[Federal Register Volume 66, Number 114 (Wednesday, June 13, 2001)]
[Rules and Regulations]
[Pages 32074-32135]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-14626]
[[Page 32073]]
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Part IV
ENVIRONMENTAL PROTECTION AGENCY
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40 CFR Part 197
Public Health and Environmental Radiation Protection Standards for
Yucca Mountain, NV; Final Rule
Federal Register / Vol. 66 , No. 114 / Wednesday, June 13, 2001 /
Rules and Regulations
[[Page 32074]]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 197
[FRL-6995-7]
RIN 2060-AG14
Public Health and Environmental Radiation Protection Standards
for Yucca Mountain, NV
AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.
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SUMMARY: We, the Environmental Protection Agency (EPA), are
promulgating public health and safety standards for radioactive
material stored or disposed of in the potential repository at Yucca
Mountain, Nevada. Section 801 of the Energy Policy Act of 1992 (EnPA,
Pub. L. 102-486) directs us to develop these standards. Section 801 of
the EnPA also requires us to contract with the National Academy of
Sciences (NAS) to conduct a study to provide findings and
recommendations on reasonable standards for protection of the public
health and safety. The health and safety standards promulgated by EPA
are to be ``based upon and consistent with'' the findings and
recommendations of NAS. On August 1, 1995, NAS released its report (the
NAS Report), titled ``Technical Bases for Yucca Mountain Standards.''
We have taken the NAS Report into consideration as the EnPA directs.
The Nuclear Regulatory Commission (NRC) will incorporate these
final standards into its licensing regulations. The Department of
Energy (DOE) must demonstrate compliance with these standards. The NRC
will use its licensing regulations to determine whether DOE has
demonstrated compliance with our standards prior to receiving the
necessary licenses to store or dispose of radioactive material in Yucca
Mountain.
DATES: Effective Date: This rule becomes effective July 13, 2001.
ADDRESSES: Documents relevant to the rulemaking. You can find and
access materials relevant to this rulemaking in: (1) Docket No. A-95-
12, located in Waterside Mall Room M-1500 (first floor, near the
Washington Information Center), 401 M Street, SW., Washington, DC
20460; (2) an information file in the Government Publications Section,
Lied Library, University of Nevada-Las Vegas, 4505 Maryland Parkway,
Las Vegas, Nevada 89154; and (3) an information file in the Public
Library in Amargosa Valley, Nevada 89020.
Background documents for this action. We have prepared additional
documents that provide more detailed technical background in support of
these standards. You may obtain copies of the Background Information
Document (BID), the Economic Impact Analysis (EIA), the Response to
Comments document, and the Executive Summary of the NAS Report, by
writing to the Office of Radiation and Indoor Air (6608J), U.S.
Environmental Protection Agency, Washington, DC 20460-0001. We placed
these documents into the docket and information files. You also may
find them on our Internet site for Yucca Mountain (see the Additional
Docket and Electronic Information section later in this document).
FOR FURTHER INFORMATION CONTACT: Ray Clark, Office of Radiation and
Indoor Air, U.S. Environmental Protection Agency, Washington, DC.
20460-0001; telephone 202-564-9310.
SUPPLEMENTARY INFORMATION:
Whom Will These Standards Regulate?
The DOE is the only entity directly regulated by these standards.
Before it may accept waste at the Yucca Mountain site, DOE must obtain
a license from NRC. Thus, DOE will be subject to our standards, which
NRC will implement through its licensing proceedings. Our standards
affect NRC only because, under the Energy Policy Act of 1992 (EnPA,
Pub. L. 102-486, 42 U.S.C. 10141 n. (1994)), NRC must modify its
licensing requirements, as necessary, to make them consistent with our
final standards.
Additional Docket and Electronic Information
When may I examine information in the docket? You may inspect the
Washington, DC, docket (phone 202-260-7548) on weekdays (8 a.m.-5:30
p.m.). The docket personnel may charge you a reasonable fee for
photocopying docket materials (40 CFR part 2).
You may inspect the information file located in the Lied Library at
the University of Nevada-Las Vegas, Research and Information Desk,
Government Publications Section (702-895-2200) when classes are in
session. Hours vary based upon the academic calendar, so we suggest
that you call ahead to be certain that the library will be open at the
time you wish to visit (for a recorded message, call 702-895-2255).
You may inspect the information file in the Public Library in
Amargosa Valley, Nevada (phone 775-372-5340). As of this date, the
hours are Tuesday through Thursday (10 a.m.-7 p.m.); Friday (10 a.m.-5
p.m.); and Saturday (10 a.m.-2 p.m.). The library is closed daily from
12:30 p.m.-1 p.m. It also is closed Sundays and Mondays.
Can I access information by telephone or via the Internet? Yes. You
may call our toll-free information line (800-331-9477) 24 hours per
day. By calling this number, you may listen to a brief update
describing our rulemaking activities for Yucca Mountain, leave a
message requesting that we add your name and address to the Yucca
Mountain mailing list, or request that an EPA staff person return your
call. You also can find information and documents relevant to this
rulemaking on the World Wide Web at http://www.epa.gov/radiation/yucca.
We also recommend that you examine the preamble and regulatory language
for the proposed rule, which appeared in the Federal Register on August
27, 1999 (64 FR 46976).
What documents are referenced in today's action? We refer to a
number of documents that provide supporting information for our Yucca
Mountain standards. All documents relied upon by EPA in regulatory
decisionmaking may be found in our docket (Docket No. A-95-12). Other
documents, e.g., statutes, regulations, proposed rules, are readily
available from other public sources. The documents below are referenced
most frequently in today's action.
Item No.
II-A-1 Technical Bases for Yucca Mountain Standards (The NAS Report),
National Research Council, National Academy Press, 1995
V-A-4 Draft Environmental Impact Statement for Yucca Mountain, DOE/
EIS-0250D, July 1999
V-A-5 Viability Assessment for Yucca Mountain, DOE/RW-0508, December
1998
V-B-1 Final Background Information Document (BID) for 40 CFR 197, EPA-
402-R-01-004
V-C-1 Final Response to Comments Document for 40 CFR 197, EPA-402-R-
01-009
V-A-17 Nevada Risk Assessment/Management Program (NRAMP)
Acronyms and Abbreviations
We use many acronyms and abbreviations in this document. These
include:
ALARA-as low as reasonably achievable
APA-Administrative Procedure Act
BID-background information document
CAA-Clean Air Act
CEDE-committed effective dose equivalent
CG-critical group
DEIS-Draft Environmental Impact Statement
DOE-U.S. Department of Energy
DOE/VA-DOE's Viability Assessment
EIS-Environmental Impact Statement
[[Page 32075]]
EnPA-Energy Policy Act of 1992
EPA-U.S. Environmental Protection Agency
GCD-greater confinement disposal
HLW-high-level radioactive waste
IAEA-International Atomic Energy Agency
ICRP-International Commission on Radiological Protection
LLW-low-level radioactive waste
MCL-maximum contaminant level
MCLG-maximum contaminant level goal
MTHM-metric tons of heavy metal
NAS-National Academy of Sciences
NCRP-National Council on Radiation Protection and Measurements
NEPA-National Environmental Policy Act
NESHAPs-National Emission Standards for Hazardous Air Pollutants
NID-negligible incremental dose
NIR-negligible incremental risk
NRC-U.S. Nuclear Regulatory Commission
NRDC-Natural Resources Defense Council
NTS-Nevada Test Site
NTTAA-National Technology Transfer and Advancement Act
NWPA-Nuclear Waste Policy Act of 1982
NWPAA-Nuclear Waste Policy Amendments Act of 1987
OMB-Office of Management and Budget
RCRA-Resource Conservation and Recovery Act
RME-reasonable maximum exposure
RMEI-reasonably maximally exposed individual
SAB-Science Advisory Board
SDWA-Safe Drinking Water Act
SNF-spent nuclear fuel
TDS-total dissolved solids
TRU-transuranic
UIC-underground injection control
UMRA-Unfunded Mandates Reform Act of 1995
UNSCEAR-United Nations Scientific Committee on the Effects of Atomic
Radiation
USDW-underground source of drinking water
WIPP LWA-Waste Isolation Pilot Plant Land Withdrawal Act of 1992
Outline of Today's Action
I. What is the History of Today's Action?
A. What is the Relationship of 40 CFR part 191 to the Yucca
Mountain Standards?
1. Evolution of 40 CFR part 191
2. The Role of 40 CFR part 191 in the Development of 40 CFR part
197
II. Background Information
A. In Making Our Final Decisions, How Did We Incorporate Public
Comments on the Proposed Rule?
1. Introduction and the Role of Comments in the Rulemaking
Process
2. How Did We Respond to General Comments on Our Proposed Rule?
B. What Are the Sources of Radioactive Waste?
C. What Types of Health Effects Can Radiation Cause?
D. What Are the Major Features of the Geology of Yucca Mountain
and the Disposal System?
E. Background on and Summary of the NAS Report
1. What Were NAS's Findings (``Conclusions'') and
Recommendations?
III. What Does Our Final Rule Do?
A. What Is the Standard for Storage of the Waste? (Subpart A,
Secs. 197.1 through 197.5)
B. What Are the Standards for Disposal? (Secs. 197.11 through
197.36)
1. What Is the Standard for Protection of Individuals?
(Secs. 197.20 and 197.25)
a. Is the Limit on Dose or Risk?
b. What Factors Can Lead to Radiation Exposure?
c. What Is the Level of Protection for Individuals?
d. Who Represents the Exposed Population?
e. How Do Our Standards Protect the General Population?
f. What Do Our Standards Assume About the Future Biosphere?
g. How Far Into the Future Is It Reasonable To Project Disposal
System Performance?
2. What Are the Requirements for Performance Assessments and
Determinations of Compliance?
(Secs. 197.20, 197.25, and 197.30)
a. What Limits Are There on Factors Included in the Performance
Assessments?
b. What Limits Are There on DOE's Elicitation of Expert Opinion?
c. What Level of Expectation Will Meet Our Standards?
d. Are There Qualitative Requirements to Help Assure Protection?
3. What Is the Standard for Human Intrusion? (Sec. 197.25)
4. How Does Our Rule Protect Ground Water? (Sec. 197.30)
a. Is the Storage or Disposal of Radioactive Material in the
Yucca Mountain Repository Underground Injection?
b. Does the Class-IV Well Ban Apply?
c. What Ground Water Does Our Rule Protect?
d. How Far Into the Future Must DOE Project Compliance With the
Ground Water Standards?
e. How Will DOE Identify Where to Assess Compliance With the
Ground Water Standards?
f. Where Will Compliance With the Ground Water Standards be
Assessed?
IV. Responses to Specific Questions for Public Comment
V. Severability
VI. Regulatory Analyses
A. Executive Order 12866
B. Executive Order 12898
C. Executive Order 13045
D. Executive Order 13084
E. Executive Order 13132
F. National Technology Transfer and Advancement Act
G. Paperwork Reduction Act
H. Regulatory Flexibility Act as amended by the Small Business
Regulatory Enforcement Fairness Act of 1996 (SBREFA) 5 U.S.C. 601 et
seq.
I. Unfunded Mandates Reform Act
J. Executive Order 13211
I. What Is the History of Today's Action?
Spent nuclear fuel (SNF) and high-level radioactive waste (HLW)
have been produced since the 1940s, mainly as a result of commercial
power production and defense activities. Since then, the proper
disposal of these wastes has been the responsibility of the Federal
government. The Nuclear Waste Policy Act of 1982 (NWPA, Pub. L. 97-425)
formalizes the current Federal program for the disposal of SNF and HLW
by:
(1) Making DOE responsible for siting, building, and operating an
underground geologic repository for the disposal of SNF and HLW;
(2) Directing us to set generally applicable environmental
radiation protection standards based on authority established under
other laws; \1\ and
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\1\ These laws include the Atomic Energy Act of 1954, as amended
(42 U.S.C. 2011-2296); Reorganization Plan No. 3 of 1970 (5 U.S.C.
Appendix 1).
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(3) Requiring NRC to implement our standards by incorporating them
into its licensing requirements for SNF and HLW repositories.
This general division of responsibilities continues for the Yucca
Mountain disposal system. Thus, today we are establishing public health
protection standards (specific to the Yucca Mountain site, rather than
generally applicable). The NRC will issue implementing regulations for
this rule. The DOE will submit a license application to NRC. The NRC
then will determine whether DOE has met the standards and whether to
issue a license for Yucca Mountain. The NRC will require DOE to comply
with all of the applicable provisions of 40 CFR part 197 before
authorizing DOE to receive radioactive material at the Yucca Mountain
site.
In 1985, we established generic standards for the management,
storage, and disposal of SNF, HLW, and transuranic (TRU) radioactive
waste (see 40 CFR part 191, 50 FR 38066, September 19, 1985), which
apply to any facilities for the storage or disposal of these wastes,
including Yucca Mountain. In 1987, the U.S. Court of Appeals for the
First Circuit remanded the disposal standards in 40 CFR part 191 (NRDC
v. EPA, 824 F.2d 1258 (1st Cir. 1987)). As discussed below, we later
amended and reissued these standards to address issues that the court
raised.
[[Page 32076]]
Also in 1987, the Nuclear Waste Policy Amendments Act (NWPAA, Pub.
L. 100-203) amended the NWPA by, among other actions, selecting Yucca
Mountain, Nevada, as the only potential site that DOE should
characterize for a long-term geologic repository.
In October 1992, the Waste Isolation Pilot Plant Land Withdrawal
Act (WIPP LWA, Pub. L. 102-579) and the EnPA became law. These statutes
changed our obligations concerning radiation standards for the Yucca
Mountain candidate repository. The WIPP LWA:
(1) Reinstated the 40 CFR part 191 disposal standards, except those
portions that were the specific subject of the remand by the First
Circuit;
(2) required us to issue standards to replace the portion of the
challenged standards remanded by the court; and
(3) exempted the Yucca Mountain site from the 40 CFR part 191
disposal standards.
We issued the amended 40 CFR part 191 disposal standards, which
addressed the judicial remand, on December 20, 1993 (58 FR 66398).
The EnPA, enacted in 1992, set forth our responsibilities as they
relate to the Yucca Mountain repository. In the EnPA, Congress directed
us to set public health and safety radiation standards for Yucca
Mountain. Specifically, section 801(a)(1) of the EnPA directs us to
``promulgate, by rule, public health and safety standards for the
protection of the public from releases from radioactive materials
stored or disposed of in the repository at the Yucca Mountain site.''
The EnPA also directed us to contract with NAS to conduct a study to
provide us with its findings and recommendations on reasonable
standards for protection of public health and safety. Moreover, it
provided that our standards shall be the only such standards applicable
to the Yucca Mountain site and are to be based upon and consistent with
NAS's findings and recommendations. On August 1, 1995, NAS released its
report, ``Technical Bases for Yucca Mountain Standards'' (the NAS
Report) (Docket No. A-95-12, Item II-A-1).
A. What Is the Relationship of 40 CFR Part 191 to the Yucca Mountain
Standards?
Throughout today's action, we refer to the provisions of 40 CFR
part 191 to support the decisions we made regarding the components of
the final Yucca Mountain rule. Pursuant to section 8(b)(2) of the WIPP
LWA, 40 CFR part 191 is not applicable to the characterization,
licensing, construction, operation, or closure of the Yucca Mountain
repository. We believe, however, that while 40 CFR part 191 is not
directly applicable to Yucca Mountain, because it contains the
fundamental components for the protection of public health and the
environment that apply to any SNF, HLW, or TRU radioactive waste
repository, certain of its basic concepts must be applied to Yucca
Mountain as appropriate. Further, because 40 CFR part 191 provides
fundamental support for today's rule, we believe it is useful to
explain here the process by which 40 CFR part 191 evolved.
1. Evolution of 40 CFR Part 191
We used the rulemaking for 40 CFR part 191 to define the
fundamental components of any environmental standard applicable to the
disposal of SNF, HLW, and TRU radioactive waste. In our proposal (47 FR
58196, December 29, 1982), we recognized two basic considerations
regarding the disposal of SNF, HLW, and TRU radioactive waste:
The intent of disposal is to isolate the wastes from the
environment for a very long time, longer than any time over which
active institutional controls might be effective; and
The disposal systems will be designed to allow only very
small releases to the environment, if not disturbed. A principal
concern is the possibility of accidental releases due to unintended
events or failure of engineered barriers.
These considerations mean that any standard that we establish and
that NRC and DOE implement: (1) Can only be implemented during
development and operation of the repository, (2) must address
unintentional releases, and (3) must accommodate significant
uncertainties. (See 47 FR 58198, December 29, 1982)
From these considerations, we proposed standards consisting of
Containment Requirements, which limit the total amount of radionuclides
that may enter the environment over 10,000 years; Assurance
Requirements, which provide several principles enhancing confidence
that the containment requirements will be met; and Procedural
Requirements, which assure the proper application of the containment
requirements. We also invited public comment on alternative approaches
for the standards, specifically on the alternative of establishing
exposure limits for individuals. Although the containment requirements,
as proposed, were designed to protect people and the environment for a
long time, we did not propose an individual exposure limit. We believed
the compliance point for such a limit would have to be some distance
from the repository. Otherwise, it would have to ignore the risks from
unplanned events such as human intrusion. It seemed likely that
individuals located extremely near the repository or who intrude into
the repository would receive doses far exceeding any existing or
reasonably acceptable radiation limits.
EPA received substantial public comment on the 40 CFR part 191
proposal. As a direct result of information provided in many of the
comments, we issued a final rule (50 FR 38066, September 19, 1985) that
differed in many respects from the proposal. In addition to containment
and assurance requirements, the final rule included two new components:
Individual Protection Requirements, which protect members
of the public for 1,000 years of undisturbed performance; and
Ground Water Protection Requirements, which protect
``special sources of ground water'' for 1,000 years of undisturbed
performance.
The risk objectives for the containment requirements in the final
rule maintained the same limiting level of health impacts as the
proposal (1000 fatal cancers over 10,000 years for a repository
containing 100,000 metric tons of heavy metal (MTHM)); however, we did
modify the radionuclide-specific release limits to reflect updated
performance analyses and updated information on the health effects of
ionizing radiation. However, members of the public and our Science
Advisory Board (SAB) expressed some concerns regarding residual risks
and the ability of the licensee of any repository to demonstrate
compliance with the standards given the uncertainties about these
facilities that arise over the long time periods at issue (see the
``Report on the Review of Proposed Environmental Standards for the
Management and Disposal of Spent Nuclear Fuel, High-Level and
Transuranic Radioactive Wastes,'' January 1984, Docket No. A-95-12,
Item V-A-21). To address these concerns, we incorporated the concept
that the standards be met with ``reasonable expectation''
(Sec. 191.13(b)). Improved performance assessments indicated that the
containment requirements could, in fact, be achieved by a variety of
repository site/design combinations without significant effects on
disposal costs. The final rule also defined for the first time a
``controlled area,'' or tract of land inside of which compliance is not
evaluated. The concept of a controlled area was carried from the
proposal, where it was included in the definition of ``accessible
environment''. In addition, we added
[[Page 32077]]
``Guidance for Implementation,'' which replaced the previous procedural
requirements section. It addresses some of the uncertainties with
demonstrating compliance, such as the limitations of passive and active
institutional controls and the degree of certainty required to
demonstrate compliance with the individual and ground water protection
requirements.
On the basis of public comments and our analyses of disposal
systems, we incorporated individual protection requirements, applicable
to all pathways of exposure effective for 1,000 years after disposal.
In addition, our analyses of disposal systems supported setting ground
water protection requirements to protect ``special sources of ground
water'' to limits very similar to the Maximum Contaminant Levels (MCLs)
at 40 CFR part 141. Public comment was very influential towards our
incorporation of individual-protection requirements and ground-water
protection requirements. To address the concerns expressed in the
proposed rule related to protection of individuals who are extremely
near the repository or who may intrude into the repository, the
individual-protection requirements apply to any member of the public in
the accessible environment for the case of undisturbed performance.
Legal challenges required us to reconsider the individual and
ground water protection requirements in a subsequent rulemaking to
amend 40 CFR part 191 (see 58 FR 66398, December 20, 1993). In 1987,
the U.S. Court of Appeals for the First Circuit remanded subpart B of
the 1985 standards to EPA for further consideration (Natural Resources
Defense Council, Inc. v. United States Environmental Protection Agency,
824 F.2d 1258 (1st Cir. 1987)). The court questioned the
appropriateness of the 1,000 year time frame for the individual
protection requirement, the inter-relationship of the individual-
protection requirement with the Safe Drinking Water Act (SDWA), and
whether the Agency provided proper notice for the ground water
protection requirements. For a more detailed discussion of the court's
decision, see the preamble to the final amendments to 40 CFR part 191
(58 FR 66399-66411, December 20, 1993). The Waste Isolation Pilot Plant
Land Withdrawal Act of 1992 reinstated the 1985 version of 40 CFR part
191 except for those portions of the rule that were the subject of the
remand. In the final amendments to 40 CFR part 191, which replaced the
remanded portions of 40 CFR part 191, we set the individual-protection
requirement at 15 mrem/yr, calculated as an annual committed effective
dose, for all pathways of exposure of any member of the public in the
accessible environment, effective for 10,000 years after disposal. The
ground water protection provisions limit the concentrations of
radioactivity in any underground source of drinking water (USDW) in the
accessible environment to the MCLs of the SDWA (40 CFR part 141).
2. The Role of 40 CFR Part 191 in the Development of 40 CFR Part 197
The EnPA directs us to develop site-specific public health
protection standards for the Yucca Mountain site. To perform this task
properly, we must answer two fundamental questions relative to the
content of the standards. These two questions are:
(1) What are the relevant components of such standards?
(2) How can they be applied in more detail in a reasonable but
conservative manner to the Yucca Mountain site?
There are two primary sources of information, insight, and guidance
on repository performance standards in general and the standards
applicable to the Yucca Mountain site in particular. These sources are
the generic standards for land disposal of SNF, HLW, and TRU
radioactive waste (40 CFR part 191) and the NAS report mentioned above.
We relied heavily on these sources in developing the Yucca Mountain
standards.
As described in the previous section, we developed 40 CFR part 191
as generic standards that apply to the land disposal of SNF, HLW, and
TRU radioactive wastes. The components of generic standards like 40 CFR
part 191, such as the individual-protection requirement, would all
apply to some degree to any candidate site, but may not be equally
important at any particular site. The WIPP LWA exempts the Yucca
Mountain site from being licensed under the generic standards; however,
the basic components of the generic standards clearly are valid
components for consideration in developing standards that apply to a
specific site. For example, in the EnPA, Congress specifically
instructs us to ``prescribe the maximum annual effective dose
equivalent to individual members of the public'' (EnPA section
801(a)(1)); such an individual dose standard is an integral part of 40
CFR part 191.
We believe that 40 CFR part 191 is a logical starting point for
developing the site-specific Yucca Mountain standards because it
contains the fundamental components necessary to evaluate whether a
potential geologic repository site will perform satisfactorily relative
to the protection of public health and the environment. Where
appropriate in the site-specific context of the Yucca Mountain
standards, we rely on the precedent of, and the reasoning in, 40 CFR
part 191 throughout this preamble as support for including specific
components in the Yucca Mountain standards. This statement does not
mean that we have applied the 40 CFR part 191 standards to Yucca
Mountain. Rather, we evaluated the 40 CFR part 191 standards de novo to
determine whether it may be appropriate for us to apply any of them in
the Yucca Mountain context. The NAS Report is relevant because it
contains recommendations on scientific issues involved with geologic
disposal in general, as well as specific recommendations based upon
examination of the Yucca Mountain site. We refer to these two sources
in the discussions that follow to explain why we structured the
standards in a particular way and how we considered the public comments
we received in response to the proposed standards.
We evaluated each generic component of 40 CFR part 191 on an
individual basis to determine whether it is appropriate to apply it to
the Yucca Mountain site as a component of a standard protective of
public health. If we found it was appropriate to apply one of 40 CFR
part 191's generic components to Yucca Mountain, we included that
component in the Yucca Mountain standards. Next, we considered how to
incorporate each appropriate component in a reasonable, but
conservative, manner to the site-specific conditions at the Yucca
Mountain site. The NAS Report was a primary source of guidance and
insight in answering that question, supplemented by the available data
on the characteristics of the site including information on the
distribution, lifestyles, and other demographic characteristics of the
population in the vicinity of the site. The BID accompanying the 40 CFR
part 197 standards contains much of this information. Other sources of
information, such as DOE's Yucca Mountain DEIS, are noted in the
following discussions as appropriate.
Before selecting and formulating specific elements of the
standards, we must consider that radiological hazards to public health
from a deep geologic repository come from the release of radionuclides
and the subsequent exposure of the population to these radionuclides.
This exposure occurs as a result of two different processes: the
expected degradation over time (caused
[[Page 32078]]
by natural processes and events) of the natural and engineered barriers
in the repository; and the breaching of these barriers by human
activities. It is necessary to include both of these release modes in a
health-based standard if it is to be protective. It also is necessary
to develop standards against which it is possible, using reasonable
means, to judge repository performance to determine compliance. Based
upon basic principles of health physics, we believe that, any releases
and consequent exposures to the public from the radionuclides emplaced
into the repository could affect public health. Therefore, it is
appropriate for us to evaluate the effects of these releases to
determine whether we should address them in our standards. The NAS
Report (Chapters 2 & 3) describes the potential pathways through which
exposures to the public can occur from geologic disposal. Part 191
contains three provisions related to these potential release pathways
that we believe are appropriate for application at Yucca Mountain. More
specifically, 40 CFR part 191 contains an individual-protection
standard (which limits exposure from all pathways by which an
individual can be exposed), ground-water protection standards (aimed at
the protection of ground water resources for use by individuals who may
be exposed from using those resources), and a human-intrusion component
of the containment requirements (aimed at protection from the
inadvertent breaching of the repository containment barriers and
subsequent exposures to the population). We believe these three basic
components of the generic 40 CFR part 191 standards apply to the Yucca
Mountain site because they represent avenues of exposure and mechanisms
of release that are reasonably foreseeable given the conditions at
Yucca Mountain.
We did not see the need to include in 40 CFR part 197 the
containment requirements in 40 CFR part 191 for several reasons. First,
we decided that, unlike the generic analyses supporting the development
of release limits in 40 CFR part 191, the potential for large-scale
dilution of radionuclides (and consequent wider exposure to large
populations), through ground water and into surface water, as modeled
in the supporting analyses for 40 CFR part 191, does not exist at Yucca
Mountain. As discussed in Chapters 7 and 8 and Appendix IV of the BID
and the preamble to proposed 40 CFR part 197 (64 FR 46991, August 27,
1999), the Yucca Mountain repository will be located in an unsaturated
rock formation with limited amounts of infiltrating water passing
through it and into the underlying tuff aquifer. Any releases into the
ground water will be heavily constrained by the geologic features of
the surrounding rocks to move in relatively confined pathways, rather
than widely dispersed into the surrounding area around the repository.
The aquifer is within a ground water system that discharges into arid
areas having high evaporation rates and very little surface water,
further limiting the potential for widespread population exposures.
As discussed in the preamble to the proposed 40 CFR part 191 (58 FR
46991), we developed the containment requirements in 40 CFR part 191
during the siting process mandated by the NWPA in the 1980s. In that
context, population doses are an important consideration. The release
limits in 40 CFR part 191 were found to be reasonably achievable for
several types of geologic settings (including tuff) and would keep the
risks to future populations acceptably small. Because the potential for
significant exposures from the Yucca Mountain repository is primarily
through a strongly directional ground water pathway (BID, Chapters 7
and 8), a ``cautious, but reasonable'' individual-protection standard
will offer the same protection as the containment requirement included
in 40 CFR part 191.
Although we included important components of 40 CFR part 191 in our
Yucca Mountain standards, we did not simply replicate the provisions of
40 CFR part 191. For example, as discussed above, we do not include
containment requirements because we believe that the individual-
protection requirements adequately will protect the general population
given the specific conditions at Yucca Mountain. Similarly, we do not
include assurance requirements because we expect NRC to incorporate
equivalent requirements into its implementing regulations. Because the
assurance requirements in 40 CFR part 191 do not apply to NRC-licensed
facilities \2\, NRC will need to include assurance requirements in its
implementing regulations for the Yucca Mountain repository. Measures
that are effectively equivalent to the 40 CFR part 191 assurance
requirements have been included in NRC's proposed 10 CFR part 63. The
site-specific nature of the Yucca Mountain standards requires us to
evaluate the unique characteristics of the Yucca Mountain site to
develop the more detailed aspects of our standards, such as appropriate
compliance points. The relative importance of the three regulatory
components of 40 CFR part 191 in determining compliance in the
regulatory review process is a direct reflection of site-specific
conditions. For example, for WIPP, evaluating releases from human
intrusion (by drilling to explore for or exploit the oil, gas and
mineral resources present at the site) was the primary test for
compliance against the standards because under expected undisturbed
conditions no releases from the repository are anticipated. Compliance
with the individual-protection standard was consequently based upon a
scenario related to the migration of radionuclides from the repository
to a near surface aquifer via an abandoned deep borehole. Consequently,
we defined details for assessing an intrusion scenario at the WIPP site
on the basis of current and historical practices regarding exploring
for and recovering natural resources in the area. In contrast, the
Yucca Mountain site is relatively poor in known attractive natural
resources, other than ground water (see Chapter 8 of the BID).
Therefore, consistent with NAS's recommendations, we adopted a stylized
human-intrusion scenario for analysis. The NAS's recommendations and
the data base of information available about the site allowed us to
develop the specific details of the human-intrusion scenario, which we
proposed in the draft rule. Comments we received during the public
comment process also played an important role in framing the contents
of the scenario. See the Response to Comments document for a more
detailed discussion of these issues.
---------------------------------------------------------------------------
\2\ NRC agreed to include assurance requirements in its
regulations for geologic repositories (10 CFR part 60, ``Disposal of
High-Level Radioactive Wastes in Geologic Repositories'', 46 FR
13980, February 25, 1981).
---------------------------------------------------------------------------
II. Background Information
A. In Making Our Final Decision, How Did We Incorporate Public Comments
on the Proposed Rule?
1. Introduction and the Role of Comments in the Rulemaking Process
Section 801(a)(1) of the EnPA requires us to set public health and
safety radiation protection standards for Yucca Mountain by
rulemaking.\3\ Pursuant to Section 4 of the Administrative Procedure
Act (APA), regulatory agencies engaging in informal rulemaking must
provide notice of a proposed rulemaking, an opportunity for the public
to comment on the proposed rule, and a general statement of the basis
and purpose of the final
[[Page 32079]]
rule.\4\ The notice of proposed rulemaking required by the APA must
``disclose in detail the thinking that has animated the form of the
proposed rule and the data upon which the rule is based.'' (Portland
Cement Association v. Ruckelshaus, 486 F. 2d 375, 392-94 (D.C. Cir.
1973)) The public thus is enabled to participate in the process by
making informed comments on the proposal. This provides us with the
benefit of ``an exchange of views, information, and criticism between
interested persons and the agency.'' (Id.)
---------------------------------------------------------------------------
\3\ EnPA, Public Law No. 102-486, 106 Stat. 2776, 42 U.S.C.
10141 n. (1994).
\4\ 5 U.S.C. 553.
---------------------------------------------------------------------------
There are two primary mechanisms by which we explain the issues
raised in public comments and our reactions to them. First, we discuss
broad or major comments in the succeeding sections of this preamble.
Second, we are publishing a document, accompanying today's action,
entitled ``Response to Comments'' (Docket No. A-95-12, Item V-C-1). The
Response to Comments document provides more detailed responses to
issues addressed in the preamble. It also addresses all other
significant comments on the proposal. We gave all the comments we
received, whether written or oral, consideration in developing the
final rule.
2. How Did We Respond to General Comments on Our Proposed Rule?
We received many comments that addressed broad issues related to
the proposed standards. Several commenters simply expressed their
support for, or opposition to, the Yucca Mountain repository. The
purpose of our standards is to ensure that any potential releases from
the repository do not result in unacceptably high radiation exposures.
Our standards make no judgment regarding the suitability of the Yucca
Mountain site or whether NRC should issue a license for the site. Such
a decision is beyond the scope of our statutory authority.
Some comments suggested our standards should consider radiation
exposures from all sources because of the site's proximity to the
Nevada Test Site (NTS) and other sources of potential contamination. We
are aware of the other such sources of radionuclide contamination in
the area. However, our mandate under the EnPA is to set standards that
apply only to the storage or disposal of radioactive materials in the
Yucca Mountain repository, not to these other sources. Our standards do
follow the widely accepted principle that, to allow for the
consideration of other exposures in developing a total acceptable dose,
any specific source accounts for only a fraction of one's total
exposure.
Several comments supported our role in setting standards for Yucca
Mountain. Other comments thought that aspects of our standards
duplicate NRC's implementation role. We believe the provisions of this
rule clearly are within our authority and they are central to the
concept of an public health protection standard. We also believe our
standards leave NRC the necessary flexibility to adapt to changing
conditions at Yucca Mountain or to impose additional requirements in
its implementation efforts, if NRC deems them to be necessary.
We received some comments that suggested we should have provided
more or better opportunities for public participation in our decision
making process. For example, that we should have rescheduled public
hearings, extended the public comment period, and provided alternatives
to the public hearing process. We provided numerous opportunities and
avenues for public participation in the development of these standards.
For example, we held public hearings in four locations: Washington, DC;
Las Vegas, NV; Amargosa Valley, NV; and Kansas City, MO. We also opened
a 90-day public comment period and met with key stakeholders during
that time, including Native American tribal groups. We fully considered
all comments that we received through May 1, 2000. We have, in effect,
provided more than 240 days of public comment on the proposal. These
measures greatly exceed the basic requirements for notice-and-comment
rulemaking, and they are in full compliance with the public
participation requirements of the APA.
Some comments argued that our standards for Yucca Mountain do not
protect Nevadans to the same level as New Mexicans around WIPP. In
fact, the individual-protection standards for Yucca Mountain and WIPP
are the same: 15 mrem annual committed effective dose equivalent. The
differences between the standards for Yucca Mountain and those for WIPP
begin with the various statutes and the subsequent regulations
promulgated under those authorities. The WIPP LWA required us to apply
our generic radioactive waste standards (40 CFR part 191) to WIPP. The
standards for Yucca Mountain, which we promulgate under authority
granted in the EnPA, are site-specific, and therefore there are some
differences compared with the standards applicable to WIPP; however, we
are confident that the standards provide essentially the same level of
protection from radiation exposure at both sites, as the exposure
limits are the same for both.
Many comments requested consideration of issues outside the scope
of our authority for this rulemaking. For example, a number of
commenters suggested that we should explore alternative methods of
waste disposal, such as neutralizing radionuclides. Comments also
expressed concern regarding risks of transporting radioactive materials
to Yucca Mountain. Considerations like these all are outside the scope
of this rulemaking. Congress delegated to us neither the authority to
postpone the promulgation of these standards in favor of the
development of other disposal methods nor the regulation of
transportation of waste to Yucca Mountain.
B. What Are the Sources of Radioactive Waste?
Radioactive wastes result from the use of nuclear fuel and other
radioactive materials. Today, we are issuing standards pertaining to
SNF, HLW, and other radioactive waste (we refer to these items
collectively as ``radioactive materials'' or ``waste'') that may be
stored or disposed of in the Yucca Mountain repository. (When we
discuss storage or disposal in this document in reference to Yucca
Mountain, please understand that no decision has been made regarding
the acceptability of Yucca Mountain for storage or disposal. To save
space and to avoid excessive repetition, we will not describe Yucca
Mountain as a ``potential'' repository; however, we intend this meaning
to apply.) These standards apply only to facilities on the Yucca
Mountain site.
Once nuclear reactions have consumed a certain percentage of the
uranium or other fissionable material in nuclear reactor fuel, the fuel
no longer is useful for its intended purpose. It then is known as
``spent'' nuclear fuel (SNF). Sources of SNF include:
(1) Commercial nuclear power plants;
(2) Government-sponsored research and development programs in
universities and industry;
(3) Experimental reactors, such as liquid metal fast breeder
reactors and high-temperature gas-cooled reactors;
(4) Federal government-controlled, nuclear-materials production
reactors;
(5) Naval and other Department of Defense reactors; and
(6) U.S.-owned, foreign SNF.
It is possible to recover specific radionuclides from SNF through
``reprocessing,'' which is a process that dissolves the SNF, thus
separating the radionuclides from one another. Radionuclides not
recovered through
[[Page 32080]]
reprocessing become part of the acidic liquid wastes that DOE plans to
convert into various types of solid materials. High-level wastes (HLW)
are the highly radioactive liquid or solid wastes that result from
reprocessing SNF. The only commercial reprocessing facility to operate
in the United States, the Nuclear Fuel Services Plant in West Valley,
New York, closed in 1972. Since then, there has been no reprocessing of
commercial SNF in the United States. In 1992, DOE decided to phase out
reprocessing of its SNF, which supported the defense nuclear weapons
and propulsion programs. The SNF that does not undergo reprocessing
prior to disposal becomes the waste form.
Where is the waste stored now? Today, storage of most SNF occurs in
water pools or in above-ground dry concrete or steel canisters at more
than 70 commercial nuclear-power reactor sites across the nation.
Approximately three percent of SNF is produced by DOE, and is in
storage at several DOE sites (see Appendix A, Figure A-2, of DOE's
Draft Environmental Impact Statement (DEIS) for Yucca Mountain (DOE/
EIS-0250D, Docket No. A-95-12, Item V-A-4)). The storage of HLW occurs
at Federal facilities in Idaho, Washington, South Carolina, and New
York.
What types of waste will be placed into Yucca Mountain? We
anticipate that most of the waste emplaced in Yucca Mountain will be
SNF and solidified HLW (in the rest of this document, HLW will refer to
solidified HLW, unless otherwise noted). Under current NRC regulations
(10 CFR 60.135), liquid HLW must be solidified, through processes such
as vitrification (mixing the waste into glass), because non-solid waste
forms are not to be stored or disposed of in Yucca Mountain. The DOE
estimates that, by the year 2010, about 66,000 metric tons of SNF and
284,000 cubic meters (containing 450 million curies of radioactivity)
of HLW in predisposal form and 2,900 cubic meters (containing 235
million curies) of the disposable form of HLW will be in storage at
various locations around the country (DOE/RW-0006, Rev. 13, December
1997). For more information, see the waste descriptions in Appendix A
of DOE's DEIS for Yucca Mountain (DOE/EIS-0250D, Docket No. A-95-12,
Item V-A-4).
In the future, other types of radioactive materials could be
identified for storage or disposal in the Yucca Mountain repository.
These materials include highly radioactive low-level waste (LLW), known
as ``greater-than-Class-C waste,'' and excess plutonium or other
fissile materials resulting from the dismantlement of nuclear weapons.
Because the plans for the disposal of these materials have not been
finalized, neither NRC nor DOE has analyzed their impact upon the
design and performance of the disposal system. However, regardless of
the types of radioactive materials that finally are disposed of in
Yucca Mountain, the disposal system must comply with 40 CFR part 197.
C. What Types of Health Effects Can Radiation Cause?
Ionizing radiation can cause a variety of health effects, which can
be either ``non-stochastic'' or ``stochastic.'' Non-stochastic effects
are those for which the damage increases with increasing exposure, such
as destruction of cells or reddening of the skin. These effects appear
in cases of exposure to large amounts of radiation. Stochastic effects
are associated with long-term exposure to low levels of radiation. The
types or severity of stochastic effects does not depend on the amount
of exposure. Instead, the chance that a stochastic effect, such as
cancer, will occur is assumed to increase with increasing exposure. For
a detailed discussion of potential health effects related to exposure
to radiation, see the preamble to the proposed rule (64 FR 46978-46979)
and Chapter 6 of the BID.
Teratogenic effects can occur following fetal exposure. We believe
that fetuses are more sensitive than are adults to the induction of
cancer by radiation (see Chapter 6.5 of the BID). The fetus also is
subject to radiation-induced physical malformations, such as small
brain size (microencephaly), small head size (microcephaly), eye
malformations, and slow growth prior to birth. Recent studies have
focused on the apparently increased risk of severe mental retardation
(as measured by the intelligence quotient). These studies indicate that
the sensitivity of the fetus is greatest during 8 to 15 weeks following
conception and continues, at a lower level, between 16 and 25 weeks.\5\
We do not know exactly the relationship between mental retardation and
dose; however, we believe it prudent to assume that there is a linear,
non-threshold, dose-response relationship between these effects and the
dose delivered to the fetus during the 8-to 15-week period (see Chapter
6.5 of the BID).
---------------------------------------------------------------------------
\5\ Health Effects of Exposure to Low Levels of Ionizing
Radiation, National Academy Press, Washington, DC, 1990.
---------------------------------------------------------------------------
The NAS published its reviews of human health risks from exposure
to low levels of ionizing radiation in a series of reports issued
between 1972 and 1990. However, scientists still do not agree on how
best to estimate the probability of cancer occurring as a result of the
doses encountered by members of the public \6\ because it is necessary
to base estimates of these effects on the effects observed at higher
doses (such as effects seen in the survivors of the Hiroshima and
Nagasaki atomic bombs). Many organizations, including the National
Council on Radiation Protection and Measurements (NCRP), the
International Commission on Radiological Protection (ICRP), the United
Nations Scientific Committee on the Effects of Atomic Radiation
(UNSCEAR), and the National Radiological Protection Board of the United
Kingdom, have recommended the use of the linear non-threshold model for
estimating cancer risks.
---------------------------------------------------------------------------
\6\ The risk of interest is not at or near zero dose, but that
due to small increments of dose above the pre-existing background
level. Background in the U.S. is typically about 3 millisieverts
(mSv), that is, 300 millirem (mrem), effective dose equivalent per
year, or 0.2 Sv (20 rem) in a lifetime. Approximately two-thirds of
this dose is due to radon, and the balance comes from cosmic,
terrestrial, and internal sources of exposure.
---------------------------------------------------------------------------
Over the last decade, the scientific community has performed an
extensive reevaluation of the doses and effects in the Hiroshima and
Nagasaki survivors (see Chapter 6.3 of the BID). These studies have
resulted in increased estimates (roughly threefold between 1972 and
1990) of the extrapolated risk of cancer occurring because of exposure
to environmental (background) levels of radiation. Nonetheless, the
estimated number of health effects induced by small incremental doses
of radiation above natural background levels remains small compared
with the total number of fatal cancers that occur from other causes. In
addition, because cancers that result from exposure to radiation are
the same as those that result from other causes, it may never be
possible to identify them in human epidemiological studies (see Chapter
6 of the BID and the example discussed later in this section). This
difficulty in identifying stochastic radiation effects does not mean
that such effects do not occur. It also is possible, however, that
effects do not occur as a result of these small doses. That is, there
might be an exposure level below which there is no additional risk
above the risk posed by natural background radiation. Sufficient data
to prove either possibility scientifically is lacking. Thus, we believe
that the best approach is to assume that the risk of cancer increases
linearly starting at zero dose. In other
[[Page 32081]]
words, any increase in exposure to ionizing radiation results in a
constant and proportionate increase in the potential for developing
cancer.
The NAS Report stated that radiation causes about five cancers for
every severe hereditary disorder caused by radiation exposure. Also,
NAS concluded that nonfatal cancers are more common than fatal cancers.
Despite this conclusion, NAS cited an ICRP study that judged that non-
fatal cancers contribute less to overall health impact than fatal
cancers ``because of their lesser severity in the affected
individuals.'' (NAS Report pp. 37-39). We based our risk estimates for
exposure of the population to low-dose-rate radiation on fatal cancers
rather than on all cancers for the same reasons enumerated by NAS.
For radiation-protection purposes, we estimate (using a linear,
non-threshold, dose-response model) an average risk for a member of the
U.S. population of 5.75 in 100 (5.75 x 10-\2\) fatal cancers
per sievert (Sv) \7\ (5.75 x 10-\4\ fatal cancers per rem)
delivered at low dose rates.\8\ For this calculation, as long as the
exposure rate is low, the number of incremental cancers depends on the
amount of radiation received, not the time period over which the dose
is delivered, because the linear non-threshold model assumes that any
incremental dose carries a risk (see Chapter 6.3 of the BID). For
example, if 100,000 people randomly chosen from the U.S. population
each received a uniform dose of 1 millisievert (mSv) (0.1 rem) to the
entire body at a rate equivalent to that observed from natural
background sources, the assumption is that approximately five to six
people will die of cancer during their remaining lifetimes because of
that exposure. These five to six deaths are in addition to the roughly
20,000 fatal cancers that would occur in the same population from other
causes. The risk of fatal childhood cancer that results from exposure
while in the fetal stage is about 3 in 100 (3 x 10-\2\)
per Sv (that is, 3 x 10-\4\ effects per rem). The risk of
severe hereditary effects in offspring is estimated to be about 1 x
10-\2\ per Sv (1 x 10-\4\ effects per rem). \9\
The risk of severe mental retardation from doses to a fetus is
estimated to be greater per unit dose than the risk of cancer in the
general population. \10\ However, the period of increased sensitivity
is much shorter. Hence, at a constant exposure rate, fatal cancer risk
in the general population remains the dominant factor. Please see the
BID for more details on this subject.
