-based level
lower than the EQC, exit criteria include meeting the EQC along with an
additional requirement that the waste meet Land Disposal Restrictions
(LDR) treatment standards from part 268, regardless of whether or not
the waste is to be land disposed. The exit table for constituents with
EQCs as exit levels is proposed appendix X of 40 CFR part 261, Table B.
a. EQCs as exit levels
Only when the comparison between the modeled or extrapolated risk-
based level with that constituent's EQC level reveals that the
constituent cannot be quantitated at the modeled or extrapolated risk-
based level, does the EQC become the exit level. For example, the
modeled risk-based level for 2-nitropropane in wastewaters is 0.00019
g/L. The EQC for 2-nitropropane in wastewaters is 0.0058
g/L. 2-nitropropane is listed in appendix X, Table B, with an
exemption level of 0.0058 g/L. In other words, the exemption
level for 2-nitropropane has been met if the claimant demonstrates that
the method used can achieve the EQC of 0.0058 g/L in the waste
matrix, and the level detected by the method does not exceed 0.0058
g/L.
The Agency believes that, for those constituents that have a
modeled or extrapolated risk-based level lower than the achievable
quantitation limit, demonstration that the constituent is not present
above the EQC is the most reasonable approach to setting a national
exemption level. The Agency is proposing that quantitation limits cap
the modeled or extrapolated risk-based levels because a reliable,
consistent measure of the constituent below the quantitation limit is
not achievable. By establishing EQCs as benchmarks (or maximum
allowable quantitation limits), the Agency is ensuring that all
exemption demonstrations will achieve acceptable analytical
sensitivity, and that wastes with high levels of contamination that
tend to confound analytical protocols are not exempted.
The Agency requests comments on whether an exemption demonstration
should be considered adequate if all proper method selection and QC
procedures are followed and the constituents are not detected, even
though the EQC level has not been analytically attained. This situation
could arise even in relatively clean matrices if the constituents bind
strongly to the matrix or if the constituents degrade rapidly during
the analysis. However, the Agency would not want the exemption to be
allowed if the EQC could not be achieved because of interference from
other contaminants in the matrix, or if inappropriate methodology,
i.e., sample preparation, cleanup (if necessary), or determinative, was
used.
EPA is not proposing that any exit level based on an EQC can serve
as a ``minimize threat'' level capping current 40 CFR part 268
treatment standards. Such levels are not sufficiently related to a
constituent's risk.
b. LDR Requirements for Constituents With EQC Exit Levels
EPA considered the option of setting exit levels for all
constituents at their modeled or extrapolated levels, regardless of
analytical considerations. EPA also considered the alternative of
making wastes containing constituents with analytical limitations
ineligible for exit. Both of these options, however, are likely to
constrain significantly the number of waste streams eligible for exit.
Approximately one-quarter of the constituents on the exit list have
EQCs above risk-based or extrapolated levels. Some of these
constituents, such as Beryllium and Arsenic, are fairly prevalent. For
less prevalent constituents, EPA has the same concerns about limiting
exit for wastes managed in centralized wastewater treatment systems
that it described above in the section on extrapolated risk levels.
Further, this approach would overregulate wastes where constituents
were in fact below risk levels. EPA prefers options which would not
prohibit all wastes with these constituents from exiting.
The most promising alternative EPA found was setting exit levels
for these constituents at EQC levels, and also requiring all wastes
containing these constituents to comply with LDR treatment standards,
even where such waste are not destined for land disposal. This
alternative offers the possibility of additional risk reductions and,
therefore, reduces the possibility that wastes posing significant
threats will escape Subtitle C control.
EPA is unable to characterize the amount of additional risk
reduction for a number of reasons. First, as explained in more detail
in the Minimize Threat section of the preamble, compliance with LDRs
already will be required after exit before land disposal for all wastes
(except those that are below exit levels at their point of generation).
The LDR requirement for constituents with EQC exit levels may provide
additional risk reduction, even for those constituents that are not
managed in land disposal units. EPA currently does not know how
frequently nonhazardous wastes are burned as fuel, incinerated, or
otherwise managed outside of land disposal.
Additionally, the Universal Treatment Standards (UTS) for
nonwastewaters, were developed based on similar analytical chemistry
considerations of detection limits. The majority of the UTS limits for
nonwastewaters were based, however, on analysis of residuals from the
treatment of what EPA determined to be the most difficult to treat
wastes and, as a result, this often represented the most difficult to
analyze treated matrix (i.e., higher detection limits than those
represented by the EQCs). The majority of the UTS limits for
wastewaters, on the other hand, were not developed based on limits of
detection but rather they were based on analysis of treated effluents
regulated under EPA's National Pollution Discharge Elimination System
(NPDES).
LDR requirements for all wastes subject to the UTS would be equal
to or higher than the EQC exit levels themselves. However, for wastes
subject to treatment standards based on application of specified
treatment methods under Sec. 268.40, extending LDR requirements may
provide additional risk reduction.
EPA believes that the combined approach of requiring non-detection
at EQC levels and compliance with LDR standards for all waste streams,
regardless of whether or not the waste will be land disposal, offers a
reasonable balance between the goals of reducing overregulation and
ensuring that wastes with significant risks remain subject to Subtitle
C. EPA, however, requests comment on all of the alternatives described
above. EPA also requests comment on the option of basing exit levels
for these constituents on EQCs alone and relying on continued,
independent applicability of LDR requirements for wastes that exit and
are destined for land disposal.
3. Exemption for Constituents Without EQCs
There are several constituents covered in today's notice for which
EQCs could not be developed. The universe of these constituents
includes 78 constituents, most of which are not widely prevalent in
wastes. Most are also found only in P and U listed wastes. These
constituents are listed in table B to appendix X without associated
exemption levels. The background document Background Document to
Support the Development of Exemption
[[Page 66379]]
Quantitation Criteria (EQCs) and Description of Analytical Methods
under the Waste Exit Rule explains why EQCs could not be created.
EPA is proposing that wastes containing these constituents (i.e.,
where an applicant has not documented that these constituents are not
present--see section VIII.A.1.b.,) may remain eligible for an exemption
under today's proposed rule by complying fully with LDR treatment
standards applicable to the waste, as codified in 40 CFR part 268,
regardless of whether the waste is to be land disposed. The Agency
believes that any potential risks posed by these constituents are
likely to be further reduced by applying LDR standards from part 268 to
the waste, before the waste may be exempt, regardless of whether or not
the waste is destined for land disposal. The Agency asks for comment on
this approach.
An alternative approach would be to allow wastes with these
constituents to exit without additional LDR obligations, but relying on
continued, independent applicability of LDR treatment requirements to
wastes destined for land disposal only. Another approach would be to
prohibit wastes containing these constituents from being eligible for
exemption under today's proposed rule. An additional approach would be
that these constituents could be deleted from the exit table. The
Agency requests comment on each of these alternatives.
EPA is not willing to propose to use LDR standards as exit levels
for any other group of constituents. The technology-based LDR standards
are not based on any risk assessment. A comparison of these standards
with the multipathway risk levels that EPA produced shows that the LDR
standards are sometimes more stringent and sometimes less stringent
than risk-based levels. EPA believes that it is more prudent to base
exit levels on risk assessment where possible because this better
assures protection of human health and the environment. EPA views use
of the LDR standards as the option of least preference, but necessary
for exit for this group of constituents. EPA is willing to consider it
only where there is no alternative to prohibiting a constituent from
being eligible for exit.
V. Presentation of Exit Levels
Today's proposed exemption criteria involves setting exemption
levels for toxicants in listed waste, and in some cases requiring
additional compliance with the requirements set forth at 40 CFR part
268. To exit Subtitle C regulation as a listed hazardous waste, all the
hazardous constituents listed in appendix X of part 261 would be
required to be in concentrations less than or equal to the numeric exit
levels and when specified, the waste would have to meet the applicable
requirements at 40 CFR part 268. Appendix C to the preamble presents
constituents, distinguishes between modeled and extrapolated
constituents, and includes EQCs for each constituent.
A. Constituents With Modeled or Extrapolated Risk-Based Exit Levels
The Table A of proposed appendix X to part 261 presents exit levels
for constituents with modeled or extrapolated risk-based levels which
can be reliably quantified. See section IV.H. for a description of how
this was determined. Listed hazardous waste would be required to
contain concentrations at or below the specified exit levels to be
eligible to be exempted from Subtitle C requirements other than LDR. In
some cases we are proposing to change the land disposal restriction
requirements at 40 CFR part 268 as well. A totals analysis would be
required for both wastewaters and nonwastewaters to show that the
constituent does not exist in the wastestream at levels above the
exemption level.
For nonwastewaters, the Agency is also proposing that generators
either use the TCLP test or a calculational screen to measure or
calculate constituents' leachate from wastes. If the TCLP test shows
leachate concentration in the waste is below the leach exit level, the
waste would be considered to not pose a hazard to groundwater.
The Agency has in the past experienced difficulty in using the TCLP
test for some types of waste. The Agency solicits comment on how to
consider oily wastes and other wastes that are difficult to filter in
the TCLP test or whose impact on groundwater is believed to be
underestimated by the TCLP (such as materials subject to non-aqueous
phase transport). Comment on alternative tests for these wastes, as
well as comment on how to define such wastes for regulatory purposes is
sought. A more complete discussion of oily waste can be found in
VIII.A.1.a.iv.
Table A of appendix X of 40 CFR part 261 presents results of two
alternatives for establishing the exit levels. These alternatives
differ only in the benchmark used to calculate the modeled risk-based
levels. For certain constituents there exists both a risk-based
toxicity benchmark and a maximum concentration level (MCL) established
under the Safe Drinking Water Act (SDWA). These numbers may differ
because the MCLs are established using some non-risk considerations
such as the cost of treatment and the availability of technology and
consider exposure contributions from other sources for non-carcinogens.
See section IV.D. of today's proposal for a complete discussion of
toxicity benchmarks and MCLs.
B. Constituents With Quantitation-Based Exit Levels; Table B to
Appendix X
Table B of proposed appendix X to part 261 presents quantitation-
based exit levels for constituents with methods that cannot reliably
quantify the modeled or extrapolated risk-based levels. All exit levels
on Table B of appendix X to 40 CFR part 261 are based on EQCs. (See
section IV.I.) Wastes containing any of these constituents must also
comply with the applicable treatment standards set forth at 40 CFR part
268, the Land Disposal Restrictions (LDR) in order to meet today's
proposed exemption, regardless of whether or not the waste is to be
land disposed.
Some constituents on Table B of appendix X of 40 CFR part 261 do
not have associated exit levels. Waste with these constituents may exit
only after complying with the LDR treatment standards for the waste.
(See section IV.I.2.b.)
C. How To Read the Exit Level Tables
For a waste to be eligible to exit Subtitle C under the exit
proposed in today's rulemaking, every constituent in the waste must be
below its exit level. Proposed appendix X of 40 CFR part 261, Tables A
and B are the exit constituents and the exit levels. The following is a
description of how to read the tables.
The constituent list is derived from constituents listed
in appendix VII, Basis for Listing Hazardous Waste; Appendix VIII,
Hazardous Constituents; and appendix IX of part 264, the Ground-Water
Monitoring List. (See section IV.C.)
Table A represents constituents and their risk exit
values--where the risk values can be measured analytically. (See
sections IV.E., and IV.I.)
Table B represents constituents with quantitation limits
(EQCs) as exit levels--where the constituent cannot be measured at the
modeled or extrapolated risk value. An additional condition of exit,
compliance with treatment standards in 40 CFR part 268, exists for any
waste becoming exempt under today's rulemaking by using a constituent
exit level on Table B. (See section IV.I.2.b.)
There will be overlap for some constituents between Tables
A & B. For
[[Page 66380]]
example, the wastewater exit level for a constituent may be on Table A,
whereas the nonwastewater exit level may be on Table B.
Where an exit level does not exist on Table A or B for a
particular constituent, the waste need not be tested for that
constituent. For example, some constituents that are hydrolyzers have
exit levels for nonwastewaters, but not for wastewaters. A complete
discussion of deletions to the master constituent list can be found in
section IV.C.
The tables' columns:
Columns 1 and 2 are the CAS numbers & constituent names.
There are two proposed options for the development of
today's proposed exit levels. Option 1 is the option whereby Maximum
Contaminant Levels (MCLs) from the Drinking Water program are used as
an acceptable toxicity exposure for human drinking water exposure and
toxicity benchmarks are used for other exposures. Option 2 is the
option whereby toxicity benchmarks are used as acceptable exposure
levels for all exposures. A more complete discussion of these two
options is found in section IV.D. of today's proposed rule. The effect
of co-proposing these two options is that there are two independent
sets of proposed exit levels.
--Columns 3, 4, and 5 represent the exit levels that were derived by
using an MCL benchmark for drinking water ingestion & using toxicity
benchmarks for all other routes of exposure.
--Columns 6, 7, and 8 represent the exit levels that were derived by
using toxicity benchmarks for all routes of exposure.
The definitions of wastewater and nonwastewater are
discussed in VIII.A.1.a.ii.
Columns 3 & 6 represent wastewater exit values. If a
generator determines he/she has a wastewater, if each constituent in
the waste meets these wastewater exit levels, it is eligible for
exemption.
--Values in columns 3 & 6 were derived from the most limiting of non-
groundwater-ecological receptor, non-groundwater-human receptor, and
groundwater pathway values from surface impoundments and tanks (the
risk assessment's wastewater units).
Columns (4 and 5) and (7 and 8) represent nonwastewater
exit values. If a generator determines he/she has a non-wastewater, if
each constituent in the waste meets both of these nonwastewater values,
it is eligible for exemption. The totals level must be met by a totals
analysis. The leach level must be met by a TCLP test or the
calculational screen.
--Values in columns 4 & 7 were derived from the most limiting of the
non-groundwater-ecological receptor and non-groundwater-human receptor
pathway values from land application units, ash monofills, and waste
piles (the risk assessment's nonwastewater units).
--Values in columns 5 & 8 were derived from the most limiting of the
groundwater pathway values from land application units, landfills, and
waste piles (the risk assessment's nonwastewater units).
VI. Minimize Threat Levels
A. Background
1. Summary of the Hazardous and Solid Waste Amendments of 1984
The Hazardous and Solid Waste Amendments (HSWA), enacted on
November 8, 1984, allow hazardous wastes to be land disposed of only if
they satisfy either of two conditions: (1) They can either be treated
or otherwise satisfy the requirements of section 3004(m), which
requires EPA to set levels or methods of treatment, if any, which
substantially diminish the toxicity of the water or substantially
reduce the likelihood of migration of hazardous constituents from the
water so that short term and long term threats to human health and the
environment are minimized; or (2) they can be land disposed in units
satisfying the so-called no migration standards in sections 3004(d)(1),
(e)(1), and (g)(5). Land disposal includes any placement of hazardous
waste in a landfill, surface impoundment, water pile, injection well,
land treatment facility, salt dome formation, underground mine or cave.
See RCRA section 3004(k).
EPA was required to promulgate land disposal prohibitions and
treatments standards by May 8, 1990 for all wastes that were either
listed or identified hazardous at the time of the 1984 amendments, a
task EPA completed within the statutory time frames. See RCRA section
3004(d), (e), and (g). EPA is also required to promulgate prohibitions
and treatment standards for wastes identified or listed after the date
of the 1984 amendments within six months after the listing or
identification takes effect. See RCRA section 3004(g)(4).
The land disposal restrictions are effective on promulgation. See
RCRA section 3004(h)(1). However, the Administrator may grant a
national capacity variance from the effective date and establish a
later effective date (not to exceed two years) based on the earliest
date on which adequate alternative treatment, recovery, or disposal
capacity that protects human health and the environment will be
available. (RCRA section 3004(h)(2).) The Administrator may also grant
a case-by-case extension of the effective date for up to one year,
renewable once for up to one additional year when an applicant(s)
successfully makes certain demonstrations. (RCRA section 3004(h)(3).)
See 55 FR 22526 (June 1, 1990) for a more detailed discussion on
national capacity variances and case-by-case extensions.
As explained in the legislative history, the purpose of the land
disposal restrictions is to reduce the risks associated with land
disposal. Congress also intended the restrictions to reduce reliance on
land disposal and promote waste minimization since land disposal was
its least favored method of managing hazardous wastes.
2. EPA's Interpretation of Standard for Treatment Requirements
The heart of the LDRs are the standards for treatment prior to land
disposal, which must meet the statutory requirement to ``substantially
diminish the toxicity of the water or substantially reduce the toxicity
of the waste so that short term and long term threats to human health
and the environment are minimized.'' RCRA Section 3004(m): EPA's
interpretation of this ``minimize threat'' requirement has evolved
through a long series of rulemakings.
When EPA proposed its first set of LDR treatment standards it took
the position that the most effective way to minimize threats was to
base standards on the capabilities of generally available treatment
technologies. (51 FR 16011 (January 14, 1986).) To avoid unnecessary
treatment, however, EPA also proposed to ``cap'' the technology based
standards with risk-based screening levels based on human health
toxicity thresholds for individual hazardous constituents and modeling
of the groundwater route for exposure. (51 FR 16011-13.)
In the final rule EPA promulgated only the technology based
standards. EPA explained that although it believed it had authority to
promulgate risk-based standards, it was not promulgating the proposed
risk-based caps because of extensive comments raising concerns about
the scientific uncertainties of risk analysis. (52 FR 40578 (November
7, 1986).) Industry challenged the final standards, claiming that they
required treatment to concentrations below ``minimize threat'' levels.
On review, the Court held that section 3004(m) authorized both
[[Page 66381]]
technology based and risk-based standards, but remanded the rule to EPA
for a fuller explanation of its decision to rely on technology-based
standards alone. (Hazardous Waste Treatment Council v. EPA, 886 F. 2d
355 (D.C. Circ. 1989). (``HWTC III'').) The court also held that EPA
was not obligated to adopt either the RCRA characteristic test levels
or the Safe Drinking Water Act Maximum Contaminant levels (MCLs) as
``minimize threat'' levels because neither ``purports to establish a
level at which safety is assured or `threats to human health and the
environment are minimized'.'' (886 F. 2d at 363.)
In its response to the remand, EPA stated that the best way to
fulfill the requirements of section 3004(m) would be to ensure that no
technology-based treatment standard required treatment of hazardous
waste containing levels of hazardous constituents posing insignificant
risks. (55 FR 6641 (Feb. 26, 1990).) EPA, however, explained that it
was not yet able to promulgate such levels. EPA believed that it lacked
a reliable predictive model for ground- water exposure, needed to
assess exposure scenarios for air pathways, needed to consider impacts
on ecological receptors, needed to develop additional analytic methods
for hazardous constituents, and needed to develop an approach for
constituents with threshold effect levels lower than detection limits.
(Id. at 6642.)
In the same notice, EPA noted that the ``minimize threat'' language
of section 3004(m) could reasonably be interpreted to require more
protection than the ``normal subtitle C command that standards be those
necessary to protect human health and the environment.'' (Id. at 6641.)
EPA found that the many portions of the 1984 amendments stressing the
inherent uncertainties of land disposal buttressed this interpretation.
See, e.g., RCRA sections 1002(b)(7), 3004(d)(1)(A), 3004(e)(i)(A),
3004(g)(5). EPA also found support in the legislative history. For
example, the Senate amendment containing the ``minimize threat''
standards replaced a committee bill that only would have required
treatment to be ``protective of human health and the environment.'' See
S. 757, section 3004(b)(7), printed at S. Pep. No. 284, 98th Cong., 2nd
Session 86. Further, EPA noted that the ``no threat'' levels it had
been using in site-specific and waste stream specific contexts, such as
clean closures, delistings, and no-migration petitions, would not
necessarily be appropriate for generally applicable standards required
to minimize threats to health and the environment. (55 FR 6641, note
1.)
At the same time, EPA took the position that section 30004(m) does
not require the elimination of every conceivable threat posed by land
disposal of hazardous waste, citing a statement by Senator Chafee that
``[i]t is not intended that every waste receive repetitive levels of
treatment, nor must all inorganic constituents be reclaimed.'' 130
Cong. Rec. S.9179 (daily ed., July 25, 1984). (55 FR 6641, note 1.)
Clearly EPA did not interpret the minimize threat language to require
the elimination of all threats.
Today, the Agency is proposing to re-evaluate the basis for some of
the existing performance standards established for listed wastes. Since
EPA's response to the HWTC III remand in 1990, the state-of-the-art in
making quantitative determinations of risk has advanced and available
methods have improved significantly. In addition, the increased
sensitivity of analytical methods has lowered achievable detection
limits, better bioassays exist than in the past, and more extensive
biological data is available for extrapolation. As a result, the
universe of available health-based and ecological data has grown
significantly, and the reliability of this information has improved.
The Agency now believes that these data can be used to establish levels
that minimize threats to human health and the environment.
B. Risk Assessment and Minimize Threat Levels
1. Rationale
a. Overview
Today the Agency is proposing to establish risk-based LDR treatment
requirements for some of the hazardous constituents for which exit
levels are being proposed. These risk-based LDR requirements will
minimize the short-term and long-term threats to human health and the
environment posed by the hazardous waste constituents. The risk-based
LDR levels (or ``minimize threat'' levels) would have the effect of
capping, or limiting, treatment of those waste constituents where the
current technology-based UTS standards require lower concentrations.
EPA also hoped to propose most of these constituent-specific levels as
``minimize threat'' levels under section 3004(m) of RCRA that would cap
current technology-based treatment standards under at these levels the
LDR program. However, EPA is proposing ``minimize threat'' levels only
for those constituents that were evaluated under the multipathway risk
analysis and are not capped by quantitation (EQC) limitations. EPA is
proposing to promulgate such levels as replacements for the
constituent-specific treatment levels in the LDR Universal Treatment
Standards (UTS). (As explained in more detail in Section VI, EPA is not
proposing to cap any LDR standards requiring the use of specified
technologies.) As shown on Table 1, Sec. 268.60, EPA is proposing
``minimize threat'' levels to cap UTS treatment requirements for either
the wastewater or nonwastewater (or both) for approximately 70
wastewater constituents and 90 nonwastewater constituents.
EPA, however, is not proposing that any extrapolated levels serve
as ``minimize threat'' levels for LDR purposes. EPA does not have as
much confidence that this alternative methodology provides enough
information on risks to human health and the environment to enable EPA
to determine that risks have been minimized. Similarly, EPA is not
proposing that any levels based on quantitation limits serve as
``minimize threat'' levels. Such levels are not based on any analysis
of risks to human health and the environment. In fact, as explained
above, EPA is proposing to require compliance with technology-based LDR
standards for all wastes which contain such constituents.
If a claimant finds that all constituents in a waste are below exit
levels at the waste's point of generation and if the claimant meets all
of the requirements for filing an exit claim, EPA will not require
compliance with the LDR treatment standards for the waste. EPA will
take the position that such as waste never became subject to subtitle C
regulations, so that LDR standards never applied to the waste. EPA is
proposing to take this position for all exit levels, regardless of
whether they were generated by the multipathway analysis, the
extrapolation method, or EQC limitations. For further explanation, see
section VI.D.
EPA, however, is proposing that all listed wastes which as
generated contain constituents exceeding exit levels must meet LDR
requirements (current or as modified by this proposal), even if the
waste subsequently becomes exempt from hazardous waste regulation under
this rule. This requirement resembles EPA's current rules for ``de-
characterized'' wastes, which must meet LDR requirements even after
they cease to exhibit the hazardous characteristic that made them
subject to Subtitle C in the first place.
[[Page 66382]]
b. ``Minimize Threat'' requirement of Section 3004(m)
EPA continues to believe that the minimize threat language of
section 3004(m) does not require the elimination of every conceivable
threat posed by land disposal of a hazardous waste. The legislative
history of LDR indicates that Congress did not intend to require wastes
to undergo repetitive or ultimate levels of treatment. Rather, Congress
wanted to require use of effective, but widely available treatment
technologies. See 130 Cong. Rec. S 9178 (daily ed. July 25, 1984)
(statement of Senator Chafee introducing the amendment that became
section 3004(m).)). Requiring elimination of all conceivable threats
would almost certainly require use of the most effective treatment
methods available, and this appears to conflict with Congresses'
treatment goals. Moreover, although the DC Circuit has cited the
dictionary definition of ``minimize'' to uphold technology-based
treatment standards below EPA standards such as MCLs and TC levels, EPA
does not believe that the court meant that EPA literally must reduce
threats to the maximum extent possible. (See Hazardous Waste Treatment
Council III, 886 F.2d at 361; Chemical Waste Management II, 976 F 2d.
at 14.) EPA notes that the court indicated that risk-based treatment
standards would satisfy section 30004(m). Hazardous Waste Treatment
Council III, 866 F.2d at 364-65. Further, in his concurring opinion,
Judge Silberman stated that Congress would allow EPA to exercise
reasonable amounts of discretion in determining the level of risk
reduction needed to meet the minimize threat requirement. Id. at 372.
The Agency believes that today's exit concentrations can serve as
risk-based land disposal restriction levels for several reasons. First,
the risk assessment, described in Section IV of today's proposal,
significantly expands beyond the scope of past Agency risk assessment
for wastes and waste constituents. Where adequate data are available,
the analysis can evaluate the potential for waste constituent migration
through almost all significant environmental fate and transport
pathways leading to exposure for human and ecological receptors. As
explained in more detail below, the Agency is also relying on
reasonable conservative risk targets for both humans and ecological
receptors in developing this risk assessment. The Agency believes that
the proposed exit levels represent levels below which further treatment
would not be needed to minimize threats to human health and the
environment.
c. Scope of Risk Assessment
The broad scope of the risk analysis is a critical factor in the
Agency's conclusion that proposed exit levels minimize both short term
and long-term threats to human health and the environment, for those
constituents where data are relatively complete.
The risk analysis evaluates all of the most common non-Subtitle C
disposal options available to waste generators and treaters. These
include disposal in landfills/monofills and by land farming, and
management in surface impoundments, tanks and waste piles. The risk
analysis assumes no minimum level of regulation of these facilities,
and relies on available data to characterize them. As described in
detail in Section IV and in the risk analysis report (EPA 1995), EPA
modeled each disposal alternative using median values for most inputs,
and high-end or conservative values for the two fate and transport and
two exposure parameters for which the modeling outcome is most
sensitive. The Agency believes that the modeling will also protect
against exposures from similar disposal alternatives not specifically
modeled.
The risk analysis evaluates the movement of waste constituents from
each of these disposal options through numerous environmental fate and
transport pathways. These include pathways involving volatiles and
respirable (PM10) particulates, particulate deposition on soil and
plant surfaces, vapor phase diffusion into surface water and plants,
and surface run-off and soil erosion. Many of these pathways can result
in waste constituent movement through the food-chains. Therefore, human
exposures resulting from these fate and transport pathways include
inhalation, soil or groundwater ingestion, and dermal contact, as well
as exposure through consumption of contaminated foods such as fish,
beef or vegetables.
EPA screened all multipathway constituents for potential to pose
threats to ecological receptors. For 45 constituents, EPA
quantitatively assessed likely risk to selected ecological receptors.
Risks to both fresh water aquatic and terrestrial organisms were
evaluated, representing different trophic levels and feeding habits of
the ecosystem. Fish, daphnids, and benthic organisms, mammals, birds,
plants, and soil organisms (nematodes, insects, etc.) were evaluated.
The sustainability of the ecosystem and reproducing populations within
the aquatic and terrestrial ecosystems was selected as an assessment
endpoint, as described in Section IV of this Notice and in detail in
Chapter 3 of the risk analysis support document (EPA 1995).
In addition, as part of this overall risk assessment effort, the
Agency has reviewed and reevaluated its modeling of waste and waste
constituent movement through groundwater. As described in Section IV
above, this responds to comments by interested parties on the original
HWIR proposal, as well as incorporates additional data submitted to the
Agency (API data base), and updated modeling of leaching from wastes
(new HELP model; get Cite).
In evaluating groundwater, the Agency examined both wells located
on the landfill edge and closest wells anywhere down-gradient. Also,
both finite source type and infinite-source type constituents (which
behave as though there is an infinite supply of the constituent in the
landfill, and will continue to leach forever) were evaluated. For
finite source type constituents, the available constituent was not
apportioned over the groundwater and other pathways, i.e., groundwater
was modeled separately. Adsorption to soil and degradation of waste
constituents (but not biodegradation) is modeled, and the toxicity of
constituent daughter products (either more or less toxic than the
parent compounds) is included. (There is a biodegradation module to the
model; however, data to run that module for national conditions are not
adequate at this time, although data were available for some sites. The
Agency will continue to evaluate biodegradation data as they become
available, and assess in the future whether national biodegradation
estimates can be defensibly made). Leaching and groundwater migration
from disposal in unregulated industrial landfills, surface
impoundments, and waste piles have been modeled.
