More detail on these aspects of the 2001 final rule may be found at 66 FR 3207432134, June 13, 2001, and 70 FR 4901949020, August 22, 2005.

B. Legal Challenges to 40 CFR Part 197

Various aspects of our standards were challenged in lawsuits filed with the U.S. Court of Appeals for the District of Columbia Circuit in July 2001. These challenges and the Court's subsequent ruling are described briefly here, emphasizing the aspects leading to today's final rule, and in more detail in the preamble to the proposed rule (70 FR 49014, August 22, 2005).

The State of Nevada, the Natural Resources Defense Council (NRDC), and several other petitioners challenged various aspects of our final standards on the grounds that they were insufficiently protective and had not been adequately justified. The focus of this challenge was the 10,000year compliance period. Nevada and NRDC claimed that EPA's promulgation of numerical standards that applied for 10,000 years after disposal violated the EnPA because such standards were not ``based upon and consistent with'' the findings and recommendations of the NAS. NAS recommended standards that would apply to the time of maximum risk, within the limits imposed by the longterm geologic stability of the site, and stated that there is ``no scientific basis for limiting the time period of the individualrisk standard to 10,000 years or any other value.'' (NAS Report p. 55) The Nuclear Energy Institute (NEI) challenged the groundwater protection standards as unnecessary to protect public health and safety, contrary to recommendations of the NAS, and outside our authority under the EnPA.

The DC Circuit Court's July 9, 2004 decision dismissed NEI's challenge, and all of the challenges by Nevada and NRDC, except one. On the question of EPA's 10,000year compliance period, the Court upheld the challenge, ruling that EPA's action was not ``based upon and consistent with'' the NAS Report, and that EPA had not sufficiently justified on policy grounds its decision to apply compliance standards only to the first 10,000 years after disposal. Nuclear Energy Institute v. Environmental Protection Agency, 373 F.3d 1251 (D.C. Cir. 2004) (NEI ).

The Court concluded that ``we vacate 40 CFR part 197 to the extent that it incorporates a 10,000year compliance period * * *.'' (Id. at 1315) The Court did not address the protectiveness of the 150 [mu]Sv/yr (15 mrem/yr) dose standard applied over the 10,000year compliance period, nor was the protectiveness of the 15 mrem/yr standard challenged. It ruled only that the compliance period was not consistent with or based upon the NAS findings and recommendations and, therefore, was contrary to the plain language of the EnPA.

As the Court noted, NAS stated that it had found ``no scientific basis for limiting the time period of the individualrisk standard to 10,000 years or any other value,'' and that ``compliance assessment is feasible * * * on the time scale of the longterm stability of the fundamental geologic regimea time scale that is on the order of 10⁶ years at Yucca Mountain.'' As a result, and given that ``at least some potentially important exposures might not occur until after several hundred thousand years * * * we recommend that compliance assessment be conducted for the time when the greatest risk occurs.'' (NAS Report pp. 67) Today's action addresses this recommendation and the DC Circuit ruling.
II. Summary of Proposed Amendments to 40 CFR Part 197 and Public Comments

The primary goal of our proposal issued in 2005 was to gather public comment on the appropriate response to the Court decision and NAS recommendation to assess compliance at the time of maximum dose (risk). Therefore, our proposed amendments centered on extending the compliance period to capture the peak projected dose from the Yucca Mountain disposal system ``within the limits imposed by the longterm stability of the geologic environment.'' (NAS Report p. 2) Of course, establishing a radiological protection standard to apply at the time of peak dose is a uniquely challenging task. Only a small number of countries have established standards of any kind for the geologic disposal of SNF and HLW. Of these, only Switzerland has established a quantitative standard applicable for as long as 1 million years, although we are aware that other regulatory bodies outside the U.S. are contemplating the need to establish some type of regulation addressing these extremely long time frames. Comments received in the course of this rulemaking have been helpful given the extraordinary technical complexity of this task.
[[Page 61260]]

A. How Did We Propose To Amend Our 2001 Standards?

We considered carefully the language and reasoning of the Court's decision in revising our 2001 standards. As originally promulgated in 2001, 40 CFR part 197 contained four sets of standards against which compliance would be assessed. The storage standard applies to exposures of the general public during the operational period, when waste is received at the Yucca Mountain site, handled in preparation for emplacement in the repository, emplaced in the repository, and stored in the repository until final closure. The three disposal standards apply to releases of radionuclides from the disposal system after final closure, and include an individualprotection standard, a human intrusion standard, and a set of groundwater protection standards.