---------------------------------------------------------------------------
\7\ The traditional unit for dose equivalent has been the rem.
The unit ``sievert'' (Sv), a unit in the International System of
Units that was adopted in 1979 by the General Conference on Weights
and Measures, is now in general use throughout the world. One
sievert equals 100 rem. The prefix ``milli'' (m) means one-
thousandth. The individual-protection limit being finalized today
may be expressed equivalently in either unit.
\8\ ``Low dose rates'' here refers to dose rates on the order of
or less than those from background radiation.
\9\ The risk of severe hereditary effects in the first two
generations, for exposure of the reproductive part of the population
(with both parents exposed), is estimated to be 5 x
10-\3\ per Sv (5 x 10-\5\ per rem). For all
generations, the risk is estimated to be 1.2 x 10-\2\
per Sv (1.2 x 10-\4\ per rem). For exposure of the
entire population, which includes individuals past the age of normal
child-bearing, each estimate is reduced to 40% of the cited value.
\10\ Assuming a linear, non-threshold dose response, estimated
risk for mental retardation due to exposure during the 8th through
15th week of gestation is 4 x 10-\1\ per Sv (4 x
10-\3\ per rem); under the same assumption, the estimated
risk from the 16th to 25th week is 1 x 10-\1\ per Sv (1
x 10-\3\ per rem).
---------------------------------------------------------------------------
Of course, our risk estimates do contain some uncertainty. A recent
uncertainty analysis published by NCRP (NCRP Report 126, Docket A-95-
12, Item II-A-13) estimated that the actual risk of cancer from whole-
body exposure to low doses of radiation could be between 1.5 times
higher and 4.8 times lower (at the 90-percent confidence level) than
our basic estimate of 5.75 x 10-\2\ per Sv (5.75 x
10-\4\ per rem). The risks of genetic abnormalities and
mental retardation are less well known than those for cancer. Thus,
they may include a greater degree of uncertainty. Further, existing
epidemiological data does not rule out the existence of a threshold. If
there is a threshold, exposures below that level would pose no
additional risk above the risk posed by natural background radiation.
However, in spite of uncertainties in the data and its analysis,
estimates of the risks from exposure to low levels of ionizing
radiation are known more clearly than are those for virtually any other
environmental carcinogen. See Chapter 6 of the BID.
D. What Are the Major Features of the Geology of Yucca Mountain and the
Disposal System?
The geology. Yucca Mountain is in southwestern Nevada approximately
100 miles northwest of Las Vegas. The eastern part of the site is on
NTS. The northwestern part of the site is on the Nellis Air Force
Range. The southwestern part of the site is on Bureau of Land
Management land. The area has a desert climate with topography typical
of the Basin and Range province. For more detailed descriptions of
Yucca Mountain's geologic and hydrologic characteristics, and the
disposal system, please see chapter 7 of the BID and the preamble to
the proposed rule (64 FR 46979-46980). These documents are in the
docket for this rulemaking (Docket No. A-95-12, Items III-B-2, V-B-1).
Yucca Mountain is made of layers of ashfalls from volcanic
eruptions that happened more than 10 million years ago. The ash
consolidated into a rock type called ``tuff,'' which has varying
degrees of compaction and fracturing depending upon the degree of
``welding'' caused by temperature and pressure when the ash was
deposited. Regional geologic forces have tilted the tuff layers and
formed Yucca Mountain's crest (Yucca Mountain's shape is a ridge rather
than a peak). Below the tuff is carbonate rock formed from sediments
laid down at the bottom of ancient seas that existed in the area.
There are two general hydrologic zones within and below Yucca
Mountain. The upper zone is called the ``unsaturated zone'' because the
pore spaces and fractures within the rock are not filled entirely with
water. Below the unsaturated zone, beginning at the water table, is the
``saturated zone,'' in which water completely fills the pores and
fractures. Fractures in both zones could act as pathways that allow for
faster contaminant transport than would the pores. The DOE plans to
build the repository in the unsaturated zone about 300 meters below the
surface and about 300 to 500 meters above the water table (DOE
Viability Assessment (DOE/VA), Docket No. A-95-12, Item V-A-5).
There are two major aquifers in the saturated zone under Yucca
Mountain. The upper one is in tuff. The lower one is in carbonate rock.
Regional ground water in the vicinity of Yucca Mountain is believed to
flow generally in a south-southeasterly direction. See Chapters 7 and 8
of the BID for a fuller discussion of the aquifers and the other
geologic attributes of the Yucca Mountain region.
The disposal system. The NAS Report described the current concept
of the potential disposal system as a system of engineered barriers for
the disposal of radioactive waste located in the geologic setting of
Yucca Mountain (NAS Report pp. 23-27). Based on DOE's current design,
entry into the repository for waste emplacement would be on gradually
downward sloping ramps that enter the side of Yucca Mountain. Section
114(d) of the NWPAA limits the capacity of the repository to 70,000
metric tons of SNF and HLW. Current DOE plans project that about 90
percent (by mass) would be commercial SNF; and 10 percent would be
defense HLW
[[Page 32082]]
(NAS Report p. 23). The NAS further stated that within 100 years after
initial emplacement of waste, the repository would be sealed by closing
the opening to each of the tunnels and sealing the entrance ramps and
shafts (NAS Report pp. 23, 26).
We expect the engineered barrier system to consist of at least the
waste form (SNF assemblies or borosilicate glass containing the HLW),
internal stabilizers for the SNF assemblies, and the waste packages
holding the waste. Spent nuclear fuel assemblies consist of uranium
oxide, fission products, fuel cladding, and support hardware, all of
which will be radioactive (see the What are the Sources of Radioactive
Waste? section above).
E. Background on and Summary of the NAS Report
Section 801(a)(2) of the EnPA directs us to contract with NAS to
conduct a study to provide findings and recommendations on reasonable
standards for protection of public health and safety. Section 801(a)(2)
specifically calls for NAS to address the following three issues:
(A) Whether a health-based standard based upon doses to individual
members of the public from releases to the accessible environment (as
that term is defined in the regulations contained in subpart B of part
191 of title 40, Code of Federal Regulations, as in effect on November
18, 1985) will provide a reasonable standard for protection of the
health and safety of the general public;
(B) Whether it is reasonable to assume that a system for post-
closure oversight of the repository can be developed, based upon active
institutional controls, that will prevent an unreasonable risk of
breaching the repository's engineered or geologic barriers or
increasing the exposure of individual members of the public to
radiation beyond allowable limits; and
(C) Whether it is possible to make scientifically supportable
predictions of the probability that the repository's engineered or
geologic barriers will be breached as a result of human intrusion over
a period of 10,000 years.
On August 1, 1995, NAS submitted to us its report, entitled
``Technical Bases for Yucca Mountain Standards.'' The NAS Report is
available for review in the docket (Docket No. A-95-12, Item II-A-1)
and the information files described earlier. You can order the report
from the National Academy Press by calling 800-624-6242 or on the World
Wide Web at http://www.nap.edu/catalog/4943.html.
1. What Were NAS's Findings (``Conclusions'') and Recommendations?
The NAS Report contained a number of conclusions and
recommendations. (The EnPA used the term ``findings;'' however, the NAS
Report used the term ``conclusions''). A summary of NAS's conclusions
appears below. See pages 1-14 of the NAS Report, or the preamble to our
proposed rule (64 FR 46980), for a list of NAS's conclusions and
recommendations. For details on public participation in our review of
the NAS Report, please see the preamble to the proposed rule (64 FR
46980-46981).
Conclusions. The conclusions in the Executive Summary of the NAS
Report (pp. 1-14) were:
(a) ``That an individual-risk standard would protect public health,
given the particular characteristics of the site, provided that policy
makers and the public are prepared to accept that very low radiation
doses pose a negligibly small risk'' (later termed ``negligible
incremental risk''). (This conclusion is the response to the issue
Congress identified in EnPA Section 801(a)(2)(A));
(b) That the Yucca Mountain-related ``physical and geologic
processes are sufficiently quantifiable and the related uncertainties
sufficiently boundable that the performance can be assessed over time
frames during which the geologic system is relatively stable or varies
in a boundable manner;''
(c) ``That it is not possible to predict on the basis of scientific
analyses the societal factors required for an exposure scenario.
Specifying exposure scenarios therefore requires a policy decision that
is appropriately made in a rulemaking process conducted by EPA;''
(d) ``That it is not reasonable to assume that a system for post-
closure oversight of the repository can be developed, based on active
institutional controls, that will prevent an unreasonable risk of
breaching the repository's engineered barriers or increasing the
exposure of individual members of the public to radiation beyond
allowable limits.'' (This conclusion is the response to the issue
Congress identified in EnPA section 801(a)(2)(B));
(e) ``That it is not possible to make scientifically supportable
predictions of the probability that a repository's engineered or
geologic barriers will be breached as a result of human intrusion over
a period of 10,000 years.'' (This conclusion is the response to the
issue Congress identified in EnPA Section 801(a)(2)(C)); and
(f) ``That there is no scientific basis for incorporating the ALARA
(as low as reasonably achievable) principle into the EPA standard or
USNRC (U.S. Nuclear Regulatory Commission) regulations for the
repository.''
Recommendations. The recommendations in the Executive Summary of
the NAS Report were:
(a) ``The use of a standard that sets a limit on the risk to
individuals of adverse health effects from releases from the
repository;''
(b) ``That the critical-group approach be used'';
(c) ``That compliance assessment be conducted for the time when the
greatest risk occurs, within the limits imposed by long-term stability
of the geologic environment;'' and
(d) ``That the estimated risk calculated from the assumed intrusion
scenario be no greater than the risk limit adopted for the undisturbed-
repository case because a repository that is suitable for safe long-
term disposal should be able to continue to provide acceptable waste
isolation after some type of intrusion.''
Other Conclusions and Recommendations. The NAS made other
conclusions and recommendations in addition to those listed above. Most
of them were related to or supported those presented in the Executive
Summary.
III. What Does Our Final Rule Do?
Our rule establishes public health and safety standards governing
the storage and disposal of SNF, HLW, and other radioactive material in
the repository at Yucca Mountain, Nevada.
As noted earlier, section 801(a)(1) of the EnPA gives us rulemaking
authority to set ``public health and safety standards for the
protection of the public from releases from radioactive materials
stored or disposed of in the repository at the Yucca Mountain site.''
The statute also directs us to develop standards ``based upon and
consistent with the findings and recommendations of the National
Academy of Sciences.'' Section 801(a)(2) of the EnPA directs us to
contract with NAS to conduct a study to provide findings and
recommendations on reasonable standards for protection of the public
health and safety. Because the EnPA directs us to act ``based upon and
consistent with'' NAS's findings, a major issue in this rulemaking is
whether we must follow NAS's findings and recommendations without
exception or whether we have discretionary decision-making authority.
As we discussed in the preamble to the proposed rule, we believe we
have discretionary decision-making authority and, therefore, are not
required to adopt,
[[Page 32083]]
without exception, NAS's findings and recommendations. See 64 FR 46981-
46983 for this discussion. As a practical matter, the difficulty of
resolving this issue is reduced because NAS expressed some of the
findings and recommendations in a non-binding manner. In other words,
in many instances NAS either stated its findings and recommendations as
starting points for the rulemaking process or recognized those
recommendations that involve public policy issues that are addressed
more properly in this public rulemaking proceeding. However, the report
also contains some findings and recommendations stated in relatively
definite terms. These issues present most squarely the question of
whether we are to treat all of NAS's findings and recommendations as
binding.
Whether the EnPA binds us to following exactly NAS's findings and
recommendations is a question that warrants close attention because it
affects the scope of our rulemaking. If we must follow every view
expressed in the NAS Report, we would have to treat any such issue as
having been addressed conclusively by NAS. We would not need to
entertain public comment upon the affected issues because the outcome
would be predetermined by NAS.
We believe the EnPA does not bind us absolutely to follow the NAS
Report. Instead, we used it as the starting point for this rulemaking.
As Congress directed, today's rule is based upon and consistent with
the NAS findings and recommendations. We were guided by the panel's
findings and recommendations because of the special role Congress gave
it and because of NAS's scientific expertise. However, the entirety of
our standards is the subject of this rulemaking. Therefore, we have not
treated the views expressed by NAS as necessarily dictating the outcome
of this rulemaking, thereby foreclosing public scrutiny of important
issues. For the reasons described below, we believe this interpretation
of the EnPA is both consistent with the statute and prudent, because it
avoids potential constitutional issues. Further, this interpretation
supports an important EPA policy objective and legal obligation:
Ensuring an opportunity for public input regarding all aspects of the
issues presented in this rulemaking.
Section 801(a)(2) of the EnPA requires NAS to provide ``findings
and recommendations on reasonable standards for protection of the
public health and safety.'' This section of the EnPA calls for NAS to
address three specific issues; however, Congress did not place any
restrictions on other issues NAS could address. The report of the
Congressional conferees underscored that ``the (NAS) would not be
precluded from addressing additional questions or issues related to the
appropriate standards for radiation protection at Yucca Mountain beyond
those that are specified.'' (H.R. Rep. No. 102-1018, 102nd Cong., 2d
Sess. 391 (1992)). Thus, given the potentially unlimited scope of NAS's
inquiry under the statute, it could have provided findings and
recommendations that would dictate literally all aspects of the public
health and safety standards for Yucca Mountain, rendering our function
a merely ministerial one.
Section 801(a)(1) of the EnPA plainly gives us the authority to
issue, by rulemaking, public health and safety standards for Yucca
Mountain. If at the same time that Congress gave NAS the authority to
provide findings and recommendations on any issues related to the Yucca
Mountain public health and safety standards, Congress also intended
that NAS's findings and recommendations would bind us, then Congress
effectively would have delegated to NAS a standard-setting authority
that overrides our rulemaking authority. Carried to its logical
conclusion, under this view of the statute, NAS would have authority to
establish the public health and safety standards without a public
rulemaking process. Congress' direction to EPA to set standards ``by
rule'' would be unnecessary or relatively meaningless. It is both
reasonable and appropriate to resolve this tension in the statute by
interpreting NAS's findings and recommendations as non-binding, but
highly influential, expert guidance to inform our rulemaking.
Thus, we do not believe the statute forces our rulemaking to adopt
mechanically NAS's recommendations as standards. If it did, the
statutory provisions would allow us to consider only those issues that
NAS did not address. Further, the provisions calling for us to use
standard rulemaking procedures in issuing the standards would be
unnecessary to reach results that NAS already established. We consider
the NAS Report's explicit references to decisions that should be made
during the rulemaking process to be support for our position.
The EnPA conference report also reveals that Congress did not
intend to limit our rulemaking discretion. The conference report
clarifies that Congress intended NAS to provide ``expert scientific
guidance'' on the issues involved in our rulemaking and that Congress
did not intend for NAS to establish the specific standards:
The Conferees do not intend for the National Academy of
Sciences, in making its recommendations, to establish specific
standards for protection of the public but rather to provide expert
scientific guidance on the issues involved in establishing those
standards. Under the provisions of section 801, the authority and
responsibility to establish the standards, pursuant to rulemaking,
would remain with the Administrator, as is the case under existing
law. The provisions of section 801 are not intended to limit the
Administrator's discretion in the exercise of his authority related
to public health and safety issues. (H.R. Rep. No. 102-1018, p. 391)
Our interpretation of the EnPA as not limiting the issues for
consideration in this rulemaking is consistent with the views we
expressed to Congress during deliberations over the legislation. The
Chair of the Senate Subcommittee on Nuclear Regulation requested our
views regarding the bill reported by the conference committee. The
Deputy Administrator of EPA indicated the NAS Report would provide
helpful input. Moreover, the Deputy Administrator pointed to the
language, cited above, stating the intent of the conferees not to limit
our rulemaking discretion and assured Congress that any standards for
radioactive materials that we ultimately issue would be the subject of
public comment and involvement and would fully protect human health and
the environment (138 Cong. Rec. 33,955 (1992)).
Our interpretation also is consistent with the role that both NAS
and Congress understood NAS would fulfill. During the Congressional
deliberations over the legislation, NAS informed Congress that while it
would conduct the study, it would not assume a standard-setting role
because such a role is properly the responsibility of government
officials. (138 Cong. Rec. 33,953 (1992)) Our interpretation of the NAS
Report also avoids implicating potentially significant constitutional
issues. Construing the EnPA as delegating to NAS the responsibility to
determine the health and safety standards at Yucca Mountain may violate
the Appointments Clause of the Constitution (Art. II, sec. 2, cl. 2),
which imposes restrictions against giving Federal governmental
authority to persons not appointed in compliance with that Clause. In
addition, the Constitution places restrictions arising under the
separation of powers doctrine upon the delegation of governmental
authority to persons not part of the Federal government. We are not
concluding, at this time, that an alternative interpretation
necessarily would run afoul of constitutional limits. We believe,
however, that it is
[[Page 32084]]
reasonable both to assume that Congress intended to avoid these issues
when it adopted section 801 of the EnPA and to interpret the EnPA
accordingly.
In summary, we do not believe we must, in this rulemaking, adopt
all of NAS's findings and recommendations. The statute does, however,
give NAS a special role. As noted previously, NAS's findings and
recommendations were instrumental in this rulemaking. Our proposal is
consistent with those findings and recommendations. We included many of
the findings and recommendations in this rule. We tended to give
greatest weight to NAS's judgments about issues having a strong
scientific component, the area in which NAS has its greatest expertise.
In addition, we reached final determinations that are congruent with
NAS's analysis whenever we could do so without departing from the
Congressional delegation of authority to us to promulgate, by rule,
public health and safety standards for protection of the public. We
believe our mandate from Congress required the consideration of public
comments and the exercise of our own expertise and discretion.
We requested public comments concerning: how we should view and
weigh NAS's findings and recommendations in the context of the specific
issues presented in this rulemaking; whether we have given proper
consideration to NAS's findings and recommendations; and whether we
should give them more or less weight, and what the resulting outcome
should be.
We received many comments regarding our EnPA authority and our
interpretation of the NAS Report. Several comments took issue with our
reasons for not simply adopting each of the NAS recommendations
verbatim and stated that we are bound to do so. One comment asserted
that our reasoning ``exaggerates the impact of the NAS Report'' on our
rulemaking authority. However, these comments generally recognized that
we can depart from the NAS panel's recommendations if it specifically
stated that policy considerations could play a role in the decision, or
if the recommendation at issue otherwise was not definitive (e.g.,
there was disagreement among the panel members). In particular, some
comments suggested that we cannot include any provision if NAS did not
recommend it. We disagree with this position. In the preamble to the
proposed rule, we clearly stated our intentions regarding our use of
the NAS Report (see 64 FR 46980-46983). We gave the NAS Report special
consideration as ``expert scientific guidance.'' However, as discussed
above, we do not believe that Congress intended the NAS Report to bind
us absolutely. We note that NAS, in its comments on our proposed rule,
did not offer an opinion on this point. Also, NAS acknowledges in
several places in its report that, for policy or other reasons, we may
elect to take approaches that differ from its recommendations. These
statements show NAS did not consider its recommendations to be binding
directions to EPA. The NAS did, however, identify aspects of the
proposal it believes are inconsistent with its recommendations. A copy
of NAS's comments on the proposal is in the docket (Docket No. A-95-12,
Item IV-D-31). See the Response to Comments document for additional
discussion of comments regarding our incorporation of the NAS
recommendations (Docket No. A-95-12, Item V-C-1).
The following sections describe our public health and safety
standards for Yucca Mountain and the considerations that underlie these
standards. The next section addresses the storage portion of the
standards. All of the other sections pertain to the disposal portion of
the standards.
A. What Is the Standard for Storage of the Waste? (Subpart A,
Secs. 197.1 Through 197.5)
Section 801(a)(1) of the EnPA calls for EPA's public health and
safety standards to apply to radioactive materials ``stored or disposed
of in the repository at the Yucca Mountain site.'' The repository is
the excavated portion of the facility constructed underground within
the Yucca Mountain site (to be differentiated from the disposal system,
which is made up of the repository, the engineered barriers, and the
natural barriers). The EnPA differentiates between ``stored'' and
``disposed'' waste, although it indicates that we must issue standards
that apply to both storage and disposal. Congress was not clear
regarding its intended use of the word ``stored'' in this context.
Also, NAS did not address the issue of storage versus disposal (see
Sec. 197.2 for our definition of ``storage'' and Sec. 197.12 for our
definition of ``disposal''). The DOE currently conceives of the Yucca
Mountain repository as a disposal facility, not a storage facility;
however, this situation could change. Therefore, we decided to
interpret the statutory language as directing us to develop standards
that apply to waste that DOE either stores or disposes of in the Yucca
Mountain repository. The storage standard, therefore, applies to waste
inside the repository, prior to disposal.
We received several comments regarding our proposed definition of
``disposal'' in Sec. 197.12, arguing that the potential benefits of
backfilling are unknown at present. In response to these comments, we
changed the definition in the final rule to exclude the requirement
that DOE use backfilling in the Yucca Mountain repository. We believe
that DOE should have the flexibility to design the repository so that
it is as protective of public health and the environment as possible.
Therefore, in order not to constrain DOE unnecessarily in its choice of
repository designs, we changed the definition of ``disposal'' as the
comments suggested. Thus, under the revised definition in our final
rule, it is no longer necessary for DOE to use backfilling for waste
disposal to occur.
Several comments also suggested that our proposed definitions of
``disposal'' and ``barrier'' run counter to established notions of deep
geologic repositories because they allow DOE to rely upon both
engineered and natural barriers, instead of natural barriers alone, to
contain the radioactive material to be stored in Yucca Mountain. These
comments suggested we amend these definitions, as appropriate, to
delete references to engineered barriers. According to the comments,
the Yucca Mountain repository must meet public health and safety
standards with no assistance from manmade structures or barriers. The
EnPA mandates that we establish site-specific standards for Yucca
Mountain. Under this mandate, we believe it is appropriate, based on
the conditions present at Yucca Mountain, to allow DOE the flexibility
to develop a combined system, using engineered barriers and natural
barriers, to contain radioactive material to be disposed of in Yucca
Mountain. For additional discussion of this topic, please see Chapter 7
of the BID.
The DOE also will handle, and might store, radioactive material
aboveground (that is, outside the repository). Our existing standards
for management and storage, codified at subpart A of 40 CFR part 191,
apply to such storage activities. Subpart A of 40 CFR part 191 requires
that DOE manage and store SNF, HLW, and transuranic radioactive wastes
at a site, such as Yucca Mountain, in a manner that provides a
reasonable assurance that the annual dose equivalent to any member of
the public in the general environment will not exceed 25 millirem
(mrem) to the whole body. (Note that a demonstration of ``reasonable
assurance'' is necessary to comply with the standard for storage,
[[Page 32085]]
while subpart B of both 40 CFR part 191 and today's 40 CFR part 197
specify a demonstration of ``reasonable expectation'' to comply with
the disposal standards. ``Reasonable assurance'' is an appropriate
measure to apply to storage, as the facility will be in operation, with
active monitoring and personnel present, during this time. The level of
certainty connected with this period of active operation is
significantly higher than can be attached to the much longer regulatory
time period applicable to disposal standards. See our discussion of
``reasonable expectation'' in section III.B.2.c., What Level of
Expectation Will Meet Our Standards?) This standard is the one that DOE
must meet for WIPP and the greater confinement disposal (GCD) facility.
(The GCD facility is a group of 120-feet deep boreholes, located within
NTS, which contain disposed transuranic wastes.)
We take this position regarding the applicability of subpart A of
40 CFR part 191 because section 801 of the EnPA specifically provides
that the standards we issue shall be the only ``such standards'' that
apply at Yucca Mountain. Thus, the EnPA is the exclusive authority for
today's action regarding storage inside the repository. The WIPP LWA
does not exclude Yucca Mountain from the management and storage
provisions in subpart A of 40 CFR part 191. The 40 CFR part 197
standards supercede our generally applicable standards (40 CFR part
191) only to the extent that the EnPA requires site-specific standards
for storage inside the repository at Yucca Mountain. Otherwise, the 40
CFR part 197 standards have no effect on our generic standards. As
noted, we interpret the scope of section 801 to include both storage
and disposal of waste in the repository. Thus, waste inside the
repository is subject to the standards in today's action. Our generic
standards (subpart A of 40 CFR part 191) will apply to waste stored at
the Yucca Mountain site, but outside of the repository.
The storage standards in 40 CFR 191.03(a) are stated in terms of an
older dose-calculation method and are set at an annual whole-body-dose
limit of 25 mrem/yr. The storage standard for Yucca Mountain uses a
modern dose-calculation method known as ``committed effective dose
equivalent'' (CEDE). Even though today's final rule uses the modern
method of dose calculation, we believe that the dose level maintains a
similar risk level as in 40 CFR 191.03(a) at the time of its
promulgation (see the discussion of the different dose-calculation
methods in the What Is the Level of Protection For Individuals? section
later in this document). The difference between these dose calculation
procedures presents a problem in combining the doses for regulatory
purposes. However, we have begun to develop a rulemaking to amend both
40 CFR parts 190 and 191. That rulemaking would update these limits to
the CEDE methodology. However, because we have not yet finalized that
change, we need to address the calculation of doses under the two
methods in another fashion (see the last paragraph in this section for
more detail).
As discussed in the preamble to the proposed rule (64 FR 46983), we
considered the differences among the conditions covered by the storage
standards in 40 CFR 191.03(a) and the conditions that could affect
storage in the Yucca Mountain repository. The most significant
difference is that the storage in Yucca Mountain would be underground,
whereas most storage covered under 40 CFR part 191 is aboveground.
Otherwise, the technical situations we anticipate under both the
existing generic standards and the Yucca Mountain standards are
essentially the same. Also, our final rule extends a similar level of
protection as in the 1985 version of subpart A of 40 CFR part 191. In
other words, under the 40 CFR part 197 storage standard, exposures of
members of the public from waste storage inside the repository would be
combined with exposures occurring as a result of storage outside the
repository but within the Yucca Mountain site (as defined in 40 CFR
197.2). The total dose could be no greater than 150 microsieverts
(Sv) (15 mrem) CEDE per year (CEDE/yr).
We requested comments regarding our interpretation of section 801
and our approach to coordinating the doses originating from inside and
outside the Yucca Mountain repository. We received two comments
regarding this issue. One comment urged us to establish a single, new,
and separate standard for the Yucca Mountain site that would encompass
the pre-closure operations both aboveground and in the repository. The
comment further stated that the suggested approach would avoid using
two different rules for the same site. This suggested approach also
would avoid the need to use the older dose methodology currently in 40
CFR part 191. Another comment stated that the application of subpart A
of 40 CFR part 191 would not be inappropriate.
We considered establishing a new standard to cover the entirety of
the management and storage operations at Yucca Mountain, as was
suggested by one comment. This had the attractive feature of applying
one standard, instead of two, to the management and storage activities
in and around Yucca Mountain.
However, after considering the comments, the wording in section
801(a)(1) of the EnPA, and the impending rulemaking to amend subpart A
of 40 CFR part 191, we have decided to cover the surface management and
storage activities within the Yucca Mountain site under 40 CFR part 191
and management and storage activities in the Yucca Mountain repository
under 40 CFR part 197. However, the combined doses incurred by any
individual in the general environment from these activities must not
exceed 150 Sv (15 mrem) CEDE/yr. This will require the
conversion of doses from the surface activities from the older dose
system (under which the 40 CFR part 191 standards were developed) into
the newer system to be able to combine the doses from the two areas of
operation. There are established methods to do this, e.g., in the
appendix to 40 CFR part 191, but we are leaving the methodology in this
case to NRC's implementation process. We are continuing to develop a
rulemaking to update the dose system used in subpart A of 40 CFR part
191. When that amendment is finished, the conversion for the activities
subject to subpart A of 40 CFR part 191 will be unnecessary.
B. What Are the Standards for Disposal? (Secs. 197.11 through 197.36)
Subpart B of this final rule consists of three separate standards
(or sets of standards) that apply after final disposal, which are
discussed in more detail in the appropriate sections of this document.
The disposal standards are:
An individual-protection standard;
Ground-water protection standards; and
A human-intrusion standard.
1. What Is the Standard for Protection of Individuals? (Secs. 197.20
and 197.25)
The first standard is an individual-protection standard. It
specifies the maximum dose that a reasonably maximally exposed
individual (RMEI) may receive from releases from the Yucca Mountain
disposal system.
a. Is the Limit on Dose or Risk? Section 801(a)(1) of the EnPA
directed that our standards for Yucca Mountain ``shall prescribe the
maximum annual effective dose equivalent to individual members of the
public from releases to the accessible environment from radioactive
materials stored or disposed of in the repository * * *.'' The EnPA
also requires us to issue our standards
[[Page 32086]]
``based upon and consistent with'' NAS's findings and recommendations.
The NAS recommended that we adopt a risk-based standard to protect
individuals, rather than a dose-based standard as Congress prescribed.
The NAS offered two reasons for its recommendation. First, a risk-based
standard is advantageous relative to a dose-based standard because it
``would not have to be revised in subsequent rulemakings if advances in
scientific knowledge reveal that the dose-response relationship is
different from that envisaged today'' (NAS Report p. 64). Second, NAS
believes a risk-based standard more readily enables the public to
comprehend and compare the standard with human-health risks from other
sources.
We reviewed and evaluated the merits of a risk-based standard as
recommended by NAS (NAS Report, pp. 41-ff.). However, we chose to adopt
a dose-based standard for the following reasons. First, EnPA section
801(a)(1) specifically directs us to promulgate a standard prescribing
the ``maximum annual dose equivalent to individual members of the
public from releases to the accessible environment from radioactive
materials stored or disposed of in the repository.'' Also, the
Conference Committee specifically stated that EPA's standards ``shall
prescribe the maximum annual dose equivalent to individual members of
the public from releases to the accessible environment from radioactive
materials stored or disposed of in the repository. (H. R. Rep. 102-
1018, 102nd Cong., 2d Sess. 390 (1992)). In a situation such as this,
where both the statutory language and the legislative history are
clear, we are obliged to implement the clearly stated plain language of
the statute and to carry out the unambiguous intent of the Congress.
Second, both national and international radiation protection
guidelines developed by bodies of non-governmental radiation experts,
such as ICRP and NCRP, generally have recommended that radiation
standards be established in terms of dose. Also, national and
international radiation standards, including the individual-protection
requirements in 40 CFR part 191, are established almost solely in terms
of dose or concentration, not risk. Therefore, a risk standard will not
allow a convenient comparison with the numerous existing dose
guidelines and standards.
However, we did establish the dose limit using the risk of
developing a fatal cancer. The level of risk, about 8.5 fatal cancers
per million members of the population per year (see the preamble to the
proposed rule at 64 FR 46984), is a level the Agency has judged to be
acceptable taking into account many factors, including existing
radiation standards (such as subpart B of 40 CFR part 191),
Congressional action (the WIPP LWA), and the comments received on the
proposed standards. On page 46985 of the preamble to the proposed rule,
we cited a risk of approximately seven in a million per year. This
value was based upon the NAS risk value of 5 x 10-\2\ per
Sv (5 x 10-\4\ per rem, NAS Report p. 47). However, for
consistency, we should have used the value which was first discussed on
page 46979 of the preamble to the proposed rule, 5.75 x
10-\2\ per Sv (5.75 x 10-\2\ per rem), and
which is from Federal Guidance Report 13 (Docket A-95-12, Item V-A-20).
This higher value associates an annual risk of about 8.5 in a million
with 150 Sv (15 mrem). Because this underlying risk level is a
matter of public policy, it is possible that the level could change if
future decisionmakers make a different judgment as to the level of risk
acceptable to the general public. Likewise, as NAS noted, it could
become necessary to change the dose limit as a result of future
scientific findings about the cancer-inducing aspects of radiation
(i.e., in correlating dose with risk). Therefore, no matter which form
of standard is used, it is subject to change in the future, though the
reasons for change may not be identical. However, either way, risk is
the underlying basis of the standards. It is for the other reasons
cited in this section that we chose to use dose. In addition, dose and
risk are closely related. It is possible to convert one to the other by
using the appropriate conversion factor. We have discussed the
correlations that we used in converting risk to dose, both in this
preamble and in Chapter 6 of the BID.
Finally, we did not receive any comments in favor of a risk
standard that provided either a compelling technical or policy
rationale for promulgating such a standard (see the Response to
Comments document).
Therefore, we establish a standard stated as a dose rather than a
risk.
We requested comments as to whether the standard should be
expressed as risk or dose. Not unexpectedly, the comments were divided
between the alternatives. Most of the comments supported the use of
dose.
One comment stated that the calculation of a dose limit through a
probabilistic performance assessment is a reasonable way to assure that
the repository will meet the overall health risk objective. It is NRC's
responsibility to determine how DOE must demonstrate compliance with
our standards; however, we envision the use of a probabilistic
assessment for the compliance demonstration. Another comment stated
that a dose limit is a reasonable way for us to incorporate cancer risk
into the regulation. As discussed to some extent in section III.B.1.b
(What Factors Can Lead to Radiation Exposure?), and in more detail in
the preamble to the proposed standards (beginning on 64 FR 46984), the
risk of fatal cancer, an annual risk of about 8.5 in a million for an
exposure of 150 Sv, is the basis of the level of protection
that we have established.
A few comments supported stating the standard in terms of risk
rather than dose. For example, NAS was concerned that a dose standard
would preclude the public from being able to compare risks with other
hazardous materials. According to NAS, the use of a dose standard also
makes it difficult for the public to compare the risks inherent in the
ground-water protection standards with the risks inherent in the
individual-protection standard. The NAS also stated that its
recommendation to use a risk standard did not preclude us from using a
dose standard, as long as the underlying risk basis was clearly
understood. We believe that we have been sufficiently clear in
describing the risk basis of the standards within this preamble and the
Response to Comments document.
b. What Factors Can Lead to Radiation Exposure? Protection of the
public from exposure to radioactive pollutants requires knowledge and
understanding of three factors: the sources of the radiation, the
pathways leading to exposure, and the recipients of the radiation dose.
The standards must consider all three factors. This section discusses
the sources of radiation and the pathways of exposure. The following
two sections discuss the recipients of the dose. Dose assessments are
conducted through a type of calculational analysis called ``performance
assessment''. The performance assessment is the quantitative analysis
of the projected behavior of the disposal system, which considers
release scenarios for the repository and carries the analysis through
various pathways in the environment that culminate in exposures to
members of the public.
Sources. The waste disposed of in Yucca Mountain will contain many
radionuclides, including unconsumed uranium, fission products (such as
cesium-137 and strontium-90), and transuranic elements (such as
plutonium and americium).
[[Page 32087]]
The inventory of radionuclides over time will depend upon the type
and amount of radionuclides originally disposed of in the repository,
the half-lives of the radionuclides, and the amount of any
radionuclides formed from the decay of parent radionuclides (see
Chapter 5 of the BID). In the time frame of tens to hundreds of
thousands of years, the short-lived radionuclides initially present in
SNF and HLW will decay. Therefore, the waste eventually will have
radiologic hazards similar to a large uranium ore body; such ore bodies
naturally occur in a variety of settings throughout the country. A
typical uranium ore body contains relatively low concentrations of very
long-lived radionuclides similar to those present in the radioactive
wastes to be disposed of in Yucca Mountain (see the preamble to the
final rule establishing 40 CFR part 191 (50 FR 38083, September 19,
1985)).
Barriers to Radionuclide Movement. To delay and limit the movement
of radionuclides into the biosphere, DOE plans to use multiple
barriers. These barriers will be both engineered (human-made) and
natural based on the design of, and conditions in and around, the
disposal system.
Both the natural and engineered barriers must delay and limit
releases of radionuclides from the repository. For example, an
engineered barrier could be the waste form. The DOE plans to convert
liquid HLW, derived from reprocessing SNF, into a solid by entraining
the radionuclides into a matrix of borosilicate glass. The molten glass
then would be poured into and solidified in a second engineered
barrier, a metal container (see Chapter 7 of the BID). In addition, it
is possible to have other engineered barriers in the repository to
serve as part of the disposal system (see Chapter 7 of the BID).
Natural barriers at Yucca Mountain also could slow the movement of
radionuclides into the accessible environment. For instance, DOE plans
to construct the repository in a layer of tuff located above the water
table. The relative dryness of the tuff around the repository would
limit the amount of water coming into contact with the waste, and would
retard the future movement of radionuclides from the waste into the
underlying aquifer. Any radioactive material that dissolved in
infiltrating water, originating as surface precipitation, still would
have to move to the saturated zone. In the saturated zone, which lies
below the unsaturated zone, water completely fills the pores and
fractures in the rock. Minerals, such as zeolites, in the tuff beneath
the repository could act as molecular filters and ion-exchange agents
for some of the released radionuclides, thereby slowing their movement.
These minerals also could limit the amount of water that contacts the
waste and could help retard the movement of radionuclides from the
waste to the water table. This mechanism would be most effective if
flow was predominantly through the matrix (the pores in the rock) (see
Chapter 7 of the BID).
Pathways. Once radionuclides have left the waste packages, water or
air could carry them to the accessible environment. Ground water will
carry most of the radionuclides released from the waste packages away
from the repository. However, air moving through the mountain will
carry away those radionuclides, such as carbon-14 (\14\C) in the form
of carbon dioxide, that escape from the waste packages in a gaseous
form. For more detailed discussions of the ground water and air
pathways, see the preamble to the proposed rule (64 FR 46986) and
Chapters 8 and 9 of the BID.
Movement via water. Radionuclides will not move instantaneously
into the water table. The length of time it will take for radionuclides
to reach the water table depends partly on how much the water moves via
fractures or through the matrix of the rock. Once radionuclides reach
the saturated zone, they would move away from the disposal system in
the direction of ground water flow.
There are currently no perennial rivers or lakes adjacent to Yucca
Mountain that could transport contaminants. Therefore, based on current
knowledge and conditions, ground water and its usage will be the main
pathways leading to exposure of humans. Current knowledge suggests that
the two major ways that people would use the contaminated ground water
are: (1) Drinking and domestic uses; and (2) agricultural uses (see
Chapters 8 and 9 of the BID). In other words, radionuclides that reach
the public could deliver a dose if an individual: (1) Drinks
contaminated ground water or uses it directly for other household uses;
(2) drinks other liquids containing contaminated water; (3) eats food
products processed using contaminated water; (4) eats vegetables or
meat raised using contaminated water; or (5) otherwise is exposed as a
result of immersion in contaminated water or air or inhalation of wind-
driven particulates left following the evaporation of the water.
Movement via air. Releases of gaseous \14\C from the wastes can
move through the tuff overlying the repository and exit into the
atmosphere following release from the waste package. Once the
radioactive gas enters the atmosphere, it would disperse across the
globe. This global dispersion would result in significant dilution of
the \14\C. The major pathway for human exposure to \14\C is the uptake
of radioactive carbon dioxide by plants that humans subsequently eat
(see Chapter 9 of the BID).
c. What Is the Level of Protection for Individuals? Our individual-
protection standard sets a limit of 150 Sv (15 mrem) CEDE/yr.
This limit corresponds approximately to an annual risk of fatal cancer
of about 8.5 chances in 1,000,000 (8.5 x 10-\6\). It is
within NAS's recommended starting range of 1 in 100,000 to 1 in
1,000,000 annual risk of fatal cancer (see the NAS Report p. 5, Docket
No. A-95-12, Item II-A-1). The NAS's recommended risk range corresponds
to approximately 20 to 200 Sv (2 to 20 mrem) CEDE/yr.
We considered NAS's findings and recommendations in our
determination of the CEDE level that would be adequately protective of
human health. We also reviewed established EPA standards and guidance,
other Federal agencies' standards for both radiation and non-radiation-
related actions, and other countries' regulations. In addition, we
evaluated guidance on dose limits provided by national and
international non-governmental advisory groups of radiation experts.
Section 801(a)(1) of the EnPA calls for our Yucca Mountain
standards to ``prescribe the maximum annual effective dose equivalent
to individual members of the public from releases of radioactive
materials.'' Development of the individual-protection standard required
us to evaluate and specify several factors, which include the level of
protection, whom the standards should protect, and how long the
standards should provide protection. Determining the appropriate dose
level is ultimately a question of both science and public policy. As
NAS stated: ``The level of protection established by a standard is a
statement of the level of the risk that is acceptable to society.
Whether posed as `How safe is safe enough?' or as `What is an
acceptable level?', the question is not solvable by science'' (NAS
Report p. 49).
We requested comment regarding the reasonableness of our proposed
15 mrem CEDE/yr individual-protection standard. We received many
comments, some of which supported the proposal, while others stated
that we should make the level higher or lower. This final rule
establishes a limit of 15 mrem CEDE/yr for the reasons discussed in the
preamble to the proposed rule (see 64
[[Page 32088]]
FR 46984 and following). Principally, the reasons were: This level is
within the NAS-recommended range (which NAS based upon its review of
other Federal actions, guidelines developed by national and
international advisory bodies, and the regulations in other countries);
the fact that many existing standards are at this level, particularly
the EPA standards (40 CFR part 191) applicable to WIPP (in the case of
some older standards, the equivalence is based upon more recent
understanding of the damage that radiation can cause); and, after
consideration of the comments and the site-specific conditions, we
believe that this level is a sufficiently stringent level of protection
for this situation.
Many comments argued that the proposed level was too low. For
example, a few comments preferred a dose level of 25 mrem/yr to
maintain consistency with current NRC regulations. Another comment
advocated a dose level of 70 mrem/yr, given the long time frames, the
national importance of the repository, and other factors. Other
comments thought that the standard should be lower. Several of these
comments supported a limit of 5 mrem/yr. Other comments supported a
zero dose limit.
Some comments stated that, though they preferred a zero-release
standard, they realized that our level was implementable. We agree that
the disposal program should ideally have a goal of no releases.
However, we believe it is incumbent upon us to set a stringent, yet
reasonable, standard. We are establishing a standard that provides
comparable protections to those of other activities related to
radioactive and non-radioactive wastes. Given the current state of
technology, it may not be possible to provide absolute certainty that
there will be no releases over a 10,000 year or longer time frame.
Therefore, we have attempted to establish a standard that is protective
that can be implemented to show compliance.
Our final consideration in selecting a level of protection was
guidance from national and international non-governmental bodies, such
as ICRP and NCRP, which have recommended a total annual dose limit for
an individual of 1 mSv (100 mrem) effective dose from exposure to all
radiation sources except background and medical procedures. The dose
level of 1 mSv (100 mrem) corresponds to an annual risk of fatal cancer
of about 6 in 100,000 (6 x 10-5). In its Publication No.
46, ``Radiation Protection Principles for the Disposal of Solid
Radioactive Waste,'' the ICRP recommends apportionment of the total
allowable radiation dose among specific practices. (Docket No. A-95-12,
Item V-A-12). The apportionment of the total dose limit among different
sources of radiation is used to ensure that the total of all included
exposures is less than 1 mSv (100 mrem) CED/yr. Thus, ICRP recommends
that national authorities apportion or allocate a fraction of the 1 mSv
(100 mrem)-CED/yr limit to establish an exposure limit for SNF and HLW
disposal facilities. Most other countries have endorsed the
apportionment principle.