In evaluating the results of this series of groundwater modeling
exercises, the Agency selected the approximate 90th percentile from a
distribution of wells closest to modelled sites. This means that there
is about a 90% probability that the drinking water well closest to the
landfill would be protected at the target concentration (MCL or HBN).
All wells more distant would be protected to a greater extent.
As described in section VI.E. above, the Agency then reviewed the
risk assessment for groundwater and the pathways for each constituent,
and selected as the exit level the concentration, back-calculated to
the waste, from the most limiting (or highest risk) pathway. By using
the most
[[Page 66383]]
limiting pathway as the basis for the risk criterion, the Agency
believes it has accounted for all significant risks resulting from
disposal and management of the waste outside of Subtitle C.
The agency believes it is also important to identify and discuss
some of the limitations of the risk assessment, especially as they
relate to determining whether short term and long-term threats to human
health and the environment have been minimized.
The analysis does not account for additivity of risk for exposure
to multiple constituents. Evaluation of risk additivity can be a
complex analysis when even a few constituents are included. In the case
of multiple waste constituents, potentially occurring in one or more
waste streams that might be considered for exit, the complexity of
conducting and analysis of additivity of risk quickly becomes
overwhelming. However, EPA believes it will often be the case that one
constituent typically drives determinations of whether waste streams
exit and additivity would often make little difference with respect to
the calculated exit levels.
Exposures to the same constituent from several pathways also are
not added together, even though the risk analysis does apportion the
available quantity of waste constituents over the different pathways
evaluated. Again, EPA believes that often one result (in this case, one
pathway) would contribute most of the risk and little would be gained
from adding across pathways. EPA requests comment on this issue.
Data also were not available for all human exposure routes for all
constituents, although data for high-risk pathways were usually
available. Nonetheless, the Agency believes the exit levels can be
considered to represent levels that minimize threats to human health
and the environment because of the comprehensive evaluation of possible
exposure routes, consideration of both human and ecologic risk,
selection of the most restrictive pathway overall, and the relatively
conservative risk target, 10-6, used in setting the exit levels
derived from cancer risk estimates.
As mentioned above, EPA conducted a screening analysis to identify
47 high priority constituents for ecological assessment. EPA did not
model the ecological impacts for 36 additional constituents that
displayed one characteristic indicating potential ecological impacts.
EPA is proposing to set minimize threat levels for 19 of these
constituents.
EPA believes that it has adequately assured that the caps to BDAT
treatment standards proposed today minimize threats to the environment.
The specific ecological risk assessment conducted for 45 constituents
(19 of which have minimize threat levels under this proposal) is the
most extensive EPA has ever conducted under the RCRA program to date.
EPA did not find threshold effects data for all seven groups of
ecological receptors for any constituent evaluated for ecological
risks. Rather, EPA typically had benchmarks for three to five groups.
Nevertheless, its consideration of a broad range of species and use of
reasonably conservative endpoints ensures that threats to ecological
receptors are minimized.
With regard to chemicals that did not undergo this detailed
assessment, EPA has conducted an extensive review of risks to human
health, including a thorough review of risks posed by indirect pathways
and risks posed by constituents that bioaccumulate in plants and
animals consumed by humans. (Bioaccumulation is a key concern for
protection of many ecological species.) EPA believes that it is
reasonable to assume that the exit levels identified by this analysis
also minimize threats to ecological receptors unless it has some
definite data indicating that additional protection is warranted.
Reliance on these levels is particularly appropriate for those
chemicals that did not display one of EPA's ecological screening
characteristics. EPA finds it also appropriate for the 15 ``minimize
threat'' chemicals which exhibited one ecological screening
characteristic. EPA acknowledges that conducting a specific assessment
of ecological risks for these 15 constituents would have provided
additional assurance that threat to ecological receptors were
minimized. EPA solicits comment on the option of declining to set
minimize threat levels for these 15 constituents until it can complete
an ecological assessment for them.
d. Risk Targets Minimize Threats
The Agency believes that the risk targets used in the risk analysis
to back calculate to waste concentrations minimize threats to human
health and the environment. For cancer risks to human, a risk target of
one in one million, over a lifetime is the risk target. For non-
carcinogens, a hazard quotient (HQ) based on a reference dose or other
comparable value from the literature could not exceed one (hazard
quotient (HQ)=1). Reference doses or comparable values are based on
studies of toxicity and no-effect levels in test animals and
extrapolated, using safety factors, to humans. For ecological
receptors, population effects inferred from individual effects and
effects on a substantial number of both aquatic and terrestrial species
were evaluated.
Other risk targets may be considered in establishing minimize
threat levels. The Agency solicits comment on whether apportionment of
the RfD ought to be used in establishing minimize threat levels (i.e.,
HQ<1). The Agency uses 20% of the Rfd in setting drinking water
standards; a similar approach might be appropriate in establishing
minimize threat levels and in establishing exit levels. EPA requests
comment on this issue.
2. Public Policy Considerations
Finally, the Agency believes that it represents good public policy
to reduce or eliminate unneeded or duplicative regulatory requirements.
In this case, the Agency believes that for the initial list of
constituents listed in Table 1 of 40 CFR 268.60, treatment to the UTS/
LDR standard is no longer required beyond waste constituent
concentrations where risks to human health and the environment are
insignificant. Because there is no purpose in terms of protecting human
health and the environment for retaining the more stringent LDR
requirements, the Agency is proposing to revise them to the risk-based
levels. This would reduce the overall number of different and distinct
regulatory requirements on waste generators and treaters, would
rationalize the RCRA regulations, and will provide significant
pollution prevention opportunities and incentives. Waste generators
would have only one target level to direct their pollution prevention
effort toward. If generators met the LDR/exit levels, the waste would
not be considered hazardous, and no additional treatment would be
required before disposal in a subtitle D facility. Where waste
continues to exceed one or more exit levels after LDR requirements are
met, subtitle C disposal would be required.
C. Risk-based LDR Levels
1. List of Constituents and Minimize Threat Concentrations
As was mentioned earlier in this section, only modeled
constituents' risk-level results are eligible to serve as risk-based
LDR levels meeting the statutory requirement of minimize threat. In
addition, minimize threat levels are only proposed for those
constituents where the risk level is higher (less stringent) than the
associated
[[Page 66384]]
technology-based treatment standard in Sec. 268.40 or the UTS level in
Sec. 268.48.
First, the Agency repeats that it is not proposing to set any
alternative risk-based LDR standards expressed as specified
technologies (rather than constituent concentrations.) Consequently,
the option of complying with minimize threat levels in lieu of levels
specified in part 268 will be available only for wastes with treatment
standards expressed as constituent concentrations. This includes both
wastes subject to waste-specific treatment requirements under the table
to Sec. 268.40 and wastes subject to the Universal Treatment Standard
levels in the table to Sec. 268.48
The Agency proposes that for purposes of establishing nonwastewater
and wastewater minimize threat values for wastes with BDAT treatment
standards expressed as constituent concentrations, the levels proposed
would utilize the LDR definitions of nonwastewater and wastewater from
40 CFR 268.2(d) and (f). Therefore, any exit levels that are considered
nonwastewater for purposes of exit will also be considered
nonwastewater for purposes of minimize threat. Likewise, wastewater
exit levels will be considered wastewater LDR levels. The Agency
believes that consistent definitions of nonwastewater and wastewater is
the only practical means to establish minimize threat levels. The
Agency realizes, however, that the modeling and subsequent development
of exit levels for today's proposed exit did not use the part 268
definition of nonwastewater and wastewater. (A complete discussion of
this may be found in section VIII.A.1.a.ii.) The effect of this would
be that some wastes that would be defined as wastewaters under today's
proposed exit scheme would be considered LDR non-wastewaters. The
Agency requests comment on whether the definition in Part 268 should be
adopted for purposes of establishing minimize threat levels.
The Agency compared the exit levels to the current LDR treatment
levels to determine whether a constituent's risk level should be
proposed as a minimize threat level. For wastewater values, the LDR
wastewater value was directly compared to the wastewater exit value.
Where the UTS nonwastewater level is a total level, the comparison was
made to the nonwastewater totals exit level. Where the LDR
nonwastewater level is a leach level, the comparison was made to the
nonwastewater leach exit level. However, for the reasons explained
below, the nonwastewater minimize threat level would contain both a
leach level and a totals level. For both wastewater and nonwastewater,
where the most comparable exit level is higher (less stringent) than
the current LDR level, the constituent's risk level is proposed as an
optional minimize threat level. The Agency requests comment on this
approach to determining which exit levels are higher than current LDR
levels.
The Agency is proposing that testing requirements when using
minimize threat levels would be consistent with the current LDR testing
requirements found in Sec. 268.7. The Agency proposes that if a
claimant wishes to meet LDR requirements by complying with a minimize
threat level, the claimant must meet the minimize threat levels with a
totals analysis, and where specified, the waste must meet the leach
level with a leachate analysis. The Agency believes that a totals
analysis is preferable to a leach analysis for establishing minimize
threat levels, as it more directly pertains to all pathways, not only
the groundwater pathway.
Today's proposed exit levels for nonwastewaters consist of two risk
levels for each constituent. The totals (mg/kg) nonwastewater risk
level is the result of the most limiting non-groundwater pathway. The
leach (mg/L) nonwastewater risk level is the result of the most
limiting groundwater pathway. The Agency believes it would be
preferable to have one exit level, but the groundwater model results
are a leach (mg/l), whereas the results from the multipathway analysis
are a totals (mg/kg), and the science to extrapolate from a leach to
totals is highly variable. Using only the leach or only the total risk
level would reflect only a portion of the risks presented by the waste.
A waste must meet both of these limits before it minimizes threats to
human health and the environment. Consequently, EPA is proposing to
include both levels in the minimize threat standards for
nonwastewaters. The Agency proposes to allow generators to either use a
calculational screen or perform the TCLP to make a determination that
constituent concentrations do not exceed nonwastewater leach minimize
threat levels. A full discussion and explanation of the calculational
screen can be found in section VIII.A.1.a.iii. of today's proposal.
Because extrapolating from a leach to a total varies with each
constituent and is not easily measured, EPA has not directly compared
both of the minimize threat levels with the LDR standard. The Agency
requests data on specific constituents where the second, less easily-
compared nonwastewater minimize threat level may be harder to achieve
than the current LDR standard. If such results occur, waste handlers
will not be required to use the new minimize threat levels. The levels
in the tables to Sec. 268.40 and Sec. 268.48 will continue to satisfy
LDR requirements as they always have. The minimize threat levels will
be located in Table 1 of Sec. 268.60, are optional, and are intended to
be used to provide treatment relief. The Agency believes that minimize
threat levels will only be used where they are less stringent than
current LDR levels. The Agency requests comment on the proposed
revisions to part 268 with respect to minimize threat levels.
Table D-1 of appendix D to the preamble presents for comparison
current LDR UTS standards and proposed minimize threat levels. The
Agency is proposing that for the constituents listed below, the risk
levels may substitute for current UTS treatment levels in 40 CFR 268.48
or for treatment standards for these constituents in 40 CFR 268.40. A
table of the proposed minimize threat levels can be found at proposed
40 CFR 268.60 subpart F in the regulatory text following this preamble.
2. Constituents for Which Exit Levels Are Not Minimize Threat Levels
As an alternative to the approach described in C.1 above, the
Agency solicits comment on the background data underlying the risk
evaluations for these constituents. The Agency believes, in general,
that the constituents evaluated in the risk analysis have relatively
complete assessments of risk. The Agency recognizes, however, that data
quality and completeness can vary among constituents, even for those
for which risk can be assessed. The Agency solicits comment on both
general criteria for assessing completeness of data, and also specific
constituents for which use as minimize threat levels to cap LDR
requirements may be inappropriate.
D. Meeting LDR Requirements
1. Wastes Below Exit Levels as Generated
EPA proposes that, if a generator samples a listed waste stream at
its point of generation and analysis of the sample shows all
constituents to be below exit levels, LDR requirements would not apply
to the waste. EPA is proposing this result both for constituents with
exit levels based on multipathway analysis (where, since exit levels
can serve as LDR ``minimize threat'' levels that cap current treatment
requirements, the LDR program will never require treatment to levels
lower than exit levels) and constituents with
[[Page 66385]]
exit levels based on extrapolation from the multipath analysis or
quantitation levels (where, since EPA has not proposed to make exit
levels into LDR minimize threat levels,the LDR programs may require
treatment to levels lower than exit levels).
To claim this relief generators would have to certify that they
sampled their wastes at the point of generation. In the interim between
sampling and receipt of analytical results, the generator would be
required to manage the waste as hazardous. However, EPA would take the
position that this brief period of Subtitle C regulation would not
subject the waste to LDR requirements.
EPA believes that position is consistent with its prior
interpretations of LDR provisions and the D.C. Circuit's opinion in
Chemical Waste Management II. At issue in that case was EPA's
determination that LDR treatment standards apply to wastes that are
characteristically hazardous at the point of generation but that
subsequently cease to exhibit characteristics and become nonhazardous
wastes. EPA took that position to ensure that characteristic wastes
receive effective treatment. Without this requirement, for example, it
would be possible to dilute characteristic wastes and evade LDR
treatment requirements. The Court held that EPA must apply this
interpretation consistently to characteristic wastes.
It is not necessary, however, to follow this interpretation for
wastes that are generated with all constituent concentrations below
exit levels. EPA can reasonably distinguish between wastes that are
below exit levels at the point of generation and wastes which achieved
such levels at some subsequent time. Only wastes which exceed exit
levels at the point of generation need continued LDR applicability to
ensure that they reduce constituent concentration or constituent
mobility by complying with LDR standards rather than using dilution or
some other inferior form of treatment. A generator of wastes that meet
exit levels as generated would not use waste treatment to evade LDR
requirements. Rather, he or she might use waste minimization techniques
to reduce concentration or mobility of constituents in the precursor to
his waste.
EPA notes that it is proposing to require listed wastes which
exceed exit levels at the point of generation to meet LDR treatment
requirements, even if the waste later meets exit levels. EPA believes
that this requirement carries out the LDR requirements set out in the
Third Third rule and the Chemical Waste decision.
Finally, EPA notes that it would be possible to articulate
alternative rationales for exempting from LDR requirements wastes which
meet today's exit levels as generated. For exit levels based on
extrapolations from the multipathway analysis, EPA could argue that
extrapolated levels are LDR ``minimize threat'' levels. EPA, however,
thinks protection of the environment is better served by refraining
from such a step and requiring wastes which exceed such levels at the
point of generation to meet current technology-based LDR standards. (As
explained above, EPA is not entirely certain that these extrapolated
levels actually minimize risks for all constituents.) For exit levels
based on quantitation limits, imposing LDR requirements would not have
any practical impact. LDR treatment standards are limited by the same
quantitation limits proposed for this rule. Consequently, treatment
standards for constituents limited by analytical capabilities are not
lower than the exit levels.
2. Wastes Above Exit Levels as Generated
Listed wastes that are above exit levels as generated would be
required to be treated to the LDR standards in force at the time if
they are placed on the land.
VII. Dilution
The 1984 RCRA Amendments (HSWA) established a vigorous national
policy for minimizing the generation of hazardous wastes. Section 1003
of RCRA, as amended in 1984, established a national waste minimization
policy stating that ``wherever feasible, the generation of hazardous
waste is to be reduced or eliminated as expeditiously as possible''.
The policy also cited the need to reduce the volume and toxicity of
hazardous wastes which is nevertheless generated. Similarly, section
3005(h) prescribed that effective September 1, 1985, all RCRA
permittees who generate waste disposed of, treated, or stored on-site
certify, on an annual basis, that the facility has waste minimization
programs in place. In addition, section 3002(b) mandates that hazardous
waste generators include a certification with their hazardous waste
manifests that the generator has a waste minimization program in place
and that the proposed method of off-site management minimizes threats
to human health and the environment. In concert with these HSWA
mandates, it is the Agency's policy to encourage source reduction
(i.e., waste minimization) and waste treatment as preferable to
disposal and dilution.
EPA has recognized that successful implementation of the land
disposal restrictions requires that, in general, dilution be prohibited
as a partial or complete substitute for adequate treatment of
restricted wastes. The legislative history indicates that such a
prohibition ``is particularly important where regulations are based on
concentrations of hazardous constituents'' (H.R. Rep. no. 198, Part I,
98th Congress, 1st Session 38 (1983)).
The Agency also opposes the dilution of hazardous wastes for
several technical reasons. Most importantly, dilution is an
environmentally inappropriate means to reduce toxicant concentrations
because it does not reduce toxicant loadings to the environment. The
same mass of toxicant is released to the environment when a diluted
waste is disposed as would be if that same waste, prior to dilution,
were to be disposed. While mass loading of the environment is itself a
serious concern, the potential for environmental damage is magnified
when toxicants (for example, pesticides and metals) bioaccumulate in
the food chain. In addition, diluted wastes can create an unnecessary
demand for scarce solid waste disposal capacity.
For these reasons, dilution is generally prohibited as a means to
achieve the exemption levels under today's proposal. Because today's
rule proposes to amend the some of the current LDR levels by
establishing minimize threat levels, allowing dilution as a means of
achieving exemptions would be inconsistent with the ban on dilution
included in the land disposal restrictions rule (40 CFR 268.3). In
addition, dilution would be inconsistent with the Congressional purpose
of encouraging waste minimization. Thus, today's proposed rule
specifically prohibits dilution as a means of attaining the exemption
levels except as provided under the LDR program under 40 CFR 268.3(b).
VIII. Implementation
Today's proposed rulemaking would establish a generic set of
constituent-specific exemption levels for listed hazardous wastes.
Wastes with hazardous constituent concentrations below the generic
exemption levels would be conditionally exempt from Subtitle C.5
Today's proposed
[[Page 66386]]
rulemaking would be self-implementing; that is, no prior governmental
approval or review of documentation would be required before wastes are
eligible to exit. Claimants of an exemption, however, would be required
to meet certain prerequisites in addition to the generic constituent
concentration levels before the wastes would be considered non-
hazardous. These testing and notification requirements are necessary to
ensure that only those hazardous wastes which truly meet the exemption
criteria exit the subtitle C system. In addition, certain testing and
record-keeping conditions would be imposed to maintain the exemption to
ensure that the waste continued to be eligible for the exemption.
Failure to satisfy the conditions would void the exemption.
\5\ Exempted wastes would continue to be solid wastes, and as
such would require proper management under subtitle D and other
applicable state laws.
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A. Implementation Requirements
To make an effective claim, persons would need to comply with the
following requirements:
--The waste must be sampled and tested in accordance with a
comprehensive sampling and analysis plan prepared prior to conducting
sampling and analysis (EPA recommends, as guidance, using the basic
elements of sampling and analysis plans described in Chapters One and
Nine of SW-846);
--Representative samples collected in support of an exemption proposed
in today's notice must consist of a sufficient number of samples to
represent the spatial and temporal variability of the waste
characteristics;
--The waste must be tested for all hazardous constituents except those
that should not be present in the waste as defined by this rule, with
documentation supporting determination not to test any constituent
available on-site at the time of the notification;
--If the claimant must test for any hazardous constituents on table B
of appendix X of 40 CFR part 261, the waste must also meet treatment
standards for those constituents listed on UTS table of 40 CFR 268.48;
--A notification must be submitted to the Regional Administrator (or
authorized State) (hereafter referred to as the implementation
authority), along with
--A certification signed by the claimant's authorized representative
attesting to the completeness and accuracy of the notification, and
--Verification that a notice of the exemption claim has been placed in
a major local newspaper of general circulation.
Any deficiencies in compliance with these requirements would
prevent the exemption from being valid; that is, the waste would not
exit the subtitle C system. Claimants would not be able to use their
knowledge of the waste alone to make a determination. Furthermore, in
order to defend a claim that a waste was exempt under today's proposed
rule and thus exempt from hazardous waste regulation, claimants would
bear the burden in an enforcement action of establishing that the waste
in question met the exit levels and the other requirements for the
exemption.
1. Testing Requirements
In today's notice, the Agency is proposing concentration-based
exemption criteria below which a listed hazardous waste would be
conditionally exempt from subtitle C compliance. To best ensure
accurate characterizations of constituent concentrations in these
wastes, the Agency is also proposing sampling and analysis requirements
for the exemption determination proposed today. Adherence to these
requirements, however, does not ensure that the characterization is
accurate and representative of a waste on a continual basis. It is the
generator's responsibility to ensure that a waste always meets the
exemption requirements proposed today for all appendix X of 40 CFR part
261 constituents, regardless of which constituents the facility is
required to test and how often testing is performed.
To be eligible for an exemption, EPA is proposing that facilities
must (1) demonstrate that each constituent of concern is not present
above the specified exemption level in the waste, (2) demonstrate that
the analysis could have detected the presence of the constituent at or
below the specified exemption level, and, (3) where specified, comply
with the LDR standards applicable to the waste. Today's proposed rule
allows that any reliable analytical method may be used to demonstrate
that no constituent of concern is present at concentrations above the
exemption levels. It is the responsibility of the generator to ensure
that the sampling and analysis is unbiased, precise, and representative
of the waste.
The Agency will consider that the exemption level was achieved in
the waste matrix if an analysis in which the constituent is spiked at
the exemption level indicates that the analyte is present at that level
within analytical method performance limits (e.g., bias and precision).
The Agency prefers this empirical demonstration of method performance
through the successful analysis at the exemption level. The Agency
requests comment on this and any other approaches to demonstrate method
performance.
In general, the Agency is proposing testing requirements that would
consist of an initial test to characterize the waste as exempt,
followed by subsequent testing to ensure ongoing compliance with
constituents of concern. A generator of a listed waste on a one-time
basis will only be required to comply with initial testing
requirements. Wastes produced on an infrequent (batch) or continuous
basis will have to comply with initial testing requirements and
subsequent testing requirements as appropriate based on the volume of
the waste. The Agency asks for comment on this general approach to
testing requirements.
a. Data Evaluation
i. Compliance With the Exit Levels
The Agency is requesting comment on three approaches of data
evaluation.
First, the Agency is proposing that, for exemptions under today's
proposed rule, generators would be required to evaluate their waste
based on the maximum detected concentrations of the exemption
constituents. If any constituent concentration is greater than its
specified exit level, then the waste would be ineligible for exemption
under today's proposed rule. One advantage of this approach is that
facilities can use process and waste knowledge to determine the
appropriate number of representative samples without relying on a
complex, potentially costly statistical approach to determine an
appropriate number of samples. However, generators will need to be
sufficiently knowledgeable about their waste and process to make an
unbiased determination regarding the appropriate number of samples.
Actual sample representativeness might be difficult to verify or
otherwise assess (on a statistical basis). Finally, the level of
uncertainty associated with the results cannot be defined. Because of
this, under this approach, a single composite sample that validly
exceeds the HWIR exit levels would indicate that the waste is hazardous
and must be handled in Subtitle C.
Second, the Agency requests comment on also allowing a second data
evaluation method whereby the analytical results are evaluated in terms
of an upper confidence limit around an average concentration. An
example of one method for determining an upper confidence limit is
presented in the statistical approach found in Chapter Nine of SW-846
(Third Edition, as amended by Updates I, II, IIA, and IIB),
[[Page 66387]]
where, for the purpose of evaluating solid wastes, the probability
level (confidence interval) of 80 percent is used. Sample measurements
for which the upper limit of the 80 percent confidence interval about
the sample mean is below the regulatory level for the chemical
contaminant are not considered to be present at levels of regulatory
concern. One main advantage of this approach is that the number of
samples is statistically determined and thus it eliminates any bias
that might otherwise be introduced when using knowledge to determine
the appropriate number of samples. In addition, the level of
uncertainty associated with the results can be determined. However, the
main disadvantage of this approach is that it could be more costly for
some facilities than the proposed approach. For example, it might
require multiple rounds of sampling to determine the mean and variance.
Highly variable wastes may require the collection of many more
additional samples than might otherwise be determined to be necessary
using the first approach. However, this statistical approach allows
occasional samples to be above exemption level, as long as the upper
confidence limit of the data overall is below the exit level.
The Agency also requests comment on a third data evaluation method
that would allow facilities to use long-term average data to
demonstrate compliance without consideration of the upper confidence
limit. A rolling average of samples would be taken over the course of a
year on a schedule determined by the initial sampling and analysis
plan. As long as the average of the samples was below the HWIR exit
level, the waste stream would be considered non-hazardous. This
approach would have the advantage of being simpler than the second
option, while allowing occasional exceedences of the exit levels by
single samples, as long as the average concentration is below exit
levels.
EPA has modelled risk with the assumption that the constituents of
concern are uniformly distributed within the waste at the exit
concentrations. In discussion with the Hazardous Waste Identification
Dialogue Group, some representatives noted that actual levels might
need to average significantly below the exit levels if the exit
criteria are to be consistently met. The second and third data
evaluation methods discussed above help address this issue.
However, EPA and the States have noted that the only practical
approach for enforcement purposes is to independently collect samples
for analysis (which may represent a composite of materials spatially or
over a short time span) and to set up the regulation so that an
exceedence by any single composite sample during an inspection could
constitute a violation. It would then be the responsibility of the
generator to refute this, using historic sampling data and possibly
additional samples to show that the sample exceedence does not
constitute an overall violation of the HWIR levels.
EPA believes it is important to retain the practical approach
whereby a single composite sample of a waste at some arbitrary point in
time or space during a short visit is considered sufficient for
enforcement purposes. However, because the exit numbers were modeled
based on long-term average concentrations, the Agency requests comment
on allowing occasional exceedences as long as the average concentration
meets the exit level.
In addition to the concern about enforceability, however, EPA has
identified two additional concerns about using average concentration to
determine compliance. First, not all waste streams would be disposed of
in the same place. Thus the wastes may on average be in compliance when
they are generated, but the wastes arriving at the disposal site
(possibly from multiple sources) may not be, on average, below the exit
levels. Second, EPA has not modeled the constituents for acute risk.
While the average concentration of constituents may be below the exit
levels, the occasional ``high'' concentration may be of concern due to
acute health or ecological effects.
One possible way to address some of these concerns is, in addition
to requiring that the average meet the exit levels (as in the second
and third data evaluation methods), EPA could require that all samples
be below some ``peak'' concentration.
Under this approach, if the average concentrations are below the
exit levels, and all individual samples are below the higher peak
level, then the generator would be in compliance and need take no
further action to support the exemption. EPA or a State would then be
able to confirm waste status without total reliance on the generator's
data and without the expense of periodic sampling by EPA or the State.
EPA requests comment on this issue, including any information on
setting peak levels.
For any of the three data evaluation approaches, representative
samples must be collected in support of exemption under today's
proposed rule, consisting of a sufficient number of samples to
represent the spatial and temporal variability of the waste
characteristics, regardless of how the sample number is determined.
For the identification and handling of ``outliers'', the Agency is
recommending that testing for outliers should be done if an observation
seems particularly high or low compared to the rest of the data set. If
an outlier is identified, the result should not be treated as such
until a specific reason for the abnormal measurement can be determined
(e.g. contaminated sampling equipment, laboratory contamination, data
transcription error). If a specific reason is documented, the result
should be excluded from further data evaluation. If a plausible reason
cannot be found, the observations should be treated as a true, albeit
extreme, value and not excluded from the data evaluation, as waste
composition can vary. The Agency solicits comments on implementable
techniques for the identification of analytical outliers.
The results of the tests of all of the constituents on the
exemption list would be required to show the constituent concentration
to be at or below the exit level in order for the claimant to be
eligible for an exemption. In the case where a constituent's exit level
is based on the quantitation criteria (EQC, as described in section
IV.E.), in addition to showing a non-detect at the exit level, the
waste would be required to meet applicable requirements set forth at 40
CFR part 268. Certain facilities may have difficulty quantifying a
constituent at the exit level due to matrix interference effects, but
the Agency expects exempted wastes to have relatively clean matrices
such that exit levels should be able to be achieved. The Agency
believes that the exit level must be met in order for a waste to exit
Subtitle C; therefore, waste streams that cannot meet exit levels would
not exit under today's rule. The Agency asks for comment on this
approach.
ii. Wastewater and Nonwastewater Categories
Throughout today's proposal and background documentation, all of
the exit levels have been described as being applicable to two
categories of wastes using the terms wastewater and non-wastewater
6. EPA used these terms as an initial means of distinguishing two
waste categories that are inherent to how the exit levels were
developed, by taking into account how these wastes
[[Page 66388]]
will be managed (i.e., stored, treated, and disposed), and also how the
wastes would be expected to behave in the environment. In the
development of the exit levels, several waste management units were
evaluated in the underlying risk analysis. The units chosen for
evaluation were those that are considered most likely to manage the
types of wastes that would be expected to exit Subtitle C regulation
under today's exemption. Although these units will likely receive to
some degree both forms of waste, in general there are technical,
physical, and sometimes legal constraints on what types of waste are
managed in each. The Agency considered ash monofills, waste piles, and
land application units as typically managing waste materials that can
be considered ``solid'' or ``non-wastewater,'' while tanks and surface
impoundments typically manage ``liquid'' or ``wastewater.'' Based on
these assumptions, results from the analysis of risk from these
specific waste management units were then used to generate the
corresponding exit levels for non-wastewater and wastewater.