The Court's ruling vacated only one aspect of 40 CFR part 197: The 10,000year compliance period applicable to the disposal standards. Therefore, the storage standard, which is applicable only for the period before disposal, is not affected by the ruling. Further, the Court recognized that the groundwater protection standards were issued as an expression of EPA's overall groundwater protection policies and were not among the standards addressed by the NAS, either in form or purpose (``NAS treated the complianceperiod and groundwater issues quite differently * * * NAS made no `finding' or `recommendation' that EPA's regulation could fail to be `based upon and consistent with' '' (NEI, 373 F.3d at 1282)). Therefore, we concluded that the Court's vacature of the 10,000year compliance period, which was explicitly tied to recommendations concerning the individualprotection standard, does not extend to the groundwater provisions. As a result, we did not propose to amend the groundwater protection standards. Nothing in today's final rule affects those standards.

We proposed to revise only the individualprotection and human intrusion standards, along with certain supporting provisions related to the way DOE must consider features, events, and processes (FEPs) in its compliance analyses (70 FR 49014, August 22, 2005). In addition, we proposed to adopt updated scientific factors for calculating doses to show compliance with the storage, individualprotection, and human intrusion standards. We requested comments only on those aspects of the individualprotection and humanintrusion standards which were to be amended. Specifically, we proposed to:

Of great concern in extending the compliance period to 1 million years is the increasing uncertainty associated with numerical projections of radionuclide releases from the Yucca Mountain disposal system and subsequent exposures incurred by the Reasonably Maximally Exposed Individual (RMEI). This uncertainty affects not only the projections themselves, but also the interpretation of the results. There is general agreement in the international community that dose projections over periods as long as 1 million years cannot be viewed in the same context or with the same confidence as projections for periods as ``short'' as 10,000 years. As a result, the nature of regulatory decisionmaking fundamentally changes when faced with the prospect of compliance projections for the next 1 million years. International guidance from the International Atomic Energy Agency (IAEA) and Nuclear Energy Agency (NEA), as well as geologic disposal programs in other countries, recognize this difficulty and accommodate it by viewing longerterm projections in a more qualitative manner, to be balanced and supplemented by other considerations that would provide confidence in the longterm safety of the disposal system. In effect, numerical dose projections are given less weight in decisionmaking at longer times.\2\ Such approaches discourage comparison of projections against a strict compliance limit.
\2\ For example, the ICRP's most recent recommendations note that ``both the individual doses and the size of the exposed population become increasingly uncertain as time increases. The Commission is of the opinion that in the decisionmaking process, owing to the increasing uncertainties, giving less weight to very low doses and to doses received in the distant future could be considered.'' (Publication 103, 2007, Docket No. EPAHQOAR2005 00830423, Paragraph 222)

This uncertainty was the overriding reason for limiting the compliance period to 10,000 years in our 2001 rule. We supplemented that 10,000year compliance period by requiring DOE to continue projections through the time of peak dose, consistent with the approach favored by the international community. However, while we believed this approach was consistent with the NAS recommendation to assess compliance at the time of maximum dose (risk) and the committee's acknowledgment that policy considerations would also play a role in determining the compliance period, the Court concluded that it was inconsistent with the NAS recommendation. We concluded that the most direct way to address the Court's ruling would be to establish a numeric compliance standard for the time of peak dose, within the period of geologic stability at Yucca Mountain, which NAS judged to be ``on the order of one million years.'' (NAS Report p. 2)

