[Federal Register Volume 81, Number 39 (Monday, February 29, 2016)]
[Proposed Rules]
[Pages 10372-10432]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-02749]
[[Page 10371]]
Vol. 81
Monday,
No. 39
February 29, 2016
Part II
Environmental Protection Agency
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40 CFR Part 300
Addition of a Subsurface Intrusion Component to the Hazard Ranking
System; Proposed Rule
Federal Register / Vol. 81 , No. 39 / Monday, February 29, 2016 /
Proposed Rules
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 300
[EPA-HQ-SFUND-2010-1086; FRL-9925-69-OLEM]
RIN 2050-AG67
Addition of a Subsurface Intrusion Component to the Hazard
Ranking System
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
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SUMMARY: The U.S. Environmental Protection Agency (EPA) is proposing to
add a subsurface intrusion (SsI) component to the Hazard Ranking System
(HRS) which is the principal mechanism that EPA uses to evaluate sites
for placement on the National Priorities List (NPL). The subsurface
intrusion component (this addition) would expand the number of
available options for EPA and state and tribal organizations performing
work on behalf of EPA to evaluate potential threats to public health
from releases of hazardous substances, pollutants, or contaminants.
This addition will allow an HRS evaluation to directly consider human
exposure to hazardous substances, pollutants, or contaminants that
enter regularly occupied structures through subsurface intrusion in
assessing a site's relative risk, and thus, enable subsurface intrusion
contamination to be evaluated for placement of sites on the NPL. The
agency is not considering changes to the remainder of the HRS except
for minor updates reflecting changes in terminology.
DATES: Comments must be received on or before April 29, 2016.
ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-
SFUND-2010-1086, to the Federal eRulemaking Portal: http://www.regulations.gov. Follow the online instructions for submitting
comments. Once submitted, comments cannot be edited or withdrawn. The
EPA may publish any comment received to its public docket. Do not
submit electronically any information you consider to be Confidential
Business Information (CBI) or other information whose disclosure is
restricted by statute. Multimedia submissions (audio, video, etc.) must
be accompanied by a written comment. The written comment is considered
the official comment and should include discussion of all points you
wish to make. The EPA will generally not consider comments or comment
contents located outside of the primary submission (i.e. on the Web,
cloud, or other file sharing system). For additional submission
methods, the full EPA public comment policy, information about CBI or
multimedia submissions, and general guidance on making effective
comments, please visit http://www.epa.gov/dockets/commenting-epa-dockets.
FOR FURTHER INFORMATION CONTACT: Terry Jeng, phone: (703) 603-8852,
email: [email protected], Site Assessment and Remedy Decisions Branch,
Assessment and Remediation Division, Office of Superfund Remediation
and Technology Innovation (Mail Code 5204P), U.S. Environmental
Protection Agency, 1200 Pennsylvania Avenue NW., Washington, DC 20460;
or the Superfund Hotline, phone (800) 424-9346 or (703) 412-9810 in the
Washington, DC metropolitan area.
SUPPLEMENTARY INFORMATION: The information presented in this preamble
is organized as follows:
I. General Information
A. What is EPA seeking comment on?
B. How does this action apply to me?
II. Statutory Authority
III. Background
A. Why is EPA proposing an addition to the HRS?
B. What is the history of the HRS?
C. What is the impact of this proposed rule?
1. Impact on Current Cleanup Programs, Resources and Cost
2. Children's Environmental Health and Environmental Justice
IV. Hazard Ranking System
A. Purpose
B. Structure
V. Approach to HRS Addition
A. General Approach
1. What is the need for regulatory action on the HRS?
2. What alternative regulatory options to this action were
considered by EPA?
3. What public outreach activities did EPA conduct?
4. What peer review process did EPA use?
5. How did EPA select the approach for including the addition in
the HRS?
B. Technical Considerations To Maintaining The Current HRS
Structure and Algorithm
1. Maintaining the Current Ground Water, Surface Water, and Air
Migration Pathways
2. Addition of the New Component to Restructure and Rename the
Soil Exposure Pathway
C. Supporting Materials
VI. Discussion of the Proposed SsI Addition to the HRS
A. Addition Within a Restructured Soil Exposure Pathway
B. SsI Component Addition
1. New Definitions
2. Delineation of Areas of Subsurface Intrusion
a. Area of Observed Exposure (AOE)
b. Area of Subsurface Contamination (ASC)
c. Other Area of Subsurface Intrusion Considered: Potential
Migration Zone
3. Likelihood of Exposure
a. Observed Exposure
b. Potential for Exposure
c. Calculation of the Likelihood of Exposure Factor Category
Value
4. Waste Characteristics
a. Toxicity/Degradation
b. Hazardous Waste Quantity
c. Calculation of the Waste Characteristics Factor Category
Value
5. Targets
a. Identification of Eligible Targets
b. Exposed Individual and Levels of Exposure
c. Population
d. Resources
e. Calculation of the Targets Factor Category Value
6. Calculation and Incorporation of the SsI Component Score Into
the HRS Site Score
a. Calculation of the SsI Component Score
b. Incorporation of the SsI Component Score Into the Soil
Exposure and Subsurface Intrusion Pathway Score
c. Incorporation of the Soil Exposure and Subsurface Intrusion
Pathway Score Into a Site Score
7. Example Site Scoring Scenarios
VII. Summary of Proposed Updates to the HRS
VIII. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 13563: Improving Regulation and Regulatory Review
B. Paperwork Reduction Act (PRA)
C. Regulatory Flexibility Act (RFA)
D. Unfunded Mandates Reform Act (UMRA)
E. Executive Order 13132: Federalism
F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
G. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks
H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution or Use
I. National Technology Transfer and Advancement Act
J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations
K. Executive Order 12580: Superfund Implementation
I. General Information
A. What is EPA seeking comment on?
EPA is proposing an addition of one new component to one part of
the current Hazard Ranking System (HRS). No major structural changes to
other parts of the HRS are proposed. EPA is seeking comments on the
addition of the subsurface intrusion component to the HRS. Comments on
unmodified parts of
[[Page 10373]]
the HRS are not being requested and will not be considered if
submitted.
B. How does this action apply to me?
This action proposes an addition to the HRS. The HRS is used for
evaluating the relative potential risk posed by the uncontrolled
release, or potential release, of hazardous substances to human health
or the environment. This addition will enable EPA to identify risks
posed by subsurface intrusion of hazardous substances into regularly
occupied structures for all populations who live and work in areas
where the subsurface environment may create exposures. The agency
considers that including the evaluation of subsurface intrusion in the
HRS serves the public interest by widening EPA's ability to evaluate
these threats.
This proposed regulatory change expands the available options for
EPA and organizations performing work on behalf of EPA (state and
tribal partners) to evaluate potential threats to public health and the
environment from subsurface intrusion contamination. State and tribal
partners may receive financial assistance from EPA to evaluate sites
through a Cooperative Agreement. EPA and states or tribes collaborate
closely throughout the Cooperative Agreement process, particularly when
identifying sites to be evaluated and establishing priorities for
performing evaluations. As necessary, sites where subsurface intrusion
threats exist may be evaluated using the HRS and, if warranted,
proposed for placement on the NPL. EPA does not expect that this
proposed change will result in additional site assessments being
conducted per year or placement of more sites on the NPL per year.
Rather, given potentially limited budgets and the possibility of
increased costs for an SsI site assessment, EPA may conduct fewer
assessments per year. The pipeline of sites will be reviewed to
identify those sites that pose the highest risk and prioritized
accordingly. This is not a change to how EPA currently evaluates and
prioritizes sites for the NPL; EPA will simply have an additional
mechanism to address sites that pose the greatest risk. Because
assessing the worst sites first is a priority, EPA will continue to
identify the sites posing the highest risk or potential risk and
develop a strategy to assess those sites in a timely manner, while
balancing their other site assessment needs.
The addition of a subsurface intrusion component to the HRS affirms
that EPA is fulfilling its regulatory requirements by ensuring ``to the
maximum extent feasible, that the hazard ranking system accurately
assesses the relative degree of risk to human health and the
environment posed by sites and facilities subject to review.'' 42
U.S.C. 9605(c)(1), as mandated by the Superfund Amendments and
Reauthorization Act (SARA) amendments to the Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA).
This proposed addition is necessary because no present authority
consistently and comprehensively addresses subsurface intrusion
contamination across all non-federal potential sites, particularly when
subsurface intrusion is the key exposure pathway. While most states
have identified sites with subsurface intrusion contamination issues,
not all states have subsurface intrusion programs, and states with
subsurface intrusion remediation programs vary in their authority,
resources, and remediation criteria. A redirection of resources
available through Cooperative Agreement funding is expected to provide
for greater national consistency in the identification and evaluation
of subsurface intrusion sites.
Additionally, EPA finalized the OSWER Technical Guide for Assessing
and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor
Sources to Indoor Air, in June 2015. This guide and this proposed
addition to the HRS would further the agency's efforts to establish
national consistency in evaluating vapor intrusion threats by enabling
EPA to use remedial authority under CERCLA.
This proposed regulatory change does not affect the status of sites
currently on or proposed to be added to the NPL.
II. Statutory Authority
The authority for these proposed technical modifications to the HRS
(40 CFR 300, Appendix A) is in section 105(a)(8)(A) of the
Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA) enacted in 1980. Under this law, the National Oil and
Hazardous Substances Pollution Contingency Plan (NCP) (40 CFR 300) must
include criteria for determining priorities among releases or
threatened releases for the purpose of taking remedial or removal
actions. In 1986, Congress passed the Superfund Amendments and
Reauthorization Act (SARA) (Pub. L. 99 499), which added section
105(c)(1) to CERCLA, requiring EPA to amend the HRS to assure ``to the
maximum extent feasible, that the hazard ranking system accurately
assesses the relative degree of risk to human health and the
environment posed by sites and facilities subject to review.''
Furthermore, CERCLA section 115 authorizes EPA to promulgate any
regulations necessary to carry out the provisions of CERCLA.
III. Background
EPA is proposing this addition to protect human health from the
threat posed by subsurface intrusion. By adding this component to the
HRS, EPA will be able to consider subsurface intrusion threats when
evaluating sites for placement on the NPL and implement the
requirements of CERCLA and the National Oil and Hazardous Substances
Pollution Contingency Plan (NCP). This proposed addition is a technical
modification to the current HRS that will allow EPA and its partners to
more comprehensively address the releases of hazardous substances into
the environment.
A. Why is EPA proposing an addition to the Hazard Ranking System?
Contaminant subsurface intrusion \1\ is defined as the migration of
hazardous substances, pollutants, or contaminants \2\ from the
subsurface environment, or more specifically, the surficial ground
water into overlying structures and/or the unsaturated zone. Subsurface
intrusion can result in people being exposed to harmful levels of
hazardous substances and cause negative health effects. While
subsurface intrusion can take multiple forms, the most common form of
subsurface intrusion is vapor intrusion. There are several reasons why
EPA is proposing this addition to the HRS.
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\1\ Subsurface intrusion, for the purposes of this preamble,
refers to the intrusion of hazardous substances from the subsurface
into a structure.
\2\ For the purpose of this preamble, the term ``hazardous
substances, pollutants or contaminants'' will be referred to simply
as ``hazardous substances.'' See section 1.1, of the current HRS for
the definition of a hazardous substance.
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First, the current HRS (40 CFR 300, Appendix A), promulgated
December 14, 1990 (hereafter referred to as the current HRS), discussed
in more detail in section IV of this preamble, does not consider the
threat posed by subsurface intrusion in its evaluation of relative risk
posed by a site; therefore, it does not provide a complete assessment
of the relative risk that a site may pose to the public. The existing
pathways used to evaluate threats posed by hazardous substances do not
include those entering a regularly occupied structure from the
subsurface. For example, the ground water migration pathway evaluates
the threat posed by
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contaminated ground water if there is an indication that ground water
is being consumed. Similarly, the soil exposure pathway evaluates the
threat posed by contaminated surfaces (e.g., surface soils) if there is
an indication of human exposure. The air migration pathway considers
the threat posed by hazardous substances released to atmospheric air
(ambient air), but does not address indoor air, and has no subsurface
component. The surface water migration pathway does not cover
subsurface intrusion as it only considers the threat posed by
contaminated surface water bodies.
In fact, in a May 2010 report,\3\ the Government Accountability
Office (GAO) concluded that if vapor intrusion sites ``are not assessed
and, if needed, listed on the NPL, some seriously contaminated
hazardous waste sites with unacceptable human exposure may not
otherwise be cleaned up.'' The GAO recommended that EPA consider vapor
intrusion as part of the NPL process; EPA agreed with the GAO
recommendation. With the addition of a subsurface intrusion component,
a site with vapor intrusion may qualify for the NPL, whereas presently
the site may not have qualified using the threats evaluated in the
current HRS. Therefore, without this addition, EPA may not be
identifying the sites that most warrant further investigation.
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\3\ EPA's Estimated Costs to Remediate Existing Sites Exceed
Current Funding Levels, and More Sites are Expected to Be Added to
the National Priorities List, GAO Report to Congressional
Requesters, GAO-10-380, May 2010.
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Second, EPA is offering this proposal because of the substantial
public support for this action. EPA conducted outreach activities to
determine the level of interest and support from the public. This
included a Notice of Opportunity for Public Input (76 FR 5370, January
31, 2011) and four public listening sessions held across the country.
More than 40 written comments, from a diverse group of private
citizens, businesses, states, American Indian tribes, environmental
action groups, and other governmental agencies, were received during
the public comment period. Of the public who attended the listening
sessions and provided comments, the majority were supportive of the
addition of a subsurface intrusion component to the HRS. In addition,
five states and two tribes submitted comments--all in support of the
addition. The Association of State and Territorial Solid Waste
Management Officials (ASTSWMO) compiled and presented input from 14
states--all but one favoring the addition of subsurface intrusion to
the HRS. The comments opposing the HRS addition were, in general, from
industry representatives.
Third, to support development of this proposal, EPA evaluated the
need for this proposed addition to the current HRS by identifying the
scope of the subsurface intrusion contamination problem. These efforts
to identify and classify sites that may pose a subsurface intrusion
threat have resulted in the identification of 1,073 sites that may or
may not qualify for the NPL but are suspected of having vapor intrusion
issues. Many of the sites in this inventory are currently listed in
EPA's Superfund Enterprise Management System \4\ (SEMS). Of the 1,073
identified sites:
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\4\ This information was previously stored in a predecessor
database called the Comprehensive Environmental Response,
Compensation and Liability Information System (CERCLIS).
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328 sites are identified as having a suspected subsurface
intrusion threat based on SEMS and Agency for Toxic Substances and
Disease Registry (ATSDR) key word searches, as well as EPA or state
self-identification, but for which no sampling data were obtained
532 sites are identified as having characteristics or
evidence that indicate subsurface intrusion (e.g., volatile hazardous
substance in ground water) may have occurred or will occur.
202 sites are identified as having a subsurface intrusion
threat documented by subslab, crawl space, or indoor air samples but
insufficient HRS-required evaluation factors to qualify for the NPL.
11 sites are identified as having a subsurface intrusion
threat with documented actual exposure of a sufficient number of
targets and sufficient other HRS-required evaluation factors to suggest
the site may qualify for the NPL.
EPA is also considering sites with another form of subsurface
intrusion, namely, intrusion of contaminated ground water into
regularly occupied structures--which is an emerging issue. For example,
a site was discovered where shallow (surficial) ground water
contaminated with chromium had intruded into residential basements and
after the water receded, or evaporated, a precipitate of chromium
remained as a residue. The presence of this residue posed a significant
threat to public health; however, the site could not be evaluated under
the current HRS due to the lack of a mechanism to evaluate human
exposure resulting from intrusion of contaminated ground water
(subsurface intrusion contamination). The only viable option to place
the site on the NPL was to rely on ATSDR to make a determination that
the exposure at the site posed a significant threat to public health.
The decision to include sites on the NPL based on a determination by
the ATSDR is made infrequently because the HRS is the primary mechanism
for placing a site on the NPL.
EPA regional site assessment programs have identified 7 additional
sites where intrusion of contaminated ground water is a potential issue
and the related threat cannot be evaluated using the current HRS. Under
the proposed SsI addition, ground water intrusion would be evaluated
using current conditions, which may involve situations where metals
have precipitated from water or where volatile substances have entered
a structure via infiltrating ground water.
As EPA further explores this emerging issue, the agency considers
it likely that other ground water intrusion sites requiring evaluation
will be identified. The inventory of sites, identified by EPA, with a
possible threat from contaminated vapor or ground water intruding into
overlying regularly occupied structures is not representative of the
magnitude of the potential scope of sites with subsurface intrusion
contamination. EPA identified these sites based on currently available
information to initially assess the subsurface intrusion problem. In
the case of vapor intrusion, certain states undertook comprehensive
efforts to identify and evaluate subsurface intrusion threats, which
resulted in the identification of a proportionately higher number of
sites with potential vapor intrusion problems in those states. In the
case of ground water intrusion, the issue is still emerging. For these
reasons, EPA recognizes that a degree of inherent uncertainty is
associated with compiling an inventory of sites with potential
subsurface intrusion problems and that additional analysis is
necessary, especially in cases where little information exists. See
Appendix A of the Technical Support Document for this proposed addition
(Proposal TSD) for the inventory of vapor intrusion sites. As
additional information is gathered and new sites are added to SEMS and
undergo the site assessment process, the number of sites with
subsurface intrusion threats is likely to change. Nevertheless, the
aforementioned illustrates that there currently exists at least 1,073
sites that have significant actual or potential human exposure due to
subsurface intrusion, but because of the shortcomings of the current
HRS, cannot be evaluated to determine if they warrant addition to the
NPL.
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It is also important to emphasize that the inventory of sites
compiled (where subsurface intrusion has been identified as a possible
issue) does not represent a list of sites that will be placed on the
NPL. EPA recognizes that, in many instances, additional information is
needed to verify the presence, and to determine the nature/extent, of a
subsurface intrusion problem. As such, the inventory should not be
considered a list of NPL candidate sites. EPA notes that less than 5%
of all sites evaluated through the site assessment process are actually
added to the NPL. This percentage is not expected to change
significantly with this addition to the HRS.
Finally, EPA has concluded that for non-federal facilities no other
national program is able to consistently and comprehensively evaluate
and, if warranted, address subsurface intrusion contamination. This
topic is further discussed in section V.A.2 of this preamble.
B. What is the history of the hazard ranking system?
In 1980, Congress enacted CERCLA (42 U.S.C. 9601 et seq.), commonly
called Superfund, in response to the dangers posed by uncontrolled
releases of hazardous substances into the environment. To implement
section 105 (a)(8)(A) of CERCLA and Executive Order 12316 (46 FR 42237,
August 20, 1981), EPA revised the NCP on several occasions, with the
most recent comprehensive revision occurring on March 8, 1990 (55 FR
8666). The NCP sets forth the guidelines and procedures needed for
responding to releases, or potential releases, of hazardous substances.
Section 105(a)(8)(A) of CERCLA required EPA to establish:
[C]riteria for determining priorities among releases or threatened
releases [of hazardous substances] throughout the United States for
the purpose of taking remedial action and, to the extent
practicable, taking into account the potential urgency of such
action, for the purpose of taking removal action. Criteria and
priorities . . . shall be based upon relative risk or danger to
public health or welfare or the environment . . . taking into
account to the extent possible the population at risk, the hazard
potential of hazardous substances at such facilities, the potential
for contamination of drinking water supplies, the potential for
direct human contact [and] the potential for destruction of
sensitive ecosystems. . . .
To meet this requirement and provide criteria to set priorities, EPA
adopted the HRS as Appendix A to the NCP (47 FR 31180, July 16, 1982).
The HRS was last revised on December 14, 1990 (55 FR 51532) to include
the evaluation of additional threats to ensure a complete assessment of
the relative risk that a site may pose to the public. The HRS is a
scoring system used to assess the relative risk associated with actual
or potential releases of hazardous substances from a site based on the
information that can be collected in a limited, typically one to two
day site inspection (SI). The HRS is designed to be applied
consistently to each site, enabling sites to be ranked relative to each
other with respect to actual or potential hazards. As EPA explained
when it originally adopted the HRS, ``the HRS is a means for applying
uniform technical judgment regarding the potential hazards presented by
a facility relative to other facilities. It does not address the
feasibility, desirability, or degree of cleanup required.'' \5\ (47 FR
31220, July 16, 1982).
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\5\ Although the HRS is designed to assess the relative risk of
a site compared to other sites, it is not designed to be used as a
site-specific quantitative risk assessment. Such an assessment is
conducted later in the Superfund process, as necessary.
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Section 105(a)(8)(B) of CERCLA requires that the statutory criteria
described in section 105(a)(8)(A) be used to prepare a list of national
priorities among the known releases, or threatened releases throughout
the United States. The list, which is Appendix B of the NCP, is the
NPL.
The HRS is a crucial part of the agency's program to address the
identification and cleanup of actual and potential releases of
hazardous substances because the HRS score is the primary criterion for
determining whether a site is to be included on the NPL. The NPL
(Appendix B to 40 CFR 300) includes those sites that emerge as
potentially posing the most serious threats to public health and the
environment and may warrant remedial investigation and possible cleanup
under CERCLA. Only sites on the NPL are eligible for Superfund-financed
remedial actions. Removal and enforcement actions can be conducted at
any site, whether or not it is on the NPL.
In 1986, Congress passed the Superfund Amendments and
Reauthorization Act (SARA) (Pub. L. 99 499), which added section
105(c)(1) to CERCLA, requiring EPA to amend the HRS to assure ``to the
maximum extent feasible, that the hazard ranking system accurately
assesses the relative degree of risk to human health and the
environment posed by sites and facilities subject to review.'' The HRS
was previously amended in 1990. This proposed action will amend the HRS
to add a subsurface intrusion component to the evaluation.
C. What is the impact of this proposed rule?
1. Impact on Current Cleanup Programs, Resources and Cost
This proposed addition to the HRS will have the most significant
impact on EPA's Superfund cleanup program. The current HRS considers
releases to the ground water, surface water and air, as well as direct
exposure to contamination such as soil in identifying releases which
warrant further investigation. If promulgated, this proposed rule will
not impact the way the current HRS addresses these releases. However,
in the course of present HRS assessments, sometimes subsurface
intrusion issues are coincident with a ground water or soil
contamination problem. The HRS presently does not consider the threat
posed at sites by subsurface intrusion problems and direct human
exposure, when ground water is not being used as a drinking water
source or surficial soils are not contaminated. If promulgated, this
proposed rule will for the first time allow the EPA site assessment
program to address sites with only subsurface intrusion issues and no
coincidental exposure. When hazardous substances are released and enter
the subsurface environment, they can move from the subsurface into
buildings as a gas, vapor, or liquid. The addition of a subsurface
intrusion component to the HRS would enable EPA to directly evaluate at
sites the relative degree of risk posed by human exposure to hazardous
substances that enter regularly occupied structures through the
subsurface environment.
To the extent practicable, EPA attempts to score all pathways that
pose significant threats. If the contribution of a pathway is minimal
to the overall score, in general, that pathway will not be scored. This
proposed regulatory change would expand available options for EPA and
organizations performing work on behalf of EPA (state and tribal
partners) to evaluate potential threats to public health and the
environment from hazardous waste sites. This modification to the HRS,
by itself, only augments the criteria for applying the HRS. EPA also
does not expect this proposed rulemaking to affect the status of sites
currently on or proposed to the NPL. Sites that are currently on or
proposed to the NPL have already been evaluated under another pathway
(i.e., ground water migration, air migration, surface water migration,
or soil exposure) and, consistent with section 105(c)(3) of CERCLA, as
amended, would not be re-evaluated. Proposal of
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this addition also will not disrupt EPA's listing of sites.
Because federal agencies currently address subsurface intrusion
issues as part of their environmental programs, it is unlikely that a
significant number of sites will be added to the NPL. However, it could
lead to an increase in site assessment activities and related costs.
Executive Order 12580 delegates broad CERCLA authority to federal
agencies for responding to actual and potential releases of hazardous
substances where a release is either on, or the sole source of the
release is from, any facility or vessel under the jurisdiction,
custody, or control of the federal agency. Federal agencies are
required to exercise this authority consistent with the requirements of
CERCLA section 120, as amended, and implement regulations under the
NCP, for both NPL and non-NPL sites. Therefore, federal agencies are in
a position to proactively identify and respond to risks posed by
subsurface intrusion of hazardous substances into regularly occupied
structures for all populations who live and work in areas where the
subsurface environment may create exposures. If it is determined that
releases of hazardous substances pose immediate threats to public
health and the environment, EPA fully expects that the appropriate
federal agency will continue to undertake response actions to address
such threats. In fact, some federal agencies, including EPA, have
developed or are developing new or updated agency-specific policy and
guidance documents to address subsurface intrusion threats.
This proposed addition will impact both resources and costs to
federal cleanup programs. EPA does not expect that this proposed change
will result in additional site assessments being conducted per year or
placement of more sites on the NPL per year. Rather, given potentially
limited budgets and the possibility of increased costs for a subsurface
intrusion (SsI) site assessment, EPA may conduct fewer assessments per
year. The pipeline of sites will be reviewed to identify those sites
that pose the highest risk and prioritized accordingly. This is not a
change to how EPA currently evaluates and prioritizes sites for the
NPL; EPA will simply have an additional mechanism to address sites that
pose the greatest risk. Because assessing the worst sites first is a
priority, EPA will continue to identify the sites posing the highest
risk or potential risk and develop a strategy to assess those sites in
a timely manner, while balancing their other site assessment needs.
The proposed addition, which could lead to the inclusion of a site
on the NPL, does not itself impose any costs on outside parties; it
does not establish that EPA will necessarily undertake response
actions, nor does it require any action by a private party or determine
liability for site response costs. Costs are limited to screening
relevant sites for subsurface intrusion contamination during site
inspections and the resulting HRS evaluation and documentation record
preparation. Costs that arise from site remedial responses are the
result of site-specific decisions made post-listing, not directly from
the act of listing itself.
Later decisions that consider information collected under the
proposed addition could separately have specific economic costs and
benefits (e.g., remediation costs and reduced risk), but these impacts
are contingent upon a series of separate and sequential actions after
listing a site on the NPL. The addition of subsurface intrusion to the
HRS is several regulatory steps removed from imposing costs on private
entities.
The HRS addition may increase the costs to government agencies
conducting assessments at subsurface intrusion sites because the scope
of a typical site inspection may need to be expanded or may require
more expensive sampling to collect information for an SsI evaluation.
SsI sampling may require additional sampling and different sample types
than those collected at other sites. This may result in an increase in
some site assessment costs at some sites with possible subsurface
intrusion issues. However, SsI site assessment costs at some other
sites may be comparable to, or even less than, sites scored under the
existing HRS. For example, a site assessment requiring sampling of deep
ground water monitoring wells under the existing HRS may cost as much
as, or more, than sampling conducted at sites with possible subsurface
intrusion issues. The exact cost of any sampling at a site, including
sites with possible SsI issues, varies greatly based on site-specific
factors (e.g., number and type of samples required, difficulty in
establishing sources of contamination or attribution of releases,
number of HRS pathways being evaluated, and availability of data from
previous sampling events). Additionally, any newly increased costs to
government agencies conducting assessments at SsI sites are expected to
be minimal because federal agencies should already be identifying and
addressing subsurface intrusion as part of their environmental
programs. Any increase in the cost of site assessments conducted by EPA
for SsI sites will require EPA to realign and prioritize its site
assessment budget to address sites with subsurface intrusion. The
addition of an SsI component to the HRS is not expected to result in
additional site assessment funding to account for any increase in site
assessment costs. Instead, the pipeline of sites will continue to be
reviewed under the current site assessment process. If it is found that
SsI-contaminated sites potentially pose a greater risk than other
sites, then these sites will be prioritized over other sites. EPA will
develop a strategy to assess these sites in a timely manner, while
balancing other site assessment needs.
2. Children's Environmental Health and Environmental Justice
This rulemaking is not subject to Executive Order 13045, Protection
of Children from Environmental Health Risks and Safety Risks because
this rulemaking is expected to only have moderate costs \6\ and this
executive order only applies to significant rulemakings. EPA has also
found that this rulemaking will have no direct impact on communities
considered under Executive Order 12898, Federal Actions to Address
Environmental Justice in Minority Populations and Low-Income
Populations.
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\6\ The regulatory impact analysis (RIA) found this rulemaking
will only have moderate costs and will not be a significant
rulemaking. The RIA for this rulemaking can be found in the official
Docket for this action.
---------------------------------------------------------------------------
Although the rule will not have any direct impact on human health
or risk within minority or low-income populations located near
potential SsI sites, populations of concern under Executive Order
12898, EPA did consider whether the proposed action might have
contingent impacts on these communities if future actions affect
remediation of these sites. This analysis concluded that potentially
affected sites are located in areas that have slightly higher
concentrations of minority populations and populations below the
poverty line than surrounding areas. Therefore, any future actions
addressing risks in these communities would not contribute to
disproportionate adverse impacts on human health.
IV. Hazard Ranking System
A. Purpose
The current HRS serves as a screening tool to evaluate the
potential for uncontrolled hazardous substances to cause human health
problems or environmental damage at one site relative to other sites
evaluated. The pre-remedial portion of the Superfund
[[Page 10377]]
program--the portion prior to placing sites on the NPL--is intended to
identify those sites which warrant further investigation and possible
cleanup under CERCLA. (See Figure 1 for a general depiction of the
Superfund Site Assessment process.) During Pre-CERCLA screening, which
is the first step of the pre-remedial process, EPA determines if there
is indication of a possible significant release. If so, EPA determines
if a substance in the release is regulated by CERCLA, whether it is
already being addressed, and whether any statutorily mandated
limitations on CERCLA response may exist. If EPA determines the release
meets these requirements, then the suspected release is listed in EPA's
Superfund Enterprise Management System (SEMS).
Determining whether hazardous substances, pollutants, or
contaminants can be addressed by CERCLA requires the application of
site-specific facts to CERCLA statutory requirements and EPA policy.
One such statutory requirement is CERCLA's limit on response actions to
some naturally occurring substances. CERCLA expressly limits any
response actions taken in response to a release, or threat of release,
of a naturally occurring substance in its unaltered form from a
location where it is naturally found, from products which are part of a
structure, or into drinking water supplies due to deterioration of the
system. (See CERCLA section 104(a)(3) and 104(a)(4) for additional
guidance on limitations on response and exception to limitations).
Therefore, even though a naturally occurring substance in its unaltered
form may potentially be regulated by CERCLA, the response actions taken
in response to these releases, or threat of releases, may be expressly
limited by CERCLA. For example, although radon and asbestos may qualify
as a CERCLA hazardous substance, CERCLA section 104(a)(3) may limit
responses to releases of radon or asbestos in some situations where the
release is from building products or occurs from in situ natural
sources, but section 104(a)(4) identifies specific circumstances that,
if present, would allow CERCLA response in such situations. (See also
EPA OSWER Directive 9360.3-12, Response Actions at Sites with
Contamination Inside Buildings, August 12, 1993). If EPA finds an
eligible release of a CERCLA eligible substance and response actions
are permissible under CERCLA, then EPA proceeds to address the release
under CERCLA. This may include a preliminary assessment.
A preliminary assessment uses readily available data to determine
if there is evidence of an unacceptable potential threat. If based on
the results of a preliminary assessment, EPA determines that a site
warrants further screening under the CERCLA remedial program, the
agency initiates a site inspection as specified in the NCP (40 CFR
300.420). The site inspection usually includes the collection of
samples for chemical analysis. Such samples aid in ascertaining what
substances are present at the site and whether they are being released.
The purpose of the site inspection is to determine if there is an
actual or potential threat to human health or the environment, to
determine if there is an immediate threat to people or the environment
in the area, and to collect sufficient data to enable the site to be
scored using the HRS.
[GRAPHIC] [TIFF OMITTED] TP29FE16.022
[[Page 10378]]
EPA has designed the Superfund program to focus its resources on
sites that warrant further investigation. Consequently, the initial
studies, the preliminary assessment and site inspection, which are
performed on a large number of sites, are relatively modest in scope
and cost compared to the remedial investigations and feasibility
studies subsequently performed on NPL sites. Because of the need to
carry out the initial studies expeditiously, EPA elected to place
certain constraints on the data requirement for an HRS evaluation. The
required HRS data should be information that, for most sites, can be
collected during a screening level site inspection or that are already
available. Thus, the HRS does not rely on data that require extensive
sampling or repeated sampling over a long period of time. The HRS has
also been designed so that it can be applied consistently to a wide
variety of sites. The HRS is not a tool for conducting quantitative
risk assessment and was designed to be a measure of relative risk among
sites rather than absolute risk at an individual site.
The narrow technical modifications being proposed reflect the
agency's actions to encompass additional risks posed by releases of
hazardous substances and to address the SARA statutory requirement that
EPA amend the HRS to assure ``to the maximum extent feasible, that the
HRS accurately assesses the relative degree of risk to human health and
the environment posed by sites subject to review.'' Thus, the
fundamental purpose and structure of the HRS approach will not be
changed when the HRS is amended to include consideration of subsurface
intrusion.
B. Structure
The current HRS (40 CFR 300, Appendix A) evaluates four pathways in
projecting the relative threat a site poses:
The ground water migration pathway evaluates the
likelihood that hazardous substances will migrate to ground water and
contaminate aquifers and drinking water wells that draw on those
aquifers.
The surface water migration pathway evaluates the
likelihood that hazardous substances can enter surface water and affect
people or the environment. Threats to human health and the environment
included in this pathway include drinking water (DW), the human food
chain (HFC) (i.e., hazardous substances accumulate in the aquatic
organisms that humans in turn consume), and sensitive environments
(ENV). The surface water migration pathway is also divided into two
``components'' reflecting different mechanisms for contaminant
transport within each component (i.e., overland/flood migration to
surface water component and ground water to surface water migration
component).
The air migration pathway evaluates the likelihood of
release of hazardous substances into the atmosphere and the number of
people and sensitive environments actually or potentially exposed to
hazardous substances carried in the ambient (outdoor) air, including
gases and particulates. The air migration pathway does not evaluate
releases to indoor air originating from the subsurface.
