KEY AGENCY COMMENTS AND RESPONSES

1. U.S. Department of the Interior
   1. Comments on the Draft EIS - Comment Document 1969
      
   2. Comments on the Supplement to the Draft EIS – Comment Document 10066

2. U.S. Environmental Protection Agency
   1. Comments on the Draft EIS - Comment Document 1632
      
   2. Comments on the Supplement to the Draft EIS – Comment Document 10231

3. U.S. Nuclear Regulatory Commission
   1. Comments on the Draft EIS - Comment Document 1898
      
   2. Comments on the Supplement to the Draft EIS – Comment Document 10248

1. On December 17, 1998, DOE requested a species list from the U.S. Fish and Wildlife Service and initiated consultation to evaluate whether the Proposed Action could affect the threatened desert tortoise or protected species at Ash Meadows, Devils Hole, or along transportation corridors. In a Biological Assessment submitted to the U.S. Fish and Wildlife Service on April 24, 2000, DOE concluded that the Proposed Action would not affect the listed species in the Ash Meadows or Devils Hole areas because these areas are in a different regional groundwater sub-basin from Yucca Mountain. The Fish and Wildlife Service concurred with this conclusion during consultation on the effects of repository construction, operation and monitoring, and closure on threatened and endangered species (see the Fish and Wildlife Service Final Biological Opinion in Appendix O of the EIS). Furthermore, there are no playas in the vicinity of Yucca Mountain where surface water could accumulate and attract migratory birds. The playa at Frenchman Flat is located approximately 35 kilometers (22 miles) east of Yucca Mountain and would be unaffected by the Proposed Action.
   DOE did determine that the Proposed Action could affect the desert tortoise and consequently has proposed mitigation measures to minimize effects. If the Secretary of Energy recommends approval of the Yucca Mountain site to the President, and Yucca Mountain is ultimately authorized for the disposal of spent nuclear fuel and high-level radioactive waste, DOE would implement all reasonable and prudent mitigation measures and comply with the terms and conditions of the Final Biological Opinion from the U.S. Fish and Wildlife Service. See Appendix O of the EIS for the Opinion.
   The Desert National Wildlife Range, approximately 48 kilometers (30 miles) east of the repository, would be unaffected by the Proposed Action unless the Valley Modified Corridor, which could be on, or adjacent to, the southern boundary of the Range, was selected. With regard to the transportation implementing alternatives in the State of Nevada, DOE believes this EIS is sufficient for the determination of the relative merits and a selection decision among the various corridors and shipment modes discussed in the EIS, but acknowledges additional environmental review would be required to assess the potential impacts of specific route alignment within a corridor. DOE would continue discussions with the U.S. Fish and Wildlife Service pursuant to Section 7 of the Endangered Species Act, as amended, on any corridor or alignment within a corridor determined to require further environmental review and would implement the terms and conditions of any subsequent Biological Opinions.

2. DOE believes that the comments expressed by the U.S. Fish and Wildlife Service concerning risks to wildlife resources are addressed in the EIS. Section 4.1.8 of the EIS discusses the potential for catastrophic events (including earthquakes) occurring at the Yucca Mountain Repository during construction, operation and monitoring, and closure of the repository, and the consequences of these events. As described in Section 4.1.3, flooding would be unlikely to release contaminants because the design of critical surface facilities would withstand the most severe reasonably possible floods. Chapter 5 discusses impacts from the long-term performance of the repository. The evaluations included impacts from volcanic (Section 5.7.2) and seismic disturbances, as well as impacts from the slow degradation of waste packages over thousands of years. This slow degradation has the highest potential to spread contaminants as they are leached into the groundwater beneath Yucca Mountain.
   Section 3.1.4.2.1 of the EIS shows that the flow path of groundwater from Yucca Mountain extends to Jackass Flats and the Amargosa Desert, and continues southward to the primary point of discharge at Franklin Lake Playa in Alkali Flat. The EIS recognizes that some groundwater reaching this far might bypass Franklin Lake Playa and continue into Death Valley. The EIS also recognizes that a fraction of the groundwater that reaches the Amargosa Desert might flow through the southeastern end of the Funeral Mountains to springs in the Furnace Creek Wash in Death Valley National Park. The springs in Ash Meadows (including Devils Hole) are not along the groundwater flow path from Yucca Mountain. As described in Section 3.1.4.2.1, groundwater beneath Yucca Mountain flows to the Amargosa Desert but does not discharge in Ash Meadows. From Ash Meadows to the low axis (Carson Slough) of the Amargosa Desert, the groundwater table declines about 64 meters (210 feet), indicating that the groundwater flows from Ash Meadows toward the Amargosa Desert, not the other way around.
   Chapter 5 of the EIS does not specifically address the risks to people and natural resources in Death Valley National Park from the use and consumption of groundwater. However, it clearly indicates that risks would decrease with increased distance from the repository. Accordingly, impacts to the Park, because it is far from Yucca Mountain, would be negligible.
   In Section 5.3 of the EIS, DOE concluded that the predicted long-term levels of radionuclide concentrations in groundwater and the resulting dose levels at the predicted discharge area in Amargosa Valley would be low. As a consequence, DOE does not expect that the dose rates to plants and animals would cause measurable detrimental effects in populations of any species because the rates would be less than 100 millirad per day. The International Atomic Energy Agency concluded that chronic dose rates of much less than 100 millirad per day are unlikely to cause measurable detrimental effects in populations of even the more radiosensitive species in terrestrial ecosystems (DIRS 103277-IAEA 1992). The DOE interim technical standard, A Graded Approach for Evaluating Dose to Aquatic and Terrestrial Biota, which the Department made available for interim use on July 20, 2000, contains more information about potential effects of radiation on biota.
   The comment also refers to a recent laboratory finding that a species of plutonium oxide has a higher solubility than the species most often considered to be the normal oxidized form of the metal (plutonium dioxide) (DIRS 150367-Haschke, Allen, and Morales 2000). Scientists working on the Yucca Mountain Project are aware of this finding. DOE believes that the finding is within the range of conservatisms built into the plutonium solubility model used to model the long-term performance of the repository.