\6\ The terms ``wastewater'' and ``non-wastewater'' are used
generically in today's preamble and rule, and do not represent the
land disposal restriction definitions in 40 CFR 268.2(d) and (f),
although one option EPA is requesting comment on in this section is
the use of those definitions.
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In considering how to develop final definitions and terms for these
two waste categories, the Agency's goal is to establish definitions
that are clear, concise, and easily distinguishable from other similar
terms such that a generator can readily determine which set of exit
levels to apply to the waste being evaluated for the exemption. EPA
requests comment on three options for defining these two waste
categories to determine which set of exit levels to apply to a listed
waste eligible for today's proposed exemption. EPA emphasizes that
these definitions will only apply in the context of today's exit rule.
The Agency also requests comment on whether it is reasonable in all
three options to allow a generator the alternative options of
separating in the laboratory the solid (or nonwastewater) portion of
the waste from the liquid (or wastewater) portion of the waste,
analyzing the resultant portions, comparing the results to the
corresponding exit levels, and treating the waste as exempt if all exit
levels are met in both portions.
Option 1: Using Percent Solids--EPA prefers the option of defining
the two categories of exit levels as ``solid'' and ``liquid'' exit
levels, where the distinction between solids and liquids is based upon
the percent solids content of the waste, as determined using Section
7.1 of the Toxicity Characteristic Leach Procedure (TCLP) in SW-846.
Specifically, the option would define wastes containing 15 percent
solids by weight or greater as solids,7, while wastes with less
than 15 percent solids by weight be defined as liquids. EPA believes
that the 15 percent cutoff is a reasonable distinction between the two
categories of exit levels, for the following reasons. Because there are
general prohibitions on liquids or wastes containing free liquids in
non-hazardous waste landfills accepting municipal wastes, the Agency
does not envision wastes containing less than 15 percent solids being
managed in these units. Similarly, it is unlikely that waste containing
less than 15 percent solids will be stored in waste piles due to
obvious physical limitations. For land application units, EPA believes
that 15 percent solids content by weight is a reasonable lower limit
for the types of wastes typically managed in these units; indeed, this
was the value used in the land application unit scenario in the
groundwater modeling portion of the risk assessment underlying today's
exit levels.
\7\ EPA will avoid use of the term ``solid waste'' when
describing the category of exit levels that are defined as solids
under this option in today's proposal. This is to avoid confusion
with the existing term ``solid waste'' in the RCRA program, which
has specific statutory and regulatory definitions, which have no
relationship to whether a waste is a physically a solid or a liquid.
---------------------------------------------------------------------------
Because of these limitations, EPA believes that wastes containing
less than 15 percent solids will more frequently be managed in the
types of units associated with wastewater treatment, such as tanks and
surface impoundments. In fact, EPA believes that many wastes falling
into the liquid category under this definition, that can realistically
exit under today's proposed exit rule, will likely be wastewaters that
have undergone treatment and that contain much less than 15 percent
solids. EPA presumes that in many cases the separation of water from
solids will be occurring as part of routine wastewater treatment, and
generators will be either be evaluating the solid residues (which would
clearly meet our solid definition), or the treated water, much of which
is currently discharged under the Clean Water Act and therefore likely
has limits on the amount of solids present.
EPA also requests comment on alternative ways of determining
percent solids content, including generator knowledge of the waste or
results of previous analyses. The Agency believes that in many cases,
particularly for fairly dry or fairly wet wastes, the generator can
immediately ascertain from a visual inspection that the percent solids
content is well above or well below the 15 percent solids value.
Option 2: Using LDR Definitions--EPA also requests comment on the
use of the same terms and definitions currently used under the land
disposal restrictions. Wastewater is defined as waste containing less
than 1 percent total suspended solids (TSS) and less than 1 percent
total organic carbon, or TOC (40 CFR 268.2(f)). Non-wastewater is
defined as any waste that is not a wastewater (40 CFR 268.2(d)). The
principle advantage of this approach is it allows the use of consistent
definitions for wastewater and nonwastewater in both today's exit
system for listed wastes, and the LDR program. The advantage of this
consistency is particularly apparent for those cases where LDR
treatment standards are conditions of exit under today's rule. One
disadvantage of this approach is that it defines wastes containing
greater than 1 percent TSS as non-wastewater, even though these wastes
will likely be managed in wastewater treatment systems using tanks and
surface impoundments, which is inconsistent with the way in which the
results from the risk analysis were used in developing exit levels. The
Agency requests comment on this approach as an alternative to Option 1.
Option 3: Using the Paint Filter Liquids Test--The third option is
to use the terms ``liquid'' and ``solid'' as in Option 1, but to use
EPA Method 9095 from SW-846, the Paint Filter Liquids Test, to
determine whether the waste being evaluated for exit is a liquid or a
solid. Under this option, any waste determined to contain free liquids
using Method 9095 would be considered a liquid, and the exit numbers
currently in the wastewater category would apply to that waste.
Conversely, a waste would be defined as a solid, and the nonwastewater
exit levels would apply, if the waste does not contain free liquids
using Method 9095. Under this option, EPA realizes that many wastes
appearing like solid materials would actually be defined as liquids.
Method 9095 is presently used in defining the term ``liquid waste''
in the solid waste disposal facility criteria, for determining
compliance with the prohibition on disposing of bulk or containerized
liquid in municipal solid waste landfills (see 40 CFR 258.28). Method
9095 is also used in determining compliance with the prohibition on
bulk or containerized liquids in hazardous waste landfills
(264.314(c)).
iii. Totals and TCLP Analyses
Today's rule proposes that the claimant would be required to test
the waste for which today's exemption is
[[Page 66389]]
being claimed to prove that constituent concentrations in the waste do
not exceed the exit level(s) for each constituent that should be
present in the waste.
The claimant would determine which category of exit levels would
apply (e.g., wastewater or nonwastewater) to his waste. In a previous
section of today's rule, the Agency requests comment on several options
to define these two categories. For a wastewater waste to be eligible
for exit, every constituent in the waste must comply with the
wastewater total constituent exit concentration. For a nonwastewater
waste to be eligible for exit, every constituent in the waste must
comply with the nonwastewater total constituent exit level as well as
the nonwastewater leach exit level.
A test for total concentration would be required for each
constituent in the waste regardless of whether the waste is a
wastewater or a nonwastewater to determine that the total constituent
exit concentration has not been exceeded. For non-wastewaters, a
claimant must also prove that the measurable leachate concentrations do
not exceed the nonwastewater leach exit levels. The Agency proposes to
allow claimants to either use a calculational screen or to use the
Toxicity Characteristic Leaching Procedure (TCLP, Test Method 1311 in
``Test Methods for Evaluating Solid Waste, Physical/Chemical Methods,''
EPA Publication SW-846) to make a determination that constituent
concentrations do not exceed nonwastewater leach exit levels.
Discussion concerning the methodology of a calculational screen is
described below.
Section 1.2 of the TCLP allows for a compositional (total) analysis
in lieu of the TCLP when the constituent of concern is absent from the
waste, or if present, is at such a low concentration that the
appropriate regulatory level could not be exceeded.
For wastes that are 100% solid as defined by the TCLP, the maximum
theoretical leachate concentration can be calculated by dividing the
total concentration of the constituent by 20. The dilution factor of 20
reflects the liquid to solid ratio employed in the extraction
procedure. This value then can be compared to the appropriate
regulatory concentration. If this value is below the regulatory
concentration, the TCLP need not be performed. If the value is above
the regulatory concentration, the waste may then be subjected to the
TCLP to determine its regulatory status.
The same principal applies to wastes that are less than 100% solid.
In this case, however, both the liquid and solid portion of the waste
are analyzed for total constituency and the results are combined to
determine the maximum leachable concentration of the waste. The
following may be used to calculate the maximum theoretical
concentration in the leachate.
[GRAPHIC][TIFF OMITTED]TP21DE95.000
where:
A = Concentration of the analyte in liquid portion of the sample (mg/L)
B = Volume of the liquid portion of the sample (L)
C = Concentration of the analyte in the solid portion of the sample
(mg/kg)
D = Weight of the solid portion of the sample (kg)
E = Maximum theoretical concentration in leachate (mg/L)
If:
Eleach
Then: A TCLP need not be performed for this constituent because, even
if 100% of the constituent leaches, the TCLP results would be less than
the regulatory leach standard. This calculation is adequate proof that
this waste is at or below its leach exit level.
The above calculational screen may be used by a claimant in order
not to perform the TCLP. The screen may be used to determine that a
total analysis of the waste demonstrates that individual contaminants
are at such low concentrations that the nonwastewater leach exit level
could not possibly be exceeded, thus eliminating the need to run the
TCLP.
Example: To illustrate the calculational screen, the following
example is provided: An analyst wishes to determine if a leach
processing sludge could fail the nonwastewater leach exit level for
lead. The sludge is reported to have a low concentration of lead, and
the analyst decides to perform a compositional analysis (totals test).
A representative sample of waste is subjected to a preliminary percent
solids determination as described in the TCLP. The percent solids is
found to be 90%. Thus, for each 100 grams of this waste filtered, 10
grams of liquid and 90 grams of solid are obtained. It is assumed for
the purpose of this calculation that the density of the filterable
liquid is equal to one. The liquid and solid portion of the sample are
then analyzed for total lead. The following data are generated:
Percent solids = 90%
Concentration of lead in the liquid phase = 0.023 mg/l
Volume of filtered liquid = 0.010 L
Concentration of lead in the solid phase = 85 mg/kg (wet weight)
Weight of the solid phase = 0.090 kg.
The calculated concentration is as follows:
[GRAPHIC][TIFF OMITTED]TP21DE95.001
In this case, the maximum leachable concentration is below the 10
mg/L regulatory concentration for lead, and the TCLP need not be
performed.
iv. Oily Wastes
In this proposed rulemaking, the Agency has modelled the transport
of solutes in groundwater as well as movement along other environmental
pathways. This groundwater modeling involves predicting rates of
constituent leaching from wastes in land-based waste disposal units. In
using this fate and transport modeling to develop regulatory exit
levels, the Agency is proposing to rely on the use of leach tests to
ensure that groundwater is not contaminated. Among the test methods
that have been developed and employed to identify wastes which might
pose an unacceptable hazard are: Methods 1310 (Extraction Procedure),
1311 (Toxicity Characteristic Leaching Procedure, TCLP), 1320 (Multiple
Extraction Procedure, MEP), and 1330 (Oily Waste Extraction Procedure,
OWEP).
However, these leach test procedures all have deficiencies in
predicting the mobility of toxic chemicals from oily
[[Page 66390]]
wastes. Method 1311 underestimates the mobility of constituents from
many oily wastes due to filter clogging problems, can be imprecise for
oily wastes, and has several operational problems. Conversely, Method
1330 is believed to overestimate mobility of constituents from oily
wastes since it emulates a worst case scenario by using solvents to
extract contaminants from the oil. None of the available laboratory
procedures is fully satisfactory. Rather, they bracket the range of
possible leaching for oily wastes.
In addition, EPA does not have a good definition for what
constitutes an oily waste. EPA originally defined oily wastes as those
materials that clogged the filter during Method 1311 (TCLP) extraction.
EPA requests comment on how to better define what an oily waste is.
EPA also requests comment on which of the two tests methods (1311
or 1330) should be used and why should one test be chosen over the
other for predicting the concentrations of contaminants in leachate
from wastes being managed in landfills. EPA also requests comment on
whether there are any alternative test methods or models that could be
used for predicting the mobility of oily materials. Such procedures
need to be both scientifically credible and environmentally protective.
Methods need to identify material that might be released from the waste
and enter the soil. Release is defined as movement of either the liquid
phase of the waste or leached contaminants through the bottom of the
waste unit to the subsurface soil immediately underlying the disposal
point. Once contaminants pass this point their ultimate fate in terms
of impact on down-gradient water supplies can be estimated by the
ground-water fate and transport model (EPACMOW model).
EPA also requests comment on any additional problems with oily
waste leachability not covered here, and whether the volatilization or
other attributes of constituents should be considered in the
development of a test.
Oily wastes also pose modeling challenges in groundwater because
they do not disperse in the same pattern as aqueous liquids. This
affects the movement of the constituents in the material. In the event
of a release of waste at or near the soil surface, the waste will
migrate downward until it reaches the water table. Light non-aqueous
phase liquids (LNAPLs) will then tend to migrate laterally, forming a
pancake on top of the water table. Dense non-aqueous phase liquids
(DNAPLs) on the other hand will sink to the base of an aquifer and not
show much lateral spreading until an impermeable layer is reached. EPA
is requesting comment on what sort of wastes or what constituents
exhibit these behaviors and how to define that set of wastes.
Constituents that have been associated with DNAPLs include
dichlorobenzenes, PCBs, napthalenes, chloroform, carbon tetrachloride
pentachlorophenol, cresols, and several PAHs. However, trace amounts of
these constituents are unlikely to pose a DNAPL problem. A DNAPL
problem is likely to occur when there is sufficient concentration to
flow as undissolved liquid that would then form the sort of complex
reservoirs that subsequently slowly dissolve into groundwater. The
Agency requests comment on concentrations of these or similar chemicals
that are likely to pose DNAPL problems and whether the proposed exit
levels in totals or, for nonwastewaters in leach levels, are sufficient
to limit wastes exiting for which a DNAPL or LNAPL problem would need
to be explicitly evaluated.
The Agency is continuing to work on developing tests and models for
determining the leaching potential of oily materials and may propose
them in future rulemaking. In the meantime, EPA is today proposing to
apply the levels as proposed in this rule to oily wastes, but seeks
comment on whether instead there is a definable class of wastes for
which these levels cannot reasonably be concluded to be protective.
b. Initial Test
The Agency is proposing in today's rule that there would be an
initial test before a facility would be eligible for an exemption. The
initial test would be the primary tool to characterize the waste as
exempt. Results from this initial test would be sent to the
implementing agency. The public could request the implementing agency
to make the results available.
EPA is proposing to require initial testing of all of the 386
constituents on appendix X of 40 CFR part 261 except those that the
claimant determines should not be present in the waste. EPA would
require the claimant to document the basis of each determination that a
constituent should not be present. The claimant must submit the
documentation to the implementing agency and retain a copy on site for
three years. No claimant may determine that any of the following
categories of constituents should not be present:
--Constituents set out in appendix VII to part 261 as the basis for
listing the wastestream for which exemption is sought;
--Constituents listed in the table to 40 CFR 268.40 as regulated
hazardous constituents for LDR treatment of the waste stream ;
--Constituents detected in any previous analysis of the same
wastestream conducted by or on behalf of the claimant;
-- Constituents introduced into the process which generates the
wastestream; and
--Constituents which the claimant knows or has reason to believe are
byproducts or side reactions to the process that generates the
wastestream.
The Agency requests comment on whether these are the appropriate
criteria to be used to determine what should not be present in the
waste. The Agency also requests comment on requiring claimants who are
not waste generators to consult the generator prior to determining that
a constituent is not introduced into the process or that a constituent
is not a byproduct or side product of the process. EPA believes that it
is unlikely that a non-generator claimant would have sufficient
knowledge of the production process to make adequate determinations on
these issues. EPA requests comment on the type of documentation that it
should require. The generator could co-sign the document that sets out
the reasons for determining that the claimant need not test for a
constituent, or the generator could prepare a separate supporting
document that would be attached to the document for submission to the
implementing agency and retention in the claimant's files.
The Agency is soliciting comment on whether the absence of
constituents in the following documents could constitute sufficient
justification for not analyzing all of the constituents listed in 40
CFR part 261 appendix X.
--40 CFR part 261 appendix VII highlighted to show which constituents
are listed for each waste code applicable to that waste;
--40 CFR 268.40 highlighted to show which constituents are regulated
under the land disposal restrictions for each waste code applicable to
that waste;
--EPCRA Toxic Release Inventory reports highlighted to show which
constituents are reported as being ``used'' in the manufacturing
process from which that waste is generated (based on the EPCRA
definition of ``use'');
--NPDES discharge permits highlighted to show which constituents are
required to be monitored in wastewaters with which that waste is
commingled or will be commingled;
[[Page 66391]]
--State or Local emissions monitoring permits or documents (e.g., stack
emissions, fugitive emissions, groundwater monitoring, wastewater
discharges, etc.,) highlighted to indicate which constituents are
required to be monitored as potential emissions from units in which
that waste is managed or will be managed;
--Responses to government and/or trade group data collection efforts
(e.g., biennial reports, TSD surveys) that require submission of waste-
specific constituent information;
--Published literature (e.g., journals, presentations, chemical and
engineering reference documents, health and safety handbooks, material
safety data sheets, etc.,) highlighted to indicate constituents that
are formed or potentially formed from side reactions, degradation, or
reactivity of the products, reactants, or solvents used in the
manufacturing process generating that waste;
--Plant-specific process flow diagrams or process descriptions
highlighted to indicate constituents that are formed or potentially
formed from side reactions, degradation, or reactivity of the products,
reactants, or solvents used in the manufacturing process generating
that waste;
--Product specifications or constituent-specific labeling requirements
under federal regulations, state regulations, or non-governmental
standards (i.e, per product-grade) that identify constituents that are
expected to be present in the products from which the waste was
generated, highlighted to indicate those constituents identified as
part of these specifications or standards (excluding chemical additives
or preservatives that are placed in the products subsequent to the
generation of the waste for which exit is claimed);
--Waste profile data sheets, such as those submitted to commercial
waste handlers, highlighted to show the constituents that were found or
expected to be present in that waste; and/or
--A certified, third party engineering analysis of the process
generating that waste that provides qualitative verification of the
theories behind the anticipated absence of certain chemical classes or
groups of Appendix X of 40 CFR 261 constituents such as pesticides,
pharmaceutical, halogenated solvents, carbamate, organo-sulfur
compounds, known gases, cyanides, etc.;
--Any other available quantitative or qualitative constituent
information specific to that waste
Relevant information includes not only those document sections that
indicate which constituents are present, but also cover pages that
indicate the source of the document segments and signature pages to
verify authenticity of government-approved documents (where
appropriate). For the verification purposes, page numbers should also
be clearly identified for each document. EPA is also soliciting
information on additional readily available documentation that could be
added to this list that would not impose an unreasonable records burden
on both the generator and enforcement officials (for example, the
Agency believes that requiring highlighted copies of copious amounts of
monitoring data would be redundant and would significantly impede
enforcement review). EPA believes that requiring copies of only
relevant portions of these documents, highlighted to indicate the
chemicals present, should minimize the burden associated with this
documentation requirement significantly.
Regardless of which constituents a facility tests, the facility is
responsible for ensuring that each constituent in the waste meets its
applicable exit level.
The Agency believes that the tailored initial test described above
will ensure accurate waste characterizations of the waste streams while
focusing testing requirements to those constituents that are of
concern. A facility could determine whether a constituent would be
present. A facility would not be authorized to determine that the
constituents in the waste meet the exemption levels based on knowledge
of the waste or material. This approach both reduces unnecessary
testing costs and allows for more frequent monitoring of those
constituents that are of concern.
The Agency is soliciting comment on whether this proposed approach
to an initial test is appropriate.
The Agency asks for comment on taking the opposite approach:
requiring each claimant to test only for those constituents that the
claimant determines ``could be present'' for that waste. This would be
a systematic way for facilities to focus the list of hazardous
constituents to those that are mostly to be present in the waste. EPA
requests comment on requiring at a minimum testing of the following
categories of constituents:
--Constituents set out in appendix VII to part 261 as the basis for
listing the wastestream for which exemption is sought;
--Constituents listed in the table to 40 CFR 268.40 as regulated
hazardous constituents for LDR treatment of the waste stream ;
--Constituents detected in any previous analysis of the same
wastestream conducted by or on behalf of the claimant;
--Constituents introduced into the process which generates the
wastestream; and
--Constituents which the claimant knows or has reason to believe are
byproducts or side reactions to the process that generates the
wastestream.
The Agency asks for comment on the completeness of the proposed
mandatory testing criteria. In addition, the Agency requests comment on
whether testing should be required for those constituents that do not
meet any of the criteria of ``could be present.'' The Agency also
requests comment on whether documentation should be required to
demonstrate that those constituents that were not tested did not meet
any of the ``could be present'' criteria.
EPA requests comment on another approach to determining which
constituents need to be analyzed by a claimant. The approach would be
that the claimant needs to provide data on all additional constituents
listed in appendix X of 40 CFR part 261 of today's rulemaking for which
a method used by the generator to detect other constituents which the
claimant is required to test can easily determine concentrations. Thus,
for example, if a waste was listed for a constituent for which GC/MS is
an appropriate method used by the claimant, the claimant would also be
required to ask the laboratory to provide information on all other
constituents listed in appendix X of 40 CFR part 261 of today's
proposed rulemaking for which the GC/MS is also an appropriate method.
EPA did not use this in its primary proposal because the Agency
realized that implementation of this concept become more complex than
it appears. For example, even when using GC/MS, there may be sample
preparation techniques, dilutions, and similar issues that determine
which constituents can be measured in the appropriate concentration
ranges using the method.
However, there is something intuitively reasonable and attractive
in asking claimant to gather and provide information that is easily
obtainable and would provide additional confidence and certainty. EPA
solicits comments on this idea and ways to implement it.
The Agency requests comment on whether there is some other way to
focus the scope of testing requirements or if the only way to ensure
accurate waste characterizations would be to require testing for all
386 constituents.
[[Page 66392]]
The FACA suggested EPA should define, for major waste streams, a
set of constituents that it believes would fairly characterize those
waste streams. The Agency believes such an approach may be desirable.
However, the Agency notes that this could require it to expend
significant resources. The Agency requests comments on the feasibility
or need for this approach in the long term.
EPA recognizes that some generators may wish to assert claims for
protection of confidential business information (CBI) for some to the
information that supports an exit claim. Material that is classified as
CBI may be reviewed by EPA, but may not be released to the public.
States may have similar provisions under state law. EPA requests
comments on two options for addressing CBI information.
First, EPA requests comment on the option of prohibiting any person
from asserting a claim of exit under this rule if that person wishes to
claim CBI protection for any data or information used to support the
exit claim, including all information submitted to the implementing
agency in the notification package and all information required to be
maintained by the claimant on site and furnished to the agency on
request. A generator who wished to rely on CBI data to support an
exemption claim for a listed hazardous waste would need to file a
delisting petition with EPA or a state authorized for delisting.
EPA believes such an approach may be necessary because the exits
proposed today are self-implementing. The public would not have the
assurance of knowing that EPA or a state agency had reviewed the
claimant's data and determined that it showed that the claimant's waste
posed low risks to human health and the environment. Members of the
public may not feel that they are adequately protected by the fact that
EPA and authorized states could obtain the CBI data and use it (with
appropriate precautions against disclosure) in an enforcement action if
warranted. They may feel that the number of claims will strain agency
inspection and enforcement resources, making it important for them to
be able to bring their own citizen enforcement actions under section
7002 of RCRA.
At the same time EPA is sensitive to potentially legitimate
business needs to protect information supporting an exit claim. Some
firms may not wish to release detailed information about the chemical
composition of their process waste streams. EPA also recognizes that
the federal delisting process is considerably slower and imposes more
procedural burdens than the self-implementing exit scheme. EPA requests
comment on the alternative of creating a limited prior approval process
for exit claims involving CBI claims. EPA anticipates that rulemaking
would not be required. However, states that wish to obtain
authorization for today's exit program might not be required to adopt
this feature because they could argue that failure to provide a review
process for CBI claims would not make their programs less stringent
than the federal program.
EPA also notes that CBI protection is not absolute. EPA has
authority under RCRA to release CBI information to the public as
necessary to support rulemaking proceedings. (In fact, EPA could try to
support the first option above by arguing that it was exercising in
this proceeding its authority to waive protection for all of the
individual exit claims that ``implement'' the rule.) Also, a citizen
that has sufficient evidence of a violation to file a complaint in
court may be able to persuade the court to order a limited release of
the data for use in the enforcement proceedings.
2. Notification Requirements
The Agency is proposing that the required notification to the
implementing authority would include the following information:
--The name, address, and RCRA ID number of the person claiming the
exemption;
--The applicable EPA Hazardous Waste Codes;
--A brief description of the process that generated the waste;
--An estimate of the average and maximum monthly and annual quantities
of each waste claimed to be exempt;
--Documentation for any claim that a constituent is not present;
--The results of all analyses and estimates of constituent
concentrations and all quantitation limits achieved;
--Documentation that any constituents on Table B to appendix X of 40
CFR part 261 have met the applicable treatment standards in
Sec. 268.48, unless the claimant is claiming the exemption under
Sec. 261.36(e);
--Evidence that the public notification requirements have been
satisfied; and
--A certification signed by the person claiming the exemption or his
authorized representative.
The Agency is taking comment on whether the following additional
information should also be sent to the implementing authority:
--The name and address of the laboratory which performed the analysis;
--A copy of the sampling and analysis plan used for making the
exemption determination;
--A description of any chain-of-custody procedures;
--Whether the identity of the disposal facility should be included in
the notification package;
--Dates of sampling and analysis; and
--A description of the (temporal and) spatial locations of the
demonstration samples.
Also, the Agency is taking comment on whether, if the disposal facility
is different than the claimant's facility, the claimant should also
include as part of the notification package documentation that the
claimant informed the disposal facility of the exempt status of the
waste.
A complete notification package would include all required
information in the notification and all required certifications signed
by the appropriate individual, as identified in the regulations.
Failure to submit a notification package if the exemption is being
claimed or submission of an incomplete notification package would be a
violation of RCRA requirements and thus subject to penalties and
injunctive relief under section 3008(a) of RCRA and possible criminal
liability under section 3008(d) of RCRA. As a necessary prerequisite to
claiming an exemption, the burden would be on the claimant to establish
that a complete notification package was submitted to the implementing
authority to assert in an enforcement action that the waste is exempt.
It should be noted that, regardless of whether the sampling and
analysis plan must be included with the notification to the
implementing agency, a current sampling and analysis plan must be
developed and used to establish the waste's eligibility for exemption,
and must be available upon request to the implementing authority at the
time the notification package is submitted and at least for three
years. The sampling and analysis plan must demonstrate that the samples
to be taken and analyzed will be representative of any spatial and
temporal variations in the subject waste.
Furthermore, it should be noted that submission of sampling and
analysis plans with the notification to the implementing authority does
not change the self-implementing nature of the exemption. Submission of
such plans would not be for review or approval of exemption claims
prior to the exemption becoming effective. The implementing agency
would be under no obligation to undertake such review or approval prior
to the exemption
[[Page 66393]]
becoming effective, and failure to undertake such prior review would
not preclude a subsequent enforcement action should the exemption claim
later be determined to be inaccurate or otherwise invalid.
As proposed, the certification required to accompany the
notification must attest that the waste in question meets all relevant
constituent concentration exit levels and that the information in the
notification package is true, accurate, and complete. The Agency is
taking comment on whether this certification is sufficient assurance
that the claimant has made best efforts to accurately characterize the
waste or if additional certification language or additional
certifications (e.g., from an analytical laboratory) are necessary.
The notification package would be required to be submitted by
certified mail with return receipt requested, or other commercial
carrier that provided written confirmation of delivery. No claim would
be effective until the claimant received the return notification
indicating that the package had been delivered.
Submission of the notification package to the implementing
authority, however, is not equivalent to approval or verification of
the exemption claim. Submission of a notification package would not
preclude or in any way limit the implementing authority's ability to
take a subsequent enforcement action should it determine that the
initial requirements of exemption were never met or that the conditions
for maintaining the exemption are not satisfied.
The Agency is taking comment on whether, instead of the exemption
becoming effective upon confirmation of delivery of the notification
package, there should be some brief waiting period prior to the
exemption becoming effective.
Such a period (e.g., 30 or 60 days) could be used by the
implementing authority to review notification packages for completeness
or for indicia of concerns that would lead to prioritized enforcement,
although the exemption would still become automatic after the period
regardless of whether any action was taken by the implementing
authority. As an alternative, the period could be designed to provide
the implementing authority an opportunity to determine that a claimant
should not be able to avail itself of the exemption without some
further review and to notify the claimant of its views.