The soil exposure pathway evaluates the potential threats
to humans and terrestrial environments posed by direct, physical
contact with, and subsequent ingestion of, hazardous substances. This
pathway includes threats to people living on property where hazardous
substances are present in the surface/subsurface, including
contaminated soils (resident population threat), and to people living
nearby with access to the contaminated area (nearby population threat).
Figure 2 illustrates the general structure of the current HRS.
[[Page 10379]]
[GRAPHIC] [TIFF OMITTED] TP29FE16.023
The scoring system for each pathway is based on a number of
individual factors associated with risk-related conditions at the site.
These factors are grouped into three factor categories as discussed
below. These categories include factors that are used to characterize
the relative risk at the site.
1. Likelihood of release/exposure (i.e., likelihood that hazardous
substances have been released or potentially could be released from a
source into the environment, or that people or sensitive environments
could come into contact with hazardous substances).
2. Waste characteristics (i.e., toxicity, mobility, and/or
persistence of the substances in the environment and the quantity of
the hazardous substances that have or could be released).
3. Targets (i.e., people or sensitive environments actually or
potentially exposed to the release).
An HRS score is determined for a site by summing the score for the
four pathways. Specifically, the score for each pathway is obtained by
evaluating a set of factors that characterize the potential of the
release to cause harm via that pathway. The factors, which represent
toxicity of the hazardous substance, or substances, at a site, waste
quantity, and population are multiplied by a weighting factor, yielding
the factor value; the factor values are used to assign factor category
values. The factor category values are then multiplied together to
develop a score for the pathway being evaluated. Finally, the pathway
scores are combined according to the root-mean-square equation
presented below to determine the HRS score for the site. See also Table
2-1 of the proposed addition (section 2.1.2) for additional discussion
regarding the method for calculating an HRS site score.
[GRAPHIC] [TIFF OMITTED] TP29FE16.024
S = site score
Sgw = ground water migration pathway score
Ssw = surface water migration pathway score
Sse = soil exposure pathway score
Sa = air migration pathway score
By using this formula to assign a site score, the HRS score will be
low if all pathway scores are low. However, the final score can be
relatively high if one pathway score is high. This approach was chosen
to ensure that the site scores do not deemphasize single-pathway
problems, underestimating their importance. EPA considers this an
important requirement for the HRS scoring methodology because some
extremely dangerous sites pose threats through only one pathway. For
example, leaking drums of hazardous substances can contaminate drinking
water wells, but if the drums are buried deeply enough and the
hazardous substances are not very volatile, they may not release any
hazardous substances to the air or to surface water.
It should be emphasized that the existing pathways can address
subsurface contamination if it enters into ground water (in the ground
water migration pathway), if it enters into surface water (in the
surface water migration pathway), if it enters into ambient air (in the
air migration pathway) from the soil surface or if it leads to surface
soil contamination (in the soil exposure pathway). However, none of
these scenarios address intrusion from the subsurface into regularly
occupied structures.
[[Page 10380]]
Finally, it should also be emphasized that the HRS score does not
represent a specific level of risk at a site. Rather, the score serves
as a screening-level indicator of the relative risk among sites
reflecting the hazardous substance releases or potential releases at
sites based on the criteria identified in CERCLA.
V. Approach to HRS Addition
The following sections detail EPA's comprehensive approach to the
consideration of exposures to hazardous substances due to subsurface
intrusion and the relevant scientific and technical considerations in
developing this proposed rule.
A. General Approach
1. What is the need for regulatory action on the HRS?
Without an evaluation of threats posed by subsurface intrusion
contamination, the HRS is not a complete assessment and omits a known
pathway of human exposure to contamination. EPA considers the addition
of subsurface intrusion to the HRS to be consistent with CERCLA section
105 because it will improve the agency's ability to identify sites for
further investigation and will enhance EPA's ability, in dialogue with
other federal agencies and the states and tribes, to determine the most
appropriate state or federal authority to address sites. As is
currently the case, EPA often defers to other state and federal cleanup
authorities based on the site assessments and HRS evaluations. While
some states/tribes have programs to address subsurface intrusion
contamination, they often have limited authority and resources, and
variable remediation criteria. The availability of the federal remedial
authority and the more comprehensive site assessment program should
complement and strengthen these programs.
Other EPA programs such as the Resource Conservation and Recovery
Act (RCRA) and the Brownfields program have limited authority and
ability to address all subsurface intrusion threats. The RCRA
Corrective Action/Enforcement is only applicable at sites subject to
RCRA permitting or sites reachable by RCRA's enforcement activities.
Furthermore, RCRA is a state delegated program and not all states
recognize subsurface intrusion as a significant issue, and those that
do may have variable remediation criteria. RCRA sites with subsurface
intrusion issues may not be addressed in all states. Also, governmental
entities with site-specific Brownfields assessment and/or revolving
loan fund cleanup may only use grant funds on the selected eligible
property. While subsurface intrusion sites may be eligible for
Brownfields cleanup grants, site or property-specific limitations may
not allow for permanent remediation where multiple properties may be
involved or where Brownfields grant funds, as limited by statute, may
not be adequate to fund long-term cleanups.\7\
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\7\ EPA's Estimated Costs to Remediate Existing Sites Exceed
Current Funding Levels, and More Sites are Expected to Be Added to
the National Priorities List, GAO Report to Congressional
Requesters, GAO-10-380, May 2010.
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EPA's removal program has the ability to quickly respond to
immediate threats to public health and the environment from the release
of hazardous substances, such as subsurface intrusion into a structure
through a removal action. A removal action can be implemented
regardless of NPL status to eliminate or reduce the threat of a
release, or a potential release, of hazardous substances, pollutants or
contaminants that pose an imminent and substantial danger to public
health. However, removal actions are not intended to necessarily serve
as a method for dealing with long term issues such as ground water
contamination. Generally, EPA considers vapor intrusion mitigation
systems as ``interim'' or ``early'' response actions to promptly reduce
threats to human health. Installation of vapor intrusion mitigation
systems addresses temporary human health problems, but fails to address
the source of the problem.
The NCP expresses the preference for response actions that
eliminate or substantially reduce the level of contamination in the
source medium to acceptable levels, thereby achieving a permanent
remedy. U.S. EPA, OSWER Technical Guide for Assessing and Mitigating
the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor
Air, OSWER Publication 9200.2-154, June 2015. OSWER's VI guidance
states:
The preferred long-term response to the intrusion of vapors into
buildings is to eliminate or substantially reduce the level of
contamination in the subsurface vapor source (e.g., groundwater,
subsurface soil, sewer lines) by vapor-forming chemicals to
acceptable-risk levels, thereby achieving a permanent remedy.
Remediation of the groundwater plume or a source of vapor-forming
chemicals in the vadose zone will eventually eliminate potential
exposure pathways and can include the following actions, among
others: removal of contaminated soil via excavation; removal of
contaminated groundwater with pump-and-treat approaches;
decontaminating and/or rehabilitating sewer lines that harbor vapor-
forming chemicals; and, treatment of contaminated soil and
groundwater in situ, using technologies such as soil vapor
extraction, multiphase extraction, and bioremediation, or natural
attenuation.
In the case of vapor intrusion resulting from a subsurface
contaminant plume, failing to address the source of contamination and
the resulting plume may result in an increased exposure to individuals
due to migration and expansion of the plume over time. In this
instance, individuals in regularly occupied structures that were
previously unaffected by the plume may become negatively impacted by
subsurface intrusion. Additionally, a subsurface contaminant plume in a
lesser-developed area has the potential to impact future development if
left untreated.
There are several other concerns related to only addressing
subsurface intrusion problems with a vapor mitigation system. The first
concern is that vapor mitigation systems require ongoing monitoring and
maintenance throughout the life of the system. Periodic inspections of
the vapor mitigation system are necessary to make sure it is operating
as designed. Over time the system can degrade, and maintenance will
also be necessary, such as replacing the fan in an active sub-slab
depressurization system. Non-mechanical failures of the system can
occur as well, such as, electric power failure, turning off the fan or
ignoring a damaged system.
A vapor intrusion mitigation system is a tool for protecting human
health, but may not contribute to the Superfund program's goal of
cleaning up uncontrolled hazardous waste sites. Furthermore, EPA still
lacks a mechanism to assess human health hazards from vapor intrusion
in the current HRS model, and therefore cannot currently evaluate the
threat of vapor intrusion as part of its ranking of sites for placement
on the NPL.
Under the Superfund remedial program for NPL sites, subsurface
intrusion is only addressed at sites placed on the NPL based on threats
from other pathways. That is, subsurface intrusion issues are addressed
later in the remedial process after placement on the NPL. For example,
this may be done as part of EPA's five-year review process. Sites with
only subsurface intrusion issues are not being included on the NPL due
to the lack of a subsurface intrusion component in the HRS. Therefore,
many sites, especially those not evaluated under another HRS pathway or
those not scoring high enough under another HRS pathway,
[[Page 10381]]
may not be addressed for threats due to subsurface intrusion because
they may not qualify for placement on the NPL. As the Government
Accountability Office (GAO) states in its May 2010 report:
EPA may not be listing some sites that pose health risks that are
serious enough that the sites should be considered for inclusion on
the NPL. While EPA is assessing vapor intrusion contamination at
listed NPL sites, EPA does not assess the relative risks posed by
vapor intrusion when deciding which sites to include on the NPL. By
not including these risks, states may be left to remediate those
sites without federal assistance, and given states' constrained
budgets, some states may not have the ability to clean up these
sites on their own . . . However, if these sites are not assessed
and, if needed, listed on the NPL, some seriously contaminated
hazardous waste sites with unacceptable human exposure may not
otherwise be cleaned up.
EPA proposes the addition of the subsurface component to ensure the
HRS does not omit this known pathway of human exposure to contamination
and provides a mechanism for complete assessment of SsI threats to
human health and the environment.
2. What alternative regulatory options to this action were considered
by EPA?
EPA considered alternatives to this proposed regulatory action for
addressing the need to evaluate subsurface intrusion threats as
discussed below.
Specifically, EPA considered whether existing programs adequately
address the risks associated with subsurface intrusion at contaminated
sites, as discussed in the previous section. If one or more programs
were in place to adequately address concerns from subsurface intrusion,
this could obviate the need for EPA action. However, no other authority
consistently and comprehensively addresses subsurface intrusion across
all potential non-federal sites, particularly when subsurface intrusion
is the key exposure route. In particular, state programs vary
significantly in addressing subsurface intrusion. In fact, not all
states have subsurface intrusion programs, and states with programs
vary in their authority, resources, and remediation criteria. The 2004
Interstate Technology and Regulatory Council's (ITRC) Vapor Intrusion
Team developed and conducted an on-line survey of state, federal, and
tribal agencies regarding vapor intrusion regulations, policy, and
guidance. Ninety-six percent (96%) of survey respondents consider vapor
intrusion a concern; however, only 11% have a procedure for evaluating
vapor intrusion codified into law, while a larger number of states have
developed, or are developing, guidance for addressing vapor intrusion
issues. A majority of the states that responded to the survey expressed
that their processes for addressing vapor intrusion were only
informally adopted by their agencies, and most defer to EPA. The 2009
Vapor Intrusion Pathway: A Guide for State and Territorial Federal
Facilities Managers study also surveyed state and territorial
subsurface intrusion programs. According to this study, there were no
states with a statute directly addressing vapor intrusion or
identifying requirements for assessing the risk. Nine states had
regulations that address vapor intrusion specifically; three states had
regulations under development. Thirty-four states either have guidance
for addressing vapor intrusion or are in the process of developing
guidance. In addition, the Association of State and Territorial Solid
Waste Management Officials (ASTSWMO) has expressed support for the
proposed rule and has requested that EPA take leadership on this issue.
Since vapor intrusion is projected to be the most significant component
of subsurface intrusion, these responses would apply to subsurface
intrusion as well. As previously discussed in section V.A.1 of this
preamble, other federal programs were reviewed; while some programs
could address subsurface intrusion at some sites, they cannot
comprehensively address all sites (federal and non-federal).
Two other mechanisms currently exist to place sites on the NPL.
First, each state can designate a single site to the NPL as a state top
priority site regardless of its HRS score; this can be done only once.
(see NCP, 40 CFR 300.425(c)(2)). This state-designated sites option has
been implemented for 44 states/territories, and the remaining state
options would not be sufficient to address the subsurface intrusion
issue nationally and comprehensively, given the projected number of
sites with subsurface intrusion problems. Second, sites may be added in
response to a health advisory from the ATSDR. (See NCP, 40 CFR
300.425(c)(3)). However, the ATSDR mechanism was designed to be used
only when the Agency for Toxic Substances and Disease Registry (ATSDR)
designated the threat found to warrant immediate dissociation from the
release and other criteria are met. This is not a mechanism that can be
used uniformly and consistently. It is highly resource intensive and
may not comprehensively address all chronic threats.
Furthermore, CERCLA section 105 clearly mandates that EPA implement
the HRS to take into account ``to the extent possible the population at
risk, the hazard potential of hazardous substances . . . , the
potential for contamination of drinking water supplies and the
potential for direct human contact.'' When the HRS was last revised in
1990, the technology to detect and evaluate subsurface intrusion
threats was not sufficiently developed. For example, there were no
health-based benchmark concentration values for residences or
standardized technologies for sampling indoor air, precision of
analytical equipment prior to computerization was limited, and
associations between contaminated ground water and soil vapors were not
well understood. However, it is now possible for subsurface intrusion
threats to be evaluated comprehensively. Therefore, it is now
appropriate, given the potential that subsurface intrusion presents for
direct human contact, to add to the HRS the consideration of threats
due to subsurface intrusion.
3. What public outreach activities did EPA conduct?
Before making the decision to issue this proposed rulemaking, EPA
conducted outreach activities to determine interest and support from
the public. Thus, on January 31, 2011, EPA published a ``Notice of
Opportunity for Public Input'' (76 FR 5370, January 31, 2011)
soliciting stakeholder comment on whether to include a subsurface
intrusion component in the HRS. Additionally, EPA sent letters to all
federally recognized tribes, asking for their comments on the FR
document. During the 75-day public comment period on this action, four
listening sessions were held throughout the country (Arlington, VA; San
Francisco, CA; Albuquerque, NM; and Edison, NJ). The comments made by a
majority of speakers, including members of the public, at the listening
sessions were supportive of the potential addition of a subsurface
intrusion component into the HRS. Of the 43 written comments received
during the public comment period, 35 were in support of adding a vapor
intrusion component to the HRS, 6 comments (generally from industry
representatives) were opposed to this addition, and 2 comments were
neutral. The comments received during the public listening sessions and
in response to the ``Notice of Opportunity for Public Input'' have been
reviewed and considered in the development of this proposed rulemaking.
EPA has also established a public Web site, http://www.epa.gov/superfund/vapor-intrusion-and-superfund-program, providing background
information on
[[Page 10382]]
why this addition to the HRS is being considered.
4. What peer review process did EPA use?
This proposed rule consists of narrow technical modifications and
is an expansion of the current HRS, which was peer reviewed by the
agency's Science Advisory Board (SAB). The 1988 SAB review was
comprehensive and addressed the basic structure and concepts of the
HRS. This proposed addition adheres to the basic structure and concepts
of the current HRS, and thus, is consistent with the recommendations of
the SAB. The 1988 SAB report focused on the following issues:
The overall algorithm for the HRS;
The inclusion of exposure in the HRS;
How the HRS could be evaluated in the future;
Work that could be done to provide better documentation
for the next revision of the HRS;
The types of toxicity the HRS should address and how it
should do so;
Distances from an uncontrolled hazardous waste site that
are relevant when considering air pollutants from sites; and
The feasibility of including waste concentration in the
HRS and whether large volume waste sites had been treated differently
than others in the HRS.
The 1988 SAB report is available in the public docket for this proposed
rulemaking.
During development of this proposed HRS update, EPA determined that
several subsurface intrusion-specific issues warranted external
independent scientific peer review. As a result, EPA has identified
elements that have undergone peer review including:
Consideration of potential for subsurface exposure
(intrusion) into regularly occupied structures;
Determination of hazardous waste quantity for the
subsurface intrusion component;
Population scoring;
Evaluating populations in multi-story and multi-subunit
structures; and
Evaluation of target values for workers.
The results of the 2011 peer review of the proposed addition are
discussed in the Summary of Peer Review Comments and Suggested
Responses on the Addition of a Subsurface Intrusion Component to the
HRS, which is available in the public docket for this proposed
rulemaking. This proposed addition reflects modifications made as a
result of EPA's peer review process.
5. How did EPA select the approach for including the addition in the
HRS?
The following six concepts were used as the basis for evaluating
possible approaches to the HRS addition and the selection of a
preferred approach:
1. Limit the proposed addition to the existing HRS structure to
avoid confusion by minimizing the portions of the present HRS that
would need to be revised.
2. Utilize the existing HRS basic structure and scoring algorithm,
and maintain the relative weighting of the different pathways.
3. Base technical decisions on sound and proven science.
4. Ensure the HRS acts as an effective screening tool and minimizes
unnecessary resource expenditures, while also minimizing the erroneous
inclusion or exclusion of sites for possible NPL placement.
5. Assemble and utilize conceptual site models, case studies, and
sensitivity analyses to test the model.
6. Ensure that an HRS scoring evaluation of the soil exposure and
subsurface intrusion pathway can be completed using the information and
level of effort that are typical of a site inspection or expanded site
inspection (ESI).
In the process of developing the proposed rule, EPA identified
multiple options that are consistent with the above concepts. Based on
literature reviews and agency experience, EPA projected the range of
conditions at which the proposed addition might be applied. Using the
basic structure of the current HRS, EPA tested each option by
simulating the scores for typical scenarios. Using the results of these
studies, EPA selected the option that best met the above criteria. To
verify that the selected option would provide comparable results at
actual sites, EPA tested the scoring algorithm using existing
subsurface intrusion data from actual sites. The results of these
studies demonstrate that the proposed addition functioned as expected.
See section 8.0 of the Technical Support Document for this proposed
addition (Proposal TSD) for supplemental information regarding EPA's
testing efforts.
B. Technical Considerations to Maintaining the Current HRS Structure
and Algorithm
1. Maintaining the Current Ground Water, Surface Water, and Air
Migration Pathways
The current approach for scoring the ground water, surface water,
and air migration pathways is not being altered by the proposed
addition of a subsurface intrusion component. Therefore, EPA is not
soliciting comments on these pathways and will not respond to comments
that are submitted on these pathways.
2. Addition of the New Component to the Soil Exposure Pathway
EPA is proposing to add the subsurface intrusion threat to the
present soil exposure pathway, which already considers direct exposure
to receptors. This pathway is proposed to be restructured and renamed
the soil exposure and subsurface intrusion pathway. The restructured
pathway will retain unchanged the existing two soil exposure threats
(resident population and nearby population) in the pathway as one
component. The threat posed by subsurface intrusion is proposed to be
added as a new component.
The internal structure of the soil exposure component, including
the two soil exposure threats within that component, remains unchanged.
Therefore, EPA is not soliciting comments on the soil exposure
component of the proposed soil exposure and subsurface intrusion
pathway, nor will it respond to comments that are submitted on the soil
exposure component.
The soil exposure pathway was selected for modification because its
structure already focuses on populations actually coming into or
potentially coming into direct contact with hazardous substances. The
present soil exposure pathway addresses direct contact with
contamination outside of structures. The new subsurface intrusion
component also addresses direct contact with contamination that has
already been demonstrated to have entered into regularly occupied
structures or where the contamination is present beneath the regularly
occupied structures and is likely to enter into regularly occupied
structures. See section VI.A of this preamble for further discussion.
C. Supporting Materials
The proposed addition to the HRS is discussed in the following
primary documents: (1) The proposed rule, (2) this preamble, (3) the
Proposal TSD (including all supporting appendices), (4) the regulatory
impact analysis (RIA). The proposed rule identifies the proposed
changes to the NCP and focuses on the specific mechanics of scoring
sites with the new component. This preamble provides an overview of the
proposed HRS addition, along with an explanation of any modifications
and the supporting justification. The Proposal TSD contains a more
detailed
[[Page 10383]]
explanation of the technical basis for the proposed additions to the
HRS, along with descriptions of the options considered, analyses that
were used to evaluate the performance of the new subsurface intrusion
component, and technical literature that was used in the development of
the addition. The Proposal TSD is available to help guide the
evaluation of subsurface intrusion sites. The Proposal TSD follows the
same general outline as the preamble, with one section describing the
necessary narrow technical modifications that affect multiple pathways,
and the remaining sections describing the addition of the subsurface
intrusion component to the current soil exposure pathway. The Proposal
TSD contains a description of the current HRS, the options considered,
and the technical justifications for the option chosen. In addition,
the Proposal TSD references other supporting documents that provide an
even greater level of detail on the proposed additions.
These four documents are available to the public in the Docket for
this rulemaking. To facilitate public review, EPA has prepared an index
to the proposed rule, the preamble to the proposed rule, and the
Proposal TSD with detailed cross referencing of issues. This index is
available in the public Docket. See the ADDRESSES section of this
preamble for further information.
VI. Discussion of the Proposed SsI Addition to the HRS
This section first discusses why the evaluation of the relative
risk posed by subsurface intrusion has been added as a component to the
same HRS pathway as for soil exposure. It then discusses how the
evaluation will be performed using a structure consistent with the
other threats, components, and pathways in the HRS, but taking into
account the unique parameters impacting the probability of exposure to
subsurface intrusion.
A. Addition Within a Restructured Soil Exposure Pathway
EPA is proposing to add the evaluation of the relative risk posed
by subsurface intrusion of hazardous substances into regularly occupied
structures by restructuring the soil exposure pathway in the current
HRS to include subsurface intrusion. As noted previously, no changes
are being proposed for the other three pathways in the present HRS. The
restructured soil exposure pathway is proposed to be renamed the soil
exposure and subsurface intrusion pathway to reflect both components of
the restructured pathway. See Figure 3 for a depiction of how the
proposed addition fits into the HRS structure.
[GRAPHIC] [TIFF OMITTED] TP29FE16.025
[[Page 10384]]
The threat posed by subsurface intrusion is proposed to be added to
the soil exposure pathway because both consider the relative risk posed
by direct contact with existing contamination areas. As identified in
the preamble to the 1988 Federal Register document proposing the
current HRS (53 FR 51997-52000, December 23, 1988), the soil exposure
pathway, proposed in 1988 to be named the ``onsite exposure'' pathway,
was added to the HRS to address the threat posed by direct contact with
existing contamination and focused on ingestion of contaminated soil.
This is in contrast with the other existing HRS pathways, which
evaluate the relative risk posed by actual or potential migration of
contamination from an original release location (called a ``source'' in
HRS terminology) via ground water, surface water, or ambient air to
other locations where exposure may occur. Given that the relative risk
posed by subsurface intrusion is also due to direct contact with
contamination already present in, or likely to be intruding into,
regularly occupied structures and no further migration away from the
existing contamination areas need occur, EPA considers it appropriate
to incorporate the subsurface intrusion threat in the same direct
exposure pathway that includes the soil exposure relative risk. See
section 6.0 of the 1988 Revised HRS Technical Support Document (1988
Revised HRS TSD) for supplemental information (originally referred to
as the onsite exposure pathway).
The existing soil exposure pathway will be retained as one
component of the restructured pathway, with the two threats within the
present soil exposure pathway, resident and nearby populations, being
retained as threats within the soil exposure component. The scoring of
the soil exposure component will remain unaltered, but the score will
be assigned as the soil exposure component score, not the pathway
score. (See section 5.1 of the Proposed HRS Addition.) The proposed
subsurface intrusion component will be added as a new component of the
restructured soil exposure and subsurface intrusion pathway. As
discussed in greater detail below, it will have the same basic
structure, scoring, and weighting as other parts of the HRS.
The score for the restructured pathway is based on a combination of
the two component scores--soil exposure and subsurface intrusion. The
soil exposure component score is added to the subsurface intrusion
component score to determine the pathway score. The two component
scores are proposed to be additive because the populations may be
subjected to exposures via both routes: The soil exposure component
reflects exposures to people when outside a structure and focuses on
ingestion and the subsurface intrusion component reflects exposures
inside a structure and focuses on inhalation. Hence, the addition of
the two component scores reflects the potential cumulative risk of
multiple exposure routes and is not double counting the relative risk.
A maximum pathway score is not contingent on scoring both the soil
exposure and subsurface intrusion components. It is possible for a site
to have only one component evaluated and still reach the maximum
pathway score. Because the scoring of the soil exposure component is
not being altered, this component would contribute the same score to
the overall site score absent the addition of subsurface intrusion.
B. Subsurface Intrusion Component Addition
The structure of the current HRS is basically the same for all
individual pathways, components, and/or threats. This structure was
first used in the original HRS (47 FR 31220, 1982) and was only
slightly altered when the HRS was revised in 1990 (55 FR 51532,
December 14, 1990) to fit pathway-specific parameters and to address
comments on the proposed rule. See also section 2.2 of the 1988 Revised
HRS TSD for supplemental information. The design of the HRS reflects a
conceptual understanding of how hazardous substance releases from
CERCLA sites can result in risks to public health and welfare and the
environment. The risk scenario at these sites is a function of:
The probability of exposure to (or releases to a medium in
a migration pathway of) hazardous substances,
The expected magnitude and duration of the releases or
exposures,
The toxicity or other potential adverse effects to a
receptor (target) from the releases,
The probability that the release will reach a receptor and
the expected change in the concentration of hazardous substances during
the movement from the location of the contamination to the receptors,
The expected dose to the receptor, and
The expected number and character of the receptors.
The above considerations are addressed in three factor categories:
likelihood of exposure (or release), waste characteristics, and
targets.
The following subsections describe the structure of the proposed
subsurface intrusion component and how this structure is consistent
conceptually with the existing structure of the other HRS pathways and
components: (1) New definitions, (2) delineation of areas of subsurface
intrusion, (3) likelihood of exposure, (4) waste characteristics, (5)
targets, and (6) calculating and incorporating the subsurface intrusion
component score into the HRS site score. For background on why this
structure was selected by EPA and peer reviewed by the SAB, see section
2.0 of the 1988 Revised HRS TSD.
1. New Definitions--See Section 1.1 of the Proposed HRS Addition \8\
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\8\ For references to a specific section of the proposed HRS
addition, please refer to the regulatory text of the proposed
rulemaking.
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EPA is proposing that 14 new definitions be added to the HRS,
section 1.1, with additional modifications to existing definitions. EPA
is adding these new definitions to aid the site evaluator in
establishing the environmental boundaries that are being evaluated in
this component (e.g., contamination in or above the surficial aquifer),
in identifying factors unique to the subsurface intrusion component
(e.g., channelized flow through which soil gas transports with no
resistance), and to ensure consistent application of the HRS.
2. Delineation of Areas of Subsurface Intrusion--See Section 5.2.0 of
the Proposed HRS Addition
EPA is proposing to include in the subsurface intrusion component
evaluation two areas in which exposure due to subsurface intrusion
contamination exists or is likely to exist: (1) Areas of observed
exposure--areas in which contaminant intrusion into regularly occupied
structures has been documented, and (2) areas of subsurface
contamination--areas in which subsurface contamination underlying
regularly occupied structures (such as in surficial ground water or
soil vapor) has been documented, but at which either sampling of indoor
air has not documented that subsurface contamination has entered a
regularly occupied structure or no sampling of indoor air has been
undertaken. See Figure 4 for an illustration of the two areas.
Additionally, special considerations are given to buildings with
multiple subunits and multiple levels (e.g., apartment buildings) when
establishing areas of subsurface intrusion. For a more detailed
discussion on the selection of these areas, see section 6.0 of the
Proposal TSD.
[[Page 10385]]
a. Area of Observed Exposure (AOE)--See Section 5.2.0 of the Proposed
HRS Addition
EPA is proposing to identify an area (or areas) of observed
exposure at a site based on the location of regularly occupied
structures with documented contamination resulting from subsurface
intrusion attributable to the site being evaluated. The area
encompassed by such structures constitutes the area of observed
exposure (AOE). Other regularly occupied structures within this
encompassed area (or areas) will also be inferred to be in the AOE
unless available information indicates otherwise. Populations occupying
structures within the AOE are considered exposed to subsurface
contamination for HRS scoring purposes, and thus, are included in the
HRS evaluation. See section 6.0 of the Proposal TSD for further
discussion on the delineation of an AOE and the rationale for the
inclusion of this area in an HRS evaluation.
b. Area of Subsurface Contamination (ASC)--See Section 5.2.0 of the
Proposed HRS Addition
EPA is proposing to also identify an area (or areas) of subsurface
contamination as an area outside that of the AOE, but for which
subsurface contamination has been documented at levels meeting observed
release criteria (contamination at levels significantly above
background and the significant increase can be attributed at least in
part to the site). The contamination would be present either in
surficial ground water samples, in subslab or semi-enclosed or enclosed
crawl space samples, in subsurface soil samples, or in soil gas samples
in the unsaturated zone. An ASC may also include regularly occupied
structures where indoor air sampling has not documented that an
observed exposure has occurred. (See current HRS section 2.3 for
observed release criteria.) In addition, EPA is proposing to limit the
delineation of an ASC based on the location of subsurface volatile
hazardous substances. However, non-volatile hazardous substances may be
used to establish an ASC if they have also been documented in an
observed exposure.
Populations in regularly occupied structures within an ASC are
considered potentially contaminated, but are weighted less in the HRS
evaluation than those populations in an AOE. The populations in an ASC
are assigned a weighting value ranging from 0.1 to 0.9 depending on
such factors as the distance of subsurface contamination to a regularly
occupied structure's foundation and the sample media (see section
5.2.1.3.2.3 of the Proposed HRS Addition). The ASC is included in the
HRS evaluation because there is currently contamination below regularly
occupied structures in the ASC, and although a sampling event has not
documented intrusion into these structures, based on previous studies,
it is likely that intrusion has occurred or could occur when suitable
climatic and lifestyle conditions were or are present. The populations
in the ASC are weighted less to reflect the relatively lower
demonstrated risk in the ASC in comparison to the AOE. See section 6.0
of the Proposal TSD for further discussion on the delineation of an ASC
and the rationale for inclusion of this area in an HRS evaluation.
[GRAPHIC] [TIFF OMITTED] TP29FE16.026
c. Other Area of Subsurface Intrusion Considered: Potential Migration
Zone
In the three current HRS migration pathways (ground water, surface
water, and air migration pathways), a projected present and future
migration distance called the target distance limit is assigned based
on studies performed when the HRS was revised in 1988. Targets
(receptors) within that distance are considered either actually or
potentially exposed and the values assigned to these receptors are
weighted based on the level of contamination, the
[[Page 10386]]
distance from a source, and the possible amount of hazardous substance
dilution.
As a result, EPA considered including within the subsurface
intrusion component an approach for incorporating populations subject
to future migration (outside the ASC) similar to that used for the
ground water migration pathway. The approach included a standard 4-mile
distance (modified if site-specific geologic information indicates
otherwise) radiating either in all directions or only in the probable
downgradient direction from each source at a site to establish this
future migration zone. This approach could account for the possibility
of future horizontal migration of either volatile substances in
contaminated ground water or as a soil gas beyond the demonstrated
boundaries of the subsurface contamination and subsequently into
regularly occupied structures (i.e., a potential future migration
zone). This might happen, for example, if hazardous substance plumes
expand or migrate due to the additional release of hazardous
substances, shift side-to-side due to ground water gradient changes
resulting from seasonal variations or tidal influences, or change
direction due to the sequencing of dry and wet years or pumping at
municipal water supply or other well fields. Additionally, natural and
anthropogenic influences, such as utility corridors, fracture patterns,
karst features, or buried stream channels or other geologic
heterogeneity may alter or enhance hazardous substance migration.
However, EPA's confidence in the present science to accurately
project hazardous substance migration through both the ground water and
the unsaturated zone is limited. Several fate and transport models,
many based on the Johnson and Ettinger Model, currently exist and are
used to project vapor migration and predict contaminant vapor intrusion
into a structure. The ability of a site assessor to accurately evaluate
the potential future migration of subsurface hazardous substances would
rely heavily on the ability to gather site-specific data in all areas
of future migration in the relatively short time period and with
minimal resources available when data collection for an HRS evaluation
is performed (i.e., during the site inspection). EPA's review of
existing models indicate that in most instances, to obtain acceptable
projections, extensive site-specific data collection efforts and often
multiple rounds of site investigations are required to develop an
accurate model for projecting the future extent of vapor migration,
especially in the unsaturated zone. As discussed in section 2.5 of the
1988 TSD, the ``. . . misapplication of a model or the use of
incomplete data would, of course, result in less accuracy . . . [and] a
very conservative model may also increase the frequency with which
sites that do not pose significant risks are placed on the NPL.''
Therefore, after thorough review of this option, the agency has
chosen not to include the consideration of future subsurface
contaminant migration in the proposed subsurface intrusion component.
The possibility of placing sites on the NPL based on speculative
projections with no demonstrated risk of actual exposure is too
significant. The exclusion of this option in the proposed HRS addition
does not directly prevent a site from being considered for listing on
the NPL based on demonstrated intrusion, nor does it restrict future
investigations from expanding the site boundaries or re-evaluating a
site if further studies indicate that the extent of contamination at a
site may have increased due to future migration. Please refer to
section 6.0 of the Proposal TSD for supplemental information regarding
consideration of a potential migration zone.
3. Likelihood of Exposure--See Section 5.2.1.1 of the Proposed HRS
Addition
A key factor considered in the HRS relative risk ranking is whether
any exposure has occurred and if not, whether there is a probability
that exposure could occur. This is termed the likelihood of exposure
for the subsurface intrusion component. For purposes of an exposure
assessment, not only must subsurface intrusion have occurred, but the
structure must be regularly occupied. Consistent with other HRS
pathways and components, likelihood of exposure is evaluated in two
ways within the proposed subsurface intrusion component. The first step
is to determine whether contamination has entered a regularly occupied
structure; if this has occurred, ``observed exposure'' is established.