There are multiple sources of potential radionuclide contamination
on and near NTS, one of which is the Yucca Mountain site. Portions of
NTS have been subjected to both underground and aboveground nuclear
weapon detonations. A substantial quantity of radionuclides was created
by these tests. An estimated inventory of 300 million curies remains
underground (see Appendix II of the BID; Chapter 8 of DOE's Draft
Environmental Impact Statement for Yucca Mountain (DOE/EIS/0250D),
Docket No. A-95-12, Item V-A-4; and Nevada Risk Assessment/Management
Program (NRAMP), Docket No. A-95-12, Item V-A-17). Elsewhere on the
NTS, DOE is burying LLW in near-surface trenches and TRU radioactive
waste has been disposed of in the Greater Confinement Disposal
facility. Finally, there is a commercial LLW disposal system located
west of Yucca Mountain near Beatty, Nevada. Each of these facilities
could have releases of radioactivity into the ground water (see Chapter
8 of DOE's Draft Environmental Impact Statement for Yucca Mountain
(DOE/EIS/0250D), Docket No. A-95-12, Item V-A-4; and Nevada Risk
Assessment/Management Program (NRAMP), Docket No. A-95-12, Item V-A-
17). The regional flow of ground water is believed to be generally from
the locations where some of these practices have occurred toward the
area where radionuclides released from the Yucca Mountain disposal
system are presumed to go (see Nevada Risk Assessment/Management
Program (NRAMP), Docket No. A-95-12, Item V-A-17). The total of the
releases from these sources should be constrained to the total dose
limit of 1 mSv (100 mrem) CED/yr, as recommended by ICRP, because the
releases from these sources could affect the same group of people. The
potential doses from these other sources might contribute to individual
doses for the reasonably maximally exposed individual (RMEI) over
different time frames. According to Chapter 8 of the DEIS for Yucca
Mountain (DOE/EIS/0250D, Docket No. A-95-12, Item V-A-4), potential
releases from LLW management and disposal operations may contribute
very small individual doses. A quantitative attempt to allocate
potential dose from these other sources would be highly speculative;
however, it would be reasonable to maintain the allocation approach
reflected in the established dose limits in both the United States and
internationally.
In summary, based on our review of the guidance, regulations, and
standards cited above, and the NAS Report, we are establishing a
standard of 150 Sv (15 mrem) CEDE/yr for the Yucca Mountain
disposal system (40 CFR 197.13). This level is 15% of the ICRP-
recommended total dose limit. It falls within the range of standards
used in other countries and the range recommended by NAS, and is also
consistent with the individual-protection requirement in 40 CFR part
191. This level will be the CEDE level with which the dose over the
compliance period must be compared. The compliance period is the time
interval over which projections of the performance of the disposal
system must be made for the purpose of assessing the future performance
of the disposal system (see the How Far Into the Future is it
Reasonable to Project Disposal System Performance? section later in
this document for more detail).
d. Who Represents the Exposed Population? To determine whether the
Yucca Mountain disposal system complies with our standard, DOE must
calculate the dose received by some individual or group of individuals
exposed to releases from the repository and compare the calculated dose
with the limit established in the standard. The standard specifies,
therefore, the representative individual for whom DOE must make the
dose calculation. We expect that NRC will define the details, beyond
those which we have specified, necessary for the dose calculation.
Our approach for the protection of individuals. We examined two
possible approaches: the critical group (CG) approach recommended by
NAS (NAS Report, pp. 49-54, Appendix C, and Appendix D) and the
reasonably maximally exposed individual (RMEI) approach. The goal in
representing the exposed population is to estimate the level of
exposure that is protective of the vast majority of individuals in that
population, but still within a reasonable range of potential exposures.
We chose the RMEI approach because we believe it more appropriately
protects individuals and is less speculative to implement than the CG
approach given the unique conditions present at Yucca
[[Page 32089]]
Mountain. Also, it remains a conservative but reasonable approach that
accomplishes the same goal as the CG approach.
The NAS definition of critical group. The NAS Report recommended
that we use the risk to a CG as the basis for the individual-protection
standard. The CG would be the group of people that, based upon
cautious, but reasonable, assumptions, has the highest risk of
incurring health effects due to releases from the disposal system. In
its report, NAS discussed two specific examples of critical groups. The
NAS considered the probabilistic critical group based upon a present-
day farming community to be more appropriate and less reliant on
speculative assumptions than the other critical group it discussed,
which was based upon subsistence farming. However, following due
consideration, we decided that the subsistence-farmer approach
discussed by NAS would be inappropriate, since we could not find nor
did any other party demonstrate that there is the subsistence-farmer
lifestyle at, or downgradient from, Yucca Mountain. For detailed
discussions of NAS's CG approaches, please see the preamble to the
proposed rule, 64 FR 46986-46988, and the NAS Report at pp. 49-54 and
145-159.
The Reasonably Maximally Exposed Individual (RMEI). As just
mentioned, NAS recommended that the standard incorporate a CG approach
for estimating individual exposures from repository release projections
(NAS Report p. 52). As NAS pointed out, the CG approach has been
examined internationally and recommendations for its application have
been proposed (NAS Report, Chapter 2). In addition to recommending the
use of the CG approach, NAS posited the use of a ``probabilistic'' CG,
which is a CG evaluated using probabilistic techniques for assessing
exposures, not only for the parameters that affect repository releases
but also for the probability that an individual will use contaminated
ground water away from the site. As NAS points out, ``the components of
a probabilistic computational approach have considerable precedent in
repository performance, we are not aware that they have previously been
combined to analyze risks to critical groups'' (NAS Report, Appendix
C). In that sense, NAS ``probabilistic'' CG is a departure from the
more widely understood application of the CG concept. The approach we
have chosen embodies the intent of the internationally accepted concept
to protect those individuals most at risk from the proposed repository
but specifies one or a few site-specific parameters at their maximum
values. We chose to use an approach involving limiting exposure to a
defined ``reasonably maximally exposed individual'', the RMEI. There
are similarities between the probabilistic CG and RMEI approaches, and
also some significant differences arising from the Yucca Mountain site,
that caused us to select the RMEI alternative (see also
``Characterization and Comparison of Alternative Dose Receptors for
Individual Radiation Protection for a Repository at Yucca Mountain'',
Docket No. A-95-12, Item V-B-3).
In both approaches, the attempt is made to consider a range of
conditions for the exposed individuals that affect exposures, including
geographic population distributions, lifestyles, and food consumption
patterns for populations at risk. The characteristics of the RMEI are
defined from consideration of current population distribution and
ground water usage, and average food consumption patterns for the
population in question. Such characterizations typically are done by
surveying existing populations, and a ``composite'' RMEI is defined
with one or more parameters that significantly affect exposure
estimates set at high values so that the individual is ``reasonably
maximally exposed.'' The CG approach typically is used under the
assumption of a larger population within which a smaller group (the
critical group) incurs a more homogeneous risk from exposures, in
contrast to the larger population group where exposures will vary
widely. Characteristics of the CG also are derived from information or
assumptions about the potentially exposed population; however, a small
group within the larger population, rather than a composite individual,
is defined. Both the CG and the RMEI are then located above the path of
the contamination plume and the exposure variations are calculated as a
function of the parameters that control radionuclide transport from the
contamination source (here, the repository). The ``probabilistic'' CG
defined in the NAS Report (Appendix C) adds an additional layer of
analytical detail by introducing the idea that the path of the
radionuclide contamination is subject to considerable uncertainty and
the exposure of the CG is further qualified by the probability that the
contamination plume is tapped by the CG at any point in time. This
approach assumes the location of the probabilistic CG is fixed
independently of the projected path(s) for radionuclide migration from
the repository, and the potential exposures then are a direct function
of the probability that the contamination plume reaches the location of
the group. The more common approach to locating the CG, for the purpose
of estimating exposures, is to determine where the group can receive
exposures from the contamination plume and then locating the CG at that
place, regardless of whether a population is currently at that location
or not. Both of these approaches appear to give essentially the same
maximum dose levels to at least some individuals, because at some point
in time the CG would tap into the contamination plume and receive the
exposures. However, if assumed to be widely distributed geographically,
many members of the CG could receive considerably smaller doses, or no
dose, resulting in an average dose which does not reflect the intent of
the CG concept. Overall, as explained further, below, the difference in
the distribution of doses using the CG approach depends upon the
implementation details describing how the total spectrum of dose
assessments would be calculated.
We relied upon many factors in making the decision to use the RMEI
concept. First, this approach is consistent with widespread practice,
current and historical, of estimating dose and risk incurred by
individuals even when it is impossible to specify or calculate
accurately the exposure habits of future members of the population, as
in this case where it is necessary to project doses for very long
periods. Second, we believe that the RMEI approach is sufficiently
conservative and that it is fully protective of the general population
(including women and children, the very young, the elderly, and the
infirm). The risk factor upon which the dose level was established is
very small, 5.75 chances in 10,000,000 per mrem for fatal cancer. The
lifetime risk then is this factor multiplied by the total dose received
in each year of the individual's lifetime. We believe that the risk
prior to birth is very similar to this risk level; however, relative to
the rest of that individual's lifetime, the difference is small. Third,
we believe that it provides protection similar to the CG recommended by
NAS. The RMEI model uses a series of assumptions about the lifestyle of
a hypothetical individual. This belief was supported by NAS in its
comments on the proposed 40 CFR part 197. The NAS agreed that EPA's
RMEI approach is ``broadly consistent with the TYMS report's
recommendation'' (Docket No. A-95-12, IV-D-31). Fourth, it is possible
to build the desired degree of
[[Page 32090]]
conservatism into the model through choices of assumed values of RME
parameters. However, these values would be within certain limits
because we require the use of Yucca Mountain-specific characteristics
in choosing those parameters and their values. In subpart B of 40 CFR
part 197, we establish a framework of assumptions for NRC to
incorporate into its implementing regulations. Fifth, we believe that
the RMEI approach is more straightforward in its application than the
CG approach (particularly the probabilistic CG approach). The RMEI can
reasonably be assumed to incur doses from the plume of contamination.
By locating the RMEI for dose assessment purposes above the plume's
direct path, high-end dose estimates will result. A probabilistic CG
implies some, or even many, locations of the members across a broader
geographic area than the plume covers. This dispersal inescapably
involves additional decisions for the method to be used for combining
dose estimates for the group members and comparison against regulatory
limits and could average some, or many, doses with a zero magnitude. In
addition, specifying certain assumptions regarding consumption habits,
e.g., requiring the assumption that the RMEI drinks a high-end estimate
of 2 liters/day of ground water and that dietary intake is determined
using surveys of today's population in the Town of Amargosa Valley,
assure that the RMEI is ``reasonably maximally'' exposed (Sec. 197.21).
We believe this approach is consistent with the NAS recommendation of
``cautious, but reasonable'' assumptions for repository dose
assessments (NAS Report p. 6). With these assumptions about the
location to be used for dose assessments and food and water
consumption, we believe that the RMEI approach would result in dose
estimates comparable to a small CG. For a CG, food and water
consumption patterns would also be determined from surveys of the local
population and, possibly, by some assumptions to push the dose
assessments toward higher-end dose estimates. The important difference
between the composite RMEI and probabilistic CG approaches is in the
assumed distribution of the group members relative to the projected
path of radionuclide contamination from the repository. And, finally,
sixth, we previously have used the RMEI approach in our regulations
(see FR 22888, 22922, May 29, 1992). We have not used the CG approach.
For example, the WIPP certification criteria (40 CFR part 194) use an
approach involving estimating doses to individuals rather than to a
defined CG.
We believe the RMEI approach is more direct and easily understood
than the probabilistic CG approach because the uncertainties of
estimating doses for a randomly located population is avoided, but the
approach is still ``cautious, but reasonable.'' We believe that the
``probabilistic'' CG described by NAS would give essentially the same
high-end dose results for situations where the group is small, located
in a relatively small area, and is above the path of the contamination
plume. However, this was not the concept recommended by NAS. Therefore,
we believe our RMEI approach captures the essential ``cautious, but
reasonable'' approach recommended by NAS while minimizing speculative
aspects of the probabilistic CG approach. We do not mean to imply that
a CG approach would never be appropriate, or that we would never use a
CG approach in a regulatory action or other decision. However, in this
particular site-specific situation, had we used a CG, we would have
considered it necessary to define it in detail (in terms of size and
location) using cautious, but reasonable, assumptions, but as discussed
elsewhere in this document, we believe that the RMEI approach is
preferable for Yucca Mountain.
Our RMEI is a theoretical individual representative of a future
population group or community termed ``rural-residential'' (see Chapter
8 of the BID for a description of this concept). The DOE will calculate
the CEDE the RMEI receives using cautious, but reasonable, exposure
parameters and parameter-value ranges as described below. The NRC would
use the projected CEDE in determining whether DOE complies with the
standard. The DOE will perform the dose calculation to estimate
exposure resulting from releases from the waste into the accessible
environment based upon the assumption of present-day conditions in the
vicinity of Yucca Mountain. Under our standard, the RMEI will have food
and water intake rates, diet, and physiology similar to those of
individuals in communities currently living in the downgradient
direction of flow of the ground water passing under Yucca Mountain.
We did, however, receive comments from tribal representatives
expressing concern regarding an alternative approach. The Paiute and
Shoshone Tribes stated that they use the Yucca Mountain area for
traditional and customary purposes, including traditional gathering,
and it is their belief that these uses should be incorporated into the
formula upon which the final standards are based. We considered the
Tribes' comments, but, for several reasons explained below, we
conclude, after considering their description of tribal uses of the
area, that the rural-residential RMEI is fully protective of tribal
resources.
First, the tribal use of natural springs is apparently occurring in
the vicinity of Ash Meadows, since we are not aware of another area
downgradient from Yucca Mountain where water discharges in natural
springs, with the possible exception of springs in the more distant
Death Valley. These natural springs are likely fed by the ``carbonate''
aquifer, which is beneath the ``alluvial'' aquifer being used Town of
Amargosa Valley (including at Lathrop Wells) now, and which we assume
will be used in the future. The available data indicate that although
it is likely that the alluvial aquifer would be contaminated by
releases from the potential Yucca Mountain repository, flow is
generally upward from the carbonate aquifer into the overlying
aquifers, suggesting that there is no potential for radionuclides to
move downward into the carbonate system. If downward movement were to
occur, however, radionuclide concentrations would be significantly
diluted in the larger carbonate flow system. As a result, springs fed
from the carbonate aquifer would have lower contamination levels than
would wells at the Lathrop Wells location, which tap aquifers closer
to, and more directly affected by, the source of potential
contamination. A more extensive discussion of the aquifer systems and
geology in the Yucca Mountain area may be found in sections II.D and
III.B.4.e of this preamble, and Chapters 7 and 8 of the BID.
Second, the tribal use of wildlife and non-irrigated vegetation
should not contribute significantly to total individual dose estimates.
Gaseous releases from the repository are not a significant contributor
to individual doses (NAS report, pg. 59) through inhalation or
rainfall, and should contribute less to contamination of wildlife and
non-irrigated vegetation than the use of contaminated well water for
raising crops and animals for food consumption. We believe our
requirement that DOE and NRC base food ingestion patterns on current
patterns for the agricultural area directly down gradient from the
repository is a more conservative requirement.
Third, the dose incurred by the RMEI is calculated at a location
closer to the disposal system than the Ash Meadows area (approximately
18 km versus 30
[[Page 32091]]
km). The RMEI would receive a higher dose from ground water consumption
than would an individual at Ash Meadows, even if the carbonate aquifer
could be contaminated by repository releases, for the reasons mentioned
above.
Fourth, the RMEI is assumed to be a full-time resident continually
exposed to radiation coming from the disposal system. It appears that
the tribal uses are intermittent and involve resources which are less
likely to be contaminated, resulting in lower doses than those to the
RMEI.
Presently, we expect the ground water pathway to be the most
significant pathway for exposure from radionuclides transported from
the repository (NAS Report p. 48; Chapter 8 of the BID). Our initial
evaluation of potential exposure pathways from the disposal system to
the RMEI suggests that the dominant fraction of the dose incurred by
the RMEI likely will be from ingestion of food irrigated with
contaminated water (see Chapter 8 of the BID). It is possible, however,
that DOE and NRC will determine that another exposure pathway is more
significant. Consequently, DOE and NRC must consider and evaluate all
potentially significant exposure pathways in the dose assessments. As a
result of the dose assessments using different combinations of
parameter values, there will be a distribution of potential doses
incurred by the RMEI. The NRC will use the mean value of that
distribution of RMEI doses to determine DOE's compliance with the
individual-protection standard. We requested comments regarding both
the use of the RMEI approach and the use of the higher of the mean or
median value to determine compliance with the individual-protection
standard. We also requested comments regarding the desirability of
adopting the CG approach rather than the RMEI approach. We further
requested that comments supporting the CG approach address the level of
detail our rule should include for the parameters used to describe the
CG. Comments on various aspects of the RMEI approach appear later in
this section. Comments on the mean/median compliance level are in the
answer to Question #13 in section IV.
We received comments supporting both the RMEI and the CG
approaches. For example, one commenter felt that NRC's proposed
licensing regulation for Yucca Mountain (64 FR 8640, February 22, 1999)
was more consistent with the NAS recommendation because it included a
farming community CG (see NRC's proposed 10 CFR 63.115). This commenter
also stated that the proposed 10 CFR part 63 contains the appropriate
level of detail to define the CG. Other commenters recommended the use
of a subsistence farmer CG approach on the grounds that such an
approach is more protective than the rural-residential RMEI. These
groups stated that the RMEI is ``purely speculative.''
As noted earlier, NAS recommended using the CG concept. This
approach can account for differences in age, size, metabolism, habits,
and environment to avoid heavily skewing the results based upon
personal traits that make certain people more or less vulnerable to
radiation releases than the average within the group. In comparison,
under the RMEI approach, the dose that the RMEI incurs is calculated
using some maximum values and some average values for the factors that
are important to estimating dose. Physical differences such as age,
size, and metabolism are also incorporated into the risk value for
development of cancer, in effect making the RMEI a ``composite''
individual. This procedure also projects doses that are within a
reasonably expected range rather than projecting the most extreme
cases.
Regarding the comments stating that the RMEI is ``purely
speculative,'' we agree that the RMEI approach is speculative; however,
it is less speculative than the scenario suggested in the comments
supporting the use of a subsistence farmer. We are not aware of any
subsistence farmers (as defined by the comments) in Amargosa Valley. If
we used the comments' approach we would, therefore, be engaging in even
more speculation than we are by using a current lifestyle. Any future
projection involves speculation. Our basis for using the RMEI is that
we are following NAS's recommendation to use current technology and
living patterns because speculation upon future society and lifestyle
variations can be endless and not scientifically supportable (NAS
Report p. 122). As stated earlier, the danger in defining a
probabilistic CG is that it may be skewed by including randomly located
people who will have minimal exposures, resulting in less conservative
estimates for the group. Given the conditions at Yucca Mountain, we
considered this to be a very real possibility. We consider using a
composite individual to be a much simpler means of accomplishing the
same purpose while maintaining more control over who is represented in
the exposure assessments. Had we opted to use a probabilistic CG, we
would have identified certain characteristics of the group in order for
it to meet our intent, as we have done with the RMEI.
Overall, we believe that the RMEI approach both meets the intent of
NAS and the EnPA and continues a regulatory methodology that we
previously have used successfully. Further, though it recommended that
we use a CG approach, NAS seemed to recognize that a non-CG approach
could accomplish the same purpose. In its report, NAS stated ``[i]t is
essential that the scenario that is ultimately selected be consistent
with the critical-group concept that we have advanced'' (NAS Report p.
10, emphasis added). In its comments on the proposed 40 CFR part 197,
NAS stated that our RMEI approach is ``broadly consistent with the TYMS
report's recommendations'' (Docket No. A-95-12, Item IV-D-31). Given
this acknowledgment by NAS, and that our evaluation of public comments
identified no significant deficiencies in our proposed approach, we see
no compelling reason to change our position that the RMEI is the
appropriate method to use at Yucca Mountain.
Exposure scenario for the RMEI. A major part of the exposure
scenario is the RMEI's location. To make this decision, we collected
and evaluated information about the Yucca Mountain area's natural
geologic and hydrologic features that may preclude drilling for water
at a specific location, such as topography, geologic structure, aquifer
depth and quality, and water accessibility. Based upon this information
and the current understanding of ground water flow in the Yucca
Mountain area, it appears that individuals theoretically could reside
anywhere along the projected ground water flow path extending from
Forty-Mile Wash, starting approximately five kilometers (km) from the
repository location, to the southwestern part of the Town of Amargosa
Valley, Nevada, where the ground water is close to the land surface and
where most of the farming in the area occurs. However, in practice an
individual's ability to reside at any particular point depends upon the
available resources. To explore these variations, we developed four
scenarios (described in the preamble to the proposed rule). See Chapter
8 of the BID for a fuller version of our evaluation of the factors
associated with these scenarios. In developing scenarios, we assumed
that the level of technology and economic considerations affecting
population distributions and life styles in the future are the same as
today (for more detail on this assumption, see the What Do Our
Standards Assume About the Future Biosphere? section below). See below
for a fuller discussion of our
[[Page 32092]]
choice for the RMEI's location. We requested comments regarding the
appropriateness of these scenarios and our preferred choice.
We selected a rural-residential RMEI as the basis of our individual
exposure scenario. We assume that the rural-residential RMEI, is
exposed through the same general pathways as a subsistence farmer.
However, this RMEI would not be a full-time farmer. Rather, this RMEI,
as part of a community typical of Amargosa Valley, might do personal
gardening and earn income from other sources of work in the area. We
assume further that the RMEI drinks two liters per day of water
contaminated with radionuclides, and some of the food (based upon
surveys) consumed by the RMEI is from the Town of Amargosa Valley. We
consider the consumption of two liters per day of drinking water to be
a high-exposure value because people consume water and other liquids
from outside sources, such as commercial products. We intended that it
would push the dose estimates towards a ``reasonably maximal
exposure.'' Similarly, we assume that local food production will use
water contaminated with radionuclides released from the disposal
system. We believe this lifestyle is similar to that of most people
living in Amargosa Valley today.
We received comments stating that: we should be more specific in
defining characteristics of the RMEI; we should take future changes in
population, land use, climate, and biota into consideration; and that
something other than a rural-residential lifestyle would be a more
appropriate choice.
One comment suggested that we should be more specific in setting
the location, behavior, and lifestyle, or allow NRC to make that
choice. There were also a few comments stating that NRC should specify
the parameter values. We believe that we have specified the
characteristics of the rural-residential RMEI in the detail necessary,
given our current understanding, for the concept to be implemented as
we intend. We also believe that our specification of the parameter
values such as location for the RMEI and drinking water intake rate is
appropriate and necessary for our standard to be implemented in the
context in which we developed it. We further believe we have the
authority to specify other parameter values; however, we believe that
NRC, in its role as the licensing authority, can and should set most of
the details for implementing the standard, such as water usage in the
community where the RMEI resides. Also, under our standard, NRC has the
flexibility to make any assumptions, other than those we specified
(assumptions we specified include location, water intake rate, and diet
reflective of current residents of the Town of Amargosa Valley), if
alternative selections prove to be more appropriate for implementing
the standard as we intend. The location we specified is not a fixed
point but rather it must be in the accessible environment above the
highest concentration of radionuclides in the plume of contamination.
To assess water usage in the hypothetical community, DOE and NRC could
use an approach similar to the representative volume approach described
later in this document (How Does Our Rule Protect Ground Water?). In
doing so, the NRC may wish to consider the volume we specified as the
representative volume for ground water protection (i.e., 3,000 acre-
feet). Given the extreme technical difficulty in modeling the small
volumes of water used by an individual, it would be reasonable for DOE
and NRC to assume that the RMEI is one of a number of people (in the
hypothetical ``community'' of which the RMEI is a member) withdrawing
water from the plume of contamination. Such an approach would involve
assumptions about the number of people withdrawing water and the
various uses for which the water is withdrawn, which would define the
overall volume of water. The RMEI would then be a representative person
using water with ``average'' concentrations of radionuclides. These
assumptions should be reflective of current water uses in the projected
path of the plume of contamination.
Among the comments regarding our assumptions about future
populations, land use, climate, and biota, one stated that it is
arrogant, as well as insensitive, to assume that all future people will
be like us today, and that it is unrealistic to assume that future
population distribution, patterned as it is today, will be static. The
comment is correct in that there are many possible futures. However, it
is necessary to limit speculation about possible futures so that the
performance assessments can provide meaningful input into the decision
process and the decision process itself is not confounded with
speculative alternatives. Therefore, we agreed with and followed NAS
when it recommended, ``[i]n view of the almost unlimited possible
future states of society * * * we have recommended that a particular
set of assumptions be used about the biosphere * * * we recommend the
use of assumptions that reflect current technologies and living
patterns'' (NAS Report p. 122).
A similar question arose when we developed the implementing
regulations for WIPP. We resolved the question by developing the
``future states'' assumption (see 40 CFR 194.25). The position we have
taken for the Yucca Mountain standards is consistent with our previous
approach to this question.
There was a spectrum of suggestions recommending alternative RMEIs
(from a fetus to the elderly and infirm). For example, one comment
suggested pregnant women and the unborn within their wombs, children,
the infirm, and the elderly as appropriate RMEIs. Other commenters
urged using a subsistence farmer. Regarding the various ages and stages
of human development, the risk value used for the development of cancer
is an overall average risk value (see Chapter 6 of the BID for more
details) that includes all exposure pathways, both genders, all ages,
and most radionuclides. However, it does not cover the ``unborn within
the womb.'' It is thought that the risk to the unborn is similar to
that for those who have been born; however, the exposure period for the
unborn is very short compared to the rest of the individual's average
lifetime (see Chapter 6 of the BID for a discussion of cancer risk from
in utero exposure). Therefore, the risk is proportionately lower and
thus would not have a significant impact upon the overall risk incurred
by an individual over a lifetime. On the other end of the spectrum,
radiation exposure of the elderly at the levels of the individual-
protection standard would be less than the overall risk value because
they have fewer years to live and, therefore, fewer years for a fatal
cancer to develop.
Some comments on our RMEI characteristics stated that they need to
be more site-specific and should consider the alternative lifestyles of
Native Americans. Other comments stated that the characteristics and
location of the RMEI are implementation issues that should be left for
determination by NRC. We believe that the final rule achieves the
proper balance of site-specific characteristics that is fully
protective of the public health and safety, and that the attributes of
the RMEI specified in this rule are necessary to ensure that the Yucca
Mountain disposal system achieves the level of protection that we
intend.
Location of the RMEI. The location of the RMEI is a basic part of
the exposure scenario. We considered locations within a region
occupying an area bordering Forty-Mile Wash, within a few kilometers of
the repository site, to
[[Page 32093]]
the southwestern border of the Town of Amargosa Valley. This region,
which we believe is hydrologically downgradient from Yucca Mountain,
can be considered as three general subareas. See the preamble to the
proposed rule, 64 FR 46989-46990, for a fuller discussion of these
subareas.
Based upon these considerations of the subareas, we proposed the
intersection of U.S. Route 95 and Nevada State Route 373, known as
Lathrop Wells, as the point where the RMEI would reside. We consider it
improbable that the rural-residential RMEI would occupy locations
significantly north of U.S. Route 95, because the rough terrain and
increasing depth to ground water nearer Yucca Mountain would likely
discourage settlement by individuals because access to water is more
difficult than it would be a few kilometers farther south. Also, there
are currently several residents and businesses near this location whose
source of water is the underlying aquifer (which we understand flows
beneath Yucca Mountain). Therefore, we believe it is reasonable to
assume that a rural community could be located near this intersection
in the future, and that population increases in the short term would
cluster preferentially around the main roads through the area.
We are requiring that the RMEI be located in the accessible
environment (i.e., outside the controlled area) above the highest
concentration of radionuclides in the plume of contamination. Based
upon a review of available site-specific information (see Chapter 8 of
the BID), we have chosen the latitude of the southern edge of the
Nevada Test Site (corresponding to the line of latitude 36 deg. 40'
13.6661" North (described in Docket A-95-12, Item V-A-29)), as the
southernmost extent of the controlled area, i.e., DOE and NRC could
establish the southern boundary of the controlled area farther north
(and presumably the location of the RMEI), but no farther south (see
Where Will Compliance With the Ground Water Standards be Assessed?).
(Even if the RMEI were to be located north of this line of latitude,
the RMEI must still have the characteristics described in
Sec. 197.21.). As noted above, we proposed the intersection of U.S.
Route 95 and Nevada State Route 373 (i.e., Lathrop Wells) as the
location of the RMEI. After further review, we determined that the
southern edge of NTS would be a more appropriate maximum distance from
the repository footprint than the location we proposed because of Nye
County's plans to develop the area between the intersection at Lathrop
Wells and NTS and the potential for members of the public to reside in
that same area (Docket No. A-95-12, Items V-14, 15, 16). This location
is also slightly more protective than the Lathrop Wells location since
it is approximately 2 km closer to the repository footprint, but still
falls within the conditions which led us to propose the Lathrop Wells
intersection, e.g., the ground water is not significantly deeper than
at the intersection and the soil conditions are the same.
Commercial farming occurs today farther south, in the southwestern
portion of the Town of Amargosa Valley in an area near the California
border and west of Nevada State Route 373. However, soil conditions in
the vicinity of Lathrop Wells are similar to those in southwestern
Amargosa Valley. Therefore, it should be feasible for the RMEI to grow
some food, using contaminated water tapped by a well. We believe that
it is reasonable to assume that other gardening, farming, and raising
of domestic animals could occur using contaminated water (see Appendix
IV of the BID). We have specified that selected parameters, such as the
percentage of food grown by the RMEI, should reflect the lifestyles of
current residents of the Town of Amargosa Valley.
Finally, we believe a rural-residential RMEI slightly north of
Lathrop Wells would be among the most highly exposed individuals
downgradient from Yucca Mountain, even though the ground water nearer
the repository could contain higher concentrations of radionuclides. If
individuals lived nearer the repository, they would be unlikely to
withdraw water from the significantly greater depth for other than
domestic use, and in the much larger quantities needed for gardening or
farming activities because of the significant cost of finding and
withdrawing the ground water. It is possible, therefore, for an
individual located closer to the repository to incur exposures from
contaminated drinking water, but not from ingestion of contaminated
food. Based upon our analyses of potential pathways of exposure,
discussed above, we believe that use of contaminated ground water
(e.g., drinking water and irrigation of crops) would be the most likely
pathway for most of the dose from the most soluble, more mobile
radionuclides (such as technetium-99 and iodine-129). The percentage of
the dose that results from irrigation would depend upon assumptions
about the fraction of all food consumed by the RMEI from gardening or
other crops grown using contaminated water, which should reflect the
lifestyle of current residents of the Town of Amargosa Valley.
Therefore, the exposure for an RMEI located approximately 18 km south
of the repository (where ingestion of locally grown contaminated food
is a reasonable assumption) actually would be more conservative than an
RMEI located much closer to the repository who is exposed primarily
through drinking water. We also are establishing that protection of a
rural-residential RMEI would be protective of the general population
downgradient from Yucca Mountain (see the How Do Our Standards Protect
the General Population? section below).
As stated above, the method of calculating the RMEI dose is to
select average values for most parameters except one or a few of the
most sensitive, which are set at their maximum. We believe that an RMEI
location above the highest concentration in the plume of contamination
in the accessible environment and a consumption rate of two liters per
day of drinking water from the plume of contamination represent high-
end values for two of these factors. The NRC may identify additional
parameters to assign high-end values in projecting the dose to the
RMEI. To the extent possible, NRC should use site-specific information
for any remaining factors. For example, NRC should use site-specific
projections of the amount of contaminated food that would be ingested
in the future. The NRC might base projections upon surveys that
indicate the percentage of the total diet of Amargosa Valley residents
from food grown in the Amargosa Valley area.
We requested comment regarding the potential approaches and
assumptions for the exposure scenario to be used for calculating the
dose incurred by the RMEI, particularly whether:
(1) Based upon the above criteria, there is now sufficient
information for us to adequately support a choice for the RMEI location
in the final rule or should we leave that determination to NRC in its
licensing process based upon our criteria;
(2) Another location in one of the three subareas identified
previously should be the location of the RMEI; and
(3) Lathrop Wells and an ingestion rate of two liters per day of
drinking water are appropriate high-end values for parameters to be
used to project doses to the RMEI.
Of the three subjects listed above, the only comments we received
suggested different locations for the RMEI. A few commenters thought
that the Lathrop Wells location is appropriate. However, a number of
others stated that the
[[Page 32094]]
RMEI's location should be at the edge of the footprint of the
repository. Finally, one commenter suggested that 30 kilometers away
from the repository (in the current farming area in southern Amargosa
Valley) would be reasonable; however, this commenter also stated that
Lathrop Wells would be acceptable using the rural-residential scenario
to provide conservatism to protect public health and safety.
As stated earlier, we are designating the location above the point
of highest concentration in the plume of contamination in the
accessible environment (no farther south than 36 deg. 40' 13.6661"
North) as the location of the RMEI. This point would be approximately
18 kilometers south of the repository footprint. We do not believe that
an RMEI likely would live much farther north of the compliance point
(toward Yucca Mountain) because of the increasing depth to ground water
and the increasing roughness of the terrain. In addition, we believe
that, at approximately 18 km, a rural-resident RMEI will likely have
the highest potential doses in the region because of both drinking
contaminated water and eating food grown using contaminated water. That
is, the rural resident at 18 km will receive a higher dose than would
an individual living much closer to Yucca Mountain because the cost of
extracting the water likely will allow only drinking the water and not
having a garden capable of supplying a portion of an individual's
annual food consumption (see Chapters 7 and 8 of the BID). Likewise, we
do not believe that hypothesizing that the RMEI lives 30 km away is a
cautious, but reasonable, assumption because: (1) At 30 km, the RMEI
likely would use water that contains much lower concentrations of
(i.e., more diluted) radionuclides; (2) the downgradient residents
closest to Yucca Mountain are currently near Lathrop Wells; and (3) Nye
County's short-term projections (20 years) show population growth at
and near that location (see Docket No. A-95-12, Items V-A-14, V-A-15,
and V-A-16). Therefore, a distance of 18 km adds to the conservatism
and provides more protection of public health, relative to one
commenter's suggested distance of 30 km.
There were a few other comments related to the location of the
RMEI. For example, one comment stated that the location should take
into account the geology and hydrology of the site rather than be
chosen in advance. Another comment believes that we should base the
location upon the ability of the RMEI to sustain itself consistent with
topography and soil conditions. Further, this commenter believes that
depth to ground water should not be a factor because it is impossible
to predict either human activities or economic imperatives.
We determined the point of compliance for the individual-protection
standard using site-specific factors and NAS's recommendation to use
current conditions (NAS Report p. 54). In preparing to propose a
compliance point for the RMEI, we collected and evaluated information
on the natural geologic and hydrologic features, such as topography,
geologic structure, aquifer depth, aquifer quality, and the quantity of
ground water, that may preclude drilling for water at a specific
location (see Chapter 7 of the BID). For example, as stated above, we
do not believe that a rural-residential individual would occupy areas
much closer to Yucca Mountain because of the increasingly rough terrain
and the increasing depth to ground water. With increasing depth to
ground water come higher costs: (1) To drill for water; (2) to explore
for water; and (3) to pump the water to the surface. We agree that it
is impossible to predict either human activities or economic
imperatives. Therefore, we followed NAS's recommendation to use current
conditions to avoid highly speculative scenarios. This approach leads
us to considering the depth to ground water as a key factor in
determining the location and activities of the RMEI. The current
location of people living in the vicinity of the repository is a
reflection of this key factor.
And, finally, one commenter stated that the proposed RMEI concept
forces DOE to assume the RMEI will withdraw water from the highest
concentration within the plume without consideration of its likelihood.
Forcing such an assumption neglects the low probability that a well
will intersect the highest concentration within the plume.
This commenter's approach, which would use a probabilistic method
to determine the radionuclide concentration withdrawn by the RMEI, is
similar to one of the example CG approaches that NAS provided in its
report (NAS Report Appendix C). The NAS approach would use statistical
sampling of various parameters, i.e., considering the likelihood
(probability) of various conditions existing to arrive at a dose for
comparison to the standard. However, we did not use the probabilistic
CG approach for the following reasons: (1) There is no relevant
experience in applying the probabilistic CG approach, (2) the CG
approach is very complex relative to the RMEI approach and is difficult
to implement in a manner that assures it would meet the requirements of
defining a CG, and (3) we are concerned that this approach does not
appear to identify clearly which individual characteristics describe
who is being protected. Finally, a significant majority of the public
comments we received on the NAS Report opposed the probabilistic CG
approach. We further believe that prudent public health policy requires
that our approach be followed to provide reasonable conservatism. In
this case, this is not a prediction of exactly whom will be exposed as
much as it is a reasonable test of the performance of the repository.
To allow the probability of any particular location being contaminated
is not a prudent approach to the ultimate goal of testing acceptable
performance.
e. How Do our Standards Protect the General Population? Pursuant to
section 801(a)(2)(A) of the EnPA, one of the issues to be addressed by
NAS in its study is whether an individual-protection standard will
provide a reasonable standard for protection of the health and safety
of the general public. NAS concluded that an individual-protection
standard could provide such protection in the case of the Yucca
Mountain disposal system. The NAS premised this conclusion on the
condition that the public and policymakers would accept the idea that
extremely small individual radiation doses spread out over large
populations pose a negligible risk (NAS Report p. 57). The NAS refers
to this concept as ``negligible incremental risk'' (NIR) (NAS Report p.
59). See the preamble to the proposed rule for a detailed discussion of
NAS's concept of NIR (64 FR 46990-46991).
We agree with NAS that an individual-protection standard can
adequately protect the general population near Yucca Mountain because
of the particular characteristics of the Yucca Mountain site. However,
we chose not to adopt either a negligible incremental dose (NID) or NIR
level because we are concerned that such an approach is not appropriate
in all circumstances, and because of reservations regarding NAS's
reasoning and analysis. We based our determination that an individual-
risk standard is adequate to protect both the local and general
population on considerations unique to the Yucca Mountain site. This is
not, however, a general policy judgment by us regarding other uses of
the NID or NIR concepts.
As noted in the preamble to the proposal (64 FR 46990), NAS
referred to the NID level of 10 Sv (1 mrem)/yr per
[[Page 32095]]
source or practice recommended by the NCRP. The International Atomic
Energy Agency (IAEA) has made similar recommendations regarding
exemptions in its Safety Series No. 89, ``Principles for the Exemption
of Radiation Sources and Practices from Regulatory Control'' (1998)
(Docket No. A-95-12, Item II-A-6). The IAEA has recommended that
individual doses not exceed 10 Sv (1 mrem)/yr from each exempt
practice (IAEA Safety Series No. 89, p. 10). The IAEA's recommendations
relate to criteria for exempting whole sources or practices, such as
waste disposal or recycling generally, not whether radiation doses from
a portion of a given practice, such as the release of gases from a
specific geologic repository, may be considered negligible. Finally,
the IAEA's recommendations intend the exemption to be for sources and
practices ``which are inherently safe'' (IAEA Safety Series No. 89, p.
11). It is not clear that the low individual doses or risks projected
from gaseous releases from the Yucca Mountain repository should be
considered on their own as a ``source'' or ``practice,'' given the
definitions of these terms in IAEA's Safety Series No. 89. Further,
given the extraordinarily large inventory of long-lived radionuclides
to be disposed of in the Yucca Mountain repository, it is not clear
that such a source or practice should be considered inherently safe.
Also, we believe it is inappropriate to not calculate a radiation dose
merely because the dose rate from a particular source is small.
Further, we do not believe it is appropriate to apply the NIR
concept to consideration of population dose. A recent NCRP report
questions the application of the NID concept to population doses.
According to NCRP Report No. 121: ``(a) Concept such as the NID
(Negligible Incremental Dose) provides a legitimate lower limit below
which action to further reduce individual dose is unwarranted, but it
is not necessarily a legitimate cut-off dose level for the calculation
of collective dose. Collective dose addresses societal risk while the
NID and related concepts address individual risk.'' (Principles and
Application of Collective Dose in Radiation Protection, NCRP Report No.
121, Docket No. A-95-12, Item II-A-8). Based upon this principle, we
think it inappropriate to use the NID or NIR concept to evaluate
whether an individual-protection standard adequately protects the
general population.
In summary, we are establishing an individual-protection standard
for Yucca Mountain that will limit the annual radiation dose incurred
by the RMEI to 150 Sv (15 mrem) CEDE. At the same time, we
chose not to adopt a separate limit on radiation releases for the
purpose of protecting the general population. Instead, we recommended
in our proposal that DOE estimate and consider collective dose in its
analyses. We based this recommendation upon several factors. The first
factor is NAS's projection of extremely small doses to individuals
resulting from air releases from Yucca Mountain. That dose level is
well below the risk corresponding to our individual-protection standard
for Yucca Mountain. It is also well below the level that we have
regulated in the past through other regulations. Further, while we
decline to establish a general Negligible Incremental Risk (NIR) level,
we do agree with NAS that estimating the number of health effects
resulting from a 0.0003 mrem/yr dose equivalent rate (NAS Report p.
59), in addition to the dose rate from background radiation, in the
general population is uncertain and controversial. The second major
factor is that, based upon current and site-specific conditions near
Yucca Mountain, there is not likely to be great dilution resulting in
exposure of a large population. In addition, we are establishing
additional ground water protection standards that would set specific
limits to protect users of ground water and that protect ground water
as a resource. Finally, we require that all of the pathways, including
air and ground water, be analyzed by DOE and considered by NRC under
the individual-protection standard. We requested comment on this
approach. We requested that commenters who disagree with this approach
specifically address why it is inappropriate for the Yucca Mountain
disposal system and make suggestions about how we might reasonably
address this issue.
Most comments supported not establishing a collective-dose limit
for Yucca Mountain. Two comments supported our decision not to
establish an NIR or NID level. The NAS went further by also opposing
our suggestion that DOE estimate collective dose for use in examining
design alternatives because it is inconsistent with the NAS Report and
with our conclusion that a collective-dose limit is unnecessary for the
purpose of protecting the general public. On page 57 of its report, NAS
stated:
``Earlier in this chapter, we recommend the form for a Yucca
Mountain standard based on individual risk. Congress has asked
whether standards intended to protect individuals would also protect
the general public in the case of Yucca Mountain. We conclude that
the form of the standards we have recommended would do so, provided
that policy makers and the public are prepared to accept that very
low radiation doses pose a negligibly small risk. This latter
requirement exists for all forms of the standards, including that in
40 CFR (part) 191. We recommend addressing this problem by adopting
the principle of negligible incremental risk to individuals.
``The question posed by Congress is important because limiting
individual dose or risk does not automatically guarantee that
adequate protection is provided to the general public for all
possible repository sites or for the Yucca Mountain site in
particular. As described in the previous section, the individual-
risk standard should be constructed explicitly to protect a critical
group that is composed of a few persons most at risk from releases
from the repository. The standards are then set to limit the risk to
the average member of that group. Larger populations outside the
critical group might also be exposed to a lower, but still
significant, risk. It is possible that a higher level of protection
for this population represented by a lower level of risk than the
one established by the standards might be considered.''
The NAS also states: ``(O)n a collective basis, the risks to future
local populations are unknowable. We conclude that there is no
technical basis for establishing a collective population-risk standard
that would limit risk to the nearby population of the proposed Yucca
Mountain repository'' (NAS Report p. 120)
After consideration of comments received on this question, we have
determined that it is not necessary for us to recommend that DOE
calculate collective dose, primarily because we believe the individual-
protection standard will adequately protect the general population.
f. What Do Our Standards Assume About the Future Biosphere? For
assessments of potential exposures, there are two important aspects of
defining the future biosphere characteristics: the selection of
parameter values to define the natural characteristics of the site, and
the assumptions necessary to define the characteristics of the
potentially exposed population. Examples of the site's natural
characteristics include rainfall projections and the hydrologic
characteristics of the rocks through which radionuclides may migrate.
Examples of the assumptions necessary to define the potentially exposed
population's characteristics include assumptions regarding population
distributions, lifestyles, and eating habits.
In conducting required analyses of repository performance,
including the performance assessment for determining compliance with
the standards, the assessment for determining compliance
[[Page 32096]]
with the ground water standards, and the human-intrusion analysis, DOE
and NRC may not assume that future geologic, hydrologic, and climatic
conditions will be the same as they are at present. We require that
these conditions be varied within reasonably ascertainable bounds over
the required compliance period. We are imposing this requirement, which
is consistent with the recommendation of the NAS Report, because we
believe it is possible to reasonably bound the parameter values in the
performance assessment that relate to these conditions.
To avoid unsupportable speculation regarding human activities and
conditions, we believe it is appropriate to assume that other
parameters describing human activities and interactions with the
repository (such as the level of human knowledge and technical
capability, human physiology and nutritional needs, general lifestyles
and food consumption patterns of the population, and potential pathways
through the biosphere leading to radiation exposure of humans) will
remain as they are today. Consistent with the NAS Report, we believe
there may be an essentially unlimited number of predictions that could
be made about future human societies, with an unlimited number of
potential impacts on the significance of future risk and dose effects.
Regulatory decision making involving many speculative scenarios for
future societies and impacts would become extraordinarily difficult
without any demonstrable improvement in public health and safety and
should be avoided as much as possible. Therefore, DOE and NRC must
assume that future states applicable to the repository, except for
geologic, hydrologic, and climatic conditions, will remain unchanged
from the time of licensing.