Under either approach, governmental review would be discretionary
and the lack of such review would not be an indication of governmental
approval of the exemption claim. To ensure that there would be no
confusion on this point, the certification could include a statement of
recognition that expiration of the delay period without comment by the
overseeing agency is not the equivalent of agency approval that the
claim is accurate. The Agency has not chosen to propose a delayed
implementation approach because it believes a short time frame,
particularly combined with an automatic effective date, would not
provide an opportunity for thorough prior review and would, at best,
provide only marginal benefits as a screening device for potentially
problematic claims. The Agency, however, requests comment on whether
such a delay would be beneficial to monitoring claims and if there are
procedural or other concerns relating to such a delay.
B. Implementation Conditions
After the exit claim has become effective, the claimant would have
to continue to meet certain conditions to maintain the exemption.
Failure to satisfy any of the conditions would void the exemption and
subject the waste to applicable subtitle C requirements.
Under this proposal, wastes must continue to meet the generic
exemption levels established for exit to remain non-hazardous. Separate
and distinct from any requirement or condition that might be
established under this rulemaking, all generators--including claimants
of today's proposed exemption--would have a continuing obligation to
identify whether they are generating a hazardous waste and to notify
the appropriate governmental official if they are generating a
hazardous waste. Section 3010; 40 CFR 261.11. If wastes claimed as
exempt under today's proposed rule test above exit levels at any time,
that waste and subsequently generated waste would have to be managed as
hazardous waste--including compliance with all notification
requirements--until testing demonstrated that the waste was below exit
levels.8
\8\ Compliance with HWIR exemption levels will be measured from
the last available test data or from the latest representative
samples taken from the waste in question. Testing which shows
constituent concentration levels above exemption levels will not
affect wastes previously generated under a valid claim of exemption
based upon representative samples. Similarly, testing, which shows
that a waste which tested above exit levels once again tested below
all relevant exit levels will exempt all waste generated on or after
the date the samples were taken. Waste which exceeded the exit
levels would not be able to requalify for the exemption.
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1. Records Maintained on Site
In addition to the information described in the Notification
Section above, the Agency is also proposing that the following
information concerning the initial testing and retesting be maintained
in the files on site at the facility making the exemption claim for at
least three years:
--All information required to be submitted to the implementing
authority as part of the notification of the claim;
--The dates and times waste samples were obtained, and the dates the
samples were analyzed;
--The names and qualifications of the person(s) who obtained the
samples;
--A description of the (temporal and) spatial locations of the samples;
--The name and address of the laboratory facility at which analyses of
the samples were performed;
--A description of the analytical methods used, including any clean-up
and extraction methods;
--All quantitation limits achieved and all other quality control
results for the analyses (including method blanks, duplicate analyses,
matrix spikes, etc.), laboratory quality assurance data, and a
description of any deviations from published analytical methods or from
the plan which occurred;
--All laboratory documentation that support the analytical results,
unless a contract between the claimant and the laboratory provides for
the documentation to be maintained by the laboratory for the period
specified in Sec. 261.36(b)(2) and also provides for the availability
of the documentation to the claimant upon request;
--If the generator claims a waste is exempt from part 268 requirements
pursuant to Sec. 261.36(e), documentation to substantiate such a claim.
The Agency requests comment on the proposed information maintenance
requirements and comment on additional information that may be
necessary.
In addition, claimants will be required to retain certain
information concerning retesting of wastes as described below and set
out in the text of proposed 40 CFR 261.36(d)(6)(ii).
2. Testing Conditions
Claimants would continue to periodically test their wastes as a
condition of the exemption.9 Failure to test and maintain
documentation of the
[[Page 66394]]
testing in accordance with the requirements of proposed 40 CFR
261.36(d) would void the exemption. The Agency believes that required
subsequent testing is necessary to maintain accurate waste
characterizations. Subsequent testing would be an ongoing exemption
condition and would be the minimum testing required to maintain an
exemption. A tailored constituent list setting out minimum requirements
for testing purposes should not be confused with the facility's ongoing
requirement to maintain constituent concentrations below exit levels
for all constituents on appendix X of 40 CFR part 261. Results from
subsequent testing would be required to be maintained on-site.
\9\ Wastes generated on a one-time basis would not be subject
to this requirement.
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The scope of subsequent testing would focus primarily on those
constituents from appendix X of 40 CFR part 261 that are of concern
based on the initial test. The list of constituents for which a
claimant would be required to test would, at a minimum, include each
constituent that was detected in the initial test within an order of
magnitude below the exit level for that constituent, and any
constituent listed in Table B of appendix X of 40 CFR part 261 that is
also identified as a basis for listing the waste or appendix VII to
part 261 or listed as a regulated hazardous constituent for the waste
in the table to 40 CFR 268.40. The claimant would also be required to
test for any other constituent which the claimant had reason to believe
was newly present in the waste since the most recent previous test.
The Agency proposes that the frequency with which a facility would
be required to perform subsequent testing would be determined based on
the volume of waste which the facility is declaring exempt. Those
facilities with large-volume waste streams would perform subsequent
testing more often than those facilities with low- or medium- volume
waste streams. The claimant would be responsible for determining the
volume of annual exempt waste. The Agency asks for ideas and comments
on whether guidance should be made available for claimants on how to
measure annual volumes. Justification of annual volumes would be sent
to the Director in the notification package. The Agency believes that
accurate waste characterizations are important for waste volumes of all
sizes; however, inaccurately characterized large-volume wastes have
greater potential to harm the environment than do smaller-volume
wastes. In today's rule, the Agency is proposing the following
requirements for the first three years of subsequent testing:
--Wastes generated at the time of exemption is initially claimed in
volumes greater than 10,000 tons/year would be tested four times a year
for the first three years of the exemption.
--Wastes generated at the time of exemption is initially claimed in
volumes greater than 1000 tons/year but less than 10,000 tons/year
would be tested twice a year for the first three years of the
exemption.
--Wastes generated at the time of exemption is initially claimed in
volumes less than 1000 tons/year would be tested once a year for the
first three years of the exemption.
EPA requests comment on whether it should allow the Agency proposes
that if a waste maintains exempt status for three years, the frequency
of subsequent testing would then be reduced to once a year, regardless
of the volume produced. The Agency believes that three years of
subsequent testing should provide a facility with adequate data to
assess the potential for variability in the waste. The Agency requests
comment on the frequency of subsequent testing.
The Agency requests comment on an approach that the FACA suggested.
The approach consisted of a comprehensive test, similar to an initial
test, that is required every 3 or 5 years of an exemption because of
the strong reliance on the initial test's results in determining the
scope of subsequent testing.
The Agency also requests comment on whether follow-up testing
should be eliminated entirely after the first three year period. In
addition, the Agency asks if a certification of compliance with all
relevant exit levels could suffice in lieu of testing at the end of
three years.
3. Testing Frequency and Process Change
Under today's proposal, the claimant has a continuing obligation to
verify that the waste continues to meet the exemption criteria,
including meeting the exemption constituent concentration levels.
Process changes that may either increase the number of hazardous
constituents in the exempted waste or increase the concentration of
hazardous constituents already present, should put a claimant on notice
that there may be changes in the waste that may affect its continued
eligibility for exemption. The Agency, however, is not proposing to
require new sampling and analysis whenever there is a process change
that may affect the exempt status of the waste.
The Agency is taking comment on whether it is necessary to require
as a condition of maintaining the exemption that wastes be re-tested
after a process change and, if so, what the scope of such re-testing
should be. The Agency would like to know if the testing frequency
proposed or more frequent testing would provide a clearer indicator of
waste changes of concern than triggering re-testing through a narrative
description of a process change. Another alternative is to require the
claimant to notify the implementing authority that a process change has
occurred and to certify that the exemption criteria continue to be met
if the claimant determines that the waste still maintains its exempt
status. The Agency is taking comment on how process change should be
defined in the event one of the alternatives is chosen. It should be
noted that if waste for which an exemption has been claimed at any time
tests above exemption levels, that waste and all subsequently generated
waste is hazardous. The claimant could not assert a new exit claim
until a new batch of waste tests below the exit levels. The exemption
proposed today would not relieve generators of their responsibility
under Sec. 262.11, nor would any test data previously obtained prevent
a claimant from failing to satisfy the exemption criteria should an
inspector conduct waste sampling that establishes hazardous
constituents at concentrations above exit levels.
C. Public Participation
As a self-implementing exemption effective upon receipt of the
notification by the implementing authority, there is no decision prior
to exit being made by the implementing authority regarding the waste.
The opportunity for public participation in an exemption claim is the
opportunity that exists at all times for the public to bring to the
implementing authority's attention any circumstance that might aid that
authority in its monitoring and enforcement efforts. The public,
furthermore, would have the ability to bring a citizen suit for a
claimant's failure to comply with any requirement of the exemption.
The Agency is proposing to require that the public be notified by
the claimant that an exemption claim is being asserted. This
notification would be accomplished by publication of a notice in a
major newspaper, local to the claimant and of general circulation, that
contains the information required by the regulations. Evidence that the
notice has been submitted for publication must be part of the
notification package submitted to the implementing facility.
[[Page 66395]]
The Agency is requesting comment on whether such a notice should be
placed in a newspaper local to the claimant's facility or to the
disposal facility or both, should those facilities be located in
different areas not served by the same newspaper.
Requiring notification of facilities receiving exiting wastes has
also been raised to the Agency in discussions. The Agency solicits
public comment on the need for and possible approaches to requiring
that waste generators that are exiting their listed waste, notify
receiving facilities that wastes are HWIR exited wastes. Additional
discussion of this issue appears in the docket under ``Receiving
Facility Notification Process.''
As discussed above, the Agency is also taking comment on whether
providing a ``delay'' in the effective date when the exemption attaches
(e.g., 30 or 60 days) would provide a significant and meaningful
opportunity for public comment prior to the waste having exited the
subtitle C system. Possible benefits of a waiting period before
effectiveness of the exit could include greater opportunity for State
review or citizen comment before waste is actually disposed outside of
Subtitle C. Under such an approach, the waiting period would begin with
receipt by the State of a complete certification package, and would run
for the designated time (30 or 60 calendar days).
The Agency is taking comment on whether access to claim
documentation through the appropriate implementing agency will be
sufficient to provide public access to documentation. One alternative
would be to require the claimant to provide access to the information.
If that option is selected, the Agency requests comment on how, and for
how long, the claimant should be required to provide access to the
documentation, and on what kind of protection for CBI would be
appropriate.
IX. Request for Comment on Options for Conditional Exemptions
The Agency has at different times considered contingent management
approaches to disposal of hazardous wastes. Under such approaches,
wastes that would be considered hazardous if managed in an uncontrolled
manner, could be considered non-hazardous if managed in a sufficiently
controlled manner. The following section discusses and requests public
comment on several approaches to setting higher exit levels tied to
meeting certain management requirements. These approaches would allow
wastes with higher concentrations of hazardous constituents to be
managed safely outside of Subtitle C.
Many Subtitle C requirements were written generically to address
all hazardous wastes and, consequently, provide protection for those
wastes that pose the greatest risks. Others are either explicitly or
implicitly technology-based rather than risk-based. Some of these
requirements are statutory and cannot easily be adjusted to take risk
into account. Nevertheless, EPA generally believes that it would be
desirable to tailor waste management requirements to more closely
coincide with risks. The exit levels proposed today take an initial
significant step in this process by allowing very low-risk hazardous
wastes to be exempt from Subtitle C requirements, leaving them subject
only to less prescriptive federal and state controls for nonhazardous
wastes. They also take an initial step towards setting different exit
levels for different situations by recognizing that wastewater and non-
wastewaters are typically handled in different ways and pose different
risks, hence today's notice proposes different exit levels for
wastewaters and non-wastewaters.
Within the time constraints imposed by the court-ordered deadline
for this proposal, EPA has begun exploring whether it would be possible
to create additional exemptions to allow more flexible management of
additional wastes now classified as hazardous without compromising
protection of human health and the environment. These options are
premised on the theory that a waste's risk is due not only to its
chemical composition, but also the manner in which it is managed, which
can greatly affect the amount of chemical constituents that ultimately
reach a human or environmental receptor. The multipathway analysis
prepared to support the exit levels shows that the concentration at
which a hazardous constituent threatens human health or the environment
varies significantly with the type of management that a waste
receives--some forms of management appear to present greater risks than
others. The following discussion presents the legal framework for
management-based exemptions, and outlines in some detail the options
which EPA finds to be most promising for rapid promulgation.
A. Legal Basis for Conditional Exemptions
EPA originally interpreted RCRA's definition of hazardous waste to
focus on the inherent chemical composition of the waste and to assume
that mismanagement would occur so that people or organisms would come
into contact with the waste's constituents. See 45 FR 33113 (May 19,
1980). However, EPA even in the past tried to consider ``reasonable''
mismanagement scenarios, scenarios that where reasonably likely or
plausible even if not proven to necessarily have occurred or be typical
for a specific waste. However, after more than a decade of experience
with waste management, EPA believes that it may no longer be accurate
or necessary to assume that worst-case mismanagement will occur. In
recent hazardous waste listing decisions, for example, EPA has
identified some likely ``mismanagement'' scenarios that are reasonable
for almost all wastewaters or non-wastewaters, and looked hard at
available data to then determine if any of these are for some reason
very unlikely for the specific wastes being considered, or if other
scenarios are likely given available information about current waste
management practices. As a further extension of that logic, EPA now
believes it may be appropriate to find that, where mismanagement is not
likely or has been adequately addressed by other programs, EPA need not
classify a waste as hazardous and that there may be ways to recognize
situations where the limitations on likely ``mismanagement'' are
specific to a State, a type of waste, or a facility-specific condition
on how a waste is managed.
EPA believes that it can interpret the definition of ``hazardous
waste'' in RCRA section 1004(5) to authorize this approach to
classifying wastes as hazardous. Section 1004(5)(B) defines as
``hazardous'' any waste which may present a substantial present or
potential hazard ``when mismanaged''. EPA reads this provision to allow
it to determine the circumstances under which a waste may present a
hazard and to regulate the waste only when those conditions occur.
Support for this reading can be found by contrasting section 1004(5)(B)
with section 1004(5)(A), which defines certain inherently dangerous
wastes as ``hazardous'' no matter how they are managed. The legislative
history of Subtitle C of RCRA also appears to support this
interpretation, stating that ``the basic thrust of this hazardous waste
title is to identify what wastes are hazardous in what quantities,
qualities and concentrations, and the methods of disposal which may
make such wastes hazardous.'' H.Rep. No. 94-1491, 94th Cong., 2d Sess.6
(1976), reprinted in A Legislative History of the Solid Waste Disposal
Act, as Amended, Congressional Research Service, Vol.1, 567 (1991)
(emphasis added).
EPA also believes that section 3001 provides it with flexibility to
consider
[[Page 66396]]
the need to regulate wastes as hazardous. Section 3001 requires that
EPA, in determining whether to list or otherwise identify a waste as
hazardous waste, decide whether a waste ``should'' be subject to the
requirements of Subtitle C. Hence, section 3001 authorizes EPA to
determine that Subtitle C regulation is not appropriate where a waste
is not likely to be managed in such a way that it will threaten human
health or the environment. Moreover, regulation of such waste under
Subtitle C would not appear ``necessary to protect human health or the
environment'' under RCRA sections 3002(a), 3003(a) and 3004(a). As
noted elsewhere in this proposal, EPA interprets these provisions to
give it broad flexibility in fashioning criteria to allow hazardous
wastes to exit the Subtitle C regulatory system. EPA's existing
regulatory standards for listing hazardous wastes also allow
consideration of a waste's potential for mismanagement. See
Sec. 261.11(a)(3) (incorporating the language of RCRA section
1004(5)(B)) and Sec. 261.11(c)(3)(vii) (requiring EPA to consider
plausible types of mismanagement). Where mismanagement of a waste is
implausible, the listing regulations do not require EPA to classify a
waste as hazardous.
Two decisions by the U.S. Court of Appeals for the District of
Columbia Circuit provide potential support for this approach to
defining hazardous waste. In Edison Electric Institute v. EPA, 2 F.3d
438, (D.C. Cir. 1993) the Court remanded EPA's RCRA Toxicity
Characteristic (``TC'') as applied to certain mineral processing wastes
because the TC was based on modeling of disposal in a municipal solid
waste landfill, yet EPA provided no evidence that such wastes were ever
placed in municipal landfills or similar units. This suggests that the
Court might approve a decision to exempt a waste from Subtitle C
regulation if EPA were to find that mismanagement was unlikely to
occur. In the same decision the Court upheld a temporary exemption from
Subtitle C for petroleum-contaminated media because such materials are
also subject to Underground Storage Tanks regulations under RCRA
Subtitle I. The court considered the fact that the Subtitle I standards
could prevent threats to human health and the environment to be an
important factor supporting the exemption. Id. at 466. In NRDC v. EPA,
25 F.3d 1063 (D.C. Cir. 1994) the Court upheld EPA's finding that
alternative management standards for used oil promulgated under section
3014 of RCRA reduced the risks of mismanagement and eliminated the need
to list used oil destined for recycling. (The Court, however, did not
consider arguments that taking management standards into account
violated the statute because petitioners failed to raise that issue
during the comment period.)
B. Improvements in Management of Non-Hazardous Waste and in Risk
Assessment Methodology
EPA's early regulations defining hazardous waste reached broadly to
ensure that wastes presenting hazards were quickly brought into the
system. When EPA promulgated its first listings and characteristic
rules in 1980, its knowledge of toxic constituents, constituent
transport pathways, and waste management options was more limited than
it is today.
In addition, significant changes and improvements in waste
management have occurred since the early 1980's. Many states have
established or strengthened industrial nonhazardous waste programs
since that time. For example, currently 26 states require liners and 28
states require ground-water monitoring for at least some surface
impoundments. Up to 45 states require ground-water monitoring and 38
states require liners for at least some landfills. It is important to
recognize however, that within a state, applicable requirements may
vary according to a number of factors, including unit type, waste
source, and location. See ``State Requirements for Industrial Non-
Hazardous Waste Management Facilities'' EPA 1994. At the same time,
industries have gained experience in managing wastes and many have
improved waste management practices under incentives such as public
access pursuant to the Emergency Preparedness and Community Right to
Know Act, and avoiding liabilities under Superfund, RCRA corrective
action and state cleanup programs.
EPA's ability to predict the risks that a waste may pose has also
improved significantly. EPA has collected much more data on a variety
of waste management units and other factors that impact the ability of
waste constituents to reach a receptor. Models such as the EPACMTP and
the models used in the multipathway analysis provide more sophisticated
means of assessing the risks of a range of waste management options. As
a result of all these changes, EPA is now in a position to begin to
implement a more carefully tailored risk-based approach to regulating
hazardous wastes.
C. Overview of Options for Conditional Exemptions
The Agency has identified several different approaches to providing
conditional exemptions that would allow more wastes to exit the
Subtitle C system. These options fall into two broad categories: (1)
Establishing national conditional exemptions based on unit type either
with or without assuming additional management controls; and (2)
granting conditional exemptions to qualified state programs that ensure
additional management controls.
1. National Approach: EPA Would Establish National Exit Levels for
Contingently Managed Waste
The contingent management program could be adopted by any state
that wants to implement it, without consideration of state programs for
non-hazardous waste. The contingent exit levels would differ according
to the degree of management/disposal restrictions imposed as a
condition of exit. The possible options would include progressively
more restrictive requirements, and allow progressively higher exit
levels as disposal options are further restricted. The options under
this approach are:
a. Distinguish Between Disposal in Land Application Units and Other
Units
The multipathway risk assessment methodology used for this
rulemaking takes into account management scenarios (such as land
treatment of a waste), or exposure pathways (such as wind transport
from an uncovered pile or volatilization from an open tank), resulting
in calculated exit levels based on the riskiest scenario. In some cases
this exit level may be significantly lower than the next most risky
exposure pathway. The riskiest exposure pathway may not be applicable
to some management situations. On review of the risk analysis results,
the Agency determined that disposal in a land application unit is
frequently the highest risk disposal option in both the multipath and
groundwater modeling.
As described in detail in Section X. below, the Agency has
developed for proposal an approach to contingent management relying on
the multipathway exposure analysis, risk level of 10-6 and HQ of 1, and
using the base case uncontrolled management scenarios, but with land
application units removed from the analysis. Exit concentrations would
still be protective across a wide variety of conditions nationally, for
all non-land application unit disposal. The Agency is proposing
[[Page 66397]]
one national exit level for each constituent based on the next riskiest
pathway, on condition that wastes are not disposed in land application
units.
This option was considered by the Agency to be the simplest
approach to contingent management. It would be somewhat easier to
enforce than other options described below, since there would still be
only one conditional exit level for each constituent. Implementation
mechanisms to assure that the wastes go only to allowable unit types
are described below.
b. Unit-Specific Exit Levels for Each Disposal
Another approach to contingent management considered by the Agency
would be to establish a set of exit levels for each waste management
unit evaluated based on risks at unregulated units of that type. Units
that would be evaluated, at HQ 1 and 1 E-6 risk, would be land
application units, waste piles, landfills, surface impoundments and
tanks. Base case assumptions would be used to describe the units. The
Agency has not included specific exit levels for this approach here,
but solicits comment on its potential benefits, and potentially greater
complexity of implementation and compliance assurance.
Under option 2 the Agency would set separate exit levels for each
type of waste management unit. Generators would be allowed to choose
the type of non-subtitle C waste management unit in which to manage
their waste, and would be required to meet the unit-specific exit
levels for all constituents in order to manage the waste in that unit.
Testing and implementation would be similar to the requirements for
exit based on the most limiting pathway. However, the Agency believes
this option would increase the complexity of tracking wastes that met
the varying concentration exit levels tied to specific allowable units.
The Agency believes allowing use of exit levels tailored to waste
management can be a practical and appropriate way to allow greater
volumes of waste to exit Subtitle C without increasing risks to above
the toxicity benchmarks described in Section IV.D, providing that
characteristics of various waste unit types can be clearly defined
(such as the difference between surface impoundments, tanks, and
perhaps covered tanks for the management of wastewaters), and providing
the Agency can design a viable implementation scheme that does not rely
primarily on statements of proposed future disposal. Tracking and
monitoring of actual waste management could be one way to assure
disposal in the appropriate facilities. Limiting disposal to on-site
facilities could also better assure proper disposal, although this
would limit the usefulness of contingent management approaches. The
Agency requests comment on additional implementation requirements that
might be needed to assure the waste is managed in the designated unit
type only.
EPA has not developed this as a general approach in this rulemaking
because the risk modelling that was done, while more multifaceted and
comprehensive than many past analyses, was not designed for this
purpose. For efficiency in modelling, EPA did not always model each
pathway for each specific unit. EPA sometimes only modelled an exposure
pathway of concern (such as air emissions) from certain types of units
that EPA thought might be the limiting scenario, and risk from organic
constituents in a landfill were not modeled. Therefore the modelling
work to date may not identify the most limiting pathway if each unit is
judged individually. To fully develop exit levels for a full range of
unit types, EPA believes it would have to do supplemental risk analysis
to fill in the gaps in modeling for each of the waste management units,
or at least evaluate whether the risk analysis done to date is
sufficiently representative. Tables 21-39 in the November 1995
Supplement to the multipath analysis present the modeled risk values
for each constituent disposed in each of the five options modeled, and
for each pathway. These tables can aid commenters in understanding what
a unit-specific exit value for any particular constituent could be.
c. Consideration of Additional Management Unit Design or Management
Practices
A third option is that EPA would use a somewhat modified
multipathway exposure model to evaluate whether adding additional
specific design or operating controls for particular unit types, would
allow less conservative exit levels. These conditional exit
concentrations would be promulgated on a unit-type specific basis, and
could be used only by units employing the specified additional controls
that would reduce the risk level to 10-6. Such an approach could be
self-implementing for a facility owner/operator, and would not
necessarily be tied into a permitting authority.
While such an approach could take into account the effects of a
combination of added controls on each unit type (such as size of the
unit, ground-water monitoring, liners, caps, etc.) the Agency believes
that there are a number of significant implications associated with
this approach. It could be interpreted by industries and states as an
indirect way to define a broader set of management standards for
industrial non-hazardous waste management units. Also, if the approach
were self-implementing, it could be extremely difficult to ascertain
that a particular unit meets a complex set of controls and therefore to
assure compliance with the conditional exit levels. The more complex a
judgement required to determine compliance with the conditions (such as
whether a liner that is hard to inspect during operation is properly
installed and protected from tears), the more appropriate it is likely
to be that such determinations be made in the context of a permitting
authority or prior approval rather than as a condition on a self-
implementing exemption.
As a variation on this approach, The Agency could take into account
certain regional, local, or site-specific factors in establishing exit
levels. These could include the effect of local rainfall, regional
hydrogeology, or size of facility on exit values. These issues are
described in greater detail in section 3 below.
Because of the complexity of implementation, the Agency would
attempt to define very limited additional control(s) to limit exposures
and reduce risks to 10-6 level. EPA particularly asks for comments on
unit design attributes that are easily ascertainable in a spot
inspection versus those that require more detailed engineering review,
or review or monitoring of operations. For this option, as with options
one and two, the Agency would have to conduct additional risk modelling
work to adequately evaluate additional parameters on a unit specific
basis.
One issue common to all of the options discussed above is the legal
status of wastes subject to such conditioned exemptions when there is a
violation of the conditions. The Agency requests comments on how to
make them enforceable in a practical way that is fair to those
involved. If the waste concentration/unit requirements are conditions
of an exemption, any violation of a condition means that the waste
generator, or other individual managing the waste, has violated the
full range of RCRA requirements and has been illegally managing a
``hazardous waste'' as a ``nonhazardous'' waste. Because the
conditional requirements are not clearly tied to other non-hazardous
waste authorities,
[[Page 66398]]
there would not be a remedy for the violations outside of the hazardous
waste program. An alternative approach is discussed in the following
options allowing conditional exit levels in states with qualified
industrial non-hazardous waste programs. As long as the state has clear
enforcement authority under its non-hazardous waste management program,
these conditions could be crafted so that a violation of the condition
was not illegal disposal of hazardous waste involving multiple RCRA
counts. Rather it would be enforced as a violation of the relevant
State authorities. The Agency requests comment on the advantages and
disadvantages of these approaches, as well as whether there might be
other approaches to ensure adequate legal remedies for violations of
the conditional exit requirements, when the contingencies are not based
on qualified state industrial non-hazardous waste programs.
2. State Program Approach
As noted earlier in this section, many state industrial non-
hazardous waste programs have improved significantly since the early
days of Subtitle C. State programs may offer the advantages both of
requiring management controls which ensure protection of human health
and the environment and ongoing oversight on a facility specific basis
through permitting, inspection and enforcement activities. While every
state program may not be operating at the same level, the Agency
believes that a number of state programs may offer reasonable,
protective systems to serve as the basis for less stringent exit
levels. Qualified state programs would be allowed to manage listed
waste in their non-hazardous waste management program under certain
conditions. These qualified state programs would ensure that risks were
reduced to protect human health and the environment.
There are three key factors the Agency believes would need to be
considered in establishing state-based contingent management programs.
These are (1) establishing a risk-based cap on waste constituent
concentrations that can be managed contingently; (2) the type of
program review of a state program that EPA would perform to identify
qualified state programs, and (3) the breadth of state program
controls.
For the risk cap, the Agency has considered using either a 1 E-4
cancer risk and HQ 1, or 1 E-3 cancer risk and HQ 10 as options. The
caps would be modeled based on management in unregulated disposal
facilities, as in the base-case exit level modeling.
Regarding program review, the Agency would either conduct a
qualitative review of the State program, examining it to ensure it
addresses key considerations, or would require states to conduct
quantitative risk assessment of planned management practices to
demonstrate their safety down to 1 E-6 cancer risk and HQ 1 or an
alternative risk target.
For the qualitative review, EPA would specify environmental and
administrative performance goals and the state would have to submit a
narrative description demonstrating how the particular combination of
technical standards and administrative requirements in their program
protects human health and the environment and meets those performance
goals, for example:
Ground-water protection: A state program must address
adequately contamination of groundwater from a facility.
Surface water protection: A state program must address
adequately prevention of contamination of surface water which may occur
through the run-off of pollutants from the disposal facility to surface
waters.
Address other environmental and performance goals such as
controlling air exposures, siting, ensuring long-term integrity of the
site, etc.
Permitting and enforcement authorities and public
participation: A state program has appropriate authorities and a system
for prior approval of waste management facilities, and public
participation either on a site-specific basis or for input to
development of class permits.
Adequate resources: A state program has adequate resources
for administration of the program including permitting, inspections and
enforcement.