3. DOE agrees that a release of hazardous materials during accidents involving spent nuclear fuel or high-level radioactive waste would be very unlikely. With regard to the potential impacts to wildlife resources, a transportation accident could result in the dispersal or death of individual members of a species within a localized area but would be unlikely to have long-term detrimental effects upon a population as a whole.

4. This comment accurately summarizes some of the issues involving the potential cumulative impacts associated with the Proposed Action and some of the ongoing evaluations being conducted by the Department and other agencies, including the U.S. Fish and Wildlife Service. In preparing Chapter 8 of the EIS, the Department reviewed many past, present, and reasonably foreseeable future actions to determine where there was potential for cumulative impacts. Chapter 8 of the EIS describes both the short-term and long-term impacts of the proposed repository, along with transportation and manufacturing cumulative impacts.

5. The shipping casks used to transport these spent nuclear fuel and high-level radioactive waste are massive and tough with design features that comply with strict regulatory requirements that ensure the casks perform their safety functions even when damaged. Numerous tests and extensive analyses have demonstrated that casks would provide containment and shielding even under the most severe kinds of accidents. In addition, since the publication of the Draft EIS, the Nuclear Regulatory Commission published Reexamination of Spent Fuel Shipment Risk Estimates (DIRS 152476-Sprung et al. 2000). Based on the revised analyses, DOE has concluded in the EIS that casks would continue to contain spent nuclear fuel fully in more than 99.99 percent of all accidents (of the thousands of shipments over the last 30 years, none has resulted in an injury due to release of radioactive materials). This means that of the approximately 53,000 truck shipments, there would be an estimated 66 accidents, each having less than a 0.01-percent chance that radioactive materials would be released. The chance of a rail accident that would cause a release from a cask would be even less. The corresponding chance that such an accident would occur in any particular locale would be extremely low. Section J.1.4.2.1 of the EIS presents consequences for accidents that could release radioactive materials.
   With regard to the containment or control of accident events, DOE would rely on a number of actions including the training of public safety officials and the implementation of safeguards and security plans. Section 180(c) of the NWPA requires DOE to provide technical assistance and funds to states for training public safety officials and appropriate units of local government and tribes through whose jurisdictions DOE shipments would pass. DOE anticipates financial and technical assistance to eligible jurisdictions to begin at least 4 years before the commencement of shipments to the repository.
   Concerning safeguards and security plans, DOE would comply with all requirements of 10 CFR Part 73, including preshipment planning, communications, armed escorts and tamper-indicating devices on shipping casks. Regarding shipment routes, pursuant to U.S. Department of Transportation regulations, 49 CFR 397.101 and DIRS 154766-NRC (1980), added protection would be afforded by the selection of routes which exhibit certain criteria including the likelihood of swift law enforcement response, avoidance of tactically disadvantageous locations such as long tunnels or bridges spanning heavily populated areas, and flexibility to adjust schedules to accommodate unexpected situations.