Comments we received on this subject strongly favored our approach,
particularly with respect to changes in natural conditions. The
comments noted that climatic variations should be expected to occur
over the time frames for which performance projections are made because
the climate has changed in the past. Another reason to consider
climatic changes is that these changes could have a significant effect
on repository performance in comparison to performance projections made
using current day conditions. Comments also pointed out the seismically
active nature of the area and implied that DOE should examine the
effects of seismic activity on the disposal system's performance. Here
again, we require DOE to consider variations in geologic conditions.
The approach we proposed on this subject is consistent with the
approach we used for the WIPP certification (40 CFR 194.25) and NAS's
recommendations. We received no comments opposing this approach.
g. How Far Into the Future Is It Reasonable To Project Disposal
System Performance? The NAS recommended that the time over which
compliance should be assessed (the compliance period) should be ``the
time when the greatest risk occurs, within the limits imposed by long-
term stability of the geologic environment'' (NAS Report p. 7). The NAS
stated that the bases for its recommendation were technical, not
policy, considerations (NAS Report pp. 54-56). The NAS acknowledged,
however, that this is not solely a technical decision, and that policy
considerations could be important to the decision (NAS Report p. 56).
We agree that the selection of the compliance period necessarily
involves both technical and policy considerations. For example, as NAS
pointed out, we could decide that it is appropriate to establish
similar policies for managing risks ``from disposal of both long-lived
hazardous nonradioactive materials and radioactive materials'' (NAS
Report p. 56). Such a decision necessarily would result in a compliance
period that is less than the period of geologic stability. As NAS
recognized, we had to consider, in this rulemaking, both the technical
and policy issues associated with establishing the appropriate
compliance period for the performance assessment of the Yucca Mountain
disposal system.
We offered for comment two alternatives for the compliance period
for the individual-protection standard. One alternative was to adopt a
compliance period as the time to peak dose within the period of
geologic stability. The second alternative was to adopt a fixed time
period during which the repository must meet the disposal standards.
For the reasons discussed below, we selected the second
alternative, which establishes a regulatory time period of 10,000
years. Therefore, the peak dose within 10,000 years after disposal must
comply with the individual-protection standard. In addition, we require
calculation of the peak dose within the period of geologic stability.
The intent of examining the disposal system's performance after 10,000
years is to project its longer-term performance. We require DOE to
include the results and bases of the additional analyses in the EIS for
Yucca Mountain as an indicator of the future performance of the
disposal system. The rule does not, however, require that DOE meet a
specific dose limit after 10,000 years. We have concerns regarding the
uncertainties associated with such projections, and whether very long-
term projections can be considered meaningful; however, existing
performance assessment results indicate that the peak dose may occur
beyond 10,000 years (see Chapter 7, Section 7.3, of the BID). Such
results may, therefore, give a more complete description of repository
behavior. We acknowledge, however, that these results, because of the
inherent uncertainties associated with such long-term projections, are
not likely to be of the quality necessary to support regulatory
decisions based upon a quantitative analysis and thus need to be
considered cautiously. In any case, these very long-term projections
will provide more complete information on disposal system performance.
As discussed below in section III.B.2.a (What Limits Are There on
Factors Included in the Performance Assessment?), the principal tool
used to assess compliance with the individual-protection standard is a
quantitative performance assessment. This method relies upon
sophisticated computer modeling of the potential processes and events
leading to releases of radionuclides from the disposal system,
subsequent radionuclide transport, and consequent health impacts. To
consider compliance for any length of time, several facets of knowledge
and technical capability are necessary. First, the scientific
understanding of the relevant potential processes and events leading to
releases must be sufficient to allow quantitative estimates of
projected repository performance. Second, adequate analytical methods
and numerical tools must exist to incorporate this understanding into
quantitative assessments of compliance. Third, scientific
understanding, data, and analytical methods must be adequately
developed to allow evaluation of performance with sufficient robustness
to judge compliance with reasonable expectation over the regulatory
period. Finally, the analyses must be able to produce estimated results
in a form capable of comparison with the standards.
The NAS evaluated these requirements for Yucca Mountain. First, it
concluded that those aspects of disposal system and waste behavior that
depend upon physical and geologic properties can be estimated within
reasonable limits of uncertainty. Also, NAS believed that these
properties and processes are sufficiently understood and boundable \11\
over the long periods
[[Page 32097]]
at issue to make such calculations possible and meaningful. The NAS
acknowledged that these factors cannot be calculated precisely, but
concluded that there is a substantial scientific basis for making such
calculations. The NAS concluded that by considering uncertainties and
natural variations, it would be possible to estimate, for example, the
concentration of radionuclides in ground water at different locations
and the times of gaseous releases. Second, NAS concluded that the
mathematical and numerical tools necessary to evaluate repository
performance are available or could be developed as part of the
standard-setting or compliance-determination processes. Third, NAS
concluded that: ``[s]o long as the geologic regime remains relatively
stable, it should be possible to assess the maximum risks with
reasonable assurance'' (NAS Report p. 69). The NAS used the term
``geologic stability'' to describe the situation where geologic
processes, such as earthquakes and erosion, that could affect the
performance assessment of the Yucca Mountain disposal system are active
or are expected to occur (NAS Report pp. 91-95). Based upon the use of
the terms ``stable'' and ``boundable'' throughout the NAS Report, one
can infer that NAS applied the term ``geologic stability'' or
``stable'' to the situation where the rate of processes and numeric
range of individual physical properties could be bounded with
reasonable certainty. The subsequent use of the term ``stable'' will
not imply static conditions or processes. Rather, it will describe the
properties and processes that can be bounded. Finally, NAS found that
the established procedures of risk analysis should enable the results
of each performance simulation of the disposal system to be combined
into a single estimate for comparison with the standard.
---------------------------------------------------------------------------
\11\ We define ``boundable'' to mean that these properties and
processes fall within certain limits. We are defining probabilities
of occurrence below which events are considered very unlikely and
need not be considered in performance assessments. We are not
otherwise constraining DOE or NRC in identifying bounding limits.
---------------------------------------------------------------------------
We previously considered the question of the appropriate compliance
period for land disposal of SNF, HLW, and TRU radioactive waste in the
40 CFR part 191 standards, where we promulgated a generic compliance
period of 10,000 years. We set the 40 CFR part 191 compliance period at
10,000 years for three reasons:
(1) After that time, there is concern that the uncertainties in
compliance assessment become unacceptably large (50 FR 38066, 38076,
September 19, 1985);
(2) There are likely to be no exceptionally large geologic changes
during that time (47 FR 58196, 58199, December 29, 1982); and
(3) Using time frames of less than10,000 years does not allow for
valid comparisons among potential sites. For example, for 1,000 years,
all of the generic sites analyzed appeared to contain the waste
approximately equally both because of long ground water travel times at
well-selected sites (47 FR 58196, 58199, December 29, 1982) and because
of the containment capabilities of the engineered barrier systems (58
FR 66401, December 20, 1993).
The purpose of geologic disposal is to provide long-term barriers
to the movement of radionuclides into the biosphere (NAS Report p. 19).
As described earlier, DOE plans to locate the Yucca Mountain repository
in tuff about 300 meters above the local water table. When the waste
packages release nongaseous radionuclides, the released radionuclides
most likely will be transported by water that moves through Yucca
Mountain from the surface toward the underlying aquifer both
horizontally between individual tuff layers and vertically downward,
through fractures in the tuff layers. Once the radionuclides reach the
aquifer, the ground water will carry them away from the repository in
the direction of ground water flow in the aquifer. The most probable
route for exposing humans to radiation resulting from releases from the
Yucca Mountain disposal system is via withdrawal of contaminated water
for local use. In the case of Yucca Mountain, DOE estimates that most
radionuclides would not reach currently populated areas within10,000
years, because of the expected performance of the engineered barrier
system (see Chapter 7 of the BID).
This finding alone seems to indicate that the compliance period for
Yucca Mountain should be longer than 10,000 years to be protective;
however, NAS concluded that the need to consider the exposures when
they are calculated to occur must be weighed against the uncertainty
associated with such calculations (NAS Report p. 72). As discussed
below, exposures could occur over tens-of thousands to hundreds-of-
thousands of years. As the compliance period is extended to such
lengths, however, uncertainty generally increases and the resulting
projected doses are increasingly meaningless from a policy perspective.
The NAS stated that there are significant uncertainties in a
performance assessment and that the overall uncertainty increases with
time. Even so, NAS found that, ``* * * there is no scientific basis for
limiting the time period of the individual-risk standard to 10,000
years or any other value'' (NAS Report p. 55). The NAS also stated that
data and analyses of some of the factors that are uncertain early in
the assessment might become more certain as the assessment
progresses(NAS Report p. 72), though this would tend to apply more to
assessments covering very long periods (i.e., longer than 10,000
years). Also, NAS stated that many of the uncertainties in parameter
values describing the geologic system are not due to the length of time
but rather to the difficulty in estimating values of site
characteristics that vary across the site. Thus, NAS concluded that the
probabilities and consequences of the relevant features, events, and
processes that could modify the way in which radionuclides are
transported in the vicinity of Yucca Mountain, including climate
change, seismic activity, and volcanic eruptions, ``are sufficiently
boundable so that these factors can be included in performance
assessments that extend over periods on the order of about one million
years'' (NAS Report p. 91). As discussed below, we believe that such an
approach is not practical for regulatory decisionmaking, which involves
more than scientific performance projections using computer models.
Today's rule requires that DOE demonstrate compliance for a period
of 10,000 years after disposal. As discussed above, NAS concluded
``there is no scientific basis for limiting the time period of the
individual-risk standard to 10,000 years or any other value'' (NAS
Report p. 55). Despite NAS's recommendation, we conclude that there is
still considerable uncertainty as to whether current modeling
capability allows development of computer models that will provide
sufficiently meaningful and reliable projections over a time frame up
to tens-of-thousands to hundreds-of-thousands of years. Simply because
such models can provide projections for those time periods does not
mean those projections are meaningful and reliable enough to establish
a rational basis for regulatory decisionmaking. Furthermore, we are
unaware of a policy basis that we could use to determine the ``level of
proof'' or confidence necessary to determine compliance based upon
projections of hundreds-of-thousands of years into the future. The NAS
indicated that analyses of the performance of the Yucca Mountain
disposal system dealing with the far future can be bounded; however, a
large and cumulative amount of uncertainty is
[[Page 32098]]
associated with those numerical projections. Setting a strict numerical
standard at a level of risk acceptable today for the period of geologic
stability would ignore this cumulative uncertainty and the extreme
difficulty of using highly uncertain assessment results to determine
compliance with that standard. We requested comments regarding the
reasonableness of adopting the NAS-recommended compliance period or
some other approach in lieu of the 10,000-year compliance period, which
we favor and describe below. We also sought comment regarding whether
it is possible to implement the NAS-recommended compliance period in a
reasonable manner and how that could be done.
The selection of the compliance period for the individual-
protection standard involves both technical and policy considerations.
It was our responsibility to weigh both during this rulemaking. In
addition to the technical guidance provided in the NAS Report, we
considered several policy and technical factors that NAS did not fully
address, as well as the experience of other EPA and international
programs. As a result of these considerations, we are establishing a
10,000-year compliance period with a quantitative limit and a
requirement to calculate the peak dose, using performance assessments,
if the peak dose occurs after 10,000 years. Under this approach, DOE
must make the performance assessment results for the post-10,000-year
period part of the public record by including them in the EIS for Yucca
Mountain.
In its discussion of the policy issues associated with the
selection of the time period for compliance, NAS suggested that we
might choose to establish consistent risk-management policies for long-
lived, hazardous, nonradioactive materials and radioactive materials
(NAS Report p. 56). We previously addressed the 10,000-year compliance
period in the regulation of hazardous waste subject to land-disposal
restrictions. Although they are subject to treatment standards to
reduce their toxicity, some of these wastes, such as heavy metals, can
essentially remain hazardous forever. Land disposal, as defined in 40
CFR 268.2(c), includes, but is not limited to, any placement of
hazardous waste in land-based units such as landfills, surface
impoundments, and injection wells. Facilities may seek an exemption
from land disposal restrictions by demonstrating that there will be no
migration of hazardous constituents from the disposal unit for as long
as the waste remains hazardous (40 CFR 268.6). This period may include
not only the operating phase of the facility, but also what may be an
extensive period after facility closure. With respect to injection
wells, we specifically required a demonstration that the injected fluid
will not migrate from the injection well within 10,000 years (40 CFR
148.20(a)). We chose the 10,000-year performance period referenced in
our guidance regarding no-migration petitions, in part, to be equal to
time periods cited in draft or final DOE, NRC, and EPA regulations (10
CFR part 960, 10 CFR part 60, or 40 CFR part 191, respectively)
governing siting, licensing, and releases from HLW disposal systems.
With respect to other land-based units regulated under the Resource
Conservation and Recovery Act (RCRA) hazardous-waste regulations, we
concluded that the compliance period for a no-migration demonstration
is specific to the waste and site under consideration. For example, for
the WIPP no-migration petition, we found that ``it is not particularly
useful to extend this model beyond 10,000 years into the future * * *
(However, t)he agency does believe * * * that modeling over a 10,000-
year period provides a useful tool in assessing the long-term stability
of the repository and the potential for migration of hazardous
constituents'' (55 FR 13068, 13073, April 6, 1990). Thus, establishing
a 10,000 year compliance period for Yucca Mountain is consistent with
risk-management policies that we have established for other long-lived,
hazardous materials.
Second, the individual-protection requirements in 40 CFR part 191
(58 FR 66398, 66414, December 20, 1993) have a compliance period of
10,000 years. The 40 CFR part 191 standards apply to the same types of
waste and type of disposal system as will be present at Yucca Mountain.
Therefore, the use of a 10,000 year time period in this regulation is
consistent with 40 CFR part 191. However, as we explained in the What
is the History of Today's Action? section earlier in this document, by
statute the 40 CFR part 191 requirements do not apply to Yucca Mountain
(WIPP LWA, section 8(b)). Nevertheless, we deem this consistency
appropriate because both sets of standards apply to the same types of
waste. Moreover, though the WIPP LWA exempts Yucca Mountain from the 40
CFR part 191 standards, it does not prohibit us from imposing standards
on Yucca Mountain that are similar to the 40 CFR part 191 standards,
if, as discussed previously, we determine in this rulemaking that the
imposition of such standards is appropriate. The question of
uncertainties over long time frames and the use of performance
projections over those time frames for regulatory decisionmaking has
been examined a number of times in our rulemaking (40 CFR parts 191 and
194) with a consistent conclusion that 10,000 years is the appropriate
choice for a compliance period.
Although 40 CFR part 191 itself does not directly apply to Yucca
Mountain, the necessity to identify a generic compliance period is an
important component of the development of radioactive waste standards,
including the Yucca Mountain standards. In a regulatory approval
process, a judgment is necessary about the technical reliability of
repository performance projections. This consensus would involve the
applicant, the regulatory authority, and the technical community in
general. In the face of increasing uncertainties in projecting
repository performance over hundreds-of-thousands of years, the
potential for technical consensus on the reliability of these
projections would decrease sharply. This decrease would lead to a
dramatic increase in the difficulty of making a compliance decision
related to such an extended time period. In setting the compliance
period in 40 CFR part 191 at 10,000 years, we addressed the issue of
increasing uncertainty by having a fixed time period rather than
requiring that the time period be determined individually for any
repository undergoing evaluation.
Third, we are concerned that there might be large uncertainty in
projecting human exposure due to releases from the repository over
extremely long periods. We agree with NAS's conclusion that it is
possible to evaluate the performance of the Yucca Mountain disposal
system and the surrounding lithosphere within certain bounds for
relatively long periods. However, we believe that NAS might not have
fully addressed two aspects of uncertainty.
One of the aspects of uncertainty relates to the impact of long-
term natural changes in climate and its effect upon choosing an
appropriate RMEI. For extremely long periods, major changes in the
global climate, for example, a transition to a glacial climate, could
occur (see Chapter 7 of the BID). We believe, however, that over the
next 10,000 years, the biosphere in the Yucca Mountain area probably
will remain, in general, similar to present-day conditions due to the
rain-shadow effect of the Sierra Nevada Mountains, which lie to the
west of Yucca Mountain (see Chapter 7 of the BID). As discussed
[[Page 32099]]
by NAS, however, for the longer periods contemplated for the
alternative of time to peak dose, the global climate regime is
virtually certain to pass through several glacial-interglacial cycles,
with the majority of time spent in the glacial state (NAS Report p.
91). These longer periods would require the specification of exposure
scenarios that would not be based upon current knowledge or cautious,
but reasonable, assumptions, but rather upon potentially arbitrary
assumptions. The NAS indicated that it knew of no scientific basis for
identifying such scenarios (NAS Report p. 96). It is for these reasons
that such extremely long-term calculations are useful only as
indicators, rather than accurate predictors, of the long-term
performance of the Yucca Mountain disposal system (IAEA TECDOC-767, p.
19, 1994, Docket No. A-95-12, Item II-A-5).
The other aspect of uncertainty concerns the range of possible
biosphere conditions and human behavior. As IAEA noted, beyond 10,000
years it may be possible to make general predictions about geological
conditions; however, the range of possible biospheric conditions and
human behavior is too wide to allow ``reliable modeling'' (IAEA-TECDOC-
767, p. 19, Docket No. A-95-12, Item II-A-5). It is necessary to make
certain assumptions regarding the biosphere, even for the 10,000-year
alternative, because 10,000 years represents a very long compliance
period for current-day assessments to project performance. For example,
it is twice as long as recorded human history (see What Do Our
Standards Assume About the Future Biosphere?, section III.B.1.f,
earlier in this document). For periods approaching the 1,000,000 years
that NAS contemplated under the peak-dose alternative, even human
evolutionary changes become possible. Thus, reliable modeling of human
exposure may be untenable and regulation to the time of peak dose
within the period of geologic stability could become arbitrary. Again,
the rational basis necessary for regulatory decisionmaking would be
difficult or impossible to achieve because of the speculative
assumptions that would be involved.
Fourth, many international geologic disposal programs use a 10,000-
year period for assessing repository performance (see, e.g., Chapter 3
of the BID, Docket No. A-95-12, Item III-B-2 or GAO/RCED-94-172, 1994,
Docket No. A-95-12, Item V-A-7). These disposal programs also have
examined this question and have opted to use a fixed time rather than
one based only on a site-specific compliance period.
Finally, an additional complication associated with the time to
peak dose within the period of geologic stability is that it could lead
to a period of regulation that has never been implemented in a national
or international radiation regulatory program. Focusing upon a 10,000-
year compliance period forces more emphasis upon those features over
which humans can exert some control, such as repository design and
engineered barriers. Those features, the geologic barriers, and their
interactions define the waste isolation capability of the disposal
system. By focusing upon an analysis of the features that humans can
influence or dictate at the site, it may be possible to influence the
timing and magnitude of the peak dose, even over times longer than
10,000 years.
Based on the extensive public comment, consistency with other EPA
radioactive and non-radioactive waste disposal programs, and a
consideration of the numerous uncertainties associated with projecting
repository performance over extended time periods, our final rule
establishes the following requirements for the individual-protection
standard and the human-intrusion analysis. For the individual-
protection standard, a 10,000-year performance assessment is required
for comparison against the 15 mrem standard. In addition, a post-
10,000-year analysis of peak dose incurred by the RMEI is to be
included in the EIS for Yucca Mountain, but is not to be held to a
particular dose limit. We view the post-10,000-year analysis as an
indicator of long-term performance that provides more complete
information. For the human-intrusion analysis, DOE must determine the
earliest time at which the human intrusion specified in the standard
will occur. Should the intrusion occur at or before 10,000 years after
disposal, DOE must demonstrate that the RMEI receives no more than 15
mrem/yr as a result of the intrusion (again, analytical results beyond
10,000 years are not judged against a dose limit, but must be included
in the EIS). Should the intrusion occur after 10,000 years, DOE must
include the analysis in the EIS for Yucca Mountain as an indicator of
long-term disposal system performance.
Public comment supported a compliance period that ranged from
10,000 years to a million years and beyond (i.e., no time limitation).
Comments supporting the 10,000-year time period expressed concern that
such a time period was the longest time over which it is possible to
obtain meaningful modeling results. Some comments agreed with our
position on the reliability of dose calculations well in excess of
10,000 years. Other comments noted that, aside from the unprecedented
nature of compliance periods exceeding 10,000 years, the greater
uncertainties present at such times only serve to complicate the
licensing process with no clear cut greater public health benefit. A
few comments agreed that, because there likely will be radiation doses
to individuals beyond 10,000 years, DOE should calculate peak dose,
within the time period of geologic stability, and include these doses
in the Yucca Mountain EIS.
Numerous comments suggested that the compliance period should
extend to times beyond 10,000 years. Foremost among these comments, NAS
suggested a compliance period that would extend to the time of peak
dose or risk, within the period of geologic stability for Yucca
Mountain (as long as one million years), based on scientific
considerations. Though NAS based its recommendation on scientific
considerations, it recognized that such a decision also has policy
aspects (NAS Report, p. 56), and that we might select an alternative
more consistent with previous Agency policy. We believe the
unprecedented nature of a compliance period beyond 10,000 years was
very persuasive and related strongly to developing a meaningful
standard that is reasonable to implement. We also harbored strong
concerns related to uncertainty in projecting human radiation exposures
over extremely long time periods, for the reasons mentioned earlier.
Some comments suggested that the compliance period of the standard
should be comparable to the amount of time that the materials to be
emplaced in the Yucca Mountain repository will remain hazardous. While
the hazardous lifetime of radioactive waste is important, it is but one
of a variety of factors that must be considered in projecting the
potential risks from disposal. The ability of the disposal system to
isolate such long-lived materials relates to the retardation
characteristics of the whole hydrogeological system within and outside
the repository, the effectiveness of engineered barriers, the
characteristics and lifestyles associated with the potentially affected
population, and numerous other factors in addition to the hazardous
lifetime of the materials to be disposed.
Thus, for a variety of technical and policy reasons, we believe
that a 10,000-year compliance period is meaningful, protective, and
practical to implement. We also believe that its use will result in a
robust disposal system that will
[[Page 32100]]
protect public health and the environment for time periods exceeding
10,000 years. We have included a 10,000-year compliance period in
regulations for non-radioactive hazardous waste. A 10,000-year
compliance period for Yucca Mountain, in conjunction with the
requirements of our existing generally applicable standard at 40 CFR
part 191, ensures that SNF, HLW, and TRU radioactive wastes disposed
anywhere in the United States have the same compliance period. Imposing
a compliance period beyond 10,000 years would be unprecedented both
nationally and internationally. Further, such an action would carry
significant and unmanageable uncertainties. Moreover, provisions to
consider radiation dose impacts beyond 10,000 years as a part of the
environmental impact review process provide more complete information
on long-term disposal system performance. We believe this approach
provides the appropriate balance that allows for meaningful
consideration of the issues related to 10,000-year and post-10,000-year
aspects of disposal system performance.
2. What Are the Requirements for Performance Assessments and
Determinations of Compliance? (Secs. 197.20, 197.25, and 197.30)
The NRC must decide whether to license the Yucca Mountain disposal
system. It must make that decision based upon whether DOE has
demonstrated compliance with our 40 CFR part 197 standards. We proposed
the quantitative analysis underlying that decision will be a
performance assessment (as defined in Sec. 197.12). The DOE and NRC
must also make some decisions about what factors to include in the
performance assessments, and how extensive those assessments must be to
satisfactorily demonstrate compliance. We have addressed some of these
performance assessment aspects in our proposal and final rule.
a. What Limits Are There on Factors Included in the Performance
Assessments? We proposed that the performance assessment exclude
natural features, events, and processes based on the probability of
occurrence. We based our proposed requirements for performance
assessment on a review of NAS's recommendations, our knowledge
regarding the extensive performance assessment work that DOE and NRC
have undertaken regarding the Yucca Mountain site, and consistency with
40 CFR part 191 and its application in the WIPP certification. We also
require NRC to determine, taking into consideration that performance
assessment, whether the disposal system's projected performance
complies with Sec. 197.20. Projecting repository performance is the
major tool to be used to develop information that will be used to make
compliance decisions relative to our standards. To provide the
necessary context for these assessments to generate results for
regulatory decisionmaking, we must specify sufficient details to assure
the standards are implemented as we intend through the use of
performance assessments. We have specified only what we believe to be
the minimum detail necessary. The remainder we believe should be left
to NRC to determine, consistent with its implementing responsibilities
and decisionmaking authority.
For repository performance assessments, our standards also require:
(1) That DOE exclude from performance assessments those natural
features, events, and processes whose likelihood of occurrence is so
small that they are very unlikely, which are those that DOE and NRC
estimate to have less than a 1 in 10,000 (1 x 10-\4\)
chance of occurring during the 10,000 years after disposal.
Probabilities below this level are associated with events such as the
appearance of new volcanoes outside of known areas of volcanic activity
or a cataclysmic meteor impact in the area of the repository. We
believe there is little or no benefit to public health or the
environment from trying to regulate the effects of such very unlikely
events;
(2) Unlikely events with probabilities higher than stated in (1)
above may be excluded from analyses for the human intrusion and ground
water protection standards. We leave it to NRC to set the probability
limit for these unlikely events in its implementing regulations; and
(3) That the performance assessment need not evaluate the releases
from features, events, processes, and sequences of events and processes
estimated to have a likelihood of occurrence greater than 1 x
10-\4\ of occurring during the 10,000 years following
disposal, if there is a reasonable expectation that the results of the
performance assessment would not be changed significantly by such
omissions. As necessary, NRC may provide DOE with specific guidance
regarding scenario selection and characterization to assure that DOE
does not exclude features, events, or processes inappropriately.
We received only a few comments on the question of including low
probability events; however, the comments we received supported our
proposal. The comments also pointed out some potential confusion in the
terms we used in describing unlikely versus very unlikely features,
events, and processes. Our intent is to establish that there is no need
to include, in the performance assessments used to demonstrate
compliance with the individual-protection standard, features, events,
and processes, and sequences of events and processes, with
probabilities of less than 1 x 10-\4\ chance of occurring in
the next 10,000 years. We consider it unlikely that features, events,
and processes with such low probabilities of occurrence will occur. We
intended to establish another demarcation for excluding unlikely
features, events, and processes with a higher probability than stated
above but that still have a low probability of occurrence. The DOE must
include processes and events in this second category in the assessments
for the individual-protection standard, unless NRC determines that
excluding them would not affect the results of the assessments. The DOE
may, however, exclude them from consideration in demonstrating
compliance with the human-intrusion and ground water protection
standards. We did not establish a particular probability level for
these unlikely features, events, and processes. Instead, we deferred
this decision to the implementing authority in Sec. 197.36 of our final
rule.
The comments we received on this question supported our contention
that the geologic record is the best source of evidence for the
frequency and magnitude of natural features, events, and processes that
could affect repository performance, and that the geologic record is
best preserved in the relatively recent past. More specifically, some
comments suggested that the Quaternary Period should be the time frame
over which DOE should examine evidence for rates and magnitudes of
natural features, events, and processes. Because the Quaternary Period
includes episodes of glaciation, it provides a means to estimate the
potential effects of future climate variations. Further, we believe
that the Period's duration (approximately two million years) provides
an adequate time frame for estimating the frequency and severity of
past seismic activity in the repository area. The NAS in its
recommendations indicated that the repository area could be assumed to
be ``geologically stable'' over a period of one million years for the
purpose of bounding natural features, events, and processes. We believe
that the Quaternary Period is a sufficiently long period of the
geologic record to allow DOE to make reasonable
[[Page 32101]]
estimates of natural features, events, and processes. We chose not to
identify a specific time frame in the regulatory language. We leave
this choice to the implementing authority.
We allow the exclusion of unlikely natural features, events, and
processes from both the ground water and human-intrusion assessments.
The approach for the ground water protection requirements is consistent
with subpart C of 40 CFR part 191, ``Environmental Standards for
Ground-Water Protection.'' The approach for the human-intrusion
analysis is consistent with NAS's recommendation (see the What Is the
Standard for Human Intrusion? section later in this document). We
requested public comment regarding whether this approach is appropriate
for Yucca Mountain. See the response to Question #10 in section IV
later in this document and the Response to Comments document for more
information.
b. What Limits Are There on DOE's Elicitation of Expert Opinion? We
requested public comment on whether we should include requirements on
the use of expert opinion and, if so, what those requirements should
be. We consider it likely, given the long time frames involved and the
significant uncertainties in the likelihood of features, events,
processes, and sequences of events and processes affecting the Yucca
Mountain disposal system, that DOE will find it useful to obtain expert
opinion to help it arrive at cautious but reasonable estimates of the
probability of future occurrence of these features, events, processes,
and sequences of events and processes. We also expect DOE to find
expert opinion useful in assessing available performance assessment
models, or in evaluating the uncertainties associated with the
variation of parameter values.
In requesting public comment on this issue, we distinguished
between expert judgment, which often is obtained informally, and expert
elicitation, in which a more formal process is used. We focused on
expert elicitation, and considered including one or all of the
following requirements: (1) NRC must consider the source and use of the
information so gathered; (2) we would have expected NRC to assure that,
to the extent possible, experts with both expertise appropriate for the
subject matter and independence from DOE will be on the expert
elicitation panel consulted to judge the validity and adequacy of the
model(s) or value(s) for use in a compliance assessment; and (3) we
would have expected that, when DOE presents information to the expert
elicitation panel, it should do so in a public meeting, and qualified
experts, such as representatives of the States of Nevada and
California, should be given an opportunity to present information.
The comments we received were uniformly opposed to our setting
requirements to address expert opinion. There was general agreement
among commenters that it would be more appropriate for NRC to use the
licensing process to address any requirements relating to expert
elicitation. Some commenters referred to NRC's NUREG-1563 (``Branch
Technical Position on the Use of Expert Elicitation in the High-Level
Radioactive Waste Program''), and to the fact that DOE has used it on
several occasions. These comments reinforced our opinion that issuing
requirements would be an implementation function better left to NRC. We
do not expect to issue guidance on this topic, although we reserve the
right to do so. We also recognize that such guidance would not be
binding, unless it is promulgated by notice and comment rulemaking.
One comment suggested that we restrict the form the expert
elicitation could take. The comment stated that it is inappropriate to
estimate parameter values using Delphi surveys or other similar
techniques that tend to ``exclude the public from vital areas of
debate.'' Given that we leave the expert elicitation process to NRC and
DOE, we choose not to address only this one particular aspect of that
process because we believe that it would be inconsistent to impose any
specific requirements on how DOE and NRC should use expert opinion. We
believe that NRC and DOE are sufficiently sensitive to public opinion
regarding the licensing of Yucca Mountain to avoid the appearance of
secrecy or targeted polling of experts to obtain a specific outcome.
Therefore, our rule does not address any aspects of DOE's ability to
use expert elicitation.
c. What Level of Expectation Will Meet Our Standards? We use the
concept of ``reasonable expectation'' in these standards to reflect our
intent regarding the level of ``proof'' necessary for NRC to determine
whether the projected performance of the Yucca Mountain disposal system
complies with the standards (see Secs. 197.20, 197.25, and 197.30). We
intend for this term to convey our position that unequivocal numerical
proof of compliance is neither necessary nor likely to be obtained for
geologic disposal systems. We believe unequivocal proof is not possible
because of the extremely long time periods involved and because
disposal system performance assessments require extrapolations of
conditions and the actions of processes that govern disposal system
performance over those long time periods. The NRC has used a similar
qualitative test, ``reasonable assurance,'' for many years in its
regulations, and has proposed applying this concept in its Yucca
Mountain regulations (proposed 10 CFR part 63). However, the NRC
approach was taken from reactor licensing, which focuses on engineered
systems with relatively short lifetimes, where performance projections
can be verified and if necessary corrective actions are possible. We
believe that for very long-term projections where confirmation is not
possible, involving the interaction of natural systems with engineered
systems complicated by the uncertainties associated with the long time
periods involved, an approach that recognizes these difficulties is
appropriate. Although NRC has adapted the reasonable assurance approach
from the reactor framework and has applied it successfully in
regulatory situations related to facility decommissioning and shallow-
land waste burial, it has not been applied in a situation as complex as
the Yucca Mountain disposal system. We believe that reasonable
expectation provides an appropriate approach to compliance decisions;
however, with respect to the level of expectation applicable in the
licensing process, NRC may adopt its proposed alternative approach. We
expect that any implementation approach NRC adopts will incorporate the
elements of reasonable expectation listed in Sec. 197.14. A more
thorough discussion of our intent concerning the application of
reasonable expectation is given below and a more exhaustive discussion
of the subject is presented in the Response to Comments document for
this regulation. We intend that the information in Sec. 197.14 of the
rule and discussions of reasonable expectation presented below and in
the Response to Comments document will provide the necessary context
for implementation of this concept.
The primary means for demonstrating compliance with the standards
is the use of computer modeling to project the performance of the
disposal system under the range of expected conditions. These modeling
calculations involve the extrapolation of site conditions and the
interactions of important processes over long time periods,
extrapolations that involve inherent uncertainties in the necessarily
limited amount of information that can be collected through field and
laboratory studies and the unavoidable uncertainties involved in
simulating the complex and time-
[[Page 32102]]
variable processes and events involved in long-term disposal system
performance. Simplifications and assumptions are involved in these
modeling efforts out of necessity because of the complexity and time
frames involved, and the choices made will determine the extent to
which the modeling simulations realistically simulate the disposal
system's performance. If choices are made that make the simulations
very unrealistic, the confidence that can be placed on modeling results
is very limited. Inappropriate simplifications can mask the effects of
processes that will in reality determine disposal system performance,
if the uncertainties involved with these simplifications are not
recognized. Overly conservative assumptions made in developing
performance scenarios can bias the analyses in the direction of
unrealistically extreme situations, which in reality may be highly
improbable, and can deflect attention from questions critical to
developing an adequate understanding of the expected features, events,
and processes. For example, a typical approach to addressing areas of
uncertainty is to perform ``bounding analyses'' of disposal system
performance. If the uncertainties in site characterization information
and the modeling of relevant features, events, and processes are not
fully understood, results of bounding analyses may not be bounding at
all. The reasonable expectation approach is aimed simply at focusing
attention on understanding the uncertainties in projecting disposal
system performance so that regulatory decision making will be done with
a full understanding of the uncertainties involved.
We received comments both supporting and opposing the concept of
``reasonable expectation'' and its application to the Yucca Mountain
standards. Comments in favor of the approach agreed that the
consideration of uncertainty is extremely important to a proper
perspective on the degree of confidence possible for projections of
disposal system performance over the long time frames involved in
assessing repository performance. Comments against the concept voiced
variations on three basic concerns: (1) That the concept is ``new,''
``untested,'' and of ``dubious legal authority'' in the regulatory
framework; (2) that it implies that less rigorous, and therefore
unacceptable, science and analysis would result from the use of
reasonable expectation; and (3) that the choice of approach to
compliance decision making is solely an implementation concern that we
should leave to NRC.
With respect to the legal authority and use of the reasonable
expectation concept in the regulatory process, we believe that the
reasonable expectation concept is well established in both the
regulatory language in standards, as well as in actual application to
deep geologic disposal of radioactive wastes, and has been judicially
tested. We developed the ``reasonable expectation'' approach in the
context of developing 40 CFR part 191, the generic standards for land
disposal of SNF, HLW, and TRU radioactive waste, and more importantly
the concept has been applied successfully in the EPA certification of
the Waste Isolation Pilot Plant (WIPP), a deep geologic repository for
TRU radioactive wastes. The WIPP repository is to date the only deep
geologic repository for radioactive wastes in the United States that
has been carried through a regulatory approval process. Therefore, we
believe that the reasonable expectation concept is neither ``new'' nor
``untried'', nor of ``dubious legal authority'' in the geologic
repository regulatory experience. In fact, the use of reasonable
expectation for the application to geologic disposal has been upheld in
court (Natural Resources Defense Council, Inc. versus U.S. E.P.A. (824
F.2d 1258, 1293 (1st Cir. 1987))).
In contrast, the reasonable assurance concept was developed and
applied many times in the context of reactor licensing--not in the
context of deep geologic disposal efforts--and has not been used in a
regulatory review and approval process for a deep geologic disposal
system. The judicial decision cited in one comment refers to the use of
reasonable assurance in the context of reactor licensing, not in the
context of deep geologic disposal. While the reasonable assurance
concept has an established record of successful application and
judicial approval in reactor licensing, it is in fact largely untried
in the arena of geologic disposal.
Some comments suggested our approach would allow the use of less
rigorous science to the assessment of disposal system performance in
licensing. This perception may have arisen from our choice of wording
in the proposal, where we stated that NRC may elect to use a more
``stringent'' approach. Such an interpretation was not our intent: the
full text of our statement is that NRC may impose requirements that are
``more stringent'' than the ``minimum requirements for implementation''
that our rule establishes; in addition, we clearly stated that
reasonable expectation ``is less stringent than the reasonable
assurance concept that NRC uses to license nuclear power plants''
(proposed Sec. 197.14(b), emphasis added). However, we will clarify our
meaning here. Performance projections for deep geologic disposal
require the extrapolation of parameter values (site characteristics
related to performance) and performance calculations (projections of
radionuclide releases and transport from the repository) over very long
time frames that make these projections fundamentally not confirmable,
in contrast to the situation of reactor licensing where projections of
performance are only made for a period of decades and confirmation of
these projections is possible through continuing observation. In this
sense, a reasonable expectation approach to repository licensing would
be necessarily ``less stringent'' than an approach to reactor
licensing. We therefore must disagree with these comments that
reasonable expectation requires less rigorous proof than NRC's
reasonable assurance approach.
We do not believe that the reasonable expectation approach either
encourages or permits the use of less than rigorous science in
developing assessments of repository performance for use in regulatory
decision making. On the contrary, the reasonable expectation approach
takes into account the inherent uncertainties involved in projecting
disposal system performance, rather than making assumptions which
reflect extreme values instead of the full range of possible parameter
values. It requires that the uncertainties in site characteristics over
long time frames and the long-term projections of expected performance
for the repository are fully understood before regulatory decisions are
made. This approach has a number of implications relative to the data
and analyses that would be used in making regulatory decisions.
Cautious use of bounding assessments is implied since sufficient
understanding of uncertainties must be developed to be sure such
analyses are truly bounding. Performance scenarios should be developed
realistically without omitting important components simply because they
may be difficult to quantify with high accuracy, or always assuming
worst case values in the absence of information. Elicited values for
relevant data should not be substituted for actual field and laboratory
studies when they can be reasonably performed, simply to conserve
resources or satisfy scheduling demands. The gathering of credible
information that would allow a better
[[Page 32103]]
understanding of the uncertainties in site characterization data and
engineered barrier performance that would bear on the long-term
performance of the repository should not be subjugated simply for
convenience. We do not believe that reasonable expectation in any way
encourages less than rigorous science and analysis. In contrast,
adequately understanding the inherent uncertainties in projecting
repository performance over the time frames required must involve a
rigorous scientific program of site characterization studies and
laboratory testing.
Some comments expressed the opinion that our use of the reasonable
expectation approach intrudes inappropriately into the area of
implementation, which is the province of NRC. We do not believe that is
the case. We have included the concept of reasonable expectation in the
Yucca Mountain standards to provide a necessary context for
understanding the standards and as context for the implementation of
the licensing process NRC will perform. Projecting disposal system
performance involves the extrapolation of physical conditions and the
interaction of natural processes with the wastes for unprecedented time
frames in human experience, i.e., many thousands of years. In this
sense, the projections of the disposal system's long-term performance
cannot be confirmed. Not only is the projected performance of the
disposal system not subject to confirmation, the natural conditions in
and around the repository site will vary over time and these changes
are also not subject to confirmation, making their use in performance
assessments equally problematical over the long-term (see Chapter 7 of
the BID). In light of these fundamental limitations on assessing the
disposal system's long-term performance, we believe that the approach
used to evaluate disposal system performance must take into account the
fundamental limitations involved (including the basic guidance given in
Sec. 197.14), and not hold out the prospect of a greater degree of
``proof'' than in reality can be obtained.
Relative to implementation, the primary task for the regulatory
authority is to examine the performance case put forward by DOE to
determine ``how much is enough'' in terms of the information and
analyses presented, i.e., implementation involves how regulatory
authority determines when the performance case has been demonstrated
with an acceptable level of confidence. We have proposed no specific
measures in our standards for that judgment. We have not specified any
confidence measures for such judgments or numerical analyses, nor
prescribed analytical methods that must be used for performance
assessments, quality assurance measures that must be applied,
statistical measures that define the number or complexity of analyses
that should be performed, nor have we proposed any assurance measures
in addition to the numerical limits in the standards. We have specified
only that the mean of the dose assessments must meet the exposure
limit, without specifying any statistical measures for the level of
confidence necessary for compliance. We believe that measure is a
minimal level for compliance determination, and we selected it to be
consistent with the individual protection requirement we applied for
the WIPP certification (40 CFR 194.55(f)). For the WIPP certification,
EPA was also the implementing agency, and in 40 CFR part 194 we also
included implementation requirements, including statistical confidence
measures for the assessments and analytical approaches
(Secs. 194.55(b), (d), (f)) along with quality assurance requirements
(Sec. 194.22), other assurance requirements (Sec. 194.41), requirements
for modeling techniques and assumptions (Secs. 194.23 and 25), use of
peer review and expert judgment (Secs. 194.26 and 194.27). We have not
incorporated a similar level of detail in the Yucca Mountain standards
because we believe we must specify only what is necessary to provide
the context for implementation. We believe that our reasonable
expectation approach provides a necessary context for understanding the
intent of the standards and for its implementation. We have provided
guidance statements in the standards (Sec. 197.14) relative to the
approach that we believe appropriately address the inherent
uncertainties in projecting the performance of the Yucca Mountain
disposal system. The implementing agency is responsible for developing
and executing the implementation process and, with respect to the level
of expectation applicable in the licensing process, is free to adopt an
approach it believes is appropriate, but we believe whatever approach
is implemented must incorporate the aspects of reasonable expectation
we have described in the standards and amplified upon in the Response
to Comments document.
d. Are There Qualitative Requirements To Help Assure Protection? In
the preamble to our proposed standards (64 FR 46998), we requested
comment upon whether it is appropriate for us to establish assurance
requirements in this final rule and if so, what those requirements
should be. The majority of public comments on the issue stated that it
was unnecessary for us to include assurance requirements in this rule.
The commenters also generally stated that the inclusion of such
requirements is an implementation matter that is properly within NRC's
jurisdiction. No comments suggested what, if any, assurance
requirements we should include in this final rule. Therefore, based
upon the public comments we received regarding this rule, the
provisions in 40 CFR part 191, and the provisions of NRC's proposed 10
CFR part 63, we did not include assurance requirements in this rule,
though we believe we have the authority to do so pursuant to the AEA
and the EnPA. For example, our generally applicable standards for the
disposal of SNF, HLW, and TRU radioactive wastes (40 CFR part 191, 58
FR 66402, December 20, 1993; 50 FR 38073 and 38078, September 19, 1985)
require the consideration of assurance requirements. The assurance
requirements in 40 CFR part 191, however, do not apply to facilities
that NRC regulates, based upon the understanding between EPA and NRC
that NRC would include them in its licensing regulations in 10 CFR part
60. The NRC is the licensing agency for Yucca Mountain; therefore, at
first glance it appears that requiring assurance requirements at Yucca
Mountain would be inconsistent with our approach in 40 CFR part 191.
The EnPA, however, mandates that we set site-specific standards for
Yucca Mountain. We believe, therefore, that we could include assurance
requirements in this rule. Because NRC's proposed licensing criteria
(see 10 CFR 63.102, 63.111, and 63.113; 64 FR 8640, 8674-8677, February
22, 1999) contain requirements similar to the assurance requirements in
40 CFR part 191 for multiple barriers, institutional controls,
monitoring, and the retrievability of waste from Yucca Mountain, we
believe that it is unnecessary for us to include similar requirements
in this rule. We encourage NRC to include the assurance requirements in
the proposed 10 CFR part 63 (64 FR 8640), or requirements similar to
those in 40 CFR part 191, in its final licensing regulations for Yucca
Mountain.
[[Page 32104]]
3. What Is the Standard for Human Intrusion? (Sec. 197.25)
We adopted NAS's suggested starting point for a human-intrusion
scenario. As NAS recommends, our standard requires a single-borehole
intrusion scenario based upon Yucca Mountain-specific conditions. The
intended purpose of analyzing this scenario ``* * * is to examine the
site-and design-related aspects of repository performance under an
assumed intrusion scenario to inform a qualitative judgment'' (NAS
Report p. 111). The assessment would result in a calculated RMEI dose
arriving through the pathway created by the assumed borehole (with no
other releases included). Consistent with the NAS Report, we also
require ``that the conditional risk as a result of the assumed
intrusion scenario should be no greater than the risk levels that would
be acceptable for the undisturbed-repository case'' (NAS Report p.
