[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.

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    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

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``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