If an observed exposure can be demonstrated in at least one structure,
the likelihood of exposure category value is assigned the highest
possible score. If observed exposure has not been documented, the
second step is to evaluate the ``potential for exposure.'' The
potential for exposure factor is assigned a score lower than that given
when an observed exposure has been documented. How to evaluate the
likelihood of exposure is discussed below. See section 4.0 of the
Proposal TSD for supplemental information regarding likelihood of
exposure.
a. Observed Exposure--See Section 5.2.1.1.1 of the Proposed HRS
Addition
For HRS purposes, an observed exposure is established if it can be
documented that a hazardous substance from the site being evaluated has
moved through the subsurface and has entered at least one regularly
occupied structure. When it can be documented that subsurface intrusion
has occurred, the likelihood of exposure is assigned its maximum value.
The HRS identifies for all the pathways a consistent approach for
establishing observed exposure (or observed release in migration
pathways) and is discussed in section 2.3 of the current HRS. Also, the
requirements for establishing observed exposure (or observed releases)
are equivalent to those used to establish releases throughout the HRS.
See section 2.6 of the 1988 Revised HRS TSD for supplemental
information. Consistent with the current HRS structure, EPA is
proposing to establish observed exposure in the subsurface intrusion
component by any of the following methods:
i. Observed Exposure by Direct Observation--See Section 5.2.1.1.1 of
the Proposed HRS Addition
The identification of an observed exposure by direct observation
can be based on a solid, liquid, or gaseous hazardous substance
attributable to the site being observed or known to have entered a
regularly occupied structure from the subsurface. This finding will
generally require the observation that a solid, liquid, or gas is
entering the structure, and can be documented from a sample of the
material that shows the hazardous substance is present due to the
release from the site being evaluated. For example, this type of direct
exposure could be documented if: (1) Contaminated vapors are found in a
sample from a sump open to the regularly occupied structure, and (2)
the same hazardous substances are found in subsurface samples collected
beneath the regularly occupied structure or otherwise can be
demonstrated as having emanated from known contamination underlying the
structure. Another example would be if chromium precipitate is found in
basements subject to ground water flooding and it is known that a
chromium contaminant plume is present, and its presence is not from
indoor sources. In neither example would a significant increase above a
background contaminant level be required. For exposures to intruded
ground water, EPA is proposing
[[Page 10387]]
documented observed exposure by direct observation as the only method
for establishing likelihood of exposure. Figure 5 below depicts an
additional example of documenting observed exposure by direct
observation through collection of a contaminated water sample taken
from the sump of an occupied structure that is known to be subject to
flooding. Other methods may also be used to establish direct
observation depending on site-specific conditions. See section 4.0 of
the Proposal TSD for further information.
[GRAPHIC] [TIFF OMITTED] TP29FE16.027
ii. Observed Exposure by Chemical Analysis--See Section 5.2.1.1.1 of
the Proposed HRS Addition
Observed exposure by ``chemical analysis'' is established by
comparing hazardous substance concentrations in background and release
samples that have been chemically analyzed. The concentration of one or
more hazardous substance in one or more indoor air sample taken from a
regularly occupied structure (termed the ``release sample'') is
compared to the concentration at appropriate background locations and
under appropriate background conditions. If the chemical analyses
document a significant increase over background levels and if at least
part of the significant increase can be shown to be attributable to a
release from the site being evaluated, then observed exposure by
chemical analysis has been documented. This option for establishing
observed exposure differs from observed exposure by direct observation
in that comparison of the hazardous substance concentration in a
release sample to a background level is required. This method for
establishing observed exposure by chemical analysis is outlined in
detail below.
Background levels for this situation, in some cases, may be
determined by chemical analysis of samples from similar environments
collected from outside the area impacted by the release, or releases,
from the site being evaluated. While the appropriate sample locations
to be used to establish this background level will vary based on site-
specific conditions, an appropriate background level needs to account
for both outdoor air concentrations and indoor air concentrations in
structures of similar construction type (e.g., basement, slab-on-grade)
within the vicinity. This is to ensure that the background level
represents the concentration of a hazardous substance in the absence of
the subsurface intrusion. In some cases it may be possible to use
published studies on typical background concentrations in establishing
an appropriate background level. See section 4.0 of the Proposal TSD
for further discussion on background levels.
The first step in determining if observed exposure by chemical
analysis has occurred is to document that the magnitude of the
difference between the background level concentration and the release
sample concentration is sufficient to rule out the possibility that
neither the difference nor the similarity is due to variation in site
conditions; and to ensure the sampling and analytical procedures are
precise and can be replicated. The magnitude of this ``significant
increase'' was established for all HRS pathways based on studies peer
reviewed by the Science Advisory Board when the HRS was last revised in
1990. See section 2.6 of the 1988 Revised HRS TSD for supplemental
information.
A significant increase is generally identified to have occurred if
the release sample hazardous substance concentration is above
quantification limits and at least three times the background level,
provided the background sample concentrations for the hazardous
substance are found at or above appropriate detection limits. If the
hazardous substance background
[[Page 10388]]
level is below the appropriate detection limit, any quantifiable level
of the hazardous substance detected in the targeted structure is
considered to have a concentration significantly above background.
The second step in determining if observed exposure by chemical
analysis has occurred is to document that at least part of the
significant increase can be attributed to a release from the site being
evaluated. This step is required for establishing observed releases or
observed exposures in all HRS pathways. See section 2.3 of the current
HRS and section 2.6 of the 1988 Revised HRS TSD for supplemental
information. This step is conducted to ensure that the increase is due
to the release being evaluated and not from other potential contaminant
sources located in the vicinity. (See section 4.0 of the Proposal TSD
for further discussion.) For the proposed subsurface intrusion
component, establishing significant increase over background is
particularly critical because many of the projected intrusion
contaminants are solvents and, in particular, chlorinated solvents.
Chlorinated solvents are commonly found in multiple household and
commercial cleaning products and in various consumer goods found in
regularly occupied structures. These products present a substantial
challenge for discerning the contribution from the environmental
release that is being evaluated. Therefore, it is critical that a
significant increase in these hazardous substances be documented as
coming from the subsurface and not simply emanating from these
products.
It is suggested that the evidence to support this determination
include multiple lines of evidence, including determining outdoor air
hazardous substance concentrations; finding the hazardous substance at
the source facility, site, or release being investigated; and finding
the hazardous substance in subsurface samples. (See section 4.0 of the
Proposal TSD regarding lines of evidence.) In addition, actions should
be taken to ensure that sources of the hazardous substances inside a
structure (e.g., household chemicals) have been removed from the
structure prior to sampling. Establishing attribution to the site in
some situations, however, may be straightforward to document, such as
when the hazardous substance is manmade, unique, and not used in
consumer products and thus, there would be no need to follow all the
steps identified above to establish attribution. EPA expects that
future advancement in methods for establishing the source of indoor
contamination will be helpful for drawing conclusions about
attribution.
In summary, if it is demonstrated that there is a significant
increase in hazardous substance levels in a regularly occupied
structure and it is demonstrated that the significant increase in the
contamination is in part due to the release from subsurface intrusion
being evaluated, then an observed release by chemical analysis has been
established.
b. Potential for Exposure--See Section 5.2.1.1.2 of the Proposed HRS
Addition
When an observed exposure has not been established, EPA is
proposing to evaluate the potential for exposure within structures
located in an ASC using the subsurface intrusion component. Given that
within an ASC, contamination has been demonstrated to be below or in
the subsurface encompassing regularly occupied structures, it is
probable that exposure to the intruding hazardous substance has
occurred but that sampling has not been performed at the time the
exposure took place. As explained in section 4.0 of the Proposal TSD,
the factors affecting when intrusion will occur and the rate of
subsurface intrusion are extremely time-, site-, and climate-specific.
Sampling may not have been performed in these structures for a number
of reasons, or, even if performed during the limited time period (due
to resource limitations, site inspections are conducted over a limited
period of time, usually 1 to 2 days) of a site inspection, the sampling
may have been conducted during conditions in which the subsurface
intrusion was not occurring, or occurring at levels not detectable or
differentiable from that in background sources of the hazardous
substance. Therefore, it is important that the potential for exposure
be included as a consideration when evaluating subsurface intrusion
threats, especially when volatile substances are documented in the
subsurface below regularly occupied structures.
As also explained in section 4.0 of the Proposal TSD, EPA is
proposing to evaluate the potential for exposure for the subsurface
intrusion component using the same concept and framework used to
estimate the potential to release in other pathways. (See section 2.3
of current HRS.) As depicted in Figure 6 below, this involves
predicting the probability of exposure in an area of subsurface
contamination based on structural containment features of the regularly
occupied structure and the route characteristics in the subsurface,
including hazardous substance physical and chemical properties and
physical subsurface properties that influence the probability that
intrusion is occurring.
[[Page 10389]]
[GRAPHIC] [TIFF OMITTED] TP29FE16.028
i. Structure Containment--See Section 5.2.1.1.2.1 of the Proposed HRS
Addition
Containment within the current HRS is used to consider barriers
that restrict the movement of hazardous substances. See the preamble to
the 1988 Revised HRS (53 FR 51985, December 23, 1988) for supplemental
information. For the proposed subsurface intrusion component, the
containment features considered represent structural features that
block the movement of hazardous substances so as to minimize or prevent
indoor exposures resulting from subsurface intrusion into a regularly
occupied structure. As is consistent with the current HRS, EPA is
proposing containment factor values that range from zero to ten where a
low containment factor value indicates a low chance for exposure. For
example, in Table 5-12 of the proposed HRS addition, a structure with
no visible open preferential pathways from the subsurface has a lower
containment value than a structure with documented open preferential
pathways because open preferential pathways (e.g., sumps, foundation
cracks) represent a situation in which a greater probability for
subsurface intrusion to occur is present. Populations in structures
that show no possible SsI intrusion route are not evaluated in this new
component. Supplemental information regarding containment and the
factor values specified in Table 5-12 is provided in section 4.0 of the
Proposal TSD.
ii. Route Characteristics--See Section 5.2.1.1.2 of the Proposed HRS
Addition
The HRS uses ``route characteristics'' to index the relative degree
to which hazardous substances move into or have already moved into
specific areas, such as from a source into ground water, or for the
subsurface intrusion component into a regularly occupied structure (see
the 1988 TSD and section 4.0 of the Proposal TSD for supplemental
information). These characteristics represent the physical and chemical
properties of the specific hazardous substances and the media in which
they must have moved through or could move through. To determine which
route characteristics are appropriate for evaluating potential exposure
to subsurface hazardous substances, EPA examined the literature to
identify the modeling methods that are currently used to estimate the
levels of hazardous substance exposure. Numerous route characteristics
and the relationship of these and site-specific input requirements were
identified. EPA also gave careful consideration to ensure that route
characteristic factors may be measured or calculated on a site-specific
basis in a manner appropriate with current HRS evaluations. See section
4.0 of the Proposal TSD for supplemental information evaluated as part
of this process.
EPA reviewed existing sensitivity analyses and performed further
analyses to evaluate the intrinsic relationships among the examined
route characteristics to identify those that have the greatest impact
on potential for exposure. Based on the agency's analysis, three
factors represented the greatest impact on potential for exposure and
for which sufficient site-specific information could be collected
during a site inspection: (1) Depth to contamination, (2) vertical
migration, and (3) vapor migration potential. These three factors are
described in the following sections.
a. Depth to Contamination--See Section 5.2.1.1.2.2 of the Proposed HRS
Addition
The depth to contamination factor represents the vertical distance
between contamination (either in soil, soil gas, or surficial ground
water) and the lowest horizontal point of an overlying regularly
occupied structure (e.g., a
[[Page 10390]]
basement floor). This distance represents how far a hazardous substance
would have to travel through the subsurface to intrude into that
structure. Based on available data, the probability of exposure
decreases as the depth to contamination increases. In addition, as part
of EPA's sensitivity analysis in developing route characteristics, at
depths greater than 150 feet it became increasingly unlikely that
exposure would occur. This is reflected in Table 5-13 (section
5.2.1.1.2.2 of the Proposed HRS Addition). EPA is proposing depth to
contamination factor values ranging from zero to ten, where increasing
depth results in a lower factor value.
EPA is also proposing to give special consideration in two
situations in which it is likely that exposure has occurred. One
situation is when subsurface profiles may be impacted by channelized
flow features, such as fractured bedrock or karst. The other situation
is at locations where the contamination is measured directly below the
structure (e.g., in subslab or enclosed/semi-enclosed crawl space
samples). These features reflect a situation with a high probability of
exposure to intruded hazardous substances because of limited resistance
to migration of the substances into the structure. See section 4.0 of
the Proposal TSD for supplemental information on how the depths to
contamination were weighted when assigning the factor values to
different distances.
b. Vertical Migration--See Section 5.2.1.1.2.3 of the Proposed HRS
Addition
The vertical migration factor considers the geologic makeup of
materials between a regularly occupied structure and the hazardous
substance plume and the rate at which substances are likely to have
moved through the materials. EPA is proposing to index vertical
migration based on two factors: Effective porosity (or equivalently,
the permeability) of geologic materials and the thickness of the lowest
porosity layer.
Factor values for effective porosity (as it relates to
permeability) of geologic materials range from one to four and are
based solely on the typical range of porosity of subsurface materials
(e.g., gravel, sand, silt and clay). These factor values are used in
conjunction with the thickness of the lowest porosity layer (greater
than 1 foot thickness) to establish a vertical migration factor value,
ranging from one to fifteen.
As part of the vertical migration factor, EPA identified soil
moisture content to potentially be a significant route characteristic
variable. Thus, to incorporate soil moisture in EPA's assessment of
potential for exposure, the agency used published ``average soil
moisture content'' values for specific soil types. These averages were
used to develop effective porosity/permeability factor values. See
section 4.0 of the Proposal TSD for supplemental information.
c. Vapor Migration Potential--See Section 5.2.1.1.2.4 of the Proposed
HRS Addition
The vapor migration potential factor is based on hazardous
substance-specific chemical properties, including both the vapor
pressure and Henry's constant values for hazardous substances
associated with the site. This factor evaluates the volatile nature of
these hazardous substances and is projected to be the most influential
route characteristic factor on calculating potential for exposure based
on a sensitivity analysis using subsurface migration modeling. When
calculating the vapor migration potential, a factor value is determined
only for the most volatile hazardous substance based on vapor pressure
and Henry's constant values. Those values are used to establish the
vapor migration potential factor value. See section 4.0 of the Proposal
TSD for supplemental information on this topic.
iii. Calculation of the Potential for Exposure Factor Value--See
Section 5.2.1.1.2.5 of the Proposed HRS Addition
Consistent with potential to release determinations in the HRS, the
potential for exposure for this component is calculated by summing all
route characteristic factor values and multiplying the sum by the
containment factor value to determine a potential for exposure factor
value.
c. Calculation of the Likelihood of Exposure Factor Category Value--See
Section 5.2.1.1.3 of the Proposed HRS Addition
As in all HRS pathways and components, the likelihood of exposure
factor category value is assigned based on the higher of the observed
exposure (or release) value or the potential for exposure (or release)
value. The maximum value assigned for the likelihood of exposure factor
category is 550 and is assigned if observed exposure is documented. If
observed exposure is not documented, the value assigned when evaluating
potential for exposure ranges between 0 and 500. This approach is
consistent with the current HRS structure. See sections 2.2 of the 1988
Revised HRS TSD for supplemental information regarding this approach.
4. Waste Characteristics--See Section 5.2.1.2 of the Proposed HRS
Addition
The waste characteristics factor category is based on factors that
are related to the relative risk considerations included in the basic
HRS structure: (1) The toxicity or other potential adverse effects to a
receptor from the releases, (2) the potential to degrade in the
subsurface prior to intruding into a regularly occupied structure, and
(3) the expected magnitude and duration of the exposure. The factors
considered in determining the waste characteristics factor category
value are the toxicity of the hazardous substances, the ability of the
hazardous substance to degrade, and an estimate of the quantity of the
hazardous substances to which occupants could be exposed. Consistent
with the soil exposure component, the assigned factor values are
multiplied together to determine this category value for the subsurface
intrusion component. (See sections 2.2 and 2.4 of the 1988 Revised HRS
TSD for further discussion on the structure of this factor category and
how it fits within the overall HRS structure.) How and why these
factors are proposed to be included in this factor category is
discussed below.
a. Toxicity/Degradation--See Section 5.2.1.2.1 of the Proposed HRS
Addition
The combined toxicity/degradation factor includes consideration of
both the toxicity and the possibility for degradation of hazardous
substances being evaluated for HRS purposes.
The toxicity factor in the overall HRS structure reflects the
toxicity of a hazardous substance associated with a release or
exposure, and is assigned the same factor value for all the pathways
and components in the current HRS. As in all HRS pathways and
components, it is proposed to be assigned the same corresponding factor
value as for other parts of the HRS. The rationale for the assignment
of the factor value is discussed in the section 2.3 of the 1988 Revised
HRS TSD. This toxicity factor is based on the toxicity of the
substances present at a site. In the HRS addition, a different factor
value is proposed to be assigned to each hazardous substance that an
occupant has been or is potentially exposed to. The factor value is
driven by the magnitude of each hazardous substance's acute and chronic
toxicity to humans. The toxicity factor value is directly related to
the concentration at which the hazardous
[[Page 10391]]
substance is known to have a health effect: The more toxic the
chemical, the higher the toxicity value. Any hazardous substance
identified in an observed exposure within the AOE or meeting the
observed release criteria in either the AOE or ASC will be assigned a
toxicity factor value. The method for assigning this value is contained
in section 2.4.1.1 of the current HRS (40 CFR 300, Appendix A) and is
discussed in section 2.3 of the 1988 Revised HRS TSD.
The degradation factor represents the possibility for a substance
to degrade in the subsurface prior to intruding into a regularly
occupied structure. The potential of a substance to degrade has been
identified as a significant factor in numerous studies evaluating the
potential for intrusion by a vapor. The possibility that a substance
may degrade is both a substance- and location-specific evaluation that
is influenced by factors such as molecular structure, makeup of the
immediate subsurface geology, and the presence or absence of oxygen
within intervening unsaturated soils.
Because many of the site-specific characteristics impacting the
rate of degradation are considered beyond the scope of a typical site
investigation, EPA is proposing to evaluate degradation based on the
substance being evaluated, the depth to contamination, and if
appropriate environmental conditions are present to ensure that
sufficient degradation will occur to diminish the threat. Based on
EPA's review of the current literature and research on this topic, the
assigned degradation factor is limited to three possible factor values,
two for substances that are readily degradable and the appropriate
environmental factors are present, and one for when either of these
parameters are not present.
EPA seeks public input on the following question regarding the
degradation factor: Is there a way to determine the presence and extent
of biologically active soil at a site during a limited site
investigation? If so, what soil characteristics should EPA consider to
determine whether biologically active soil is documented to be present?
EPA proposes the degradation factor also be based on the half-life
of a substance, with the half-life being determined by biodegradation
and hydrolysis rates. If this information is not available then a
hazardous substance's estimated half-life will be based on the
substance's chemical structure, unless available information indicates
otherwise. Substances with relatively low structural complexity, such
as petroleum and petroleum-like substances (having straight carbon
chain or simple ring structures), have the greatest potential to
degrade in the subsurface while halogenated and poly-aromatic ringed
substances (e.g., tetrachloroethylene, PCBs) are less likely to
significantly degrade as result of subsurface microbial activity.
If it has been documented that a hazardous substance has been found
to have entered a regularly occupied structure, regardless of the
substance or the site conditions, the degradation value is assigned to
reflect the likelihood that the substance is not significantly
degrading in the subsurface. Also, if the substance is a daughter, or
degradation product, of a parent substance that is also present, then
the degradation factor will reflect this relationship. Parent and
daughter substances are assigned values to reflect that the daughter
substance will be continuously created by degradation of the parent
substance. See also section 5.0 of the Proposal TSD for additional
discussion regarding the inclusion of a degradation factor.
The toxicity and degradation factors are multiplied together to
assign a combined factor value. If multiple substances are present, the
highest combined factor value is selected for use in determining the
waste characteristics factor category value, as discussed below.
b. Hazardous Waste Quantity--See Section 5.2.1.2.2 of the Proposed HRS
Addition
In the basic HRS structure used in all pathways and components, the
hazardous waste quantity factor reflects the risk consideration related
to the magnitude and duration of either the release for a migration
pathway or the exposure for an exposure pathway. In other words, for an
exposure pathway, the risk posed by a release of hazardous substances
is directly related to the amount of hazardous substances to which
receptors (targets) are exposed and the length of the exposure.
As explained in the preamble to the 1990 HRS and in the 1988
Revised HRS TSD, an estimate of the waste quantity associated with a
site was the best surrogate for the amount of hazardous substances that
receptors were exposed to and that the duration of the exposure was
probably correlated to the magnitude of the exposure. In the current
three migration pathways (ground water, surface water, air), the
hazardous waste quantity factor reflects the total amount of hazardous
substances in sources at the site to take into account not only where
contamination has already migrated to, but also future migration of
contamination to other locations. For the soil exposure pathway,
however, the estimate does not include the total amount in or released
from the site sources, but only the amount of hazardous substance in
the top two feet of contaminated soils sources and in the surface
portions of other source types in an area of observed contamination.
(See section 5.0.1 of the current HRS.)
EPA is proposing that since the subsurface intrusion component also
focuses on exposure and not the amount of hazardous substances that
might migrate to targets in the future, the waste quantity factor value
for this component should also reflect only the amount of hazardous
substances that people currently are exposed to, that is, the amount in
regularly occupied structures. EPA is proposing a four-tiered
hierarchical approach consistent with the current HRS (see section
III.C of the preamble of the current HRS (55 FR 51542, December 14,
1990)) as well as minimum waste quantity factors (see section 2.4.2 of
the current HRS). The minimum waste quantity factors are included
because of insufficient information at many sites to adequately
estimate waste quantity with confidence, as discussed in section I of
the preamble to the current HRS (55 FR 51533, December 14, 1990). The
current HRS establishes a minimum waste quantity factor value of 10 for
each pathway or component at sites with no actually contaminated
targets and a waste quantity factor value of 100 for the migration
pathways if observed exposure has been documented. (See section 2.4.2
of the current HRS.)
It is proposed for the estimation of waste quantity for the
subsurface intrusion component, that regularly occupied structures
within the AOE and ASC be considered. For sites at which the component
waste quantity (the sum waste quantities for all occupied structures in
the AOE and ASC) is below 10, it is proposed that a minimum factor of
10 should apply the same as in other pathways and components. This
minimum factor reflects that in a limited site inspection, it is likely
that information on the actual waste quantity at a site may not be
available and a lower value would likely underestimate the actual
conditions. Furthermore, if any target is subject to Level I or II
contaminant concentrations a minimum hazardous waste quantity factor
value of 100 could be assigned.
EPA seeks public input on the following question regarding the
calculation of hazardous waste quantity: How could EPA further take
into account the differences in dilution and
[[Page 10392]]
air exchange rates in large industrial buildings as compared to smaller
residential and commercial structures when calculating the hazardous
waste quantity for the HRS SsI Addition?
The component waste quantity is the sum of all the waste quantities
for all the regularly occupied structures found in both the AOE and
ASC. The component waste quantity factor value assigned is then based
on the magnitude of this sum, subject to minimum values. See section
5.0 of the Proposal TSD for supplemental information regarding this
topic.
c. Calculation of the Waste Characteristics Factor Category Value--See
Section 5.2.1.2.3 of the Proposed HRS Addition
As in all HRS pathways and components, the waste characteristics
category value is the product of the toxicity/degradation factor value
(or the functional equivalent) and the hazardous waste quantity factor
value, scaled so as to be weighted consistently in all pathways.
Similar to the likelihood of exposure factor category, the waste
characteristics factor category is subject to a maximum value to
maintain the balance between factor categories. This approach is
consistent with the current HRS structure. See sections 2.2 and 2.4 of
the 1988 Revised HRS TSD for supplemental information regarding this
approach.
5. Targets--See section 5.2.1.3 of the Proposed HRS Addition
The targets factor is based upon estimates of the expected dose to
each receptor and the number and type of receptors present. In a human
health risk assessment, it is critical to understand the nature and
extent of exposure to individuals, populations, and resources. The
relative risk assessment embodied within the current HRS uses the
targets factor as an index of the nature and extent of exposure to
individuals, populations, resources, if appropriate for the migration
or exposure route being evaluated, sensitive environments. This will
remain the same in the proposed HRS addition, except sensitive
environments will not be considered an eligible target.
a. Identification of Eligible Targets--See Section 5.2.1.3 of the
Proposed HRS Addition.
The target factors evaluated by all pathways under the current HRS
include the following:
The most exposed individual (i.e., nearest well for ground
water migration, nearest intake for drinking water threat, food chain
individual for human food chain threat, resident individual for
resident population threat, and nearest individual for nearby
population threat and air migration),
Populations (including residents, workers, students, and
those in daycare),
Resources (including economic and cultural uses of
contaminated resources),
Sensitive environments (except for the ground water
migration pathway). (Examples of sensitive environments include
government designated protected areas (e.g., national wildlife refuge),
wetlands and critical habitat known to be used by a State or Federally-
designated threatened or endangered species.)
See sections 2.5 and 5.1.3 of the current HRS for supplemental
information on how eligible targets are identified.
Given that the subsurface intrusion component is proposed to be
included as an exposure component within the modified soil exposure and
subsurface intrusion pathway, the agency is proposing to use the same
target categories used in the current soil exposure pathway, including
exposed individual, resident populations, workers, and resources.
However, unlike the current soil exposure pathway, workers are proposed
to be evaluated as exposed individuals and as part of the population
within an area of subsurface contamination instead of being evaluated
under a separate worker factor value. See section 5.2.0 and its
subsections of the proposed HRS addition. Additionally, sensitive
environments are not being considered as eligible targets because
exposures related to subsurface intrusion are limited to indoor areas
and it is unlikely that sensitive environments would be exposed. See
section 5.2.1.3 of the proposed HRS addition.
EPA seeks public input on the following question regarding
subsurface source strength: The HRS SsI Addition considers source
strength in delineating ASCs and AOEs, in scoring likelihood of
exposure, in assigning waste quantity specifically when estimating
hazardous constituent quantity and in weighting targets in an ASC. The
HRS algorithm for all pathways incorporates the consideration of source
strength in determining an HRS site score. Could EPA further take into
account source strength in performing an HRS evaluation?
b. Exposed Individual and Levels of Exposure--See Section 5.2.1.3.1 of
the Proposed HRS Addition
This section introduces the methods used to identify and establish
the levels of contamination and benchmarks proposed to be used within
the subsurface intrusion component. Additionally, the exposed
individual factor is discussed, as well as how to apply a factor value
based on the benchmarks and the resulting levels of exposure.
i. Identifying Levels of Exposure and Benchmarks for Subsurface
Intrusion--See Section 5.2.1.3.1 of the Proposed HRS Addition
For all current HRS pathways, the magnitude of the values assigned
to the individual and population factors depend on the concentration of
the contamination to which the receptors (targets) are exposed. If
receptors are exposed to hazardous substance levels that meet observed
release criteria, they are identified as actually contaminated;
however, if the receptors are not exposed to hazardous substances that
meet the observed release criteria but are within the target area being
evaluated, they may be considered potentially contaminated. Potential
targets are evaluated because a typical site inspection may not
identify the extent of contamination. A site inspection typically
includes 1 to 3 days of sampling and investigation activities. These
limited investigations may not adequately characterize the annual or
longer term indoor exposure levels (see page 4 of the 1988 SAB report
and section 6.0 of the Proposal TSD), especially in the case of
subsurface intrusion where seasonal and temporal fluctuations can
significantly impact the rate of subsurface intrusion.
Actually contaminated targets are further divided into two
categories based on whether the hazardous substance concentrations are
above standard health-based benchmarks (or for environmental receptors,
ambient water quality criteria). If so, they are identified as Level I;
if they are not, they are identified as Level II. See section 2.5.2 of
the current HRS for a discussion of applicable benchmarks.
EPA is proposing to use a similar target weighting structure in the
subsurface intrusion component. (See sections 5.2.1.3.1 and 5.2.1.3.2
of the proposed HRS addition.) Those targets in the AOE are considered
actually contaminated, whereas, those in the ASC are considered
potentially contaminated. The targets in an AOE are further divided
into Level I and II, based
[[Page 10393]]
on whether the hazardous substance concentrations are at or above
identified health-based benchmarks. EPA is proposing to use the
following benchmarks for the subsurface intrusion component:
Screening concentrations for cancer
Screening concentrations for noncancer toxicological responses
Targets associated with an observed exposure by direct observation
are only considered subject to Level II contamination in all parts of
the HRS and EPA is proposing that this remains consistent in the
subsurface intrusion component. Furthermore, because intrusion by
contaminated ground water is documented by direct observation only,
targets residing within a structure subject to intrusion by
contaminated ground water are also proposed to be evaluated as Level II
(see section 2.5 of the proposed HRS addition).
The targets within an ASC are also further divided based on the
type of sample (e.g., gas, soil, water) and the distance of the sample
from the targets (e.g., the depth of the sample below the structure).
Weighting factors ranging from 0.1 to 0.9 are then assigned accordingly
as discussed below in section 5.c.ii. See also section III.H. of the
preamble to the current HRS (55 FR 51547, December 14, 1990) for
supplemental information.
ii. Exposed Individual--See Section 5.2.1.3.1 of the Proposed HRS
Addition
The standard HRS approach for scoring targets includes a measure
reflecting the maximum level of exposure to individuals. The evaluation
of exposed individuals is proposed to include individuals living,
attending school or day care, or working in a regularly occupied
structure. The reasonably maximally exposed individuals are those
individuals in the eligible target population that are expected to be
exposed to the highest concentration of the hazardous substance in
question for a significant time. See section V.C.9 of the preamble to
the proposed 1988 HRS (53 FR 51978, December 28, 1988) for supplemental
information.
EPA is proposing to retain the basic scoring approach used
throughout the current HRS for evaluating the exposed individual
factor. As is consistent with all pathways, a value of 50 points is
assigned if there is any individual exposed to Level I concentrations
or 45 points if there is any individual exposed to Level II
concentrations. If there are no individuals exposed to Level I or Level
II concentrations, but at least one individual is living, attending
school or day care, or working in a regularly occupied structure within
an ASC, EPA proposes to assign a value of 20. See section 2.5 of the
current HRS for supplemental information as to how EPA addresses
exposed individuals within the HRS structure.
c. Population--See Section 5.2.1.3.2 of the Proposed HRS Addition
The population factor is evaluated using media-specific, health-
based benchmarks as discussed above. EPA proposes the population factor
include all populations qualifying as exposed individuals, including
residents, students, workers and those attending day care. However,
workers are weighted slightly differently than other exposed
individuals to reflect that a worker's exposure is limited to the time
present in a workplace. Additionally, as workers may be employed on a
full-time or part-time basis, the number of workers present in a
structure or subunit is proposed to be adjusted by an appropriate
factor reflecting this difference in exposure durations. EPA is
proposing to retain the current scoring methodology for weighting
populations used throughout the HRS, with actual exposure more heavily
weighted than those potentially exposed. The proposed subsurface
intrusion component will evaluate populations based on the number of
individuals located within an identified AOE (i.e., those populations
exposed to Level I and Level II concentrations) and the number of
individuals located within an ASC (i.e., potential contamination as
determined based on subsurface sampling), which is further subdivided
as described in subsection ii below.
i. Weighting of Targets in the Area of Observed Exposure (AOE)--See
Sections 5.2.1.3.2.1 and 5.2.1.3.2.2 of the Proposed HRS Addition
EPA is proposing to establish an AOE based on documented
contamination meeting observed exposure criteria (either by direct
observation or chemical analysis). Consistent with the weighting of
populations throughout the HRS (see section 2.5 of the current HRS),
the proposed subsurface intrusion component will weight targets subject
to Level I contaminant concentrations by a factor of 10 and weight
targets subject to Level II contaminant concentrations by a factor of
1. As noted previously, eligible populations also include individuals
working in regularly occupied structures. However, the number of
workers present in a regularly occupied structure will be adjusted to
reflect that their exposure is limited to the time they are in a
workplace. Therefore, the number of full- and part-time workers in a
structure or subunit will be identified and divided by an appropriate
factor prior to being summed with the number of other individuals
present. If information is unavailable to classify a worker as full- or
part-time, that worker will be evaluated as full-time.
For example, if a single residence occupied by a family of four was
observed to be exposed to hazardous substance concentrations above a
media-specific, health-based benchmark, the number of residents would
be multiplied by 10 for a factor value of 40. However, if that same
family was exposed to a hazardous substance and the hazardous substance
concentration was below the applicable benchmark but met the criteria
for observed exposure, the number of residents would be multiplied by 1
for a factor value of 4. To ensure the entire population within an AOE
is included in the HRS evaluation, both Level I and Level II factor
values are counted and summed together.
Within the AOE, EPA is proposing to consider as actually
contaminated those populations in regularly occupied structures for
which observed exposures have not been established but the structures
are surrounded by regularly occupied structures in which observed
exposures have been identified, unless evidence indicates otherwise.
This action is proposed because it is considered likely that if these
structures were sampled during the correct conditions, observed
exposures would be identified at levels similar to those in surrounding
structures. Targets inferred to be exposed to this contamination will
be weighted as Level II as there are no actual sample results to
compare against benchmarks. However, EPA has included an exception to
allow for situations where site-specific conditions clearly document
that there may be no observed exposures in these structures. The rule
language states that targets can be inferred to have observed exposures
in these situations ``unless available information indicates
otherwise''. This concept of inferred exposure is also included in the
existing soil exposure pathway and in the air migration pathway.
In the case of multi-story/multi-subunit structures, all regularly
occupied subunits on a level with an observed exposure and all levels
below are considered to be within an AOE, unless available information
indicates otherwise. For multi-story/multi-subunit structures located
within an AOE, but where an observed exposure has not been documented,
only those
[[Page 10394]]
regularly occupied spaces on the lowest level are considered to be
within an AOE, unless available information indicates otherwise. (See
sections 5.0.1 and 6.3 of the current HRS.)
ii. Weighting of Targets in the Area of Subsurface Contamination
(ASC)--See Section 5.2.1.3.2.3 of the Proposed HRS Addition
EPA is proposing to establish an ASC as defined by documented
ground water, subslab, soil, semi-enclosed or enclosed crawl space, or
soil gas contamination meeting observed release criteria. These areas
are included in the subsurface intrusion component due to the potential
that limited sampling conducted during a site inspection may not
identify that subsurface intrusion is occurring because of the high
temporal and spatial variability associated with detecting subsurface
intrusion. Temporal and spatial differences can significantly impact
the rate at which volatile hazardous substances enter a structure.