6. Transportation shipments would be protected from sabotage. The Nuclear Regulatory Commission has developed a set of rules specifically aimed at protecting the public from harm that could result from sabotage of spent nuclear fuel casks. Known as physical protection or safeguards regulations (10 CFR 73.37), these security rules are distinguished from other regulations that deal with issues of safety affecting the environment and public health. The objectives of the safeguards regulations are to minimize the possibility of sabotage and facilitate recovery of spent nuclear fuel shipments that could come under control of unauthorized persons.
   Cask safety features that provide containment, shielding, and thermal protection also provide protection against sabotage. The casks would be massive. The spent nuclear fuel in a cask would typically be only about 10 percent of the gross weight; the remaining 90 percent would be shielding and structure.
   Although it is not possible to predict the types of potential sabotage events with certainty, DOE has examined various accident scenarios, which can provide a sense of the consequences that could occur in such events. In addition, DOE has specifically analyzed the potential consequences of sabotage against a truck or rail cask. The results of this analysis indicate that the maximally exposed individual would increase the risk of incurring a fatal cancer from approximately 23 percent (the current risk of incurring a fatal cancer from all other causes) to about 29 percent. The same event could cause 48 latent cancer fatalities in an assumed population of a large urban area.
   Because of the attacks on September 11, 2001, the Department and other agencies are reexamining the protections built into their physical security and safeguards systems for transportation shipments. As dictated by results of this reexamination, DOE would modify its methods and systems as appropriate.
   In response to public comments, DOE has included a discussion on the range of potential costs of cleanup following a severe transportation accident in Appendix J of the EIS. This discussion reviews calculations of land area contaminated and costs for cleanup presented in past studies, including a report used in the 1986 Environmental Assessments (DIRS 154814-Sundquist et al. 1985), and information submitted by the State of Nevada in its comments on the Draft EIS. The information submitted by the State included estimates of cleanup costs as high as $270 billion. Cost data used in the studies reviewed in Section J.1.4.2.5 included data compiled from case studies involving actual cleanup of radioactive materials contamination. Section J.1.4.2.5 discusses environmental restoration after a release of radioactive material.

7. Transportation shipments would be protected from sabotage. The Nuclear Regulatory Commission has developed a set of rules specifically aimed at protecting the public from harm that could result from sabotage of spent nuclear fuel casks. Known as physical protection or safeguards regulations (10 CFR 73.37), these security rules are distinguished from other regulations that deal with issues of safety affecting the environment and public health. The objectives of the safeguards regulations are to minimize the possibility of sabotage and facilitate recovery of spent nuclear fuel shipments that could come under control of unauthorized persons.

8. The interpretation is correct. In the Draft EIS, the maximally exposed individual would receive an estimated dose of 38 to 100 millirem over 70 years. Table 4-35 (Footnote c) and Section 4.1.7.5.3 of the Draft EIS explain this dose. Section 4.1.2 of the EIS discusses the highest potential annual dose would be less than 2 millirem per year.
   Exposure scenarios at reclaimed uranium mines or mills are much different from the potential exposure near the proposed repository at the Yucca Mountain site. The key differences at Yucca Mountain would be the lack of high uranium and uranium decay product source material, lack of tailings with enhanced concentrations of uranium decay chain radionuclides, and the location of the potential public dose receptor at the boundary of the controlled area (15 millirem per 40 CFR Part 197). Further, potential public exposures at Yucca Mountain would be held to a much more rigorous standard than 100 millirem per year. The discussions in Sections 4.1.2 and 4.1.7, along with the supporting information in Section G.2, explain potential public radiation doses.

9. Sections 6.3.1, 6.3.2, and 6.3.3 of the EIS address the potential impacts of Nevada legal-weight truck, heavy-haul truck, and branch rail line implementing alternatives, respectively, including land-use impacts. These sections recognize and describe the impacts related to construction and operation of branch rail lines and developing or upgrading highways, including traffic impacts. Section 6.2.4.2 addresses impacts from accidents, including spills.
   DOE acknowledges that some land-use conflicts could be inevitable during the construction and operation of a transportation corridor for the Yucca Mountain Repository. The implementing alternatives for transportation described in the EIS were based in part on attempts to avoid or minimize potential land-use conflicts.
   DOE has identified mostly rail as its preferred mode of transportation, both nationally and in Nevada. At this time, however, the Department has not identified a preference among the five candidate rail corridors in Nevada. Should the branch rail line implementing alternative be selected and a preferred rail corridor identified, additional engineering and environmental studies would be conducted as a basis for detailed design and for appropriate National Environmental Policy Act reviews. During this process, DOE would initiate consultations with responsible local, State, Federal, and tribal agencies, landowners, and other stakeholders to identify, acquire, and evaluate additional information and develop mitigative actions necessary to minimize potential impacts, including land use.

