The Nuclear Waste Policy Act of 1982 (NWPA, P.L. 97-425 ) defined the basic roles of the three federal agencies with responsibility over the selection, licensing, and health and safety of the first U.S. high-level radioactive waste disposal site. The Environmental Protection Agency's (EPA's) role is to establish the public health and safety standards for high-level waste disposal; the Nuclear Regulatory Commission (NRC) licenses and regulates the repository, using EPA's standards as the compliance measure; the Department of Energy (DOE) constructs and operates the repository. The Energy Policy Act (EPAct) of 1992 ( P.L. 102-486 ) maintained these roles, but established new requirements specific to the Yucca Mountain, Nevada site. EPA was directed to issue new environmental standards specifically for the Yucca Mountain repository site. General EPA repository standards previously issued and subsequently revised no longer could be applied to Yucca Mountain. DOE and NRC had raised concerns that some of EPA's general standards might have been impossible or impractical to meet at Yucca Mountain. EPAct also required EPA to contract with the National Academy of Sciences (NAS) for a technical study of "reasonable" standards that might apply to the Yucca Mountain site, and required that any standard set by EPA be "based upon and consistent with" the National Academy's findings and recommendations. The resulting study was issued August 1, 1995. The NAS study recommended that the Yucca Mountain environmental standards establish a limit on risk to individuals near the repository, rather than setting specific limits for the releases of radioactive material or on radioactive doses, as under previous EPA standards. The NAS study also examined the potential for human intrusion into the repository and found no scientific basis for predicting human behavior thousands of years into the future. On June 13, 2001, EPA issued a final Health and Safety Standard for the Yucca Mountain High-Level Radioactive Waste Repository. The regulation established a 15 millirem/year (mrem/yr) exposure standard for the facility that applied for 10,000 years based on projected doses to a Reasonably Maximally Exposed Individual (RMEI) from the undisturbed repository as well as circumstances of human intrusion. The rule established a separate groundwater protection standard equivalent to today's drinking water standards also applicable for 10,000 years. EPA's rule also required DOE to continue RMEI projections beyond 10,000 years to the time of peak dose, but declined to set numerical standards beyond the 10,000-year time frame. EPA calculated that its standard would result in an annual risk of fatal cancer for the RMEI of seven chances in a million. The nuclear industry criticized the EPA proposal as being unnecessarily stringent, particularly the groundwater standard. On the other hand, environmental groups contended that the 10,000-year standard proposed by EPA was too short, because DOE had projected that radioactive releases from the repository would peak after about 400,000 years. Despite DOE's opposition to the EPA standards, the Department's site suitability evaluation determined that the Yucca Mountain site would be able to meet them. NRC revised its repository regulations on September 7, 2001, to conform to the EPA standards. Various aspects of the 2001 regulation were challenged in lawsuits filed with the U.S. Court of Appeals for the District of Columbia in July 2001. The State of Nevada, the Natural Resources Defense Council (NRDC), and the Nuclear Energy Institute (NEI) each challenged different aspects of the rule. Nevada and the NRDC challenged the rule on the grounds that it was not sufficiently protective and had not been adequately justified, focusing on the 10,000-year time period. NEI challenged the groundwater protections as unnecessary, contrary to recommendations of the NAS, and outside the agency's authority under the EPAct. On July 9, 2004, the U.S. Circuit Court of Appeals for the District of Columbia dismissed the NEI groundwater challenge, and all but one of the challenges by Nevada and NRDC. On the issue of the 10,000-year compliance standard, the Court upheld the challenge and vacated the 2001 standard, ruling that the 10,000-year compliance time frame was not "based upon and consistent with" the NAS finding that "there is no scientific basis for limiting the time period to 10,000 years or any other value ..." and their recommendation "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." In response to the court decision, EPA proposed a new version of the Yucca Mountain standard on August 22, 2005. The proposal retained the dose limits of the 2001 standard for the first 10,000 years but proposed a higher annual dose of 350 mrem/yr for the period of 10,000 years through 1 million years. EPA based the standard on variations in natural background radiation between Colorado and Amargosa Valley, Nevada, arguing that it was reasonable to use natural background as a benchmark for exposure when the compliance point was up to 1 million years in the future. The agency also argued that it was reasonable to consider protective exposures no greater than residents