However, when an ASC has been defined, that area represents a location
where subsurface hazardous substances have the potential to intrude
into a structure. EPA is limited in its extent of preliminary screening
activities, and a single indoor air sampling event is unlikely to
identify the full threat posed by subsurface intrusion.
As is consistent with the 1990 HRS, EPA is proposing to weight
these potentially exposed targets at a value less than those targets
that have been identified to be actually exposed. Due to the
variability in subsurface intrusion rates, the potential weighting
factor values for targets within an ASC range from 0.1 to 0.9 and
depend on where the subsurface contamination has been found. Using
EPA's vapor intrusion attenuation factors published in 2012 and basic
subsurface contaminant transport concepts, EPA developed a relatively
proportional weighting for potential targets based on the sampling
media being considered. This range of weighting factors represents the
proportional probability of a target to be exposed as a result of
contaminant intrusion from the subsurface in a variety of likely
sampling scenarios. The potential target weighting factors presented in
the proposed addition do not directly correspond to attenuation factors
in themselves. Instead, the relative weighting between these values is
based on the published attenuation factors. These weighting factors are
presented in this manner to project that contaminants found in a crawl
space sample, for example, are more likely to attenuate less before
entering into an overlying structure, and thus more likely to pose a
threat, as opposed to those found in a shallow ground water sample.
EPA is proposing that the weighting of potential targets also
reflect the distance to or the depth at which contamination is found.
For any contamination found at a horizontal or vertical distance of
five feet or less from a regularly occupied structure's foundation, EPA
is proposing to assign a minimum weighting factor of 0.4 regardless of
the sample medium. Similarly, EPA is proposing to assign a weighing
factor of 0.1 to any contamination found or inferred at depths greater
than 30 feet regardless of sampling medium. These minimum weighting
values are in response to an analysis of the data used in deriving
published attenuation values. The attenuation values were published
based on real-world sampling data collected from numerous sites across
the United States. The majority of sampling data collected as part of
this effort came from sites where contamination was generally found at
depths less than 30 feet. Therefore, EPA considers the attenuation
factors and relative weightings between them to only be appropriate for
shallower depths. The minimum value for the upper five feet allows
consideration of sites where contamination is found at extremely
shallow depths and therefore has a minimal vertical distance to travel
before intruding into a regularly occupied structure.
In the case of multi-story/multi-subunit structures, all regularly
occupied subunits on a level above one where an observed exposure has
been documented or inferred, or where a gaseous indoor air sample
meeting observed release criteria is present, are considered to be
located within an ASC, unless available information indicates
otherwise. For multi-story/multi-subunit structures located only within
an ASC, only those regularly occupied subunits within the lowest level
are considered in an HRS evaluation.
EPA proposes eligible populations include individuals living in, or
attending school or day care in the structure, and workers in regularly
occupied structures. The number of workers is adjusted to reflect that
their exposure is limited to the time they are in a workplace.
Therefore, the number of full- and part-time workers in a structure or
subunit will be divided by an appropriate factor prior to being summed
with the number of other individuals present. If information is
unavailable to classify a worker as full- or part-time, that worker
will be evaluated as full-time.
The proposed weighting factors for exposed individuals in any
structure within an ASC are based on the probability of contamination
entering into occupied structures from the subsurface. The weighting
factors reflect depth to contamination, sample type, and media. The
magnitude of the factor is also based on attenuation factors from
current scientific literature including EPA's 2012 vapor intrusion
attenuation factors publication. Additional information regarding this
analysis is presented in section 6.0 of the Proposal TSD.
d. Resources--See Section 5.2.1.3.3 of the Proposed HRS Addition
The resources target factor is evaluated in all pathways under the
current HRS. A factor value of five is assigned if at least one
resource is present and a factor value of zero if no resource is
present. Eligible resources are pathway-, component-, or threat-
specific. These resources represent uses of a contaminated medium or
area where exposures occur and are not covered by the other identified
targets. For example, resources within the air migration pathway
include commercial agriculture or silviculture and major/designated
recreation areas. The resident population threat also includes
commercial livestock production or grazing. See section III.I of the
preamble to the current HRS (55 FR 51549, December 14, 1990) for
supplemental information.
Because subsurface intrusion is limited to indoor spaces, EPA is
proposing to include regularly occupied structures that are located
within a defined AOE or ASC (as previously discussed in section VI.B.2
of this preamble) and in which populations, not including those already
counted as exposed individuals, may be exposed to contamination due to
subsurface intrusion. For example, libraries, recreational facilities,
and religious or tribal structures used by individuals, may qualify as
eligible resources.
e. Calculation of the Targets Factor Category Value--See Section
5.2.1.3.4 of the Proposed HRS Addition
As is done throughout the HRS, EPA is proposing to sum all of the
target factor values together to establish a target factor category
value in calculating the proposed subsurface intrusion component score.
Unlike the likelihood of exposure and waste characteristics factor
category values in all HRS pathways, which are subject to maximum
values, the target factor
[[Page 10395]]
category is not limited in the current HRS. This is to ensure that all
individuals, populations, resources, and sensitive environments are
included; thereby, representing the full relative risk associated with
the identified threat. It is also consistent with the direction of
CERCLA section 105 to amend the HRS ``to the maximum extent feasible''
to address ``the relative degree of risk to human health and the
environment'' by putting the emphasis on the number of receptors
exposed to contamination.
6. Calculation and Incorporation of the SsI Component Score Into the
HRS Site Score
The following subsections summarize the calculation of the
subsurface intrusion component score, how the component score is then
used in the calculation of the soil exposure and subsurface intrusion
pathway score, and how, in turn, the pathway score is subsequently
incorporated into the HRS site score.
a. Calculation of the SsI Component Score--See Section 5.2.2 of the
Proposed HRS Addition
EPA is proposing to calculate the subsurface intrusion component
score using the same algorithm as in other components and pathways of
the HRS. (See section 2.2 of the 1988 Revised HRS TSD.) This involves
multiplying the likelihood of exposure factor category value times the
waste characteristics factor category value times the targets factor
category value and dividing that value by a weighting factor so that it
has equal magnitude to other component scores (subject to a maximum
value). The values are multiplied to reflect that it is the product of
these values that represents a relative risk level.
In a relative risk (or in a site-specific risk) assessment, the use
of the product of the factor category values is considered appropriate
because the magnitude of each of the factor category values reflects
the probability of exposure occurring: Likelihood of releases reflects
the probability of exposure actually occurring, waste characteristics
reflects the probable quantity and duration of the exposure, and
targets reflect the probable number of receptors at risk. Thus, since
each factor category value reflects a probability in a series of
events, the overall probability associated with the series is the
product of the individual probabilities. For example, if any factor
category value is zero, such as when there are no targets exposed or
potentially exposed to subsurface intrusion, the component score is
zero, consistent with there being no risk due to subsurface intrusion.
b. Incorporation of the SsI Component Score Into the Soil Exposure and
Subsurface Intrusion Pathway Score--See Section 5.3 of the Proposed HRS
Addition
The score for this restructured pathway is proposed to be a
combination of two component scores. The subsurface intrusion component
score is added to the soil exposure component score (subject to a
maximum value) to determine the pathway score. The two component scores
are proposed to be additive because the populations may be subjected to
exposures separately via both routes: The soil exposure component
reflects exposures to people when outside a structure and focuses on
ingestion, while the subsurface intrusion component reflects exposures
to people when inside a structure and focuses on inhalation. Hence, the
addition of the two component scores reflects the cumulative potential
risk and is not double counting the relative risk.
In addition, a pathway score can be assigned without scoring both
the soil exposure and subsurface intrusion components using this
approach. It is possible for a site to have only one component
evaluated and still reach the same pathway score as under the current
HRS. It should be observed that because the scoring of the soil
exposure component is not being altered, the soil exposure component
would contribute the same score to the overall site score as it would
if the subsurface intrusion component is not added.
c. Incorporation of the Soil Exposure and Subsurface Intrusion Pathway
Score Into a Site Score--See Section 2.1.1 of the Proposed HRS Addition
EPA is not proposing any changes to the methodology used to assign
an overall site score due to the addition of the subsurface intrusion
component to the soil exposure pathway and renaming that pathway the
soil exposure and subsurface intrusion pathway. The overall site score
remains a function of four pathway scores and the same weighting is
given to each pathway score as in the current HRS. See section 2.2 of
the 1988 Revised HRS TSD for supplemental information on why the
existing methodology was chosen.
7. Example Site Scoring Scenarios
To evaluate the proposed subsurface intrusion component and factor
category weighting, EPA developed three conceptual site scenarios: One
that would not qualify for the NPL (score below 28.50); one that would
qualify marginally for the NPL (score of about 28.50); and one that
should clearly qualify for the NPL (site score considerably above
28.50).
The first scenario consists of a ground water plume contaminated
with a hazardous substance with moderate toxicity that underlies
approximately 3 acres of a residential neighborhood comprised of
single-family detached homes. Indoor air samples have been collected
from inside two homes and have reported hazardous substance
concentrations above background, but below the applicable benchmarks.
Additionally, several other occupied structures were sampled for indoor
air and subslab contaminant concentrations; however, no other
detections of hazardous substances were observed. This site would not
qualify for the NPL based on available information (i.e., score below
28.50).
The second scenario also consists of a ground water plume
contaminated with a hazardous substance with moderate toxicity as in
the first scenario, but it has a considerably larger plume and more
targets. The ground water plume underlies approximately 20 acres of a
residential neighborhood and commercial area comprised of single-family
detached homes, a daycare facility, and a single-story office building.
Indoor air samples collected inside 19 homes, the daycare facility, and
office building have hazardous substance concentrations above the
applicable benchmark. Indoor air samples in 5 homes, the daycare
facility with approximately 25 children enrolled and 6 full-time and 2
part-time workers, and the office building with 18 full-time workers
have hazardous substance concentrations above background, but below the
applicable benchmark. The homes and daycare facility were checked for
indoor sources of hazardous substances prior to sampling and such
sources were removed if found. This site would likely qualify for the
NPL based on available information (i.e., score of about 28.50).
The third scenario consists of a ground water plume contaminated
with a highly toxic hazardous substance and a larger number of targets
than the second scenario. The plume underlies approximately 25 acres of
a residential neighborhood and hazardous substance concentrations above
a benchmark were detected in indoor air samples from 25 homes and one
daycare with approximately 25 children enrolled and 5 full-time
workers. Hazardous substance concentrations above background but below
benchmarks were
[[Page 10396]]
detected within 15 homes. The homes and daycare facility were checked
for indoor sources of hazardous substances prior to sampling and such
sources were removed if found. Based on available information, this
site would qualify for the NPL and would likely achieve the maximum HRS
score for a single component and pathway (i.e., 50.00).
Further evaluation of the varying factor values and resulting HRS
site scores, along with further discussion of these three scenarios is
presented in section 8.1.c of the Proposal TSD.
VII. Summary of Proposed Updates to the HRS (Sections 2, 5, 6, and 7)
A. Addition of an SsI Component to the HRS (Sections 2, 5, and 7)
1. Chapter 5
The proposed addition of a subsurface intrusion component is
proposed to be added to the existing Soil Exposure pathway as section
5.2 in Chapter 5 to the current HRS. The new pathway name is proposed
as the Soil Exposure and Subsurface Intrusion Pathway. The existing
method for evaluating the soil exposure threat will remain unchanged.
2. Chapter 2
Evaluations Common to All Pathways is proposed to be updated to
reflect the addition of the subsurface intrusion component to the
existing soil exposure pathway. The evaluations for the current four
pathways remain unchanged and a comparable evaluation will be added for
the subsurface intrusion component.
3. Chapter 7
Sites Containing Radioactive Substances currently reflects how
radioactive substances are evaluated in the context of the four current
HRS pathways. Updates will be made to reflect how radioactive
substances are evaluated using the proposed subsurface intrusion
component.
B. Terminology Updates Affecting Specific Sections of the HRS (Sections
2, 5 and 6)
During the development of this proposed addition to the HRS, the
agency determined that the following terms should be updated to reflect
current terminology and procedures used by EPA in performing risk
assessments.
1. Ambient Water Quality Criteria
Ambient Water Quality Criteria (AWQC) are now identified also as
National Recommended Water Quality Criteria (NRWQC). In addition, the
acute AWQC are now identified as the Criterion Maximum Concentration
(CMC) and the chronic criteria are referred to as the Criterion
Continuous Concentration (CCC). (See section 1.1 of the proposed HRS
addition.) These criteria are used to determine the level of threat to
environmental targets.
2. Reference Concentrations
For inhalation exposures, EPA is adopting the use of Reference
Concentrations (RfCs) instead of Reference Doses (RfDs) when
determining non-cancer related risk levels. RfCs are used in
determining the level of threat to human targets due to possible
inhalation and when determining the toxicity of the substances.
3. Cancer Unit Risk
For inhalation exposures, EPA is adopting the use of Inhalation
Unit Risk (IUR) instead of cancer slope factors in determining cancer-
related risk levels. IURs are used in determining the level of threat
to human targets due to possible inhalation and when determining the
toxicity of the substances.
4. Weight-of-Evidence Groupings
The 2005 EPA weight-of-evidence groupings supporting the
designation of a substance as a human carcinogen have been incorporated
into the HRS algorithm for determining the toxicity factor value. (The
former EPA weight-of-evidence categories included as part of the 1990
HRS have been retained as EPA has not yet completed assigning all
substances to the revised categories and are doing so at the time the
EPA substance literature reviews are updated.)
VIII. Statutory and Executive Order Reviews
Additional information about these statutes and Executive Orders
can be found at http://www2.epa.gov/laws-regulations/laws-and-executive-orders.
A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 13563: Improving Regulation and Regulatory Review
This action is a significant regulatory action that was submitted
to the Office of Management and Budget (OMB) for review. This action
may raise novel legal or policy issues arising out of legal mandates,
the President's priorities, or the principles set forth in the EO. Any
changes made in response to OMB recommendations have been documented in
the docket.
EPA prepared an analysis of the potential costs and benefits
associated with this action. This analysis, Addition of a Subsurface
Intrusion (SsI) Component to the Hazard Ranking System (HRS):
Regulatory Impact Analysis is available in the docket for this action.
B. Paperwork Reduction Act (PRA)
This action does not impose any new information collection burden
under the PRA. OMB has previously approved the information collection
activities contained in the existing regulations and has assigned OMB
control number 2050-0095.
This proposed regulatory change will only affect how EPA and
organizations performing work on behalf of EPA (state or tribal
partners) conduct site assessments and HRS scoring at sites where
certain environmental conditions exist. This proposed regulatory change
will result in data collection at these types of sites to allow
evaluation under the HRS. EPA expects that the total number of site
assessments performed and the number of sites added to the NPL per year
will not increase, but rather expects that there will be a realignment
and reprioritization of its internal resources and state cooperative
agreement funding.
C. Regulatory Flexibility Act (RFA)
I certify that this action will not have a significant economic
impact on a substantial number of small entities under the RFA. This
action will not impose any requirements on small entities. This
proposed regulatory change enables the HRS evaluation to directly
consider human exposure to hazardous substances that enter building
structures through subsurface intrusion. This addition to the HRS would
not impose direct impacts on any other entities. For additional
discussion on this subject see section 4.9 of the Regulatory Impact
Analysis (see the docket for this action).
D. Unfunded Mandates Reform Act (UMRA)
This action does not contain any unfunded mandate as described in
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect
small governments. The action imposes no enforceable duty on any state,
local, or tribal governments or the private sector.
E. Executive Order 13132: Federalism
This action does not have federalism implications. It will not have
substantial direct effects on the states, on the relationship between
the national government and the states, or on the distribution of power
and
[[Page 10397]]
responsibilities among the various levels of government.
F. Executive Order 13175: Consultation and Coordination With Indian
Tribal Governments
This action does not have tribal implications, as specified in
Executive Order 13175. EPA's evaluation of a site using the HRS does
not impose any costs on a tribe (except those already in a cooperative
agreement relationship with EPA). Thus, Executive Order 13175 does not
apply to this action.
Although Executive Order 13175 does not apply to this action, EPA
consulted with tribal officials through meetings and correspondence,
including a letter sent to all federally recognized tribes asking for
comment on the ``Notice of Opportunity for Public Input'' that was
published in the Federal Register on January 31, 2011 (76 FR 5370), and
public listening sessions regarding the decision to proceed with the
development of this action. All tribal comments indicated support for
this action.
EPA specifically solicits additional comment on this proposed
action from tribal officials.
G. Executive Order 13045: Protection of Children From Environmental
Health Risks and Safety Risks
EPA interprets Executive Order 13045 as applying only to those
regulatory actions that concern environmental health or safety risks
that EPA has reason to believe may disproportionately affect children,
per the definition of ``covered regulatory action'' in section 2-202 of
the Executive Order. This action is not subject to Executive Order
13045 because it does not concern an environmental health risk or
safety risk.
H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution or Use
This action is not a ``significant energy action'' because it is
not likely to have a significant adverse effect on the supply,
distribution, or use of energy. The site assessment activities affected
by this rule are limited in scope and number and rely on existing
energy distribution systems. Further, we have concluded that this
proposed rule would not significantly expand the energy demand for site
assessments, and would not require an entity to conduct any action that
would require significant energy use, that would significantly affect
energy supply, distribution, or usage. Thus, Executive Order 13211 does
not apply to this action.
I. National Technology Transfer and Advancement Act
This rulemaking does not involve technical standards.
J. Executive Order 12898: Federal Actions To Address Environmental
Justice in Minority Populations and Low-Income Populations
EPA believes the human health or environmental risk addressed by
this action will not have potential disproportionately high and adverse
human health or environmental effects on minority, low-income or
indigenous populations. The results of this evaluation are contained in
section III.C.4 of this preamble and section 4.3 (and all subsections)
and Appendix C of the Regulatory Impact Analysis for this proposed
rulemaking. A copy of the Addition of a Subsurface Intrusion (SsI)
Component to the Hazard Ranking System (HRS): Regulatory Impact
Analysis is available in the docket for this action.
K. Executive Order 12580: Superfund Implementation
Executive Order 12580, section 1(d), states that revisions to the
NCP shall be made in consultation with members of the National Response
Team (NRT) prior to publication for notice and comment. Revisions shall
also be made in consultation with the Director of the Federal Emergency
Management Agency (FEMA) and the Nuclear Regulatory Commission (NRC) to
avoid inconsistent or duplicative requirements in the emergency
planning responsibilities of those agencies. Executive Order 12580
delegates responsibility for revision of the NCP to EPA.
The agency has complied with Executive Order 12580 to the extent
that it is related to the addition of a new component to the HRS,
through consultation with members of the NRT.
List of Subjects in 40 CFR Part 300
Environmental protection, Air pollution control, Chemicals,
Hazardous substances, Hazardous waste, Intergovernmental relations,
Natural resources, Oil pollution, Penalties, Reporting and
recordkeeping requirements, Superfund, Water pollution control, Water
supply.
Dated: February 3, 2016.
Gina McCarthy,
Administrator.
For the reasons set out in the preamble, Title 40, Chapter 1 of the
Code of Federal Regulations is proposed to be amended as follows:
PART 300--NATIONAL OIL AND HAZARDOUS SUBSTANCES POLLUTION
CONTINGENCY PLAN
0
1. The authority citation for part 300 continues to read as follows:
Authority: 33 U.S.C. 1251 et seq.
0
2. Amend Appendix A to Part 300:
0
a. In section 1.1 by:
0
i. Amending by removing the definition heading ``Ambient Water Quality
Criteria (AWQC) and adding ``Ambient Water Quality Criteria (AWQC)/
National Recommended Water Quality Criteria'', in its place; and
removing the text ``maximum acute or chronic toxicity'' and adding
``maximum acute (Criteria Maximum Concentration or CMC) or chronic
(Criterion Continuous Concentration or CCC) toxicity.'' in its place;
0
ii. Adding in alphabetical order the definitions ``Channelized flow''
and ``Crawl space'';
0
iii. Revising the definitions ``Distance weight'' and ``Half-life'';
0
iv. Amending the definition ``HRS pathway'' by removing the word
``soil,'' and adding ``soil exposure and subsurface intrusion,'' in its
place;
0
v. Adding in alphabetical order the definitions ``Indoor air'',
``Inhalation Unit Risk (IUR)'', ``Occupied structures'', ``Preferential
subsurface intrusion pathways''; and ``Reference concentration (RfC)'';
0
vi. Revising the definition ``Reference dose (RfD)''; ``Screening
concentration'', and ``Slope factor (also referred to as cancer potency
factor)'';
0
vii. Adding in alphabetical order the definitions ``Soil gas'', ``Soil
porosity''; ``Subslab'', ``Subsurface Intrusion'', ``Surficial ground
water'', ``Unit Risk'', and ``Unsaturated Zone''; and
0
viii. Revising the introductory text of the definition ``Weight-of-
evidence''.
0
b. Revising section 2.0 to include sections 2.0 through 2.5.2;
0
c. Revising section 5.0 to include sections 5.0 through 5.3;
0
d. In section 6.0 by revising Table 6-14, entitled ``Health-Based
Benchmarks for Hazardous Substances in Air''; and
0
e. In section 7.0 by:
0
i. Revising the table entitled ``Table 7-1. HRS Factors Evaluated
Differently For Radionuclides'';
0
ii. Under Table 7-1, the second undesignated paragraph, revising the
third sentence ;
0
iii. Revising sections 7.1, 7.1.1, and 7.1.2; 7.2.3; 7.2.4; 7.2.5.1,
7.2.5.1.1 through 7.2.5.1.3; 7.2.5.2; 7.2.5.3; 7.3, 7.3.1, and 7.3.2;
and
0
iv. Adding section 7.3.3.
The revisions and additions read as follows:
[[Page 10398]]
Appendix A of Part 300--Hazard Ranking System
* * * * *
1.1 Definitions
* * * * *
Channelized flow: Natural geological or manmade features such as
karst, fractures, lava tubes, and utility conduits (e.g., sewer lines),
which allow ground water and/or soil gas to move through the subsurface
environment more easily.
* * * * *
Crawl space: The enclosed or semi-enclosed area between a regularly
occupied structure's foundation (e.g., pier and beam construction) and
the ground surface. Crawl space samples are collected to determine the
concentration of hazardous substances in the air beneath a regularly
occupied structure.
* * * * *
Distance weight: Parameter in the HRS air migration pathway, ground
water migration pathway, and the soil exposure component of the soil
exposure and subsurface intrusion pathway that reduces the point value
assigned to targets as their distance increases from the site.
[unitless].
* * * * *
Half-life: Length of time required for an initial concentration of
a substance to be halved as a result of loss through decay. The HRS
considers five decay processes for determining surface water
persistence: Biodegradation, hydrolysis, photolysis, radioactive decay,
and volatilization. The HRS considers two decay processes for
determining subsurface intrusion degradation: Biodegradation and
hydrolysis.
* * * * *
Indoor air: The air present within a structure.
Inhalation Unit Risk (IUR): The upper-bound excess lifetime cancer
risk estimated to result from continuous exposure to an agent (i.e.,
hazardous substance) at a concentration of 1[micro]g/m3 in air.
* * * * *
Occupied structures: Structures with enclosed air space, either
where people are present on a regular basis or that were previously
occupied but vacated due to a site-related hazardous substance(s).
* * * * *
Preferential subsurface intrusion pathways: Subsurface features
such as animal burrows, cracks in walls, spaces around utility lines or
drains through which a hazardous substance moves more easily into a
regularly occupied structure.
* * * * *
Reference concentration (RfC): An estimate of a continuous
inhalation exposure to the human population that is likely to be
without an appreciable risk of deleterious effects during a lifetime.
Reference dose (RfD): An estimate of a daily oral exposure to the
human population that is likely to be without an appreciable risk of
deleterious effects during a lifetime.
* * * * *
Screening concentration: Media-specific benchmark concentration for
a hazardous substance that is used in the HRS for comparison with the
concentration of that hazardous substance in a sample from that media.
The screening concentration for a specific hazardous substance
corresponds to its reference concentration for inhalation exposures or
reference dose for oral exposures, as appropriate, and, if the
substance is a human carcinogen with either a weight-of-evidence
classification of A, B, or C, or a weight-of-evidence classification of
carcinogenic to humans, likely to be carcinogenic to humans or
suggestive evidence of carcinogenic potential, to that concentration
that corresponds to its 10 -\6\ individual lifetime excess
cancer risk for inhalation exposures or for oral exposures, as
appropriate.
* * * * *
Slope factor (also referred to as cancer potency factor): Estimate
of the probability of response (for example, cancer) per unit intake of
a substance over a lifetime. The slope factor is typically used to
estimate upper-bound probability of an individual developing cancer as
a result of exposure to a particular level of a human carcinogen with
either a weight-of-evidence classification of A, B, or C, or a weight-
of-evidence classification of carcinogenic to humans, likely to be
carcinogenic to humans or having suggestive evidence of carcinogenic
potential. [(mg/kg-day) -\1\ for non-radioactive substances
and (pCi) -\1\ for radioactive substances].
Soil gas: The gaseous elements and compounds in the small spaces
between particles of soil.
Soil porosity: The degree to which the total volume of soil is
permeated with pores or cavities through which fluids (including air or
gas) can move. It is typically calculated as the ratio of the pore
spaces within the soil to the overall volume of the soil.
* * * * *
Subslab: The area immediately beneath a regularly occupied
structure with a basement foundation or a slab-on-grade foundation.
Subslab samples are collected to determine the concentration of
hazardous substances in the soil gas beneath a home or building.
Subsurface Intrusion: The migration of hazardous substances from
the unsaturated zone and/or the surficial ground water into overlying
structures.
Surficial ground water: The uppermost saturated zone, typically
unconfined.
* * * * *
Unit Risk: The upper-bound excess lifetime cancer risk estimated to
result from continuous exposure to an agent (i.e., hazardous substance)
at a concentration of 1 [micro]g/L in water, or 1 [micro]g/m\3\ in air.
Unsaturated Zone: The portion of subsurface between the land
surface and the zone of saturation. It extends from the ground surface
to the surficial water table (excluding localized or perched water).
* * * * *
Weight-of-evidence: EPA classification system for characterizing
the evidence supporting the designation of a substance as a human
carcinogen. The EPA weight-of-evidence groupings, depending on the date
EPA updated the profile, include either:
* * * * *
2.0 Evaluations Common to Multiple Pathways
2.1 Overview. The HRS site score (S) is the result of an evaluation
of four pathways:
Ground Water Migration (Sgw).
Surface Water Migration (Ssw).
Soil Exposure and Subsurface Intrusion
(Ssessi).
Air Migration (Sa).
The ground water and air migration pathways use single threat
evaluations, while the surface water migration and soil exposure and
subsurface intrusion pathways use multiple threat evaluations. Three
threats are evaluated for the surface water migration pathway: Drinking
water, human food chain, and environmental. These threats are evaluated
for two separate migration components--overland/flood migration and
ground water to surface water migration. Two components are evaluated
for the soil exposure and subsurface intrusion pathway: Soil exposure
and subsurface intrusion. The soil exposure component evaluates two
threats: Resident population and nearby population, and the subsurface
[[Page 10399]]
intrusion component is a single threat evaluation.
The HRS is structured to provide a parallel evaluation for each of
these pathways, components and threats. This section focuses on these
parallel evaluations, starting with the calculation of the HRS site
score and the individual pathway scores.
2.1.1 Calculation of HRS site score. Scores are first calculated
for the individual pathways as specified in sections 2 through 7 and
then are combined for the site using the following root-mean-square
equation to determine the overall HRS site score, which ranges from 0
to 100:
[GRAPHIC] [TIFF OMITTED] TP29FE16.029
2.1.2 Calculation of pathway score. Table 2-1, which is based on
the air migration pathway, illustrates the basic parameters used to
calculate a pathway score. As Table 2-1 shows, each pathway (component
or threat) score is the product of three ``factor categories'':
Likelihood of release, waste characteristics, and targets. (The soil
exposure and subsurface intrusion pathway uses likelihood of exposure
rather than likelihood of release.) Each of the three factor categories
contains a set of factors that are assigned numerical values and
combined as specified in sections 2 through 7. The factor values are
rounded to the nearest integer, except where otherwise noted.
2.1.3 Common evaluations. Evaluations common to all four HRS
pathways include:
Characterizing sources.
-- Identifying sources (and, for the soil exposure and subsurface
intrusion pathway, areas of observed contamination, areas of observed
exposure and/or areas of subsurface contamination (see sections 5.1.0
and 5.2.0)).
-- Identifying hazardous substances associated with each source (or
area of observed contamination, or observed exposure, or subsurface
contamination).
-- Identifying hazardous substances available to a pathway.
Table 2-1--Sample Pathway Scoresheet
------------------------------------------------------------------------
Factor category Maximum value Value assigned
------------------------------------------------------------------------
Likelihood of Release
------------------------------------------------------------------------
1. Observed Release............... 550
2. Potential to Release........... 500
3. Likelihood of Release (higher 550
of lines 1 and 2)................
------------------------------------------------------------------------
Waste Characteristics
------------------------------------------------------------------------
4. Toxicity/Mobility.............. (\a\)
5. Hazardous Waste Quantity....... (\a\)
6. Waste Characteristics.......... 100
------------------------------------------------------------------------
Targets
------------------------------------------------------------------------
7. Nearest Individual: .................
7a. Level I................... 50
7b. Level II.................. 45
7c. Potential Contamination... 20
7d. Nearest Individual (higher 50
of lines 7a, 7b, or 7c)......
8. Population..................... (\b\)
8a. Level I................... (\b\)
8b. Level II.................. (\b\)
8c. Potential Contamination... (\b\)
8d. Total Population (lines
8a+8b+8c).
9. Resources...................... 5
10. Sensitive Environments........ (\b\)
10a. Actual Contamination..... (\b\)
10b. Potential Environments... (\b\)
10c. Sensitive Environments (\b\)
(lines 10a+10b)..............
11. Targets (lines 7d+8d+9+10c)... (\b\)
12. Pathway Score is the product
of Likelihood of Release, Waste
Characteristics, and Targets,
divided by 82,500. Pathway scores
are limited to a maximum of 100
points...........................
------------------------------------------------------------------------
\a\ Maximum value applies to waste characteristics category. The product
of lines 4 and 5 is used in Table 2-7 to derive the value for the
waste characteristics factor category.
\b\ There is no limit to the human population or sensitive environments
factor values. However, the pathway score based solely on sensitive
environments is limited to a maximum of 60 points.
Scoring likelihood of release (or likelihood of exposure)
factor category.
--Scoring observed release (or observed exposure or observed
contamination).
--Scoring potential to release when there is no observed release.
Scoring waste characteristics factor category.
--Evaluating toxicity.
[ssquf] Combining toxicity with mobility, persistence, degradation
and/or bioaccumulation (or ecosystem bioaccumulation) potential, as
appropriate to the pathway (component or threat).
[ssquf] Evaluating hazardous waste quantity.
--Combining hazardous waste quantity with the other waste
characteristics factors.
[ssquf] Determining waste characteristics factor category value.
Scoring targets factor category.
[[Page 10400]]
--Determining level of contamination for targets.
These evaluations are essentially identical for the three migration
pathways (ground water, surface water, and air). However, the
evaluations differ in certain respects for the soil exposure and
subsurface intrusion pathway.
Section 7 specifies modifications that apply to each pathway when
evaluating sites containing radioactive substances.
Section 2 focuses on evaluations common at the pathway, component
and threat levels. Note that for the ground water and surface water
migration pathways, separate scores are calculated for each aquifer
(see section 3.0) and each watershed (see sections 4.1.1.3 and 4.2.1.5)
when determining the pathway scores for a site. Although the
evaluations in section 2 do not vary when different aquifers or
watersheds are scored at a site, the specific factor values (for
example, observed release, hazardous waste quantity, toxicity/mobility)
that result from these evaluations can vary by aquifer and by watershed
at the site. This can occur through differences both in the specific
sources and targets eligible to be evaluated for each aquifer and
watershed and in whether observed releases can be established for each
aquifer and watershed. Such differences in scoring at the aquifer and
watershed level are addressed in sections 3 and 4, not section 2.
2.2 Characterize sources. Source characterization includes
identification of the following:
Sources (and areas of observed contamination, areas of
observed exposure or areas of subsurface contamination) at the site.
Hazardous substances associated with these sources (or
areas of observed contamination, areas of observed exposure or areas of
subsurface contamination).
Pathways potentially threatened by these hazardous
substances.
Table 2-2 presents a sample worksheet for source characterization.
2.2.1 Identify sources. For the three migration pathways, identify
the sources at the site that contain hazardous substances. Identify the
migration pathway(s) to which each source applies. For the soil
exposure and subsurface intrusion pathway, identify areas of observed
contamination, areas of observed exposure, and/or areas of subsurface
contamination at the site (see sections 5.1.0 and 5.2.0).
Table 2-2--Sample Source Characterization Worksheet
Source:__
A. Source dimensions and hazardous waste quantity.
Hazardous constituent quantity:__
Hazardous wastestream quantity:__
Volume:__
Area:__
Area of observed contamination:__
Area of observed exposure:__
Area of subsurface contamination:__
B. Hazardous substances associated with the source.
[[Page 10401]]
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Available to pathway
--------------------------------------------------------------------------------------------------------------------------------------
Air Surface water (SW) Soil exposure/subsurface intrusion (SESSI)
------------------------------- -----------------------------------------------------------------------------------------
Hazardous substance Soil exposure Subsurface intrusion
Ground water -------------------------------------------------------------
Gas Particulate (GW) Overland/ GW to SW Area of
flood Resident Nearby observed Area of subsurface
exposure contamination
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
............ ............... ............ ............ ............ ............ ............ ............ ..................
............ ............... ............ ............ ............ ............ ............ ............ ..................
............ ............... ............ ............ ............ ............ ............ ............ ..................
............ ............... ............ ............ ............ ............ ............ ............ ..................
............ ............... ............ ............ ............ ............ ............ ............ ..................