10. DOE agrees that most of the faulting occurred during this period and Section S.4.1.3 of the EIS Summary has been changed to, "Yucca Mountain is a product of volcanic and seismic activity that occurred 14 million to 11.5 million years ago."

11. DOE has corrected the name of the repository host rock to "Topopah Spring Tuff."

12. DOE agrees that it cannot predicate its selection of the Topopah Spring Tuff for the repository on the lack of proximity to seismically active faults. The Department has changed the statement in the Summary and Section 3.1.3 of the EIS to indicate that it chose the repository emplacement area because of its location away from major faults that could adversely affect the stability of underground openings.

13. The comment is correct that the Solitario Canyon fault is not the only block-bounding fault identified in the EIS. However, DOE did not modify the text of the Summary in order to keep it understandable to a wide range of readers. DOE has, however, clarified the text in Section 3.1.3.2 of the EIS, which also refers readers to numerous reference materials on the subject.

14. The purpose of Section 3.1.3.1 is to provide a broad overview of regional and site geology. The purpose of the subsections that are part of Section 3.1.3.1 is to address specific issues of particular concern or interest to the public (such as faulting and seismic activity) or that are a definite change of topic (for example, mineral and energy resources). DOE agrees that it could put the topics identified in the comment in separately numbered sections, but made an editorial decision not to do so.

15. Although the EIS is concerned with the sedimentary history of the region and sedimentary rock units at Yucca Mountain, the main focus is on those units important for the study of groundwater infiltration, flow, and transport. Table 3-6 is highly generalized and identifies only the Topopah Spring Tuff, the repository host rock, by name. The commenter is referred to other parts of Section 3.1.3 of the EIS that describe the history and stratigraphy of the Yucca Mountain area, and to Table 3-7, which describes the Tertiary rock units at Yucca Mountain in more detail than Table 3-6.

16. DOE has revised the text of Section 3.1.3.1 of the EIS such that the parenthetical explanation "(that is, Paleozoic and Precambrian)" follows the reference to Pre-Cenozoic.

17. This comment is correct. DOE has revised Section 3.1.3.1 of the EIS to include the exposures at Calico Hills and Striped Hills.

18. DOE has revised Section 3.1.3.1 of the EIS to state that volcanic rocks younger than Tertiary age pertain only to the four northeast-trending cinder cones in the center of Crater Flat, dated at about 1 million years old, and the Lathrop Wells basaltic cinder cone, dated at 70,000 to 90,000 years old.

19. DOE has updated the general bedrock geology figure in Section 3.1.3.1 in the EIS as described in the comment to show additional faults in the repository block area. The figure is now consistent with the simplified geologic cross-section figure that follows it.
    This comment suggested that the cross-section line in these figures should be named A-A’, not B-B’. DOE has made this modification.
    DOE provided the upper block label in the figure to help the reader identify the area shown because the EIS discusses other blocks.

20. The maps in Chapter 3 of the EIS depicting fault information are simplified and show only selected faults. However, DOE has added more faults to the general bedrock geology in Section 3.1.3.1 to make it more consistent with the cross-section figure that follows.

21. Section 3.1.3 of the EIS has been changed to indicate that the alluvial deposits on fans and in stream beds includes boulders, cobbles, pebbles, sand, silt and clay; Section 3.1.4.1.2 has been modified to indicate that mud flows may include boulder-size material.

22. DOE has modified the discussion in Section 3.1.3.2 of the EIS. The faults described are well-defined structures; joints, along which there is no appreciable movement, also occur in the rock units mapped at the site. Within the Paintbrush Group (Tiva Canyon, Yucca Mountain, Pah Canyon, and Topopah Spring tuffs), joints have been subdivided into three groups based on how they developed and their approximate time of origin: early cooling joints, later tectonic joints, and joints due to erosional unloading (DIRS 151945-CRWMS M&O 2000). Each group of joints exhibits specific characteristics with respect to joint length, orientation, and connectivity. The cooling and tectonic joints have similar orientations (generally trending north-south), whereas cooling joints include irregularly spaced horizontal joints as well. Joints that developed from erosional unloading are variably oriented but trend predominantly east to west, perpendicular to the cooling and tectonic joints. Tectonic joints occur throughout the Paintbrush Group; cooling joints occur in each of the welded units. In general, the Tiva Canyon tuff and the Topopah Spring tuff have the highest joint frequencies and joint connectivities. The nonwelded Yucca Mountain tuff and the Pah Canyon tuff have the fewest joints. Geologic, geoengineering, and hydrologic aspects of fractures are discussed in detail in the Yucca Mountain Site Description (DIRS 151945-CRWMS M&O 2000). DOE has added to Section 3.1.3.2 of the EIS more information about joints and fractures in the volcanic rock at Yucca Mountain.