Under a quantitative risk review approach, a state would have to
document their permitting and enforcement authorities and public
participation requirements, as well as the adequacy of their program
resources. The state would also have to demonstrate to EPA how the
particular combination of technical management controls or design
standards in its industrial non-hazardous waste program would ensure
meeting 10-6 risk levels. In order to do this, EPA would have to refine
or expand the multipathway exposure model. EPA would then either make
its multipath model available to states or work with them to
demonstrate that unit-specific state program controls would meet the
10-6 risk level for a particular class of facilities receiving
conditionally exited wastes. The Agency solicits public comment on
whether states can propose alternative risk targets for use in state
contingent management programs.
Regarding program breadth, the Agency believes either broad, state-
wide programs, or more narrowly focused contingent management programs
could be developed. Under a broad-based state program approach, the
Agency would approve as qualified only those state subtitle D programs
that adequately regulate all state non-hazardous waste management and
wastes. Under this approach, states with programs deficient in certain
aspects would be required to upgrade before participating in the
contingent management program. However, the Agency recognizes that
state subtitle D programs vary widely in the particular units and waste
types that are covered, among other factors. Therefore, as an
alternative approach, EPA might determine that a program qualifies for
conditional exit only for particular units (i.e. for landfills only, or
for landfills and surface impoundments, etc.). In other cases, a state
program might focus narrowly on developing appropriate contingent
management for particular waste streams generated by key industries in
the state.
In considering how to use these key factors in developing
contingent management regulations, the Agency identified three options
in addition to the three options described above under the national
programs. These will be identified in this discussion as options four,
five and six.
Under option four, the Agency would use the 1 E-4 and HQ 1 risk cap
on waste and would conduct a qualitative review of the state program
using the criteria described above. This could be done either on a
narrow program basis, or based on a program that qualifies broadly.
Under option five, the Agency would also use the 1 E-4 and HQ 1
risk cap for waste being contingently managed, but would require that
states conduct risk modeling of proposed disposal to demonstrate that
risks from the waste as disposed would be not greater than the 1E-6 and
HQ1 risk targets of the base case. This approach could be taken either
with the entire state program, or only certain waste management
practices. In particular, site-specific factors, as described below,
could be considered under this approach. These could include facility
size, local rainfall, or local hydrogeology, among others. Location of
the nearest drinking water well might also be considered by the state
in evaluating risks, if allowed under state regulations and regulatory
policies. In this case, the state would be
[[Page 66399]]
required to demonstrate to EPA, using the multipathway analysis or
another risk assessment model, how they would ensure on a site-specific
basis that facilities disposing of conditionally exited wastes meet a
10-6 risk level. Development of this approach might also require quite
different risk models, since the multipathway model as it currently
exists incorporates a number of simplifying assumptions to capture a
broad range of possible conditions. The Agency would have to ensure
that a model used for this analysis can incorporate complex site-
specific variables, or develop a set of simplified models that could be
applied by states. However, this approach would provide maximum
flexibility to states and generators to tailor exit levels to
particular waste and site characteristics.
Under option six, the Agency would allow wastes posing up to 1 E-3
cancer risk and HQ 10 (in an unregulated management setting), and allow
either a qualitative or quantitative review of the state program, but
allow participation only by state programs that are broadly qualified,
i.e., that are qualified in all aspects of the program, for currently
managed industrial non-hazardous waste. The Agency would be more
comfortable with this approach because it would be more assured of safe
management of the waste regardless of where in the state it is
disposed.
The Agency also solicits public comment on whether more than one of
the options discussed above should be developed at the same time. For
example, the Agency might establish both the option 1 proposal
described below, and establish a state-based contingent management
program based on any of options four, five or six. By doing so, the
Agency would establish option 1 as a minimum national standard, but
this approach would allow that states to go further they choose to do
so.
3. Establish Exit Levels That Consider Regional or Site-Specific
Factors That Might Affect Constituent Fate and Transport'
In addition to facility design factors, there are other location-
specific factors that may substantially affect the risks and the
appropriate exit levels for waste management units. Examples of such
factors include: Rainfall and hydrogeology at the site and the distance
to off-site receptors. The average amount of precipitation falling on
these waste management units may affect both the amount of leachate to
groundwater and soil run off to off-site receptors. Thus, the Agency
could determine geographic regions based upon climatic zones, could
require precipitation data from the most appropriate certified rain
gauge, or could require site specific precipitation information.
However, in order to do this the Agency would need to verify that the
other model inputs are appropriate for each of the regions or else
develop new region-specific inputs. Therefore, the Agency solicits data
and comment on technically appropriate ways to establish exit levels
based on rainfall levels.
Other site-specific factors that may significantly affect the
groundwater pathway are the hydraulic conductivity of the soil
surrounding the waste management unit and the distance to the nearest
drinking water wells. If the hydraulic conductivity of surrounding soil
is relatively low--such as in soils dominated by clays--then the flow
of any potentially contaminated leachate to ground water could be
effectively retarded for long periods of time (though flow to surface
waters or other pathways might change, perhaps increasing). Landfills
located in soils with low hydraulic conductivities (for example, 10-6
cm/sec or lower) could provide an extra level of environmental
protectiveness for ground water that could be considered in developing
this approach. For example, the Agency might address this effect by
developing exit levels corresponding to different classes of hydraulic
conductivity. Alternatively, differences in hydraulic conductivity
could be considered through a site-specific process. This approach
would not be relying on engineered controls, but on natural attributes
of the location. EPA solicits comments on whether such attributes can
be readily determined or in what circumstances they can be readily
determined and relied upon.
The Agency did some limited sensitivity analysis with respect to
ground water risk modelling to look at the concept of developing
different exit levels depending on broad hydrogeological regions. The
results of that analysis are in the docket. The Agency requests comment
as to the value of investing in this approach and practical
considerations the Agency should weigh in deciding whether to pursue
this approach.
Finally, where the nearest drinking water wells are at an unusually
great distance from the waste management unit, corresponding exit level
concentrations associated with groundwater exposures that took that
distance into account could be significantly lower if the Agency's goal
were solely the prevention of current exposure to groundwater
contamination. However, many states have policies to not degrade
groundwater and EPA believes it is quite difficult to predict future
needs for uncontaminated groundwater. EPA believes that the groundwater
modelling done for this rule reflects a balanced view by using the
distribution of nearest wells. However, EPA expects it will receive
comments suggesting that it should consider allowing facilities with no
moderately nearby drinking water wells to take that into account. The
Agency seeks comment on the implementation issues associated with
taking these factors into account and the related policy judgement as
to whether the goal of more site-specific assessment should be
prevention of risk based on current ground water use, reasonably
foreseeable use, or based on distances that would be more protective of
the potential future use of ground water.
The Agency also seeks comment on other location-specific factors or
combinations of factors that may be particularly important in
mitigating the risks associated with waste disposal. The Agency also
requests comment on alternative approaches for taking these location-
specific factors into consideration in developing exit levels for waste
management. One option for doing so would be to develop additional
tables of exit levels (in addition to Option 2) for waste management
units that reflect the effect of some of the most important location-
specific factors (e.g., exit levels for areas with low annual rainfall,
or indexed to landfill size). As an alternative option, the Agency
could develop ``reduced form'' equations that specifically relate the
exit level concentration to critical location-specific factors (such as
annual rainfall). The Agency requests comment on the merits of these
approaches and on alternative options that might be used to better
accommodate the effect of location-specific factors on exit levels.
D. Land Disposal Restrictions for Contingent Management Options
Any conditional exemption would offer much more significant relief
if it eliminated or reduced the need to comply with more stringent LDR
treatment requirements. As explained above in Section VI of today's
proposed rulemaking, however, under Chemical Manufacturers Association
v. EPA (the ``Third Third'' decision) LDR treatment standards generally
continue to apply even if a waste ceases to be classified as a
hazardous waste. If an LDR treatment standard were lower (more
stringent) than a contingent management exit level, the waste would
still need to meet the LDR standard.
[[Page 66400]]
EPA has proposed two approaches to integrating HWIR exit levels and
LDR treatment requirements for the base option. First, EPA is proposing
that LDR treatment requirements will never apply to wastes that meet
all applicable exit levels at the point of generation. Second, for
wastes which meet exit levels subsequent to the point of generation
and, consequently, remain subject to the LDR regime, EPA is proposing
to allow some exit levels to serve as alternative risk-based treatment
standards meeting the ``minimize threat'' standard under RCRA section
3004(m). EPA expects these proposals to reduce the burden of complying
with LDR requirements.
As explained more fully in the detailed presentation of option 1
below, EPA is proposing both of these approaches for contingent
management option 1 (relaxed exit values for wastes that are not placed
in land application units). EPA's rationales are set out in that
discussion.
EPA anticipates that it might also be willing to propose to use
exit levels developed under option 2 (separate exit levels for each
major type of waste management unit) to serve as risk-based ``minimize
threat'' standards. If EPA filled the gaps in its current multipathway
risk assessment, it would feel fairly confident that the multipathway
analysis plus the groundwater analysis identified constituent
concentrations that minimize threats to human health and the
environment for each class of waste management units. The modeling for
both analyses would assume each type of unit was located in a
``reasonable worst case'' physical setting and was subject to minimal
management controls. EPA, however, would expect some members of the
public to argue that unit-specific exit levels should not be considered
``minimize threat'' levels because risks to human health and the
environment would not be minimized if exempted waste ended up in the
wrong type of management unit. EPA might try to address such concerns
by imposing conditions such as tracking or reporting systems on persons
claiming the exemptions.
EPA would expect similar objections to the option of allowing
wastes that meet option 2 levels to exit if their constituent
concentrations met unit-specific exit levels at the point of
generation. Members of the public might again be concerned about the
possibility that wastes could be placed in a unit type requiring lower
(more restrictive) exit levels. As suggested above, however, EPA could
impose conditions to help ensure that exempted waste goes only to a
unit where the exit levels in fact minimize threats.
Providing LDR relief for the remaining options for conditional
exemptions would raise additional legal and practical issues. All of
the remaining national and state-based options rely on design or
operating controls (such as liners) to help prevent dangerous
concentrations of hazardous constituents from reaching human or
environmental receptors. EPA, for example, would be reluctant to take
into account control measures that would be difficult for inspectors to
verify during site visits.
It might be somewhat easier to take into account factors--such as
annual rainfall, depth to groundwater, and subsurface soil and rock
formations--that relate to a unit's physical setting. EPA has already
proposed to interpret section 3004(m) to allow consideration of a
unit's physical setting in making site-specific minimize threat
findings. See the proposed LDR standards for contaminated soil, 58 Fed.
Reg. 48123 and 48155 (Sept. 14, 1993). EPA requests comments on all of
these issues related to the integration of conditional exemption
options to the LDR standards.
E. Contingent Management of Mixed Waste
The Department of Energy (DOE) has also expressed interest in EPA's
contingent management approaches to managing waste that is mixed
radiologic and RCRA hazardous waste (``mixed waste''). Mixed waste may
be managed by DOE-regulated facilities or commercial facilities
regulated by the Nuclear Regulatory Commission (NRC). EPA expects that
the general approach in today's proposed regulation would be applicable
to mixed wastes as well as listed-only hazardous wastes. DOE has
suggested that because mixed wastes subject to RCRA are also subject to
AEA disposal requirements which control releases of and exposure to
radioactive hazards, these AEA requirements may address releases of
chemically hazardous constituents as well, and it would be reasonable
to allow more mixed wastes to exit Subtitle C because of the AEA
requirements. DOE believes these AEA requirements would also provide
adequate protection of human health and the environment from
chemically-hazardous constituents. DOE has submitted several studies to
EPA in support of their views, and the Agency has placed those
documents in the public docket for review. The Agency will also
undertake a review of these data to better understand the additional
increment of protection provided by AEA low-level waste site
performance standards. With that review ongoing, the Agency is
proposing, and requesting public comment on, adaption of option four
above to DOE's special circumstances. The Agency requests comment on
allowing mixed waste meeting conditional exit levels for chemical
toxicity estimated at 10-4 cancer risk and HQ 1 (modeled at an
uncontrolled site), to exit Subtitle C if managed in AEA disposal
facilities.
DOE has also urged the Agency to consider establishing a
categorical exclusion from RCRA requirements for mixed waste debris
that is immobilized. One of several macro- or microencapsulation
methods could be used to immobilize the debris, including use of
portland or other cement products, or various polymer products. Under
such an exclusion, all immobilized mixed debris could be managed
outside of Subtitle C, but would still be required to be disposed in
AEA disposal facilities. No testing of the debris would be required to
identify toxic constituents or the levels at which they might be
present. DOE has conducted a study of leaching rates for certain toxic
constituents from stabilized debris and submitted it to the Agency for
review in support of DOE's conclusion that immobilized debris can be
managed safely outside of subtitle C if disposed in an AEA facility.
Because the Agency has only recently received this study, it has been
unable to adequately review and evaluate the data presented. The Agency
solicits public comment on this approach, the DOE study, and solicits
any other available data that are relevant to this topic.
Finally, DOE has developed data on vitrified waste, and requested
that the Agency consider the environmental protection conferred by this
treatment process. Again, the Agency has not had adequate time to
review and evaluate the DOE data, but has placed it in the public
docket and solicits public comment on the data and DOE's preferred
approach to mixed waste management.
In soliciting comment on these exit procedures for mixed waste, the
Agency recognizes that a number of states hosting DOE facilities have
expressed concern over the proposal's effect on their states ability to
adequately regulate mixed waste under states and federal law as
intended by RCRA and the Federal Facilities Compliance Act. These
states also believe that significant details of the DOE proposal are
lacking and additional analysis would need to occur before the
procedures can receive adequate comment. Therefore, the Agency intends,
to the extent consistent
[[Page 66401]]
with the schedule negotiated in the consent decree for this rulemaking,
to publish a supplemental proposal on HWIR mixed waste exit criteria
after initial comments have been received. The supplemental proposal
would further describe the regulatory options being considered and will
solicit additional comment on more specific options.
X. Implementation of Conditional Exemption Option 1
A. Introduction
Using the concept of contingent management, EPA is proposing to
create a second, alternative set of exit levels for nonwastewaters that
are managed in landfills or monofills, but not land treatment units.
Persons wishing to utilize this alternative exit scheme would not only
have to meet the recalculated concentration limits for all constituents
in their wastes, but also comply with conditions prohibiting land
treatment. Compliance with notification and tracking requirements
described in more detail below will also be necessary. The exit levels
for this alternative are set out in appendix XI of 40 CFR part 261; the
requirements and conditions are set out in proposed Sec. 261.37.
Nonwastewaters that do not meet the exit levels in appendix X to 40 CFR
part 261 will be eligible for exit only if they meet the more relaxed
levels in appendix XI of 40 CFR part 261 and comply with all relevant
conditions.
EPA derived the levels for this alternative by deleting all of the
modeling results for the land treatment scenario from its risk
assessment data base, and selecting the lowest remaining exit value
from the remaining modeling results for other types of waste management
units. The same approach used to establish exit levels presented in
Section V. of today's proposed rulemaking was used to establish exit
levels under this option. That is, where complete risk data was not
available, surrogates were used to extrapolated exit levels (see
Section IV.H) and where analytical limitations existed, EQCs were used
as exit levels (see Section IV.I). As a practical matter, this approach
affects only the exit levels for nonwastewaters. As explained above in
section IV, EPA created the original exit levels for nonwastewaters by
grouping the modeling results for the unit types typically used to
manage solid materials (ash monofills, piles, and land treatment units)
and selecting the lowest value from all pathways modeled for these
scenarios. EPA created the separate wastewater exit levels by grouping
the results from units typically used to manage liquid wastes (tanks
and surface impoundments). Consequently, the wastewater exit levels are
not based on the modeling of land treatment units, and these levels are
not affected by the decision to exclude results from the land treatment
scenario.
The Agency is proposing that the contingent management exemption be
self-implementing. Therefore, the claimant would have the burden of
demonstrating that all of the provisions for the contingent management
exemption described herein have been met. In an enforcement action, a
waste for which a contingent management exemption is claimed would be
considered a Subtitle C hazardous waste unless the claimant was able to
produce evidence that all of the conditions of the exemption have been
met.
B. When Contingent Management Exemptions Become Effective
The Agency is proposing two options for the point at which the
contingent management exemption would become effective.
1. Option 1A--Placement of the Waste in a Qualifying Unit
Under the first option, the conditional exemption for ``contingent
management'' nonwastewaters would not become effective until the waste
had been placed in a qualifying unit. Prior to actual disposal, the
nonwastewater would be managed as a hazardous waste according to all
applicable RCRA provisions, including 40 CFR parts 262 (for generators)
and 263 (for transporters) and part 268 (regarding treatment prior to
land disposal). These requirements include compliance with the waste
manifest provisions of 40 CFR part 262, subpart B, and the pre-
transport provisions of 40 CFR part 262, subpart C, which contains,
among other provisions, the provisions governing hazardous waste
accumulation. Treatment and storage prior to disposal would remain
subject to parts 264, 265, and 270.
The Agency believes this approach makes it easier to ensure
consistent implementation and safe management of the waste. It also
decreases the potential implementation concerns that may arise if some
states adopt this rule as part of their authorized programs and others
do not. For example, this approach would reconcile transportation
concerns that could arise if waste, conditionally-exempt in one state,
were transported through a state that had not adopted the contingent
management exemption as part of its authorized program.
Under this option, the Agency is considering and requesting comment
on the applicability of amending 40 CFR 264.1 and 265.1 to allow off-
site disposal facilities to store candidate contingent management
exempt wastes for up to 10 days without becoming a subtitle C
treatment, storage, and disposal facility, prior to ultimate disposal
in a monofill or landfill. The Agency requests comment on whether 10
days is a sufficient or appropriate length of time, and if not, what
time period may be appropriate.
Under the above approach, contingent management exempt
nonwastewaters being disposed of on-site also would not become exempt
until placed in a disposal unit meeting the requirements established
under this rule. However, since the current waste accumulation
provisions of 40 CFR 262.34, allow a generator to store hazardous waste
on-site in tanks, containers or containment buildings for 90 days
without becoming a Subtitle C storage facility, EPA believes that this
approach should not place undue burdens on a generator. EPA requests
comment on whether Sec. 262.34 will in fact enable generators of exempt
nonwastewaters to store wastes on-site in unpermitted units for a
reasonable period of time prior to land disposal. EPA acknowledges that
nonwastewaters are typically not stored in tanks.
2. Option 1B--Effective Upon Meeting the Exit Levels
The second option that EPA is considering would allow a
nonwastewater to become exempt from all hazardous waste requirements
except part 268 as soon as it meets appendix XI of 40 CFR part 261 exit
levels and the claimant has met all the requirements and conditions of
the exemption, including certifying that the waste will be managed in a
monofill or land disposal unit. The goal of this approach is to ensure
nonwastewaters will not be managed in a land treatment unit, which was
found to pose the greatest risk for many routes of exposure. Under this
approach, storage, treatment and transportation of the nonwastewater
could take place outside of Subtitle C control upon meeting the
requirements and conditions for the exemption. If EPA were to adopt
such an approach, it would impose conditions to ensure that the
exempted nonwastewater reached the types of units for which the
exemption was designed. Various options are suggested below in Section
D.1.
Finally, EPA notes that the proposed approaches have different
implications for LDR relief. These differences, which
[[Page 66402]]
principally concern the availability of LDR relief for nonwastewaters
which meet the appendix XI of 40 CFR part 261 exit levels at their
point of generation, are discussed in more detail in section H. below.
C. Requirements for Obtaining an Exemption
The following requirements would be applicable to both of the
approaches discussed above. Requirements for meeting the contingent
management exemption would include the sampling and testing
requirements of Sec. 261.37 (b)(1), the public notice requirements of
Sec. 261.37 (b)(3) and the notification to the implementing Agency
requirements of Sec. 261.37 (b)(4), similar to those respective
requirements for the base exemption in Secs. 261.36 (b) (1), (3) and
(4). The Agency notes that these provisions would be directly
enforceable Subtitle C requirements imposed prior to obtaining an
exemption rather than conditions for maintaining the exemption.
1. Sampling and Testing Requirements for Contingent Management
Exemptions
The Agency is proposing that the sampling and testing requirements
for the contingent management exemption be the same as those proposed
for the base exemption in Section 261.36 (b)(1). The Agency requests
comment on whether the sampling and testing requirements for the base
exemption would be appropriate for the contingent management exemption.
2. Requirements for Public Participation in Contingent Management
Exemptions
To provide the public with access to information, the Agency is
proposing to require compliance with the public notice requirements in
proposed Sec. 261.37(b)(3), similar to those in Sec. 261.36(b)(3). The
first time a claimant provides the Agency with notification of an
exemption claim for contingent management wastes, he will be required
to publish a notice of the claim in a major local newspaper general
circulation. The notice must include the name and address of the
facility, the description of the waste (as contained in the
notification), a brief general description of the process producing the
waste, an estimate of the quantities of waste claimed to be exempt, and
information about the Agency where the claimant has sent the
notification and supporting information. In addition, the public notice
must include that the waste meets the contingent management exemption
levels in appendix XI of 40 CFR part 261 and that the waste will be
disposed of in a monofill or land disposal unit.
3. Notification Requirements for Contingent Management Exemptions
To qualify for a contingent management exemption, a claimant would
need to submit to the authorized State Agency Director a formal
notification of its claim that waste meets the contingent management
exemption levels in Appendix XI of 40 CFR part 261 and will be managed
in accordance with the management conditions. In addition to the
requirements under Sec. 261.36 (b)(4), the contingent management
exemption notification to the implementing Agency must include an
accompanying certification that the waste meets the contingent
management exemption levels in appendix XI of 40 CFR part 261 and that
the waste will be disposed of in a monofill or land disposal unit.
The Agency requests comment on whether these requirements, similar
to Sec. 261.36 (b)(1),(3) and (4), will provide adequate information to
the implementing agency and the public on what exemption levels, i.e.,
appendix X to 40 CFR part 261 or appendix XI of 40 CFR part 261, are
being claimed and on how the waste is being managed. These provisions
would be requirements rather than conditions.
D. Implementation Conditions
As set out in Sec. 261.37 (d) and explained in the base exemption
implementation preamble (section VIII. B., Implementation Conditions)
certain conditions have to be met to maintain the exemption after the
claim has become effective. Under both option 1A and 1B, the following
conditions would have to be met to maintain the contingent management
option: Submitting changes in notification information to the Director
within 10 days of the change, following the schedule for retesting,
preparing and complying with a sampling and analysis plan for every
retest, maintaining constituent concentrations in the nonwastewater at
or below the exemption levels in appendix XI, meeting applicable
treatment levels under Sec. 268.40, and maintaining records on-site for
three years. These conditions are very similar to those proposed for
the base exit in Section VIII of today's proposed rulemaking. In
addition to those conditions established for the base exemption, the
claimant would also have to ensure that the waste was managed in a
qualifying unit.
Claimants, under both options, always have the obligation to
identify whether they are generating a hazardous waste and to notify
the appropriate government official if they are generating a hazardous
waste. (Section 3010; 40 CFR 261.11.) If any nonwastewater claimed as
exempt under the contingent management proposal tested above the exit
levels in appendix XI to 40 CFR part 261 at any time, that waste and
any mixture or derived-from forms of that waste would have to be
managed as hazardous waste, including compliance with all notification
requirements, until testing demonstrated that the waste was below the
exit levels.
1. Tracking Conditions
EPA is proposing to modify the manifest regulations to reflect the
fact that wastes exiting under this exemption need not be disposed of
in treatment, storage or disposal facilities that are subject to the
requirements of Sec. 264.71-264.72 or Section 265.71-264.72 requiring
the facility that receives the waste to sign and return the manifest.
EPA is not proposing to require the owners and operators of
nonhazardous waste facilities that accept wastes exempted under this
option to comply with these duties. As EPA concluded when it decided
not to extend recordkeeping duties related to the LDR program to
nonhazardous waste facilities accepting de-characterized hazardous
wastes, it would probably be difficult to provide reasonable notice to
all the members of this diverse universe, which has little or no other
contact with the hazardous waste management regime, of these Subtitle C
responsibilities.
EPA is proposing instead that the claimant of the exemption be
responsible for ensuring that the manifest is returned and that it--or
some other document--provides information showing that the facility
designated on the manifest did in fact receive the waste and did place
it in a landfill or monofill (and not a land treatment unit). Billing
documents may already supply some of the needed information. Where they
do not, EPA believes that claimants should generally be able to
contract with the receiving facilities to obtain the necessary
information. In some states, nonhazardous waste rules may also require
disposers to furnish generators with some of the necessary information.
EPA proposes to revise the manifest document as necessary to ensure
that nonhazardous waste facilities can be designated as receiving
facilities for listed wastes meeting all of the other requirements for
obtaining an exemption under this option.
[[Page 66403]]
The alternative to this approach would be to require owners and
operators of nonhazardous waste facilities to sign and return manifests
as a condition of the exemption. Failure to satisfy this condition
would void the exemption and return the waste to the hazardous waste
management regime, even if it were in fact safely placed in an
appropriate waste management unit. EPA requests comment on this
alternative.
Under option 1A, where all Subtitle C regulations apply until
placement of the nonwastewater in a monofill or landfill, EPA is
proposing conditions that make the claimant responsible for obtaining a
copy of the manifest to ensure the waste has reached its destination.
The claimant would also have the burden of acquiring evidence from the
receiving facility that the waste was placed in either a monofill or
land disposal unit.
Under Option 1B, where the exemption becomes effective upon the
waste meeting the appendix XI of 40 CFR part 261 exit levels, any
tracking system established would be a condition that the claimant
would have to meet to maintain the contingent management exemption. To
ensure that listed wastes exempted under this option actually go to a
landfill or monofill, EPA is proposing to require exemption claimants
to comply with the requirements of part 262 (with the modification
discussed above) relating to the uniform hazardous waste manifest.
Since this option allows wastes to go to facilities that are not
subject to the duty to return the manifest under Sec. 264.71-264.72 or
Sec. 265.71-264.72, EPA is proposing to require the claimant to ensure
that the manifest is returned and that it--or some other document--
provides information showing that the facility designated on the
manifest did in fact receive the waste and did place it in a landfill
or monofill (and not a land treatment unit). The duties would be
identical to those proposed above for claimants under the first option.
The rationale for imposing the duties on the claimant--and not the
receiving facility--is also the same.
An alternative which EPA requests comment on is the concept of
imposing conditions that require a uniform, national tracking document
similar to the current uniform manifest to accompany the waste until it
reaches its final destination. This document could inform transporters
and other waste handlers that the waste is an exempt hazardous waste
that must be managed in a monofill or land disposal facility and loses
its exemption if it is managed in a land treatment unit. EPA could
further require that the disposal facility certify that the
nonwastewater was disposed in a monofill or land disposal unit and
return the tracking document and certification to the original
exemption claimant. EPA could also ensure that the implementing agency
(EPA or an authorized state) received notice of any problems in waste
disposal by imposing requirements similar to the current Sec. 262.42
exception reporting provisions.
Another alternative would be to require, in lieu of a tracking
document, a contractual agreement between the exemption claimant and
the receiving facility specifying the type of waste the receiving
facility will accept, the type of units it will use, and information on
the volume and frequency of deliveries. EPA could require either the
claimant or the receiving facility (or both) to maintain a copy of the
agreement on-site and make it available to state or EPA inspectors. EPA
also could require exemption claimants and transporters to create and
keep similar contracts. EPA, however, requests comment on whether
transporters would require claimants to provide information on the
exempted waste's origin and the regulatory limits on its disposal
options even without federal regulation.
EPA requests comment on whether any of these alternatives can
adequately ensure that mismanagement will not occur so that these
wastes managed under this option 1B approach would not need to be
classified as hazardous.
2. Qualifying Unit
A ``qualifying unit'' for today's contingent management proposal is
a landfill or monofill. For purposes of today's proposal, a landfill is
defined in Sec. 260.10 as being ``a disposal facility or part of a
facility where hazardous waste is placed in or on land and which is not
a pile, a land treatment facility, a surface impoundment, an
underground injection well, a salt dome formation, a salt bed
formation, an underground mine, a cave or a corrective action
management unit.'' The Agency is proposing a definition for monofill in
Sec. 260.10 as a landfill where waste of only one kind or type is
placed in or on land and which is not a pile, a land treatment
facility, a surface impoundment, an underground injection well, a salt
dome formation, a salt bed formation, an underground mine, a cave, or a
corrective action management unit. Also, for today's proposal, a land
treatment facility is defined in Sec. 260.10 as being ``a facility or
part of a facility at which hazardous waste is applied onto or
incorporated into the soil surface; such facilities are disposal
facilities if the waste will remain after closure.'' The Agency
requests comment on whether other units could be considered
``qualifying units'' for contingent management exempt waste and whether
additional modeling is needed to assess risks from management of
nonwastewaters from other units.