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
[[Page 10402]]
2.2.2 Identify hazardous substances associated with a source. For
each of the three migration pathways, consider those hazardous
substances documented in a source (for example, by sampling, labels,
manifests, oral or written statements) to be associated with that
source when evaluating each pathway. In some instances, a hazardous
substance can be documented as being present at a site (for example, by
labels, manifests, oral or written statements), but the specific
source(s) containing that hazardous substance cannot be documented. For
the three migration pathways, in those instances when the specific
source(s) cannot be documented for a hazardous substance, consider the
hazardous substance to be present in each source at the site, except
sources for which definitive information indicates that the hazardous
substance was not or could not be present.
For an area of observed contamination in the soil exposure
component of the soil exposure and subsurface intrusion pathway,
consider only those hazardous substances that meet the criteria for
observed contamination for that area (see section 5.1.0) to be
associated with that area when evaluating the pathway.
For an area of observed exposure or area of subsurface
contamination (see section 5.2.0) in the subsurface intrusion component
of the soil exposure and subsurface intrusion pathway, consider only
those hazardous substances that:
Meet the criteria for observed exposure, or
Meet the criteria for observed release in an area of
subsurface contamination and has a vapor pressure greater than or equal
to one torr or a Henry's constant greater than or equal to
10-\5\ atm-m\3\/mol, or
Meet the criteria for an observed release in a structure
within, or in a sample from below, an area of observed exposure and has
a vapor pressure greater than or equal to one torr or a Henry's
constant greater than or equal to 10-\5\ atm-m\3\/mol.
2.2.3 Identify hazardous substances available to a pathway. In
evaluating each migration pathway, consider the following hazardous
substances available to migrate from the sources at the site to the
pathway:
Ground water migration.
-- Hazardous substances that meet the criteria for an observed release
(see section 2.3) to ground water.
-- All hazardous substances associated with a source with a ground
water containment factor value greater than 0 (see section 3.1.2.1).
Surface water migration--overland/flood component.
-- Hazardous substances that meet the criteria for an observed release
to surface water in the watershed being evaluated.
-- All hazardous substances associated with a source with a surface
water containment factor value greater than 0 for the watershed (see
sections 4.1.2.1.2.1.1 and 4.1.2.1.2.2.1).
Surface water migration--ground water to surface water
component.
-- Hazardous substances that meet the criteria for an observed release
to ground water.
-- All hazardous substances associated with a source with a ground
water containment factor value greater than 0 (see sections 4.2.2.1.2
and 3.1.2.1).
Air migration.
-- Hazardous substances that meet the criteria for an observed release
to the atmosphere.
-- All gaseous hazardous substances associated with a source with a gas
containment factor value greater than 0 (see section 6.1.2.1.1).
-- All particulate hazardous substances associated with a source with a
particulate containment factor value greater than 0 (see section
6.1.2.2.1).
For each migration pathway, in those instances when the
specific source(s) containing the hazardous substance cannot be
documented, consider that hazardous substance to be available to
migrate to the pathway when it can be associated (see section 2.2.2)
with at least one source having a containment factor value greater than
0 for that pathway.
In evaluating the soil exposure and subsurface intrusion pathway,
consider the following hazardous substances available to the pathway:
Soil exposure component--resident population threat.
-- All hazardous substances that meet the criteria for observed
contamination at the site (see section 5.1.0).
Soil exposure component--nearby population threat.
-- All hazardous substances that meet the criteria for observed
contamination at areas with an attractiveness/accessibility factor
value greater than 0 (see section 5.1.2.1.1).
Subsurface intrusion component.
-- All hazardous substances that meet the criteria for observed
exposure at the site (see section 5.2.0).
--All hazardous substances with a vapor pressure greater than or equal
to one torr or a Henry's constant greater than or equal to
10-5 atm-m\3\/mol that meet the criteria for an observed
release in an area of subsurface contamination (see section 5.2.0).
--All hazardous substances that meet the criteria for an observed
release in a structure within, or in a sample from below, an area of
observed exposure (see section 5.2.0).
2.3 Likelihood of release. Likelihood of release is a measure of
the likelihood that a waste has been or will be released to the
environment. The likelihood of release factor category is assigned the
maximum value of 550 for a migration pathway whenever the criteria for
an observed release are met for that pathway. If the criteria for an
observed release are met, do not evaluate potential to release for that
pathway. When the criteria for an observed release are not met,
evaluate potential to release for that pathway, with a maximum value of
500. The evaluation of potential to release varies by migration pathway
(see sections 3, 4 and 6).
Establish an observed release either by direct observation of the
release of a hazardous substance into the media being evaluated (for
example, surface water) or by chemical analysis of samples appropriate
to the pathway being evaluated (see sections 3, 4 and 6). The minimum
standard to establish an observed release by chemical analysis is
analytical evidence of a hazardous substance in the media significantly
above the background level. Further, some portion of the release must
be attributable to the site. Use the criteria in Table 2-3 as the
standard for determining analytical significance. (The criteria in
Table 2-3 are also used in establishing observed contamination for the
soil exposure component and for establishing areas of observed exposure
and areas of subsurface contamination in the subsurface intrusion
component of the soil exposure and subsurface intrusion pathway, see
section 5.1.0 and section 5.2.0). Separate criteria apply to
radionuclides (see section 7.1.1).
Table 2-3--Observed Release Criteria for Chemical Analysis
------------------------------------------------------------------------
-------------------------------------------------------------------------
Sample Measurement < Sample Quantitation Limit.\a\
No observed release is established.
[[Page 10403]]
Sample Measurement >= Sample Quantitation Limit.\a\
An observed release is established as follows:
If the background concentration is not detected (or is less
than the detection limit), an observed release is established when
the sample measurement equals or exceeds the sample quantitation
limit.\a\
If the background concentration equals or exceeds the
detection limit, an observed release is established when the sample
measurement is 3 times or more above the background concentration.
\a\ If the sample quantitation limit (SQL) cannot be established,
determine if there is an observed release as follows:
If the sample analysis was performed under the EPA Contract Laboratory
Program, use the EPA contract-required quantitation limit (CRQL) in
place of the SQL.
If the sample analysis is not performed under the EPA Contract
Laboratory Program, use the detection limit (DL) in place of the SQL.
------------------------------------------------------------------------
2.4 Waste characteristics. The waste characteristics factor
category includes the following factors: Hazardous waste quantity,
toxicity, and as appropriate to the pathway or threat being evaluated,
mobility, persistence, degradation, and/or bioaccumulation (or
ecosystem bioaccumulation) potential.
2.4.1 Selection of substance potentially posing greatest hazard.
For all pathways (components and threats), select the hazardous
substance potentially posing the greatest hazard for the pathway
(component or threat) and use that substance in evaluating the waste
characteristics category of the pathway (component or threat). For the
three migration pathways (and threats), base the selection of this
hazardous substance on the toxicity factor value for the substance,
combined with its mobility, persistence, and/or bioaccumulation (or
ecosystem bioaccumulation) potential factor values, as applicable to
the migration pathway (or threat). For the soil exposure component of
the soil exposure and subsurface intrusion pathway, base the selection
on the toxicity factor alone. For the subsurface intrusion component of
the soil exposure and subsurface intrusion pathway, base the selection
on the toxicity factor value for the substance, combined with its
degradation factor value. Evaluation of the toxicity factor is
specified in section 2.4.1.1. Use and evaluation of the mobility,
persistence, degradation, and/or bioaccumulation (or ecosystem
bioaccumulation) potential factors vary by pathway (component or
threat) and are specified under the appropriate pathway (component or
threat) section. Section 2.4.1.2 identifies the specific factors that
are combined with toxicity in evaluating each pathway (component or
threat).
2.4.1.1 Toxicity factor. Evaluate toxicity for those hazardous
substances at the site that are available to the pathway being scored.
For all pathways and threats, except the surface water environmental
threat, evaluate human toxicity as specified below. For the surface
water environmental threat, evaluate ecosystem toxicity as specified in
section 4.1.4.2.1.1.
Establish human toxicity factor values based on quantitative dose-
response parameters for the following three types of toxicity:
Cancer--Use slope factors (also referred to as cancer
potency factors) combined with weight-of-evidence ratings for
carcinogenicity for all exposure routes except inhalation. Use
inhalation unit risk (IUR) for inhalation exposure. If an inhalation
unit risk or a slope factor is not available for a substance, use its
ED10 value to estimate a slope factor as follows:
[GRAPHIC] [TIFF OMITTED] TP29FE16.030
Noncancer toxicological responses of chronic exposure--use
reference dose (RfD) or reference concentration (RfC) values as
applicable.
Noncancer toxicological responses of acute exposure--use
acute toxicity parameters, such as the LD50.
Assign human toxicity factor values to a hazardous substance using
Table 2-4, as follows:
If RfD/RfC and slope factor/inhalation unit risk values
are available for the hazardous substance, assign the substance a value
from Table 2-4 for each. Select the higher of the two values assigned
and use it as the overall toxicity factor value for the hazardous
substance.
If either an RfD/RfC or slope factor/inhalation unit risk
value is available, but not both, assign the hazardous substance an
overall toxicity factor value from Table 2-4 based solely on the
available value (RfD/RfC or slope factor/inhalation unit risk).
If neither an RfD/RfC nor slope factor/inhalation unit
risk value is available, assign the hazardous substance an overall
toxicity factor value from Table 2-4 based solely on acute toxicity.
That is, consider acute toxicity in Table 2-4 only when both RfD/RfC
and slope factor/IUR values are not available.
If neither an RfD/RfC, nor slope factor/inhalation unit
risk, nor acute toxicity value is available, assign the hazardous
substance an overall toxicity factor value of 0 and use other hazardous
substances for which information is available in evaluating the
pathway.
Table 2-4--Toxicity Factor Evaluation
------------------------------------------------------------------------
Assigned
value
------------------------------------------------------------------------
Chronic toxicity (Human)
------------------------------------------------------------------------
Reference dose (RfD) (mg/kg-day):
RfD < 0.0005........................................... 10,000
0.0005 <= RfD < 0.005.................................. 1,000
0.005 <= RfD < 0.05.................................... 100
0.05 <= RfD < 0.5...................................... 10
0.5 <= RfD............................................. 1
RfD not available...................................... 0
Reference concentration (RfC) (mg/m\3\):
RfC < 0.0001........................................... 10,000
0.0001 <= RfC < 0.006.................................. 1,000
0.006 <= RfC < 0.2..................................... 100
0.2 <= RfC < 2.0....................................... 10
2.0 <= RfC............................................. 1
RfC not available...................................... 0
------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------
Carcinogenicity (Human)
-----------------------------------------------------------------------------------------------------------------
B or Likely to be C or Suggestive evidence
A or Carcinogenic to humans carcinogenic to humans of carcinogenic potential Assigned value
----------------------------------------------------------------------------------------------------------------
Weight-of-evidence a/Slope factor (mg/kg-day)-1
----------------------------------------------------------------------------------------------------------------
0.5 <= SF \b\.......................... 5 <= SF.................. 50 <= SF................. 10,000
[[Page 10404]]
0.05 <= SF < 0.5....................... 0.5 <= SF < 5............ 5 <= SF < 50............. 1,000
SF < 0.05.............................. 0.05 <= SF < 0.5......... 0.5 <= SF < 5............ 100
-- SF < 0.05................ SF < 0.5................. 10
Slope factor not available............. Slope factor not Slope factor not 0
available. available.
----------------------------------------------------------------------------------------------------------------
Weight-of-evidence a/Inhalation unit risk ([mu]g/m3)
----------------------------------------------------------------------------------------------------------------
0.00004 <= IUR \c\..................... 0.0004 <= IUR............ 0.004 <= IUR............. 10,000
0.00001 <= IUR < 0.00004............... 0.0001 <= IUR < 0.0004... 0.001 <= IUR < 0.004..... 1,000
IUR < 0.00001.......................... 0.00001 <= IUR < 0.0001.. 0.0001 <= IUR < 0.001.... 100
-- < 0.00001................ IUR < 0.0001............. 10
Inhalation unit risk not available..... Inhalation unit risk not Inhalation unit risk not 0
available. available.
----------------------------------------------------------------------------------------------------------------
\a\ A, B, and C, as well as Carcinogenic to humans, Likely to be carcinogenic to humans, and Suggestive evidence
of carcinogenic potential refer to weight-of-evidence categories. Assign substances with a weight-of-evidence
category of D (inadequate evidence of carcinogenicity) or E (evidence of lack of carcinogenicity), as well as
inadequate information to assess carcinogenic potential and not likely to be carcinogenic to humans a value of
0 for carcinogenicity.
\b\ SF = Slope factor.
\c\ IUR = Inhalation Unit Risk.
----------------------------------------------------------------------------------------------------------------
Acute Toxicity (Human)
-----------------------------------------------------------------------------------------------------------------
Dust or mist LC50 Gas or vapor LC50
Oral LD50 (mg/kg) Dermal LD50 (mg/kg) (mg/l) (ppm) Assigned value
----------------------------------------------------------------------------------------------------------------
LD50 < 5........................ LD50 < 2........... LC50 < 0.2........ LC50 < 20......... 1,000
5 <= LD50 < 50.................. 2 <= LD50 < 20..... 0.2 <= LC50 < 2... 20 <= LC50 <200... 100
50 <= LD50 < 500................ 20 <= LD50 < 200... 2 <= LC50 <20..... 200 <= LC50 <2,000 10
500 <= LD50..................... 200 <= LD50........ 20 <= LC50........ 2,000 <= LC50..... 1
LD50 not available.............. LD50 not available. LD50 not available LD50 not available 0
----------------------------------------------------------------------------------------------------------------
If a toxicity factor value of 0 is assigned to all hazardous
substances available to a particular pathway (that is, insufficient
toxicity data are available for evaluating all the substances), use a
default value of 100 as the overall human toxicity factor value for all
hazardous substances available to the pathway. For hazardous substances
having usable toxicity data for multiple exposure routes (for example,
inhalation and ingestion), consider all exposure routes and use the
highest assigned value, regardless of exposure route, as the toxicity
factor value.
For HRS purposes, assign both asbestos and lead (and its compounds)
a human toxicity factor value of 10,000.
Separate criteria apply for assigning factor values for human
toxicity and ecosystem toxicity for radionuclides (see sections 7.2.1
and 7.2.2).
2.4.1.2 Hazardous substance selection. For each hazardous substance
evaluated for a migration pathway (or threat), combine the human
toxicity factor value (or ecosystem toxicity factor value) for the
hazardous substance with a mobility, persistence, and/or
bioaccumulation (or ecosystem bioaccumulation) potential factor value
as follows:
Ground water migration.
--Determine a combined human toxicity/mobility factor value for the
hazardous substance (see section 3.2.1).
Surface water migration--overland/flood migration
component.
--Determine a combined human toxicity/persistence factor value for the
hazardous substance for the drinking water threat (see section
4.1.2.2.1).
--Determine a combined human toxicity/persistence/bioaccumulation
factor value for the hazardous substance for the human food chain
threat (see section 4.1.3.2.1).
--Determine a combined ecosystem toxicity/persistence/bioaccumulation
factor value for the hazardous substance for the environmental threat
(see section 4.1.4.2.1).
Surface water migration--ground water to surface water
migration component.
--Determine a combined human toxicity/mobility/persistence factor value
for the hazardous substance for the drinking water threat (see section
4.2.2.2.1).
--Determine a combined human toxicity/mobility/persistence/
bioaccumulation factor value for the hazardous substance for the human
food chain threat (see section 4.2.3.2.1).
--Determine a combined ecosystem toxicity/mobility/persistence/
bioaccumulation factor value for the hazardous substance for the
environmental threat (see section 4.2.4.2.1).
Air migration.
Determine a combined human toxicity/mobility factor value
for the hazardous substance (see section 6.2.1).
Determine each combined factor value for a hazardous substance by
multiplying the individual factor values appropriate to the pathway (or
threat). For each migration pathway (or threat) being evaluated, select
the hazardous substance with the highest combined factor value and use
that substance in evaluating the waste characteristics factor category
of the pathway (or threat).
For the soil exposure and subsurface intrusion pathway, determine
toxicity and toxicity/degradation factor values as follows:
Soil exposure and subsurface intrusion--soil exposure
component.
Select the hazardous substance with the highest human
toxicity factor value from among the substances that meet the criteria
for observed contamination for the threat evaluated and use that
substance in evaluating the waste characteristics factor category (see
section
[[Page 10405]]
5.1.1.2.1).
Soil exposure and subsurface intrusion--subsurface intrusion
component.
Determine a combined human toxicity/degradation factor
value for each hazardous substance being evaluated that:
[ssquf] Meets the criteria for observed exposure, or
[ssquf] Meets the criteria for observed release in an area of
subsurface contamination and has a vapor pressure greater than or equal
to one torr or a Henry's constant greater than or equal to
10-5 atm-m\3\/mol, or
[ssquf] Meets the criteria for an observed release in a structure
within, or in a sample from below, an area of observed exposure and has
a vapor pressure greater than or equal to one torr or a Henry's
constant greater than or equal to 10-5 atm-m\3\/mol.
Select the hazardous substance with the highest combined
factor value and use that substance in evaluating the waste
characteristics factor category (see sections 5.2.1.2.1 and 5.2.1.2).
2.4.2 Hazardous waste quantity. Evaluate the hazardous waste
quantity factor by first assigning each source (or area of observed
contamination, area of observed exposure or area of subsurface
contamination) a source hazardous waste quantity value as specified
below. Sum these values to obtain the hazardous waste quantity factor
value for the pathway being evaluated.
In evaluating the hazardous waste quantity factor for the three
migration pathways, allocate hazardous substances and hazardous
wastestreams to specific sources in the manner specified in section
2.2.2, except: Consider hazardous substances and hazardous wastestreams
that cannot be allocated to any specific source to constitute a
separate ``unallocated source'' for purposes of evaluating only this
factor for the three migration pathways. Do not, however, include a
hazardous substance or hazardous wastestream in the unallocated source
for a migration pathway if there is definitive information indicating
that the substance or wastestream could only have been placed in
sources with a containment factor value of 0 for that migration
pathway.
In evaluating the hazardous waste quantity factor for the soil
exposure component of the soil exposure and subsurface intrusion
pathway, allocate to each area of observed contamination only those
hazardous substances that meet the criteria for observed contamination,
for that area of observed contamination and only those hazardous
wastestreams that contain hazardous substances that meet the criteria
for observed contamination for that area of observed contamination. Do
not consider other hazardous substances or hazardous wastestreams at
the site in evaluating this factor for the soil exposure component of
the soil exposure and subsurface intrusion pathway.
In evaluating the hazardous waste quantity factor for the
subsurface intrusion component of the soil exposure and subsurface
intrusion pathway, allocate to each area of observed exposure or area
of subsurface contamination only those hazardous substances and
hazardous wastestreams that contain hazardous substances that:
Meet the criteria for observed exposure, or
Meet the criteria for observed release in an area of
subsurface contamination and has a vapor pressure greater than or equal
to one torr or a Henry's constant greater than or equal to
10-5 atm-m\3\/mol, or
Meet the criteria for an observed release in a structure
within, or in a sample from below, an area of observed exposure and has
a vapor pressure greater than or equal to one torr or a Henry's
constant greater than or equal to 10-5 atm-m\3\/mol.
Do not consider other hazardous substances or hazardous
wastestreams at the site in evaluating this factor for the subsurface
intrusion component of the soil exposure and subsurface intrusion
pathway. When determining the hazardous waste quantity for multi-
subunit structures, use the procedures identified in section 5.2.1.2.2.
2.4.2.1 Source hazardous waste quantity. For each of the three
migration pathways, assign a source hazardous waste quantity value to
each source (including the unallocated source) having a containment
factor value greater than 0 for the pathway being evaluated. Consider
the unallocated source to have a containment factor value greater than
0 for each migration pathway.
For the soil exposure component of the soil exposure and subsurface
intrusion pathway, assign a source hazardous waste quantity value to
each area of observed contamination, as applicable to the threat being
evaluated.
For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, assign a source hazardous waste quantity
value to each regularly occupied structure within an area of observed
exposure or an area of subsurface contamination that has a structure
containment factor value greater than 0.
For determining all hazardous waste quantity calculations except
for an unallocated source or an area of subsurface contamination,
evaluate using the following four measures in the following hierarchy:
Hazardous constituent quantity.
Hazardous wastestream quantity.
Volume.
Area.
For the unallocated source, use only the first two measures. For an
area of subsurface contamination, evaluate non-radioactive hazardous
substances using only the last two measures and evaluate radioactive
hazardous substances using hazardous wastestream quantity only. See
also section 7.0 regarding the evaluation of radioactive substances.
Separate criteria apply for assigning a source hazardous waste
quantity value for radionuclides (see section 7.2.5).
2.4.2.1.1 Hazardous constituent quantity. Evaluate hazardous
constituent quantity for the source (or area of observed contamination)
based solely on the mass of CERCLA hazardous substances (as defined in
CERCLA section 101(14), as amended) allocated to the source (or area of
observed contamination), except:
For a hazardous waste listed pursuant to section 3001 of
the Solid Waste Disposal Act, as amended by the Resource Conservation
and Recovery Act of 1976 (RCRA), 42 U.S.C. 6901 et seq., determine its
mass for the evaluation of this measure as follows:
--If the hazardous waste is listed solely for Hazard Code T (toxic
waste), include only the mass of constituents in the hazardous waste
that are CERCLA hazardous substances and not the mass of the entire
hazardous waste.
-- If the hazardous waste is listed for any other Hazard Code
(including T plus any other Hazard Code), include the mass of the
entire hazardous waste.
For a RCRA hazardous waste that exhibits the
characteristics identified under section 3001 of RCRA, as amended,
determine its mass for the evaluation of this measure as follows:
--If the hazardous waste exhibits only the characteristic of toxicity
(or only the characteristic of EP toxicity), include only the mass of
constituents in the hazardous waste that are CERCLA hazardous
substances and not the mass of the entire hazardous waste.
--If the hazardous waste exhibits any other characteristic identified
under
[[Page 10406]]
section 3001 (including any other characteristic plus the
characteristic of toxicity [or the characteristic of EP toxicity]),
include the mass of the entire hazardous waste.
Based on this mass, designated as C, assign a value for hazardous
constituent quantity as follows:
For the migration pathways, assign the source a value for
hazardous constituent quantity using the Tier A equation of Table 2-5.
For the soil exposure and subsurface intrusion pathway--
soil exposure component, assign the area of observed contamination a
value using the Tier A equation of Table 5-2 (section 5.1.1.2.2).
For the soil exposure and subsurface intrusion pathway--
subsurface intrusion component, assign the area of observed exposure a
value using the Tier A equation of Table 5-18 (section 5.2.1.2.2).
If the hazardous constituent quantity for the source (or area of
observed contamination or area of observed exposure) is adequately
determined (that is, the total mass of all CERCLA hazardous substances
in the source and releases from the source [or in the area of observed
contamination or area of observed exposure] is known or is estimated
with reasonable confidence), do not evaluate the other three measures
discussed below. Instead assign these other three measures a value of 0
for the source (or area of observed contamination or area of observed
exposure) and proceed to section 2.4.2.1.5.
If the hazardous constituent quantity is not adequately determined,
assign the source (or area of observed contamination or area of
observed exposure) a value for hazardous constituent quantity based on
the available data and proceed to section 2.4.2.1.2.
Table 2-5--Hazardous Waste Quantity Evaluation Equations
------------------------------------------------------------------------
Equation for
Tier Measure Units assigning value
\a\
------------------------------------------------------------------------
A............. Hazardous constituent lb............ C
quantity (C).
B \b\......... Hazardous wastestream lb............ W/5,000
quantity (W).
C \b\......... Volume (V)...........
Landfill............. yd\3\......... V/2,500
Surface impoundment.. yd\3\......... V/2.5
Surface impoundment yd\3\......... V/2.5
(buried/backfilled).
Drums \c\............ gallon........ V/2.5
Tanks and containers yd\3\......... V/2.5
other than drums.
Contaminated soil.... yd\3\......... V/2,500
Pile................. yd\3\......... V/2.5
Other................ yd\3\......... V/2.5
D \b\......... Area (A).............
Landfill............. ft\2\......... A/3,400
Surface impoundment.. ft\2\......... A/13
Surface impoundment ft\2\......... A/13
(buried/backfilled).
Land treatment....... ft\2\......... A/270
Pile \d\............. ft\2\......... A/13
Contaminated soil.... ft\2\......... A/34,000
------------------------------------------------------------------------
\a\ Do not round to nearest integer.
\b\ Convert volume to mass when necessary: 1 ton = 2,000 pounds = 1
cubic yard = 4 drums = 200 gallons.
\c\ If actual volume of drums is unavailable, assume 1 drum = 50
gallons.
\d\ Use land surface area under pile, not surface area of pile.
2.4.2.1.2 Hazardous wastestream quantity. Evaluate hazardous
wastestream quantity for the source (or area of observed contamination
or area of observed exposure) based on the mass of hazardous
wastestreams plus the mass of any additional CERCLA pollutants and
contaminants (as defined in CERCLA section 101[33], as amended) that
are allocated to the source (or area of observed contamination or area
of observed exposure). For a wastestream that consists solely of a
hazardous waste listed pursuant to section 3001 of RCRA, as amended or
that consists solely of a RCRA hazardous waste that exhibits the
characteristics identified under section 3001 of RCRA, as amended,
include the mass of that entire hazardous waste in the evaluation of
this measure.
Based on this mass, designated as W, assign a value for hazardous
wastestream quantity as follows:
For the migration pathways, assign the source a value for
hazardous wastestream quantity using the Tier B equation of Table 2-5.
For the soil exposure and subsurface intrusion pathway--
soil exposure component, assign the area of observed contamination a
value using the Tier B equation of Table 5-2 (section 5.1.1.2.2).
For the soil exposure and subsurface intrusion pathway--
subsurface intrusion component, assign the area of observed exposure a
value using the Tier B equation of Table 5-18 (section 5.2.1.2.2).
Do not evaluate the volume and area measures described below if the
source is the unallocated source or if the following condition applies:
The hazardous wastestream quantity for the source (or area
of observed contamination) is adequately determined--that is, total
mass of all hazardous wastestreams and CERCLA pollutants and
contaminants for the source and releases from the source (or for the
area of observed contamination) is known or is estimated with
reasonable confidence.
If the source is the unallocated source or if this condition
applies, assign the volume and area measures a value of 0 for the
source (or area of observed contamination) and proceed to section
2.4.2.1.5. Otherwise, assign the source (or area of observed
contamination) a value for Hazardous wastestream quantity based on the
available data and proceed to section 2.4.2.1.3.
[[Page 10407]]
2.4.2.1.3 Volume. Evaluate the volume measure using the volume of
the source (or the volume of the area of observed contamination, area
of observed exposure, or area of subsurface contamination). For the
soil exposure and subsurface intrusion pathway, restrict the use of the
volume measure to those areas of observed contamination, areas of
observed exposure, or areas of subsurface contamination as specified in
sections 5.1.1.2.2 and 5.2.1.2.2.
Based on the volume, designated as V, assign a value to the volume
measure as follows:
For the migration pathways, assign the source a value for
volume using the appropriate Tier C equation of Table 2-5.
For the soil exposure and subsurface intrusion pathway--
soil exposure component, assign the area of observed contamination a
value for volume using the appropriate Tier C equation of Table 5-2
(section 5.1.1.2.2).
For the soil exposure and subsurface intrusion pathway--
subsurface intrusion component, assign the value based on the volume of
the regularly occupied structures within the area of observed exposure
or area of subsurface contamination using the Tier C equation of Table
5-18 (section 5.2.1.2.2).
If the volume of the source (or volume of the area of observed
contamination, area of observed exposure, or area of subsurface
contamination, if applicable) can be determined, do not evaluate the
area measure. Instead, assign the area measure a value of 0 and proceed
to section 2.4.2.1.5. If the volume cannot be determined (or is not
applicable for the soil exposure and subsurface intrusion pathway),
assign the source (or area of observed contamination, area of observed
exposure, or area of subsurface contamination) a value of 0 for the
volume measure and proceed to section 2.4.2.1.4.
2.4.2.1.4 Area. Evaluate the area measure using the area of the
source (or the area of the area of observed contamination, area of
observed exposure, or area of subsurface contamination). Based on this
area, designated as A, assign a value to the area measure as follows:
For the migration pathways, assign the source a value for
area using the appropriate Tier D equation of Table 2-5.
For the soil exposure and subsurface intrusion pathway--
soil exposure component, assign the area of observed contamination a
value for area using the appropriate Tier D equation of Table 5-2
(section 5.1.1.2.2).
For the soil exposure and subsurface intrusion pathway--
subsurface intrusion component, assign a value based on the area of
regularly occupied structures within the area of observed exposure or
area of subsurface contamination using the Tier D equation of Table 5-
18 (section 5.2.1.2.2).
2.4.2.1.5 Calculation of source hazardous waste quantity value.
Select the highest of the values assigned to the source (or areas of
observed contamination, areas of observed exposure, or areas of
subsurface contamination) for the hazardous constituent quantity,
hazardous wastestream quantity, volume, and area measures. Assign this
value as the source hazardous waste quantity value. Do not round to the
nearest integer.
2.4.2.2 Calculation of hazardous waste quantity factor value. Sum
the source hazardous waste quantity values assigned to all sources
(including the unallocated source) or areas of observed contamination,
areas of observed exposure, or areas of subsurface contamination for
the pathway being evaluated and round this sum to the nearest integer,
except: If the sum is greater than 0, but less than 1, round it to 1.
Based on this value, select a hazardous waste quantity factor value for
the pathway from Table 2-6.
Table 2-6--Hazardous Waste Quantity Factor Values
------------------------------------------------------------------------
Assigned
Hazardous waste quantity value value
------------------------------------------------------------------------
0.......................................................... 0
1 \a\ to 100............................................... \b\ 1
Greater than 100 to 10,000................................. 100
Greater than 10,000 to 1,000,000........................... 10,000
Greater than 1,000,000..................................... 1,000,000
------------------------------------------------------------------------
\a\ If the hazardous waste quantity value is greater than 0, but less
than 1, round it to 1 as specified in text.
\b\ For the pathway, if hazardous constituent quantity is not adequately
determined, assign a value as specified in the text; do not assign the
value of 1.
For a migration pathway, if the hazardous constituent quantity is
adequately determined (see section 2.4.2.1.1) for all sources (or all
portions of sources and releases remaining after a removal action),
assign the value from Table 2-6 as the hazardous waste quantity factor
value for the pathway. If the hazardous constituent quantity is not
adequately determined for one or more sources (or one or more portions
of sources or releases remaining after a removal action) assign a
factor value as follows:
If any target for that migration pathway is subject to
Level I or Level II concentrations (see section 2.5), assign either the
value from Table 2-6 or a value of 100, whichever is greater, as the
hazardous waste quantity factor value for that pathway.
If none of the targets for that pathway is subject to
Level I or Level II concentrations, assign a factor value as follows:
--If there has been no removal action, assign either the value from
Table 2-6 or a value of 10, whichever is greater, as the hazardous
waste quantity factor value for that pathway.
--If there has been a removal action:
[ssquf] Determine values from Table 2-6 with and without
consideration of the removal action.
[ssquf] If the value that would be assigned from Table 2-6 without
consideration of the removal action would be 100 or greater, assign
either the value from Table 2-6 with consideration of the removal
action or a value of 100, whichever is greater, as the hazardous waste
quantity factor value for the pathway.
[ssquf] If the value that would be assigned from Table 2-6 without
consideration of the removal action would be less than 100, assign a
value of 10 as the hazardous waste quantity factor value for the
pathway.
For the soil exposure component of the soil exposure and subsurface
intrusion pathway, if the hazardous constituent quantity is adequately
determined for all areas of observed contamination, assign the value
from Table 2-6 as the hazardous waste quantity factor value. If the
hazardous constituent quantity is not adequately determined for one or
more areas of observed contamination, assign either the value from
Table 2-6 or a value of 10, whichever is greater, as the hazardous
waste quantity factor value.
For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, if the hazardous constituent quantity is
adequately determined for all areas of observed exposure, assign the
value from Table 2-6 as the hazardous waste quantity factor value. If
the hazardous constituent quantity is not adequately determined for one
or more areas of observed exposure, assign either the value from Table
2-6 or assign a factor value as follows:
If any target for the subsurface intrusion component is
subject to Level I or Level II concentrations (see section 2.5), assign
either the value from Table 2-6 or a value of 100, whichever is
[[Page 10408]]
greater, as the hazardous waste quantity factor value for this
component.
If none of the targets for the subsurface intrusion
component is subject to Level I or Level II concentrations and if there
has been a removal action, assign a factor value as follows:
--Determine the values from Table 2-6 with and without consideration of
the removal action.
--If the value that would be assigned from Table 2-6 without
consideration of the removal action would be 100 or greater, assign
either the value from Table 2-6 with consideration of the removal
action or a value of 100, whichever is greater, as the hazardous waste
quantity factor value for the component.
--If the value that would be assigned from Table 2-6 without
consideration of the removal action would be less than 100, assign a
value of 10 as the hazardous waste quantity factor value for the
component.
Otherwise, if none of the targets for the subsurface
intrusion component is subject to Level I or Level II concentrations
and there has not been a removal action, assign a value from Table 2-6
or a value of 10, whichever is greater.
2.4.3 Waste characteristics factor category value. Determine the
waste characteristics factor category value as specified in section
2.4.3.1 for all pathways and threats, except the surface water-human
food chain threat and the surface water-environmental threat. Determine
the waste characteristics factor category value for these latter two
threats as specified in section 2.4.3.2.
2.4.3.1 Factor category value. For the pathway (component or
threat) being evaluated, multiply the toxicity or combined factor
value, as appropriate, from section 2.4.1.2 and the hazardous waste
quantity factor value from section 2.4.2.2, subject to a maximum
product of 1x10\8\. Based on this waste characteristics product, assign
a waste characteristics factor category value to the pathway (component
or threat) from Table 2-7.