23. The text in Section 3.1.3.2 has been modified to indicate that major east-west crustal compression occurred periodically in the Great Basin between about 350 million years ago to about 65 million years ago. This compression moved large sheets of older rock great distances upward and eastward over younger rocks to produce mountains. References to support this discussion include Armstrong (DIRS 101583-1968), Fleck (DIRS 150625-1970), CRWMS M&O (DIRS 100127-1998), and Dunne (DIRS 102861-1986).

24. DOE has updated the subject reference.

25. DOE has clarified this paragraph in Section 3.1.3.2 of the EIS, as suggested by the comment.

26. The comment is correct; text in Section 3.1.3.2 has been revised for clarity. The Solitario Canyon fault is not the only block-bounding fault identified.

27. DOE has reorganized the paragraph in question to discuss the Ghost Dance fault, which occurs in the middle of the repository block, before discussing the northwest-trending faults.

28. The description of faults in Figure 3-9 of the Final EIS has been clarified.

29. DOE has changed the legend on the mapped faults figure in Section 3.1.3.2 to label the arrows in the figure as strike-slip faults.

30. DOE believes that it has made the table in Section 3.1.3.2 of the EIS more accurate by removing the word "late" from the column heading related to Quaternary displacement.

31. During EIS preparation, DOE decided to omit a seismicity map in favor of a simpler presentation. The Department made this decision with the understanding that more detailed seismic information is available in the Yucca Mountain Site Description (DIRS 151945-CRWMS M&O 2000). With regard to showing faults on a seismic map, seismic events do not correlate with mapped surface traces or Quaternary faults, as indicated in Section 3.1.3.3 of the EIS.

32. DOE believes the paragraph is correct as written. The main point of this paragraph is that the strain rate is significantly less than the rate reported by Wernicke et al. (DIRS 103485-1998), which did not account for the coseismic and postseismic effects of the 1992 Little Skull Mountain earthquake.

33. The EIS presents the results of various investigations on mineral and energy resources. DOE considers the likelihood of finding oil or gas to be low in the vicinity of the proposed repository. Drilling of numerous boreholes to depths beyond 1829 meters (6,000 feet) in the area found no indications or shows of oil of gas. Therefore, DOE decided not to include a detailed discussion of mineral and energy resource potential in the EIS, but rather to refer the reader to the numerous references that discuss these issues. This approach is consistent with the regulations of the Council on Environmental Quality [40 CFR Part 1501.7(a)(3)] that direct agencies to identify and eliminate from detailed study those issues which are not significant.

34. DOE, in cooperation with Nye County, has initiated a program (called the Early Warning Drilling Program) to characterize further the saturated zone along possible groundwater pathways from Yucca Mountain, as well as the relationships among the volcanic, alluvial, and carbonate aquifers. Information from the ongoing site characterization program and from the performance confirmation program (if Yucca Mountain is approved for a repository), would be used in conjunction with that of the Early Warning Drilling Program to refine the Department’s understanding of the flow and transport mechanics of the saturated alluvium and valley-fill material south of the proposed repository site, and to update conceptual and numerical models used to estimate waste isolation performance of the repository. When DOE published the Draft EIS, only limited information from the Early Warning Drilling Program was available. Since then, however, this program has gathered additional information (see Section 3.1.4.2.1 of the Final EIS).

35. The EIS describes why the quantity of water moving through the proposed repository would be small compared to other sources of recharge in the region and to the amount of groundwater moving through the area. DOE believes that presenting ranges of infiltration rates in this case would add unnecessary complexity. More information, including temporal and spatial ranges of net infiltration, is in the Water Source and Movement discussion in Section 3.1.4.2.2 of the EIS.
    DOE disagrees that description of an average net infiltration over the area of the repository is misleading. (It should be noted that the EIS now presents a different infiltration estimate due to the results of an updated infiltration study.) The EIS also considers smaller areas of higher and lower infiltration. Section 3.1.4.2.2 identifies infiltration rates over an order of magnitude higher in areas where thin alluvium overlies highly permeable rock. It would be misleading to imply that these higher infiltration rates occur over large areas.
    DOE agrees that it is difficult to predict which fractures or faults would act as highly transmissive zones. However, much has been learned from studies, particularly chlorine-36 studies, that have suggested a correlation between subsurface locations where there is evidence of "fast pathways" (less than 50 years) and physical conditions in the mountain and on the surface. The Water Source and Movement discussion in Section 3.1.4.2.2 describes these correlations.