113). We interpreted NAS's term ``undisturbed'' to mean that the Yucca
Mountain disposal system is not disturbed by human intrusion but that
other processes or events that are likely to occur could disturb the
system.
We require that the human-intrusion analysis of disposal system
performance use the same methods and RMEI characteristics for the
performance assessment as those required for the individual-protection
standard, with two exceptions. The first exception is that the human-
intrusion analysis would exclude unlikely natural features, events, and
processes. The second exception is that the analysis only would address
the releases occurring through the borehole (see the What Are the
Requirements for Performance Assessments and Determinations of
Compliance? section earlier in this document).
As noted earlier, our rule uses the same RMEI description for this
analysis and scenario as in the assessment for compliance with the
individual-protection standard. It is possible that one could postulate
that an individual occupies a location above the repository footprint
in the future and is impacted by radioactive material brought to the
surface during an intrusion event; however, the level of exposure of
such an individual would be independent of whether the repository
performs acceptably when breached by human intrusion in the manner
prescribed in the scenario. Movement of waste to the surface as a
result of human intrusion is an acute action. The resulting exposure is
a direct consequence of that action. Thus, we interpret the NAS-
recommended test of ``resilience'' to be a longer-term test as measured
by exposures caused by releases that occur gradually through the
borehole, not suddenly as with direct removal. In addition, the effects
of direct removal depend on the specific parameters involved with the
drilling, not on the disposal system's containment characteristics. We
also require that the test of the disposal system's resilience be the
dose incurred by the same RMEI used for the individual-protection
standard. This approach is consistent with NAS's recommendation.
The DOE must determine when the intrusion would occur based upon
the earliest time that current technology and practices could lead to
waste package penetration without the drillers noticing the canister
penetration. In general, we believe that the time frame for the
drilling intrusion should be within the period that a small percentage
of the waste packages have failed but before significant migration of
radionuclides from the engineered barrier system has occurred because,
based upon our understanding of drilling practices, this period would
be about the earliest time that a driller would not recognize an impact
with a waste package. Our review of information about drilling and
experiences of drillers indicates that special efforts, such as
changing to a specialized drill bit, would likely be necessary to
penetrate intact, non-degraded waste packages of the type DOE plans to
use. As stated earlier, DOE would determine the timing as part of the
licensing process. The DOE's waste-package performance estimates
indicate that a waste package would be recognizable to a driller for at
least thousands of years (see Chapter 8 of the BID).
We requested comment regarding how much the human-intrusion
analysis will add to protection of public health. Also, given current
drilling practice in the vicinity of Yucca Mountain, we sought comment
regarding whether our stylized, human-intrusion scenario is reasonable.
Comments on our intrusion scenario focused on a number of concerns.
Some comment expressed opinions that the intrusion scenario was
unrealistic since actual drilling to tap ground water would more
probably be done not from the crest of Yucca Mountain but rather from
the adjacent valley floors. Other comments stated that multiple
drilling intrusions should be assumed rather than only one, and offered
alternative scenarios for intrusion frequency and purposes other than
tapping ground water. Some comments acknowledged that the scenario was
an adequate test of repository resiliency independent of the question
of attempting to predict future activities, and that the difficulty of
reliably predicting future activities and human intention were
unavoidable, as NAS concluded. Some comment stated that the probability
of such an intrusion was so remote as to make the scenario useless for
any type of repository analysis, while some comment expressed opinions
that the entire question of human intrusion was an implementation issue
that should be left to the discretion of NRC. Detailed responses to
comments we received on the human intrusion question is found in the
Response to Comments document accompanying this rule. Our response to
some of the most common issues raised in the comments is given below.
A number of comments criticized the stylized definition of the
scenario on the grounds it did not address the reality of the site
location and resource potential. A convincing case can be made that
intrusion is unlikely because of the low resource potential of the
immediate Yucca Mountain area (see BID, Chapter 8), and that actual
drilling to tap the underlying ground water would most probably be done
in the valleys adjacent to Yucca Mountain, as some comments pointed
out. We recognize these conditions and the relatively low resource
potential; however, as NAS pointed out, there is no scientifically
defensible basis to preclude intrusion (NAS Report p. 111). For this
reason, the panel recommended that an intrusion scenario should be
assessed separately from the expected repository performance case (NAS
Report p. 109), and that a stylized intrusion scenario consisting of
one borehole penetration should be considered (NAS Report p. 112) as a
test of repository resilience to modest intrusion (p. 113). We agree
with the NAS conclusions in this regard. As we have pointed out early
in the preamble, releases and consequent exposures can come from either
the gradual degradation of the disposal system under expected
conditions or through disruption, most notably by human activities.
Since intrusion cannot unequivocally be ruled out, and exposures can
result from intrusions that release radionuclides, we believe it is
necessary to consider human intrusion in the context of a repository
standard focused on public health protection, even though the resource
potential at the site is low. The nature of the intrusion, how it is
analyzed and how it should be evaluated in the regulatory context, are
the next issues to consider after the basic need to assess a human
intrusion scenario is recognized.
[[Page 32105]]
The NAS was very specific in its recommendations about assessing human
intrusion. The panel recommended that the intrusion scenarios be
considered in the EPA's rulemaking process (NAS Report p. 109) and that
``EPA should specify in its standard a typical intrusion scenario to be
analyzed'' (p. 108). The panel recommended that a drill hole
penetration through a waste package be assumed, which would make a
connection from the repository to the underlying saturated zone (pp. 12
and 111). The panel recommended that a ``consequences-only analysis''
be performed (p. 111) and that the standard ``should require such an
analysis'' (p. 111), i.e., the analysis should only deal with the fate
of releases through the borehole and the potential doses resulting. The
NAS recommended that ``the conditional risk as a result of the assumed
intrusion scenario should be no greater than the risk levels * * *
acceptable for the undisturbed repository case'' (NAS Report p. 113).
We agree with these NAS recommendations and therefore we have
constructed the stylized intrusion scenario as described as separate
from the individual-protection standard, and imposed a dose limit no
greater than the dose limit imposed for the individual-protection
standard. We have also followed the NAS recommendation for the time
frame for the intrusion (NAS Report p. 112) by linking it to the
expected time when the containers first reach a state when a drilling
penetration can occur unnoticed by the drillers. This time frame serves
as a means of establishing the radionuclide inventory available for
release and the transport and dose analysis required by the standard.
Comments we received proposing alternative drilling frequencies and
intentions, such as deliberately drilling into the repository, did not
provide a sufficient rationale to abandon the NAS recommendations and
we therefore retained our original framing for the scenario. Additional
discussion of the intrusion scenario is to be found in the discussion
of comments we received on Question 10 from the proposed rule preamble
(see section IV below).
Another line of comment we received stated that framing the
intrusion scenario in part, or in any way whatever, should be
considered an implementation detail that should be left to NRC. As
stated earlier in this document (see section I.A.2, The Role of 40 CFR
part 191 in the Development of 40 CFR part 197), human intrusion is a
process that can contribute to exposures of the public, and it is
therefore appropriate to address it in a public health protection
standard. In addition, we believe the NAS recommendations as mentioned
above were very explicit in stating that human intrusion should be
included in the EPA standard and that framing the intrusion scenario
should be part of the EPA rulemaking, rather than in implementing
regulations. We have followed the NAS recommendations closely, as noted
in its comments on our proposed rule. We are also concerned that the
implementing authority have some flexibility in implementing the rule
and we have framed the standard to allow that flexibility. We have
specified in the rule only enough of the details of the scenario to
assure it is implemented as we intend. We have in fact not specified
enough of the detail to allow an analysis to actually be performed from
our description alone. For example, we have not specified the
mechanisms by which radionuclides are released from the breached
container and make their way down the borehole to the ground water
table. Without specifying release and transport mechanisms the analysis
cannot be performed. We have left this essential detail for the
implementation process. We believe this flexibility is necessary so
that the intrusion analyses can consider a range of conditions for the
stylized intrusion so it can be an actual test of the repository
``resilience'' for a limited by-passing of the engineered barrier
system. Although we have defined the stylized drilling intrusion
scenario to closely follow the NAS recommendations, if NRC determines
during its implementation efforts that additional intrusion scenarios
are necessary to make a licensing decision, NRC can require additional
analyses as part of its implementing authority.
We offered for comment two alternatives for the human intrusion
standard. The first alternative simply stated that DOE must demonstrate
a reasonable expectation that the annual dose incurred by the RMEI
would not exceed 15 mrem CEDE as a result of an intrusion event, for
10,000 years after disposal. This parallels the basic individual-
protection standard.
The second alternative incorporated our concern that assessments of
longer-term performance be made available, if not explicitly used for
compliance purposes. Under this alternative, we made a distinction
based on how long after disposal the intrusion could occur. If the
intrusion were to occur at or earlier than 10,000 years after disposal,
DOE must demonstrate a reasonable expectation that annual exposures to
the RMEI as a result of the intrusion event would not exceed 15 mrem
CEDE. There would be no time limit for this analysis; as our proposal
stated, ``[i]f that intrusion can happen within 10,000 years, then DOE
must do an analysis which projects the peak dose that would occur as a
result of the intrusion within 10,000 years.'' (64 FR 46999, August 27,
1999) However, if the intrusion occurred after 10,000 years, DOE would
not have to compare its results against a numerical standard, but would
have to include those results in its EIS.
We have selected the second alternative for our final human
intrusion standard (Sec. 197.25). However, we are not requiring that
DOE calculate a peak dose beyond 10,000 years for comparison against a
numerical standard. If the intrusion event occurs earlier than 10,000
years after disposal, DOE need only compare the dose within 10,000
years to the numerical standard. DOE must include post-10,000-year
results in its EIS, no matter when the intrusion occurs. We believe
this alternative provides assurance that the full effects of an
intrusion event will be assessed, regardless of when it occurs. We also
believe that the selected alternative is more consistent with the NAS
recommendations that a ``consequence-based'' analysis be performed (NAS
Report p. 111).
The time frame for the intrusion has implications on how the
projected doses are handled and evaluated. We are distinguishing
between intrusion events that occur within 10,000 years and those that
occur later than 10,000 years after disposal. In assessing events that
occur within 10,000 years, we further distinguish the results based on
whether exposures are incurred by the RMEI within the 10,000-year
period. We have established the 10,000-year compliance period to
reflect past precedents and a realization of the inherent uncertainties
in long-term performance projections (see section III.(B)(1)(g)). For
intrusion events that occur within 10,000 years and exposures are
incurred by the RMEI within 10,000 years, doses are compared against
the 15 mrem/yr limit given in the standard as part of the compliance
case for licensing. For consistency in the treatment of post-10,000-
year dose assessments, we are specifying that, when the dose to the
RMEI from human intrusion events occurs after the 10,000 year period,
the dose assessments are to be included in the EIS, along with the
post-10,000 year performance assessments for the individual protection
standard. Regardless of when the intrusion occurs, if exposures are
incurred later than 10,000 years, they
[[Page 32106]]
are to be included in the EIS up to the time of peak dose.
We formulated the selected alternative to be responsive to the NAS
recommendations, in addition to addressing our concern regarding the
availability of post-10,000 year analyses. A key factor in evaluating
an intrusion scenario is predicting when such an event might take
place. However, as NAS concluded, ``there is no scientific basis for
estimating the probability of intrusion at far-future times' but that
``we believe it is useful to assume that the intrusion occurs during a
period when some of the canisters will have failed * * *'' NAS Report
p. 107, 112. Therefore, we specify that DOE must assume the intrusion
occurs at ``the earliest time after disposal that the waste package
would degrade sufficiently that a human intrusion could occur without
recognition by the drillers' (proposed Sec. 197.25). This time would be
determined through the licensing process, presumably by assessing the
expected performance of the engineered barrier system. This provides
DOE the flexibility to demonstrate that its engineered barrier system
is sufficiently robust to withstand intrusion for a predictable time
period, which then determines the nature of the waste inventory used in
the analysis, i.e., the relative proportions of long-and short-lived
radionuclides.
4. How Does Our Rule Protect Ground Water? (Sec. 197.30)
The inclusion of separate ground water protection standards in
today's rule continues a longstanding Agency policy of protecting
ground water resources and the populations who may use such resources.
This policy is articulated in our primary ground water protection
strategy document titled ``Protecting the Nation's Ground Water: EPA's
Strategy for the 1990's'' (Docket No. A-95-12, Item V-A-13). We
designed today's standards to protect the ground water in the vicinity
of Yucca Mountain to benefit the current and future residents of the
area who could use this ground water as a resource for drinking water
and other domestic, agricultural, and commercial purposes. The
following sections discuss the Agency's general approach to ground
water protection, the NAS comments regarding ground water protection at
Yucca Mountain, and some of the legal and regulatory issues associated
with our final ground water protection standards.
Policy and Technical Rationales for Separate Ground Water
Protection Standards
Our General Approach to Ground Water Protection
Ground water is one of our nation's most precious resources because
of its many potential uses. A significant portion (over 50 percent in
the early 1990s) of the U.S. population draws on ground water for its
potable water supply (``Protecting the Nation's Ground Water: EPA's
Strategy for the 1990's,'' Docket No. A-95-12, Item II-A-3). In
addition to serving as a source of drinking water, people use ground
water for irrigation, stock watering, food preparation, showering, and
various industrial processes. When that water is radioactively
contaminated, each of these uses completes a radiation exposure pathway
for people. Ground water contamination is also of concern to us because
of potential adverse impacts upon ecosystems, particularly sensitive or
endangered ecosystems (``Protecting the Nation's Ground Water: EPA's
Strategy for the 1990's,'' Docket No. A-95-12, Item II-A-3). For these
reasons, we believe it is a resource that needs protection. Therefore,
we require protection of ground water that is a current or potential
source of drinking water to the same level as the maximum contaminant
levels (MCLs) for radionuclides that we established previously under
the authority of the Safe Drinking Water Act (SDWA).
In January 1990, the Agency completed a strategy to guide future
EPA and state activities in ground water protection and cleanup. The
Agency-wide Ground Water Task Force developed two papers, which it
issued for public review: an EPA Statement of Ground Water Principles
and an options paper covering the issues involved in defining the
Federal/State relationship in ground water protection. We combined
these papers and other Task Force documents into an EPA Ground Water
Task Force Report: ``Protecting The Nation's Ground Water: EPA's
Strategy for the 1990's'' (``the Strategy,'' EPA 21Z-1020, July 1991
(Docket No. A-95-12, Item II-A-3)). Our approach in this rule is
consistent with this strategy.
Key elements of our ground water protection and cleanup strategy
are the strategy's overall goals of preventing adverse effects on human
health and the environment and protecting the environmental integrity
of the nation's ground water resources. Our strategy also recognizes,
however, that our efforts to protect ground water must consider the
use, value, and vulnerability of the resource, as well as social and
economic values. We believe it is important to protect ground water to
ensure the preservation of the nation's currently used and potential
underground sources of drinking water (USDWs) for present and future
generations. Also, we believe it is important to protect ground water
to ensure that where it interacts with surface water it does not
interfere with the attainment of surface-water-quality standards; these
standards are also necessary to protect human health and the integrity
of ecosystems. We employ MCLs to protect ground water in numerous
regulatory programs. Our regulations pertaining to hazardous-waste
disposal (40 CFR part 264); municipal-waste disposal (40 CFR parts 257
and 258); underground injection control (UIC) (40 CFR parts 144, 146,
and 148); generic SNF, HLW, and TRU radioactive waste disposal (40 CFR
part 191); and uranium mill tailings disposal (40 CFR part 192) reflect
this approach. These programs have demonstrated that such protection is
scientifically and technically achievable, within the constraints that
each program applies (``Progress In Ground Water Protection and
Restoration,'' EPA 440/6-90-001, Docket No. A-95-12, Item V-A-6).
Another critical issue in ground water protection is that ground
water generally is not directly accessible. Thus, it is much more
difficult to monitor and/or decontaminate ground water than is the case
with other environmental media (``Ground-Water Protection Strategy'' p.
11, August 1984, Docket No. A-95-12, Item V-A-13). Because of the
expenses and difficulties associated with remediation of contaminated
ground water, it is prudent and cost-effective to prevent the
occurrence of such contamination (Id.). It is possible for large
amounts of contaminants to enter a body of ground water and remain
undetected until the contaminated water reaches a water well or
surface-water body. Moreover, ground water contaminants, unlike
contaminants in other environmental media such as air or surface water,
generally move in plumes with limited mixing or dispersion into
uncontaminated water surrounding the plume. These plumes of relatively
concentrated contaminants can move slowly through aquifers. They may
persist, and thus may make the contaminated resource unusable, for
extended periods of time (Id.). Because an individual plume may
underlie only a very small part of the land surface, it can be
difficult to detect by aquifer-wide or regional monitoring. Also,
monitoring
[[Page 32107]]
is unlikely to occur over greatly extended time periods, during which
time an aquifer may become dangerously contaminated (Id.). Further, the
affected area may become quite large over long time periods. Thus, we
believe that it is prudent and responsible to protect ground water
resources from contamination through pollution prevention rather than
to rely on clean-up of preventable pollution. The pollution prevention
approach to protecting ground water resources we are adopting for Yucca
Mountain avoids requiring present or future communities to implement
expensive clean-up or treatment procedures. This approach also protects
individual ground water users. Moreover, absent the protection we have
built into the rule, the ground water in aquifers around the repository
itself could be subject to expensive clean-up by future generations if
releases from the repository contaminate the surrounding ground water
to levels that exceed legal limits. A guiding philosophy in radioactive
waste management, as well as waste disposal in general, has been to
avoid imposing burdens on future generations for clean-up efforts as a
result of disposal approaches that would knowingly result in pollution
in the future (see, for example, IAEA Safety Series No. 111-F, ``The
Principles of Radioactive Waste Management,'' Docket No. A-95-12, Item
V-A-10). With respect to radioactive waste disposal, we believe the
fundamental principle of inter-generational equity is important. We
should not knowingly impose burdens on future generations that we
ourselves are not willing to assume. Disposal technologies and
regulatory requirements are developed with the aim of preventing
pollution from disposal operations, rather than assuming that clean-up
in the future is an unavoidable cost of disposal operations today.
Designing a disposal system, and imposing performance requirements that
avoid polluting resources that reasonably could be used in the future,
therefore, is a more appropriate choice than imposing clean-up burdens
on future generations. The approach to ground water protection in
today's standards is consistent with our overall approach to ground
water protection: it prevents the contamination of current and
potential sources of drinking water downgradient from Yucca Mountain.
NAS Comments on Ground Water Protection
In its report, NAS clearly identified the ground water pathway as
the significant pathways of to the biosphere in the vicinity of Yucca
Mountain(NAS Report pp. 52 and 81). The NAS also recognized that ground
water modeling for the Yucca Mountain site is complex. Because the
modeling for Yucca Mountain involves water movement through pore spaces
(the matrix) and fractures in the rocks, as well as the degree of
interconnectedness between the water moving in the two pathways, there
is uncertainty regarding which model or models to use in the analysis:
Because of the fractured nature of the tuff aquifer below Yucca
Mountain, some uncertainty exists regarding the appropriate
mathematical and numerical models required to simulate advective
transport * * * [E]ven with residual uncertainties, it should be
possible to generate quantitative (possibly bounding) estimates of
radionuclide travel times and spatial distributions and
concentrations of plumes accessible to a potential critical group.
(NAS Report p. 90)
In its report, NAS did not recommend specifically that we include a
separate ground water protection provision in our environmental
protection standards for Yucca Mountain. Neither, however, did NAS
state that we should not include such a provision.
However, in its comments on the proposed rule, NAS specifically
addressed our decision to include separate ground water protection
standards for the Yucca Mountain site:
``(i)n the preamble (to the proposed rule), EPA implies that
there is a scientific basis for inclusion of separate ground-water
limits in the standards `` for example, EPA provides a detailed
analysis of approaches to calculating such limits * * * The (NAS)
respectfully disagrees and does not believe that there is a basis in
science for establishing such limits for the reasons described
above. The (NAS) recognizes EPA has the authority under the Energy
Policy Act to establish separate ground-water limits as a matter of
policy, but if it does so it should explicitly state the policy
decisions embedded in the proposed standard and ask the public to
comment on those decisions.
``If EPA wishes to establish such standards on the basis of
science, it must make more cogent scientific arguments to justify
the need for this standard''
(NAS Comments, p. 11, Docket No. A-95-12, Item IV-D-31).
EPA's Review of the Ground Water Standards
For the reasons discussed above (see Our General Approach to Ground
Water Protection), we believe that separate ground water protection
standards designed to protect the ground water resource are necessary
elements of our Yucca Mountain standards. Our decision to include
separate ground water standards is a policy decision that we make
pursuant to our statutory authority under the Energy Policy Act.
Regarding the protectiveness of the standards, 40 CFR part 197
incorporates the current MCLs. We believe that this approach is
necessary to provide stability for NRC and DOE in the licensing
process. We based these MCLs on the best scientific knowledge regarding
the relationship between radiation exposure and risk that existed in
1975 when they were developed. Scientific understanding has evolved
since 1975. We recently concluded a review of the existing MCLs based
on a number of factors, including the current understanding of the risk
of developing a fatal cancer from exposure to radiation; pertinent risk
management factors (such as information about treatment technologies
and analytical methods); and applicable statutory requirements. See 65
FR 76708-76753, December 7, 2000. Our analyses indicate that, when the
risks associated with the individual radionuclide concentrations
derived from the MCLs are calculated in accordance with the latest
dosimetry models described in Federal Guidance Report 13, they still
generally fall within the Agency's current risk target range for
drinking water contaminants of 10-\4\ to 10-\6\
lifetime risk for fatal cancer. Therefore, the MCLs for the
radionuclides of concern at Yucca Mountain have not changed.
Our analyses, and those of NAS, indicate that, of all the potential
environmental pathways for radionuclides, travel through ground water
is the most likely pathway to lead to human exposure to radiation from
the Yucca Mountain disposal system (see Chapters 7 and 8 of the BID).
The ground water protection standards in this rule protect ground water
that is being used or that might be used as drinking water by
restricting potential future contamination. Water from the aquifer
beneath Yucca Mountain currently serves as a source of drinking water
20 to 30 km south of Yucca Mountain in the communities directly
protected by the individual-protection standard. It is also a potential
source of drinking water for more distant communities. As noted by NAS,
the available ground water supply in the vicinity of Yucca Mountain
could sustain a substantially larger population than that presently in
the area (NAS Report p. 92).
Technical Approach for Protecting Ground Water at Yucca Mountain
As noted above, NAS asserted in its comments regarding the proposed
rule, that we implied that there was a scientific basis for including
separate ground water limits in the regulations. The NAS urged us to
clearly state the
[[Page 32108]]
policy reasons for including such limits. We believe that we clearly
articulated in the preamble to the proposed rule that we included a
ground water protection provision in the proposal based upon our long-
standing policy.
In keeping with the site-specific nature of these standards, we
believe that it is appropriate to outline an approach to determining
compliance with the ground water standards consistent with the geologic
conditions along the anticipated ground water flow path for releases
from the repository. The approach that we have devised consists of
several components. The first component is to define a ground water
resource use common for the current population making use of the ground
water along the potential path of releases. The population living
downgradient from the repository typically uses the ground water for
domestic consumption and for agricultural activities. The dominant
agricultural activity is alfalfa cultivation (see Chapter 8 of the
BID). The next component of the approach is to define a method for
assessing the extent of potential contamination in the aquifer that can
be used for comparison against established limits. To address the
unique setting of the repository, we are defining a ``representative
volume'' of ground water consistent with the uses of the resource (see
Sec. 197.31(b)). The third component is to propose alternatives to
defining how DOE could use the representative volume in making
assessments of potential ground water contamination (see Sec. 197.31).
See the Representative Volume of Ground Water discussion later in this
section for our responses to comments on the representative volume
approach.
We proposed to use the MCLs as appropriate standards against which
to measure compliance. Comment upon our proposal was mixed. Some
comments claimed that we misapplied the MCL concept in the Yucca
Mountain standards compared with how we apply MCLs in other situations,
such as the use of MCLs to define when drinking water from public water
supplies is acceptable. Some comments supported the use of MCLs. Other
comments pointed out that the dosimetry system used for the current
MCLs has been superceded by newer approaches to assessing dose and risk
from ground water use and that we should, therefore, not use the MCLs.
A number of comments claimed that the use of separate ground water
standards is completely unnecessary because the individual-protection
standard includes the drinking water exposure pathway and, therefore,
the ground water standards are unnecessary as a health protection
measure.
Retaining separate ground water protection standards is consistent
with both our national policy to protect ground water resources and
with previous Agency regulations for geologic disposal facilities. Our
generic standards in 40 CFR part 191, which apply to the same kinds of
wastes contemplated for disposal at Yucca Mountain, contain separate
ground water protection provisions. We believe that there is no
question that separate ground water protection standards are
appropriate for deep geologic disposal facilities. We believe that the
use of contaminated ground water for purposes that could result in
exposures to individuals should be of concern, and that avoiding
contaminating useable ground water resources is in the general interest
of the public at large. More specifically, contamination of water
resources could result in the exposure of individuals well removed from
the repository location. Also, if ground water were withdrawn from the
repository sub-basin, and transported to other locations to supply
water needs, a larger population would be exposed than if the water
were used only locally. We commonly apply MCLs to water treatment
facilities to assure that exposures to the subsequent users of the
water are acceptable and the users are protected. The intent of using
the MCLs as a compliance measure for the Yucca Mountain disposal system
is to encourage a robust containment and isolation design that will not
result in unacceptable contamination during the regulatory time frame,
which would require future generations to shoulder the burden of water
treatment due to contamination from the wastes. We also included ground
water protection requirements in our certification process for WIPP,
which is the only deep geologic disposal facility in the country that
has actually gone through a regulatory review and approval process. We
see no reason why we should not apply the same approach to protection
for the Yucca Mountain disposal facility as we afforded to the
population around WIPP. In fact, the Yucca Mountain disposal system
will be located above aquifers that are the ground water supply for the
residents living downgradient from the repository, whereas the aquifers
potentially subject to contamination at the WIPP facility are highly
saline, non-potable water sources. We recognize that the individual-
protection standard includes a drinking water exposure pathway;
however, from a policy perspective it is appropriate and consistent for
us to provide separate protection for ground water resources in the
Yucca Mountain area. As illustrated by the examples above, the
protection of ground water resources is in the general interest of the
public at large, because it is easily conceivable that uses of the
resource could result in exposures well beyond the immediate vicinity
of the repository. From a more practical perspective, it would be
extremely difficult to predict with any reliability what the total
range of potential exposures (and consequent health effects) would be
for all possible uses of the resource, because such predictions would
involve considerable speculation. It makes more sense to assure the
resource is not contaminated in the first place. We are taking the more
prudent course of attempting to prevent ground water contamination
above the MCLs by imposing separate ground water protection
requirements.
The NRC's determination of compliance with the ground-water
protection standards will be based largely upon DOE's projections of
potential future contaminant concentrations. The DOE will include these
projections in the license application it submits to NRC. These
projections, by their very nature, inevitably will contain uncertainty.
An important cause of uncertainty, as NAS recognized, is the choice of
conceptual site models (NAS Report p. 75). The conceptual models used
for Yucca Mountain can differ fundamentally. For example, water can be
presumed to flow through either pores in the rock or conduits through
the rock (such as discrete fractures or a network of fractures that can
act as preferential pathways for faster ground water flow), or a
combination of the two. To further complicate the situation, any of
these flow scenarios, with the possible exception of flow through
conduits, can occur at Yucca Mountain whether or not the rock is
saturated completely with water.
We believe that adequate data and the choice of models will be
critical to any compliance calculation or determination because such
data and models are the backbone of the performance assessment used to
show compliance. The NAS examined the use of ground-water flow and
contaminant-transport models in regulatory applications (``Ground Water
Models: Scientific and Regulatory Applications,'' 1990, Docket No. A-
95-12, Item V-A-26). In that report, NAS concluded that data inadequacy
is an impediment to the use of unsaturated fracture flow models for
Yucca Mountain. However, NAS noted that data inadequacy also
[[Page 32109]]
was an impediment to using models that assume the pores in the rock are
either saturated or unsaturated or that assume flow through fractures
that are filled completely with water. However, despite the recognition
of the importance of the choice of the site conceptual model, we
believe that the need for sufficient quantity, types, and quality of
data to adequately analyze the site, because of its hydrogeologic
complexity, is even more important. In other words, the complexity of
the ground water flow system requires adequate site characterization to
justify the choice of the conceptual flow model.
The choice of modeling approaches to address the ground water
system in the area of Yucca Mountain, based upon the conceptual model
of the site developed from site characterization activities, is
important to characterize contaminant migration, particularly the
mixing of uncontaminated water with water that has been contaminated
with radionuclides released from breached waste packages. The extent of
the dilution afforded by mixing contaminated water with other ground
water moving through the rocks below the repository but above the water
table and the dispersion of the plume of contamination within the
saturated zone as the ground water system carries radionuclides
downgradient are critical elements of the dose assessments.
At one end of the spectrum of approaches to modeling the Yucca
Mountain area's ground water system is the assumption that it is
possible to model the system based upon flow through pores over a large
area (tens of square kilometers). At the other extreme is the
assumption that radionuclides are carried through fast-flow fractures
in the unsaturated zone separately from uncontaminated ground water
also passing through the repository footprint. Those radionuclides then
are assumed to be carried through the saturated zone in fractures that
allow little or no dispersion within, or mixing with, uncontaminated
water in the saturated zone. This scenario is essentially ``pipe flow''
from the repository to the receptor. Although the flow of ground water
at the site is influenced strongly by fractures, which the models
should reflect, we believe that it is unreasonable to assume that no
mixing with uncontaminated ground water would occur along the
radionuclide travel paths because such mixing is a natural process, and
would be governed by the degree of interconnection between individual
fractures in the rocks. We requested comment upon this approach,
including consideration of the practical limitations on characterizing
the flow system over several or tens of square kilometers.
Comments varied from statements that we should not allow DOE to
consider mixing of contaminated water from the repository with
uncontaminated water along potential flow paths, that such dilution is
an expected process in the natural system, and that these decisions
about the flow system modeling are implementation details which we
should defer to NRC. We agree that some degree of mixing along the
ground water flow paths is to be expected and, if supported by the
hydrogeologic characterization, should be considered in modeling
approaches used to make projections of radionuclide migration from
repository releases. We also agree that detailed decisions about the
approach to modeling the ground water flow system at the site are an
implementation concern for NRC. We therefore make no specific
requirements in this regard. We do believe that whatever specific
modeling approach and attendant assumptions that DOE or NRC make should
attempt to model realistically the expected behavior of the actual flow
regime downgradient from the repository. Recalling the ``pipe-flow''
scenario described above, we believe it would be highly unrealistic to
assume that no mixing of the contaminated water with ground water along
the flow path occurs along the distance from the repository to the
furthest allowable boundary of the controlled area. Although the actual
dispersion effects for the fractured rock geohydrologic setting are
anticipated to be small (see Chapter 7 of the BID), ignoring such
processes is still inappropriately over-conservative because it would
neglect a natural process that is expected to occur. Consistent with
this perspective, we specify two alternative methods that DOE could use
for determining radionuclide concentrations in the representative
volume of ground water. We believe these two alternatives provide
appropriate direction for making the compliance determination while
allowing ample flexibility for the implementation decisions concerning
the details of characterizing the ground water flow and modeling
approaches that DOE ultimately must select and defend in the licensing
process.
Our intent was to develop ground water protection standards that
NRC can reasonably implement. In this regard, NAS indicated that
quantitative estimates of ground water contamination should be possible
(NAS Report p. 90). We thus require DOE to project the level of
radioactive contamination it expects to be in the representative volume
of ground water. The representative volume could be calculated to be in
a contaminated aquifer that contains less than 10,000 mg/L of TDS and
that is downgradient from Yucca Mountain. Through the use of this
method, we intend to avoid requiring DOE and NRC to project the
contamination in every small, possibly unrepresentative amount of water
because we believe that this approach is not scientifically defensible
considering the inherent uncertainties in hydrologic data and the
limitations of modeling calculations. For example, we do not intend
that NRC must consider whether a few gallons of water in a single
fracture would exceed the standards. Thus, we allow use of a larger
volume of water that must, on average, meet the standards. See below
for a discussion of this larger volume, the ``representative volume.''
Because the purpose of the engineered and natural barriers of the
geologic repository at Yucca Mountain is to contain radionuclides and
minimize their movement into the general environment, we anticipate
that radionuclide releases from the repository will not occur for a
long period of time. With this assumption in mind, we believe that
ground water protection for the Yucca Mountain site should focus upon
the protection of the ground water as a resource for future human use.
It is the general premise of this rule that the individual-protection
standard will adequately protect those few current residents closest to
the repository. The intent of the ground water standards is protecting
the aquifer as both a resource for current users, and a potential
resource for larger numbers of future users either near the repository
or farther away in communities comprised of a substantially larger
number of people than presently exist in the vicinity of Yucca
Mountain. To implement this conceptual approach and develop an approach
for compliance determinations, we believe that the ground water
standards currently used, the MCLs, should apply to public water
supplies downgradient from the repository in aquifers at risk of
contamination from repository releases. There is presently no public
water supply providing treatment to meet MCLs before the water reaches
consumers downgradient of Yucca Mountain, and there is no guarantee
that such a system will be in place to protect future users from
contamination caused by releases from the disposal system. Applying the
MCLs in the ground water assures that the level of protection
[[Page 32110]]
currently required for public water supplies elsewhere in the nation
also is maintained for future communities using the water supply
downgradient from the Yucca Mountain disposal system.
Representative Volume of Ground Water
To implement the standards in Sec. 197.30, we require that DOE use
the concept of a ``representative volume'' of ground water. Under this
approach, DOE and NRC will project the concentration of radionuclides
released from the Yucca Mountain disposal system, for comparison
against the MCLs, that would be present in the representative volume in
the accessible environment over the 10,000-year period of the
standards. The representative volume will be a volume of water
projected to supply the annual water demands for defined resource uses.
We believe that water demand estimates for calculation of the
representative volume should reflect the current resource demands for
the general lifestyles and demographics of the area, but not be rigidly
constrained by current activities, because potential contamination
would occur far into the future. In the area south of Yucca Mountain,
people currently use ground water for domestic purposes, commercial
agriculture (for example, dairy cattle, feed crops, other crops, and
fish farming), residential gardening, commercial, and municipal uses
(see Chapter 8 of the BID). The ground water resources, as reflected by
estimates of current usage and aquifer yields, indicate that there is
theoretically enough water to support a substantially larger population
than presently exists at each of the four alternative locations we
proposed for the point of compliance (Id.). The representative volume
approach sets an upper bound on the size of the hypothetical community
and its water demand. On the other hand, the SDWA defines the minimum
size for a public water system as a system with 15 service connections
or that regularly supplies at least 25 people. The SDWA was designed to
address, and typically is applied to, situations where contamination
can be monitored in the present and where monitoring is done close to
the disposal facility rather than many kilometers away. If necessary,
corrective actions can be taken if contamination limits are exceeded.
In contrast, the geologic disposal application involves potential
contamination releases that are expected to occur no sooner than far
into the future. It simply is not reasonable to assume that monitoring
for the purpose of detecting radionuclide contamination around the
repository will be performed continually far into the future.
Consequently, it is not prudent to assume that corrective actions would
be taken to reduce contamination levels. As noted by NAS, active
institutional controls (including active monitoring and maintenance)
can play an important role in assuring acceptable repository
performance for some initial period, not exceeding a time scale of
centuries (NAS Report p. 106). Another approach to protecting the
ground water resource into the future is necessary. Projecting
repository performance, and consequently assessing potential repository
releases to the surrounding ground waters, can only be based upon
mathematical modeling of the repository's engineered and natural
barrier performance. A method of assessing potential contamination must
be developed that involves ground water modeling capabilities. The
approach we have developed to assess ground water contamination
(described previously) is the use of a representative volume of ground
water in modeling calculations.
We believe that, ideally, the representative volume should be fully
consistent with the protection objectives of the ground water
protection strategy; however, we also recognize the unusual features of
these standards. That is, the 10,000-year compliance period introduces
unresolvable uncertainties that make this situation fundamentally
different from the situations of clean-up or foreseeable, near-term
potential contamination to which the SDWA ground water protection
strategy ordinarily applies. The size of the area that must be modeled
(tens of km\2\) around the site and the complexity of the site
characteristics introduce fundamental limitations on the size of the
water volume that it is possible to model with reasonable confidence.
It is Agency policy to protect ground water as a resource and we intend
our ground water protection standards to accomplish that policy goal.
We intend the representative volume concept we have incorporated into
the standards to serve as context for the application of our ground
water protection policy to the Yucca Mountain site, which differs from
the more common application of the SDWA as described above. The
representative volume concept addresses two needs in this respect.
First, the size of the representative volume (measured as an annual
volume in acre-feet) must be sufficiently large that the uncertainties
in projecting site characteristics (such as the hydrologic properties
along the flow paths) that control ground water flow are not so great
that performing calculations to determine radionuclide concentrations
in that volume becomes meaningless from an analytical perspective. That
is, we should not expect a higher level of confidence and exactness
than the scientific tools and available data are capable of providing.
Second, the representative volume should be an appropriate measure of
the resource to be protected. From both perspectives, analytical
limitations and resource characterization, the representative volume of
1,285 acre-feet that we proposed is the potential choice that could
satisfy those needs. As described in the preamble to the proposed rule,
we preferred the 1,285 acre-feet alternative because we believed it
reflected both perspectives. The major resource use for ground water in
the area downgradient from the repository is agriculture, and the most
water intensive agricultural activity in the area is alfalfa farming.
The 1,285 acre-feet representative volume (including 10 acre-feet for
domestic use for the farm community) is the water demand for an average
alfalfa farm in the Amargosa Valley area (see Chapter 8 of the BID).
From consideration of the inherent limitations of modeling the
geohydrologic setting at the site, we believe that approximately a 100
acre-feet representative volume is the smallest volume for which it is
possible to perform reasonably reliable calculations (Memo to Docket
from Frank Marcinowski, EPA, Docket No. A-95-12, Item II-E-10). The
1,285 acre-feet volume is sufficiently above this limit; therefore,
questions about the scientific capabilities of performance modeling to
assess radionuclide concentrations in the 1,285 acre-feet volume should
not be a concern. While still feasible to model, 120 acre-feet is much
closer to the lower limit of defensible modeling, and uncertainties at
this volume are potentially unwieldy and overwhelming. We requested
comment regarding both our use of a representative volume of ground
water and possible alternatives for the size of the representative
volume. We based these alternative volumes upon variations in possible
lifestyles for residents downgradient from the repository and upon
current and near-term projections of population growth and land use in
the area.
We specifically requested comment upon whether 1,285 acre-feet is
the most appropriate representative volume of ground water, or whether
other values within the ranges discussed below are more appropriate. We
believe that there may be significant technical, policy, or
[[Page 32111]]
practical obstacles with the use of either very small or very large
water volumes. Modeling capabilities limit the volumes of ground water
for which it is possible to make meaningful and scientifically
defensible calculations. At the other extreme, excessively large
volumes of water allow artificially high dilution of radionuclide
releases, and do not actually simulate the natural process that would
occur along the radionuclide ground water travel path from the
repository to the compliance point. The selection of the representative
volume must consider both modeling limitations and realistic approaches
to modeling, and must be both a reasonable representation of the
resource to be protected and be possible to implement from a modeling
perspective.
Comments on our alternatives for the representative volume size
varied from agreement with our preferred volume of 1,285 acre-ft to
favoring larger and smaller volumes. We believe that the larger volume
mentioned in the proposed rule, 4,000 acre-ft, is not a suitable choice
for a number of reasons. This number is an estimate of the perennial
yield in the sub-basin containing Yucca Mountain. It is an estimate of
the amount of ground water that can be removed annually without
seriously depleting the aquifer. Because there are relatively few wells
in this sub-basin, the 4,000 acre-ft estimate is not highly reliable
and is difficult to justify. This is one reason why we did not select
this number. Perhaps more importantly, the perennial yield is not a
physical location in the aquifer and the challenge of projecting
repository performance is to project the path of potential
contamination from the repository. The perennial yield concept is not
consistent with the idea that the modeling of potential contamination
from the repository should use an actual volume of water, the
representative volume, to determine compliance with the standards.
Small volumes of ground water would be difficult to model with
confidence over the long time frames and distances appropriate for the
Yucca Mountain repository. More specifically, we believe it is not
possible to model for the 10 acre-ft representative volume (see the
Response to Comments document for more detail). Comment on the 120
acre-ft volume was generally that this volume was too small for
defensible modeling, which agrees with our assessment. As stated above,
we consider 120 acre-ft to be within the range of feasible modeling,
but very close to the lower limit of scientifically defensible modeling
capabilities. It also does not reflect the typical use of the ground
water resource, which is better represented by the agricultural
scenario we have selected.
There are a number of fundamental limitations involved in modeling
the flow of ground water over long distances that are direct functions
of the variability of the hydrologic properties in the aquifers along
its dimensions. Averaging assumptions are used in modeling to greater
and lesser extents to address these limitations, as a function of the
information available regarding the natural variability of hydrologic
properties along the flow paths. Our approach to calculating ground
water contaminant concentrations (the well capture zone or slice-of-
the-plume methods described in Sec. 197.31(b)) centers the
representative volume to include the highest concentration portion of
the projected plume. If the representative volume is too small, it does
not capture a volume large enough to reflect the natural processes that
will occur along the flow path. Therefore, the concentrations will be
unrealistically high and will not be a reasonable representation of the
variations that should be expected in the actual situation. The exact
limit on the lowest size of the representative volume adequately
reflecting modeling limitations and the data base of hydrologic
information about the site is a difficult expert judgment. An exact
lower limit is not possible to identify because of the inherent
limitations in gathering site data and performing modeling. Our opinion
after extensive discussions with qualified experts is that a
representative volume on the order of 100 acre-ft or below is the lower
limit of modeling capability for the Yucca Mountain ground water flow
regime (Yucca Mountain Docket, A-95-12, Item II-E-10).
We based the 1,285 acre-ft representative volume on a hypothetical
small farming community of 25 people and an alfalfa farm with 255 acres
under cultivation. This approach assumes a small community whose water
needs include domestic consumption and an agricultural component
comparable to present water usage in the vicinity of the repository. We
based the size of the average area of alfalfa cultivation, 255 acres,
on site-specific information for the nine existing alfalfa-growing
operations in Amargosa Valley in 1998, which ranged in size from about
65 acres to about 800 acres (see Chapter 8 of the BID). Using a water
demand for alfalfa farming in Amargosa Valley of 5 acre-feet per acre
per year, we estimate that the annual water demand for the average
operation is 1,275 acre-ft (Chapter 8 of the BID). An average value of
0.4 acre-ft per person for domestic water use is typical of the area
(Chapter 8 of the BID), which for the small community of 25 people
would add 10 acre-ft for domestic uses, resulting in a total
representative volume of 1,285 acre-ft. Comments on the derivation of
the 1,285 acre-ft representative volume supported this size as being
technically feasible for modeling and consistent with water resource
demands in the area downgradient from the repository.
To implement the standards in Sec. 197.30, we require that DOE use
the concept of a ``representative volume'' of ground water. Under this
approach, DOE will project the concentration of radionuclides or the
resultant doses within a ``representative volume'' of ground water for
comparison against the standards. We have selected a value of 3,000
acre-ft/yr as the representative volume. This value is a ``cautious,
but reasonable'' figure for protecting users of the ground water
downgradient of the repository, as described below. Our approach
focuses on the anticipated water use immediately downgradient of the
repository, and is closely aligned with the alternatives offered for
public comment in our proposed rule.
The preamble to the proposed rule noted that the representative
volume should reflect the water usage of a hypothetical community that
may exist in the future. The preamble also noted that the water usage
should reflect the current general lifestyles and demographics of the
area, but not be rigidly constrained by current activities. Using
current activities and near-term projections of planned activities in
the downgradient area leads us to three types of water demands that can
be identified for the downgradient area: Water demand for individual
domestic and municipal uses, water demand for commercial/industrial
uses, and water demand for agricultural uses.
In deciding how to make this projection, we have concluded in the
final rule that our focus in developing an appropriate representative
volume should be to consider the spectrum of likely downgradient uses
of the ground water resources, as well as the site-specific hydrologic
characteristics of the disposal system itself. To avoid speculation on
all possible uses of ground water, we have been guided by the premise
that current uses in the immediate downgradient area, as well as short-
term projections for water uses reflecting growth projections for the
area, should be considered in defining an appropriate representative
volume for the ground water standard. We believe that the most likely
future uses
[[Page 32112]]
will in fact take place where they are currently located, since there
is no reason to anticipate that they will cease occurring.