Table 2-7--Waste Characteristics Factor Category Values
------------------------------------------------------------------------
Assigned
Waste characteristics product value
------------------------------------------------------------------------
0.......................................................... 0
Greater than 0 to less than 10............................. 1
10 to less than 1x10\2\.................................... 2
1x10\2\ to less than 1x10\3\............................... 3
1x10\3\ to less than 1x10\4\............................... 6
1x10\4\ to less than 1x10\5\............................... 10
1x10\5\ to less than 1x10\6\............................... 18
1x10\6\ to less than 1x10\7\............................... 32
1x10\7\ to less than 1x10\8\............................... 56
1x10\8\ to less than 1x10\9\............................... 100
1x10\9\ to less than 1x10\10\.............................. 180
1x10\10\ to less than 1x10\11\............................. 320
1x10\11\ to less than 1x10\12\............................. 560
1x10\12\................................................... 1,000
------------------------------------------------------------------------
2.4.3.2 Factor category value, considering bioaccumulation
potential. For the surface water-human food chain threat and the
surface water-environmental threat, multiply the toxicity or combined
factor value, as appropriate, from section 2.4.1.2 and the hazardous
waste quantity factor value from section 2.4.2.2, subject to:
A maximum product of 1x10\12\, and
A maximum product exclusive of the bioaccumulation (or
ecosystem bioaccumulation) potential factor of 1x 10\8\.
Based on the total waste characteristics product, assign a waste
characteristics factor category value to these threats from Table 2-7.
2.5 Targets. The types of targets evaluated include the following:
Individual (factor name varies by pathway, component, and
threat).
Human population.
Resources (these vary by pathway, component, and threat).
Sensitive environments (included for the surface water
migration pathway, air migration pathway, and soil exposure component
of the soil exposure and subsurface intrusion pathway).
The factor values that may be assigned to each type of target have
the same range for each pathway for which that type of target is
evaluated. The factor value for most types of targets depends on
whether the target is subject to actual or potential contamination for
the pathway and whether the actual contamination is Level I or Level
II:
Actual contamination: Target is associated either with a
sampling location that meets the criteria for an observed release (or
observed contamination or observed exposure) for the pathway or with an
observed release based on direct observation for the pathway
(additional criteria apply for establishing actual contamination for
the human food chain threat in the surface water migration pathway, see
sections 4.1.3.3 and 4.2.3.3). Sections 3 through 6 specify how to
determine the targets associated with a sampling location or with an
observed release based on direct observation. Determine whether the
actual contamination is Level I or Level II as follows:
--Level I:
[ssquf] Media-specific concentrations for the target meet the
criteria for an observed release (or observed contamination or observed
exposure) for the pathway and are at or above media-specific benchmark
values. These benchmark values (see section 2.5.2) include both
screening concentrations and concentrations specified in regulatory
limits (such as Maximum Contaminant Level (MCL) values), or
[ssquf] For the human food chain threat in the surface water
migration pathway, concentrations in tissue samples from aquatic human
food chain organisms are at or above benchmark values. Such tissue
samples may be used in addition to media-specific concentrations only
as specified in sections 4.1.3.3 and 4.2.3.3.
--Level II:
[ssquf] Media-specific concentrations for the target meet the
criteria for an observed release (or observed contamination or observed
exposure) for the pathway, but are less than media-specific benchmarks.
If none of the hazardous substances eligible to be evaluated for the
sampling location has an applicable benchmark, assign Level II to the
actual contamination at the sampling location, or
[ssquf] For observed releases or observed exposures based on direct
observation, assign Level II to targets as specified in sections 3, 4,
5, and 6, or
[ssquf] For the human food chain threat in the surface water
migration pathway, concentrations in tissue samples from aquatic human
food chain organisms, when applicable, are below benchmark values.
--If a target is subject to both Level I and Level II concentrations
for a pathway (or threat), evaluate the target using Level I
concentrations for that pathway (or threat).
Potential contamination: Target is subject to a potential
release (that is, target is not associated with actual contamination
for that pathway or threat).
Assign a factor value for individual risk as follows (select the
highest value that applies to the pathway or threat):
50 points if any individual is exposed to Level I
concentrations.
45 points if any individual is exposed to Level II
concentrations.
[[Page 10409]]
Maximum of 20 points if any individual is subject to
potential contamination. The value assigned is 20 unless reduced by a
distance or dilution weight appropriate to the pathway.
Assign factor values for population and sensitive environments as
follows:
Sum Level I targets and multiply by 10. (Level I is not
used for sensitive environments in the soil exposure component of the
soil exposure and subsurface intrusion and air migration pathways.)
Sum Level II targets.
Multiply potential targets in all but the soil exposure
and subsurface intrusion pathway by distance or dilution weights
appropriate to the pathway, sum, and divide by 10. Distance or dilution
weighting accounts for diminishing exposure with increasing distance or
dilution within the different pathways. For targets within an area of
subsurface contamination in the subsurface intrusion component of the
soil exposure and subsurface intrusion pathway, multiply by a weighting
factor as directed in section 5.2.1.3.2.3.
Sum the values for the three levels.
In addition, resource value points are assigned within all pathways
for welfare-related impacts (for example, impacts to agricultural
land), but do not depend on whether there is actual or potential
contamination.
2.5.1 Determination of level of actual contamination at a sampling
location. Determine whether Level I concentrations or Level II
concentrations apply at a sampling location (and thus to the associated
targets) as follows:
Select the benchmarks applicable to the pathway (component
or threat) being evaluated.
Compare the concentrations of hazardous substances in the
sample (or comparable samples) to their benchmark concentrations for
the pathway (component or threat), as specified in section 2.5.2.
Determine which level applies based on this comparison.
If none of the hazardous substances eligible to be
evaluated for the sampling location has an applicable benchmark, assign
Level II to the actual contamination at that sampling location for the
pathway (component or threat).
In making the comparison, consider only those samples, and only
those hazardous substances in the sample, that meet the criteria for an
observed release (or observed contamination or observed exposure) for
the pathway, except: Tissue samples from aquatic human food chain
organisms may also be used as specified in sections 4.1.3.3 and 4.2.3.3
of the surface water-human food chain threat. If any hazardous
substance is present in more than one comparable sample for the
sampling location, use the highest concentration of that hazardous
substance from any of the comparable samples in making the comparisons.
Treat sets of samples that are not comparable separately and make a
separate comparison for each such set.
2.5.2 Comparison to benchmarks. Use the following media-specific
benchmarks for making the comparisons for the indicated pathway (or
threat):
Maximum Contaminant Level Goals (MCLGs)--ground water
migration pathway and drinking water threat in surface water migration
pathway. Use only MCLG values greater than 0.
Maximum Contaminant Levels (MCLs)--ground water migration
pathway and drinking water threat in surface water migration pathway.
Food and Drug Administration Action Level (FDAAL) for fish
or shellfish--human food chain threat in surface water migration
pathway.
EPA Ambient Water Quality Criteria (AWQC/National
Recommended Water Quality Criteria) for protection of aquatic life--
environmental threat in surface water migration pathway.
EPA Ambient Aquatic Life Advisory Concentrations (AALAC)--
environmental threat in surface water migration pathway.
National Ambient Air Quality Standards (NAAQS)--air
migration pathway.
National Emission Standards for Hazardous Air Pollutants
(NESHAPs)--air migration pathway. Use only those NESHAPs promulgated in
ambient concentration units.
Screening concentration for cancer corresponding to that
concentration that corresponds to the 10-\6\ individual
cancer risk for inhalation exposures (air migration pathway or
subsurface intrusion component of the soil exposure and subsurface
intrusion pathway) or for oral exposures (ground water migration
pathway; drinking water and human food chain threats in surface water
migration pathway; and soil exposure and subsurface intrusion pathway).
Screening concentration for noncancer toxicological
responses corresponding to the RfC for inhalation exposures (air
migration pathway and subsurface intrusion component of the soil
exposure and subsurface intrusion pathway) or RfD for oral exposures
(ground water migration pathway; drinking water and human food chain
threats in surface water migration pathway; and soil exposure and
subsurface intrusion pathway).
Select the benchmark(s) applicable to the pathway (component or
threat) being evaluated as specified in sections 3 through 6. Compare
the concentration of each hazardous substance from the sampling
location to its benchmark concentration(s) for that pathway (component
or threat). Use only those samples and only those hazardous substances
in the sample that meet the criteria for an observed release (or
observed contamination or observed exposure) for the pathway, except:
Tissue samples from aquatic human food chain organisms may be used as
specified in sections 4.1.3.3 and 4.2.3.3. If the concentration of any
applicable hazardous substance from any sample equals or exceeds its
benchmark concentration, consider the sampling location to be subject
to Level I concentrations for that pathway (or threat). If more than
one benchmark applies to the hazardous substance, assign Level I if the
concentration of the hazardous substance equals or exceeds the lowest
applicable benchmark concentration.
If no hazardous substance individually equals or exceeds its
benchmark concentration, but more than one hazardous substance either
meets the criteria for an observed release (or observed contamination
or observed exposure) for the sample (or comparable samples) or is
eligible to be evaluated for a tissue sample (see sections 4.1.3.3 and
4.2.3.3), calculate the indices I and J specified below based on these
hazardous substances.
For those hazardous substances that are carcinogens (that is, those
having either a carcinogen weight-of-evidence classification of A, B,
or C or a weight-of-evidence classification of carcinogenic to humans,
likely to be carcinogenic to humans, or suggestive evidence of
carcinogenic potential), calculate an index I for the sample location
as follows:
[GRAPHIC] [TIFF OMITTED] TP29FE16.031
Where:
Ci = Concentration of hazardous substance i in sample (or
highest concentration of hazardous substance i from among comparable
samples).
SCi = Screening concentration for cancer corresponding to
that concentration that corresponds to its 10-6
individual cancer risk for applicable exposure (inhalation or oral)
for hazardous substance i.
n = Number of applicable hazardous substances in sample (or
comparable
[[Page 10410]]
samples) that are carcinogens and for which an SCi is
available.
For those hazardous substances for which an RfD or RfC is
available, calculate an index J for the sample location as follows:
[GRAPHIC] [TIFF OMITTED] TP29FE16.032
Where:
Cj = Concentration of hazardous substance j in sample (or
highest concentration of hazardous substance j from among comparable
samples).
CRj = Screening concentration for noncancer toxicological
responses corresponding to RfD or RfC for applicable exposure
(inhalation or oral) for hazardous substance j.
m = Number of applicable hazardous substances in sample (or
comparable samples) for which a CRj is available.
If either I or J equals or exceeds 1, consider the sampling
location to be subject to Level I concentrations for that pathway
(component or threat). If both I and J are less than 1, consider the
sampling location to be subject to Level II concentrations for that
pathway (component or threat). If, for the sampling location, there are
sets of samples that are not comparable, calculate I and J separately
for each such set, and use the highest calculated values of I and J to
assign Level I and Level II.
See sections 7.3.1 and 7.3.2 for criteria for determining the level
of contamination for radioactive substances.
* * * * *
5.0 Soil Exposure and Subsurface Intrusion Pathway
5.0. Exposure components. Evaluate the soil exposure and subsurface
intrusion pathway based on two exposure components:
Soil exposure component (see section 5.1).
Subsurface intrusion component (see section 5.2).
Score one or both components considering their relative importance.
If only one component is scored, assign its score as the soil exposure
and subsurface intrusion pathway score. If both components are scored,
sum the two scores and assign it as the soil exposure and subsurface
intrusion pathway score, subject to a maximum of 100.
[[Page 10411]]
[GRAPHIC] [TIFF OMITTED] TP29FE16.033
5.1 Soil exposure component. Evaluate the soil exposure component
based on two threats: Resident population threat and nearby population
threat. Evaluate both threats based on three factor categories:
[[Page 10412]]
Likelihood of exposure, waste characteristics, and targets. Figure 5-1
indicates the factors included within each factor category for each
type of threat.
Determine the soil exposure component score (Sse) in
terms of the factor category values as follows:
[GRAPHIC] [TIFF OMITTED] TP29FE16.034
Where:
LEi = Likelihood of exposure factor category value for
threat i (that is, resident population threat or nearby population
threat).
WCi = Waste characteristics factor category value for
threat i.
Ti = Targets factor category value for threat i.
SF = Scaling factor.
Table 5-1 outlines the specific calculation procedure.
Table 5-1--Soil Exposure Component Scoresheet
------------------------------------------------------------------------
Value
Factor categories and factors Maximum value assigned
------------------------------------------------------------------------
Resident Population Threat
------------------------------------------------------------------------
Likelihood of Exposure
1. Likelihood of Exposure........... 550 ..............
Waste Characteristics
2. Toxicity......................... (\a\) ..............
3. Hazardous Waste Quantity......... (\a\) ..............
4. Waste Characteristics............ 100 ..............
Targets
5. Resident Individual.............. 50 ..............
6. Resident Population:
6a. Level I Concentrations (\b\) ..............
6b. Level II Concentrations (\b\) ..............
6c. Resident Population (lines 6a + (\b\) ..............
6b)
7. Workers.......................... 15 ..............
8. Resources........................ 5 ..............
9. Terrestrial Sensitive (c) ..............
Environments.......................
10. Targets (lines 5 + 6c + 7 + 8 + (\b\) ..............
9).................................
Resident Population Threat Score
11. Resident Population Threat (\b\) ..............
(lines 1x4x10).....................
------------------------------------------------------------------------
Nearby Population Threat
------------------------------------------------------------------------
Likelihood of Exposure
12. Attractiveness/Accessibility.... 100 ..............
13. Area of Contamination........... 100 ..............
14. Likelihood of Exposure.......... 500 ..............
Waste Characteristics
15. Toxicity........................ (\a\) ..............
16. Hazardous Waste Quantity........ (\a\) ..............
17. Waste Characteristics........... 100 ..............
Targets
18. Nearby Individual............... 1 ..............
19. Population Within 1 Mile........ (\b\) ..............
20. Targets (lines 18 + 19)......... (\b\) ..............
Nearby Population Threat Score
21. Nearby Population Threat (lines (\b\) ..............
14x17x20)..........................
Soil Exposure Component Score
22. Soil Exposure Component Score 100 ..............
\d\ (Sse), (lines [11+21]/82,500,
subject to a maximum of 100).......
------------------------------------------------------------------------
\a\ Maximum value applies to waste characteristics category.
\b\ Maximum value not applicable.
\c\ No specific maximum value applies to factor. However, pathway score
based solely on terrestrial sensitive environments is limited to
maximum of 60.
\d\ Do not round to nearest integer.
5.1.0 General considerations. Evaluate the soil exposure component
based on areas of observed contamination:
Consider observed contamination to be present at sampling
locations where analytic evidence indicates that:
--A hazardous substance attributable to the site is present at a
concentration significantly above background levels for the site (see
Table 2-3 in section 2.3 for the criteria for determining analytical
significance), and
--This hazardous substance, if not present at the surface, is covered
by 2 feet or less of cover material (for example, soil).
Establish areas of observed contamination based on
sampling locations at which there is observed contamination as follows:
--For all sources except contaminated soil, if observed contamination
from the site is present at any sampling location within the source,
consider that entire source to be an area of observed contamination.
-- For contaminated soil, consider both the sampling location(s) with
observed contamination from the site and the area lying between such
locations to be an area of observed contamination, unless available
information indicates otherwise.
If an area of observed contamination (or portion of such
an area) is covered by a permanent, or otherwise maintained,
essentially
[[Page 10413]]
impenetrable material (for example, asphalt) that is not more than 2
feet thick, exclude that area (or portion of the area) in evaluating
the soil exposure component.
For an area of observed contamination, consider only those
hazardous substances that meet the criteria for observed contamination
for that area to be associated with that area in evaluating the soil
exposure component (see section 2.2.2).
If there is observed contamination, assign scores for the resident
population threat and the nearby population threat, as specified in
sections 5.1.1 and 5.1.2. If there is no observed contamination, assign
the soil exposure component of the soil exposure and subsurface
intrusion pathway a score of 0.
5.1.1 Resident population threat. Evaluate the resident population
threat only if there is an area of observed contamination in one or
more of the following locations:
Within the property boundary of a residence, school, or
day care center and within 200 feet of the respective residence,
school, or day care center, or
Within a workplace property boundary and within 200 feet
of a workplace area, or
Within the boundaries of a resource specified in section
5.1.1.3.4, or
Within the boundaries of a terrestrial sensitive
environment specified in section 5.1.1.3.5.
If not, assign the resident population threat a value of 0, enter
this value in Table 5-1, and proceed to the nearby population threat
(section 5.1.2).
5.1.1.1 Likelihood of exposure. Assign a value of 550 to the
likelihood of exposure factor category for the resident population
threat if there is an area of observed contamination in one or more
locations listed in section 5.1.1. Enter this value in Table 5-1.
5.1.1.2 Waste characteristics. Evaluate waste characteristics based
on two factors: Toxicity and hazardous waste quantity. Evaluate only
those hazardous substances that meet the criteria for observed
contamination at the site (see section 5.1.0).
5.1.1.2.1 Toxicity. Assign a toxicity factor value to each
hazardous substance as specified in section 2.4.1.1. Use the hazardous
substance with the highest toxicity factor value to assign the value to
the toxicity factor for the resident population threat. Enter this
value in Table 5-1.
5.1.1.2.2 Hazardous waste quantity. Assign a hazardous waste
quantity factor value as specified in section 2.4.2. In estimating the
hazardous waste quantity, use Table 5-2 and:
Consider only the first 2 feet of depth of an area of
observed contamination, except as specified for the volume measure.
Use the volume measure (see section 2.4.2.1.3) only for
those types of areas of observed contamination listed in Tier C of
Table 5-2. In evaluating the volume measure for these listed areas of
observed contamination, use the full volume, not just the volume within
the top 2 feet.
Use the area measure (see section 2.4.2.1.4), not the
volume measure, for all other types of areas of observed contamination,
even if their volume is known.
Enter the value assigned in Table 5-1.
Table 5-2--Hazardous Waste Quantity Evaluation Equations for Soil
Exposure Component
------------------------------------------------------------------------
Equation for
Tier Measure Units assigning value
\a\
------------------------------------------------------------------------
A............. Hazardous Constituent lb........... C
Quantity (C).
B \b\......... Hazardous Wastestream lb........... W/5,000
Quantity (W).
C \b\......... Volume (V)...........
Surface Impoundment yd \3\....... V/2.5
\c\.
Drums \d\............ gallon....... V/500
Tanks and Containers yd \3\....... V/2.5
Other Than Drums.
D \b\......... Area (A).............
Landfill............. ft \2\....... A/34,000
Surface Impoundment.. ft \2\....... A/13
Surface Impoundment ft \2\....... A/13
(Buried/backfilled).
Land treatment....... ft \2\....... A/270
Pile \e\............. ft \2\....... A/34
Contaminated Soil.... ft \2\....... A/34,000
------------------------------------------------------------------------
\a\ Do not round nearest integer.
\b\ Convert volume to mass when necessary: 1 ton = 2,000 pounds = 1
cubic yard = 4 drums = 200 gallons.
\c\ Use volume measure only for surface impoundments containing
hazardous substances present as liquids. Use area measures in Tier D
for dry surface impoundments and for buried/backfilled surface
impoundments.
\d\ If actual volume of drums is unavailable, assume 1 drum = 50
gallons.
\e\ Use land surface area under pile, not surface area of pile.
5.1.1.2.3 Calculation of waste characteristics factor category
value. Multiply the toxicity and hazardous waste quantity factor
values, subject to a maximum product of 1 x 10\8\. Based on this
product, assign a value from Table 2-7 (section 2.4.3.1) to the waste
characteristics factor category. Enter this value in Table 5-1.
5.1.1.3 Targets. Evaluate the targets factor category for the
resident population threat based on five factors: Resident individual,
resident population, workers, resources, and terrestrial sensitive
environments.
In evaluating the targets factor category for the resident
population threat, count only the following as targets:
Resident individual--a person living or attending school
or day care on a property with an area of observed contamination and
whose residence, school, or day care center, respectively, is on or
within 200 feet of the area of observed contamination.
Worker--a person working on a property with an area of
observed contamination and whose workplace area is on or within 200
feet of the area of observed contamination.
Resources located on an area of observed contamination, as
specified in section 5.1.1.
Terrestrial sensitive environments located on an area of
observed contamination, as specified in section 5.1.1.
5.1.1.3.1 Resident individual. Evaluate this factor based on
whether
[[Page 10414]]
there is a resident individual, as specified in section 5.1.1.3, who is
subject to Level I or Level II concentrations.
First, determine those areas of observed contamination subject to
Level I concentrations and those subject to Level II concentrations as
specified in sections 2.5.1 and 2.5.2. Use the health-based benchmarks
from Table 5-3 in determining the level of contamination. Then assign a
value to the resident individual factor as follows:
Assign a value of 50 if there is at least one resident
individual for one or more areas subject to Level I concentrations.
Assign a value of 45 if there is no such resident
individuals, but there is at least one resident individual for one or
more areas subject to Level II concentrations.
Assign a value of 0 if there is no resident individual.
Enter the value assigned in Table 5-1.
5.1.1.3.2 Resident population. Evaluate resident population based
on two factors: Level I concentrations and Level II concentrations.
Determine which factor applies as specified in sections 2.5.1 and
2.5.2, using the health-based benchmarks from Table 5-3. Evaluate
populations subject to Level I concentrations as specified in section
5.1.1.3.2.1 and populations subject to Level II concentrations as
specified in section 5.1.1.3.2.2.
Table 5-3--Health-Based Benchmarks for Hazardous Substances in Soils
------------------------------------------------------------------------
-------------------------------------------------------------------------
Screening concentration for cancer corresponding to that concentration
that corresponds to the 10-\6\ individual cancer risk for oral
exposures.
Screening concentration for noncancer toxicological responses
corresponding to the Reference Dose (RfD) for oral exposures.
------------------------------------------------------------------------
Count only those persons meeting the criteria for resident
individual as specified in section 5.1.1.3. In estimating the number of
people living on property with an area of observed contamination, when
the estimate is based on the number of residences, multiply each
residence by the average number of persons per residence for the county
in which the residence is located.
5.1.1.3.2.1 Level I concentrations. Sum the number of resident
individuals subject to Level I concentrations and multiply this sum by
10. Assign the resulting product as the value for this factor. Enter
this value in Table 5-1.
5.1.1.3.2.2 Level II concentrations. Sum the number of resident
individuals subject to Level II concentrations. Do not include those
people already counted under the Level I concentrations factor. Assign
this sum as the value for this factor. Enter this value in Table 5-1.
5.1.1.3.2.3 Calculation of resident population factor value. Sum
the factor values for Level I concentrations and Level II
concentrations. Assign this sum as the resident population factor
value. Enter this value in Table 5-1.
5.1.1.3.3 Workers. Evaluate this factor based on the number of
workers that meet the section 5.1.1.3 criteria. Assign a value for
these workers using Table 5-4. Enter this value in Table 5-1.
Table 5-4--Factor Values for Workers
------------------------------------------------------------------------
Assigned
Number of workers value
------------------------------------------------------------------------
0........................................................... 0
1 to 100.................................................... 5
101 to 1,000................................................ 10
Greater than 1,000.......................................... 15
------------------------------------------------------------------------
5.1.1.3.4 Resources. Evaluate the resources factor as follows:
Assign a value of 5 to the resources factor if one or more
of the following is present on an area of observed contamination at the
site:
--Commercial agriculture.
--Commercial silviculture.
--Commercial livestock production or commercial livestock grazing.
Assign a value of 0 if none of the above are present.
Enter the value assigned in Table 5-1.
5.1.1.3.5 Terrestrial sensitive environments. Assign value(s) from
Table 5-5 to each terrestrial sensitive environment that meets the
eligibility criteria of section 5.1.1.3.
Calculate a value (ES) for terrestrial sensitive environments as
follows:
[GRAPHIC] [TIFF OMITTED] TP29FE16.035
where:
Si=Value(s) assigned from Table 5-5 to terrestrial
sensitive environment i.
n=Number of terrestrial sensitive environments meeting section
5.1.1.3 criteria.
Because the pathway score based solely on terrestrial sensitive
environments is limited to a maximum of 60, determine the value for the
terrestrial sensitive environments factor as follows:
Table 5-5--Terrestrial Sensitive Environments Rating Values
------------------------------------------------------------------------
Terrestrial sensitive environments Assigned value
------------------------------------------------------------------------
Terrestrial critical habitat \a\ for Federal 100
designated endangered or threatened species.........
National Park
Designated Federal Wilderness Area
National Monument
Terrestrial habitat known to be used by Federal 75
designated or proposed threatened or endangered
species.............................................
National Preserve (terrestrial)
National or State Terrestrial Wildlife Refuge
Federal land designated for protection of natural
ecosystems
Administratively proposed Federal Wilderness Area
Terrestrial areas utilized for breeding by large or
dense aggregations of animals \b\
Terrestrial habitat known to be used by State 50
designated endangered or threatened species.........
Terrestrial habitat known to be used by species
under review as to its Federal designated endangered
or threatened status
State lands designated for wildlife or game 25
management..........................................
State designated Natural Areas
Particular areas, relatively small in size,
important to maintenance of unique biotic
communities
------------------------------------------------------------------------
\a\ Critical habitat as defined in 50 CFR 424.02.
[[Page 10415]]
\b\ Limit to vertebrate species.
Multiply the values assigned to the resident population
threat for likelihood of exposure (LE), waste characteristics (WC), and
ES. Divide the product by 82,500.
--If the result is 60 or less, assign the value ES as the terrestrial
sensitive environments factor value.
--If the result exceeds 60, calculate a value EC as follows:
[GRAPHIC] [TIFF OMITTED] TP29FE16.036
Assign the value EC as the terrestrial sensitive environments
factor value. Do not round this value to the nearest integer.
Enter the value assigned for the terrestrial sensitive environments
factor in Table 5-1.
5.1.1.3.6 Calculation of resident population targets factor
category value. Sum the values for the resident individual, resident
population, workers, resources, and terrestrial sensitive environments
factors. Do not round to the nearest integer. Assign this sum as the
targets factor category value for the resident population threat. Enter
this value in Table 5-1.
5.1.1.4 Calculation of resident population threat score. Multiply
the values for likelihood of exposure, waste characteristics, and
targets for the resident population threat, and round the product to
the nearest integer. Assign this product as the resident population
threat score. Enter this score in Table 5-1.
5.1.2 Nearby population threat. Include in the nearby population
only those individuals who live or attend school within a 1-mile travel
distance of an area of observed contamination at the site and who do
not meet the criteria for resident individual as specified in section
5.1.1.3.
Do not consider areas of observed contamination that have an
attractiveness/accessibility factor value of 0 (see section 5.1.2.1.1)
in evaluating the nearby population threat.
5.1.2.1 Likelihood of exposure. Evaluate two factors for the
likelihood of exposure factor category for the nearby population
threat: Attractiveness/accessibility and area of contamination.
5.1.2.1.1 Attractiveness/accessibility. Assign a value for
attractiveness/accessibility from Table 5-6 to each area of observed
contamination, excluding any land used for residences. Select the
highest value assigned to the areas evaluated and use it as the value
for the attractiveness/accessibility factor. Enter this value in Table
5-1.
5.1.2.1.2 Area of contamination. Evaluate area of contamination
based on the total area of the areas of observed contamination at the
site. Count only the area(s) that meet the criteria in section 5.1.0
and that receive an attractiveness/accessibility value greater than 0.
Assign a value to this factor from Table 5-7. Enter this value in Table
5-1.
Table 5-6--Attractiveness/Accessibility Values
------------------------------------------------------------------------
Area of observed contamination Assigned value
------------------------------------------------------------------------
Designated recreational area............................ 100
Regularly used for public recreation (for example, 75
fishing, hiking, softball).............................
Accessible and unique recreational area (for example, 75
vacant lots in urban area).............................
Moderately accessible (may have some access 50
improvements, for example, gravel road), with some
public recreation use..................................
Slightly accessible (for example, extremely rural area 25
with no road improvement), with some public recreation
use....................................................
Accessible, with no public recreation use............... 10
Surrounded by maintained fence or combination of 5
maintained fence and natural barriers..................
Physically inaccessible to public, with no evidence of 0
public recreation use..................................
------------------------------------------------------------------------
Table 5-7--Area of Contamination Factor Values
------------------------------------------------------------------------
Total area of the areas of observed contamination
(square feet) Assigned value
------------------------------------------------------------------------
Less than or equal to 5,000............................. 5
Greater than 5,000 to 125,000........................... 20
Greater than 125,000 to 250,000......................... 40
Greater than 250,000 to 375,000......................... 60
Greater than 375,000 to 500,000......................... 80
Greater than 500,000.................................... 100
------------------------------------------------------------------------
5.1.2.1.3 Likelihood of exposure factor category value. Assign a
value from Table 5-8 to the likelihood of exposure factor category,
based on the values assigned to the attractiveness/accessibility and
area of contamination factors. Enter this value in Table 5-1.
Table 5-8--Nearby Population Likelihood of Exposure Factor Values
--------------------------------------------------------------------------------------------------------------------------------------------------------
Attractiveness/accessibility factor value
Area of contamination factor value ---------------------------------------------------------------------------------------------------------------
100 75 50 25 10 5 0
--------------------------------------------------------------------------------------------------------------------------------------------------------
100..................................... 500 500 375 250 125 50 0
80...................................... 500 375 250 125 50 25 0
60...................................... 375 250 125 50 25 5 0
40...................................... 250 125 50 25 5 5 0
[[Page 10416]]
20...................................... 125 50 25 5 5 5 0
5....................................... 50 25 5 5 5 5 0
--------------------------------------------------------------------------------------------------------------------------------------------------------
5.1.2.2 Waste characteristics. Evaluate waste characteristics based
on two factors: Toxicity and hazardous waste quantity. Evaluate only
those hazardous substances that meet the criteria for observed
contamination (see section 5.1.0) at areas that can be assigned an
attractiveness/accessibility factor value greater than 0.
5.1.2.2.1 Toxicity. Assign a toxicity factor value as specified in
section 2.4.1.1 to each hazardous substance meeting the criteria in
section 5.1.2.2. Use the hazardous substance with the highest toxicity
factor value to assign the value to the toxicity factor for the nearby
population threat. Enter this value in Table 5-1.
5.1.2.2.2 Hazardous waste quantity. Assign a value to the hazardous
waste quantity factor as specified in section 5.1.1.2.2, except:
Consider only those areas of observed contamination that can be
assigned an attractiveness/accessibility factor value greater than 0.
Enter the value assigned in Table 5-1.
5.1.2.2.3 Calculation of waste characteristics factor category
value. Multiply the toxicity and hazardous waste quantity factor
values, subject to a maximum product of 1 x 10\8\. Based on this
product, assign a value from Table 2-7 (section 2.4.3.1) to the waste
characteristics factor category. Enter this value in Table 5-1.
5.1.2.3 Targets. Evaluate the targets factory category for the
nearby population threat based on two factors: Nearby individual and
population within a 1-mile travel distance from the site.
5.1.2.3.1 Nearby individual. If one or more persons meet the
section 5.1.1.3 criteria for a resident individual, assign this factor
a value of 0. Enter this value in Table 5-1.
If no person meets the criteria for a resident individual,
determine the shortest travel distance from the site to any residence
or school. In determining the travel distance, measure the shortest
overland distance an individual would travel from a residence or school
to the nearest area of observed contamination for the site with an
attractiveness/accessibility factor value greater than 0. If there are
no natural barriers to travel, measure the travel distance as the
shortest straight-line distance from the residence or school to the
area of observed contamination. If natural barriers exist (for example,
a river), measure the travel distance as the shortest straight-line
distance from the residence or school to the nearest crossing point and
from there as the shortest straight-line distance to the area of
observed contamination. Based on the shortest travel distance, assign a
value from Table 5-9 to the nearest individual factor. Enter this value
in Table 5-1.
Table 5-9--Nearby Individual Factor Values
------------------------------------------------------------------------
Travel distance for nearby individual
(miles) Assigned value
------------------------------------------------------------------------
Greater than 0 to \1/4\.................... \a\1
Greater than \1/4\ to 1.................... 0
------------------------------------------------------------------------
\a\ Assign a value of 0 if one or more persons meet the section 5.1.1.3
criteria for resident individual.
5.1.2.3.2 Population within 1 mile. Determine the population within
each travel distance category of Table 5-10. Count residents and
students who attend school within this travel distance. Do not include
those people already counted in the resident population threat.
Determine travel distances as specified in section 5.1.2.3.1.
In estimating residential population, when the estimate is based on
the number of residences, multiply each residence by the average number
of persons per residence for the county in which the residence is
located.
Based on the number of people included within a travel distance
category, assign a distance-weighted population value for that travel
distance from Table 5-10.
Calculate the value for the population within 1 mile factor (PN) as
follows:
[GRAPHIC] [TIFF OMITTED] TP29FE16.037
Where:
Wi = Distance-weighted population value from Table 5-10
for travel distance category i.
If PN is less than 1, do not round it to the nearest integer; if PN
is 1 or more, round to the nearest integer. Enter this value in Table
5-1.
5.1.2.3.3 Calculation of nearby population targets factor category
value. Sum the values for the nearby individual factor and the
population within 1 mile factor. Do not round this sum to the nearest
integer. Assign this sum as the targets factor category value for the
nearby population threat. Enter this value in Table 5-1.
[[Page 10417]]
Table 5-10--Distance Weighted Population Values for Nearby Population Threat a
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Number of people within the travel distance category
-----------------------------------------------------------------------------------------------------------------------------------------------------------
Travel distance category (miles) 301 to 1,001 to 3,001 to 10,001 to 30,001 to 100,001 to 300,001 to
0 1 to 10 11 to 30 31 to 100 101 to 300 1,000 3,000 10,000 30,000 100,000 300,000 1,000,000
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Greater than 0 to \1/4\............. 0 0.1 0.4 1.0 4 13 41 130 408 1,303 4,081 13,034
Greater than \1/4\ to \1/2\......... 0 0.05 0.2 0.7 2 7 20 65 204 652 2,041 6,517
Greater than \1/2\ to 1............. 0 0.02 0.1 0.3 1 3 10 33 102 326 1,020 3,258
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Round the number of people present within a travel distance category to nearest integer. Do not round the assigned distance-weighted population value to nearest integer.
[[Page 10418]]
5.1.2.4 Calculation of nearby population threat score. Multiply the
values for likelihood of exposure, waste characteristics, and targets
for the nearby population threat, and round the product to the nearest
integer. Assign this product as the nearby population threat score.
Enter this score in Table 5-1.