36. Thank you for your comment.

37. DOE acknowledges and appreciates the offer of technical support from the U.S. Department of the Interior and its individual bureaus on the Yucca Mountain Project monitoring programs. Such cooperation will inevitably increase the knowledge base on the local environment and help ensure minimal impacts of the Proposed Action on regional wildlife and other natural resources.

 

RESPONSES TO U.S. DEPARTMENT OF THE INTERIOR
COMMENTS ON THE SUPPLEMENT TO THE DRAFT EIS
(Comment Document 10066)

1.    Thank you for your reply.

 

 

 

RESPONSES TO U.S. ENVIRONMENTAL PROTECTION AGENCY
COMMENTS ON THE DRAFT EIS
(Comment Document 1632)

1. Thank you for your comment.

2. DOE assumes that the fundamental data referred to in the comment mean such things as aquifer properties, retardation coefficients, hydraulic heads, etc. Such data are detailed in the documents referenced in Appendix I of the EIS.
   Appendix I contains detailed information in support of Chapter 5 of the EIS. As stated in the introduction to Appendix I, the long-term performance analysis was conducted using a TSPA model and supporting data derived from the TSPA models and data that support other Yucca Mountain Project documents. As also stated, the purpose of Appendix I is not to republish the large body of available information but to reference the sources of the information and describe any special additional modeling and data used for the EIS. Some common background material was duplicated as an overview to enhance understanding of the incremental material. Thus, much of the detailed data on saturated zone modeling in this EIS is from the Total System Performance Assessment for the Site Recommendation (DIRS 153246-CRWMS M&O 2000) and the FY 01 Supplemental Science and Performance Analyses (DIRS 155950-BSC 2001), as referenced in the Final EIS.
   The Final EIS discusses the new Environmental Protection Agency standard (40 CFR Part 197).

3. DOE agrees with the Environmental Protection Agency’s assertions regarding future actions should the United States decide to not proceed with construction and operation of a repository at Yucca Mountain. As stated in Section 2.2 of the EIS, if Yucca Mountain was determined to be unsuitable or was not approved by the President or Congress, DOE would prepare a report to Congress. This report, required by the NWPA, would contain DOE recommendations for further action to ensure the safe, permanent disposal of spent-nuclear fuel and high-level radioactive waste, including the need for new legislative authority. Other than this action, the future course that Congress, DOE, and the commercial nuclear utilities would take is uncertain. Several possibilities could be pursued, including centralized interim storage or the study of another location for a a deep geologic repository. However, it would be too speculative to say that any of these actions would be pursued.

4. As explained in the EIS, the purpose of the pretreatment process is to separate the high-activity fraction, which requires the permanent isolation afforded by a repository, from the low-activity fraction. This large volume of low-activity waste is subject to a "waste incidental to reprocessing determination," as provided for in DOE’s Radioactive Waste Management Manual (DOE M435.1-1). A waste stream can be managed as low-level waste if the waste incidental to reprocessing determination shows that it meets the following criteria:
   • The key radionuclides are removed to the extent technically and economically practical (this is accomplished by pretreatment).
   • It is managed to meet safety requirements comparable to the performance objectives set out in 10 CFR Part 61, Subpart C, Performance Objectives.
   • It is managed in accordance with the DOE M 435.1-1 low-level waste requirements and is incorporated into a solid physical form at a concentration less than the Class C limits set out in 10 CFR 61.55.
   The Waste Incidental to Reprocessing provision was included in the August 6, 1998, drafts of DOE Order 435.1 and DOE M 435.1-1 that were made available for public comment. DOE has since issued DOE Order 435.1 for implementation.
   DOE has modified Section 1.2.3 of the EIS to reflect that low-level waste would be disposed of in accordance with applicable regulations.