In establishing our final standards, we have considered that the level of uncertainty increases as the time period covered by DOE's performance
[[Page 61261]]
assessment increases.\3\ Therefore, it is reasonable for us to consider how the compliance standard itself might also need to change. Specifically, we do not believe that extending the 10,000year individualprotection standard of 15 mrem/yr to apply for 1 million years adequately accounts for the considerations outlined above or represents a reasonable test of the disposal system (more extensive discussion of uncertainty in performance assessments is in section III.A.4 of this document, ``How Did We Consider Uncertainty and Reasonable Expectation?''); see also 66 FR 32098. We turned back to the international technical literature for advice regarding appropriate points of comparison for doses projected over hundreds of thousands of years. A number of sources suggested that natural sources of radioactivity would provide an appropriate benchmark for such comparisons. In exploring this approach further, we found that the variation in background radiation across the United States covered a wide range (from roughly 100 mrem/yr to 1 rem/yr), primarily because of local variation in radon exposures. We chose for our proposal a level of 350 mrem/yr, which is close to a widelycited estimate of 300 mrem/ yr for the national average background radiation exposure (NAS Report Table 21), but specifically represented the difference between estimated background levels in Amargosa Valley and the State of Colorado. This level was proposed for both the individualprotection and humanintrusion standards as offering both a reasonable level of protection and a sound basis for regulatory decisionmaking when exposures are projected to occur hundreds of thousands of years into the future. Selecting such a level would also provide an indication that exposures incurred by the RMEI in the far future from the combination of natural background radiation and releases from the Yucca Mountain disposal system would not exceed exposures incurred by residents of other parts of the country today from natural sources alone. Today's final rule adopts a more stringent standard that is not derived from an analysis of background radiation, as explained in sections III.A.1 (``What is the Peak Dose Standard Between 10,000 and 1 Million Years After Disposal?'') and III.A.5 (``How Did We Consider Background Radiation in Developing The Peak Dose Standard?'') of this document.
\3\ ``We recognize that there are significant uncertainties in the calculations and that these uncertainties increase as the time at which peak risk occurs increases.'' (NAS Report p. 56)

Uncertainty in longterm projections also influenced our proposal. Given the probabilistic nature of performance assessments, it is possible that some combinations of parameter values will result in very high doses, even if such combinations have an extremely low probability of occurring. Although there may be only a few results that are very high, extreme results have the potential to exert a strong influence on the arithmetic mean, which could make the mean less representative of all performance projections. This possibility may be increased by the introduction of additional, and possible excessive, conservatisms as a way to account for uncertainties. We expressed a preference for a statistical measure that would not be strongly affected by either very high or lowend estimates, believing it appropriate to focus on the ``central tendency'' of the distribution, where the bulk of the results might be expected to be found. We proposed the median of the distribution as being most representative of central tendency. Because it is always located at the point where half the distribution is higher and half lower, the median depends only on the relative nature of the distribution, rather than the absolute calculated values. Given our concerns about specifying a peak dose compliance value against which performance would be judged for a period up to 1 million years, we believed the median might also provide a reasonable test of longterm performance. Today's final rule departs from the proposal by adopting the arithmetic mean as the statistical measure of compliance to be applied at all times, as explained in section III.A.9 of this document (``How Will NRC Judge Compliance?'').

Our consideration of FEPs also was affected to some extent by uncertainty, as well as by conclusions of the NAS committee. In our proposal, the overall probability threshold for inclusion of FEPs remained the same as in the 2001 rule, which we believe provides a very inclusive initial screen that captures both major and minor factors potentially affecting performance. Uncertainty plays a role in the sense that very gradual or infrequent processes and events may begin to influence performance only at times in the hundreds of thousands of years, when the overall uncertainty of assessments is increasing. The additional uncertainty introduced by these slowacting FEPs led us to propose the exclusion of FEPs if they were not significant to the assessments in the initial 10,000 years. We believed this would still provide for robust assessments that would address the factors of most importance over the entire 1 millionyear period. We did consider in our proposal whether significant FEPs might not be captured using this approach. In evaluating whether excluded FEPs might become more probable or more significant after 10,000 years, and therefore should not be eliminated, we identified general corrosion as a FEP that is certain to occur and represents a significant failure mechanism at longer times, even though it is less significant in the initial 10,000 years.

We also consulted the NAS Report for advice on handling longterm FEPs. NAS identified three ``modifiers'' that it believed could reasonably be included in assessments: seismic events, igneous events, and climate change. (NAS Report p. 91) We developed provisions addressing these FEPs that incorporated the views expressed by the NAS. For seismic and igneous events, we proposed that DOE focus its attention on events causing direct damage to the engineered barriers. We took this approach because failure of the engineered barrier system, particularly the waste packages, is the predominant factor in determining the timing and magnitude of the peak dose, and is the overriding uncertainty in assessing performance of the disposal system. To address climate change, we required DOE to focus on the effects of increased water flow through the repository, which is the climatic effect with the most influence on release and transport of radionuclides. We determined that such a focus would provide the basis for a reasonable test of the disposal system, and that climate change beyond 10,000 years could be represented by constant conditions reflecting precipitation levels that differ from current conditions, which eliminates unresolvable speculation regarding the timing, magnitude, and duration of climatic cycles over this time frame. We also directed that NRC establish the exact nature of future climate characteristics to be used in performance assessments. NRC subsequently issued a proposal to specify a range of values for deep percolation into the repository, which DOE would use as another parameter in its probabilistic performance assessments. (70 FR 53313, September 8, 2005)