5.1.3 Calculation of soil exposure component score. Sum the
resident population threat score and the nearby population threat
score, and divide the sum by 82,500. Assign the resulting value,
subject to a maximum of 100, as the soil exposure component score
(Sse). Enter this score in Table 5-1.
5.2 Subsurface intrusion component. Evaluate the subsurface
intrusion component based on three factor categories: Likelihood of
exposure, waste characteristics, and targets. Figure 5-1 indicates the
factors included within each factor category for the subsurface
intrusion component.
Determine the component score (Sssi) in terms of the
factor category values as follows:
[GRAPHIC] [TIFF OMITTED] TP29FE16.038
Where:
LE = Likelihood of exposure factor category value.
WC = Waste characteristics factor category value.
T = Targets factor category value.
SF = Scaling factor.
Table 5-11 outlines the specific calculation procedure.
Table 5-11--Subsurface Intrusion Component Scoresheet
------------------------------------------------------------------------
Factor categories and factors Maximum value Value assigned
------------------------------------------------------------------------
Subsurface Intrusion Component
------------------------------------------------------------------------
Likelihood of Exposure:
1. Observed Exposure 550
2. Potential for Exposure:
2a. Structure Containment....... 10
2b. Depth to contamination...... 10
2c. Vertical Migration.......... 15
2d. Vapor Migration Potential... 25
3. Potential for Exposure (lines 2a 500
* (2b + 2c + 2d), subject to a
maximum of 500)....................
4. Likelihood of Exposure (higher of 550
lines 1 or 3)......................
Waste Characteristics:
5. Toxicity/Degradation............. \(a)\
6. Hazardous Waste Quantity......... \(a)\
7. Waste Characteristics (subject to 100
a maximum of 100)..................
Targets:
8. Exposed Individual............... 50
9. Population:......................
9a. Level I Concentrations...... \(b)\
9b. Level II Concentrations..... \(b)\
9c. Population within an Area of \(b)\
Subsurface Contamination.......
9d. Total Population (lines 9a + \(b)\
9b + 9c).......................
10. Resources....................... 5
11. Targets (lines 8 + 9d + 10)..... \(b)\
Subsurface Intrusion Component Score:
12. Subsurface Intrusion Component 100
(lines 4 x 7 x 11)/82,500 \c\
(subject to a maximum of 100)......
Soil Exposure and Subsurface Intrusion
Pathway Score:
13. Soil Exposure Component + 100
Subsurface Intrusion Component
(subject to a maximum of 100)......
------------------------------------------------------------------------
\a\ Maximum value applies to waste characteristics category.
\b\ Maximum value not applicable.
\c\ Do not round to the nearest integer.
5.2.0--General considerations. The subsurface intrusion component
evaluates the threats from hazardous substances that have or could
intrude into regularly occupied structures via surficial ground water
or the unsaturated zone. Evaluate the subsurface intrusion component
based on the actual or potential intrusion of hazardous substances into
a regularly occupied structures that has structure containment value
greater than zero; or actual or potential intrusion of hazardous
substances exists in the unsaturated zone or the surficial ground water
below the regularly occupied structures. These structures may or may
not have subunits. Subunits are partitioned areas within a structure
with separate heating, ventilating, and air conditioning (HVAC) systems
or distinctly different air exchange rates. Subunits include regularly
occupied partitioned tenant spaces such as office suites, apartments,
condos, common or shared areas, and portions of residential, commercial
or industrial structures with separate heating, ventilating, and air
conditioning (HVAC) systems.
In evaluating the subsurface intrusion component, consider the
following:
Area(s) of observed exposure: An area of observed exposure
is delineated by regularly occupied structures with documented
contamination meeting observed exposure criteria; an area of observed
exposure includes regularly occupied structures with samples meeting
observed exposure criteria or inferred to be within an area of observed
exposure based on samples meeting observed exposure criteria (see
section 5.2.1.1.1 Observed Exposure). Establish areas of observed
exposure as follows:
--For regularly occupied structures that have no subunits, consider
both the regularly occupied structures containing sampling location(s)
meeting observed exposure criteria for the site and the regularly
occupied structure(s) in the area lying between such locations to be an
area of observed exposure (i.e., inferred to be in an area of observed
exposure), unless available information indicates otherwise.
[[Page 10419]]
--In multi-story, multi-subunit, regularly occupied structures,
consider all subunits on a level with sampling locations meeting
observed exposure criteria from the site and all levels below, if any,
to be within an area of observed exposure, unless available information
indicates otherwise.
--In multi-tenant structures, that do not have a documented observed
exposure, but are located in an area lying between locations where
observed exposures have been documented, consider only those regularly
occupied subunits, if any, on the lowest level of the structure, to be
within an area of observed exposure (i.e., inferred to be in an area of
observed exposure, unless available information indicates otherwise.
Area(s) of subsurface contamination: An area of subsurface
contamination is delineated by sampling locations meeting observed
release criteria for subsurface intrusion, excluding areas of observed
exposure (see Table 2-3 in section 2.3). The area within an area of
subsurface contamination includes potentially exposed populations. If
the significant increase in hazardous substance levels cannot be
attributed at least in part to the site and cannot be attributed to
other sites, attribution can be established based on the presence of
hazardous substances in the area of subsurface contamination. Establish
areas of subsurface contamination as follows:
-- Exclude those areas that contain structures meeting the criteria
defined as an area of observed exposure.
-- Consider both the sampling location(s) with subsurface contamination
meeting observed release criteria from the site and the area lying
between such locations to be an area of subsurface contamination (i.e.,
inferred to be in an area of subsurface contamination), unless
available information indicates otherwise.
-- Evaluate an area of subsurface contamination based on hazardous
substances that:
[ssquf] Meet the criteria for observed exposure, or
[ssquf] Meet the criteria for observed release in an area of subsurface
contamination and have a vapor pressure greater than or equal to one
torr or a Henry's constant greater than or equal to 10-\5\
atm-m\3\/mol, or
[ssquf] Meet the criteria for an observed release in a structure
within, or in a sample from below, an area of observed exposure and has
a vapor pressure greater than or equal to one torr or a Henry's
constant greater than or equal to 10-\5\ atm-m\3\/mol.
See Section 7.0 for establishing an area of subsurface
contamination based on the presence of radioactive hazardous
substances.
-- Evaluate all structures with no subunits to be in an area of
subsurface contamination if they are lying between locations of
subsurface intrusion samples meeting observed release criteria.
-- Evaluate multi-subunit structures as follows:
[ssquf] If an observed exposure has been documented based on a gaseous
indoor air sample, consider all regularly occupied subunit(s), if any,
on the level immediately above the level where an observed exposure has
been documented (or has been inferred to be within an area of observed
exposure), to be within an area of subsurface contamination, unless
available information indicates otherwise.
[ssquf] If observed release criteria have been met based on a gaseous
indoor air sample collected from a level not regularly occupied,
consider all regularly occupied subunit(s), if any, on the level
immediately above the level where the observed release criteria has
been documented, to be within an area of subsurface contamination,
unless available information indicates otherwise.
[ssquf] If an observed exposure has been documented based on an
intruded liquid or particulate sample, do not consider any regularly
occupied subunit(s) above the level where an observed exposure has been
documented to be within an area of subsurface contamination, unless
available information indicates otherwise.
[ssquf] If any regularly occupied multi-subunit structure is inferred
to be in an area of subsurface contamination, consider only those
regularly occupied subunit(s), if any, on the lowest level, to be
within an area of subsurface contamination, unless available
information indicates otherwise.
If there is no area of observed exposure and no area of subsurface
contamination, assign a score of 0 for the subsurface intrusion
component.
5.2.1 Subsurface intrusion component. Evaluate this component only
if there is an area of observed exposure or area of subsurface
contamination:
Within or underlying a residence, school, day care center,
workplace, or
Within or underlying a resource specified in section
5.2.1.3.3.
5.2.1.1 Likelihood of exposure. Assign a value of 550 to the
likelihood of exposure factor category for the subsurface intrusion
component if there is an area of observed exposure in one or more
locations listed in section 5.2.1. Enter this value in Table 5-11.
5.2.1.1.1 Observed exposure. Establish observed exposure in a
regularly occupied structure by demonstrating that a hazardous
substance has been released into a regularly occupied structure via the
subsurface. Base this demonstration on either of the following
criterion:
Direct observation:
-- A solid, liquid or gaseous material that contains one or more
hazardous substances attributable to the site has been observed
entering a regularly occupied structure through migration via the
subsurface or is known to have entered a regularly occupied structure
via the subsurface, or
-- When evidence supports the inference of subsurface intrusion of a
material that contains one or more hazardous substances associated with
the site into a regularly occupied structure, demonstrated adverse
effects associated with that release may be used to establish observed
exposure.
Chemical analysis:
-- Analysis of indoor samples indicates that the concentration of
hazardous substance(s) has increased significantly above the background
concentration for the site for that type of sample (see section 2.3).
-- Some portion of the significant increase must be attributable to the
site to establish the observed exposure. Documentation of this
attribution should account for possible concentrations of the hazardous
substance(s) in outdoor air or from materials found in the regularly
occupied structure, and should provide a rationale for the increase
being from subsurface intrusion.
If observed exposure can be established in a regularly occupied
structure, assign an observed exposure factor value of 550, enter this
value in Table 5-11, and proceed to section 5.2.1.1.3. If no observed
exposure can be established, assign an observed exposure factor value
of 0, enter this value in Table 5-11, and proceed to section 5.2.1.1.2.
5.2.1.1.2 Potential for exposure. Evaluate potential for exposure
only if an observed exposure cannot be
[[Page 10420]]
established, but an area of subsurface contamination has been
delineated. Evaluate potential for exposure based only on the presence
of hazardous substances with a vapor pressure greater than or equal to
one torr or a Henry's constant greater than or equal to 10\-5\ atm-
m\3\/mol. Evaluate potential for exposure for each area of subsurface
contamination based on four factors: structure containment (see section
5.2.1.1.2.1), depth to contamination (see section 5.2.1.1.2.2),
vertical migration (see section 5.2.1.1.2.3) and vapor migration
potential (see section 5.2.1.1.2.4). For each area of subsurface
contamination, assign the highest value for each factor. If information
is insufficient to calculate any single factor value used to calculate
the potential for exposure factor values at an identified area of
subsurface contamination, information collected for another area of
subsurface contamination at the site may be used when evaluating
potential for exposure. Calculate the potential for exposure value for
the site as specified in section 5.2.1.1.2.5.
5.2.1.1.2.1 Structure containment. Calculate containment for
eligible hazardous substances within this component as directed in
Table 5-12 and enter this value into Table 5-11. Assign each regularly
occupied structure within an area of subsurface contamination the
highest appropriate structure containment value from Table 5-12 and use
the regularly occupied structure at the site with the highest structure
containment value in performing the potential for exposure calculation.
Assign a structure containment factor value of 10 to any regularly
occupied structure located within an area of observed exposure that is
established based on documented surficial ground water intrusion,
unless available information indicates otherwise.
Table 5-12--Structure Containment
------------------------------------------------------------------------
Evidence of structure
No. containment Assigned value
------------------------------------------------------------------------
1......................... Regularly occupied structure 10
with evidence of subsurface
intrusion, including
documented observed
exposure or sampling of bio
or inert gases, such as
methane and radon.
2......................... Regularly occupied structure 10
with open preferential
pathways from the
subsurface (e.g., sumps,
foundation cracks, unsealed
utility lines).
3......................... Regularly occupied structure 7
with an engineered vapor
migration barrier system
that does not address all
preferential pathways.
4......................... Regularly occupied structure 6
with an engineered passive
vapor mitigation system
without documented
institutional controls
(e.g., deed restrictions)
or evidence of regular
maintenance and inspection.
5......................... Regularly occupied structure 4
with no visible open
preferential pathways from
the subsurface (e.g.,
sumps, foundation cracks,
unsealed utility lines).
6......................... Regularly occupied structure 3
with an engineered passive
vapor mitigation system
(e.g., passive venting)
with documented
institutional controls
(e.g., deed restrictions)
or evidence of regular
maintenance and inspection.
7......................... Regularly occupied structure 2
with an engineered, active
vapor mitigation system
(e.g., active venting)
without documented
institutional controls
(e.g., deed restrictions)
and funding in place for on-
going operation, inspection
and maintenance.
8......................... Regularly occupied structure 2
with unknown containment
features.
9......................... Regularly occupied structure 0
with a permanent
engineered, active vapor
mitigation system (e.g.,
active venting) with
documented institutional
controls (e.g., deed
restrictions) and funding
in place for on-going
operation, inspection and
maintenance. This does not
include mitigation systems
installed as part of a
removal or other temporary
response by federal, state
or tribal authorities.
10........................ Regularly occupied structure 0
with a foundation raised
greater than 6 feet (e.g.,
structure on stilts) or
structure that has been
built, and maintained, in a
manner to prevent
subsurface intrusion.
------------------------------------------------------------------------
5.2.1.1.2.2 Depth to contamination. Assign each area of subsurface
contamination a depth to contamination based on the least depth to
either contaminated crawl space or subsurface media underlying a
regularly occupied structure. Measure this depth to contamination based
on the distance between the lowest point of a regularly occupied
structure to the highest known point of hazardous substances eligible
to be evaluated. Use any regularly occupied structure within an area of
subsurface contamination with a structure containment factor greater
than zero. Subtract from the depth to contamination the thickness of
any subsurface layer composed of features that would allow channelized
flow (e.g., karst, lava tubes, open fractures).
Based on this calculated depth, assign a factor value from Table 5-
13. If the necessary information is available at multiple locations,
calculate the depth to contamination at each location. Use the location
having the least depth to contamination to assign the factor value.
Enter this value in Table 5-11.
Table 5-13--Depth to Contamination
------------------------------------------------------------------------
Depth to
Depth range 1 2 contamination
assigned value
------------------------------------------------------------------------
0 to 10 ft.(Including subslab and semi-enclosed or 10
enclosed crawl space contamination)....................
>10 to 20 ft............................................ 8
>20 to 50 ft............................................ 6
>50 to 100 ft........................................... 4
>100 to 150 ft.......................................... 2
>150 ft................................................. 0
------------------------------------------------------------------------
\1\ If any part of the subsurface profile has channelized flow features,
assign that portion of the subsurface profile a depth of 0.
\2\ Measure elevation below any regularly occupied structure within an
area of subsurface contamination at a site. Select the regularly
occupied structure with the least depth to contamination below a
structure.
5.2.1.1.2.3 Vertical migration. Evaluate the vertical migration
factor for each area of subsurface contamination based on the geologic
materials in the interval between the lowest point of a regularly
occupied structure and the highest known point of hazardous substances
in the subsurface. Use any regularly occupied structure either within
an area of subsurface contamination or overlying subsurface soil gas or
ground water contamination. Assign a value to the vertical migration
factor as follows:
If the depth to contamination (see section 5.2.1.1.2.2) is
10 feet or less, assign a value of 15.
[[Page 10421]]
Do not consider layers or portions of layers within the
first 10 feet of the depth to contamination.
If, for the interval identified above, all layers that
underlie a portion of a regularly occupied structure at the site are
karst or otherwise allow channelized flow, assign a value of 15.
Otherwise:
--Select the lowest effective porosity/permeability layer(s) from
within the above interval. Consider only layers at least 1 foot thick.
(If site-specific data is not available, use the layer with the highest
value assigned in Table 5-14.)
--Assign a value for individual layers from Table 5-14.
--If more than one layer has the same assigned porosity/permeability
value, include all such layers and sum their thicknesses. Assign a
thickness of 0 feet to a layer with channelized flow features found
within any area of subsurface contamination at the site.
--Assign a value from Table 5-15 to the vertical migration factor,
based on the thickness and assigned porosity/permeability value of the
lowest effective porosity/permeability layer(s).
Determine vertical migration only at locations within an area of
subsurface contamination at the site. If the necessary subsurface
geologic information is available at multiple locations, evaluate the
vertical migration factor at each location. Use the location having the
highest vertical migration factor value to assign the factor value.
Enter this value in Table 5-11.
Table 5-14--Effective Porosity/Permeability of Geologic Materials
------------------------------------------------------------------------
Assigned
porosity/
Type of material permeability
value
------------------------------------------------------------------------
Gravel; highly permeable fractured igneous and 1
metamorphic rocks; permeable basalt; karst limestones
and dolomites..........................................
Sand; sandy clays; sandy loams; loamy sands; sandy 2
silts; sediments that are predominantly sand; highly
permeable till (coarse-grained, unconsolidated or
compact and highly fractured); peat; moderately
permeable limestones and dolomites (no karst);
moderately permeable sandstone; moderately permeable
fractured igneous and metamorphic rocks................
Silt; loams; silty loams; loesses; silty clays; 3
sediments that are predominantly silts; moderately
permeable till (fine-grained, unconsolidated till, or
compact till with some fractures); low permeability
limestones and dolomites (no karst); low permeability
sandstone; low permeability fractured igneous and
metamorphic rocks......................................
Clay; low permeability till (compact unfractured till); 4
shale; unfractured metamorphic and igneous rocks.......
------------------------------------------------------------------------
Table 5-15 Vertical Migration Factor Values a
--------------------------------------------------------------------------------------------------------------------------------------------------------
Thickness of lowest porosity layer(s) \b\ (feet)
-----------------------------------------------------------------------------------------------
Assigned porosity/ permeability value Greater than 5 Greater than Greater than Greater than Greater than
0 to 5 to 10 10 to 20 20 to 50 50 to 100 100 to 150
--------------------------------------------------------------------------------------------------------------------------------------------------------
1....................................................... 15 15 14 11 8 6
2....................................................... 15 14 12 9 6 4
3....................................................... 15 13 10 7 5 2
4....................................................... 15 12 9 6 3 1
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ If depth to contamination is 10 feet or less or if, for the interval being evaluated, all layers that underlie a portion of the structure at the
site are karst or have other channelized flow features, assign a value of 15.
\b\ Consider only layers at least 1 foot thick.
5.2.1.1.2.4 Vapor migration potential. Evaluate this factor for
each area of subsurface contamination as follows:
If the depth to contamination (see section 5.2.1.1.2.2) is
10 feet or less, assign a value of 25.
Assign a value for vapor migration potential to each of
the gaseous hazardous substances associated with the area of subsurface
contamination (see section 2.2.2) as follows:
--Assign values from Table 5-16 for both vapor pressure and Henry's
constant to each hazardous substance. If Henry's constant cannot be
determined for a hazardous substance, assign that hazardous substance a
value of 2 for the Henry's constant component.
--Sum the two values assigned to each hazardous substance.
--Based on this sum, assign each hazardous substance a value from Table
5-17 for vapor migration potential.
Assign a value for vapor migration potential to each area
of subsurface contamination as follows:
--Select the hazardous substance associated with the area of subsurface
contamination with the highest vapor migration potential value and
assign this value as the vapor migration potential factor for the area
of subsurface contamination.
Enter this value in Table 5-11.
Table 5-16--Values for Vapor Pressure and Henry's Constant
------------------------------------------------------------------------
Vapor pressure (Torr) Assigned value
------------------------------------------------------------------------
Greater than 10......................................... 3
1 to 10................................................. 2
Less than 1............................................. 0
------------------------------------------------------------------------
Henry's constant (atm-m\3\/mol) Assigned value
------------------------------------------------------------------------
Greater than 10-\3\..................................... 3
Greater than 10-\4\ to 10-\3\........................... 2
10-\5\ to 10-\4\........................................ 1
Less than 10-\5\........................................ 0
------------------------------------------------------------------------
[[Page 10422]]
Table 5-17--Vapor Migration Potential Factor Values for a Hazardous
Substance
------------------------------------------------------------------------
Sum of values for vapor pressure and Henry's constant Assigned value
------------------------------------------------------------------------
0....................................................... 0
1 or 2.................................................. 5
3 or 4.................................................. 15
5 or 6.................................................. 25
------------------------------------------------------------------------
5.2.1.1.2.5 Calculation of potential for exposure factor value. For
each identified area of subsurface contamination, sum the factor values
for depth to contamination, vertical migration and vapor migration
potential, and multiply this sum by the factor value for structure
containment. Select the highest product for any area of subsurface
contamination and assign this value as the potential for exposure
factor value for the component. Enter this value in Table 5-11.
5.2.1.1.3 Calculation of likelihood of exposure factor category
value. If observed exposure is established for the site, assign the
observed exposure factor value of 550 as the likelihood of exposure
factor category value for the site. Otherwise, assign the potential for
exposure factor value for the component as the likelihood of exposure
value. Enter the value assigned in Table 5-11.
5.2.1.2 Waste characteristics. Evaluate waste characteristics based
on two factors: Toxicity/degradation and hazardous waste quantity.
5.2.1.2.1 Toxicity/degradation. For each hazardous substance,
assign a toxicity factor value, a degradation factor value and a
combined toxicity/degradation factor value as specified in sections
2.2.3, 2.4.1.2 and 5.2.1.2.1.1 through 5.2.1.2.1.3.
5.2.1.2.1.1 Toxicity. Assign a toxicity factor value to each
hazardous substance as specified in sections 2.2.2 and 2.4.1.1.
5.2.1.2.1.2 Degradation. Assign a degradation factor value to each
hazardous substance as follows:
For any hazardous substance that meets the criteria for an
observed exposure, assign that substance a degradation factor value of
1.
For all hazardous substances at the site that meet
subsurface intrusion observed release criteria but not observed
exposure criteria, assign a degradation factor value of 1 if the depth
to contamination below an area of subsurface contamination or area of
observed exposure is less than 10 feet or if available evidence
suggests that there is less than 10 feet of biologically active soil in
the subsurface anywhere underneath a regularly occupied structure
within an area of subsurface contamination or area of observed
exposure.
For all other situations first calculate the half-life for each
hazardous substance that meets subsurface intrusion observed release
criteria as follows:
The half-life or a substance in the subsurface is defined for HRS
purposes as the time required to reduce the initial concentration in
the subsurface by one-half as a result of the combined decay processes
of two components: biodegradation and hydrolysis.
Estimate the half-life (t1/2) of a hazardous substance
as follows:
[GRAPHIC] [TIFF OMITTED] TP29FE16.039
Where:
h=Hydrolysis half-life.
b=Biodegradation half-life.
If one of these component half-lives cannot be estimated for the
hazardous substance from available data, delete that component half-
life from the above equation.
If no half-life information is available for a hazardous substance
and the substance is not already assigned a value of 1, unless
information indicates otherwise, all straight-chain and simple-ring
structure substances will be considered to have a half-life less than
30 days if not the hazardous substance will be assigned a half-life of
greater than 100 days.
Based on the hazardous substance's assigned half-life the
degradation factor is assigned as follows:
For all hazardous substances at the site that meet
subsurface intrusion observed release criteria but not observed
exposure criteria, assign a degradation factor value of 0.1, if:
--The depth to contamination at the site is greater than or equal to 10
feet, but not if available evidence suggests that at least 10 feet of
biologically active soil is not present in the subsurface anywhere
underneath a structure within an area of subsurface contamination or
area of observed exposure, and
--The hazardous substance has a half-life of 30 days or less.
For all hazardous substances at the site that meet
subsurface intrusion observed release criteria but not observed
exposure criteria, assign a degradation factor value of 0.5, if:
--The depth to contamination at the site is greater than 30 feet, but
not if available evidence suggests that at least 30 feet of
biologically active soil is not present in the subsurface anywhere
underneath a structure within an area of subsurface contamination or
area of observed exposure, and
--The hazardous substance has a half-life equal to or less than 100
days.
For all other situations assign a degradation factor of 1
for all hazardous substances at the site that meet subsurface intrusion
observed release criteria.
In addition, for hazardous substances that meet observed release
criteria, have a parent-daughter degradation relationship, and the
daughter substance is found only in samples with a depth greater than
10 feet, assign the daughter substance degradation factor value as
follows:
1. Identify the shallowest subsurface sample that contains the
daughter substance.
2. Determine if the selected sample or another sample from the same
relative position in the media of concern, or in a shallower sample,
contains the parent substance.
3. If the parent substance is not present in the identified
samples, assign the degradation factor value for the daughter substance
based on the half-life for the daughter substance.
4. If the parent substance is present in a sample from the same
relative position in the subsurface or in a shallower sample, compare
the half-life-based degradation factor value for the daughter substance
to the degradation factor value assigned to the parent substance.
Assign the greater of the two values as the degradation factor value
for the daughter substance.
5.2.1.2.1.3 Calculation of toxicity/degradation factor value.
Assign each substance a toxicity/biodegradation value by multiplying
the toxicity factor value by the degradation factor value. Use the
hazardous substance with the highest combined toxicity/degradation
value to assign the factor value to the toxicity/degradation factor for
the subsurface intrusion threat. Enter this value in Table 5-11.
5.2.1.2.2 Hazardous waste quantity. Assign a hazardous waste
quantity factor value as specified in section 2.4.2. Consider only
those regularly occupied structures with a non-zero structure
containment value. In estimating the hazardous waste quantity, use
Tables 2-5 and 5-18 and:
For Tier A, hazardous constituent quantity, use the mass
of constituents found in the regularly occupied structure(s) where the
observed exposure has been identified.
--For multi-subunit structures, when calculating Tier A, use the mass
of
[[Page 10423]]
constituents found in the regularly occupied subunit space(s) where the
observed exposure has been identified.
For Tier B, hazardous wastestream quantity, use the flow-
through volume of the regularly occupied structures where the observed
exposure has been identified.
--For multi-subunit structures, when calculating Tier B, use the flow-
through volume of the regularly occupied subunit spaces where the
observed exposure has been identified.
For Tier C, volume, use the volume divisor listed in Tier
C of Table 5-18. Volume is calculated for those regularly occupied
structures located within areas of observed exposure with observed or
inferred intrusion and within areas of subsurface contamination.
--In evaluating the volume measure for these listed areas of observed
exposure and areas of subsurface contamination based on a gaseous/vapor
intrusion or the potential for gaseous/vapor intrusion, consider the
following:
Calculate the volume of each regularly occupied structure
based on actual data. If unknown, use a ceiling height of 8 feet.
For multi-subunit structures, when calculating Tier C,
calculate volume for those subunit spaces with observed or inferred
exposure and all other regularly occupied subunit spaces on that level,
unless available information indicates otherwise. If the structure has
multiple stories, also include the volume of all regularly occupied
subunit spaces below the floor with an observed exposure and one story
above, unless evidence indicates otherwise.
For multi-subunit structures within an area of subsurface
contamination and no observed or inferred exposure, consider only the
volume of the regularly occupied subunit spaces on the lowest story,
unless available information indicates otherwise.
--In evaluating the volume measure for these listed areas of observed
exposure and areas of subsurface contamination where intrusion of
contaminated ground water has occurred, do not calculate the volume of
each regularly occupied structure. Instead, consider only the volume of
contaminated ground water known to have intruded into a regularly
occupied structure.
For Tier D, area, if volume is unknown, use the area
divisor listed in Tier D of Table 5-18 for those regularly occupied
structures within areas of observed exposure with observed or inferred
intrusion and within areas of subsurface contamination. In evaluating
the area measure for these listed areas of observed exposure and areas
of subsurface contamination, calculate the area of each regularly
occupied structure (including multi-subunit structures) based on actual
footprint area data. If the actual footprint area of the structure(s)
is unknown, use an area of 1,740 square feet for each structure (or
subunit space).
Table 5-18--Hazardous Waste Quantity Evaluation Equations for Subsurface
Intrusion Component
------------------------------------------------------------------------
Equation for
Tier Measure Units assigning value
\a\
------------------------------------------------------------------------
A Hazardous Constituent lb............. C.
Quantity (C).
B \b\ Hazardous Wastestream lb............. W/5,000.
Quantity (W).
------------------------------------------------------------------------
C b c Volume (V).
------------------------------------------------------------------------
Regularly occupied yd \3\......... V/2.5.
structure(s) in areas
of observed exposure
or subsurface
contamination.
------------------------------------------------------------------------
D b d Area (A).
------------------------------------------------------------------------
Regularly occupied ft \2\......... A/13.
structure(s) in areas
of observed exposure
or subsurface
contamination.
------------------------------------------------------------------------
\a\ Do not round to the nearest integer.
\b\ Convert volume to mass when necessary: 1 ton = 2,000 pounds = 1
cubic yard = 4 drums = 200 gallons.
\c\ Calculate volume of each regularly occupied structure or subunit
space in areas of observed exposure and areas of subsurface
contamination--Assume 8-foot ceiling height unless actual value is
known.
\d\ Calculate area of the footprint of each regularly occupied structure
in areas of observed exposure and areas of subsurface contamination.
If the footprint area of a regularly occupied structure is unknown,
use 1,740 square feet as the footprint area of the structure or
subunit space.
For the subsurface intrusion component, if the hazardous
constituent quantity is adequately determined for all areas of observed
exposure, assign the value from Table 2-6 as the hazardous waste
quantity factor value. If the hazardous constituent quantity is not
adequately determined for one or more areas of observed exposure or if
one or more areas of subsurface contamination are present, assign
either the value from Table 2-6 or assign a factor value as follows:
If any target for the subsurface intrusion component is
subject to Level I or Level II concentrations (see section 2.5), assign
either the value from Table 2-6 or a value of 100, whichever is
greater, as the hazardous waste quantity factor value for this
component.
If none of the targets for the subsurface intrusion
component is subject to Level I or Level II concentrations and if there
has been a removal action that does not permanently interrupt target
exposure from subsurface intrusion, assign a factor value as follows:
--Determine the values from Table 2-6 with and without consideration of
the removal action.
--If the value that would be assigned from Table 2-6 without
consideration of the removal action would be 100 or greater, assign
either the value from Table 2-6 with consideration of the removal
action or a value of 100, whichever is greater, as the hazardous waste
quantity factor value for the component.
--If the value that would be assigned from Table 2-6 without
consideration of the removal action would be less than 100, assign a
value of 10 as the hazardous waste quantity factor value for the
component.
Otherwise, if none of the targets for the subsurface
intrusion component is subject to Level I or Level II concentrations
and there has not been a removal action, assign a minimum value of 10.
Enter the value assigned in Table 5-11.
[[Page 10424]]
5.2.1.2.3 Calculation of waste characteristics factor category
value. Multiply the toxicity/degradation and hazardous waste quantity
factor values, subject to a maximum product of 1 x 10\8\. Based on this
product, assign a value from Table 2-7 (section 2.4.3.1) to the waste
characteristics factor category. Enter this value in Table 5-11.
5.2.1.3 Targets. Evaluate the targets factor category for the
subsurface intrusion threat based on three factors: Exposed individual,
population, and resources in regularly occupied structures. Evaluate
only those targets within areas of observed exposure and areas of
subsurface contamination (see section 5.2.0).
In evaluating the targets factor category for the subsurface
intrusion threat, count only the following as targets:
Exposed individual--a person living, attending school or
day care, or working in a regularly occupied structure with observed
exposure or in a structure within an area of observed exposure or
within an area of subsurface contamination.
Population--exposed individuals in a regularly occupied
structure within an area of observed exposure or within an area of
subsurface contamination.
Resources--located within an area of observed exposure or
within an area of subsurface contamination as specified in section
5.2.1.3.3.
If a former structure that has been vacated due to subsurface
intrusion attributable to the site, count the initial targets as if
they were still residing in the structure. In addition, if a removal
action has occurred that has not completely mitigated the release,
count the initial targets as if the removal action has not permanently
interrupted target exposure from subsurface intrusion.
For populations residing in or working in a multi-subunit structure
with multiple stories in an area of observed exposure or area of
subsurface contamination, count these targets as follows:
If there is no observed exposure within the structure,
include in the evaluation only those targets, if any, in the lowest
occupied level, unless available information indicates otherwise.
If there is an observed exposure in any level, include in
the evaluation those targets in that level, the level above and all
levels below, unless available information indicates otherwise. (The
weighting of these targets is specified in Section 5.2.1.3.2.)
5.2.1.3.1 Exposed individual. Evaluate this factor based on whether
there is an exposed individual, as specified in sections 2.5.1, 2.5.2
and 5.2.1.3, who is subject to Level I or Level II concentrations.
First, determine those regularly occupied structures or partitioned
subunit(s) within structures in an area of observed exposure subject to
Level I concentrations and those subject to Level II concentrations as
specified as follows (see section 5.2.0):
Level I Concentrations: For contamination resulting from
subsurface intrusion, compare the hazardous substance concentrations in
any sample meeting the observed exposure by chemical analysis criteria
to the appropriate benchmark. Use the health-based benchmarks from
Table 5-19 to determine the level of contamination.
--If the sample is from a structure with no subunits and the
concentration equals or exceeds the appropriate benchmark, assign Level
I concentrations to the entire structure.
--If the sample is from a subunit within a structure and the
concentration from that subunit equals or exceeds the appropriate
benchmark, assign Level I concentrations to that subunit.
Level II Concentrations: Structures, or subunits within
structures, with one or more samples that meet observed exposure by
chemical analysis criteria but do not equal or exceed the appropriate
benchmark; structures, or subunits, that have an observed exposure by
direct observation; and structures inferred to be in an area of
observed exposure based on samples meeting observed exposure, are
assigned Level II concentrations.
[cir] For all regularly occupied structures, or subunits in such
structures, in an area of observed exposure that are not assigned Level
I concentrations, assign Level II concentrations.
Then assign a value to the exposed individual factor as follows:
Assign a value of 50 if there is at least one exposed
individual in one or more regularly occupied structures subject to
Level I concentrations.
Assign a value of 45 if there are no Level I exposed
individuals, but there is at least one exposed individual in one or
more regularly occupied structures subject to Level II concentrations.
Assign a value of 20 if there is no Level I or Level II
exposed individual but there is at least one individual in a regularly
occupied structure within an area of subsurface contamination.
Enter the value assigned in Table 5-11.
5.2.1.3.2 Population. Evaluate population based on three factors:
Level I concentrations, Level II concentrations, and population within
an area of subsurface contamination. Determine which factors apply as
specified in section 5.2.1.3.1, using the health-based benchmarks from
Table 5-19. Evaluate populations subject to Level I and Level II
concentrations as specified in section 2.5.