5. As the Environmental Protection Agency notes, the Draft EIS evaluated the preliminary design concept described in the Viability Assessment of a Repository at Yucca Mountain (DIRS 101779-DOE 1998) for repository surface facilities, and disposal containers (waste packages). DOE noted in the Draft EIS (in Section 2.1.1.5, for example) that the analyzed designs were preliminary and were likely to evolve in various ways. Since it issued the Draft EIS, DOE has continued to evaluate design features and operating modes that would reduce uncertainties in or improve long-term repository performance, and improve operational safety and efficiency. The results of the design evolution process was the development of the Science and Engineering Report flexible design. This design focuses on controlling the temperature of the rock between the waste emplacement drifts (as opposed to areal mass loading), but the basic elements of the Proposed Action to construct, operate and monitor, and eventually close a geologic repository at Yucca Mountain are unchanged. DOE evaluated the flexible design in a Supplement to the Draft EIS, which was released for public review and comment in May 2001.
   Aspects of the design in the Supplement to the EIS (as well as this Final EIS) are likely to continue to evolve, particularly in relation to the means of controlling heat generated by spent nuclear fuel and high-level radioactive waste. Under Section 114(a) of the NWPA, DOE must provide a description of the proposed repository, including preliminary design specifications, as part of any Site Recommendation. If the Yucca Mountain site was approved, a more refined flexible design would be determined only at the time of License Application to the Nuclear Regulatory Commission. That design probably would continue to change as a result of the License Application process.
   In this Final EIS, DOE varied design parameters to create lower- and higher-temperature operating modes in such a way to provide the range of potential environmental impacts. DOE believes that the EIS adequately analyzes each design element investigated, the resulting short- and long- term environmental impacts, and mitigation measures. Further, the analyses incorporate conservative assumptions that tend to overestimate impacts, as identified in the EIS. For example, in Section G.1.1 of the EIS the total nonradiological air quality impacts were the sum of the calculated maximum concentrations regardless of wind direction. This conservatively maximized air quality impacts. This type of approach to estimate impacts conservatively was applied to all other resources, as appropriate.
   Because of the various implementing alternatives and scenarios analyzed as well as the conservative nature of the analyses, DOE believes that the analyses represent a realistic upper bound of environmental impact that could occur from the implementation of the Proposed Action.

6. The Draft EIS evaluates the preliminary design concept described in the Viability Assessment of a Repository at Yucca Mountain (DIRS 101779-DOE 1998) for repository surface and subsurface facilities as well as disposal containers (waste packages). It also evaluates the plans for the construction, operation and monitoring, and closure of the repository. DOE recognized before it published the Draft EIS that plans for a repository would continue to evolve during the development of any final repository design and as a result of any licensing review of the repository by the U.S. Nuclear Regulatory Commission. The design evolution is evaluated in the Supplement to the Draft EIS and integrated into the Final EIS. The Supplement to the Draft EIS incorporates new information, including an improved understanding of the interactions of potential repository features with the natural environment, the addition of design features for enhanced waste containment and isolation, and evolving regulatory requirements. The design will continue to evolve in response to additional site characterization information, technological developments, and interactions with oversight agencies.
   As described in the Supplement to the Draft EIS and incorporated into the Final EIS, the waste package has been redesigned to include a thick outer shell of corrosion-resistant high-nickel alloy (Alloy-22) and a thick inner shell of stainless steel for strength. This newer design resists corrosion far better than the design described in the Draft EIS, and has improved the predicted performance of the repository and reduced uncertainties associated with that performance. A description of the flexible design waste package can be found in Section 2.3.4.1of the Supplement to the Draft EIS and Section 2.1.2.2.2 of the Final EIS.
   The type and amount of neutron absorber necessary for a specific waste package design would be determined by DOE prior to receipt of a license from the Nuclear Regulatory Commission to receive and posses spent nuclear fuel and high-level radioactive waste. This would have to be done consistent with a criticality analysis methodology that has been accepted by the Commission. The specifics of that methodology are presented in Disposal Criticality Analysis Methodology Topical Report, which DOE submitted to the Commission in January 1999.

7. DOE has considered onsite and offsite locations for the Cask Maintenance Facility. A site for the landfill has not yet been identified. DOE would identify an appropriately sized landfill at the repository site for nonhazardous and nonradiological construction and sanitary solid waste, and for similar waste generated during operation, monitoring, and closure of the repository. Although the Cask Maintenance Facility may not be located at the Yucca Mountain site (therefore not depicted on current site drawings), the EIS analysis assumed the landfill and the Cask Maintenance Facility would be located at the repository. By doing so, the environmental impacts of these facilities were considered in the EIS. DOE believes that the amount of information in the EIS on these facilities is adequate to determine representative environmental impacts.

8. Figure 2-10 shows the location of the cooling tower at the North Portal Operations Area. DOE would use the cooling tower exclusively for air conditioning of surface facilities at the repository. The tower would not be a source of chemical contamination or radiological emissions. The Final EIS has been revised to state that the cooling tower is not a source of chemical or radiological emissions or contamination.