Finally, we proposed to update the factors used to calculate dose for the storage, individualprotection, and humanintrusion standards. Our generic standards in 40 CFR part 191, and by inference our Yucca Mountain standards in 2001, specified the factors associated with ICRP Publications 26
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and 30 (Docket Nos. EPAHQOAR200500830425 and 0428, respectively). Since we issued 40 CFR part 191, ICRP has modified the models and associated organweighting factors to more accurately calculate dose. See ICRP Publications 60 and 72 (Docket Nos. EPAHQOAR200500830421 and 0427, respectively). We used this newer method in 1999 to develop our Federal Guidance Report 13, ``Cancer Risk Coefficients from Exposure to Radionuclides'' (Docket No. EPAHQOAR200500830072). Where possible, we believe it is appropriate to adopt the latest scientific methods.\4\
\4\ ICRP published its most recent recommendations in
Publication 103, issued in 2007 (Docket No. EPAHQOAR20050083 0423). EPA has not determined the impact of these recommendations on its current dose and risk estimates, but may decide to adopt them in the future. Today's final rule will incorporate the ICRP 60 recommendations as consistent with EPA's current federal guidance; however, we have provided some flexibility for use of newer dosimetry in the future if deemed appropriate by NRC.
C. In Making Our Final Decisions, How Did We Incorporate Public Comments on the Proposed Rule?

Section 801(a)(1) of the EnPA requires us to set public health and safety radiation protection standards for Yucca Mountain by rulemaking. 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 rule.\5\ 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, 39294 (DC 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.)

\5\ 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. EPAHQOAR20050083 0431). 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.

D. What Public Comments Did We Receive?

The public comment period ended November 21, 2005. We received more than 300 individual submittals, although any particular submittal could contain many specific comments. We also received many more submissions as part of mass comment efforts, in which organizations encourage commenters to use prepared texts or comment on specific aspects of the proposal. All, or representative, comments are available electronically through the Federal Document Management System (FDMS), available at http://www.regulations.gov. See the ``General Information'' section of this document for instructions on how to access the electronic docket. Some submittals may be duplicated in FDMS, as a commenter may have used several methods to ensure the comments were received, such as fax, e mail, U.S. mail, or directly through FDMS.

A significant number of comments addressed the proposed peak dose standard of 350 mrem/yr, which would apply between 10,000 and 1 million years. Most commenters opposed our proposal, arguing that it is much higher than any previous standard, is not protective, is not equitable to future generations, and is based on inappropriate use of background radiation data. Many commenters also took issue with our proposal to use the median of the distribution of results as the statistical measure between 10,000 and 1 million years, viewing this measure as inconsistent with NAS recommendations to use the mean. Commenters also viewed the median as too ``lax'' and likely to discount scenarios that would result in high exposures. We also received comment on our proposal concerning the assessment of FEPs beyond 10,000 years, with some comments expressing the opinion that we had inappropriately constrained the analyses, leaving out potentially significant FEPs. Some commenters disagreed with our general premise that uncertainty increases with assessment time and further disagreed that we should take uncertainties into account when considering standards applicable to the far future. These specific comments, and our responses to them, will be discussed in more detail in section III of this document and in the Response to Comments document associated with this action (Docket No. EPAHQOAR200500830431).

Some commenters also questioned our conclusion that extending the compliance period is the appropriate way to respond to the Court ruling. These commenters point out that the Court's opinion could be interpreted to permit us to justify the approach taken in our 2001 standards. They cite statements by the Court such as ``[i]t would have been one thing had EPA taken the Academy's recommendations into account and then tailored a standard that accommodated the agency's policy concerns'' and ``[h]ad EPA begun with the Academy's recommendation to base the compliance period on peak dosage and then made adjustments to accommodate policy considerations not considered by NAS, this might be a very different case'' (NEI, 373 F.3d at 1270 and 1273, respectively) to support the thesis that the Court's judgment was based primarily on the presentation of our case, rather than the substance. In the commenters' view, the Court would have been receptive to our arguments had they been presented differently, and the Court provided a clear ``road map'' to justify keeping our original standards in place. In addition, these and other commenters viewed extending the compliance period to 1 million years as not justifiable either scientifically or as a matter of public policy. We believe that the approach we are taking is the most appropriate way to address the concerns raised by the Court's decision, particularly given the weight accorded by the Court to the NAS technical recommendations concerning the period of geologic stability. As we stated in our proposal, ``it is not clear how EPA's earlier explanation of its policy concerns might be reconciled with NAS's technical recommendation.'' (70 FR 49032) Accordingly, today's final rule implements the NAS technical recommendation with regard to the length of time for the compliance period while still accommodating our policy concerns in the provisions related to the peak dose standard, and FEPs.