of Colorado experience today from natural background radiation alone. EPA also proposed basing the post-10,000-year standard on the median dose, rather than the mean, an approach that some argued would make it easier for DOE to meet the standard. Nevada state officials called EPA's proposed standard far too lenient and charged that it was "unlawful and arbitrary." Comments submitted to the public docket both praised and attacked EPA's proposal. Those in favor of the proposal focused on the unprecedented time frames and the reasonableness of drawing comparisons with natural levels of radioactivity; opponents claimed that the proposal violated EPA's basic principles of public health protection and was designed specifically to allow the facility to be built. In its final standard, EPA has established a dual compliance standard: 15 mrem/yr with a separate groundwater protection standard for the first 10,000 years, and 100 mrem/yr for the period from 10,000 up to 1 million years. The concept of a dual standard was introduced in EPA's August 2005 proposal and has remained controversial. EPA maintains that the dual approach provides a reasonable measure of the disposal system's performance that appropriately combines protectiveness with recognition of the limitations of modeling in predicting the evolution of the system over hundreds of thousands of years. Critics argue that the dual standard explicitly condones a lesser level of protection for future generations and is designed to make it easier for the Department of Energy to ultimately meet the standard. EPA also specified that the mean of the distribution of results should be used to demonstrate compliance with the standard at all times. This is a departure from the proposal, in which EPA specified the mean during the pre-10,000-year period, but chose the median for the post-10,000-year period. At the time, EPA stated its belief that the median better represented the central tendency of the likely distribution of results in DOE's performance assessment. In the final rule, EPA returned to the mean for both time periods, citing public comments that pointed to a recommendation in the NAS report that the mean be used as the basis for any standard. In choosing 100 mrem/yr as the final standard for the 10,000 to 1 million-year time period, EPA abandoned the controversial "variations in natural background" approach it proposed in 2005. That approach would have set the standard based on comparisons of background levels between Amargosa Valley (the closest populated area to the proposed facility) and another geographical location in the United States. For the proposal, EPA chose Colorado. Their concept was that, so long as the hypothetical future residents of Amargosa Valley did not receive more radiation exposure in the far future than residents of Colorado receive from natural background radiation today, the exposure could be considered protective. EPA cited the unprecedented time period as one justification for its approach and referenced international precedent for using natural background levels as a "reasonable and logical reference point." In the final standard, EPA changed its approach. EPA states that it was not possible to reliably estimate levels of background exposure in a way that was relevant to making the kinds of comparisons between locations it envisioned in the proposal. EPA concluded that "comparing background radiation estimates from specific locations does not provide a clear or sufficient basis for a regulatory standard applicable to the Yucca Mountain disposal system." The agency did not abandon comparisons to background completely. The final rule notes that the 100 mrem/yr level "reasonably comports" with background estimates in Amargosa Valley, but relies more heavily on arguments that 100 mrem/yr is directly protective of public health. EPA cites both national and international standards in support of its decision, and points to existing domestic regulations, which each use 100 mrem/yr, as well as the National Council on Radiological Protection (NCRP) endorsement of the 100 mrem/yr level incorporated in the international system of radiation protection. EPA went on to state that it "acknowledges and concurs with the broad consensus in the protectiveness of the 100 mrem/yr level and, furthermore, considers it especially suitable for application to the extreme far future, when planning for and protecting public exposures is much less certain." Comments submitted to the public docket both praised and attacked EPA's 2005 proposal. Those in favor of the proposal emphasized the unprecedented time frame and the reasonableness of drawing comparisons with natural levels of radioactivity at such long time frames. Supporters of the repository see EPA's regulation as the last tool NRC needs to complete its technical review. Opponents raised issues with the 2005 proposal in three key areas: 1) they claimed that the proposal was not protective of public health, 2) that it was legally indefensible; and 3) it was designed specifically to allow the facility to be built. Nevada state officials called EPA's proposed standard far too lenient and charged that it was "unlawful and arbitrary."