Deriving a representative volume involves identifying water demands
for the spectrum of likely uses, and includes an examination of
projected plume characteristics. This leads us to focus primarily on
projected uses occurring downgradient of the repository. As noted
above, the current and anticipated water demands downgradient of the
repository consist of residential/municipal uses, commercial/industrial
uses and agricultural uses.
Currently, the population at the Lathrop Wells is small, about ten
people (BID Chapter 8), however near-term projections for the area
between Lathrop Wells and the NTS boundary indicate that a science
museum and industrial park are under development (Docket No. A-95-12,
Items V-A-16, V-A-19). There are also growth projections for the
Amargosa Valley area (Docket No. A-95-12, Items V-A-14, 15), leading us
to believe that residential/municipal water demands as well as
commercial/industrial water demands are likely in the near-term for the
area between Lathrop Wells and the NTS boundary.
Projected water demand for the science museum and industrial park
are on the order of 100 acre-ft/yr (Docket No. A-95-12, Item V-A-19).
Based upon the growth projections, we believe that some residential
population growth should be anticipated for the area in addition. In
the preamble for the proposed rule, we included a representative volume
of 120 acre-ft/yr for a small residential community of approximately
150 persons, which included water uses for individuals and municipal
uses. We believe that these water demands should be incorporated into
the representative volume, so that the representative volume addresses
all potential water users. Limiting the water demand to only one of
these uses, we believe, would not be representative of the spectrum of
potential users that might be exposed to contaminated water from
repository releases. For example, the water demand for the small
population at Lathrop Wells would be on the order of less than 10 acre-
ft/yr. Our evaluations of representative volume options in the proposed
rule (Docket No. A-95-12, Item II-E-10), and the responses we received
concerning these options, consistently concluded that such small
volumes would not allow credible scientifically defensible projections
to be made.
The contribution of agricultural activities to the representative
volume can be derived from a consideration of current farming
activities in Amargosa Valley. In the Town of Amargosa Valley,
agricultural activities consume the largest volumes of ground water,
but are largely confined to the location approximately 25-30 km
downgradient from the repository location. However, the ground water
used for these activities could be contaminated if radionuclide
releases from the disposal system were sufficiently high to exceed the
limits given in Sec. 197.30. To protect the agricultural resource use,
we have used alfalfa farming as a measure of water demand. Although
there is no alfalfa farming currently at the compliance location, and
no near-term planning for it, our approach to protecting the resource
is to include the appropriate water demand in the representative volume
at the compliance location. By protecting this volume upgradient of
where the actual resource is anticipated to be tapped, we will be
protecting the larger actual volume of water that will be used for
agricultural purposes downgradient from the compliance location.
As described previously, alfalfa cultivation is the largest water
consumer in the agricultural sector, and this activity is anticipated
to continue (BID Chapter 8). We have defined an average-sized alfalfa
farm based upon current information about acreage under cultivation in
Amargosa Valley (BID Chapter 8). We have retained this value to avoid
speculation about the future of this particular activity for the
following reasons. The demand for alfalfa cultivation to support the
local dairy industry in Amargosa Valley is anticipated to be strong for
the near-term. The hydrologic basin in which this activity takes place
is fully allocated, suggesting that dramatic increases in alfalfa
cultivation are unlikely since the water allocations necessary for
dramatic increases are not readily available (BID Chapter 8).
Therefore, we are using the value of 1,275 acre-feet/yr for an average-
sized farm for developing a representative volume figure (this
represents the proposed value of 1,285 acre-feet, less the 10 acre-feet
assumed for purely domestic use).
The anticipated behavior of the ground-water flow system from Yucca
Mountain is important in determining the total contribution of the
agricultural water demand to the representative volume, since the width
of potential contamination plumes will determine how large a volume of
contaminated ground water could be tapped for agricultural purposes and
consequently should be protected from unacceptable contamination.
Projections of ground water flow, from particle-tracking analyses, have
been performed by DOE to determine the path of possible contaminant
flow from advective transport (ground water movement) alone (Docket No.
A-95-12, Items V-A-5, V-A-27). The particle tracks near the compliance
boundary, the southwesternmost corner of NTS (a distance of
approximately 18 km from the southern end of the repository), indicate
that the width of a potential contamination plume at the compliance
location is about 1.8-2.0 kilometers. Farther downgradient, the width
of the particle-track ground water travel path widens slightly to a
width of between 2 and 3 km. This width does not consider dispersive
effects that will occur, which contribute to uncertainty in projecting
the actual size of a potential contamination plume. The actual width
will be a function of a number of other factors, including the location
of failed waste packages over time within the repository and the
particular values of dispersion parameters chosen for analyses.
Somewhat smaller or larger contamination plume widths could result, but
the particle track approach results offer a satisfactory approximation.
The average alfalfa farm we have defined (255 acres in a square
shape) is only approximately one kilometer on an edge. Since the exact
location of a contamination plume and the variations in radionuclide
contaminant concentrations within it are uncertain and cannot be
projected with high confidence, we are using two average sized alfalfa
farms across the path of the contamination plume to increase confidence
that the highest concentration portions of a potential contamination
plume will be included in the representative volume, giving a total
contribution of 2,550 acre-ft/yr for the agricultural component of the
representative volume. Again, we are not assuming the existence of
actual farms at the compliance location, but we are assessing the
effects of radionuclide contamination on the water volume that they
could use at more distant locations.
In total, the contributions to the representative volume consist of
the agricultural use water demand for two average size alfalfa farms
(2,550 acre-ft/yr), the commercial/industrial water demand for the
Lathrop Wells development projections (100 acre-ft/yr), and individual/
municipal use water demand for a small community consistent with the
near-term growth projections for the area (120 acre-ft/yr). These three
components amount to 2,770 acre-ft/yr. As mentioned above,
[[Page 32113]]
there is significant uncertainty in the exact location and radionuclide
concentrations in potential contamination plumes from the repository,
and therefore we cannot be absolutely certain that two average-sized
alfalfa farms will cover the total possible width of a contamination
plume, but we believe including the water demand from more than two
farms would not be entirely justified. Our intent in using the two
alfalfa farms (each 1 km in width) is to assure that the highest
concentration portion of any contamination plume is tapped by the wells
supplying this water demand. We have also modified Sec. 197.31 to allow
the use of multiple pumping wells (rather than a single well as
described in the proposed rule) to tap the representative volume so
that technical limitations on constructing a well withdrawal scenario
can be eliminated or minimized, should DOE elect this alternative for
calculating radionuclide concentrations in the representative volume.
There is, of course, uncertainty in projecting the size and shape
of contamination plumes from the repository as well as projecting human
activities into the future, and we have limited this source of
uncertainty by considering only near-term projections for growth and
development in the area, but some degree of inherent uncertainty will
always remain. To address these residual uncertainties in this
approach, we increase the representative volume by about 10%, to a
total 3,000 acre-ft/yr. We believe that this figure represents a
cautious, but reasonable, estimate of the representative volume to
protect the ground water resource downgradient of the repository.
We considered an alternative way of evaluating the representative
volume concept for application to the ground water protection
standards. This approach considers the larger scale ground water flows
and uses in the larger basin (Basin 230) which receives outflow from
the basin where the repository is located (Basin 227A). The primary
water use in this region is in the Amargosa Desert hydrographic basin
(Basin 230, see BID Chapter 8), where farming, mining, and other
industrial uses occur. This water comes from four basins that have an
estimated total water budget of about 43,800 acre-feet, which
represents ground water that flows into the Amargosa Desert basin.
The Jackass Flats basin (Basin 227A, which includes Yucca Mountain
and the point of compliance location) is one of four basins that flow
from the north into the Amargosa Desert basin and provide the ground
water that is used for these activities. It is the only one of these
basins into which it is reasonable to anticipate that water
contaminated by releases from the repository would flow. The Jackass
Flats basin contributes about 8,100 acre-feet to the total Amargosa
Valley water budget (Table 8-6, BID). Considering the approximate
nature of these values, it is reasonable to approximate the
contribution of the Jackass Flats to flow into the Amargosa Desert
basin and to current water uses at 20%.
Although the Amargosa Desert basin has a water appropriation limit
of about 41,093 acre-feet, in 1997, the reported ground water use in
the Amargosa Desert basin was about 13,900 acre-feet (BID Chapter 8).
That is, the use was less than appropriated. Moreover, actual water use
fluctuates significantly, depending primarily on the level of
irrigation and mining activities in a given year (BID Chapter 8). To
estimate the actual contribution of flow from Jackass Flats, we again
refer to the largest water use in the area downgradient from the
repository, which is for irrigation, particularly for the cultivation
of feed for livestock (primarily alfalfa). There are nine alfalfa farms
in the affected area, ranging from approximately 65 to 800 acres (BID
Chapter 8). Estimates of acreage under cultivation for feedstock has
shown a steady increase from 1994 to 1999 (Table 8-6, BID), with an
increase of 50% from 1997 to 1999. Assuming that it also increased by
50%, the 1997 irrigation use of 9,379 acre-feet (Table 8-4, BID) could
have increased by approximately 4,700 acre-feet in 1999. This
assessment gives a range of water use from approximately 13,900 acre-
feet in 1997 to an estimate of 18,600 acre-feet in 1999, placing the
corresponding 20% contribution from Jackass Flats in a range of
approximately 2,800 to 3,700 acre-feet. From this range of possible
values, we again selected 3,000 acre-feet as a value that is
conservative (toward the low end of the range), but also makes an
allowance for the uncertainty inherent in these estimates.
In summary, both approaches to deriving a ``cautious, but
reasonable'' representative volume for the purpose of ground water
protection converge on a value of 3,000 acre-ft/yr. Our approach to
developing an appropriate representative volume considered the size of
the ground water resource and its current and projected uses.
Accordingly, we have selected a representative volume of 3,000 acre-
feet for this rule. This volume is within the 10 to 4,000 acre-feet
range described in the proposed rule and addressed in the public
comments and represents a reasonable and site-specific approach to
protecting groundwater resources in the vicinity of Yucca Mountain.
Our standards require DOE to assume that the entire representative
volume is drawn at the compliance point, that is, 18 km south of the
repository, rather than in the Amargosa Valley itself, at 25 to 30 km
south of the repository. Therefore, it is adequate not only to protect
downgradient uses, but also to protect all of these reasonably
projected uses, should the representative volume be withdrawn at the
compliance point. As noted above, we believe that given the
uncertainties of projecting any particular future and the difficulties
of modeling that using the small volumes that would be required by
relying only on current projected uses, this is a reasonable approach
for determining how ground water should be protected at this particular
site.
There are two basic approaches that DOE must choose between for
calculating the concentrations of radionuclides in the accessible
environment. The DOE may perform this analysis by determining how much
contamination is in: (1) A ``well-capture zone;'' or (2) a ``slice of
the plume'' (see immediately below for explanations of these
approaches). For either approach, the volume of water used in the
calculations is equal to the representative volume, i.e., the annual
water demand for the future group using the ground water.
The ``well-capture zone'' is the portion of the aquifer containing
a volume of water that one or more water supply wells, pumping at a
defined rate, withdraw from an aquifer. The dimensions of the well-
capture zone are determined by the pumping rate in combination with
aquifer characteristics assumed for calculations, such as hydraulic
conductivity, gradient, and the screened interval. If DOE uses this
approach, it must assume that the:
(1) Wells have characteristics consistent with public water supply
wells in Amargosa Valley, for example, well bore size and length of the
screened interval;
(2) Screened interval includes the highest concentration in the
plume of contamination at the point of compliance; and
(3) Pumping rate is set to produce an annual withdrawal equal to
the representative volume.
To include an appropriate measure of conservatism in the compliance
calculations for the well-withdrawal approach, for the purpose of the
analysis, DOE should assume that pumping wells that tap the highest
concentration within the projected plume of contamination would supply
[[Page 32114]]
the community water demand. This approach achieves conservatism by
requiring that the entire water demand is withdrawn from wells
intercepting the center of the plume of contamination so that the
highest radionuclide concentrations in the plume are included in the
volume used for the compliance calculations. The well-capture zone
concept is described in more detail in Bakker and Strack, ``Capture
Zone Delineation in Two-Dimensional Groundwater Flow Models,'' (1996)
(Docket No. A-95-12, Item V-A-25).
The ``slice of the plume'' is a cross-section of the plume of
contamination centered at the point of compliance with sufficient
thickness parallel to the prevalent flow of the plume such that it
contains the representative volume. If DOE uses this approach, it must:
(1) Propose to NRC, for its approval, where the edge of the plume
of contamination occurs, for example, where the concentration of
radionuclides reaches 0.1% of the level of the highest concentration at
the point of compliance;
(2) Assume that the slice of the plume is perpendicular to the
prevalent direction of flow of the aquifer; and
(3) Set the volume of ground water contained within the slice of
the plume equal to the representative volume.
Both alternatives require DOE to determine the physical dimensions
and orientation of the representative volume during the licensing
process, subject to approval by NRC. Factors that would go into
determining the orientation of the representative volume would include
hydrologic characteristics of the aquifer and the well.
The DOE must demonstrate compliance with the ground water
protection standards (Sec. 197.30) assuming undisturbed performance of
the disposal system. The term ``undisturbed performance'' means that
human intrusion or the occurrence of unlikely, disruptive, natural
processes and events do not disturb the disposal system. The intent of
the ground water protection standards is to assess whether the expected
performance of the repository system will lead to contamination of the
ground water resource above the MCLs. The assessment of resource
pollution potential is based upon the engineered design of the
repository being sufficiently robust under expected conditions to
prevent unacceptable degradation of the ground water resource over
time. Disruption of the disposal system is inconsistent with that
intent. For this reason we have specified that the ground water
standards apply to undisturbed performance. Our approach also
recognizes that human behavior is difficult to predict and, if human
intrusion occurs, that individuals may be exposed to radiation doses
that would be more attributable to human actions than to the quality of
repository design (NAS Report p. 11). The requirement that DOE project
performance for comparison with the ground water protection standards
based on undisturbed-performance scenarios is consistent with our
generally applicable standards for SNF, HLW, and TRU radioactive waste
in 40 CFR part 191 (58 FR 66402, December 20, 1993; 50 FR 38073 and
38078, September 19, 1985).
We also require that DOE combine certain estimated releases from
the Yucca Mountain disposal system with the pre-existing naturally
occurring or man-made radionuclides to determine the concentration in
the representative volume. This requirement means that DOE must show a
reasonable expectation that the releases of radionuclides from
radioactive material in the Yucca Mountain disposal system will not
cause the projected level of radioactivity in the accessible
environment to exceed the limits in Sec. 197.30.
We requested public comment regarding these approaches to ground
water protection (i.e., the use of the MCLs, the concept of
representative volume and the alternatives for its size and modeling
approaches, and calculational approaches for the representative volume
application). We also requested comments regarding whether it is
desirable and appropriate for us to provide additional detail for the
representative volume in the final standards.
Comments generally approved of the idea of providing alternate
approaches for determining the concentration of contaminants in the
representative volume. Other comments requested additional
clarification of the approaches. We developed these approaches to
measuring the representative volume in the plume of contamination to
provide conservative but reasonable methods of assessing contaminant
concentrations. We intend both methods to avoid extreme assumptions
that would involve using only the highest potential area of
contamination in a contamination plume for comparison against the
standards and to allow reasonable consideration of the expected
behavior of the flow regime downgradient of the repository. For
example, the well capture-zone approach has conservative aspects
consistent with our general approach to regulations (a ``cautious, but
reasonable'', approach). These aspects include locating the well in the
path of the plume and requiring it to have characteristics similar to
water supply wells in the area, while also allowing DOE to consider
well-bore dilution effects for the water supply wells that
realistically would be expected in actual practice. To keep the
modeling analyses from becoming too complicated to perform and assess
with a reasonable degree of confidence, we specify that DOE use average
hydrologic properties to avoid the problem of summing up possibly
thousands of individual model runs. We attempt to specify only the most
important specifics for the two methods to provide a necessary context
to assure the standards are understood as we intend, but still to
provide flexibility for NRC in its implementation of the standards. For
example, we neither established requirements nor made recommendations
regarding models to be used for the plume modeling methods. We left the
applicant (DOE) and the implementing authority (NRC) the decision on
defining the outer boundary of the contamination plume for this
approach.
We received some comment asking for additional clarification
concerning the two methods proposed for calculating radionuclide
concentrations in a contamination plume, and in response we have made
some wording changes in the final standards. We proposed that the
screened interval for the withdrawal well be centered in the middle of
the contamination plume (proposed Sec. 197.36 (b)(1)(ii)). The intent
was to take a conservative approach and assume that the well taps the
contamination plume where the highest contamination occurs, rather than
being positioned such that only a portion of the lower concentration
margin of the plume is included in the representative volume--such a
situation would allow a high dilution of the contamination from pumping
effects. For a physical situation where the contamination plume is very
narrow and located at the top of the aquifer, a physically unrealistic
situation could occur if the well's screened interval must be centered
on the middle of the contamination plume, i.e., the screened interval
could extend into the unsaturated zone above the aquifer making
calculations of well capture zones unrealistic since a water supply
well would not be deliberately screened in that way. To remove this
unrealistic physical situation from consideration, we have modified the
language
[[Page 32115]]
describing the location of the screened interval to state that it must
include the highest concentration portion of the plume, with the intent
being that the screened interval should cross as much of the plume
diameter as possible so that the conservative approach is taken to
calculating radionuclide concentrations in the ground water (final
Sec. 197.31(b)(1)(ii)).
Another clarifying change we have made addresses the ``averaging''
of hydrologic properties (Sec. 197.31(a)(2)) in the downgradient
portions of the ground water flow system for the purpose of making
calculations for comparison against the ground water protection
standards. In the proposed standards, we used the phrase ``average
hydrologic characteristics''. We did not intend to imply that a simple
arithmetic averaging process would adequately represent the expected
variation in hydrologic properties that results from heterogeneity of
the flow system at the site (Chapter 7 and Appendix VI of the BID), or
that simple arithmetic averaging would be an allowable approach. We
believe that a simple arithmetic averaging approach would mask the
expected heterogeneity of the flow system. The values for hydrologic
properties of the aquifers along the flow path used in calculations
should be conservative but reasonable values, which are representative
of the expected heterogeneity in the aquifers. Heterogeneity can be
accounted for by using spatial statistical averaging methods that can
limit extrapolation of data obtained from field measurements in one
locale and which are applied to other locations represented by fewer or
poorer quality data. By using such techniques, conservative but
reasonable data can be developed that adequately represent the
heterogeneity of the aquifers for modeling purposes. We have modified
the proposed language to reflect that the ``averaged'' values should be
conservative but reasonable representations of the aquifer's hydrologic
properties.
a. Is the Storage or Disposal of Radioactive Material in the Yucca
Mountain Repository Underground Injection? As we discussed in detail in
the preamble to the proposed rule, we do not believe that the disposal
of radioactive waste in geologic repositories is underground injection
for purposes of the SDWA (42 U.S.C. 300f to 300j-26). We received one
comment supporting our position and one comment disagreeing with us.
See 64 FR 47004-47007 (August 27, 1999) for our comprehensive
discussion of this issue.
b. Does the Class-IV Well Ban Apply? We previously indicated that
we would review whether the Class-IV injection-well ban would apply to
Yucca Mountain. See 64 FR 47006-47007 for our previous discussion of
this issue. This rulemaking does not apply the Class-IV injection-well
ban to the Yucca Mountain repository. We believe this approach is
appropriate in light of the statutory and regulatory provisions,
discussed above and in the preamble to the proposed rule, relating to
``underground injection,'' and the differences in the purposes of the
Underground Injection Control (UIC) program and the authority delegated
to us under the EnPA to establish public health and safety standards
for Yucca Mountain.
It is important to emphasize that our decision not to apply the
Class-IV well ban to Yucca Mountain does not affect other disposal
systems that dispose of hazardous or radioactive waste into or above a
formation which, within one-quarter (1/4) mile of the disposal system,
contains a USDW. We based today's rule upon site and facility-specific
characteristics of the Yucca Mountain disposal system. Today's rule is
limited to the Yucca Mountain disposal system.
c. What Ground Water Does Our Rule Protect? Although we find that
the Yucca Mountain disposal system is not underground injection as
contemplated by the SDWA, we nevertheless consider the ground water
protection principles embodied in the SDWA to be important. Therefore,
although we do not apply all aspects of the SDWA, we are establishing
separate ground water protection standards consistent with the levels
of the radionuclide MCLs under the SDWA.
We requested public comment upon our approaches designed to protect
ground water resources in the vicinity of the repository. We are
concerned that ground water resources in the vicinity of Yucca Mountain
receive adequate protection from radioactive contamination. The primary
purpose of our ground water standards is to prevent contamination of
drinking-water resources. Because the compliance period is 10,000 years
after disposal, references to levels of contamination mean those levels
projected to exist at specific future times, unless otherwise noted.
However, these projections will be made at the time of licensing. This
approach prevents placing the burden upon future generations to
decontaminate that water by implementing expensive clean-up or
treatment procedures. We believe it is prudent to protect drinking
water from contamination through prevention rather than to rely upon
clean-up afterwards. Absent the protection this prevention provides,
future generations might find it necessary to intrude into the sealed
repository to remediate radionuclides released from waste packages
inside the repository, in addition to treating contaminated ground
water along the ground water flow path. Thus, our ground water
protection standards stress pollution prevention and provide protection
from contamination of sources of drinking water containing up to 10,000
mg/L of total dissolved solids (TDS). We emphasize that the individual-
protection standard (Sec. 197.20) covers all ground water pathways,
including drinking water.
The definition of USDW received extensive discussion in the
legislative history of the SDWA as reflected in the report of the House
Committee on Interstate and Foreign Commerce. To guide the Agency, the
Committee Report suggested inclusion of aquifers with fewer than 10,000
mg/L of TDS (H.R. Rep. No. 1185, 93d Cong., 2d Sess. 32, 1974). We have
reviewed the current information regarding the use of aquifers for
drinking water which contain high levels of TDS. This review found that
ground water containing up to 3,000 mg/L of TDS that is treated is in
widespread use in the U.S. In the Yucca Mountain vicinity, with few
exceptions (one being the Franklin Playa area), ground water contains
less than 1,000 mg/L of TDS. Our review also found that ground water
elsewhere in the nation, containing as much as 9,000 mg/L of TDS,
currently supplies public water systems. Based upon this review and the
legislative history of the SDWA, we are proposing that it is reasonable
to protect the aquifers potentially affected by releases from the Yucca
Mountain disposal system. Therefore, the provisions in Sec. 197.30
would apply to all aquifers, or their portions, containing less than
10,000 mg/L of TDS. We took the definitions associated with Sec. 197.30
directly from our UIC regulations (40 CFR parts 144 through 146).
One comment suggested that we change the definition of ``aquifer''
in the final rule to exclude perched water bodies. A perched water body
is a static area of ground water, usually above the water table, that
is unconnected to an aquifer but that may infiltrate into an aquifer
over time. Based upon our review of this comment, typical definitions
of ``aquifer'' in the technical literature, and the available site-
specific information regarding the existence of perched water bodies in
the vicinity of Yucca Mountain, we decided to make the suggested
change. This comment
[[Page 32116]]
argued for this change based upon the fact that perched water would be
of little value to future residents because few such formations exist
in the area and because of abundant water in the aquifer underlying
Yucca Mountain. The comment also argued that it would be difficult to
make specific predictions regarding the location and characteristics of
perched water bodies. Finally, the comment stated it would not be
meaningful to attempt to model perched water bodies in any performance
assessment. There are only a few, small perched water bodies known to
be in the vicinity of Yucca Mountain (see Chapter 7 of the BID). Also,
traditional definitions of ``aquifer'' usually do not include perched
water bodies (see the Glossary in the BID). Our intent also is to
provide protection to water resources of sufficient size to supply
water on a continuing basis to targeted uses. Perched water bodies,
particularly as they have been observed in the Yucca Mountain area, are
relatively small and would not provide a continual source of water to
wells used for irrigation or for community water demands. Based upon
this information, we believe that it is unnecessary to include these
bodies in the definition of ``aquifer'' because it is extremely
unlikely that they could serve as a consistent source of drinking
water. Therefore, we amended the definition of ``aquifer'' to exclude
perched water bodies.
d. How Far Into the Future Must DOE Project Compliance With the
Ground Water Standards? We are establishing a 10,000-year compliance
period for ground water protection. The primary rationale for
establishing a 10,000 year compliance period is that we are
significantly concerned about the uncertainty associated with
projecting radiation doses over periods longer than 10,000 years. The
NAS indicated that beyond 10,000 years it is likely that uncertainty
will continue to increase (NAS Report p. 72). As a result, it will
become increasingly difficult to discern a difference between the
radiation dose from drinking water containing radionuclides (limited by
the MCLs) and the total dose arriving through all pathways (limited by
the individual-protection standard). Moreover, this approach is
consistent with the 10,000-year compliance period we are establishing
for the individual-protection standard. Therefore, it provides internal
consistency within the standards. It is also consistent with
regulations covering long-lived chemically hazardous wastes, which
present potential health risks similar to those from radioactive waste,
and with the compliance period that we established in our generally
applicable radioactive waste disposal standards at 40 CFR part 191.
We requested comment regarding our proposal to impose the ground
water protection standards during the first 10,000 years following
disposal. Question 14 in the preamble to our proposal specifically
asked: ``Is the 10,000-year compliance period for protecting the RMEI
and ground water reasonable or should we extend the period to the time
of peak dose?'' (64 FR 47010-47011) Comments related to the compliance
period applied to both the RMEI and ground water. See the discussion of
issues pertaining to both the RMEI and ground water protection in
section III.B.1.g (How Far Into the Future Is It Reasonable to Project
Disposal System Performance?) along with our rationale for adopting a
10,000-year compliance period.
e. How Will DOE Identify Where to Assess Compliance With the Ground
Water Standards? To provide a basis for determining projected
compliance with the ground water protection standards in Sec. 197.30,
it is necessary to establish a geographic location where DOE must
project the concentrations of radionuclides in the ground water over
the compliance period. This location is the ``point of compliance.''
Our understanding, based upon current knowledge, of the flow of
ground water passing under Yucca Mountain is as follows (except where
noted otherwise, Chapter 7 and Appendix VI of the BID are the sources
for the information in this paragraph). The general direction of ground
water movement in the aquifers under Yucca Mountain is south and
southeast. The major aquifers along the flow path are in fractured
tuff, alluvium, and, underlying both of these, the deeper carbonate
rocks. At the edge of the repository, the tuff aquifer is relatively
(several hundred meters) thick. The tuff aquifer gets closer to the
surface toward its natural discharge points. Potential releases of
radionuclides from the engineered barrier system into the surrounding
rocks would be highly directional and would reflect the orientation of
fractures, rock unit contacts, and ground water flow in the area
downgradient from Yucca Mountain. Directly under the repository, we
anticipate that any waterborne releases of radionuclides will move
through the unsaturated zone and downward into the tuff aquifer, in an
easterly direction, between layers of rocks that slant to the east, and
downward along generally vertical fractures in the rock units until
reaching the saturated zone. The layer of tuff gradually thins
proceeding south (downgradient) from Yucca Mountain. As the tuff
aquifer thins, the overlying alluvium becomes thicker until the tuff
disappears and the water in the aquifer moves into the alluvium to
become the ``alluvial aquifer.'' Along the flow path, there might be
movement of water between the carbonate aquifer and either the tuff or
alluvial aquifers. If there is significant upward flow from the
carbonate aquifer, contamination in overlying aquifers could be
diluted. It is generally believed, however, that any such flow would
not significantly affect the concentration of radionuclides in the
overlying aquifers. Conversely, downward movement of ground water from
the tuff aquifer could contaminate the carbonate aquifer. Limited
information currently available indicates that ground water from the
lower carbonate aquifer moves upward into the overlying aquifer;
however, this interpretation may not be correct for the entire flow
path from beneath the repository to the compliance points southward
from Yucca Mountain. Today, most of the water for human use is
withdrawn between 20 and 30 km away from the repository footprint (that
is, at Lathrop Wells and farther south through the Town of Amargosa
Valley) where it is more easily and economically accessed for
agricultural use and human consumption. It is likely that the alluvial
aquifer is the major source of this water (see Chapter 8 and Appendix V
of the BID).
Another basis of our understanding is the historical record of
water use in the region. The record indicates that significant, long-
term human habitation has not occurred in the southwestern area of NTS,
or for that matter anywhere in the vicinity of Yucca Mountain, except
where ground water is very easily accessed (for example, in Ash
Meadows) (see Chapter 8 of the BID). This observation coincides with
current practice whereby the number of wells generally decreases with
greater depth to ground water (see Chapter 8 of the BID). The
difficulty in accessing ground water in the tuff aquifer in the near
vicinity of Yucca Mountain increases because of the rough terrain, the
relative degree of fracturing of the tuff formations containing the
aquifer, and the great depth to ground water there. As described
earlier, the ground water flow from under Yucca Mountain is thought to
be generally south and southeast. In those directions, the ground water
gets progressively closer to the Earth's surface the farther away it
[[Page 32117]]
gets from Yucca Mountain until it is thought to discharge to surface
areas 30-40 km away (the southwestern boundary of NTS is about 18 km
from Yucca Mountain). This means that access to the upper aquifer is
easier at increasing distance from Yucca Mountain.
Because of DOE's ongoing site characterization studies, it is
possible that, at the time of licensing, data not now available will
reveal important inaccuracies in the preceding conception of the ground
water flow under, and downgradient from, Yucca Mountain. We intend
compliance with the ground water standards to be assessed where DOE and
NRC project the highest concentrations of radionuclides in the
representative volume of ground water in the accessible environment.
The DOE will determine this location by modeling releases into the
saturated zone beneath the repository and the subsequent movement of
radionuclides downgradient from Yucca Mountain. After selecting a
location, however, DOE must continue to evaluate new information
regarding ground water flow. If this new information indicates that the
highest concentrations would occur at a location in the accessible
environment different from the one selected by DOE and NRC, DOE must
propose a new compliance location to NRC. The new location is subject
to NRC's approval. The next section discusses the concept of accessible
environment as it relates to the controlled area.
f. Where Will Compliance With the Ground Water Standards be
Assessed? We presented four alternatives for comment prior to
determining the location of the point of compliance. See the preamble
to the proposed rule (64 FR 47000-47004) for a detailed discussion of
these four alternatives. We asked commenters to address the
effectiveness of these or other alternatives for protecting ground
water, including consideration of site-specific characteristics and
reasonable methods of implementing the alternatives.
After reviewing and evaluating the public comments, various
precedents, the EnPA, and NAS's recommendations, we adopted the concept
of a controlled area as an essential precondition to assessing
compliance with the ground water standards. The ground water standards
must be met in the accessible environment where the highest
radionuclide concentrations in the representative volume of ground
water are projected to occur during the compliance period (10,000
years). The highest projected concentrations will be compared to the
regulatory limits established in today's rule. The accessible
environment includes any location outside the controlled area. The
controlled area may extend no more than 5 km in any direction from the
repository footprint, except in the direction of ground water flow. In
the direction of ground water flow, the controlled area may extend no
farther south than latitude 36 deg.40'13.6661" North, which corresponds
to the latitude of the southwest corner of the Nevada Test Site, as it
exists today (Department of Energy submittal of Public Land Order 2568,
dated December 19, 1961, Docket No. A-95-12, Item V-A-29). The size of
the controlled area may not exceed 300 km2 (see below for
further discussion). Such a limitation is derived by combining the
concept of the controlled area as used in 40 CFR part 191 and the
requirement for a site-specific standard in the case of Yucca Mountain.
If fully employed by DOE, and based on current repository design, the
controlled area could extend approximately 18 km in the direction of
ground water flow (presently believed to be in a southerly direction)
and extend no more than 5 km from the repository footprint in any other
direction. Allowing for a nominal repository footprint of a few square
kilometers, this results in a rectangle with approximate dimensions of
12 km in an east-west direction and 25 km in a north-south direction,
or approximately 300 km2. The DOE may define the size and
shape of the controlled area, but the boundaries cannot extend farther
south than latitude 36 deg.40'13.6661" North in the direction of ground
water flow and 5 km in any other direction.
The alternatives for the ground water standards' compliance point
presented in the proposed rule correspond to downgradient distances of
approximately 5, 18, 20, and 30 km from the repository footprint. The
first alternative mirrored the approach used in 40 CFR part 191. This
approach incorporates the concept of a controlled area, not to exceed
100 km2, and not to extend more than 5 km in any direction from the
repository footprint. The second alternative also incorporated the
concept of a controlled area, not to extend more than 5 km in any
direction from the footprint, except that DOE could include any
contiguous area within the boundary of NTS. The last two alternatives
described specific points of compliance at distances of about 20 and 30
km, respectively, from the repository footprint. We also intended these
controlled areas and points of compliance to be in the predominant
direction of ground water movement from the repository. Consequently,
they would reflect the transport path for radionuclides released from
the repository. We intended the controlled area options to describe
that area of land dedicated to the sole use of serving as the natural
barrier portion of the disposal system. Compliance with the standards
within the controlled area is not an issue in regulatory decision
making because this area is considered part of the overall disposal
system and is dedicated to limiting radionuclide transport by means of
the natural processes operative within it. Rather, compliance will be
judged at the location where projected concentrations are highest and
that is no closer to the repository than the edge of the controlled
area. The controlled area also serves as the basis for institutional
control measures intended to limit access around the repository site.
This use of the controlled area, to limit access to the site, is an
assurance measure we have left to the discretion of NRC as the
implementing authority. Our rule does not require any specific
institutional controls to be applied to the controlled area. As part of
the licensing process, DOE will propose the specific shape and size of
the controlled area. The NRC's proposed rule establishing licensing
criteria for the Yucca Mountain facility specifically requires that DOE
have permanent control of the land. We anticipate that Congress and the
President will authorize a legislative withdrawal of an area within
which the site is located. The DOE will determine the extent of land
that will be requested of Congress to legislatively withdraw from all
other public or private use. For its DEIS (Docket No. A-95-12, Item V-
A-4), DOE analyzed a potential land withdrawal area of 600 km2 in the
context of site characterization needs. The legislative land withdrawal
represents the societal decision on the area of land to be dedicated to
the characterization and operation of a disposal system. Although the
land withdrawal may exceed 300 km2, we limit the controlled
area to 300 km2 for the purpose of defining the maximum
geological volume which may be included in the disposal system.
We adopted the concept of a controlled area from the generic
standards in 40 CFR part 191. Those standards state that the maximum
size of the controlled area is 100 km\2\ (40 CFR 191.12). After
examining the available information concerning the characteristics of
the Yucca Mountain site, the current understanding of the expected
performance of the disposal
[[Page 32118]]
system and the repository engineered barrier system design, and
comments received on our proposed approach to ground water protection,
we believe that a controlled area of up to 300 km\2\ will adequately
address the site-specific conditions at Yucca Mountain.
It would be unreasonable for us to limit DOE's flexibility while
site characterization and disposal system design are continuing, or to
issue standards that do not account for the uncertainties of ground
water flow in the region. Therefore, today's rule provides that the
size of the controlled area may be up to 300 km\2\.
In reaching this decision regarding the maximum size of the
controlled area, we must draw a contrast between the approach used in
40 CFR part 191 and today's rule. As mentioned earlier, although the
WIPP LWA exempted the Yucca Mountain site from licensing under the
provisions of 40 CFR part 191, the radiation protection principles in
40 CFR part 191 are still applicable, and we examined them while
developing site-specific standards for Yucca Mountain. Throughout this
preamble, we note where and why we have carried some of the concepts
forward from 40 CFR part 191 if we believe they are necessary for
protective standards at Yucca Mountain, and how we have applied them in
ways consistent with the site-specific information and understanding of
the Yucca Mountain site. Part 191 established a controlled area with a
maximum distance in any direction of 5 km from the repository footprint
to provide a location for judging compliance with the individual-
protection (Sec. 191.15), ground water protection (Sec. 191.24), and
containment requirements (Sec. 191.13). Thus, the controlled-area
concept in 40 CFR part 191 links a 5 km maximum distance from the
repository footprint to a limit on the size of the controlled area (100
km\2\ maximum). Within this area, compliance with the standards is not
required because the geologic media therein comprise an essential part
of the disposal system. This combination of controlled area and
protection of individuals and ground water is appropriate for generic
standards because generic standards' provisions must account for the
wide variety of possible site conditions (e.g., releases could move in
many directions from the repository toward the population), engineered
alternatives, and population characteristics. Note that in the 1980s,
when 40 CFR part 191 was being developed, DOE was considering nine
candidate HLW repository sites. It is also important to recognize that
40 CFR part 191 contained a mechanism for substituting alternative
provisions, should they be deemed necessary.
By contrast, 40 CFR part 197 is site-specific. The 1987 NWPA
amendments specified Yucca Mountain as the only potential repository
site where DOE may conduct characterization activities. Therefore,
since passage of the 1987 amendments, the Yucca Mountain site has been
under an intense characterization effort. Because of these efforts, a
significant amount of information has been generated regarding past,
present, and planned population patterns, land use, engineered design,
and the hydrogeological characteristics of the host rock and ground
water systems at the Yucca Mountain site. Based upon information
currently available, it appears that contaminated ground water will
flow predominantly in a relatively narrow path from the Yucca Mountain
repository. See the Yucca Mountain DEIS, Chapter 3 (DOE/EIS-0250 D,
July 1999, Docket No. A-95-12, Item V-A-4, and the Viability
Assessment, Docket No. A-95-12, Item V-A-5). In addition to the
extensive data base compiled over the years, we have the
recommendations of NAS. Significantly, NAS endorsed the use of present
knowledge using ``cautious, but reasonable'' assumptions in defining
exposure scenarios (NAS Report p. 100).
Concerning the size of the controlled area, though we have a
general understanding of the primary direction of ground water flow,
our present knowledge continues to evolve through site
characterization. As a result, we believe the ``cautious, but
reasonable'' approach allows DOE the flexibility to utilize a
controlled area up to a maximum of 300 km\2\. Given the uncertainty in
ground water flow paths, and the fact that releases could occur
anywhere within the repository, we believe it is prudent to ensure that
any potential contamination plumes from repository releases are
contained within the controlled area, and to ensure that access to and
human activity within the area of potential contamination is limited,
thereby minimizing the potential for human exposure. We recognize that
300 km\2\ represents an increase in the maximum size of the controlled
area, and is larger than we allow in 40 CFR part 191. However, for
site-specific reasons, we are increasing the maximum extent of the
controlled area only in the direction of ground water flow to no
farther south than latitude 36 deg. 40' 13.6661" North, while
simultaneously limiting the extent of the controlled area in any other
direction to no greater than 5 km from the repository footprint.
The size and shape of the controlled area proposed by DOE in the
licensing process will depend upon two fundamental elements: (1) The
dimensions of the repository layout for the waste inventory and thermal
loading, as defined in the final repository design; and (2) uncertainty
in ground water flow directions. Both of these aspects are evolving
since studies for both site characterization and repository design are
still in progress. However, DOE provides some indication in its DEIS of
the range of repository-design layouts under various assumed waste
inventories and thermal loading alternatives. Combining these
repository alternatives in the DEIS, with projected ground water flow
paths to the southern most extension of the controlled area at latitude
36 deg. 40' 13.6661" North, gives potential controlled area sizes from
100 km\2\ or less to around 300 km\2\. These estimates are based upon
the uncertainties in ground water flow directions and repository
designs that currently exist. When characterization and design studies
are completed, a well-defined controlled area size can be determined
during the licensing process, where the uncertainties will be examined
in closer detail and a final controlled area size can be determined.
However, uncertainties can only be reduced, not eliminated completely,
even when site characterization is completed--some residual uncertainty
will remain. As stated earlier, we believe it is important to allow
flexibility for DOE and NRC at this time to continue the
characterization and design work, and allow the licensing process to
operate within certain bounds while knowledge of the site is evolving.
In addition to ground water flow path uncertainties, the size and
shape of the controlled area also depend upon understanding how and
where (in relation to the repository layout) radionuclides could be
introduced into the ground water. Failed waste packages during the
regulatory time-frame supply the releases carried into the ground water
system. While DOE has adopted a new highly engineered waste package
anticipated to have containment lifetimes into the tens of thousands of
years (TRW Environmental Safety Systems Inc., ``Repository Safety
Strategy: Plan to Prepare the Postclosure Safety Case to Support Yucca
Mountain Site Recommendation and Licensing Considerations'', TDR-WIS-
RL-000001, January 2000, Docket No. A-95-12, Item V-A-24), some small
number of waste packages can be anticipated to fail within the
regulatory period due to
[[Page 32119]]
undetected manufacturing defects. While these failures can be minimized
through rigorous quality control efforts during manufacturing, the
potential cannot be totally eliminated. The location of such
``premature failures'' in the repository is, however, unpredictable.
Other unpredictable disruptive events and processes, such as roof falls
that damage waste packages and accelerate corrosion processes, could
also result in releases in advance of the anticipated containment
lifetime of the containers under expected conditions. The location of
these types of waste package failures is also not amenable to reliable
prediction. Therefore, releases from such failures could originate
anywhere within the repository footprint and would consequently enter
the ground water flow envelope at any location. Recognizing this, the
process of defining the controlled area would focus upon the two
factors discussed above, the repository footprint, which will reflect
the waste inventory and the repository design choices, and the envelope
of potential ground water flow paths around that footprint. ``Cautious,
but reasonable'' assumptions regarding these factors can then be
applied to define a controlled area that will include potential
releases from a small number of premature waste package failures. A
more detailed discussion of the influence of these factors on the
potential size of the controlled area may be found in ``Considerations
for Defining a Site-Specific Controlled Area for the Yucca Mountain
Proposed Repository Location'' (Docket No. A-95-12, Item V-B-7).
Regarding the alternatives we proposed for the ground water point
of compliance, none of the information we have reviewed suggests that
it is likely or reasonable to assume that year-round residents will
live within 5 km of the repository footprint. As discussed in Chapter 8
and Appendix IV of the BID, it would be extremely difficult to farm
that close to Yucca Mountain, partly because extracting ground water at
that location would be both technically challenging and very expensive
for an individual or small group. In addition, much of this area has
rough terrain and soils not conducive to farming. Our understanding of
projections of future land use does not indicate significant population
growth much farther north of Lathrop Wells, i.e., closer than about 18
km from the repository footprint (see Appendix I of the BID, Docket No.
A-95-12, Items V-A-14, 15, 16). Given the small likelihood of a year-
round resident at 5 km, we chose not to select a distance of 5 km as
the limiting distance from the repository footprint to the controlled
area boundary.
As one goes farther away from Yucca Mountain in the direction of
ground water flow, it is easier to drill for ground water because the
water table is closer to the ground surface and the geologic medium
changes from tuff to alluvium. In addition, the soil characteristics
improve such that agricultural pursuits become more feasible, as
evidenced by the widespread agricultural activity in Amargosa Valley
some 30 km from Yucca Mountain. There are approximately 10 residents at
about 20 km (Lathrop Wells) and hundreds of residents at a distance of
30 km. Current projections of population growth indicate southern
Nevada as one of the fastest growing areas in the country (see the
Yucca Mountain DEIS, Chapter 3 (DOE/EIS-0250D, July 1999, Docket No. A-
95-12, Item V-A-4), and reports prepared for Nye County and Amargosa
Valley (Docket No. A-95-12, Items V-A-14, V-A-15, and V-A-16)). We
selected latitude 36 deg. 40' 13.6661" North, which corresponds to the
southwest corner of NTS as it exists today (Docket No. A-95-12, Item V-
A-29), as the maximum distance that the controlled area may extend in
the direction of ground water flow (south). Given the expected
population growth in southern Nevada, it is reasonable to project that
some population growth may occur slightly north of Lathrop Wells,
although the boundaries of NTS are likely to remain and restrict
population expansion in this direction, at least for the near future.
As indicated previously, the representative volume of ground water used
to demonstrate compliance would reflect a small community including
alfalfa cultivation and some residential and light industrial
development. At distances progressively closer than 18 km to the
repository, it becomes more difficult to drill for water, soil
conditions become less favorable for agriculture, and more land is
subject to restricted access by the Federal government. We believe,
based upon the site-specific information now available, and using
cautious, but reasonable assumptions, the southwest corner of NTS, or
an equivalent distance in the direction of ground water flow, would be
the closest location for a small group to be accessing ground water.