We received some comments that suggested we should have provided more or better opportunities for public participation in our decision making process. For example, comments suggested 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 Washington, DC; Las
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Vegas, NV; and Amargosa Valley, NV. We also opened a 60day public comment period and met with key stakeholders before and during that time. In response to requests from stakeholders, we extended the public comment period by 30 days and held an additional public hearing in Las Vegas. We conducted targeted outreach to Native American tribal groups and have fully considered all comments received through December 31, 2005, after the end of the extended public comment period. These measures are in full compliance with the public participation requirements of the Administrative Procedure Act.

Several commenters supported our role in setting standards for Yucca Mountain. Other commenters 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 a 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 also received many general comments, and others addressing topics that are outside the scope of our authority under the EnPA. For example, several commenters simply expressed their support for, or opposition to, the Yucca Mountain repository. Other comments suggested our standards should explicitly consider radiation exposures from all sources because of the site's proximity to the Nevada Test Site (NTS) and other sources of potential contamination. Also, 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. These comments all raise considerations that are outside the scope of our authority and this rulemaking.

Many comments touched on issues related to our authority and standards, but outside the limited scope of this rulemaking. In particular, many comments urged us to extend the groundwater protection limits to the time of peak dose within the 1 millionyear compliance period. Many of these commenters disagreed with our position that the groundwater standards were not the subject of the Court's ruling, and that in fact the Court left us with discretion regarding the content and application of those standards. Others believed that we are obligated to accept comments on this topic, since we were proposing not to change the standards. We stated clearly in our proposal that we were not soliciting, and would not consider, comments on this issue. III. What Final Amendments Are We Issuing With This Action?

This section describes the provisions of our final rule, our rationale, and our response to public comments on various aspects of our proposal. Today's final rule establishes the dose standards applicable for a period up to 1 million years after disposal, the statistical measures used to determine compliance with those standards, the methods to be used to calculate the dose, and the requirements for including features, events, and processes (FEPs) in the performance assessments.

A. What Dose Standards Will Apply?

Today's final rule includes an individualprotection standard consisting of two parts, which will apply over different time frames. The post10,000year public health protection standard limits the long term peak dose to the RMEI from the Yucca Mountain disposal system to 1 mSv/yr (100 mrem/yr) committed effective dose equivalent (CEDE). This post10,000year (also referred to as the ``peak dose'') standard addresses and responds to the DC Circuit ruling that our 2001 standards, with the compliance period limited to 10,000 years, were inconsistent with the recommendations of the NAS. The post10,000year standard was the focus of our proposal and will apply after 10,000 years through the period of geologic stability, up to 1 million years after disposal. The other part of the individualprotection standard, which will apply over the initial 10,000 years after disposal, consists of the 150 [mu]Sv/yr (15 mrem/yr) CEDE individualprotection standard promulgated in 2001 as 40 CFR 197.20. We believe this approach maintains an appropriate emphasis on the initial condition of the repository and its critical early evolution, including the period when thermal stresses will be most significant.\6\ As the disposal system evolves, today's final rule establishes a peak dose standard for the period up to 1 million years that is responsive to the Court's ruling, consistent with the NAS recommendation to establish a compliance standard for the time of peak risk, and satisfies our statutory mandate to protect public health and safety. The final rule also provides a reasonable test of disposal system performance by appropriately recognizing the relatively more difficult challenge in treating the uncertainties associated with projecting performance to such distant times, and the resulting lessened level of confidence that can be derived from such performance projections.
\6\ We noted in our 2001 rule: ``Focusing upon a 10,000year 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.'' (66 FR 32099)