The Agency modeled risks from waste piles in both its multipathway
and groundwater analyses. It modeled only groundwater risks form
landfills. As explained elsewhere in this preamble, EPA believes that
the nongroundwater risks posed by piles generally are higher than the
nongroundwater risks posed by landfills. EPA, however, is not proposing
to allow wastes placed in piles to be exempt under the exit levels for
contingent management option 1. Piles, as defined in Part 260, are
temporary units. To ensure that exempted wastes removed form piles went
only to landfills or monofills, EPA would have to impose additional
tracking conditions. These could be difficult to craft and enforce
effectively. EPA currently thinks that excluding piles from eligibility
will provide much better assurance that exempted wastes will not be
mismanaged.
EPA acknowledges that the exit levels for this option, which are
based in many cases on the evaluation of waste piles, may, for some
pathways, be more restrictive than levels for landfills. If EPA later
completes a multipathway analysis of landfill units, it will be able to
use the levels from that modeling in lieu of the modeling from piles to
derive exit levels for this option.
The Agency requests comment on the proposal to exclude wastes
placed in piles from being eligible for exemption under this option.
The Agency also requests comment on the alternatives of allowing wastes
to be exempt either permanently or temporarily (e.g., for one year)
after they are placed in piles.
3. Claimant's Duty To Ensure Compliance With All Requirements and
Conditions
Today's proposal requires that, in order to claim a contingent
management exemption, the person submitting the claim must manage the
waste for which the exemption is claimed in accordance with the
requirements and conditions established by this rule. To satisfy this
rule, the claimant must ensure that the waste is actually disposed of
in a qualifying unit. The burden of satisfying all conditions for the
exemption falls on the claimant as the person in the best position to
determine eligibility of a waste for an exemption and to ensure
informed waste management decisions. The claimant may enter into
contractual
[[Page 66404]]
arrangements with receiving facilities to allocate responsibility for
satisfaction of the conditions among themselves although such
arrangements will not relieve the claimant of liability if the
receiving facility manages the waste improperly. It should be noted,
however, that facilities receiving contingent management exemption
wastes could also become liable for violations of permitting, Subtitle
C treatment, storage and disposal standards should they dispose of the
nonwastewaters that do not qualify.
Under today's proposal, Sec. 261.37(g), the burden of proof to
establish conformance with the exemption criteria is on the claimant in
the event of an enforcement action. One alternative for simplifying the
claimant's burden of proving compliance with all conditions would be to
set out in the rule certain documentation that, while not necessarily
required of the claimant, presumptively would be sufficient evidence of
satisfaction of the management condition. Of course, EPA could rebut
this presumption regarding actual disposal through evidence that the
claimant's documentation is deficient or inaccurate. For example,
claimants might be able to develop rebuttable evidence of proper off-
site disposal by keeping correspondence with the receiving facility,
indicating that the waste went to a landfill or monofill, and by
keeping a returned manifest which indicates that the waste reached that
facility. The Agency is taking comment on whether establishing certain
evidentiary standards would provide useful guidance to claimants on how
to satisfy the management condition and provide helpful incentive for
claimants to maintain proper documentation of their exemption claims.
Comment is also requested on whether any additional conditions or
requirements, substantive or procedural, should be imposed on claimants
to ensure that the contingent management exemption waste is actually
managed in a qualifying unit.
E. Retesting and Recordkeeping Conditions for Contingent Management
Exemptions
Claimants continuing to generate or otherwise manage waste for
which they continue to claim a contingent management exemption would be
required, under Sec. 261.37(d)(2), to retest the waste with the same
frequency and under the same conditions as is being proposed for the
base exemptions, Sec. 261.36(d)(2). If a claimant finds that the
exempted waste no longer meets the constituent concentration levels on
Appendix XI of 40 CFR part 261 for the contingent management exemption,
or that the waste has not been placed in a landfill or monofill, the
claimant must comply with all applicable requirements for generators of
listed wastes (including disposal of waste at a Subtitle C facility)
and the disposal facility would have to comply with all of the
requirements for owner/operators of treatment, storage, and disposal
facilities under 40 CFR parts 262-270. The generator and disposal
facility's obligations would also include renotifying the Agency of
hazardous waste management activity using EPA form 8700-12.
Under Sec. 261.37(d)(6), claimants also would be required to
maintain on-site, for at least three years after Agency receipt of the
notification and certification, all documentation required under this
rule including, but not limited to, the sampling and analysis plan and
test data and the accompanying notification and certification. These
requirements are similar to those proposed for the ``base'' exemption
in Sec. 261.36.
The Agency requests comment on alternative record retention periods
for claimants such as 5 years, which corresponds to the applicable
statute of limitations period at 28 U.S.C. 2462. An extended record
retention period may assist claimants in substantiating their
conformance with the contingent management exemption criteria. The
documentation must be available for review by the Agency or an
authorized State at the time of site inspection. The three-year
claimant record retention period will be automatically extended during
the course of any unresolved enforcement action regarding the regulated
activity.
F. Compliance Monitoring and Enforcement for Contingent Management
Exemptions
Since contingent management exemptions are self-implementing, the
Agency needs to rely on its enforcement authorities to ensure that the
exemptions are being applied in an appropriate manner and that only
those wastes that are truly nonhazardous are relieved from Subtitle C
disposal requirements. Compliance monitoring and enforcement of the
contingent management program would be carried out under existing
authorities and conditions with which the regulated community should
already be familiar.
Claimants must comply with all of the previously described
conditions of the exemptions to qualify for the exemptions. All persons
who manage waste for which an exemption has been claimed must manage
the waste as required under Subtitle C during periods when any of those
conditions are not met. Claimants that fail to comply with the
applicable conditions of the contingent management exemption risk
enforcement action for violations of Subtitle C requirements, including
administrative, civil and criminal penalties.
1. Compliance Monitoring
The Agency is proposing that compliance monitoring of the
contingent management exemption occur through EPA and State oversight,
primarily through review of notifications and inspections.
The Agency has the authority, under section 3007 of RCRA, to
require submission of information and to conduct inspections of
facilities which EPA has reason to believe may be generating or
managing a hazardous waste. EPA and States may do confirmatory sampling
and analysis to determine whether a waste meets the exemption levels.
Under this authority, the Agency would be able to inspect a non-
Subtitle C facility receiving contingent management exemption waste.
Inspections of off-site laboratories may also be performed.
2. Enforcement
The contingent management exemption criteria proposed today would
create an exit from the Subtitle C system only so long as the
requirements and conditions established for the exemption are met.
Failure to comply with any of the conditions for the exemption would
mean that the wastes would not be exempt from Subtitle C, and the
claimant could be subject to immediate enforcement action for violation
of Subtitle C requirements.
The Agency has the authority under this regulation and RCRA Section
3007 to require submission of information on the management of exempted
wastes in a situation where the Agency suspects the claimant has not
satisfactorily determined whether a waste meets the appropriate
exemption levels. Alternatively, the Agency may require improved
analysis using an administrative or civil action under section 3013.
Failure to manage the contingent management exemption waste in
accordance with the conditions would void the exemption and the
conditionally exempt waste would be subject to full Subtitle C
regulation. The receiving facility, therefore, would become a Subtitle
C treatment, storage, and/or disposal facility requiring a permit.
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In an enforcement action, compliance with the terms and conditions
of the exemption may be raised as an affirmative defense, but the
burden will be on the defendant to establish eligibility for the
exemption and compliance with the conditions necessary to maintain the
exemption. See 50 FR 642 (Jan. 4, 1985) for a discussion of EPA's
authority to place such burdens on defendants.
Claimants may not use the contingent management exemption as a
means of avoiding enforcement actions. For example, a generator who is
the subject of an Agency enforcement action cannot claim that the waste
in question is exempted from Subtitle C under the contingent management
exemption unless a valid exemption notification for that waste has been
previously submitted to the Agency and the required documentation to
support the claim exists at the facility and satisfies the requirements
of the regulations. The contingent management exemption cannot be used
in a retroactive fashion to avoid enforcement actions. Similarly, these
exemptions cannot be used as a legal defense prior to the effective
date of promulgation of this rule.
G. Exports of Wastes Eligible for Contingent Management Exemptions
Under option 1A of today's proposal, contingent management
exemption wastes would remain hazardous until actually disposed of in a
qualifying unit. The waste would thus remain subject to all applicable
requirements of 40 CFR parts 262 and 263, including export
requirements.
Under option 1B where the waste becomes exempt upon meeting the
contingent management exit levels, comment is requested on whether
these exempt wastes should still remain subject to the export
requirements of 40 CFR part 262. Comment is requested on whether these
export requirements are necessary to ensure that the contingent
management exemption waste will be properly managed in the receiving
country.
H. Land Disposal Restrictions
As discussed above in section VI, EPA is proposing two approaches
to integrating LDR requirements with the exit levels for the base
option. First, EPA is proposing that LDR treatment requirements will
never apply to wastes that meet exit levels for the base option at the
point of generation. Second, for wastes which remain subject to LDR
requirements, EPA is proposing to allow exit levels based solely on the
combined multipathway and groundwater analyses to serve as alternative
risk-based LDR standards meeting the ``minimize threat'' standard in
section 3004(m) of RCRA. EPA believes that both approaches are
appropriate for contingent management option 1.
To eliminate the duty to comply with the LDR rules for wastes that
meet the base option exit level at the point of generation, EPA is
taking the position that such wastes are defined as hazardous waste
pursuant to their listing descriptions for such a brief period of time
that they effectively never become subject to Subtitle C requirements,
and LDR requirements never apply. It is relatively easy to apply this
theory to option 1B presented above in section B.2. that allows
nonwastewaters to exit as soon as they have met the appropriate
concentration limits and to remain exempt so long as they are managed
in landfills or monofills. Such wastes need only meet the exit levels
to obtain their exemption. If they meet them at the point of
generation, they would appear just as entitled to LDR relief as wastes
meeting the exit levels for the base option.
Under option 1A, however, nonwastewaters will not exit until they
both meet the exit levels and are placed in a landfill or monofill.
Such wastes would not be eligible for exit at the point of generation
even if their constituent concentrations were low enough. Rather, they
would be subject to Subtitle C regulation for a significant portion of
their ``cradle-to-grave'' management cycle. It would be difficult to
argue that these wastes had never really been regulated as hazardous
wastes, and that LDR treatment requirements did not apply.
Consequently, EPA is not proposing to allow nonwastewaters to become
exempt from LDR requirements at the point of generation under this sub-
option. EPA requests comment on alternative legal theories that would
provide a better basis for arguing that nonwastewaters subject to this
sub-option could be exempt for the LDR rules if they meet exit levels
at the point of generation.
Both options 1A and 1B have identical exit levels based on removing
the predictions for land treatment units and using the next-highest
concentration as the exit level. EPA is proposing to allow the exit
levels that are based solely on the multipathway/groundwater risk
analyses to serve as minimize threat levels for both options 1A and 1B.
These levels represent concentrations posing minimal low threats for
nonwastewater placed in landfills, monofills and waste piles. They are
based on the same risk assessment used for the assessment for the base
option. They make the same ``reasonable worst case'' assumptions about
the units' physical setting and the same minimal assumptions about
control measures. Hence, EPA believes that these exit levels
sufficiently reduce threats to human health and the environment to meet
section 3004(m)'s ``minimize threat'' standard.
EPA acknowledges that option 1B, allowing wastes to exit Subtitle C
before they are placed in the right kind of land disposal unit,
presents an additional type of risk. Under option 1B, it may be more
difficult for EPA to ensure that exited wastes will not be placed in
land treatment units. (Under the alternative option, option 1A,
Subtitle C manifest and tracking requirements would apply.) As
explained above in section B., however, EPA will create conditions for
option 1B to help ensure that exempted wastes are not disposed of in
land treatment units. EPA believes that these conditions will
sufficiently reduce the risk of inappropriate disposal that the exit
levels will continue to minimize threats. EPA requests comment on this
aspect of the proposal.
XI. Relationship to Other RCRA Regulatory Programs
Today's rule proposes specific conditions and exit criteria that
would exempt listed hazardous wastes, including waste mixtures and
derived-from wastes, from Subtitle C regulation. Below is a discussion
of how this proposed rule would affect other relevant RCRA regulatory
programs.
A. Hazardous Waste Determination
Under current RCRA regulations, any person who generates a solid
waste must determine if that waste is a hazardous waste in accordance
with the procedures outlined in 40 CFR 262.11. According to 262.11,
generators must first determine if their waste is excluded from
regulation under 40 CFR 261.4. Generators must then determine if the
waste is listed in subpart D of part 261. If the waste was not listed,
or for purposes of compliance with 40 CFR part 268, generators must
then determine if the waste exhibits a characteristic defined in
subpart C of part 261.
Today's proposed rule is an exemption for listed wastes meeting the
exit criteria, and does not change the general requirements for
generators making hazardous waste determinations under Sec. 262.11 (see
discussion of characteristic waste below).
B. Characteristic Hazardous Waste
Today's proposed rule establishes exemption criteria for hazardous
[[Page 66406]]
constituents in eligible listed wastes, waste mixtures, or derived-from
wastes. If the waste satisfies the exemption criteria proposed today,
the waste would not be considered listed hazardous waste. However, the
generator must still determine whether the waste exhibits any
characteristics of a hazardous waste as specified in 40 CFR 261.21
through 261.24 and continue to meet hazardous waste requirements if the
waste does exhibit a characteristic.
C. Toxicity Characteristic Level for Lead
Toxicity characteristic constituents are among those evaluated for
exit values in this proposal. In developing the risk assessment for all
constituents, including the TC constituents, the Agency examined risks
via groundwater and other pathways to humans, and also environmental
receptors. In evaluating risks resulting from the groundwater pathway,
the Agency used its newly developed CMTP model, and the MINTEQ metals
speciation component. The CMTP model estimates groundwater transport
using finite source assumptions, and accounting for hydrolysis and
adsorption of chemicals to soils. The MINTEQ component estimates
dissolution and speciation of metals in groundwater. Using these
models, the Agency has developed and is proposing estimates of
transport through groundwater specific to each constituent. These
estimates are analogous to constituent-specific dilution and
attenuation factors (DAFs). These constituent-specific DAFs were
contemplated for several constituents proposed for regulation in the TC
rulemaking, but not finalized, because the modeling work was not
complete. TC levels were set using generic DAFs of 100.
In developing the constituent-specific DAFs, the Agency estimated
that lead moves through groundwater much more slowly than predicted by
the generic DAF of 100. While the modeling analyses supporting the TC
rule and today's proposed rule are somewhat different from one another,
the constituent-specific DAF for lead leaching from a landfill was
estimated as 5000 rather than the 100 used in the TC rule. Higher
leaching rates (giving lower DAF values) were estimated for some other
disposal options evaluated in the updated modeling, such as land
application and management in surface impoundments. This analysis
raised the question of how the TC and today's proposed rules would
relate to one another, and whether these results warranted
consideration of a change to the TC level of 5 mg/l for lead (updated
groundwater modeling of other TC constituents did not show the large
disparity between the TC and exit level proposed in today's notice for
lead).
In considering these issues, the Agency reviewed several factors.
First, the human health risk evaluation for lead has changed since the
TC rule was promulgated, resulting in the MCL (on which the TC is
based) for lead being reduced from 50 ppb to 15 ppb. Using the new DAF
from the landfill scenario plus the new drinking water standard could
raise the TC level to 75 mg/l from the current 5 mg/l. However, when
lead movement from a land treatment scenario was modeled, a DAF of
approximately 770 resulted, and a TC level based on this and the new
drinking water standard could be approximately 10 mg/l. Another
relevant reference point for lead in the environment includes the
current OSWER soil direct ingestion level for lead of 400 ppm (as a
total concentration, not leachate).
The Agency considered several approaches to potentially proposing
revisions to the TC level, including basing a new TC level on
groundwater modeling only, basing it on the soil ingestion estimate, or
basing it on the driving pathway value and exit level, which considers
adverse ecologic effects.
After carefully considering the issue, the Agency concluded that
the issue of lead toxicity and movement through the environment is very
complex and changes to existing rules could have significant impacts on
management of lead-bearing waste and public health. The agency believes
regulation of lead-bearing wastes warrants careful consideration and
full evaluation of and review of the policy issues associated with
considering all potential exposure pathways and risk to human health
and the environment. Questions include whether the TC level would be a
leachate or totals value, and whether it would be based on groundwater
only or other exposure routes and whether it would be human health
based or based on ecological risk considerations. Such a comprehensive
evaluation is not feasible in the context of the rulemaking proposed
today, and so the agency has determined to defer any action on the lead
TC level. The Agency recognizes that this is an issue of considerable
interest to the public, and will consider review of management of lead-
bearing waste at the soonest practical time. In the interim, the lead
TC regulation and the exemption regulation proposed today (when
finalized) would co-exist as independent regulations.
As described in Section IV.E.3, the Agency has developed
groundwater modeling based on both 10,000 year and 1000 year time
frames. Today's proposal is based on the 10,000 year modeling time
horizon, and the Agency is soliciting public comment on the alternative
of using 1000 years. One aspect of the 1000 year modeling results is
that the groundwater-based exit levels for more constituents would be
above current TC levels for those constituents. These constituents
include, in addition to lead, chromium, cadmium, selenium, and mercury.
The Agency seeks public comment on this aspect of using the 1000 year
time horizon modeling for risk assessment in the HWIR rule.
D. Hazardous Waste Listings
The Agency evaluated the likelihood that untreated hazardous wastes
would be able to meet the exemption criteria in an ``pure'' state
(e.g., untreated and unmixed) and determined that it is unlikely that
the constituent concentrations in many untreated hazardous wastes would
be below today's proposed exemption levels or the applicable BDAT
standards, particularly for nonwastewaters. Specifically, the Agency's
hazardous waste characterization data indicate that the concentrations
of toxicants of concern in untreated listed wastes are typically
present at levels many times higher than health-based levels or BDAT
values. Therefore, it is unlikely that the Agency's current criteria
for listing wastes as hazardous will change as a result of the
introduction of today's exit criteria into the RCRA regulations.
However, EPA has been utilizing a more comprehensive risk analysis in
the listing program, looking at multiple pathways for the movement of
constituents through the environment, similar to the approach taken in
today's proposal. Today's proposed approach may also provide the Agency
with a means of assessing whether or not future listings might
inadvertently bring into the RCRA system the types of low-concentration
wastestreams that would subsequently be eligible for exit under today's
proposal.
E. Delisting
The evaluation criteria used for delisting may vary from today's
exemption criteria for various reasons. First, delisting is an
interactive process that considerable oversight by EPA or authorized
State agencies. In delisting, the overseeing agency evaluates the
processes generating a specific wastestream in order to determine the
constituents likely to be present, as well as the potential variability
in the waste.
[[Page 66407]]
EPA (or the State) closely reviews sampling procedures, analytical test
results, and the accompanying QA/QC data. This oversight increases the
confidence in the quality and representativeness of the waste analysis.
Second, delisting is specific to one wastestream, which decreases
uncertainties that arise in the more generic approach proposed today.
For example, a delisting petition will typically provide the annual
generation volume of the waste. Using a specific waste volume as an
input to various models has allowed EPA to calculate exit levels that
may be somewhat higher than the levels proposed in today's rule. EPA
believes that it is reasonable to use higher exit levels for the
smaller waste volumes in delisting petitions (see 56 FR 32993 (Reynolds
Metals) for further description of volume impact).
The delisting process also allows more certainty in the plausible
management scenarios that are modeled to generate exit levels. For
example, the characteristics of the waste may dictate the likely
disposal method (e.g., disposal in a landfill of de-watered process
sludge). In some cases, special management standards may also be a
factor (e.g., radioactive wastes are regulated under the Atomic Energy
Act, therefore if such a hazardous waste were delisted, disposal
options would be severely limited (see 60 FR 6054 (Hanford delisting)).
EPA also considers the applicability of available groundwater
monitoring data from land-based waste management units that have
received the petitioned waste. Such data are typically required under
permitting regulations for hazardous waste facilities (see 40 CFR parts
264 and 265). If any contamination of groundwater appears to be due to
constituents from the petitioned waste, EPA will consider this as a
basis to deny the petition. The more generic waste identification rule
proposed today does not incorporate this additional evaluation
criterion.
EPA may also require special testing regimes to ensure waste
consistently meets delisting criteria (e.g., see (cite Reynolds Metals,
CSI, Hanford)). Because the overseeing agency reviews the petition in
some detail, the testing frequency may be closely tied to the potential
variability of the waste. A facility that accepts and treats waste from
diverse sources would typically have frequent testing requirements (see
40 CFR part 261 appendix IX (Envirite)). In other cases, the testing
requirements for some initial period will be extensive, but the
subsequent testing may be reduced.
Delisting petitions for wastes that contain toxic constituents
which exceed the exemption levels proposed today will continue to be
accepted and reviewed by the Agency after promulgation of today's rule.
With the exception of a potentially reduced petition review burden, the
Agency does not anticipate any changes in the current review of
delisting petitions as a result of the implementation of today's
proposed exemption. EPA does request comment on which risk models
should be used to evaluate future delisting petitions.
F. Requirements for Treatment, Storage, and Disposal Facilities and
Interim Status Facilities
In order to implement the changes proposed today, owners or
operators of RCRA permitted or interim status facilities may have to
amend their waste analysis plans if required under 40 CFR 264.13 and
265.13. Such changes will most likely include the addition of the
appropriate analysis methods and changes that may be required in the
frequency of testing.
Permitted facilities, in unauthorized States, who elect to employ
the exemption procedures and who subsequently prepare changes to their
waste analysis plans should, following promulgation of this rule,
submit a Class I permit modification to EPA. (EPA is aware that
although most States have either become authorized for, or have
adopted, the 3-class permit modification regulations, some states may
still be operating under the older ``major/minor'' permit modification
procedures. Under those procedures, changes to the waste analysis plan
would be considered a major modification).
G. Closure
Under today's proposed rule, a hazardous waste management unit that
receives wastes that are exempt under today's exit criteria would
continue to be a regulated Subtitle C unit subject to the requirements
of 40 CFR parts 264 or 265, including closure requirements, until the
owner/operator completed clean closure of the unit or unless all of the
waste in the unit were delisted. A unit receiving only waste that is
exempt under today's proposal would no longer be receiving hazardous
waste upon the effective date of the exemption; such a unit would
normally become subject to Subtitle C closure requirements, which are
triggered by the final receipt of hazardous waste by the unit. The
facility owner or operator is required to complete closure activities
within 180 days after receiving the final volume of hazardous waste. 40
CFR 264.113(b) and 265.113(b). However, RCRA closure requirements do
allow certain waste management units to delay closure, while continuing
to receive non-hazardous waste (such as waste exempt under today's
proposed rule), provided certain conditions are met.
The RCRA delay-of-closure regulations, promulgated on August 14,
1989 (54 FR 33376), allow owners or operators to delay the closure of
landfills, land treatment units, and surface impoundments in cases
where the unit stops receiving hazardous waste but the owner or
operator wishes to continue using the unit to manage only non-hazardous
waste. These requirements are outlined in 40 CFR 264.113(d) and (e) and
265.113(d) and (e). Owners or operators wishing to delay closure must
request a permit modification at least 120 days prior to final receipt
of hazardous wastes, or, if the facility is in interim status, submit
an amended part B application at least 180 days prior to the final
receipt of hazardous wastes. The request for a permit modification or
the amended part B application must include demonstrations that the
unit has the existing design capacity to manage non-hazardous wastes,
and that the non-hazardous wastes are not incompatible with any wastes
in the unit. In addition, certain facility information including the
waste analysis plan, groundwater monitoring plans, closure and post-
closure plans, cost estimates, and financial assurance demonstrations
must be updated as necessary to account for receipt of only non-
hazardous waste. Sections 264.113(d) and 265.113(d). In addition,
surface impoundments that do not meet the minimum technological
requirements (MTRs) for liners and leachate collection of RCRA 3004(o)
must comply with additional requirements in order to delay closure,
including the removal of hazardous wastes to the extent practicable
from the unit. Sections 264.113(e) and 265.113(e).
The delay of closure regulations apply only to landfills, land
treatment units, and surface impoundments. In the case of other RCRA
units such as tanks and waste piles, the Agency did not feel that the
delay-of-closure regulations were necessary for these types of units in
order to receive only non-hazardous wastes (54 FR 33383). The closure
requirements in subpart G for these units include removal or
decontamination of waste residues, containers, liners, bases and
contaminated soils, equipment, and other containment system components;
these closure requirements are not incompatible with the reuse of these
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units for receipt of only non-hazardous waste. Once the unit has been
emptied of all hazardous wastes and decontaminated, it could receive
non-hazardous waste. However, the Agency also recognizes that some
flexibility may be warranted in converting the use of a unit such as a
tank from hazardous to non-hazardous waste management. EPA solicits
comment on whether an owner or operator might demonstrate removal of
hazardous waste residues from the tank by demonstrating that all waste
in the tank is below exemption levels, without removing the waste from
the tank. In cases where the owner or operator could not demonstrate
that all wastes in the tank were below exemption levels, he or she
would have to remove the hazardous waste in order to achieve closure of
the unit. In some cases, the facility owner or operator may be able to
demonstrate that a tank no longer managed hazardous waste (because the
waste met today's proposed exemption criteria), but did not achieve
clean closure because of soil and perhaps groundwater contamination. In
this case, EPA solicits comment on whether the facility owner or
operator should be required to remove the contamination to clean
closure levels, or close the area as a landfill while using the tank to
manage nonhazardous wastes, as long as this activity did not interfere
with cleanup activities or control of the contaminated areas.
The Agency also believes that the availability of a delay-of-
closure option provides much of the flexibility needed to allow for the
uninterrupted management of exempt waste, while providing assurance
that the protections afforded by the closure regulations for Subtitle C
units (e.g., evaluation of soil and groundwater at closure) are not
lost. This approach makes sense in light of the fact that today's
proposed exemption is self-implementing, which the Agency feels is
appropriate for waste identification purposes, but not necessarily so
for determining whether a Subtitle C unit may become a Subtitle D unit
without first undergoing closure.
H. HWIR-Media Rule/Subtitle C Corrective Action
The Agency is currently planning on proposing a rule (``HWIR
Media'') addressing waste management issues relating to environmental
media (e.g., soil, groundwater, and sediments). The goal of this rule
is to allow more effective cleanups at contaminated sites. As currently
drafted, the media proposal will supplement the regulatory system under
RCRA for the management of RCRA hazardous contaminated media,
applicable to sites that are undergoing cleanup overseen by EPA or
authorized States. Such sites include cleanups at RCRA corrective
action sites, State cleanups, and Superfund remedial actions. The media
rule will propose a ``bright-line'' distinction between hazardous
contaminated media (i.e., media containing hazardous waste that is
therefore regulated as hazardous) subject to modified Subtitle C
standards, and less contaminated media subject to more site-specific,
flexible standards implemented by State agencies. This new system will
supplement the current approach(es) to identifying RCRA applicability
to the management of contaminated media. The rule will also propose
streamlined permit requirements for cleanups. It will not specify
cleanup standards.
Today's proposal applies to listed hazardous wastes (e.g. process
wastes, sludges, discarded commercial chemical products, etc.),
including mixtures of one or more listed wastes with other solid
wastes, and residues derived from the treatment, storage, or disposal
of one or more listed hazardous wastes. Media that contain listed
hazardous wastes, mixtures, or derived-from wastes with constituent
concentrations below today's proposed exemption levels will be eligible
for exemption under the procedures proposed today. EPA or an authorized
State may continue to assess contaminated media with concentrations
higher or lower than the exit levels proposed today on a case-by-case
basis by making site-specific determinations as to whether a media
``contains'' a RCRA hazardous waste.
I. Land Disposal Restriction Program
Today's rule contains several important areas of overlap with the
RCRA Land Disposal Restrictions (LDR) program that are discussed
elsewhere in today's rule. First, as described in more detail elsewhere
in this notice, EPA is proposing that exit levels produced under the
multipathway analysis for constituents with adequate analytical methods
should ``cap'' existing technology-based LDR standards, where the exit
levels are less stringent than the current LDR values. If a waste
contains only constituent with ``capped'' LDR values, it should be able
to satisfy LDR requirements and exit Subtitle C for all other purposes
as soon as the waste achieved those levels.
Under today's proposal the uncapped LDR requirements for listed
hazardous wastes continue to apply to a waste even after the waste
becomes exempt from Subtitle C under the exemption criteria.
Furthermore, for listed wastes containing certain constituents with
analytical problems, compliance with the LDRs (either numerical levels,
specified treatment, or both) is part of the criteria for exempting
that waste under today's proposal. Specifically, for constituents where
there are no adequate analytical methods for determining whether or not
the exit levels have been met, a combination of meeting applicable LDR
standards and a showing of non-detect estimated quantitation
concentration is required to satisfy the exit criteria for these
constituents. This is explained in more detail in Section IV.I of
today's rule.