Table 5-19--Health-Based Benchmarks for Hazardous Substances in the
Subsurface Intrusion Component
------------------------------------------------------------------------
------------------------------------------------------------------------
Screening concentration for cancer corresponding to that
concentration that corresponds to the 10-\6\ individual cancer risk
using the inhalation unit risk. For oral exposures use the oral
cancer slope factor................................................
Screening concentration for noncancer toxicological responses
corresponding to the reference dose (RfD) for oral exposure and the
reference concentration (RfC) for inhalation exposures.............
------------------------------------------------------------------------
Count only those persons meeting the criteria for population as
specified in section 5.2.1.3. In estimating the number of individuals
in structures in an area of observed exposure or area of subsurface
contamination if the actual number of residents is not known, multiply
each residence by the average number of persons per residence for the
county in which the residence is located.
5.2.1.3.2.1 Level I concentrations. Assign the population subject
to Level I concentrations as follows:
1. Identify all exposed individuals regularly present in a
structure, or if the structure has subunits, identify those regularly
present in each subunit, located in an area of observed exposure
subject to Level I concentrations as described in sections 5.2.0 and
5.2.1.3.1. Identify only once per structure those exposed individuals
that are using more than one eligible subunit of the same structure
(e.g., using a common or shared area and other parts of the same
structure).
2. For each structure or subunit count the number of individuals
residing in or
[[Page 10425]]
attending school or day care in the structure or subunit.
3. Count the number of full-time and part-time workers in the
structure or subunit(s) subject to Level I concentrations. If
information is unavailable to classify a worker as full- or part-time,
evaluate that worker as being full-time. Divide the number of full-time
workers by 3 and the number of part-time workers by 6, and then sum
these products with the number of other individuals for each structure
or subunit.
4. Sum this combined value for all structures, or subunits, within
areas of observed exposure and multiply this sum by 10.
Assign the resulting product as the combined population factor
value subject to Level I concentrations for the site. Enter this value
in line 9a of Table 5-11.
5.2.1.3.2.2 Level II concentrations. Assign the population subject
to Level II concentrations as follows:
1. Identify all exposed individuals regularly present in an
eligible structure, or if the structure has subunits, identify those
regularly present in each subunit, located in an area of observed
exposure subject to Level II concentrations as described in sections
5.2.0 and 5.2.1.3.1. Identify only once per structure those exposed
individuals that are using more than one eligible subunit of the same
structure (e.g., using a common or shared area and other parts of the
same structure).
2. Do not include exposed individuals already counted under the
Level I concentrations factor.
3. For each structure or subunit(s), count the number of
individuals residing in or attending school or day care in the
structure, or subunit, subject to Level II concentrations.
4. Count the number of full-time and part-time workers in the
structure or subunit(s) subject to Level II concentrations. If
information is unavailable to classify a worker as full- or part-time,
evaluate that worker as being full-time. Divide the number of full-time
workers by 3 and the number of part-time workers by 6, and then sum
these products with the number of other individuals for each structure
or subunit.
5. Sum the combined population value for all structures within the
areas of observed exposure for the site.
Assign this sum as the combined population value subject to Level
II contamination for this factor. Enter this value in line 9b of Table
5-11.
5.2.1.3.2.3 Population within area(s) of subsurface contamination.
Assign the population in area(s) of subsurface contamination factor
value as follows, unless available information indicates otherwise (see
sections 5.2.0 and 5.2.1.3.1):
1. Identify the regularly occupied structures with a structure
containment value greater than zero and the eligible population
associated with the structures or portions of structures in each area
of subsurface contamination:
For each regularly occupied structure or portion of a
structure in an area of subsurface contamination, sum the number of all
individuals residing in or attending school or day care, in the
structure or portion of the structure in the area of subsurface
contamination.
Count the number of full-time and part-time workers
regularly present in each structure or portion of a structure in an
area of subsurface contamination. If information is unavailable to
classify a worker as full- or part-time, evaluate that worker as being
full-time. Divide the number of full-time workers by 3 and the number
of part-time workers by 6. Sum these products with the number of
individuals residing in or attending school or day care in the
structure.
Use this sum as the population for the structure.
2. Estimate the depth or distance to contamination at each
regularly occupied structure within an area of subsurface contamination
based on available sampling data, and categorize each eligible
structure based on the depth or distance to contamination and sampling
media as presented in Table 5-20. Weight the population in each
structure using the appropriate weighting factors in Table 5-20. If
samples from multiple media are available, use the sample that results
in the highest weighting factor.
3. Sum the weighted population in all structures within the area(s)
of subsurface contamination and assign this sum as the population
subject subsurface contamination factor value. Enter this value in line
9c of Table 5-11.
Table 5-20--Weighting Factor Values for Populations Within an Area of
Subsurface Contamination
------------------------------------------------------------------------
Population
Eligible populations \a\ in structures \b\ within an weighting
area of subsurface contamination factor
------------------------------------------------------------------------
Population in a structure with levels of contamination 0.9
in a semi-enclosed or enclosed crawl space sample
meeting observed release criteria
or......................................................
Population in a subunit of a multi-story structure
within an area of subsurface contamination located
directly above a level in an area of observed exposure
or a gaseous indoor air sample meeting observed release
criteria...............................................
Population in a structure where levels of contaminants 0.4
meeting observed release criteria are found in any
sampling media at or within five feet horizontally or
vertically of the structure foundation.................
Population occupying a structure where levels of 0.2
contaminants meeting observed release criteria are
found or inferred based on any underlying non-ground
water subsurface sample at a depth less than or equal
to 30 feet
or......................................................
Population in a structure within an area of subsurface
contamination where levels of contaminants meeting
observed release criteria are inferred based on semi-
enclosed or enclosed crawl space samples in surrounding
structures.............................................
Population in a structure where levels of contaminants 0.1
meeting observed release criteria are found or inferred
based on underlying ground water samples greater than
five feet from the structure foundation
or......................................................
Population in a structure where levels of contaminants
meeting observed release criteria are found or inferred
based on any underlying sample at depths greater than
30 feet................................................
------------------------------------------------------------------------
\a\ Eligible populations include residents (including individuals living
in, or attending school or day care in the structure), and workers in
regularly occupied structures (see HRS Section 5.2.1.3).
\b\ Eligible structures may include single- or multi-tenant structures
where eligible populations reside, attend school or day care, or work.
These structures may also be mixed use structures.
[[Page 10426]]
5.2.1.3.2.4 Calculation of population factor value. Sum the factor
values for Level I concentrations, Level II concentrations, and
population in the area(s) of subsurface contamination. Assign this sum
as the population factor value. Enter this value in line 9d of Table 5-
11.
5.2.1.3.3 Resources. Evaluate the resources factor as follows:
Assign a value of 5 if a resource structure (e.g.,
library, church, tribal facility) is present and regularly occupied
within either an area of observed exposure or area of subsurface
contamination.
Assign a value of 0 if there is no resource structure
within an area of observed exposure or area of subsurface
contamination.
Enter the value assigned in Table 5-11.
5.2.1.3.4 Calculation of targets factor category value. Sum the
values for the exposed individual, population, and resources factors.
Do not round to the nearest integer. Assign this sum as the targets
factor category value for the subsurface intrusion component. Enter
this value in Table 5-11.
5.2.2 Calculation of subsurface intrusion component score. Multiply
the factor category values for likelihood of exposure, waste
characteristics and targets and round the product to the nearest
integer. Divide the product by 82,500. Assign the resulting value,
subject to a maximum of 100, as the subsurface intrusion component
score and enter this score in Table 5-11.
5.3 Calculation of the soil exposure and subsurface intrusion
pathway score: Sum the soil exposure component score and subsurface
intrusion component. Assign the resulting value, subject to a maximum
of 100, as the soil exposure and subsurface intrusion pathway score
(Ssessi). Enter this score in Table 5-11.
6.0 Air Migration Pathway
* * * * *
Table 6-14--Health-Based Benchmarks for Hazardous Substances in Air
------------------------------------------------------------------------
-------------------------------------------------------------------------
Concentration corresponding to National Ambient Air Quality
Standard (NAAQS).
Concentration corresponding to National Emission Standards for
Hazardous Air Pollutants (NESHAPs).
Screening concentration for cancer corresponding to that
concentration that corresponds to the 10-6 individual cancer risk for
inhalation exposures.
Screening concentration for noncancer toxicological responses
corresponding to the Reference Concentration (RfC) for inhalation
exposures.
------------------------------------------------------------------------
* * * * *
7.0 Sites Containing Radioactive Substances
* * * * *
[[Page 10427]]
[GRAPHIC] [TIFF OMITTED] TP29FE16.040
[[Page 10428]]
[GRAPHIC] [TIFF OMITTED] TP29FE16.041
* * * * *
* * * These differences apply largely to the soil exposure and
subsurface intrusion pathway and to sites containing mixed radioactive
and other hazardous substances. * * *
7.1 Likelihood of release/likelihood of exposure. Evaluate
likelihood of release for the three migration pathways and likelihood
of exposure for the soil exposure and subsurface intrusion pathway as
specified in sections 2 through 6, except: Establish an observed
release, observed contamination, and/or observed exposure as specified
in section 7.1.1. When an observed release or exposure cannot be
established for a migration pathway or the subsurface intrusion
component of the soil exposure and subsurface intrusion pathway,
evaluate potential to release as specified in section 7.1.2. When
observed contamination cannot be established, do not evaluate the soil
exposure component of the soil exposure and subsurface intrusion
pathway.
7.1.1 Observed release/observed contamination/observed exposure.
For radioactive substances, establish an observed release for each
migration pathway by demonstrating that the site has released a
radioactive substance to the pathway (or watershed or aquifer, as
appropriate); establish observed contamination or observed exposure for
the soil exposure and subsurface intrusion pathway as indicated below.
Base these demonstrations on one or more of the following, as
appropriate to the pathway being evaluated:
Direct observation:
--For each migration pathway, a material that contains one or more
radionuclides has been seen entering the atmosphere, surface water, or
ground water, as appropriate, or is known to have entered ground water
or surface water through direct deposition, or
--For the surface water migration pathway, a source area containing
radioactive substances has been flooded at a time that radioactive
substances were present and one or more radioactive substances were in
contact with the flood waters.
--For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, a material that contains one or more
radionuclides has been observed entering a regularly occupied structure
via the subsurface or is known to have entered a regularly occupied
structure via the subsurface. Also, when evidence supports the
inference of subsurface intrusion of a material that contains one or
more radionuclides by the site into a regularly occupied structure,
demonstrated adverse effects associated with that release may also be
used to establish observed exposure by direct observation.
Analysis of radionuclide concentrations in samples
appropriate to the pathway (that is, ground water, soil, air, indoor
air, surface water, benthic, or sediment samples):
--For radionuclides that occur naturally and for radionuclides that are
ubiquitous in the environment:
[ssquf] Measured concentration (in units of activity, for example,
pCi per kilogram [pCi/kg], pCi per liter [pCi/L], pCi per cubic meter
[pCi/m3]) of a given radionuclide in the sample are at a level that:
[cir] Equals or exceeds a value 2 standard deviations above the
mean site-specific background concentration for that radionuclide in
that type of sample, or
[cir] Exceeds the upper-limit value of the range of regional
background concentration values for that specific radionuclide in that
type of sample.
[ssquf] Some portion of the increase must be attributable to the
site to establish the observed release (or observed contamination or
observed exposure), and
[ssquf] For the soil exposure component of the soil exposure and
subsurface intrusion pathway only, the radionuclide must also be
present at the surface or covered by 2 feet or less of cover material
(for example, soil) to establish observed contamination.
--For man-made radionuclides without ubiquitous background
concentrations in the environment:
[ssquf] Measured concentration (in units of activity) of a given
radionuclide in a sample equals or exceeds the sample quantitation
limit for that specific radionuclide in that type of media and is
attributable to the site.
[ssquf] However, if the radionuclide concentration equals or
exceeds its sample quantitation limit, but its release can also be
attributed to one or more neighboring sites, then the measured
concentration of that radionuclide must also equal or exceed a value
either 2 standard deviations above the mean concentration of that
radionuclide contributed by those neighboring sites or 3 times its
background concentration, whichever is lower.
[ssquf] If the sample quantitation limit cannot be established:
[cir] If the sample analysis was performed under the EPA Contract
Laboratory Program, use the EPA contract-required quantitation limit
(CRQL) in place of the sample quantitation limit in establishing an
observed release (or observed contamination or observed exposure).
[cir] If the sample analysis is not performed under the EPA
Contract Laboratory Program, use the detection limit in place of the
sample quantitation limit.
[[Page 10429]]
[ssquf] For the soil exposure component of the soil exposure and
subsurface intrusion pathway only, the radionuclide must also be
present at the surface or covered by 2 feet or less of cover material
(for example, soil) to establish observed contamination.
Gamma radiation measurements (applies only to observed
contamination or observed exposure in the soil exposure and subsurface
intrusion pathway):
--The gamma radiation exposure rate, as measured in microroentgens per
hour ([mu]R/hr) using a survey instrument held 1 meter above the ground
surface or floor or walls of a structure (or 1 meter away from an
aboveground source for the soil exposure component), equals or exceeds
2 times the site-specific background gamma radiation exposure rate.
--Some portion of the increase must be attributable to the site to
establish observed contamination. The gamma-emitting radionuclides do
not have to be within 2 feet of the surface of the source.
For the three migration pathways and for the subsurface intrusion
component of the soil exposure and subsurface intrusion pathway, if an
observed release or observed exposure can be established for the
pathway (or threat, aquifer, or watershed, as appropriate), assign the
pathway (or threat, aquifer, or watershed) an observed release or
observed exposure factor value of 550 and proceed to section 7.2. If an
observed release or observed exposure cannot be established, assign an
observed release or observed exposure factor value of 0 and proceed to
section 7.1.2.
For the soil exposure component of the soil exposure and subsurface
intrusion pathway, if observed contamination can be established, assign
the likelihood of exposure factor for resident population a value of
550 if there is an area of observed contamination in one or more
locations listed in section 5.1.1; evaluate the likelihood of exposure
factor for nearby population as specified in section 5.1.2.1; and
proceed to section 7.2. If observed contamination cannot be
established, do not evaluate the soil exposure component of the soil
exposure and subsurface intrusion pathway.
At sites containing mixed radioactive and other hazardous
substances, evaluate observed release (or observed contamination or
observed exposure) separately for radionuclides as described in this
section and for other hazardous substances as described in sections 2
through 6.
For the three migration pathways and the subsurface intrusion
component of the soil exposure and subsurface intrusion pathway, if an
observed release or observed exposure can be established based on
either radionuclides or other hazardous substances, or both, assign the
pathway (or threat, aquifer, or watershed) an observed release or
observed exposure factor value of 550 and proceed to section 7.2. If an
observed release or observed exposure cannot be established based on
either radionuclides or other hazardous substances, assign an observed
release or observed exposure factor value of 0 and proceed to section
7.1.2.
For the soil exposure component of the soil exposure and subsurface
intrusion pathway, if observed contamination can be established based
on either radionuclides or other hazardous substances, or both, assign
the likelihood of exposure factor for resident population a value of
550 if there is an area of observed contamination in one or more
locations listed in section 5.1.1; evaluate the likelihood of exposure
factor for nearby population as specified in section 5.1.2.1; and
proceed to section 7.2. If observed contamination cannot be established
based on either radionuclides or other hazardous substances, do not
evaluate the soil exposure component of the soil exposure and
subsurface intrusion pathway.
7.1.2 Potential to release/potential for exposure. For the three
migration pathways and the subsurface intrusion component of the soil
exposure and subsurface intrusion pathway, evaluate potential to
release or potential for exposure for sites containing radionuclides in
the same manner as specified for sites containing other hazardous
substances. Base the evaluation on the physical and chemical properties
of the radionuclides, not on their level of radioactivity. For the
subsurface intrusion component of the soil exposure and subsurface
intrusion pathway, if the potential for exposure is based on the
presence of gamma emitting radioactive substances, assign a potential
for exposure factor value of 500 only if the contamination is found
within 2 feet beneath a regularly occupied structure, otherwise assign
a potential for exposure factor value of 0.
For sites containing mixed radioactive and other hazardous
substances, evaluate potential to release or potential for exposure
considering radionuclides and other hazardous substances together.
Evaluate potential to release for each migration pathway and the
potential for exposure for the subsurface intrusion component of the
soil exposure and subsurface intrusion pathway as specified in sections
3 through 6, as appropriate.
* * * * *
7.2.3 Persistence/Degradation. In determining the surface water
persistence factor for radionuclides, evaluate the surface water
persistence this factor based solely on half-life; do not include
sorption to sediments in the evaluation as is done for nonradioactive
hazardous substances. Assign a persistence factor value from Table 4-10
(section 4.1.2.2.1.2) to each radionuclide based on half-life (t
1/2) calculated as follows:
[GRAPHIC] [TIFF OMITTED] TP29FE16.042
Where:
r = Radioactive half-life.
v = Volatilization half-life.
If the volatilization half-life cannot be estimated for a
radionuclide from available data, delete it from the equation. Select
the portion of Table 4-10 to use in assigning the persistence factor
value as specified in section 4.1.2.2.1.2.
At sites containing mixed radioactive and other hazardous
substances, evaluate the persistence factor separately for each
radionuclide and for each nonradioactive hazardous substance, even if
the available data indicate that they are combined chemically. Assign a
persistence factor value to each radionuclide as specified in this
section and to each nonradioactive hazardous substance as specified in
section 4.1.2.2.1.2. When combined chemically, assign a single
persistence factor value based on the higher of the two values assigned
(individually) to the radioactive and nonradioactive components.
In determining the subsurface intrusion degradation factor for
radionuclides, when evaluating this factor based solely on half-life.
Assign a degradation factor value from section 5.2.1.2.1.2 to each
radionuclide based on half-life (t1/2) calculated as
follows:
[GRAPHIC] [TIFF OMITTED] TP29FE16.043
Where:
r = Radioactive half-life.
At sites containing mixed radioactive and other hazardous
substances,
[[Page 10430]]
evaluate the persistence or degradation factor separately for each
radionuclide and for each nonradioactive hazardous substance, even if
the available data indicate that they are combined chemically. Assign a
persistence or degradation factor value to each radionuclide as
specified in this section and to each nonradioactive hazardous
substance as specified in sections 4.1.2.2.1.2 and 5.2.1.2.1.2. When
combined chemically, assign a single persistence or degradation factor
value based on the higher of the two values assigned (individually) to
the radioactive and nonradioactive components.
7.2.4 Selection of substance potentially posing greatest hazard.
For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway and each migration pathway (or threat,
aquifer, or watershed, as appropriate), select the radioactive
substance or nonradioactive hazardous substance that potentially poses
the greatest hazard based on its toxicity factor value, combined with
the applicable mobility, persistence, degradation and/or
bioaccumulation (or ecosystem bioaccumulation) potential factor values.
Combine these factor values as specified in sections 2 through 6. For
the soil exposure component of the soil exposure and subsurface
intrusion pathway, base the selection on the toxicity factor alone (see
sections 2 and 5).
* * * * *
7.2.5.1 Source hazardous waste quantity for radionuclides For each
migration pathway, assign a source hazardous waste quantity value to
each source having a containment factor value greater than 0 for the
pathway being evaluated. For the soil exposure component of the soil
exposure and subsurface intrusion pathway, assign a source hazardous
waste quantity value to each area of observed contamination, as
applicable to the threat being evaluated. For the subsurface intrusion
component, assign a source hazardous waste quantity value to each
regularly occupied structure located within areas of observed exposure
or areas of subsurface contamination. Allocate hazardous substances and
hazardous wastestreams to specific sources (or areas of observed
contamination, area of observed exposure or area of subsurface
contamination) as specified in sections 2.4.2 and 5.2.0.
7.2.5.1.1 Radionuclide constituent quantity (Tier A). Evaluate
radionuclide constituent quantity for each source (or area of observed
contamination or area of observed exposure) based on the activity
content of the radionuclides allocated to the source (or area of
observed contamination or area of observed exposure) as follows:
Estimate the net activity content (in curies) for the source
(or area of observed contamination or area of observed exposure) based
on:
--Manifests, or
--Either of the following equations, as applicable:
[GRAPHIC] [TIFF OMITTED] TP29FE16.044
Where:
N = Estimated net activity content (in curies) for the source (or
area of observed contamination or area of observed exposure).
V = Total volume of material (in cubic yards) in a source (or area
of observed contamination or area of observed exposure) containing
radionuclides.
ACi = Activity concentration above the respective
background concentration (in pCi/g) for each radionuclide i
allocated to the source (or area of observed contamination or area
of observed exposure).
n = Number of radionuclides allocated to the source (or area of
observed contamination or area of observed exposure) above the
respective background concentrations.
or,
[GRAPHIC] [TIFF OMITTED] TP29FE16.045
Where:
N = Estimated net activity content (in curies) for the source (or
area of observed contamination or area of observed exposure).
V = Total volume of material (in gallons) in a source (or area of
observed contamination or area of observed exposure) containing
radionuclides.
ACi = Activity concentration above the respective
background concentration (in pCi/1) for each radionuclide i
allocated to the source (or area of observed contamination or area
of observed exposure).
n = Number of radionuclides allocated to the source (or area of
observed contamination or area of observed exposure) above the
respective background concentrations.
Estimate volume for the source (or volume for the area of
observed contamination or area of observed exposure) based on records
or measurements.
For the soil exposure component, in estimating the volume
for areas of observed contamination, do not include more than the first
2 feet of depth, except: For those types of areas of observed
contamination listed in Tier C of Table 5-2 (section 5.1.1.2.2),
include the entire depth, not just that within 2 feet of the surface.
For the subsurface intrusion component, in estimating the
volume for areas of observed exposure, only use the volume of air in
the regularly occupied structures where observed exposure has been
documented.
Convert from curies of radionuclides to equivalent pounds
of nonradioactive hazardous substances by multiplying the activity
estimate for the source (or area of observed contamination or area of
observed exposure) by 1,000.
Assign this resulting product as the radionuclide
constituent quantity value for the source (or area of observed
contamination or area of observed exposure).
If the radionuclide constituent quantity for the source (or area of
observed contamination or area of observed exposure) is adequately
determined (that is, the total activity of all radionuclides in the
source and releases from the source [or in the area of observed
contamination or area of observed exposure] is known or is estimated
with reasonable confidence), do not evaluate the radionuclide
wastestream quantity measure in section 7.2.5.1.2. Instead, assign
radionuclide wastestream quantity a value of 0 and proceed to section
7.2.5.1.3. If the radionuclide constituent quantity is not adequately
determined, assign the source (or area of observed contamination or
area of observed exposure) a value for radionuclide constituent
quantity based on the available data and proceed to section 7.2.5.1.2.
7.2.5.1.2 Radionuclide wastestream quantity (Tier B). Evaluate
radionuclide wastestream quantity for the source (or area of observed
contamination, area of observed exposure, or area of subsurface
contamination) based on the activity content of radionuclide
wastestreams allocated to the source (or area of observed
contamination, area of observed exposure, or area of subsurface
contamination) as follows:
Estimate the total volume (in cubic yards or in gallons)
of wastestreams containing radionuclides allocated to the source (or
area of observed contamination, area of observed exposure, or area of
subsurface contamination).
Divide the volume in cubic yards by 0.55 (or the volume in
gallons by 110) to convert to the activity content expressed in terms
of equivalent pounds of nonradioactive hazardous substances.
[[Page 10431]]
Assign the resulting value as the radionuclide wastestream
quantity value for the source (or area of observed contamination, area
of observed exposure, or area of subsurface contamination).
For the subsurface intrusion component of the soil
exposure and subsurface intrusion pathway, estimate the total
wastestream volume for all regularly occupied structures located within
areas of observed exposure with observed or inferred intrusion and
within areas of subsurface contamination. Calculate the volume of each
regularly occupied structure based on actual data. If unknown, use a
ceiling height of 8 feet.
7.2.5.1.3 Calculation of source hazardous waste quantity value for
radionuclides. Select the higher of the values assigned to the source
(or area of observed contamination, area of observed exposure, and/or
area of subsurface contamination) for radionuclide constituent quantity
and radionuclide wastestream quantity. Assign this value as the source
hazardous waste quantity value for the source (or area of observed
contamination, area of observed exposure, or area of subsurface
contamination). Do not round to the nearest integer.
7.2.5.2 Calculation of hazardous waste quantity factor value for
radionuclides. Sum the source hazardous waste quantity values assigned
to all sources (or areas of observed contamination, areas of observed
exposure, or areas of subsurface contamination) for the pathway being
evaluated and round this sum to the nearest integer, except: If the sum
is greater than 0, but less than 1, round it to 1. Based on this value,
select a hazardous waste quantity factor value for this pathway from
Table 2-6 (section 2.4.2.2).
For a migration pathway, if the radionuclide constituent quantity
is adequately determined (see section 7.2.5.1.1) for all sources (or
all portions of sources and releases remaining after a removal action),
assign the value from Table 2-6 as the hazardous waste quantity factor
value for the pathway. If the radionuclide constituent quantity is not
adequately determined for one or more sources (or one or more portions
of sources or releases remaining after a removal action), assign a
factor value as follows:
If any target for that migration pathway is subject to
Level I or Level II concentrations (see section 7.3), assign either the
value from Table 2-6 or a value of 100, whichever is greater, as the
hazardous waste quantity factor value for that pathway.
If none of the targets for that pathway is subject to
Level I or Level II concentrations, assign a factor value as follows:
--If there has been no removal action, assign either the value from
Table 2-6 or a value of 10, whichever is greater, as the hazardous
waste quantity factor value for that pathway.
--If there has been a removal action:
[ssquf] Determine values from Table 2-6 with and without
consideration of the removal action.
[ssquf] If the value that would be assigned from Table 2-6 without
consideration of the removal action would be 100 or greater, assign
either the value from Table 2-6 with consideration of the removal
action or a value of 100, whichever is greater, as the hazardous waste
quantity factor value for the pathway.
[ssquf] If the value that would be assigned from Table 2-6 without
consideration of the removal action would be less than 100, assign a
value of 10 as the hazardous waste quantity factor value for the
pathway.
For the soil exposure component of the soil exposure and subsurface
intrusion pathway, if the radionuclide constituent quantity is
adequately determined for all areas of observed contamination, assign
the value from Table 2-6 as the hazardous waste quantity factor value.
If the radionuclide constituent quantity is not adequately determined
for one or more areas of observed contamination, assign either the
value from Table 2-6 or a value of 10, whichever is greater, as the
hazardous waste quantity factor value.
For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, if the radionuclide constituent quantity
is adequately determined for all areas of observed exposure, assign the
value from Table 2-6 as the hazardous waste quantity factor value. If
the radionuclide constituent quantity is not adequately determined for
one or more areas of observed exposure, assign either the value from
Table 2-6 or a value of 10, whichever is greater, as the hazardous
waste quantity factor value.
7.2.5.3 Calculation of hazardous waste quantity factor value for
sites containing mixed radioactive and other hazardous substances. For
each source (or area of observed contamination, area of observed
exposure, or area of subsurface contamination) containing mixed
radioactive and other hazardous substances, calculate two source
hazardous waste quantity values--one based on radionuclides as
specified in sections 7.2.5.1 through 7.2.5.1.3 and the other based on
the nonradioactive hazardous substances as specified in sections
2.4.2.1 through 2.4.2.1.5, and sections 5.1.1.2.2, 5.1.2.2.2 and
5.2.1.2.2 (that is, determine each value as if the other type of
substance was not present). Sum the two values to determine a combined
source hazardous waste quantity value for the source (or area of
observed contamination, area of observed exposure, or area of
subsurface contamination). Do not round this value to the nearest
integer.
Use this combined source hazardous waste quantity value to
calculate the hazardous waste quantity factor value for the pathway as
specified in section 2.4.2.2, except: If either the hazardous
constituent quantity or the radionuclide constituent quantity, or both,
are not adequately determined for one or more sources (or one or more
portions of sources or releases remaining after a removal action) or
for one or more areas of observed contamination, areas of observed
exposure, or areas of subsurface contamination, as applicable, assign
the value from Table 2-6 or the default value applicable for the
pathway, whichever is greater, as the hazardous waste quantity factor
value for the pathway.
7.3 Targets. For radioactive substances, evaluate the targets
factor category as specified in section 2.5 and sections 3 through 6,
except: Establish Level I and Level II concentrations at sampling
locations as specified in sections 7.3.1 and 7.3.2 and establish
weighting factors for populations associated with an area of subsurface
contamination in the subsurface intrusion component of the soil
exposure and subsurface intrusion pathway as specified in section
7.3.3.
For all pathways (components and threats), use the same target
distance limits for sites containing radioactive substances as is
specified in sections 3 through 6 for sites containing nonradioactive
hazardous substances. At sites containing mixed radioactive and other
hazardous substances, include all sources (or areas of observed
contamination, areas of observed exposure, or areas of subsurface
contamination) at the site in identifying the applicable targets for
the pathway.
7.3.1 Level of contamination at a sampling location. Determine
whether Level I or Level II concentrations apply at a sampling location
(and thus to the associated targets) as follows:
[[Page 10432]]
Select the benchmarks from section 7.3.2 applicable to the
pathway (or component or threat) being evaluated.
Compare the concentrations of radionuclides in the sample
(or comparable samples) to their benchmark concentrations for the
pathway (or component or threat) as specified in section 7.3.2. Treat
comparable samples as specified in section 2.5.1.
Determine which level applies based on this comparison.
If none of the radionuclides eligible to be evaluated for
the sampling location have an applicable benchmark, assign Level II to
the actual contamination at that sampling location for the pathway (or
component or threat).
In making the comparison, consider only those samples, and
only those radionuclides in the sample, that meet the criteria for an
observed release (or observed contamination or observed exposure) for
the pathway, except: Tissue samples from aquatic human food chain
organisms may also be used for the human food chain threat of the
surface water pathway as specified in sections 4.1.3.3 and 4.2.3.3.
7.3.2 Comparison to benchmarks. Use the following media specific
benchmarks (expressed in activity units, for example, pCi/l for water,
pCi/kg for soil and for aquatic human food chain organisms, and pCi/m3
for air) for making the comparisons for the indicated pathway (or
threat):
Maximum Contaminant Levels (MCLs)--ground water migration
pathway and drinking water threat in surface water migration pathway.
Uranium Mill Tailings Radiation Control Act (UMTRCA)
standards--soil exposure component of the soil exposure and subsurface
intrusion pathway only.
Screening concentration for cancer corresponding to that
concentration that corresponds to the 10-\6\ individual
cancer risk for inhalation exposures (air migration pathway and
subsurface intrusion component of the soil exposure and subsurface
intrusion pathway) or for oral exposures (ground water migration
pathway; drinking water or human food chain threats in surface water
migration pathway; and soil exposure and subsurface intrusion pathway).
--For the soil exposure and subsurface intrusion pathway, include two
screening concentrations for cancer--one for ingestion of surface
materials and one for external radiation exposures from gamma-emitting
radionuclides in surface materials.
Select the benchmark(s) applicable to the pathway (component or
threat) being evaluated. Compare the concentration of each radionuclide
from the sampling location to its benchmark concentration(s) for that
pathway (component or threat). Use only those samples and only those
radionuclides in the sample that meet the criteria for an observed
release (or observed contamination or observed exposure) for the
pathway, except: Tissue samples from aquatic human food chain organisms
may be used as specified in sections 4.1.3.3 and 4.2.3.3. If the
concentration of any applicable radionuclide from any sample equals or
exceeds its benchmark concentration, consider the sampling location to
be subject to Level I concentrations for that pathway (component or
threat). If more than one benchmark applies to the radionuclide, assign
Level I if the radionuclide concentration equals or exceeds the lowest
applicable benchmark concentration. In addition, for the soil exposure
and subsurface intrusion pathway, assign Level I concentrations at the
sampling location if measured gamma radiation exposure rates equal or
exceed 2 times the background level (see section 7.1.1).
If no radionuclide individually equals or exceeds its benchmark
concentration, but more than one radionuclide either meets the criteria
for an observed release (or observed contamination or observed
exposure) for the sample or is eligible to be evaluated for a tissue
sample (see sections 4.1.3.3 and 4.2.3.3), calculate a value for index
I for these radionuclides as specified in section 2.5.2. If I equals or
exceeds 1, assign Level I to the sampling location. If I is less than
1, assign Level II.
At sites containing mixed radioactive and other hazardous
substances, establish the level of contamination for each sampling
location considering radioactive substances and nonradioactive
hazardous substances separately. Compare the concentration of each
radionuclide and each nonradioactive hazardous substance from the
sampling location to its respective benchmark concentration(s). Use
only those samples and only those substances in the sample that meet
the criteria for an observed release (or observed contamination or
observed exposure) for the pathway except: Tissue samples from aquatic
human food chain organisms may be used as specified in sections 4.1.3.3
and 4.2.3.3. If the concentration of one or more applicable
radionuclides or other hazardous substances from any sample equals or
exceeds its benchmark concentration, consider the sampling location to
be subject to Level I concentrations. If more than one benchmark
applies to a radionuclide or other hazardous substance, assign Level I
if the concentration of the radionuclide or other hazardous substance
equals or exceeds its lowest applicable benchmark concentration.
If no radionuclide or other hazardous substance individually exceed
a benchmark concentration, but more than one radionuclide or other
hazardous substance either meets the criteria for an observed release
(or observed contamination or observed exposure) for the sample or is
eligible to be evaluated for a tissue sample, calculate an index I for
both types of substances as specified in section 2.5.2. Sum the index I
values for the two types of substances. If the value, individually or
combined, equals or exceeds 1, assign Level I to the sample location.
If it is less than 1, calculate an index J for the nonradioactive
hazardous substances as specified in section 2.5.2. If J equals or
exceeds 1, assign Level I to the sampling location. If J is less than
1, assign Level II.
7.3.3 Weighting of targets within an area of subsurface
contamination. For the subsurface intrusion component of the soil
exposure and subsurface intrusion pathway, assign a weighting factor as
specified in section 5.2.1.3.2.3 except when an area of subsurface
contamination is bound by gamma radiation exposure rates meeting
observed release criteria with a depth to contamination of 2 feet or
less. For those populations residing, working, or attending school or
day care in a structure, assign a weighting factor of 0.9.
[FR Doc. 2016-02749 Filed 2-26-16; 8:45 am]
BILLING CODE 6560-50-P