As we noted in our proposal, there was no legal challenge to, and the Court made no ruling on, the protectiveness of our standards up to 10,000 years. Further, the Court ruled that we must address peak dose, but did not state, and we do not believe intended, that we could not have additional measures to bolster the overall protectiveness of the standard. We believe that promulgating the post10,000year peak dose standard to protect public health and safety while retaining a separate individualprotection standard that focuses attention on the early evolution of the repository in the pre10,000year period enhances the overall protectiveness of our rule and is consistent with the findings and recommendations of the NAS committee. As the Court noted, the EnPA requires that EPA ``establish a set of health and safety standards, at least one of which must include an EDEbased, individual protection standard'' (NEI, 373 F.3d at 1281), but does not restrict us from issuing additional standards. Thus, as long as we address the NAS recommendation regarding peak dose, as we are doing today by issuing the post10,000year standard, we are not precluded from issuing other, complementary, standards to apply for a different compliance period. The Court's concern was whether we had been inconsistent with the NAS recommendation by not extending the period of compliance to capture the peak dose ``within the limits imposed by the longterm stability of the geologic environment.'' (NAS Report p. 2) Today's final rule defines the period of geologic stability for purposes of compliance as ending at 1 million years after disposal. We believe our decision to retain a separate standard applicable for the first 10,000 years after disposal during this period, along with ``at least one * * * EDEbased, individual protection standard'' applying to the peak dose during the period of geologic
[[Page 61264]]
stability between 10,000 years and 1 million years, protects public health and safety pursuant to the EnPA, complies with the Court's decision, falls well within our policy discretion and is supported by scientific considerations concerning the impact of uncertainties in projecting doses over extremely long time frames, as discussed in Section III.A.4 of this document (``How Did We Consider Uncertainty and Reasonable Expectation?'').

The NAS Report recognized the possible outcome of a rulemaking establishing separate standards that apply over different time periods. As discussed in more detail in Section III.A.6 (``How Does Our Rule Protect Future Generations?''), the committee contrasted an approach in which ``a healthbased risk standard could be specified to apply uniformly across time and generations'' with ``some other expression of the principle of intergenerational equity'' to be determined by ``social judgment.'' (NAS Report pp. 5657) The committee also recognized, as we have just explained, that ``the scientific basis for analysis changes with time'' in potentially significant ways as the time to peak dose increases. (NAS Report pp. 3031) We also find it useful to consider the testimony of Mr. Robert Fri, chair of the NAS committee, before the Senate Environment and Public Works Committee on March 1, 2006, in his personal capacity, wherein he pointed out that ``the specification of the time horizon and the selection of the person to be protected are intimately connected.'' As a result, he explained that retaining the RMEI as the receptor (which the NAS committee recognized as more conservative than, but ``broadly consistent'' with, its preferred probabilistic critical group \7\) while at the same time extending the compliance period ``runs the risk of excessive conservatism,'' potentially putting the rule where the ``committee specifically did not want to be.'' He noted that the committee had considered and rejected such an approach. (See NAS Report pp. 100103) Mr. Fri viewed our proposal of a higher dose limit between 10,000 and 1 million years as a way ``to avoid becoming overly conservative.'' Therefore, while he (like the NAS committee itself) offered no opinion on the level of the proposed post10,000year standard, he indicated that, in his opinion, our approach was not in conflict with the committee's intention, and would be closer to the committee's overall goal than would applying the 15 mrem/yr standard to the 1 millionyear compliance period. He concluded by stating ``the committee recognized that EPA properly had considerable discretion in applying policy considerations outside the scope of our study to the development of the health standard for Yucca Mountain.'' (See generally NAS Report p. 3) See the hearing transcript at Docket No. EPAHQOAR200500830380 and Mr. Fri's prepared testimony at Docket No. EPAHQOAR200500830402. We believe the decision to establish two compliance standards falls well within our policy discretion and in that context the 10,000year individualprotection standard is analogous to our groundwater protection standards, which were also not addressed by NAS recommendations.
\7\ In discussing an alternative subsistencefarmer receptor, the committee noted that ``it makes the most conservative assumption that wherever and whenever the maximum concentration of
radionuclides occurs in a ground water plume accessible from the surface, a farmer will be there to access it.'' (NAS Report p. 102) We have defined the RMEI to incorporate this same assumption. 1. What Is the Peak Dose Standard Between 10,000 and 1 Million Years After Disposal?