If, however, a listed waste is below the exit concentrations
proposed today at the point where the waste is ``first'' generated,
that is, the point where the waste first meets the listing description
and is potentially subject to Subtitle C, then a hazardous waste is
never really ``generated'' and the LDR requirements do not attach to
the waste. The EPA does not expect many listed wastes to be at or below
the exit criteria at the point of first generation, where waste
characterization data indicate that this is where wastes contain higher
concentrations of hazardous constituents. Nonetheless, where a
particular process generates a waste that is perhaps inappropriately
captured by a listing, or where pollution prevention efforts by the
generator result in a waste of lower constituent concentrations, if the
waste meets the exemption criteria at the moment it is first generated,
the LDR requirements would not apply. In contrast, once a listed waste
is generated and managed the LDR requirements attach, and remain even
after the waste exits Subtitle C under today's exemption (unless, as
stated, where the exit levels are considered equivalent to a minimize
threat standard). This issue is discussed in more detail in Section VI
in today's proposal.
It should be noted that the Agency is currently reviewing the
definition of ``point-of-generation'' with respect to the application
of the LDRs. Since November 1986 (51 FR 40620), EPA has required LDR
determinations to be made at the point which hazardous wastes are
generated. In the Phase III LDR rule (March 2, 1995, 60 FR 11702), EPA
solicited comment on the issue of where the point of generation should
be defined. EPA presented three options to narrowly redefine the point
at which the land disposal prohibitions attach: (1) Similar
wastestreams generated by similar processes, (2) wastestreams from a
single process, and (3) ``battery limits.'' With Option 1 the point of
generation would be defined at the point after which like wastestreams
are generated from like processes and combined as a matter of routine
[[Page 66409]]
practice. Option 2 would consider the point of generation to occur when
wastestreams from a single process are combined (e.g., residual
wastestreams collected in a common unit such as a sump). In many cases,
these wastestreams are similar in composition because they all come
from a common unit process. The Option 3 ``battery limits,'' is similar
to Option 2; however instead of limiting aggregation to that normally
occurring within a single unit process, the facility would view an
entire battery of processes (associated with making a single product or
related group of products) as a single manufacturing step. In the Phase
III LDR proposal, EPA identified listed hazardous wastes as situations
where existing point of generation determinations may remain
appropriate. This is because EPA has carefully reviewed the various
waste streams and has defined the point of generation as part of the
listing description. Therefore, it may be inappropriate to modify that
description with a more generic ``point of prohibition'' rule. This is
important because today's rule applies only to listed hazardous wastes.
Lastly, under today's proposal, mixtures containing listed
hazardous waste and residues from the treatment, storage, or disposal
of listed hazardous waste that contain some constituents with
concentrations below exit levels and some constituents with
concentrations above exit levels would continue to be managed as listed
hazardous wastes. Today's notice does not allow for partial exemptions,
because the Agency does not believe that a self-implemented exemption
process is well suited to partial exemptions. It is not always clear
what the origin of a hazardous constituent is, particularly for
constituents that are formed as by-products of treatment or waste
interactions. Further, the proposed exemption criteria are not waste-
specific, and thus are not suited to waste-specific or partial
exemptions. Thus, the determination that a waste that carries two
listing numbers should no longer bear one of the listing numbers is not
always a straight-forward decision. The Agency has designed the
exemption process proposed today to remove as much subjective decision
making from the process as possible.
However, while the Agency is not today proposing an alternative
that would allow these wastes to use only the hazardous waste codes for
those listed wastes that are the origin of the constituents above the
exit levels, the Agency believes that there could be merit in the
concept for a future proposed rulemaking should the implementation
concerns stated above be overcome. Therefore, the Agency requests
information on actual cases with waste characterization data where a
waste bears more than one waste code which results in conflicting
treatment standards under the land disposal restrictions rules. If the
Agency finds that there is a serious compliance issue for multiple
listing wastes, the Agency may reconsider this decision, as well as
other potential solutions to any documented problems.
J. RCRA Air Emission Standards
Today's proposed rule, when promulgated, may have an impact on the
effectiveness of two other RCRA rules developed by the Agency under
HSWA authority. Section 3004(n) of HSWA directed the Agency to
promulgate regulations controlling air emissions from hazardous waste
TSDFs ``as necessary to protect human health and the environment.''
Subsequent Agency analysis demonstrated that air emissions from TSDFs
do pose substantial risk in the absence of controls, and that controls
were therefore required under the HSWA mandate. The Agency is
fulfilling this mandate in phases; EPA completed the first phase when
it promulgated RCRA air standards that control organic emissions vented
from certain hazardous waste treatment processes, as well as from leaks
in certain ancillary equipment used for hazardous waste management
processes (55 FR 25454, June 21, 1990; 40 CFR part 264/265, subparts AA
and BB). More recently, EPA completed the second phase when it
promulgated RCRA air standards for tanks, surface impoundments,
containers, and miscellaneous units operated at TSDFs (59 FR 62896,
December 6, 1994; 40 CFR part 264/265, subpart CC). Together, these
rules would reduce the risk from air emissions from the vast majority
of these facilities to well within the risk range of other RCRA
standards. After more thorough analysis, the Agency may issue a third
phase of these regulations to address any residual risk. The emission
reductions achieved by these rules would also significantly reduce the
formation of ozone, which has adverse effects on human health and the
environment.
Hazardous waste that satisfies the exemption criteria proposed
today (including any constituent-specific exit concentrations for
volatile organic chemicals, or VOCs), would be exempt from Subtitle C
regulations, including regulations promulgated to date under RCRA
3004(n). In other words, once a waste is no longer regulated as
hazardous, any unit in which the waste is managed (assuming no other
hazardous wastes are being/have been managed in the unit) is not
subject to Subtitle C regulations, including 40 CFR parts 264 and 265,
subparts AA, BB, and CC. However, the Agency believes that it is
important to ensure that the risks associated with air emissions both
from hazardous wastes, and from wastes that would be eligible for exit
under today's proposal, are adequately addressed. In the final rule
establishing air emission controls for tanks, surface impoundments,
containers, and miscellaneous units (the ``Subpart CC'' rule), the
Agency established a threshold level of 100 ppmw (parts per million by
weight) for total volatile organics in a waste, a concentration which
if equaled or exceeded that would trigger the emission control
requirements for these units. Because there are examples of exit levels
proposed today for specific volatile organic constituents that exceed
this 100 ppmw threshold, the Agency considered whether today's exit
levels adequately addressed the air emission concerns of 3004(n) in
allowing waste to exit Subtitle C. There are important differences in
the underlying risk modeling between the two rules. However, the Agency
believes that the constituent-specific risk evaluation done for this
rulemaking results in proposed exit levels that for VOCs will not be
less protective than the standards established to date under RCRA
3004(n). Despite these differences, the Agency requests comment on
whether or not a total VOC concentration of 100 ppmw (parts per million
weight), which is the concentration that triggers air emission controls
under the Subpart CC rule, would be appropriate for use in the exit
rule proposed today, and if so, how this level would be used.
K. Hazardous Debris
Hazardous debris that contains one or more listed hazardous wastes
is eligible for exiting Subtitle C under today's proposed rule. The EPA
notes, however, that certain exemptions already exist relating to
hazardous debris. On August 18, 1992, the EPA published a final rule on
the Land Disposal Restrictions for Newly Listed Wastes and Hazardous
Debris (57 FR 37194). In that rule, EPA required that hazardous debris
be treated prior to land disposal, using specified treatment
technologies from the treatment categories of extraction, destruction,
or immobilization. (See 40 CFR 268.45, Table 1.) EPA also added a
conditional exemption at Sec. 261.3(f) for non-characteristic hazardous
debris (i.e.,
[[Page 66410]]
debris that is hazardous solely because it contains one or more listed
hazardous wastes). Section 261.3(f)(1) exempts debris from Subtitle C
regulation provided that the debris is treated using one of the
extraction or destruction technologies specified in Table 1 of
Sec. 268.45. Alternatively, non-characteristic hazardous debris can be
exempt under Sec. 261.3(f)(2) if it is determined to be no longer
hazardous by the Regional Administrator, after considering the extent
of contamination of the debris, i.e., after a ``contained-in''
determination is made. However, non-characteristic hazardous debris
contaminated with a listed waste, that is treated by a specified
immobilization technology is not eligible for the conditional exemption
in Sec. 261.3(f)(1), and therefore remains subject to Subtitle C
regulation after treatment.
In today's rule, EPA is not proposing to change the current
exemption under Sec. 261.3(f); therefore, non-characteristic hazardous
debris that requires LDR treatment by extraction or destruction
technologies will be exempt from Subtitle C regulation, once treated.
As was explained more thoroughly in the final rule for hazardous
debris, the Agency gave careful consideration to many factors before
exempting certain treated debris, including whether each debris/
contaminant type would be effectively treated by each BDAT technology
to levels that would no longer pose a hazard to human health or the
environment (57 FR 37240). However, hazardous debris that contains
listed waste, and for which immobilization is the specified LDR
treatment, may exit using today's proposed exit criteria. See also the
discussion of a contingent management option above for a description of
an alternative for encapsulated debris contaminated by radioactive
``mixed'' hazardous wastes. Finally, EPA is not proposing to change the
contained-in exemption under Sec. 261.3(f)(2) for hazardous debris;
that is, the Regional Administrator may continue to determine on a
case-by-case basis that hazardous debris no longer contains listed
hazardous waste, and should therefore be exempt from RCRA Subtitle C.
L. Hazardous Wastes Used in a Manner Constituting Disposal
Section 266.20 (b) of the regulations states that hazardous wastes
and hazardous waste-derived products that are legitimately recycled by
being applied to or placed on the land are largely exempt from subtitle
C regulation provided they satisfy three conditions: the recyclable
materials must have undergone a chemical reaction so as not to be
separable by physical means, the product must be produced for the
general public's use, and land disposal restriction treatment standards
for every hazardous waste in the hazardous waste-derived product must
be satisfied. (The shorthand for this type of recycling is ``use in a
manner constituting disposal''. See Sec. 261.2(c)(1).) EPA developed
Sec. 266.20(b) largely as a stop-gap to provide some modicum of safety
while EPA studied further whether various disposal-like uses of
hazardous waste-derived products in fact were safe or warranted
control. 50 FR 614, 628-29, 647 (Jan,. 4, 1985). Since then, the Agency
has studied particular use constituting disposal practices and
determined, or proposed, that such uses either be prohibited or allowed
based on more individualized determinations of risk. See 53 FR 31138,
31164 (August 17, 1988) (allowing use of fertilizers derived from waste
K 061 because of similarity to other zinc-containing fertilizers); 59
FR 43496, 43500 (August 24, 1994) (prohibiting anti-skid uses of K 061-
derived sags); 59 FR 67256 (Dec. 29, 1994) (proposing to allow certain
uses of K 061 if risk-based criteria are satisfied); 60 FR 11702, 11732
(March 2, 1995) (proposing to prohibit hazardous waste use as fill
material).
EPA solicits comment today on the relationship of today's proposed
exit levels and the general use constituting disposal provisions in
Sec. 266.20(b) stating that such uses can occur if land disposal
restriction treatment standards are satisfied. These land disposal
restriction standards are not fully protective in all cases: the
standards are technology-based rather than risk-based, and, for metal
hazardous constituents, only control leachable amounts of the metal.
Yet in many situations, total metal levels, rather than leachable
levels, will be the critical factor because of the possibilities of
direct contact through inhalation of abraded or wind-dispersed
contaminants, or surface runoff. These exposure pathways are critical
for uses constituting disposal because the hazardous waste are not
placed in a confined unit. 60 FR at 11733, 59 FR at 43499.
The exit levels proposed today, on the other hand, are risk-based
(although some are capped by quantitation limits), are expressed as
both total and leachable concentrations, and consider exposure pathways
in some cases similar to those relevant in analyzing uses constituting
disposal. The Agency solicits comment as to the appropriateness of
applying these levels to hazardous wastes used in a manner constituting
disposal (or at least to those uses where the hazardous waste-derived
products are not comparable to non-hazardous waste based products that
would be used in their place). One approach would be to replace the
requirement to meet LDR treatment standards with a requirement to meet
the exit levels proposed today. This approach should assure that exit
levels for unconfined hazardous wastes (i.e. hazardous wastes used in a
manner constituting disposal) are never less stringent than exit levels
for hazardous wastes placed in confined units. EPA believes that the
risk assessment it conducted for the exit levels considered scenarios
sufficiently similar to use constituting disposal scenarios to ensure
that the exit levels would be reasonably protective for uses (and more
protective than LDR levels, in many cases, because of the analysis of
impacts from total concentrations of constituents). EPA, however,
requests comment on the reasonableness of this approach.
Another option would be to require persons wishing to use hazardous
wastes in a manner constituting disposal to meet the lower of the LDR
treatment standards and the exit levels. Because EPA is today proposing
setting exit levels for both total and leachable concentrations, and
because LDR standards are expressed as either total or leachable
levels, however, EPA is not certain how to meaningfully compare
relative stringency.
With respect to the current requirement in Sec. 266.20(b) that
persons wishing to use waste in a manner constituting disposal meet the
treatment standards from the LDR program, EPA notes that compliance
with LDR tracking and recordkeeping rules is not required. EPA proposes
today to require compliance only with the exit levels where they
substitute for LDR treatment levels, although it requests comment on
the option of requiring persons using wastes in this manner also to
file the exit notification package proposed today. EPA does not intend
that such persons be required to comply with conditions that continue
to apply after exit, such as periodic retesting.
Finally, EPA proposes to eliminate the requirement that wastes to
be used in a manner constituting disposal undergo a chemical reaction
so as to be inseparable by physical means. EPA does not believe it is
necessary to retain this requirement since wastes will be evaluated for
total constituent concentrations. (EPA, however, will retain this
requirement for wastes with treatment standards expressed as a
specified technology, rather than concentration levels.)
[[Page 66411]]
Were EPA to proceed on this course, the Agency would adjust the
timing of any regulatory action so that it does not supersede the
separate rulemaking the Agency is now conducting on certain uses of
residues derived from K 061 recovery facilities. 59 FR 67256. Thus, the
Agency does not intend to take final action affecting these uses until
the analysis begun in that rulemaking is completed on the schedule
established in that rulemaking.
With respect to the other pending proposal, involving a prohibition
on placement of hazardous waste as fill material, the Agency requests
comment on whether it should substitute permission to use waste that
has met the proposed exit levels for the proposed prohibition. The risk
assessment underlying today's proposal addressed the major pathways
that would arise from use as fill, but may not have used input values
that fully reflect the fill scenario for some important parameters. For
example, unit depths may be greater for fill sites than for land
application units. At the same time, use of hazardous waste as fill is
a proven cause of human health and environmental harm, contributing
significantly to a number of Superfund sites. See Docket F-95-PH3P-
FFFFF (record for the pending proposal). In light of this, the Agency
questions whether to substitute today's proposed exit approach for the
proposed prohibition.
XII. CERCLA Impacts
All listed hazardous wastes are listed as hazardous substances
under section 101(14)(C) of the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA) of 1980, as amended. Under
section 103(a) of CERCLA, notification must be made to the Federal
government of a release of any CERCLA hazardous substance in an amount
equal to or greater than the reportable quantity (RQ) assigned to that
substance within a 24 hour period. (See 40 CFR part 302 for a list of
CERCLA hazardous substances and their Rqs.) If a specific waste from a
particular facility meets the exemption criterion in this rule, the
waste is not a listed hazardous waste and therefore not a hazardous
substance by virtue of its hazardous waste listing. Thus, notification
under CERCLA of a release of the exempted waste may not be necessary.
In this situation, CERCLA notification of releases of the waste would
only be required if the waste or any of the constituents of the waste
are CERCLA hazardous substances by virtue of Section 101(14) (A), (B),
(D), (E), or (F) of CERCLA or 40 CFR 302.4(b), and are released in
amounts greater than or equal to their Rqs. The Agency requests comment
on this approach.
Exit levels also may be applicable to the CERCLA program where it
has been documented that RCRA listed hazardous waste has been disposed
of at the site. Section 121(d) of CERCLA, as amended by the Superfund
Amendments and Reauthorization Act (SARA) of 1986, requires that CERCLA
actions comply with, or justify a waiver of, applicable or relevant and
appropriate requirements (ARARs) under federal and state environmental
laws. The options proposed in this rule would determine the legal
applicability of federal RCRA managements requirements to remediation
wastes generated at Superfund sites. They may also be considered in
determining whether RCRA is relevant and appropriate in cases where it
is not applicable.
At sites undergoing CERCLA remedial activities where no listed
hazardous wastes have been identified, the Agency will generally use a
site-specific risk assessment for all chemicals for which there are no
ARARs. In some cases, these health-based cleanup levels will be higher
than the exemption levels, based on a reasonably conservative exposure
scenario which does not include leachate ingestion. In other cases, the
CERCLA health-based clean-up levels will be lower than exemption levels
when additive effects are considered or when specialized analytical
techniques are required in order to lower quantitation limits. The
CERCLA health-based clean-up levels may also be different than
exemption levels based on the consideration of site-specific factors.
XIII. State Authority
A. Applicability of Rules in Authorized States
Under section 3006 of RCRA, EPA may authorize qualified States to
administer and enforce the RCRA program within the State. (See 40 CFR
part 271 for the standards and requirements for authorization.)
Following authorization, EPA retains enforcement authority under
sections 3008, 7003, and 3013 of RCRA, although authorized States have
primary enforcement responsibility.
Prior to the Hazardous and Solid Waste Amendments (HSWA) of 1984, a
State with final authorization administered its hazardous waste program
entirely in lieu of EPA administering the Federal program in that
State. The Federal requirements no longer applied in the authorized
State and EPA could not issue permits for any facility in the State
that the State was authorized to permit. When new, more stringent
Federal requirements were promulgated or enacted, the State was obliged
to enact equivalent authority within specified time frames. New Federal
requirements did not take effect in an authorized State until the State
adopted the requirements as State law.
In contrast, under section 3006(g) of RCRA, 42 U.S.C. 6926(g), new
requirements and prohibitions imposed by the HSWA take effect in
authorized States at the same time that they take effect in non-
authorized States. EPA is directed to implement HSWA requirements and
prohibitions in an authorized State, including the issuance of permits,
until the State is granted authorization to do so. While States must
still adopt HSWA-related provisions as State law to retain final
authorization, HSWA applies in authorized States in the interim.
B. Effect of State Authorizations
Today's proposal, if finalized, will promulgate regulations that
are not effective under HSWA in authorized States. Thus, the exemption
will be applicable only in those States that do not have final
authorization.
Authorized States are only required to modify their programs when
EPA promulgates Federal regulations that are more stringent or broader
in scope than the authorized State regulations. For those changes that
are less stringent or reduce the scope of the Federal program, States
are not required to modify their programs. This is a result of section
3009 of RCRA, which allows States to impose more stringent regulations
than the Federal program. Today's proposal for exit levels is
considered to be less stringent than, or a reduction in the scope of,
the existing Federal regulations because it would exempt certain wastes
now subject to RCRA Subtitle C. Therefore, authorized States are not
required to modify their programs to adopt regulations consistent with
and equivalent to today's proposal.
Even though States are not required to adopt most options in
today's proposal, EPA strongly encourages States to do so as quickly as
possible. As already explained in this preamble, today's proposal will
reduce over-regulation of dilute wastes and will provide an alternative
to delisting. States are therefore urged to consider the adoption of
today's proposal (when promulgated); EPA will expedite review of
authorized State program revision applications.
C. Streamlining Issues
EPA is considering a new approach to state authorization for rules
revising the
[[Page 66412]]
RCRA program. Under this new approach EPA would vary the requirements
for state submissions and for EPA's review to reflect differences in
the scope and complexity of various program revisions. This
differential approach to authorization also would recognize the fact
that many states now have more than a decade of experience in
implementing large portions of the RCRA program and commensurate
experience in obtaining authorization for program revisions. EPA
believes that adjusting authorization requirements will strike an
appropriate balance between recognizing state experience and ensuring
environmental protection.
EPA recently proposed a greatly streamlined set of procedures for
the least complex changes to the LDR program in the ``LDR Phase IV''
rulemaking. EPA, however, proposed to retain the current authorization
process for other portions of the rule that presented more complex and
novel regulations.
EPA is also developing a different approach to streamlining
authorization for the ``HWIR media'' proposal scheduled for publication
later in 1995. Although EPA expects some aspects of these state
authorization procedures to be unique to the HWIR- media rulemaking,
EPA will determine whether some of the concepts can be used to craft
streamlined procedures for additional RCRA rules.
EPA was not able to develop a streamlined authorization process for
this rule in time to include it in this proposal. EPA, however, intends
to describe such a process in more detail in the preamble to the
proposed HWIR-media rule. EPA anticipates that most elements of the
basic waste exit scheme proposed in today's notice would be eligible
for a greatly streamlined approach to authorization. For example, the
new LDR standards based on ``minimize threat'' findings would be good
candidates for streamlined authorization because states that are
already authorized for significant portions of the LDR program are
familiar with the type of rule changes needed, have adopted all or most
of the underlying LDR program, and have experience in implementing and
enforcing the rules. The exit levels, along with the self-implementing
approach to exit determinations, are also likely to be eligible for a
greatly streamlined approach. The scheme is very similar to the
existing program for determining whether a waste exhibits any of the
hazardous waste characteristics, particularly the 1980 EP Toxicity
Characteristic and the expanded 1990 Toxicity Characteristic. Under
both the characteristic rules and today's proposal, generators are
responsible for determining whether or not a waste meets a numerical
definition of ``hazard''. States must then enforce by reviewing records
of determinations and/or conducting their own analysis of wastes
determined not to be hazardous. Consequently, States which have been
authorized for the base program already have experience in adopting and
enforcing rules which resemble the exit scheme proposed today. EPA,
however, notes that adopting the exit scheme proposed in today's notice
will place additional demands on state inspection and enforcement
resources. EPA will give careful consideration to balancing the need to
ensure that a state has sufficient resources to implement an exit
program with the goal of streamlining the authorization process.
Today's scheme does differ from the original characteristics and
the 1990 Toxicity Characteristic by including some requirements which
must be enforced as conditions of exit. These requirements, however,
are requirements for testing, notification and recordkeeping that are
relatively easy to meet and relatively easy to detect if violated.
Accordingly, EPA does not at this time anticipate that these conditions
would require it to retain the current authorization process.
EPA currently finds it unlikely that it will propose a greatly
streamlined authorization process for any of the contingent management
options presented for discussion in today's proposal. These options
will raise novel legal, implementation and enforcement issues. A more
conventional approach to the review of state authorities and
capabilities may be warranted. If EPA proposes any of these options in
the future, it will consider the possibility of adapting the approach
to authorization that it is currently developing for the HWIR-media
proposal.
XIV. Regulatory Requirements
A. Analytical Requirements
1. Executive Order 12866
Under Executive Order 12866, (58 FR 51735 (October 4, 1993)) the
Agency must determine whether this regulatory action is
``significant.'' A determination of significance will subject this
action to full OMB review and compliance under Executive Order 12866
requirements. The order defines ``significant regulatory action'' as
one that is likely to result in a rule that may:
(a) Have an annual effect on the economy of $100 million or more,
adversely affect in a material way the economy, a sector of the
economy, productivity, competition, jobs, the environment, public
health or safety, or state, local, or tribal governments or
communities;
(b) Create a serious inconsistency or otherwise interfere with an
action taken or planned by another agency;
(c) Materially alter the budgetary impact of entitlement, grants,
user fees, or loan programs, or the rights and obligations of
recipients thereof; or
(d) Raise novel legal or policy issues arising out of legal
mandates, the President's priorities, or the principles set forth in
the terms of the Executive Order.
The proposed rule is expected to have an annual effect on the
economy greater than $100 million. Furthermore, although voluntary, the
adoption of this action may burden state or tribal governments with
increased regulatory review requirements. Today's action may also raise
novel legal or policy issues as they relate to the President's
priorities for environmental protection within a regulatory system
facing resource limitations. The Agency, therefore, has determined that
today's proposed rule is a ``significant regulatory action.'' As a
result, this rulemaking action, and supporting analyses, are subject to
full OMB review under the requirements of the Executive Order. The
Agency has prepared an Assessment of The Potential Costs and Benefits
of The Hazardous Waste Identification Rule for Industrial Process
Wastes, as Proposed, in support of today's action. A summary of this
Assessment and findings is presented in section D below.
2. Regulatory Flexibility Analysis
Pursuant to the Regulatory Flexibility Act of 1980, 5 U.S.C. 601 et
seq., when an agency publishes a notice of rulemaking, for a rule that
will have a significant effect on a substantial number of small
entities, the agency must prepare and make available for public comment
a regulatory flexibility analysis. This analysis shall consider the
effect of the rule on small entities (i.e.: Small business, small
organizations, and small governmental jurisdictions).
Under the Agency's revised Guidelines for Implementing the
Regulatory Flexibility Act, dated May 4, 1992, the Agency committed to
considering regulatory alternatives in rulemakings when there were any
economic impacts estimated on any small entities. Previous guidance
required alternatives to be examined only when significant economic
effects were estimated for a substantial number of small entities. The
Agency has
[[Page 66413]]
prepared a Regulatory Flexibility Analysis in support of today's
action. A summary of this analysis and findings is presented in section
E below.
3. Environmental Justice
Executive Order 12898, ``Federal Actions to Address Environmental
Justice in Minority Populations and Low-Income Populations,'' directs
each Federal Agency to ``make achieving environmental justice part of
its mission by identifying and addressing, as appropriate,
disproportionately high and adverse human health and environmental
effects of its programs, policies, and activities on minority
populations and low-income populations * * *''
The Executive Order requires that where environmental justice
concerns or the potential for concerns are identified, appropriate
analysis of the issue(s) be evaluated. To the extent practicable, the
ecological, human health (taking into account subsistence patterns and
sensitive populations) and socio-economic impacts of the proposed
decision-document in minority and low-income communities should also be
evaluated.
The Agency has examined Environmental Justice concerns relevant to
today's action. A summary of this analysis and findings is presented in
section F below.
4. Paperwork Reduction Act
The information collection requirements in this proposed rule have
been submitted for approval to the Office of Management and Budget
(OMB) under the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. An
Information Collection Request (ICR) document has been prepared by EPA
(ICR No. 1766.01) and a copy may be obtained from Sandy Farmer, OPPE
Regulatory Information Division; U.S. Environmental Protection Agency
(2137); 401 M St., SW.; Washington, DC 20460 or by calling (202) 260-
2740.
This information collection is required to provide documentation of
solid waste exemptions from Subtitle C requirements, and will allow for
certification and verification as the program evolves. Exemptions under
today's action require no formal preapproval. As such, information
collection, maintenance and reporting issues are especially important
due to the self-implementing nature of this action. Successful
implementation of today's proposal will depend upon the documentation,
certification, and verification provided by the information collection.
The general authority for this proposal is sections 2002(a), 3001,
3002, 3004, and 3006 of the Solid Waste Disposal Act of 1970, as
amended by the Resource Conservation and Recovery Act of 1976 (RCRA),
as amended by the Hazardous and Solid Waste Amendments of 1984 (HSWA),
42 U.S.C. 6912(a), 6921, 6922, 6924, and 6926. The specific authority
for the collection of information is 40 CFR 261.36, Exemption for
Listed Hazardous Wastes Containing Low Concentrations of Hazardous
Constituents.
The Agency has prepared a full Information Collection request (ICR)
in support of today's action. A summary of the methodology and findings
from this document is presented in section G below.
B. Background
In 1976, Congress passed the Resource Conservation and Recovery Act
(RCRA) to address problems associated with annual nationwide generation
of large quantities of municipal and industrial solid waste. This Act
was significantly amended in 1984 by the Hazardous and Solid Waste
Amendments (HSWA). Under RCRA, the Agency regulates non-hazardous solid
waste through the Subtitle D program, and hazardous solid waste under
the Subtitle C program. Subtitle C regulations differ from Subtitle D
in two important areas. First, Subtitle C regulations are developed and
promulgated by EPA, while Subtitle D requirements have been largely
delegated to the states. Second, non-hazardous wastes regulated under
Subtitle D are generally subject to standards that are considerably
less stringent and less costly than those under Subtitle C. All wastes
addressed under this action are currently managed under Subtitle C
regulations.