Several comments suggested that we should locate the point of
compliance for ground water protection purposes at the boundary of the
Yucca Mountain repository footprint. As discussed above, 40 CFR part
191 established the concept that a certain amount of geology
surrounding a repository is part of the overall disposal system. The
controlled-area concept limited considerations of radiation dose to
individuals or contamination of ground water to areas outside of this
controlled area. The controlled area in 40 CFR part 191 applies at a
distance from the repository, to be determined by the implementing
agency, but not to exceed 5 km from the footprint. We continue to
support the concept of a compliance point at some distance beyond the
repository footprint. In the case of Yucca Mountain, most of the land
within the repository footprint is rugged terrain, with extreme depths
to ground water, and land unsuitable for agricultural pursuits (see
Chapter 8 of the BID). Therefore, we did not choose a compliance point
at the edge of the Yucca Mountain repository footprint.
A number of comments suggested we locate the point of compliance,
or limit the distance to the boundary of the controlled area, at
distances ranging from 5 km to 30 km from the repository footprint. As
we indicated previously, we adopted NAS's recommendations to use
present knowledge and cautious, but reasonable, assumptions in making
regulatory decisions. For the reasons discussed earlier, we did not
choose to base compliance with the standards upon a uniform 5 km
distance from the repository. Other comments supported placing the
compliance point at 30 km, citing the volume of water currently
withdrawn at that distance. Indeed, most of the agricultural activities
in the vicinity of Yucca Mountain currently take place in this area,
and it is home to hundreds of residents. This situation occurs because
of the easy accessibility of ground water and soil conditions conducive
to a variety of agricultural activities. However, a distance of 30 km
would effectively ignore the existence of populations who presently
access ground water closer to the repository. Given the prospect of
future population growth as well, at distances of about 20 to 30 km
from the repository footprint, it would appear more reasonable to
protect ground water resources at distances closer than 30 km.
Therefore, we did not choose the ``30 km'' alternative as the
compliance point.
Distances approximating 20 km appear more reasonable to consider to
assess compliance with the ground water standards. As described in
Chapter 8 of the BID, no farming currently occurs closer than about 23
km from the repository footprint. Also, as one gets closer than about
18 km to the repository footprint, the depth to water begins to
increase dramatically from about 100 m at a distance of 20 km to a few
hundred meters at a distance of
[[Page 32120]]
5 km. Given the expectation of future population growth and the
precious nature of ground water resources in the area, it is reasonable
to assume that a small group may annually extract the representative
volume of ground water at a distance slightly closer than 20 km,
namely, latitude 36 deg. 40' 13.6661" North, which corresponds to the
southwest corner of NTS as it exists today (Docket No. A-95-12, Item V-
A-29). This approach is protective of the ground water resources
reasonably anticipated to be accessed in the vicinity of Yucca
Mountain. To determine compliance with the ground water standards, DOE
must define the controlled area and calculate the concentrations of
radionuclides in the representative volume of ground water at a
location outside the controlled area where the concentrations are the
highest. The controlled area may encompass no more than 300 km\2\ and
may extend no farther south, in the direction of ground water flow,
than latitude 36 deg. 40' 13.6661" North, which corresponds to the
southwest corner of NTS (Docket No. A-95-12, Item V-A-29). In any other
direction, the controlled area may extend no more than 5 km from the
repository footprint. We emphasize that these dimensions describe the
maximum size of the controlled area. In defining the actual dimensions
of the controlled area, DOE may extend the southern boundary of the
controlled area as far as latitude 36 deg. 40' 13.6661" North, which
corresponds to the southwest corner of the NTS (Docket No. A-95-12,
Item V-A-29). The DOE could place the boundary of the controlled area
anywhere along that distance. Therefore, when we say we did not base
compliance with the standard upon a distance of 5 km from the
repository footprint, we mean that we neither selected the alternative
that would have set the maximum dimension of the controlled area as 5
km in any direction, nor did we identify a specific point of compliance
at that distance. The DOE is free to define the controlled area such
that it extends only 5 km, or less than 5 km, in any direction (i.e.,
DOE is not required to extend the controlled area as far as latitude
36 deg. 40' 13.6661" North in the direction of ground water flow, or as
far as 5 km from the repository footprint in any other direction), and
to assess compliance at the location outside the controlled area where
concentrations are highest. In the context of waste disposal, the
ground water protection standards do not apply inside the controlled
area, consistent with the approach in 40 CFR part 191.
IV. Responses to Specific Questions for Public Comment
In addition to requesting comments regarding all aspects of this
rulemaking, many of which we have highlighted in the preceding sections
of this document, we also requested comment based upon sixteen specific
questions. These specific questions appear below, along with brief
summaries of the comments we received and our responses to those
comments. As with each of the comments discussed elsewhere in this
document, we present detailed and comprehensive responses in the
accompanying Response to Comments document.
1. The NAS Recommended That We Base The Individual-protection Standard
Upon Risk. Consistent With This Recommendation and the Statutory
Language of the EnPA, We are Proposing a Standard in Terms of Annual
CEDE Incurred by Individuals. Is Our Rationale for This Aspect of Our
Proposal Reasonable?
Comments/Our Responses. Many of the comments we received on this
issue supported the promulgation of a standard stated in terms of dose.
Moreover, section 801(a)(1) of the EnPA specifically provides that EPA
shall ``promulgate, by rule, public health and safety standards for
protection of the public from releases from radioactive materials
stored or disposed of in the repository at the Yucca Mountain site.
Such standards shall prescribe the maximum annual effective dose
equivalent to individual members of the public from releases from
radioactive materials stored or disposed of in the repository.''
Consistent with the specific statutory language of the EnPA, and the
numerous comments supporting the use of a standard stated in terms of
dose, we choose to use dose as the form of the individual-protection
standard. See section III.B.1.a above for a discussion of our
rationales for making this choice. As discussed to some extent in
section III.B.1.c, and in more detail in the preamble to the proposed
standards (beginning on 64 FR 46984), the primary basis of the dose
limit, 150 microsieverts (15 mrem), is the risk of fatal cancer. This
level equates to an annual risk of about 8.5 in one million of
developing a fatal cancer. This level is within the risk range
recommended by NAS. Thus, the 15 mrem CEDE standard is consistent with
NAS's recommendation.
2. We Are Proposing an Annual Limit of 150 Sv (15 mrem) CEDE
To Protect the RMEI and the General Public From Releases From Waste
Disposed of in the Yucca Mountain Disposal System. Is Our Proposed
Standard Reasonable To Protect Both Individuals and the General Public?
Comments/Our Responses. As noted in section III.B.1.c above, we are
establishing an individual-protection standard for Yucca Mountain that
limits the annual radiation dose incurred by the RMEI to 150
Sv (15 mrem) CEDE. See section III.B.1.c for a discussion of
the comments regarding the appropriateness of the level of protection.
We chose not to adopt a separate limit on radiation releases for the
purpose of protecting the general population. There is a full
description of our reasoning in section III.B.1.e, above. However, in
summary, we based this decision upon several factors. The first factor
is NAS's estimate of extremely small doses to be received by
individuals resulting from air releases from the Yucca Mountain
disposal system. The projected level of these doses is well below the
risk level corresponding to our individual-protection standard for
Yucca Mountain. It also is well below the level that we have regulated
in the past through other regulations. We also declined to establish a
negligible incremental dose (NID) level below which doses would not
have to be calculated. The second factor is that, based upon current,
site-specific conditions near Yucca Mountain, it is unlikely that there
will be great dilution and wide dispersal of radionuclides transported
in ground water leading to exposure of a large population. This means
that the individual-dose standard will suffice to protect the general
population. There should be no confusion between establishment of this
standard and our establishment of ground water protection standards
intended to protect that water for future use. The final factor is that
we require all of the pathways, including air and ground water, to be
analyzed by DOE and considered by NRC under the individual-protection
standard.
Regarding the concepts of negligible incremental dose or risk,
though we have recognized elsewhere in this preamble that individual
doses from \14\ C are below the level at which the Agency has
historically regulated individual doses, we have declined to establish
an NID or NIR level for the reasons enumerated in section III.B.1.e in
this preamble. As described by NCRP, the concepts of NID and NIR relate
to
[[Page 32121]]
individual-dose assessments, not collective dose assessments (Docket A-
95-12, Item II-A-8). Therefore, we are not prepared to accept the NIR
concept as discussed by NAS.
We also disagree with NAS when it states on page 120 of its report:
``On a collective basis, the risks to future local populations are
unknowable.'' There is no question that there will be uncertainty in
the estimate; however, even without our recommendation, DOE has already
published projected collective doses for Yucca Mountain (see Table 4-34
on p. 4-39 of the Yucca Mountain DEIS, Docket No. A-95-12, Item V-A-4),
and is likely to refine these estimates. These estimates could fulfill
the NCRP recommendation to use collective dose in a non-regulatory
fashion to assess acceptability of a facility (Docket No. A-95-12, Item
II-A-8).
Most comments on this issue supported not establishing a
collective-dose limit for Yucca Mountain. Two other comments supported
our decision to not establish an NIR or NID level. One comment went
further by opposing our suggestion that DOE use estimated collective
dose to examine design alternatives on the grounds that such action is
unnecessary to protect the general public. That comment also stated
that we have not provided guidance on what to do with the collective
dose estimates and that we are making policy judgments with respect to
collective dose estimation. Upon consideration of those comments, we
are not recommending that DOE estimate collective dose, primarily
because we believe that the individual-protection standard will
adequately protect the general population.
3. To Define Who Should Be Protected by the Proposed Individual-
protection Standard, We Are Proposing To Use an RMEI as the
Representative of the Rural-residential CG. Is Our Approach Reasonable?
Would it be More Useful to Have DOE Calculate the Average Dose
Occurring Within the Rural-residential CG Rather Than the RMEI Dose?
Comments/Our Responses. We decided that the RMEI in the individual-
protection scenario will have a rural-residential lifestyle. A number
of comments supported the use of the CG approach. One commenter
suggested specifically that it preferred a rural-residential CG to the
rural-residential RMEI because it is possible to estimate exposures
with much greater confidence. However, in general, we decided to use
the rural-residential RMEI rather than a rural-residential CG for the
same reasons that we selected RMEI instead of the CG (see section
III.B.1.d above, and Docket No. A-95-12, Item V-B-3).
In summary, those reasons are that the RMEI approach:
(1) Is consistent with widespread practice, current and historical,
of estimating dose and risk incurred by individuals even when it is
impossible to specify or calculate accurately the exposure habits of
future members of the population (as in this case where it is necessary
to project doses for very long periods);
(2) Is sufficiently conservative and fully protective of the
general population;
(3) Provides protection similar to the probabilistic CG approach
recommended by NAS for small groups--it has the same goal and purpose
as does NAS's recommended probabilistic CG approach, i.e., to protect
the vast majority of the public while ensuring that the acceptability
of the repository is not driven by unreasonable and extreme cases. It
accomplishes this by employing some maximum parameter values and some
average parameter values (similar to the NAS's concept of using
``cautious, but reasonable'' assumptions) for the factors most
important to estimating the dose to arrive at a conservative, but
reasonable, projection of future dose;
(4) Allows the desired degree of conservatism to be built but
within the site-specific limits and the framework which we have
established.
(5) Is straightforward and relatively simple to understand, and is
more appropriate than the probabilistic CG for the situation at Yucca
Mountain. It is less speculative to implement than is the probabilistic
CG approach given the unique conditions present at Yucca Mountain (and
is a cautious, but reasonable, approach). For example, given the known
characteristics of ground water flow at Yucca Mountain, locating the
receptor in the direct path is more protective, and easier to
implement, than assessing an average dose incurred by a randomly-
located group of receptors; and,
(6) Has been used by us in the past (whereas we have not used the
CG concept).
A number of other comments suggested other groups or individuals
that would represent more appropriately the individual to be protected
by the individual-protection standard. The suggestions included a
fetus, the elderly and infirm, and subsistence farmers. Regarding the
various ages and stages of development, the risk value used for the
development of cancer is an overall average risk value (see Chapter 6
of the BID for more details) that includes all exposure pathways, both
genders, all ages, and most radionuclides. However, it does not cover
the ``unborn within the womb'' (see Chapter 6 of the BID). It is
thought that the risk per unit dose for prenatal exposures is similar
to the average risk per unit dose for postnatal exposures; however, the
exposure period is very short compared to the rest of the individual's
average lifetime. (See Chapter 6 of the BID for a discussion of cancer
risk from in utero exposure). Therefore, the risk is proportionately
lower and would not have a significant impact upon the overall risk
incurred by an individual over a lifetime (see Chapter 6 of the BID).
On the other end of the age spectrum, radiation exposure of the elderly
at the levels of the individual-protection standard would be less than
the overall risk value because they have fewer years to live and,
therefore, fewer years for a fatal cancer to develop (see Chapter 6 of
the BID). Finally, we did not use subsistence farmers because we do not
believe that they are representative of the current lifestyle in
Amargosa Valley and that, therefore, they would not constitute a
cautious, but reasonable, assumption in relation to the guidance from
NAS to use current technology and lifestyle.
4. Is it Reasonable To Use RMEI Parameter Values Based Upon
Characteristics of the Population Currently Located in Proximity to
Yucca Mountain? Should We Promulgate Specific Parameter Values in
Addition To Specifying the Exposure Scenarios?
Comments/Our Responses. The basis of the RMEI dose calculations
will be the current population downgradient from Yucca Mountain. This
approach is consistent with NAS's recommendation to use current
lifestyles to avoid the endless speculation that could result from
trying to project future human activities. See section III.B.1.d above
for a discussion of this issue. Most commenters supported this
approach. However, a number of commenters preferred using a
subsistence-farmer lifestyle. We have been unable to identify this
lifestyle in the area around the Yucca Mountain site. Also, a few
commenters stated that we should take future changes in population,
land use, climate, and biota into consideration. Again, with the
exception of climate and geologic processes, these factors are subject
to the potentially endless speculation of which NAS spoke in its
report. We do require DOE and NRC to take climate change and probable
variations in geologic conditions into
[[Page 32122]]
account because they are factors that scientific study can reasonably
bound.
5. Is it Reasonable To Consider, Select, and Hold Constant Today's
Known and Assumed Attributes of the Biosphere for Use In Projecting
Radiation-related Effects Upon the Public of Releases From the Yucca
Mountain Disposal System?
Comments/Our Responses. The comments we received on this question
generally favored our position of holding present biosphere conditions
constant for the purpose of making performance projections for the
disposal system. Some comments pointed to the unexpected dynamic
population growth in the southern Nevada area, or stated that current
conditions were not a reliable means to predict future conditions. Some
comments also pointed out that the target receptor for dose assessments
could not be defined independently of assumptions about the biosphere.
The tenor of these comments is a general agreement that unreasonably
speculative assumptions about biosphere conditions are inappropriate
and should be avoided. We agree with this general theme of not making
unreasonably speculative assumptions about the future. The NAS also
made this point in its recommendations for a reference biosphere. We
made some fundamental assumptions in this rule about biosphere
conditions to assure that dose assessments for the RMEI are cautious,
but reasonable. For example, we require that DOE assume that the RMEI
consumes 2 liters/day of drinking water and that DOE base food
consumption patterns on surveys of the current residents in the area
downgradient from Yucca Mountain. We have left it to NRC to establish
other details of the biosphere dose assessment calculations for Yucca
Mountain, such as details of pathway-specific dose conversion factors
and details necessary for assessing all potential exposure pathways.
For additional discussion of these issues, see section III.B.1.f above.
A related aspect of fixing biosphere conditions for dose
assessments is the question of potential variations in climate and
geologic conditions because these factors play an important part in
developing the ground water contaminant concentrations that serve as
input for the biosphere dose assessments. We specify that DOE should
vary climate and geologic conditions over a reasonable range of values
based on an examination of evidence in the geologic record for
conditions in the area. The evidence preserved in the relatively recent
geologic record provides a means to reasonably bound the range of
possible conditions.
6. In Determining the Location of the RMEI, We Considered Three
Geographic Subareas and Their Associated Characteristics. Are There
Other Reasonable Methods or Factors Which We Could Use to Change the
Conclusion We Reached Regarding the Location of the RMEI? For Example,
Should We Require an Assumption That for Thousands of Years Into the
Future People Will Live Only in the Same Locations That People do
Today? Please Include Your Rationale for Your Suggestions
Comments/Our Responses. See section III.B.1.d above for a further
discussion of this subject. The many comments we received on this topic
suggested a variety of locations, some closer and some farther than
Lathrop Wells. A few commenters thought that the Lathrop Wells location
is appropriate. However, a number of others stated that the location
should be at the repository footprint. One commenter stated that the
current farming area in southern Amargosa Valley would be a reasonable
location for the RMEI.
Based on further review of site-specific information, we decided to
locate the RMEI in the accessible environment above the highest
concentration of radionuclides in the plume of contamination. The
accessible environment begins at the edge of the controlled area, which
may extend no farther south than the southern boundary of NTS (latitude
36 deg. 40' 13.6661'' North), which is approximately 18 km south of the
repository (roughly 2 km closer than the Lathrop Wells location we
proposed). We do not believe that an RMEI likely would live much closer
to the Yucca Mountain repository because of the increasing depth to
ground water and the increasing roughness of the terrain (see Chapter 8
of the BID), although the RMEI would still have rural-residential
characteristics described in Sec. 197.21 if the controlled area does
not extend as far south as the NTS boundary. In addition, we believe
that, at 18 km, a rural resident likely will receive the highest
potential doses in the region because, as we have defined the RMEI, the
potential dose at this location will be from drinking water, as well as
through ingestion of food grown with contaminated ground water. With
the RMEI eating food grown using contaminated water, the rural resident
at 18 km will have a higher dose than an individual would have living
much closer than 18 km because the cost of water likely would preclude
a garden and likely would allow only drinking the water and domestic
uses (see Chapter 8 of the BID). Likewise, we do not think that
hypothesizing that the RMEI lives 30 km away is a cautious or
reasonable assumption because: (1) At 30 km, the RMEI likely would use
water in which contaminants would be much more diluted; (2) the
downgradient residents closest to Yucca Mountain are currently near
Lathrop Wells; and (3) Nye County projects short-term (20 years) growth
between U.S. Route 95 and the southern boundary of NTS; therefore,
population there is not an ephemeral phenomenon. Therefore, placing the
RMEI at about 18 km from the repository footprint reflects the location
of existing residents, is reasonably conservative, and provides more
protection of public health, relative to one commenter's suggested
location of 30 km.
There were a few other comments related to the location of the
RMEI. For example, one comment suggested that, in selecting the
location, we should consider the geology and hydrology of the site
rather than choosing the location in advance. Another comment stated
that we should base the location of the RMEI on the ability of the RMEI
to sustain itself consistent with topography and soil conditions. This
comment also stated that depth to ground water should not be a factor
because it is impossible to predict either human activities or economic
imperatives.
We determined the point of compliance for the individual-protection
standard using site-specific factors and NAS's recommendation to use
current conditions (NAS Report p. 54). In preparing to propose a
location for the RMEI, we collected and evaluated information on the
natural geologic and hydrologic features such as topography, geologic
structure, aquifer depth, aquifer quality, and the quantity of ground
water, that may preclude drilling for water at a specific location (see
Chapters 7 and 8, and Appendices IV and VI, of the BID). We also
considered geologic conditions, for example, we do not believe that a
rural-residential individual would occupy areas much closer to Yucca
Mountain because of the increasing rough terrain and the increasing
depth to ground water (see Chapter 8 of the BID). With increasing depth
to ground water come higher costs: (1) To explore for water; (2) to
drill for water; and (3) to pump the water to the surface (see Appendix
IV of the BID). Our final standard requires DOE and NRC to consider
other, more appropriate locations based upon
[[Page 32123]]
potential, future site characterization data. We agree that it is
impossible to predict either human activities or economic imperatives.
Therefore, we followed NAS's recommendation to use current conditions.
This approach allows us to avoid forcing the use of potentially
excessive speculative assumptions as the bases of regulatory
decisionmaking. It also leads us to consider the depth to ground water
as a key factor in determining the location and activities of the RMEI
and the current location of people living downgradient from the
repository as a reflection of this key factor. We note that some wells
providing drinking water are located less than 18 km from the
repository footprint; however, those wells have been installed by the
Federal government to serve the needs of NTS, and we do not consider
them typical of wells that would serve, or be installed by, a rural-
residential RMEI. See Chapter 8 (Table 8-5) of the BID.
Finally, one comment stated that the proposed RMEI concept forces
DOE to assume the RMEI will withdraw water from the highest
concentration within the plume without consideration of the likelihood.
According to this comment, forcing such an assumption neglects the low
probability that a well will intersect the highest concentration within
the plume.
This comment's approach, which would utilize a probabilistic method
to determine the radionuclide concentration withdrawn by the RMEI, is
similar to one of the example critical group approaches that NAS
provided in its report (NAS Report, Appendix C). The NAS's approach
would use statistical sampling of various parameters, i.e., considering
the likelihood (probability) of various conditions existing, to arrive
at a dose for comparison to the standard. However, we did not use this
CG approach for the following reasons: (1) There is no relevant
experience in applying the probabilistic CG approach, (2) the
probabilistic CG approach is very complex and is difficult to implement
in a manner that assures it would meet the requirements of defining a
CG (i.e., a small group of people who are homogeneous in regards to
exposure characteristics, including receiving the highest doses among
the general population), and (3) we are concerned that this approach
does not appear to identify clearly which individual characteristics
describe who is being protected. A probabilistic approach for CG dose
assessment could include members that would receive little or no
exposure and members that would receive much higher exposures. An RMEI
is a more conservative approach, based upon site-specific conditions,
because the RMEI serves to represent those individuals in the community
who would receive the highest doses, based on cautious, but reasonable,
assumptions. Finally, a significant majority of the comments on the NAS
Report opposed the use of the probabilistic CG approach. We further
believe that prudent public health policy requires that our approach be
followed to provide reasonable conservatism. To allow the probability
of any particular location being contaminated is not a prudent approach
to the ultimate goal of testing acceptable performance.
7. The NAS Suggested Using an NIR Level to Dismiss From Consideration
Extremely Low, Incremental Levels of Dose to Individuals When
Considering Protection of the General Public. For Somewhat Different
Reasons, We are Proposing To Rely Upon the Individual-Protection
Standard To Address Protection of the General Population. Is This
Approach Reasonable in the Case of Yucca Mountain? If Not, What is an
Alternative, Implementable Method To Address Collective Dose and the
Protection of the General Population?
Comments/Our Responses. A number of commenters agreed with us that
the general population is protected by the individual-protection
standard in the site-specific case of Yucca Mountain. Nearly all
commenters agreed with our position that a collective-dose limit is
unnecessary, again, in the site-specific case of Yucca Mountain. Some
commenters stated that EPA should not use an NIR level. One commenter
stated that we should not suggest that DOE use a collective-dose
estimate in the consideration of design alternatives. We decided not to
include a collective-dose limit (see section III.B.1.e), and are not
recommending that DOE estimate collective doses.
Regarding the NIR, we decline to set such a level. We agree with
NAS's conclusion that `` * * * an individual risk standard [will]
protect the public health, given the particular characteristics of the
site * * *'' (NAS Report p. 7). However, we do not accept the remainder
of that statement: `` * * * provided that policy makers and the public
are prepared to accept that very low radiation doses pose a negligibly
small risk'' (NAS Report p. 7). We do not agree that collective doses
made up of very small individual doses are necessarily negligible. We
base our decision on the site-specific characteristics of Yucca
Mountain and the levels of individual risk that we previously have
used. See the preamble to the proposed rule (64 FR 46991) for the full
discussion of our reasoning. We summarize this discussion immediately
below.
The NAS based its recommendations upon guidance from NCRP in which
NCRP proposed a ``Negligible Incremental Dose'' level of 1 mrem/yr.
Dose levels below 1 mrem/yr would be considered ``negligible'' for any
source or practice (see the NAS Report pp. 59-61 and NCRP Report No.
116, p. 52, Docket No. A-95-12, Item II-A-7). The IAEA has made similar
recommendations to define an ``exempt practice'' (see IAEA Safety
Series No. 89, p. 10, Docket No. A-95-12, Item II-A-6). However, it is
not clear to us that an exemption for whole sources or practices, such
as waste disposal in general, should apply to such specific situations
such as gaseous releases from a particular repository because gaseous
releases comprise only one category of releases from a repository;
other releases are projected via the ground water pathway. In addition,
we believe that it is inappropriate to avoid calculating a radiation
dose merely because it is small on an individual basis (NCRP Report No.
121, p. 62, Docket No. A-95-12, Item II-A-8). Finally, we do not
believe that it is appropriate to apply the NIR concept to population
doses (NCRP Report No. 121, p. 62, Docket A-95-12, Item II-A-8). In its
Report No. 121, NCRP stated: ``[a] concept such as the NID (Negligible
Incremental Dose) * * * is not necessarily a legitimate cut-off dose
level for the calculation of collective dose. Collective dose addresses
societal risk while the NID and related concepts address individual
risk'' (NCRP Report No. 121, p. 62, Docket No. A-95-12, Item II-A-8).
Despite our belief that it is inappropriate to set an NID level, we
acknowledge that the extremely low levels of individual risk from the
doses that NAS cited (NAS Report p. 59) (i.e., 0.0003 millirem/yr, for
airborne releases) are well below those levels that we have used for
other regulations.
In addition, the standards in 40 CFR part 191 provide both release
limits, which act as a form of collective dose protection, and
individual-protection limits. The release limits act to restrict the
potential of dilution being used by disposal system designers to meet
the individual-protection limit. However, the potential for large-scale
dispersal of radionuclides through ground water and into surface water
does not exist at Yucca Mountain.
Therefore, for the reasons enumerated above, we believe that we do
not need to include a general population-
[[Page 32124]]
protection provision in our Yucca Mountain standards. See the Response
to Comments document for a fuller discussion of our responses to
comments we received on these issues.
8. Is Our Rationale for the Period of Compliance Reasonable in Light of
the NAS Recommendations?
Comments/Our Responses. Public comments supported a compliance
period that ranged from 10,000 years to a million years and beyond
(i.e., no time limitation). Most of the comments supporting the 10,000-
year period were concerned that such a period was the longest time over
which it would be possible to obtain meaningful modeling results.
Comments noted that just because performance assessment models may be
set to run dose calculations to times well in excess of 10,000 years
does not necessarily mean that at this time the level of confidence in
the reliability of these calculations remains the same. Other comments
noted that because of the unprecedented nature of compliance periods
exceeding 10,000 years, the greater uncertainties at such times only
serves to complicate the licensing process without providing a clearly
identifiable increased benefit to public health. A few commenters
suggested that because there will likely be radiation doses incurred by
individuals beyond 10,000 years, DOE should calculate peak dose, within
the time period of geologic stability, and include these doses in the
Yucca Mountain Environmental Impact Statement. These comments
essentially supported the rationale upon which we based our final rule.
On the other hand, numerous comments suggested that a compliance
period of 10,000 years is not reasonable. They urged us to extend the
compliance period beyond 10,000 years for a variety of reasons.
Foremost among these reasons is that NAS suggested a compliance period
that would extend to the time of peak dose or risk, within the period
of geologic stability for Yucca Mountain, which it estimated could be
as long as one million years. The NAS based its recommendations on
scientific considerations. The NAS concluded that it is possible to
assess the performance of the repository over times during which the
geologic system is ``relatively stable'' or varies in a ``boundable
manner'' (NAS Report p. 9). It also noted that policy considerations
could act to shorten this period. Other comments suggested that the
compliance period of the standard should be comparable to the hazardous
lifetime of the materials to be emplaced in the Yucca Mountain
repository.
It is unclear whether an assessment of the disposal system based on
NAS's recommendation for a standard that would apply to time of peak
dose within the period of geologic stability (about one million years)
would be meaningful given the expected rigor of a licensing process. As
discussed above in section III.B.1.g, we believe that the substantial
uncertainty in projecting human radiation exposures over extremely long
time periods, such as a million years, is unacceptable. For example,
analyzing long-term natural changes would require unprecedented
performance assessment modeling of numerous and different climate
regimes including several glacial-interglacial cycles. This situation
could require the specification of exposure scenarios based on
arbitrary assumptions rather than ``cautious, but reasonable''
assumptions rooted in present-day knowledge. In fact, NAS indicated it
knew of no scientific basis for identifying such scenarios (NAS Report
p. 96). Another concern relates to the possible biosphere conditions
and human behavior. Even for a period as ``short'' as 10,000 years, it
is necessary to make certain assumptions. For periods on the order of
one million years, even natural human evolutionary changes become a
consideration. Regulating to such long time periods could become
arbitrary. Moreover, NAS based its time-frame recommendation on
scientific considerations; however, it recognized that such a decision
also has policy aspects (NAS Report p 56). The NAS recognized that the
existence of these policy aspects might lead us to select an
alternative more consistent with previous Agency policy. Indeed, we
considered the longest practical regulatory periods associated with
other Agency programs, as well as 40 CFR part 191. We believe the
unprecedented nature of a compliance period beyond 10,000 years argues
against imposing such a long regulatory period here. Also, numerous
international disposal programs use a 10,000-year compliance period.
Many of these same programs have committed to consider more qualitative
evaluations beyond 10,000 years. (See GAO/RCED-94-172, 1994, Docket No.
A-95-12, Item V-A-7. Chapter 3 of the BID also contains information on
international programs.) Of course, as knowledge and technical
capabilities grow, this situation could change over time.
The hazardous lifetime of radioactive waste is important; however,
it is but one of several factors that a regulator must consider in
projecting the potential risks from disposal. Indeed, some of the
radionuclides expected to be in the waste inventory at Yucca Mountain
have half-lives extending to thousands or hundreds of thousands of
years (and even a million years or more in a few cases). The ability of
the repository to isolate such long-lived materials relates to the
retardation characteristics of the whole hydrogeological system within
and outside the repository, the effectiveness of engineered barriers,
the characteristics and lifestyles associated with the potentially
affected population, and numerous other factors in addition to the
hazardous lifetime of the materials to be disposed.
With respect to uncertainty in the projected peak dose, one
commenter suggested that NRC should deny the license application if
modeling results show an uncertainty range of five orders of magnitude
above the dose limit in our individual-protection standard. Modeling
results, and their associated uncertainties, are but a part of the
complete record on which NRC will determine whether the disposal system
complies with 40 CFR part 197. For the reasons cited above, we consider
a 10,000-year compliance period, and the additional requirement that
DOE calculate the peak dose beyond 10,000 years and include this
assessment in the Yucca Mountain Environmental Impact Statement, to be
the most appropriate approach, given the state of technology and
knowledge today. In addition, we require DOE to provide a ``reasonable
expectation'' that disposal system performance will meet the standard.
Calculation of doses to the RMEI involves projecting doses that are
within a reasonably expected range rather than projecting the most
extreme case. This approach is in concert with NAS's recommendations to
use ``cautious, but reasonable'' assumptions to define who is to be
protected (NAS Report pp. 5-6). The degree of uncertainty in the dose
assessments considered acceptable in the licensing process is, in our
opinion, an implementation decision that should be the responsibility
of NRC. We believe that we have provided sufficient detail in the
standard to provide the context needed to assure the standard is
applied as we intend (see, e.g., our discussions of ``reasonable
expectation'' in section III.B.2.c and in the Response to Comments
Document that accompanies this rule); however, the final decision
regarding the acceptable degree of uncertainty is NRC's responsibility.
For a variety of technical and policy reasons, we believe that a
10,000-year compliance period is meaningful, protective, practical to
implement, and will result in a robust disposal system protective for
periods beyond 10,000
[[Page 32125]]
years. In other programs we have regulated non-radioactive hazardous
waste for as long as 10,000 years. Having a 10,000-year compliance
period for Yucca Mountain, in conjunction with 40 CFR part 191, ensures
that SNF, HLW, and TRU radioactive wastes disposed anywhere in the
United States must be regulated for a 10,000-year compliance period.
9. Does Our Requirement That DOE and NRC Determine Compliance with
Sec. 197.20 Based Upon the Mean of the Distribution of the Highest
Doses Resulting From the Performance Assessment Adequately Address
Uncertainties Associated With Performance Assessments?
Comments/Our Responses. Comments on this question ranged from
advocating that we should use the maximally exposed individual and
``worst-case'' measures to expressing general agreement with the
proposed approach. Some comments stated that any measure applied to the
performance assessments should be considered an implementation decision
that we should leave to NRC. See the Response to Comments document for
additional discussion of comments we received regarding performance
assessments.
We specify a compliance measure we believe is reasonable but still
conservative: the mean of the distribution of projected doses from
DOE's performance assessments. The primary reason we impose this
requirement is that it provides a necessary context for implementation
of the standard. In addition, we note that it is also consistent with
the approach we implemented in certifying WIPP.
We consider it necessary to supply context for understanding the
intent of the standard to constrain and direct the otherwise unbounded
range of approaches to demonstrating compliance that could be justified
in the absence of such context. For example, it would be possible to
use only a small number of assessments to demonstrate compliance if the
standard specified only an exposure limit. In such a case, the full
range of relevant site conditions and processes might not be
considered. Further, the analyses and the regulatory decision making
might not capture the uncertainties in projecting long-term
performance. At the other extreme, without a defined performance
measure, endless and exhaustive site characterization studies and
analyses could be required. The impetus for these endless and
exhaustive studies and analyses would be a perceived need to identify
the most extreme ``worst-case'' scenarios (regardless of their actual
likelihood of occurring). We believe that a thorough assessment of
repository performance expectations should examine the full range of
reasonably foreseeable site conditions and relevant processes expected
during the regulatory time frame. In making quantitative estimates of
repository performance, we believe that unrealistic or extreme
situations or assumptions should not dominate estimates of expected
performance (see additional discussions about ``reasonable
expectation'' in this preamble and the Response to Comments Document).
With these considerations in mind, we believe that specifying a
performance measure is necessary to supply the proper context for
implementing the standard in the regulatory process, as well as
providing the applicant (DOE) a focus for its efforts to build the
compliance arguments and supporting calculations.
In line with our use of the term ``reasonable expectation,'' the
fundamental compliance measure consistent with a literal mathematical
interpretation of this term would be the mean value of the distribution
of calculated doses. However, as the only alternative for a compliance
measure, the mean may in some cases be interpreted too restrictively.
In actuality, some situations may result in very high dose estimates
for situations that have low probabilities. Simply averaging these
``outliers'' into the distribution of calculated dose estimates can
bias the mean levels that may be unrealistically high. Although this is
certainly a conservative (and therefore desirable) approach, its
effects can be unrealistically conservative (not a desirable
situation). The result of overly conservative effects is to drive
regulatory decision making on the basis of very low probability and
potentially unrealistic situations.
Because of these potential situations, we also proposed using the
median of the expected range of calculated values as another
interpretation of the ``expected'' situation. The median (reflecting a
value exceeded half of the time) may be more conservative if some of
the variables involved in the performance calculations have skewed
distributions. However, we conclude that, in the case of Yucca
Mountain, the mean is an appropriate measure.
By specifying the mean as the performance measure and probability
limits for the processes and events to be considered (Sec. 197.36), and
in concert with the intent of our ``reasonable expectation'' approach
in general, we have implied that probabilistic approaches for the
disposal system performance assessments are expected. The probabilistic
approach is well established in DOE's approach to performance
projections (see the DEIS and Vol. 3 of the Viability Assessment,
Docket No. A-95-12, Items V-A-4 and V-A-5). Based on DOE's past actions
and stated intent, we believe that DOE will continue to follow this
approach and that, therefore, it is unnecessary for us to specify
additional requirements in the standard to assure that DOE continues to
follow this approach. We also believe that specifying such requirements
could be interpreted to exclude the use of deterministic analyses.
These analyses can be useful for carefully focused bounding analyses
and sensitivity studies. For these reasons we have specified only the
fundamental performance measures to provide the context for
understanding, without additional qualifications, the intent of the
standard for implementation efforts.
A number of comments stated that, though they agreed with our
selection of performance measures, the choice should be left as an
implementation detail for NRC. Relative to the implementation question,
we believe that specifying the fundamental compliance measure is
necessary as a means to supply the proper context for understanding the
intent of the rule and for implementation guidance as explained above.
We feel this is distinctly different than the implementation
responsibility of NRC, as explained below.
We do not believe that setting the fundamental compliance measure
intrudes into NRC's implementation authority because the primary task
for the regulatory authority is to examine the performance case put
forward by DOE to determine ``how much is enough'' in terms of the
information and analyses presented (i.e., how will the regulatory
authority determine when the performance case has been demonstrated
with an acceptable level of confidence). Our standard contains no
specific measures for that judgment. We do not specify any confidence
measures for such judgments or numerical analyses. Also, we do not
prescribe analytical methods that must be used for performance
assessments, quality assurance measures that must be applied,
statistical measures that define the number or complexity of analyses
that should be performed, or any assurance measures in addition to the
numerical limits in the standard. We specify only that the mean of the
dose assessments must meet the exposure limit. There are many other
considerations and decisions that
[[Page 32126]]
describe the extent of the assessments or level of rigor necessary to
ensure that the mean is a meaningful measure upon which a licensing
decision can rest. These considerations and decisions properly belong
to the implementing authority. For example, we believe setting a
confidence level clearly is an implementation function that should be
left to NRC; therefore, we make no requirements in the standard to
foreclose NRC's flexibility in setting appropriate confidence measures.
In the development of the WIPP certification criteria, where we had
both the standard-setting and implementing authority, we did establish
a confidence measure (40 CFR 194.55 (d) and (f)) in addition to the
basic performance measure. We also included implementation requirements
in the WIPP certification criteria, including analytical approaches
(Sec. 194.55(b)), quality assurance requirements (Sec. 194.22), other
assurance requirements (Sec. 194.41), requirements for modeling
techniques and assumptions (Secs. 194.23 and 194.25), and use of peer
review and expert judgment (Secs. 194.26 and 194.27). These
requirements go well beyond the simple statement of a compliance
measure. We did not incorporate a similar level of detail in the Yucca
Mountain standards because we believe we must specify only what is
necessary to provide the context for implementation that NRC will
execute. We therefore agree with comments that support our choice of
the performance measure, but disagree for the reasons described above
that this choice is an intrusion into the implementation
responsibilities of NRC.
For the WIPP certification, the compliance measure selected for the
individual-protection standard was the higher of the mean or median of
the calculated distributions of doses from releases (40 CFR 194.55(f)).
The mean or median are reasonably conservative measures because they
are influenced by high exposure estimates found when analyzing the full
range of site conditions and relevant processes, without being geared
to exclusively reflect high-end results, as would be the case if we
selected as the measure a high-end percentile of the calculated dose
distribution (such as the 95th or 99th percentile). Our final rule for
Yucca Mountain specifies only that the mean be used, as we believe that
it is appropriately conservative in this situation.
10. Is the Single-borehole Scenario a Reasonable Approach To Judge the
Resilience of the Yucca Mountain Disposal System Following Human
Intrusion? Are There Other Reasonable Scenarios Which We Should
Consider, for Example, Using the Probability of Drilling Through a
Waste Package Based Upon the Area of the Package Versus the Area of the
Repository Footprint or Drilling Through an Emplacement Drift but not
Through a Waste Package? Why Would Your Suggested Scenario(s) be a
Better Measure of the Resilience of the Yucca Mountain Disposal System
than the Proposed Scenario?
Comments/Our Responses. Comments upon this question varied from
agreement that the proposed intrusion scenario is an adequate test of
repository resiliency to opinions that the analysis of any human-
intrusion scenario would be irrelevant to the Yucca Mountain setting.
Some comments proposed alternative intrusion scenarios, most commonly
the use of multiple drilling intrusions. Some comments also proposed
alternative ways of treating the intrusion scenario relative to
repository requirements. We also received comments concerning other
aspects of the intrusion scenario as well as in response to the
specific questions asked above. Discussion on all the issues raised in
comments about the human-intrusion scenario appears in the Response to
Comments document.
Comments in favor of the intrusion scenario as we framed it in the
proposed rule focused upon the difficulties in defending any
predictions about the probability of drilling intrusions through the
repository and in reliably predicting a hypothetical drilling intrusion
in any detail. These comments echoed NAS's conclusions about the
reliability of post-closure institutional controls to prevent
intrusion, and the inability to make scientifically supportable
predictions of the probability of human-intrusion events over the
regulatory period (NAS Report pp. 104-109). The NAS reasoned that
because it is not possible to reliably eliminate the potential for
human intrusion, the only reasonable approach would be to assume an
intrusion occurs and assess the consequences on disposal system
performance. In this light, NAS recommended that a simple stylized
drilling intrusion through the repository to the underlying ground
water table be assessed as a test of the resiliency of the disposal
system (NAS Report Chap. 4). Because it is impossible to scientifically
exclude the potential for an intrusion, and because proposing the
nature of an intrusion is at best speculative, these comments agreed
that the stylized approach that assumes an intrusion and assesses the
consequences is appropriate. We have followed the NAS's recommendations
closely in framing the human intrusion standard.
Some comments on the framing of the intrusion scenario proposed
that, for various reasons, multiple intrusions should be considered,
rather than simply assuming one borehole penetration through the
repository. Because of certain site-specific considerations with
respect to Yucca Mountain, and in light of the rationale underlying the
NAS recommendations, it is not appropriate to modify the scenario to
include multiple penetrations through the repository. It is impossible
to accurately predict the potential for intrusion in the distant
future. Therefore, postulating multiple intrusions is just as
speculative as postulating a single intrusion at any given time or
specific location over the repository. For this reason, NAS recommended
that we develop a stylized intrusion in our rulemaking (NAS Report p.
111). We agree with this recommendation because disruption of the
engineered and natural barriers is a means through which radionuclides
can escape the repository and be transported to the accessible
environment where exposures of individuals can result. Therefore, an
evaluation of human-intrusion consequences is appropriate for a
repository standard. The NAS also recommended that we define a typical
intrusion scenario for analysis (NAS Report p. 108) and recommended a
stylized approach to framing the scenario (NAS Report p. 111) and a
consequence analysis of the scenario (NAS Report p. 111). The intent of
this approach is that the disposal system should be resilient ``to at
least moderate inadvertent intrusions'' (NAS Report p. 113). Scenarios
ranging from single penetrations to many penetrations through the
repository over the regulatory time period would give a very wide range
of results--none more or less defensible than any other, making their
use in regulatory decision making ambiguous at best. To avoid the
speculative aspects of defining intrusion scenarios, we believe the
stylized single intrusion recommended by NAS is sufficient and would
provide a suitable test of the Yucca Mountain disposal system's
performance.
Related comments offered opinions that the prospect of drilling for
water resources at the top of Yucca Mountain is not a credible scenario
because drilling for water would be more sensible in the adjacent
valleys. These comments, however, did not offer
[[Page 32127]]
alternatives for the drilling intrusion. Rather, they stated or implied
that the intrusion scenario was unnecessary. We agree that drilling for
water, or any other mineral resources at Yucca Mountain, is unlikely
because of the very limited resource potential at the site (see Chapter
8 of the BID). However, as NAS concluded, it is impossible to totally
eliminate the possibility of intrusion (see Chapter 4 of the NAS
Report). This question again goes back to the difficulty in making
defensible predictions about the probability of human activities over
very long time periods and the fact that intrusion is a means through
which releases, and consequent exposures, can occur. Therefore, it is
necessary to consider the consequences of inadvertent intrusions in a
health-based standard. Some comments suggested that there is a strong
possibility for deliberate intrusion into the repository to access its
contents as possible resources. We believe that there is no useful
purpose to assessing the consequences of deliberate intrusions because
in that case the intruders would be aware of the risks and consequences
and would have decided to assume the risks. This is consistent with
NAS's conclusion regarding intentional intrusion (NAS Report p. 114).
Some comments stated that defining the stylized scenario as we did
effectively makes the human-intrusion dose assessment results into
design constraints for the repository. We do not believe the stylized
scenario imposes any design constraints because the waste package
penetration is assumed to occur regardless of the particular design
chosen for the waste package. Here again, none of these comments
proposed alternative scenarios. Rather, they simply questioned the
basic relevance of a human intrusion standard. For the reasons
mentioned previously, however, we reiterate our belief that an analysis
of human-intrusion is necessary, and we also note that NAS (NAS Report
p. 108) stated that ``EPA should specify in its standard a typical
intrusion scenario...''. We do not believe it should be regarded as a
design constraint unless the results of the consequence analyses
indicate that the limited breaching of the natural and engineered
barriers would result in the standard being exceeded. Even though the
probability of drilling intrusions may be low, it is impossible to
unequivocally eliminate them. Therefore, we agree with NAS's conclusion
that the ``repository should be resilient to at least modest
inadvertent intrusions'' (NAS Report p. 113).
11. Is it Reasonable To Expect That the Risks to Future Generations Be
No Greater Than the Risks Judged Acceptable Today?