In establishing a public health and safety standard applicable at the time of peak dose, as required by the EnPA and recommended by the NAS, and after considering public comments on the issue, today's final rule adopts a more stringent standard than the proposed 3.5 mSv/yr (350 mrem/yr) standard. Specifically, we are today establishing an individualprotection standard of 1 mSv/yr (100 mrem/yr) to apply beyond 10,000 years and up to 1 million years after disposal.

As discussed in more detail later in this section, NAS expressly refrained from recommending any specific dose or risk limit for the compliance standard, but instead described ``the spectrum of regulations already promulgated that imply a level of risk, all of which are consistent with recommendations from authoritative radiation protection bodies'' for EPA's consideration. (NAS Report p. 49) Further, while NAS stated that a single standard ``could be specified to apply uniformly over time and generations,'' it also recognized that other approaches are possible as ``a matter for social judgment.'' (NAS Report pp. 5657) NAS also recognized that the level of protection was a matter best left to EPA to establish through rulemaking: ``We do not directly recommend a level of acceptable risk.'' (NAS Report p. 49) NAS further noted that, while ``there is a considerable body of analysis and informed judgment from which to draw in formulating a standard for the proposed Yucca Mountain repository,'' ``EPA's process for setting the Yucca Mountain standard is presumably not bound by this experience.'' (NAS Report p. 39) Thus, the NAS Report contains no finding or recommendation as to the dose limit at the time of peak dose in our Yucca Mountain standards.

In selecting this final standard, we started with a range of annual fatal cancer risk (10⁵ to 10⁶) that encompassed the 15 mrem/yr standard established in 2001 for the initial 10,000 years after disposal. We also considered the ``starting range'' identified by NAS in determining the appropriate level for the individualprotection standard to apply in the time period beyond 10,000 years. (NAS Report p. 49 and Tables 23 and 24) For the reasons discussed below, we determined that it would not be reasonable to apply a standard within that starting range for the entire millionyear compliance period. Rather, we identified dose levels that are protective of public health and safety and that reasonably accommodate our policy concerns regarding the implementation of a compliance standard for 1 million years. For the same reasons, the Agency has determined that it is not reasonable to apply its traditional risk management policies when establishing a compliance standard applicable for periods beyond 10,000 years and up to 1 million years (see section III.A.3, ``How Do Our Standards Protect Public Health and Safety?''). EPA does not believe it is realistic to demand that projections for such complex systems over this far future time frame be readily distinguishable at the level of incremental risk customarily addressed by the Agency in situations where results can be confirmed, modeling is utilized on a more limited scale, or institutional controls are more applicable.

In selecting 100 mrem/yr as the peak dose standard for the period beyond 10,000 years, we took particular note of the NAS's discussion of that dose level: ``Consistent with the current understanding of the related consequences, ICRP, NCRP, IAEA, UNSCEAR, and others have recommended that radiation doses above background levels to members of the public not exceed 1 mSv/yr (100 mrem/yr) effective dose for continuous or frequent exposure from radiation sources other than medical exposures. Countries that have considered national radiation protection standards in this area have endorsed the ICRP recommendation of 1 mSv per year radiation dose limit above natural background radiation for members of
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the public.'' (NAS Report pp. 4041) We also note that the 100 mrem/yr level is included in the range of regulations offered by NAS for EPA's consideration. (NAS Report Table 23)

Therefore, as we discussed in our proposal, a dose level of 100 mrem/yr level is wellestablished as protective of public health under current dose limits, and, as such, represents a robust public health protection standard in the extreme far future. (70 FR 49040) As noted by NAS, international organizations such as ICRP, IAEA, and NEA recommend its use as an overall public dose limit in planning for situations where exposures may be reasonably expected to occur. Although it had used the concept of public dose limits previously, ICRP first described its recommendations for a comprehensive system of radiation protection in Publication 60 (``1990 Recommendations of the ICRP'') (Docket No. EPAHQOAR200500830421). ICRP considered two referents in recommending a public dose limit: health detriment and ``variation in the existing level of dose from natural sources.'' ICRP concluded that estimates of hea

FOR FURTHER INFORMATION CONTACT Ray Clark, Office of Radiation and Indoor Air, Radiation Protection Division (6608J), U.S. Environmental Protection Agency, 1200 Pennsylvania Ave., NW., Washington, DC 20460 0001; telephone number: 2023439360; fax number: 2023432305; email address: clark.ray@epa.gov.