RCRA is divided into four programs: Underground storage, medical
waste, nonhazardous solid waste, and hazardous solid waste. Under RCRA
3001(a), Congress has required EPA to identify those wastes that should
be classified as hazardous. In accordance with this provision, the
Agency has designated wastes as hazardous in two ways:
``characteristic,'' or ``listed.'' Hazardous waste is considered
characteristic if it has any of the properties or characteristics that
would present a potential hazard if managed improperly. The Agency has
identified four characteristics which, if exhibited, lead to hazardous
classification. These are: Ignitability, corrosivity, reactivity, and
toxicity. Under the toxicity characteristic, specific health-based
concentration standards have been developed for approximately forty
(40) constituents. Wastes exhibiting any of these characteristics are
subject to Subtitle C regulation. Hazardous wastes are identified as
listed based on an extensive listing procedure. This procedure may
identify a waste as hazardous under three broad categories: if it
exhibits one of the characteristics identified above but has not been
classified as characteristically hazardous, if it is determined to be
acutely toxic or hazardous, or if the waste meets the statutory
definition of a hazardous waste.
The Agency, however, was concerned that generators and managers of
hazardous waste might avoid regulatory requirements in two major ways:
(1) By mixing listed hazardous waste with non-hazardous solid waste,
and, (2) by minimal processing and treatment of hazardous waste. These
activities could result in a waste or residual material that was no
longer legally defined as hazardous under Subtitle C. In many cases,
the Agency believed these materials could continue to pose unacceptable
hazards to human health and the environment. The Agency promulgated
mixture and derived-from rules in May of 1980, in response to these
potential loopholes.
C. Need for Regulation
The mixture and derived-from rules created what was perceived as
being federal over-regulation, where listed hazardous waste continued
to remain under Subtitle C jurisdiction regardless of constituent
concentration or presence in the waste, either before or after
treatment. This problem was exacerbated with the passage of HSWA in
1984. HSWA set Land Disposal Restrictions (LDR) requiring best
demonstrated available technology (BDAT) treatment for all listed
hazardous wastes prior to disposal. In cases where a specific listed
wastestream contained relatively innocuous constituents, or very low
concentrations, BDAT treatment requirements were felt to be overly
protective, and unnecessarily expensive.
By requiring Subtitle C management for some low risk wastes, the
current RCRA regulatory system may inhibit the efficient allocation of
limited societal resources. From a social perspective, too many
resources devoted to managing low risk wastes may reduce resource
availability for managing higher risk wastes. Resource availability for
general productivity investments and innovative technologies are also
reduced. The Agency's delisting program has not provided an efficient
solution to this problem. The delisting process has proven to be overly
time
[[Page 66414]]
and resource intensive for both industry and EPA.
The Agency believes that a simpler exemption process is necessary
to reduce the over-regulation of low risk hazardous waste while, at the
same time, reducing the time and resource burden on industry and
government. This revised exemption process would also reduce the burden
on the delisting program which will continue under current regulations.
To meet these goals, the Agency is proposing the current action that
would establish a single set of exit levels for constituents found in
listed hazardous waste. This action would cover wastes as-generated,
derived-from wastes, including BDAT treatment residuals, mixtures with
solid wastes, and environmental media that contain hazardous wastes.
D. Assessment of Potential Costs and Benefits
1. Introduction and Summary
The U.S. Environmental Protection Agency (EPA) has prepared an
Assessment of The Potential Costs and Benefits (Assessment) to
accompany today's proposed rulemaking action. This action will
establish concentration-based exemption criteria for certain hazardous
wastes, creating a mechanism to exclude from Subtitle C regulation
those listed industrial process wastes that the Agency believes are
clearly not of Federal regulatory concern. Today's proposed rule
addresses low hazard wastes, mixtures, treatment residuals, and media
that contain hazardous wastes.
The Agency anticipates that the proposed rule will provide cost
savings to selected generators and managers of low hazard wastes. Under
the preferred option, annual nationwide treatment and disposal cost
savings for exempted wastes may be as high as $75 million. Annual cost
savings for a single facility may be as high as $5.03 million.
Potential cost reductions beyond treatment and disposal savings may be
associated with waste minimization incentives, avoided treatment costs
for wastes remaining within Subtitle C, and administrative cost
savings.
Exemption of eligible wastes from Subtitle C management
requirements is projected to have negligible effects on human health
and the environment. The proposed exemption levels are based on
detailed analysis of numerous possible routes of exposure. These
exemption levels are designed to be protective of both human health and
ecological systems when exempted wastes are managed under Subtitle D,
including state regulated waste disposal systems.
The Agency has also evaluated other impacts of the proposed rule.
These include: Environmental justice, unfunded mandates, regulatory
takings, and waste minimization incentives. Environmental justice
concerns associated with today's proposed action may be in the form of
economic benefits and/or human health effects. Today's proposal
implements no enforceable requirements on states. Federal unfunded
mandates, therefore, are not relevant to today's proposed rulemaking.
Regulatory takings under today's proposed rulemaking will not approach
land or productive value impacts discussed in past House and Senate
Bills presented on this issue. This rulemaking provides opportunities
for generators to implement waste minimization procedures to gain
additional savings.
The complete document, Assessment of The Potential Costs and
Benefits of The Hazardous Waste Identification Rule for Industrial
Process Wastes, as Proposed (Assessment), is available in the docket
established for this proposed rule. This document details the data,
methodology, findings, regulatory issues, and analytical limitations
associated this Assessment. The rapid evolution of this action resulted
in continuous technical modifications throughout the development of
this proposal. An Addendum to the Assessment document that details
final quantity and cost savings estimates is included in the docket
materials. Findings presented in this preamble present final estimates.
A summary of the Assessment methodology and findings is presented
below. The analysis conducted for this Notice of Proposed Rulemaking is
to be considered preliminary. The Agency welcomes review and comment of
this document and urges the submission of data in support of any
comment or response.
2. Regulatory Options
The Agency's Assessment, conducted in support of today's action,
addresses the costs, benefits, and other potential impacts of the
preferred option. The Assessment also examines various other regulatory
options based on exit levels that are both more and less stringent.
Findings presented in this preamble discuss the preferred option and
one primary alternative. A full discussion of findings associated with
various alternative regulatory options is presented in the Assessment
and Addendum.
a. Preferred (Proposed) Option
Under the preferred option, exit criteria are established for
approximately 400 constituents, allowing hazardous wastes (including
waste mixed with or derived-from listed wastes) to exit Subtitle C if
the concentration of all constituents is less than or equal to the
exemption criteria. The exit levels apply to all listed wastes,
regardless of origin.
Exit levels for most constituents are based on risks posed to human
health and the environment. The Agency's goal is to ensure, through
Federal or State management requirements, that humans are not exposed
to carcinogens in concentrations that will increase the statistical
risk of cancer by more that one-in-one-million (1 x 10-6). For
non-carcinogens, the Agency's goal is to ensure that humans are not
exposed to concentrations where the hazard quotient exceeds one (1).
The Agency feels that, above this level, selected populations may
experience carcinogenic effects at a 10-6 risk level and non-
carcinogenic effects at a hazard quotient greater than one (1).
To determine the concentrations at which exempt wastes would not
pose human health risks in excess of these target levels, EPA conducted
a ``Multipathway'' Analysis that included ecological exposure pathways.
In addition, EPA considered the effects of direct exposure to
contaminants in groundwater. The analyses consider several types of
waste management units. For non-wastewaters these unit types include
landfills, land application units, waste piles, and ash monofills. For
wastewaters management units included tanks and surface impoundments.
The concentrations from all other pathways were compared to the
groundwater concentrations in determining the exit level. The more
stringent of the multipathway or groundwater numbers was chosen as the
exit level. Exit levels for some constituents are based on surrogates,
or Exemption Quantitation Criteria (EQCs). MCLs were not used in the
development of exit levels analyzed for this option. The Agency
believes that levels established under this process will ensure
protection of human health and the environment. These exit levels are
presented in the regulatory language for this proposed rulemaking.
b. Other Options
In developing the preferred option, the Agency compared the
proposed rule to several alternative regulatory options. These are
discussed in the full
[[Page 66415]]
document, Assessment of The Potential Costs and Benefits of The
Hazardous Waste Identification Rule for Industrial Process Wastes, as
Proposed. Additional options are discussed in the supporting Addendum
to the Assessment document. These options consider alternative waste
management requirements, target risk levels, dilution and attenuation
factors (DAFs), and exposure pathways. This Preamble discusses one
primary alternative to the preferred option. This alternative is the
same as the preferred option but drops land application units from
consideration as a management source. Exempt nonwastewater wastestreams
could not be land applied. There would be no change for wastewaters.
3. Implementation Requirements
Implementation requirements include the steps that generators (or
waste managers) must take to achieve exemption of their wastes,
regardless of the exit levels selected. These requirements include
waste sampling and analysis, and related recordkeeping and reporting.
Under the proposed rule, the facility must first perform a
comprehensive analysis of the waste, testing for all constituents
identified in appendix X to 40 CFR part 261. Reduced initial testing
may be possible only if a facility is able to document that such
constituents are not present in the waste. The generator must then
prepare a notification/certification package and submit it to the EPA
Regional Administrator or authorized state agency. The generator must
repeat a comprehensive analysis periodically according to the schedule
established in the proposed rule, along with more frequent tailored
scans that focus on the constituents of concern. Related documentation
must be maintained on-site and be available for review.
The Agency has estimated annual sampling, analysis, recordkeeping,
and reporting costs (collectively referred to as ``implementation
costs'') that may be required under this rule. These estimates range
from approximately $21,000 for a less complex, solvent wastestream with
testing every 12 months, to $169,000 for a complex high quantity F039
wastestream with testing every three months.
4. Analysis and Findings
Under the proposed rule, listed wastes from industrial processes
may be eligible for exemption from Subtitle C hazardous waste
requirements if they contain low concentrations of contaminants. This
exemption may allow generators and waste managers to avoid some or all
costs associated with Subtitle C requirements. The most significant
cost savings relate to waste treatment and disposal; this rule will
allow generators to avoid the costs of treatment required for
compliance with the Land Disposal Restrictions as well as the costs of
disposing wastes in highly protective Subtitle C facilities.
In addition to assessing these cost savings, the Assessment
addresses a number of other potential effects of the regulations. It
analyzes the relative effects of the regulatory options on human health
and the environment and considers issues related to ensuring
environmental justice, eliminating federal mandates, encouraging waste
minimization, and providing flexibility for small businesses.
a. Eligible Waste
The universe of annual listed waste generation, both wastewaters
and nonwastewaters, potentially affected by today's proposed rulemaking
is estimated to total 303.6 million tons. The universe of potentially
affected wastes includes approximately 25,300 wastestreams from 10,700
facilities. Wastewaters account for the vast majority of total waste
quantity (99 percent).
To determine whether these wastes are likely to be eligible for
exemption, EPA developed the Process Waste Model. This model uses data
on the characteristics of individual listed waste-streams first
collected in 1986 for EPA's National Survey of Hazardous Waste
Generators, which has since been updated, refined, and in some cases,
corrected. The model first compares the reported concentrations of
constituents in each wastestream to the proposed rule exit levels to
determine whether the waste is likely to be eligible for exemption
without further treatment. If the waste is not eligible as-reported,
the model then considers whether it may be eligible after treatment. In
this comparison, the concentration standards established under EPA's
Land Disposal Restrictions (which are based on the use of the best
demonstrated and available technology) are used as a proxy for the
lowest concentrations achievable by treatment. If the waste is not
eligible for exemption as-reported or after treatment, EPA assesses
whether waste minimization or pollution prevention methods could be
used to cost-effectively achieve the exit levels. This model does not
address contaminated media.
The analysis indicates that:
Under the preferred option, total nonwastewater quantity
exempted, including BDAT treatment residuals and sludge from
wastewater, is estimated at 0.40 million tons. Total wastewater
(liquid) quantity exempted is approximately 64 million tons.
Under the primary alternative option (no land
application), approximately 65 million tons of wastewaters, and 0.60
million tons of nonwastewaters, including BDAT treatment residuals and
sludge from wastewaters, may be eligible for exemption.
b. Cost Savings
The proposed rule will allow waste generators and managers to avoid
costs associated with Subtitle C requirements. Specifically, this
exemption will allow them to avoid treatment costs and/or costs of
disposing wastes in Subtitle C facilities. Wastes which meet exit
levels at the point of generation may accrue treatment cost savings
because the wastes will not require any treatment that would have been
needed to comply with the Subtitle C Land Disposal Restrictions prior
to disposal. All exempt wastes are likely to accrue disposal cost
savings because the costs of disposing wastes in non-Subtitle C
facilities are generally lower than the cost of more protective
Subtitle C facilities.
The analysis indicates that:
Under the preferred option, the high-end estimate of
annual treatment and disposal cost savings is approximately $75
million.
--A large portion of these savings are attributable to avoided
treatment costs.
Under the primary alternative, the high-end estimate of
cost savings is $99 million.
The above estimates for quantities exempted and cost savings assume
zero implementation costs. The incorporation of implementation costs
into the analytical model will have a significant impact on facilities
and wastestreams affected, while having only a marginal impact on total
quantities exempted.
c. Affected Wastestreams and Facilities
Under the preferred option (unconditional exemption), as high as 41
percent (10,300) of the potentially affected wastestreams may be
eligible for exemption. These eligible wastestreams are generated by 56
percent (6000) of the facilities producing listed waste. Total
wastestreams and facilities potentially eligible for exemption under
the primary alternative option (no land application) are estimated at
12,200 (48 percent), and 7,000 (65 percent), respectively.
[[Page 66416]]
The majority of the wastestreams eligible for exemption under the
preferred option are very small in quantity. The median annual
generation size of an eligible wastewater wastestream is 20 tons. The
median for eligible nonwastewaters is 2.0 tons. For small wastestreams,
the costs accrued due to the exemption are likely to be counterbalanced
by the costs associated with gaining the exemption.
While a relatively large number of wastestreams and facilities meet
the eligibility criteria for exemption, many may not gain exemption
because the costs of exemption may outweigh the estimated cost savings
from exemption. For example, if implementation costs average $35,000
annually per wastestream, the estimate of facilities generating an
exempted wastestream may be overstated by as much as 90 percent.
However, small generators may choose to aggregate their wastes to avoid
this problem.
d. Relative Impacts on Human Health and the Environment
Today's proposed rule will allow low concentration hazardous wastes
to exit RCRA Subtitle C regulation and be disposed of in Subtitle D
nonhazardous waste units. The Agency believes that today's proposed
rule will have little effect on human health for the following reasons:
The acceptable daily exposure levels used to set the exit
levels are based on maximum risk levels for carcinogens of 10-6
and on acceptable daily doses for non-carcinogens at which no adverse
effects are likely to occur.
The waste management units modeled in the Multipathway
Analysis provide high potential release rates for the various groups of
constituents being considered in the analysis based on their physical
and chemical properties.
The pathways included in the Multipathway Analysis are
generally considered to be the most critical.
The Multipathway Analysis includes populations that are
likely to be exposed more than the average adult due to proximity to a
contaminant source, behavior patterns, activities, and body size.
High-end values were used for selected parameters in the
Multipathway Analysis to calculate acceptable waste concentrations.
Exit levels represent acceptable constituent concentration
levels for Subtitle D waste management based on all of the potential
combinations of management units, and receptors in the Multipathway
Analysis.
Exit levels for several constituents are below the
acceptable waste concentrations for human health due to the inclusion
of ecological receptors.
Ecological risks were also evaluated for selected key constituents.
The inclusion of such risk in solid waste regulation at a national
level is an important step, and is preferable to establishing exit
criteria based only on human health risks.
5. Other Regulatory Issues
a. Environmental Justice
Economic benefits may occur to selected communities as affected
local facilities reinvest cost savings derived from reduced treatment
and/or disposal costs. Human health effects are expected to be
negligible due to the stringency of the exit levels. Included in these
exit levels are pathways of particular concern for selected low income
populations such as subsistence fishing and farming.
b. Other Issues
Today's proposal is expected to have no impact in the area of
Unfunded Federal Mandates or Regulatory Takings. Waste minimization
procedures are likely to be stimulated under this proposal.
6. Implications and Conclusions
The analysis indicates that approximately 11 percent of the
quantity of all nonwastewaters containing listed codes, and 21 percent
of all such wastewaters may be eligible for exemption under the
proposed rule. This exempt quantity is dominated by a small number of
very large wastestreams, and includes a large number of very small
wastestreams. For some small wastestreams, exemption may not be cost
effective unless generators aggregate their wastes or otherwise work
cooperatively to minimize the costs of gaining the exemptions.
Today's proposal could also provide incentives for industry to
implement process changes and increased recycling in an effort to gain
additional savings. Preliminary estimates indicate that savings from
these activities, when combined with treatment and disposal savings
from the preferred option, are likely to result in total annual cost
savings greater than $100 million. However, limitations of our analysis
suggest that the cost savings estimates from such activities are highly
uncertain. Additional savings related to administrative requirements
and reduced treatment for hazardous wastes may also accrue. These
potential additional cost savings are discussed in greater detail in
the Assessment document.
The Agency believes that today's proposal will result in a net
benefit to society. Wastes gaining exemption under the preferred option
will not pose unacceptable incremental risks to human health and the
environment because the exit levels are based on extensive analysis of
possible human and ecological risks associated with exempt wastes.
EPA's analysis of the impact of today's proposal on industry groups
indicates that a limited number of industries are likely to benefit
from exemption. Under the preferred option (unconditional exemption),
three industries account for 51 percent of eligible nonwastewater and
wastewater sludge quantity and 53 percent of total treatment and
disposal cost savings. These industries are: Chemicals and allied
products (SIC 28); fabricated metals (SIC 34); and primary metals (SIC
33).
The Agency also compared benefits gained from exemption to key
industry data such as national pollution abatement expenditures and
considered facility level impacts of the proposal. To evaluate the
relative magnitude of cost savings that would accrue under the proposed
rule, EPA compared cost savings estimates to total pollution abatement
expenditures and the total value of industry shipments. Total treatment
and disposal cost savings under the preferred option account for
approximately 3.5 percent of annual operating costs for hazardous waste
pollution abatement activities, and less than 0.002 percent of the
total value of industry shipments. The facility-level impacts of the
proposal vary greatly.
E. Regulatory Flexibility Analysis.
The Regulatory Flexibility Act requires analysis of the impact of
regulations on small entities. Because today's proposal is
deregulatory, it is not expected to have adverse impacts on small
businesses. In general, generators of large quantity wastestreams
posing low hazards will benefit substantially from the regulations. The
impacts on small quantity generators is less certain and depends on the
degree to which they aggregate their wastes and work cooperatively to
cost-effectively gain exemption.
F. Environmental Justice
It is the Agency's policy that environmental justice be considered
as an integral part in the development of all policies, guidance and
regulations. Further, Executive Order 12898, ``Federal Actions to
Address
[[Page 66417]]
Environmental Justice in Minority Populations and Low-Income
Populations'', directs each Federal Agency to ``make achieving
environmental justice part of its mission by identifying and
addressing, as appropriate, disproportionately high and adverse human
health and environmental effects of its programs, policies, and
activities on minority populations and low-income populations * * * ''
The Executive Order requires that where environmental justice
concerns or the potential for concerns are identified, appropriate
analysis of the issue(s) be evaluated. To the extent practicable, the
ecological, human health (taking into account subsistence patterns and
sensitive populations) and socio-economic impacts of the proposed
decision-document in minority and low-income communities should also be
evaluated. Examples include how a policy on future land use would
impact minority or low-income communities versus non-minority, affluent
communities, or how subsistence farming or fishing patterns relate to
risk-assessment policies.
For the purposes of today's proposed rulemaking, the Agency has
taken an approach for proposal consistent with Executive Order 12898.
As currently drafted, the multipathway analysis which was used to
develop the exit levels takes into account subsistence farmers and
subsistence fishers; however, subsistence fishers were evaluated using
a recreational fisher database (one does not exist for subsistence
fishers). Sensitive populations are accounted for in the RfDs, RfCs,
and slope factors and ecological receptors were also evaluated.
G. Paperwork Reduction Act
As stated earlier, the level of implementation costs (i.e.
sampling, analysis, recordkeeping, and reporting) will have a
significant impact on the number of wastestreams and facilities
affected by this proposal. Assuming annual implementation costs of
$35,000 per wastestream, as many as 269 facilities, generating up to
285 different wastestreams may seek exemptions, and therefore be
affected by the recordkeeping and reporting requirements. The actual
number of facilities and wastestreams affected will depend upon the
level of implementation costs. The higher the implementation cost to
the facility, the fewer the number of facilities expected to
participate in the HWIR program.
The estimated hour burden ranges from 382 hours to 573 hours per
wastestream in the first year, and from 31 hours to 146 hours per
wastestream in years two and three. The variation in burden estimates
results from different assumptions in (1) the complexity of the waste
(and therefore of the test methods required), and (2) the frequency of
reporting. The estimated total hour burden over the first three years
ranges from 206,900 to 293,465 hours, averaging 68,967 to 97,821 hours
per year.
The estimated total start-up cost of recordkeeping and reporting in
the first year ranges from $55,000 to $235,000 per wastestream. The
annual cost in the second and third years is estimated to be $9,000 to
$209,000 per wastestream (of which $8,000 to $203,000 is the cost of
shipping samples to a laboratory and paying to have them tested). In
years four and five the high-end cost drops to $53,000. The estimated
annual recordkeeping and reporting cost per wastestream, annualized at
seven percent over five years, is $21,000 to $170,000. The total
recordkeeping and reporting cost burden over the first three years is
$28,000,000 to $32,000,000.
Burden means the total time, effort, or financial resources
expended by persons to generate, maintain, retain, or disclose or
provide information to or for a Federal agency. This includes the time
needed to review instructions; develop, acquire, install, and utilize
technology and systems for the purposes of collecting, validating, and
verifying information, processing and maintaining information, and
disclosing and providing information; adjust the existing ways to
comply with any previously applicable instructions and requirements;
train personnel to be able to respond to a collection of information;
search data sources; complete and review the collection of information;
and transmit or otherwise disclose the information.
An Agency may not conduct or sponsor, and a person is not required
to respond to a collection of information unless it displays a
currently valid OMB control number. The OMB control numbers for EPA's
regulations are listed in 40 CFR part 9 and 48 CFR chapter 15.
Comments are requested on the Agency's need for this information,
the accuracy of the provided burden estimates, and any suggested
methods for minimizing respondent burden, including through the use of
automated collection techniques. Send comments on the ICR to the
Director, OPPE Regulatory Information Division; U.S. Environmental
Protection Agency (2137); 401 M St., SW.; Washington, DC 20460; and to
the Office of Information and Regulatory Affairs, Office of Management
and Budget, 725 17th St., NW., Washington, DC 20503, marked
``Attention: Desk Officer for EPA.'' Include the ICR number in any
correspondence. Since OMB is required to make a decision concerning the
ICR between 30 and 60 days after December 21, 1995, a comment to OMB is
best assured of having its full effect if OMB receives it by January
22, 1996. The final rule will respond to any OMB or public comments on
the information collection requirements contained in this proposal.
List of Subjects in 40 CFR 261 and 268
Identification and listing of hazardous waste. Land disposal
restrictions.
Dated: November 13, 1995.
Carol Browner,
Administrator.
XV. References
U.S. Environmental Protection Agency, Environmental Monitoring
Systems Laboratory; ``Performance Testing of Method 1312--QA Support
for RCRA Testing.'' EPA/600/4-89/022, June 1989.
Research Triangle Institute; ``Interlaboratory Comparison of Methods
1310, 1311, and 1312 for Lead in Soil''. U.S. EPA Contract 68-01-
7075, November 1988.
U.S. Environmental Protection Agency, Office of Solid Waste and
Emergency Response; OSWER Directive No. 9285.7; ``Human Health
Evaluation Manual, Part B: Development of Risk-based Preliminary
Remediation Goals;'' from Henry Longest II, Director, Office of
Emergency and Remedial Response; and Bruce Diamond, Director, Office
of Waste Programs Enforcement; to Regional Waste Management Division
Directors; December 13, 1991.
U.S. Environmental Protection Agency, Office of Solid Waste and
Emergency Response; OSWER Directive No. 9850.4; ``Interim Final
Guidance for Soil Ingestion Rates;'' from J. Winston Porter, OSWER
Assistant Administrator; to Regional Administrators (I-X); January
27, 1989.
U.S. Environmental Protection Agency, Office of Research and
Development, Office of Health and Environmental Assessment;
``Exposure Factors Handbook;'' EPA/600/8-89/043, March 1990.
U.S. Environmental Protection Agency, Office of Solid Waste: EPA's
Composite Model for Leachate Migration with Transformation Products
(EPACMTP), Background Document, 1995a.
U.S. Environmental Protection Agency, Office of Solid Waste: EPA's
Composite Model for Leachate Migration with Transformation Products
(EPACMTP), User's Guide, 1995b.
U.S. Environmental Protection Agency, Office of Solid Waste: Finite
Source Methodology for Non-Degrading and Degrading Chemicals with
Transformation Products, 1995c.
U.S. Environmental Protection Agency, Office of Solid Waste:
Background
[[Page 66418]]
Document for EPACMTP: Fate and Transport Modeling of Metals, 1995d.
U.S. Environmental Protection Agency, Office of Research
Development. Finite Source Methodology for Wastes Containing Metals,
1992.
U.S. Environmental Protection Agency, Office of Research Development
MINTEQA2/PRODEFA2, A Geochemical Assessment Model for Environmental
Systems: Version 3.0 User's Manual. EPA/600/3-91/021, March 1991.
U.S. Environmental Protection Agency, Office of Research
Development. Environmental Fate Constants for Chemicals Under
Consideration for EPA's Hazardous Waste Identification Projects,
compiled by Heinz Kollig, 1993.
Appendix A
Table A-1.--Human Exposure Pathways
----------------------------------------------------------------------------------------------------------------
Exposure medium Route of exposure Type of fate and transport Pathway a
----------------------------------------------------------------------------------------------------------------
Groundwater................. Ingestion................... Groundwater................ 1
WMU
groundwater
humans
Ingestion of
contaminated
groundwater as a
drinking water source.
Air......................... Inhalation.................. Direct air................. 2a (on site or off
site)
WMU air humans
Inhalation of volatiles
Air......................... Inhalation.................. Direct air................. 2b (on site or off
site)
WMU air humans
Inhalation of suspended
particulates
Soil........................ Ingestion................... Direct soil................ 3 (on site)
WMU humans
Ingestion of
contaminated soil
Soil........................ Ingestion................... Overland................... 3 (off site)
WMU overland
humans
Ingestion of
contaminated soil
Soil........................ Ingestion................... Air deposition............. 4
WMU air deposition to
soil humans
Ingestion of
contaminated soil
Soil........................ Dermal...................... Direct soil................ 5 (on site)
WMU humans
Dermal contact with
contaminated soil
Soil........................ Dermal...................... Overland................... 5 (off site)
WMU overland
humans
Dermal contact with
contaminated soil
Soil........................ Dermal...................... Air deposition............. 6
WMU air deposition to
surface soil
humans
Dermal contact with
contaminated soil
Plant (veg/root)............ Ingestion................... Air deposition............. 8
WMU air deposition to
soil/gard crops garen crops humans
Consumption of
contaminated crops
grown in home gardens
Plant (veg)................. Ingestion................... Air diffusion.............. 8a
WMU air garden crops humans
Consumption of
contaminated crops
grown in home gardens
Plant (veg/root)............ Ingestion................... Direct soil................ 9 (on site)
WMU garden
crops humans
Consumption of
contaminated crops
grown in home gardens
Plant (veg/root)............ Ingestion................... Overland................... 9 (off site)
WMU overland
garden crops
humans
Consumption of
contaminated crops
grown in home gardens
Animal (beef/milk).......... Ingestion................... Air deposition............. 10
WMU air deposition to
soil/feed crops cattle humans
Consumption of animal
products with elevated
levels of toxicant
caused by eating
contaminated feed
crops and soil
Animal (beef/milk).......... Ingestion................... Air diffusion.............. 10a
WMU air feed crops cattle humans
Consumption of animal
products with elevated
levels of toxicant
caused by eating
contaminated feed
crops
Animal (beef/milk).......... Ingestion................... Direct soil................ 11 (on site)
WMU feed
crops cattle
humans
Consumption of animal
products with elevated
levels of toxicant
caused by eating
contaminated feed
crops and soil
Animal (bedf/milk).......... Ingestion................... Overland................... 11 (off site)
WMU overland
feed crops/
soil cattle
humans
Consumption of animal
products with elevated
levels of toxicant
caused by eating
contaminated feed
crops and soil
Groundwater................. Dermal (bathing)............ Groundwater................ 14
WMU
groundwater
humans
Ingestion of
contaminated surface
water as a drinking
water source
Surface water............... Ingestion................... Air diffusion.............. 17
WMU
groundwater
humans
Dermal bathing contact
with contaminated
groundwater
[[Page 66419]]
Surface water............... Ingestion................... Overland................... 19
WMU overland
flow surface
water humans
Ingestion of
contaminated surface
water as a drinking
water source
Surface water............... Ingestion................... Air deposition............. 20
WMU air deposition to
soil