Comments/Our Responses. Comments we received upon this question
strongly favored the position that we should not allow greater risks
for future generations than what is judged to be acceptable today. Some
comments speculated that with advances in medical technology and other
areas, the risks assessed today most likely would be less in the future
because society would be more effective in mitigating the effects of
radiation exposures. Some comments advised that risks from the disposal
effort should be reviewed periodically so that decisions could be made
about their acceptability at a future date. We believe we have set the
standards conservatively, but reasonably, and consistent with our
policies for radiation exposure from radioactive waste disposal
applications and NAS's recommendations. In this regard, our standards
apply over the entire regulatory period of 10,000 years. Our standards
thus protect future generations for a very significant time period. In
addition, we require DOE to calculate the peak dose to the RMEI beyond
10,000 years. Although our standards do not apply to the results of
this calculation, this post-10,000-year analysis will provide more
complete information regarding disposal system performance beyond
10,000 years. This approach to the post-10,000-year period is
consistent with our understanding of the limits imposed by inherent
uncertainties in making such long-term performance projections. The
question of periodic re-evaluation of repository performance is an
implementation question that should be left to the discretion of NRC.
12. What Approach Is Appropriate for Modeling the Ground Water Flow
System Downgradient From Yucca Mountain at the Scale (Many Kilometers
to Tens of Kilometers) Necessary for Dose Assessments Given the
Inherent Limitations of Characterizing the Area? Is it Reasonable To
Assume That There Will be Some Degree of Mixing With Uncontaminated
Ground Water Along the Radionuclide Travel Paths From the Repository?
Comments/Our Responses. Comments on this question shared a general
theme that we should not be prescriptive in indicating a preference or
requirement for any specific modeling approach that should be used.
Rather, the bulk of the comments suggested that DOE (the organization
responsible for developing the license application) and NRC (the
authority responsible for the approval of the disposal facility) should
make these decisions. We agree with this general theme; therefore, our
rule does not specify that DOE must use a particular modeling approach
to demonstrate compliance with the standards. We believe that DOE and
NRC should avoid extreme assumptions and approaches and should identify
and consider the inherent uncertainties in projecting performance in
the regulatory process. More specifically for Yucca Mountain, we
believe that it is necessary to avoid extreme modeling approaches. One
example of an extreme modeling approach is assuming the transportation
of releases from the repository through the natural barriers without
mixing with other ground waters. In this regard we retained our
recommendation that ``reasonable expectation'' be the standard used to
assess repository performance. We have provided detail in the standards
only to the extent needed to provide the context necessary to assure
that the components of the standards are implemented in the manner we
intended when we developed the standards. Ultimately, it is NRC's task
to select and apply the appropriate measure to determine compliance
with our standards.
13. Which Approach for Protecting Ground Water in the Vicinity of Yucca
Mountain is the Most Reasonable? Is There Another Approach Which Would
be Preferable and Reasonably Implementable? If so, Please Explain the
Approach, Why It Is Preferable, and How It Could Be Implemented
Comments/Our Responses. We received public comments advising us of
a variety of approaches towards protecting ground water in the vicinity
of Yucca Mountain. Two primary approaches emerged. One group of public
comments suggested that an all-pathways, individual-dose standard, with
no separate or specific ground water protection provisions, would be
fully protective of the public health. On the other hand, a second set
of public comments suggested that we should promulgate separate ground-
water protection standards applicable to the Yucca Mountain disposal
system. The final rule reflects the latter approach.
We believe as a matter of prudent policy that ground water
protection standards are neither redundant nor unnecessary because they
address specific aspects of natural resource protection not covered by
the individual-protection standard. Rather, such standards are
complementary to the public health and safety standards applicable to
the Yucca Mountain
[[Page 32128]]
disposal system. In particular, we consider ground water that is, or
that could be, drinking water to be the most valuable ground water
resource. We believe that it deserves the highest level of protection.
At Yucca Mountain, water from the aquifer beneath the proposed
repository currently serves as a source of drinking water in
communities 20 to 30 km south of Yucca Mountain. This aquifer has the
potential to supply drinking water to a substantially larger population
than that presently in the area (NAS Report p. 92).
Over the years, many of our regulatory programs have incorporated
the MCLs as an important part of our regulations related to both
radioactive and non-radioactive wastes. This approach grew out of the
development and implementation of our ground water protection strategy,
``Protecting the Nation's Ground-Water: EPA's Strategy for the 1990s''
(``the Strategy,'' Docket No. A-95-12, Item II-A-3). The use of ground
water protection requirements, including the use of MCLs, is reflected
in our regulations pertaining to hazardous waste disposal (40 CFR part
264), municipal waste disposal (40 CFR parts 257 and 258), underground
injection control (UIC) (40 CFR parts 144, 146, and 148), and uranium
mill tailings disposal (40 CFR part 192). We also have incorporated the
MCLs into our generally applicable standards for the disposal of SNF,
HLW, and TRU radioactive waste (40 CFR part 191). These generic
regulations apply to the land disposal of these materials everywhere in
the United States except at Yucca Mountain. Extending comparable
ground-water protection standards to the proposed Yucca Mountain
disposal system will assure reasonable and similar protections wherever
the disposal of SNF, HLW, or TRU radioactive waste occurs in this
country.
In our response to Question 15, we note our concerns related to
adopting only an all-pathways individual-protection standard with no
specific ground-water protection provisions. For a more detailed
discussion of the issues associated with these two options (all-
pathways with and without separate ground water protection), please see
the Response to Comments document.
14. Is the 10,000-year Compliance Period for Protecting the RMEI and
Ground Water Reasonable or Should we Extend the Period to the Time of
Peak Dose? If We Extend it, How Could NRC Reasonably Implement the
Standards While Recognizing the Nature of the Uncertainties Involved in
Projecting the Performance of the Disposal System Over Potentially
Extremely Long Periods?
Comments/Our Responses. As discussed in the response to Question 8
above, comments both supported and questioned our compliance period for
the RMEI and ground water protection standards. Commenters who
supported the 10,000-year compliance period thought that this time
period was ``sufficient'' and that it represented an appropriate
balance between long-term coverage and implementability. These
commenters agreed with us that, though it is possible to make longer-
term calculations, such calculations should be used only for regulatory
insight because of the considerable uncertainty involved in making the
calculations. These comments support our rationale and choice of a
10,000-year compliance period for protecting the RMEI and ground water.
Numerous commenters suggested that we should extend the compliance
period beyond 10,000 years for a variety of reasons. Foremost is that
NAS suggested a compliance period extending up to the time of peak dose
or risk, within the period of geologic stability for Yucca Mountain
(i.e., up to one million years). Other commenters suggested that the
compliance period should be comparable to the hazardous lifetime of the
materials to be emplaced in the Yucca Mountain repository. As indicated
in our response to Question 8 above and in section III.B.1.g, we have
significant concerns relating to making meaningful projections of
repository performance over the time periods implied by NAS's
recommendations. These concerns extend to modeling the time to peak
concentration to judge compliance with the ground water standards,
which NAS did not explicitly consider. Modeling of exposure scenarios
and climatic conditions very different from those experienced over the
last 10,000 years, coupled with the potential for human evolutionary
changes over such extended time frames, introduces tremendous
uncertainties. This situation may result in making arbitrary
assumptions in performance assessment modeling, rather than making
informed choices based upon cautious, but reasonable, assumptions
rooted in present-day knowledge. Regarding the hazardous lifetime of
the materials to be emplaced in the Yucca Mountain repository, it is
true that there will be radioactive materials remaining after the end
of the 10,000-year regulatory period. Nevertheless, the ability of a
repository to isolate such long-lived radionuclides depends upon a
variety of other factors, including the retardation characteristics of
the whole hydrogeological system within and outside of the repository,
the effectiveness of the engineered barriers, the characteristics and
lifestyles associated with the potentially affected population, as well
as the hazardous lifetime of the materials to be emplaced in the
repository.
Although we received numerous comments suggesting that 10,000 years
was insufficient as a compliance period, we received little in the way
of suggestions regarding on how to reasonably implement standards
covering these potentially very extended time periods. For example, one
commenter suggested that we put the burden on NRC and DOE to develop
methods to estimate, with some degree of certainty, the effects after
10,000 years without explaining how the agencies could achieve these
results. Please note that NAS specifically addressed this matter (NAS
Report, pp. 12-13):
``It might be possible that some of the current gaps in
scientific knowledge and uncertainties that we have identified might
be reduced by future research * * *. Conducting such an appraisal,
however, should not be seen as a reason to slow down ongoing
research and development programs, including geologic site
characterization, or the process of establishing a standard to
protect public health.''
We agree with NAS's conclusion. We expect more information will be
developed in the time between the promulgation of this rule and the NRC
licensing decision to address some of the remaining uncertainties.
15. As Noted by NAS, Some Countries Have Individual-Protection Limits
Higher Than We Have Proposed. In Addition, Other Federal Authorities
Have suggested Higher Individual-dose Iimits With No Separate
Protection of Ground Water. Therefore, We Request Comment Upon the Use
of an Annual CEDE of 250 Sv (25 mrem) With No Separate Ground
Water Protection, Including the Consistency of Such a Limit With Our
Ground Water Protection Policy
Comments/Our Responses. Our promulgation of only an all-pathways,
individual-protection standard, such as 25 mrem/yr, with no ground-
water
[[Page 32129]]
protection provisions, would provide no assurance that ground water
resources will be protected adequately. The separate ground water
protection standards in our rule will preserve the integrity of the
ground-water resources in the vicinity of Yucca Mountain for present
and future generations.
The all-pathways, individual-protection standard is the primary
mechanism to protect public health from releases of radioactivity from
the Yucca Mountain repository. We believe that an all-pathways limit,
supplemented with ground water protection standards, provides complete
public health protection and assures that ground water resources will
be safe for use by future generations. In addition, the ground water
resources in the vicinity of Yucca Mountain support a diverse
agricultural community and important ecological systems (e.g., the
endangered Devil's Hole pupfish).
We believe that separate ground water protection standards designed
to protect the ground water resource in the vicinity of Yucca Mountain
is a necessary element of our Yucca Mountain standards. Our decision to
include separate ground water protection standards is a policy
decision. As explained in section III.B.4 (How Does Our Rule Protect
Ground Water?), we developed a ground water protection strategy to
guide Agency programs in their efforts to prevent adverse effects on
human health and the environment and in protecting the environmental
integrity of the nation's ground water resources (see ``The Strategy,''
Docket No. A-95-12, Item II-A-3). We have employed ground water
protection programs and standards in a variety of regulatory programs
for hazardous and non-hazardous waste. We also have incorporated ground
water protection standards in our generally applicable disposal
regulations for SNF, HLW, and TRU radioactive wastes (see 40 CFR part
191), and implemented them at WIPP. Incorporation of ground water
standards in our overall Yucca Mountain standards provides consistency
with other Agency programs and assures consistent protection wherever
SNF, HLW, and TRU radioactive waste may be disposed of in this country.
We believe that both ground-water protection standards,
incorporating the MCLs to protect ground-water resources, and an
individual-protection standard, as embodied in an all-pathways
standard, are complementary and necessary to provide adequate public
health protection and protection of an invaluable national natural
resource. For a more detailed discussion of the issues associated with
the options for the individual-protection standard and the ground-water
protection standards, please see the Response to Comments document.
16. We Are Proposing To Require, in the Individual-Protection Standard,
That DOE Must Project the Disposal System's Performance After 10,000
Years. Are the Specified Uses of the Projections Appropriate and
Adequate?
Comments/Our Responses. Some comments supporting our 10,000-year
compliance period also endorsed the idea that projections of the
disposal system's performance beyond 10,000 years would, among other
things, be fraught with greater uncertainties and would not necessarily
provide greater public health protection. A few comments supported our
requirement that DOE project doses beyond 10,000 years and include the
results of these projections in the Yucca Mountain EIS. In addition, a
few comments suggested that any post-10,000-year projection should
serve only to provide ``regulatory insight.''
Comments supporting the use of a post-10,000-year projection for
regulatory purposes cited the long-term hazard posed by the wastes
planned for Yucca Mountain, the need to protect future generations, and
the possibility that the individual doses would exceed our standard in
the post-10,000-year time frame. As indicated in our response to
Question 8 above, we considered these and other issues in determining
that a 10,000-year compliance period is most appropriate. This
compliance period is protective, meaningful, and practical to
implement. By also including a post-10,000-year dose assessment in the
EIS, which provides more complete information on long-term performance,
we believe a robust disposal system protective for time periods beyond
10,000 years will result.
In considering the appropriate use of the post-10,000-year dose
assessment, we have had to balance these very difficult issues. It is
possible to set computer models to run for time periods beyond 10,000
years; however, this approach does not necessarily result in an equal
or higher level of confidence that the exposed individuals will be
protected. As numerous comments pointed out, it is likely that such
results will contain greater uncertainties. We agree with these
comments. Yet, despite these greater uncertainties, such assessments
can be somewhat informative though not necessarily reliable dose
predictions. We note, for example, the considerations that supported
Sweden's proposed regulations for SNF and nuclear waste (``The Swedish
Radiation Protection Institute's Proposed Regulations Concerning the
Final Management of Spent Nuclear Fuel or Nuclear Waste,'' SSI Report
97:07, May 1997, Docket No. A-95-12, Item V-A-11). Regarding long-term
assessments (beyond 1,000 years), such studies ``do not mean that the
full protective capacity of the repository can be forecasted, e.g., on
the scale of a million years into the future. However, studies of such
(repository) subsystems can provide valuable information without
actually being considered as a prediction of doses to living organisms'
(Id. at 11). We believe that requiring DOE to include a post-10,000-
year dose assessment in the EIS is an appropriate means to address the
issues associated with such long-term impacts. We note that in our
proposal, we stated that ``NRC is not to use'' post-10,000-year results
in assessing compliance with the individual-protection standard.
However, in its comments on our proposal, NRC stated that, if DOE uses
post-10,000-year results to bolster its compliance case, ``the
Commission should not be constrained from considering such
information'' (Docket No. A-95-12, Item II-D-92). We agree. At the very
least, more complete information on long-term disposal system
performance will be available. In addition, during this time, the
repository design will become more clearly defined by new information.
For more extensive discussions of this issue, please see our response
to Question 8 above and the Response to Comments document.
VI. Severability
As discussed above at Section III.B.1, the purpose of the
Individual Protection Standard is to protect public health and safety.
As discussed in Section III.B.4, the Ground Water Protection Standard
serves two purposes. First, it protects the ground water resource.
Second, by protecting that resource, the Ground Water Protection
Standard also furthers the goal of public health and safety. Consistent
with the recommendations of the National Academy of Sciences, the
Individual Protection Standard is adequate in itself to protect public
health and safety. In addition, EPA is adopting the Ground Water
Protection Standard in its discretion in order to provide additional
protection to the vital ground water resource, and in so doing, is also
providing an extra measure of public health and safety protection.
Thus, notwithstanding that the Individual Protection and Ground Water
Standards have coincident
[[Page 32130]]
compliance points and, as implemented by NRC, may have other
similarities, these two provisions are wholly severable.
VI. Regulatory Analyses
A. Executive Order 12866
Under Executive Order 12866 [58 Federal Register 51735 (October 4,
1993)], the Agency must determine whether the regulatory action is
``significant'' and therefore subject to review by the Office of
Management and Budget (OMB) and the requirements of the Executive
Order. Executive Order 12866 defines a ``significant regulatory
action'' as one that is likely to result in a rule that may:
(1) Have an annual effect upon the economy of $100 million or
more or adversely affect in a material way the economy, a sector of
the economy, productivity, competition, jobs, the environment,
public health or safety, or state, local, or tribal governments or
communities;
(2) Create a serious inconsistency or otherwise interfere with
an action taken or planned by another agency;
(3) Materially alter the budgetary impact of entitlements,
grants, user fees, or loan programs or the rights and obligations of
recipients thereof; or
(4) Raise novel legal or policy issues arising out of legal
mandates, the President's priorities, or the principles set forth in
the Executive Order.
In accordance with the terms of Executive Order 12866, EPA
determined that this rule is a ``significant regulatory action''
because it raises novel legal or policy issues arising out of the
specific legal mandate of Section 801 of the Energy Policy Act of 1992.
Thus, this action was submitted to OMB for review.
In accordance with the terms of Executive Order 12866, EPA
determined that this rule is a ``significant regulatory action''
because it raises novel legal or policy issues arising out of the
specific legal mandate of Section 801 of the Energy Policy Act of 1992.
Thus, this action was submitted to OMB for review. Any changes to the
rule that were made in response to OMB suggestions or recommendations
have been documented in the public record.
B. Executive Order 12898
Executive Order 12898, ``Federal Actions to Address Environmental
Justice in Minority Populations And Low-income Populations
(Environmental Justice),'' directs us to incorporate environmental
justice as part of our overall mission by identifying and addressing
disproportionately high and adverse human health and environmental
effects of programs, policies, and activities upon minority populations
and low-income populations.
We find no disproportionate impact in the outcome of this
rulemaking. No plan has thus been devised to address a disproportionate
impact.
C. Executive Order 13045
Executive Order 13045, ``Protection of Children from Environmental
Health Risks and Safety Risks,'' (62 FR 19885, April 23, 1997) applies
to any rule that (1) is determined to be ``economically significant''
as defined under Executive Order 12866, and (2) concerns an
environmental health or safety risk that we have reason to believe may
have a disproportionate effect upon children. If the regulatory action
meets both criteria, we must evaluate the environmental health or
safety effects of the planned rule upon children, and explain why the
planned regulation is preferable to other potentially effective and
reasonably feasible alternatives that we considered.
As discussed in the preamble in sections II.C and III.B.1.a, the
primary risk factor considered in our risk assessment is incidence of
fatal cancer. We have derived a risk value for the onset of fatal
cancer that considers children, since it is an overall average risk
value (see Chapter 6 of the BID for more details) that includes all
ages from birth onward, all exposure pathways, both genders, and most
radionuclides. We do note that the risk factor does not include the
fetus. However, we believe that the risk of fatal cancer per unit dose
incurred by the unborn is similar to that for those who have been born,
but the exposure period is very short compared to the rest of the
individual's average lifetime, so the risk of fatal cancer to the
unborn is proportionately lower and does not have a significant impact
upon the overall risk of fatal cancer incurred by an individual over a
lifetime. (See Chapter 6 of the BID for more discussion of the risk of
fatal cancer resulting from in utero exposure.)
Therefore, this final rule is not subject to Executive Order 13045
because we do not have reason to believe the environmental health risks
or safety risks addressed by this action present a disproportionate
risk to children.
D. Executive Order 13084
On January 1, 2001, Executive Order 13084 was superseded by
Executive Order 13175. However, this rule was developed when Executive
Order 13084 was still in force, and so tribal considerations were
addressed under Executive Order 13084.
Under Executive Order 13084, ``Consultation and Coordination with
Indian Tribal Governments,'' we may not issue a regulation that is not
required by statute, that significantly or uniquely affects the
communities of Indian tribal governments, and that imposes substantial
direct compliance costs upon those communities, unless the Federal
government provides the funds necessary to pay the direct compliance
costs incurred by the tribal governments, or we consult with those
governments. If we comply by consulting, Executive Order 13084 requires
us to provide to OMB, in a separately identified section of the
preamble to the rule, a description of the extent of our prior
consultation with representatives of affected tribal governments, a
summary of the nature of their concerns, and a statement supporting the
need to issue the regulation. In addition, Executive Order 13084
requires us to develop an effective process permitting elected
officials and other representatives of Indian tribal governments ``to
provide meaningful and timely input in the development of regulatory
policies on matters that significantly or uniquely affect their
communities.''
The radiological protection standards promulgated by today's rule
are applicable solely and exclusively to the Department of Energy's
potential storage and disposal facility at Yucca Mountain. Therefore,
this rule does not significantly or uniquely affect the communities of
Indian tribal governments, nor does it impose any direct compliance
costs on such communities. Accordingly, the requirements of section
3(b) of Executive Order 13084 do not apply to this rule.
E. Executive Order 13132
Executive Order 13132, entitled ``Federalism'' (64 FR 43255, August
10, 1999), requires EPA to develop an accountable process to ensure
``meaningful and timely input by State and local officials in the
development of regulatory policies that have federalism implications.''
``Policies that have federalism implications'' is defined in the
Executive Order to include regulations that have ``substantial direct
effects on the States, on the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government.''
This final rule 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 responsibilities among the various
[[Page 32131]]
levels of government, as specified in Executive Order 13132. Thus,
Executive Order 13132 does not apply to this rule. Nonetheless, in
developing its proposed rule EPA held public meetings in Nevada and
Washington, D.C. during which comment was received from and discussions
were had with representatives from the State of Nevada and various
county officials. EPA also had informal meetings with State and local
officials to apprise them of the status of the rulemaking.
F. National Technology Transfer and Advancement Act
Section 12(d) of the National Technology Transfer and Advancement
Act of 1995 (NTTAA), Public Law 104-113, section 12(d) (15 U.S.C. 272
note) directs us to use voluntary consensus standards in our regulatory
activities unless to do so would be inconsistent with applicable law or
otherwise impractical. Voluntary consensus standards are technical
standards (e.g., materials specifications, test methods, sampling
procedures, and business practices) that are developed or adopted by
voluntary consensus standards bodies. The NTTAA directs us to provide
Congress, through OMB, explanations when we decide not to use available
and applicable voluntary consensus standards.
In our proposal, we requested public comment on potentially
applicable voluntary consensus standards that would be appropriate for
inclusion in the Yucca Mountain rule. We received no comments on this
aspect of the rule. The closest analogy to consensus standards for
radioactive waste disposal facilities are our regulations at 40 CFR
part 191. As discussed above in this preamble, Congress expressly
prohibited the application of the 40 CFR part 191 standards to the
Yucca Mountain disposal facility, and, therefore, the standards
promulgated today are site-specific standards developed solely for
application to the Yucca Mountain disposal facility.
G. Paperwork Reduction Act
We have determined that this rule contains no information
collection requirements within the scope of the Paperwork Reduction
Act, 42 U.S.C. 3501-20.
H. Regulatory Flexibility Act (RFA), as amended by the Small Business
Regulatory Enforcement Fairness Act of 1996 (SBREFA), 5 U.S.C. 601 et
seq
The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the
Small Business Regulatory Enforcement Fairness Act of 1996, generally
provides that before a rule may take effect, the agency promulgating
the rule must submit a rule report, which includes a copy of the rule,
to each House of the Congress and to the Comptroller General of the
United States. Section 804, however, exempts from section 801 the
following types of rules: rules of particular applicability; rules
relating to agency management or personnel; and rules of agency
organization, procedure, or practice that do not substantially affect
the right or obligations of non-agency parties. (5 U.S.C. 804(3)) The
EPA is not required to submit a rule report regarding today's action
under section 801 because this is a rule of particular applicability.
I. Unfunded Mandates Reform Act
Title II of the Unfunded Mandates Reform Act of 1995 (UMRA, Public
Law 104-4) establishes requirements for Federal agencies to assess the
effects of their regulatory actions upon state, local, and tribal
governments and the private sector. Under section 202 of UMRA, we
generally must prepare a written statement, including a cost-benefit
analysis, for proposed and final rules with ``Federal mandates'' that
may result in expenditures by state, local, and tribal governments, in
the aggregate, or to the private sector, of $100 million or more in any
one year. Before we promulgate a rule for which a written statement is
needed, section 205 of UMRA generally requires us to identify and
consider a reasonable number of regulatory alternatives and adopt the
least costly, most cost-effective, or least burdensome alternative that
achieves the objectives of the rule. The provisions of section 205 do
not apply when they are inconsistent with applicable law. Moreover,
section 205 allows us to adopt an alternative other than the least
costly, most cost-effective, or least burdensome if the Administrator
publishes with the final rule an explanation as to why that alternative
was not adopted. Before we establish any regulatory requirements that
significantly or uniquely affect small governments, including tribal
governments, we must develop, under section 203 of UMRA, a small-
government-agency plan. The plan must provide for notifying potentially
affected small governments, enabling officials of affected small
governments to have meaningful and timely input into the development of
regulatory proposals with significant Federal intergovernmental
mandates, and informing, educating, and advising small governments on
compliance with the regulatory requirements.
Today's rule contains no Federal mandates (under the regulatory
provisions of Title II of UMRA) for State, local, or tribal governments
or the private sector. The final rule promulgates radiological
protection standards applicable solely and exclusively to the
Department of Energy's potential storage and disposal facility at Yucca
Mountain. The rule imposes no enforceable duty on any State, local or
tribal governments or the private sector. Thus, today's rule is not
subject to the requirements of sections 202 and 205 of UMRA.
J. Executive Order 13211
Executive Order 13211, ``Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use,'' (66 FR
28355 (May 22, 2001)), provides that agencies shall prepare and submit
to the Administrator of the Office of Information and Regulatory
Affairs, Office of Management and Budget, a Statement of Energy Effects
for certain actions identified as ``significant energy actions.''
Section 4(b) of Executive Order 13211 defines ``significant energy
actions'' as ``any action by an agency (normally published in the
Federal Register) that promulgates or is expected to lead to the
promulgation of a final rule or regulation, including notices of
inquiry, advance notices of proposed rulemaking, and notices of
proposed rulemaking: (1)(i) That is a significant regulatory action
under Executive Order 12866 or any successor order, and (ii) is likely
to have a significant adverse effect on the supply, distribution, or
use of energy; or (2) that is designated by the Administrator of the
Office of Information and Regulatory Affairs as a significant energy
action.''
We have not prepared a Statement of Energy Effects because this
rule is not a significant energy action, as defined in Executive Order
13211. While this rule is a significant regulatory action under
Executive Order 12866, we have determined that it is not likely to have
an adverse effect on the supply, distribution, or use of energy.
List of Subjects in 40 CFR Part 197
Environmental protection, High-level radioactive waste Nuclear
energy, Radiation protection, Radionuclides, Spent nuclear fuel,
Uranium, Waste treatment and disposal.
Dated: June 5, 2001.
Christine Todd Whitman,
Administrator.
The Environmental Protection Agency is adding a new part 197 to
Subchapter
[[Page 32132]]
F of Chapter I, title 40 of the Code of Federal Regulations, as
follows:
Subchapter F--Radiation Protection Programs
PART 197--PUBLIC HEALTH AND ENVIRONMENTAL RADIATION PROTECTION
STANDARDS FOR YUCCA MOUNTAIN, NEVADA
Subpart A--Public Health and Environmental Standards for Storage
Sec.
197.1 What does subpart A cover?
197.2 What definitions apply in subpart A?
197.3 How is subpart A implemented?
197.4 What standard must DOE meet?
197.5 When will this part take effect?
Subpart B--Public Health and Environmental Standards for Disposal
197.11 What does subpart B cover?
197.12 What definitions apply in subpart B?
197.13 How is subpart B implemented?
197.14 What is a reasonable expectation?
197.15 How must DOE take into account the changes that will occur
during the 10,000 years after disposal?
Individual-Protection Standard
197.20 What standard must DOE meet?
197.21 Who is the reasonably maximally exposed individual?
Human-Intrusion Standard 197.25 What standard must DOE meet?
197.26 What are the circumstances of the human intrusion?
Ground Water Protection Standards
197.30 What standards must DOE meet?
197.31 What is a representative volume?
Additional Provisions
197.35 What other projections must DOE make?
197.36 Are there limits on what DOE must consider in the
performance assessments?
197.37 Can EPA amend this rule?
197.38 Are The Individual Protection and Ground Water Protection
Standards Severable?
Authority: Sec. 801, Pub. L. 102-486, 106 Stat. 2921, 42 U.S.C.
10141 n.
Subpart A--Public Health and Environmental Standards for Storage
Sec. 197.1 What does subpart A cover?
This subpart covers the storage of radioactive material by DOE in
the Yucca Mountain repository and on the Yucca Mountain site.
Sec. 197.2 What definitions apply in subpart A?
Annual committed effective dose equivalent means the effective dose
equivalent received by an individual in one year from radiation sources
external to the individual plus the committed effective dose
equivalent.
Committed effective dose equivalent means the effective dose
equivalent received over a period of time (e.g., 30 years,), as
determined by NRC, by an individual from radionuclides internal to the
individual following a one-year intake of those radionuclides.
DOE means the Department of Energy.
Effective dose equivalent means the sum of the products of the dose
equivalent received by specified tissues following an exposure of, or
an intake of radionuclides into, specified tissues of the body,
multiplied by appropriate weighting factors.
EPA means the Environmental Protection Agency.
General environment means everywhere outside the Yucca Mountain
site, the Nellis Air Force Range, and the Nevada Test Site.
High-level radioactive waste means:
(1) The highly radioactive material resulting from the reprocessing
of spent nuclear fuel, including liquid waste produced directly in
reprocessing and any solid material derived from such liquid waste that
contains fission products in sufficient concentrations; and
(2) Other highly radioactive material that the Commission,
consistent with existing law, determines by rule requires permanent
isolation.
Member of the public means anyone who is not a radiation worker for
purposes of worker protection.
NRC means the Nuclear Regulatory Commission.
Radioactive material means matter composed of or containing
radionuclides subject to the Atomic Energy Act of 1954, as amended (42
U.S.C. 2014 et seq.). Radioactive material includes, but is not limited
to, high-level radioactive waste and spent nuclear fuel.
Spent nuclear fuel means fuel that has been withdrawn from a
nuclear reactor following irradiation, the constituent elements of
which have not been separated by reprocessing.
Storage means retention (and any associated activity, operation, or
process necessary to carry out successful retention) of radioactive
material with the intent or capability to readily access or retrieve
such material.
Yucca Mountain repository means the excavated portion of the
facility constructed underground within the Yucca Mountain site.
Yucca Mountain site means:
(1) The site recommended by the Secretary of DOE to the President
under section 112(b)(1)(B) of the Nuclear Waste Policy Act of 1982 (42
U.S.C. 10132(b)(1)(B)) on May 27, 1986; or
(2) The area under the control of DOE for the use of Yucca Mountain
activities at the time of licensing, if the site designated under the
Nuclear Waste Policy Act is amended by Congress prior to the time of
licensing.
Sec. 197.3 How is subpart A implemented?
The NRC implements this subpart A. The DOE must demonstrate to NRC
that normal operations at the Yucca Mountain site will and do occur in
compliance with this subpart before NRC may grant or continue a license
for DOE to receive and possess radioactive material within the Yucca
Mountain site.
Sec. 197.4 What standard must DOE meet?
The DOE must ensure that no member of the public in the general
environment receives more than an annual committed effective dose
equivalent of 150 microsieverts (15 millirems) from the combination of:
(a) Management and storage (as defined in 40 CFR 191.2) of
radioactive material that:
(1) Is subject to 40 CFR 191.3(a); and
(2) Occurs outside of the Yucca Mountain repository but within the
Yucca Mountain site; and
(b) Storage (as defined in Sec. 197.2) of radioactive material
inside the Yucca Mountain repository.
Sec. 197.5 When will this part take effect?
The standards in this part take effect on July 13, 2001.
Subpart B--Public Health and Environmental Standards for Disposal
Sec. 197.11 What does subpart B cover?
This subpart covers the disposal of radioactive material in the
Yucca Mountain repository by DOE.
Sec. 197.12 What definitions apply in subpart B?
All definitions in subpart A of this part and the following:
Accessible environment means any point outside of the controlled
area, including:
(1) The atmosphere (including the atmosphere above the surface area
of the controlled area);
(2) Land surfaces;
(3) Surface waters;
(4) Oceans; and
(5) The lithosphere.
Aquifer means a water-bearing underground geological formation,
group of formations, or part of a formation (excluding perched water
bodies) that can yield a significant amount of ground water to a well
or spring.
Barrier means any material, structure, or feature that, for a
period to be determined by NRC, prevents or substantially reduces the
rate of
[[Page 32133]]
movement of water or radionuclides from the Yucca Mountain repository
to the accessible environment, or prevents the release or substantially
reduces the release rate of radionuclides from the waste. For example,
a barrier may be a geologic feature, an engineered structure, a
canister, a waste form with physical and chemical characteristics that
significantly decrease the mobility of radionuclides, or a material
placed over and around the waste, provided that the material
substantially delays movement of water or radionuclides.
Controlled area means:
(1) The surface area, identified by passive institutional controls,
that encompasses no more than 300 square kilometers. It must not extend
farther:
(a) South than 36 deg. 40' 13.6661" north latitude, in the
predominant direction of ground water flow; and
(b) Than five kilometers from the repository footprint in any other
direction; and
(2) The subsurface underlying the surface area.
Disposal means the emplacement of radioactive material into the
Yucca Mountain disposal system with the intent of isolating it for as
long as reasonably possible and with no intent of recovery, whether or
not the design of the disposal system permits the ready recovery of the
material.
Disposal of radioactive material in the Yucca Mountain disposal
system begins when all of the ramps and other openings into the Yucca
Mountain repository are sealed.
Ground water means water that is below the land surface and in a
saturated zone.
Human intrusion means breaching of any portion of the Yucca
Mountain disposal system, within the repository footprint, by any human
activity.
Passive institutional controls means:
(1) Markers, as permanent as practicable, placed on the Earth's
surface;
(2) Public records and archives;
(3) Government ownership and regulations regarding land or resource
use; and
(4) Other reasonable methods of preserving knowledge about the
location, design, and contents of the Yucca Mountain disposal system.
Peak dose means the highest annual committed effective dose
equivalent projected to be received by the reasonably maximally exposed
individual.
Performance assessment means an analysis that:
(1) Identifies the features, events, processes, (except human
intrusion), and sequences of events and processes (except human
intrusion) that might affect the Yucca Mountain disposal system and
their probabilities of occurring during 10,000 years after disposal;
(2) Examines the effects of those features, events, processes, and
sequences of events and processes upon the performance of the Yucca
Mountain disposal system; and
(3) Estimates the annual committed effective dose equivalent
incurred by the reasonably maximally exposed individual, including the
associated uncertainties, as a result of releases caused by all
significant features, events, processes, and sequences of events and
processes, weighted by their probability of occurrence.
Period of geologic stability means the time during which the
variability of geologic characteristics and their future behavior in
and around the Yucca Mountain site can be bounded, that is, they can be
projected within a reasonable range of possibilities.
Plume of contamination means that volume of ground water in the
predominant direction of ground water flow that contains radioactive
contamination from releases from the Yucca Mountain repository. It does
not include releases from any other potential sources on or near the
Nevada Test Site.
Repository footprint means the outline of the outermost locations
of where the waste is emplaced in the Yucca Mountain repository.
Slice of the plume means a cross-section of the plume of
contamination with sufficient thickness parallel to the prevalent
direction of flow of the plume that it contains the representative
volume.
Total dissolved solids means the total dissolved (filterable)
solids in water as determined by use of the method specified in 40 CFR
part 136.
Undisturbed performance means that human intrusion or the
occurrence of unlikely natural features, events, and processes do not
disturb the disposal system.
Undisturbed Yucca Mountain disposal system means that the Yucca
Mountain disposal system is not affected by human intrusion.
Waste means any radioactive material emplaced for disposal into the
Yucca Mountain repository.
Well-capture zone means the volume from which a well pumping at a
defined rate is withdrawing water from an aquifer. The dimensions of
the well-capture zone are determined by the pumping rate in combination
with aquifer characteristics assumed for calculations, such as
hydraulic conductivity, gradient, and the screened interval.
Yucca Mountain disposal system means the combination of underground
engineered and natural barriers within the controlled area that
prevents or substantially reduces releases from the waste.
Sec. 197.13 How is subpart B implemented?
The NRC implements this subpart B. The DOE must demonstrate to NRC
that there is a reasonable expectation of compliance with this subpart
before NRC may issue a license. In the case of the specific numerical
requirements in Sec. 197.20 of this subpart, and if performance
assessment is used to demonstrate compliance with the specific
numerical requirements in Secs. 197.25 and 197.30 of this subpart, NRC
will determine compliance based upon the mean of the distribution of
projected doses of DOE's performance assessments which project the
performance of the Yucca Mountain disposal system for 10,000 years
after disposal.
Sec. 197.14 What is a reasonable expectation?
Reasonable expectation means that NRC is satisfied that compliance
will be achieved based upon the full record before it. Characteristics
of reasonable expectation include that it:
(a) Requires less than absolute proof because absolute proof is
impossible to attain for disposal due to the uncertainty of projecting
long-term performance;
(b) Accounts for the inherently greater uncertainties in making
long-term projections of the performance of the Yucca Mountain disposal
system;
(c) Does not exclude important parameters from assessments and
analyses simply because they are difficult to precisely quantify to a
high degree of confidence; and
(d) Focuses performance assessments and analyses upon the full
range of defensible and reasonable parameter distributions rather than
only upon extreme physical situations and parameter values.
Sec. 197.15 How must DOE take into account the changes that will occur
during the next 10,000 years after disposal?
The DOE should not project changes in society, the biosphere (other
than climate), human biology, or increases or decreases of human
knowledge or technology. In all analyses done to demonstrate compliance
with this part, DOE must assume that all of those factors remain
constant as they are at the time of license application submission to
NRC. However, DOE must
[[Page 32134]]
vary factors related to the geology, hydrology, and climate based upon
cautious, but reasonable assumptions of the changes in these factors
that could affect the Yucca Mountain disposal system over the next
10,000 years.
Individual-Protection Standard
Sec. 197.20 What standard must DOE meet?
The DOE must demonstrate, using performance assessment, that there
is a reasonable expectation that, for 10,000 years following disposal,
the reasonably maximally exposed individual receives no more than an
annual committed effective dose equivalent of 150 microsieverts (15
millirems) from releases from the undisturbed Yucca Mountain disposal
system. The DOE's analysis must include all potential pathways of
radionuclide transport and exposure.
Sec. 197.21 Who is the reasonably maximally exposed individual?
The reasonably maximally exposed individual is a hypothetical
person who meets the following criteria:
(a) Lives in the accessible environment above the highest
concentration of radionuclides in the plume of contamination;
(b) Has a diet and living style representative of the people who
now reside in the Town of Amargosa Valley, Nevada. The DOE must use
projections based upon surveys of the people residing in the Town of
Amargosa Valley, Nevada, to determine their current diets and living
styles and use the mean values of these factors in the assessments
conducted for Secs. 197.20 and 197.25; and
(c) Drinks 2 liters of water per day from wells drilled into the
ground water at the location specified in paragraph (a) of this
section.
Human-Intrusion Standard
Sec. 197.25 What standard must DOE meet?
The DOE must determine the earliest time after disposal that the
waste package would degrade sufficiently that a human intrusion (see
Sec. 197.26) could occur without recognition by the drillers. The DOE
must:
(a) If complete waste package penetration is projected to occur at
or before 10,000 years after disposal:
(1) Demonstrate that there is a reasonable expectation that the
reasonably maximally exposed individual receives no more than an annual
committed effective dose equivalent of 150 microsieverts (15 millirems)
as a result of a human intrusion, at or before 10,000 years after
disposal. The analysis must include all potential environmental
pathways of radionuclide transport and exposure; and
(2) If exposures to the reasonably maximally exposed individual
occur more than 10,000 years after disposal, include the results of the
analysis and its bases in the environmental impact statement for Yucca
Mountain as an indicator of long-term disposal system performance; and
(b) Include the results of the analysis and its bases in the
environmental impact statement for Yucca Mountain as an indicator of
long-term disposal system performance, if the intrusion is not
projected to occur before 10,000 years after disposal.
Sec. 197.26 What are the circumstances of the human intrusion?
For the purposes of the analysis of human intrusion, DOE must make
the following assumptions:
(a) There is a single human intrusion as a result of exploratory
drilling for ground water;
(b) The intruders drill a borehole directly through a degraded
waste package into the uppermost aquifer underlying the Yucca Mountain
repository;
(c) The drillers use the common techniques and practices that are
currently employed in exploratory drilling for ground water in the
region surrounding Yucca Mountain;
(d) Careful sealing of the borehole does not occur, instead natural
degradation processes gradually modify the borehole;
(e) Only releases of radionuclides that occur as a result of the
intrusion and that are transported through the resulting borehole to
the saturated zone are projected; and
(f) No releases are included which are caused by unlikely natural
processes and events.
Ground Water Protection Standards
Sec. 197.30 What standards must DOE meet?
The DOE must demonstrate that there is a reasonable expectation
that, for 10,000 years of undisturbed performance after disposal,
releases of radionuclides from waste in the Yucca Mountain disposal
system into the accessible environment will not cause the level of
radioactivity in the representative volume of ground water to exceed
the limits in the following Table 1:
Table 1.--Limits on Radionuclides in the Representative Volume
------------------------------------------------------------------------
Radionuclide or type of Is natural
radiation emitted Limit background included?
------------------------------------------------------------------------
Combined radium-226 and 5 picocuries per Yes.
radium-228. liter.
Gross alpha activity 15 picocuries per Yes.
(including radium-226 but liter.
excluding radon and
uranium).
Combined beta and photon 40 microsieverts (4 No.
emitting radionuclides. millirem) per year
to the whole body
or any organ, based
on drinking 2
liters of water per
day from the
representative
volume.
------------------------------------------------------------------------
Sec. 197.31 What is a representative volume?
(a) It is the volume of ground water that would be withdrawn
annually from an aquifer containing less than 10,000 milligrams of
total dissolved solids per liter of water to supply a given water
demand. The DOE must project the concentration of radionuclides
released from the Yucca Mountain disposal system that will be in the
representative volume. The DOE must then use the projected
concentrations to demonstrate a reasonable expectation to NRC that the
Yucca Mountain disposal system complies with Sec. 197.30. The DOE must
make the following assumptions concerning the representative volume:
(1) It includes the highest concentration level in the plume of
contamination in the accessible environment;
(2) Its position and dimensions in the aquifer are determined using
average hydrologic characteristics which have cautious, but reasonable,
values representative of the aquifers along the radionuclide migration
path from the Yucca Mountain repository to the
[[Page 32135]]
accessible environment as determined by site characterization; and
(3) It contains 3,000 acre-feet of water (about 3,714,450,000
liters or 977,486,000 gallons).
(b) The DOE must use one of two alternative methods for determining
the dimensions of the representative volume. The DOE must propose its
chosen method, and any underlying assumptions, to NRC for approval.
(1) The DOE may calculate the dimensions as a well-capture zone. If
DOE uses this approach, it must assume that the:
(i) Water supply well(s) has (have) characteristics consistent with
public water supply wells in the Town of Amargosa Valley, Nevada, for
example, well-bore size and length of the screened intervals;
(ii) Screened interval(s) include(s) the highest concentration in
the plume of contamination in the accessible environment; and
(iii) Pumping rates and the placement of the well(s) must be set to
produce an annual withdrawal equal to the representative volume and to
tap the highest concentration within the plume of contamination.
(2) The DOE may calculate the dimensions as a slice of the plume.
If DOE uses this approach, it must:
(i) Propose to NRC, for its approval, where the location of the
edge of the plume of contamination occurs. For example, the place where
the concentration of radionuclides reaches 0.1% of the level of the
highest concentration in the accessible environment;
(ii) Assume that the slice of the plume is perpendicular to the
prevalent direction of flow of the aquifer; and
(iii) Assume that the volume of ground water contained within the
slice of the plume equals the representative volume.
Additional Provisions
Sec. 197.35 What other projections must DOE make?
To complement the results of Sec. 197.20, DOE must calculate the
peak dose of the reasonably maximally exposed individual that would
occur after 10,000 years following disposal but within the period of
geologic stability. No regulatory standard applies to the results of
this analysis; however, DOE must include the results and their bases in
the environmental impact statement for Yucca Mountain as an indicator
of long-term disposal system performance.
Sec. 197.36 Are there limits on what DOE must consider in the
performance assessments?
Yes. The DOE's performance assessments shall not include
consideration of very unlikely features, events, or processes, i.e.,
those that are estimated to have less than one chance in 10,000 of
occurring within 10,000 years of disposal. The NRC shall exclude
unlikely features, events, and processes, or sequences of events and
processes from the assessments for the human intrusion and ground water
protection standards. The specific probability of the unlikely
features, events, and processes is to be specified by NRC. In addition,
unless otherwise specified in NRC regulations, DOE's performance
assessments need not evaluate, the impacts resulting from any features,
events, and processes or sequences of events and processes with a
higher chance of occurrence if the results of the performance
assessments would not be changed significantly.
Sec. 197.37 Can EPA amend this rule?
Yes. We can amend this rule by conducting another notice-and-
comment rulemaking. Such a rulemaking must include a public comment
period. Also, we may hold one or more public hearings, if we receive a
written request to do so.
Sec. 197.38 Are The Individual Protection and Ground Water Protection
Standards Severable?
Yes. The individual protection and ground water protection
standards are severable.
[FR Doc. 01-14626 Filed 6-8-01; 2:05 pm]
BILLING CODE 6560-50-P