9. DOE would emplace waste packages in underground tunnels at the same time it was constructing additional tunnels. However, the two areas of operation would be isolated from one another. Section 4.1.3.2 of the EIS discusses potential impacts to surface water from repository construction, operations, maintenance, monitoring, and closure. As stated in that section, DOE would pump water from subsurface construction areas to a lined evaporation pond at the South Portal Operations Area. It would pump water from the emplacement areas, if any, to a lined evaporation pond at the North Portal Operations Area, but only after verifying that it was not contaminated.
   DOE would remove solid materials through mining operations, but only from the development area. Bulkheads would isolate this area from the emplacement side, and the ventilation system would ensure that air leaks would be from the development side to the emplacement side (because it would maintain a lower pressure on the emplacement side).

10. As described in the Supplement to the Draft EIS and incorporated into the Final EIS, the waste package has been redesigned to include a thick outer shell of a corrosion-resistant high-nickel alloy (Alloy-22) and a thick inner shell of stainless steel for strength. This newer design would resist corrosion far better than the design described in the Draft EIS, and would improve the predicted performance of the repository and reduced uncertainties associated with that performance. Section 2.1.2.2.4 of the EIS describes the waste package design.

11. DOE agrees that the limitation or prevention of intentional and unintentional activities around the closed repository could not be guaranteed.

12. DOE would design and implement a postclosure monitoring program in compliance with the Nuclear Regulatory Commission regulations (10 CFR Part 63). Before closure, DOE would submit an application for a license amendment to the Commission for review and approval. The application would include, among other items:
    1. An update of the assessment of the performance of the repository for the period after closure

    2. A description of the postclosure monitoring program

    3. A detailed description of measures to regulate or prevent activities that could impair the long-term isolation of the waste, and to preserve relevant information for use by future generations

    The application also would describe DOE’s proposal for continued oversight to prevent any activity at the site that would pose an unreasonable risk of breaching the repository’s engineered barriers, or increase the exposure of individual members of the public to radiation beyond limits allowed by the Nuclear Regulatory Commission. DOE has modified Chapter 9 of the EIS to include the types of monitoring and other institutional controls that would be contemplated. The Department would develop the details of this program during the consideration of the license amendment for closure. This would allow the Department to take advantage of new technological information, as appropriate.

13. DOE agrees that the limitation or prevention of intentional and unintentional activities around the closed repository could not be guaranteed.

14. DOE believes that the mostly rail scenario, in which more than 95 percent of spent nuclear fuel and high-level radioactive waste would be shipped by rail, and the rest by legal-weight truck, would most closely approximate the actual mix of truck and rail shipments. In reaching this conclusion, DOE considered the capabilities of the sites to handle larger (rail) casks, the distances to suitable railheads, and historic experience in actual shipments of nuclear fuel, waste or other large reactor-related components. DOE also considered relevant information published by sources such as the Nuclear Energy Institute and the State of Nevada. In addition, DOE has identified mostly rail as its preferred mode of transportation, both nationally and in Nevada. At this time, however, the Department has not identified a preference among the five candidate rail corridors in Nevada.

15. The EIS focuses on analyses of potential environmental impacts, including impacts to human health and safety. DOE provided the estimated cost information as a point of comparison between the Proposed Action and the No-Action Alternative. The cost estimates in the Draft EIS were in 1998 dollars with no escalation or discount rates. The reference cited in the comment (DIRS 104980-CRWMS M&O 1999) provides the basis for the Proposed Action cost estimate for the period from 2002 to 2116. As stated in that reference, most of the detailed information came from existing cost estimates for the 1999 to 2116 period in the Viability Assessment of a Repository at Yucca Mountain (DIRS 101779-DOE 1998) and from the Analysis of the Total System Life Cycle Cost of the Civilian Radioactive Waste Management Program (DIRS 102031-DOE 1998), which both provide detailed year-by-year cost estimates. The EIS estimates include all costs from 2002 forward (when DOE anticipates a decision regarding development of a repository at Yucca Mountain). Costs for the Proposed Action and the No-Action Alternative would be the same up to that time. Costs for siting and characterization of the Yucca Mountain site were not included in the Draft EIS estimates. Section 2.1.5 of the Final EIS provides revised cost estimates for the repository flexible design.
    The No-Action Alternative cost estimate in Section 2.2.3 of the EIS is a comparative cost estimate and only includes costs different from the costs of the Proposed Action. For example, the No-Action costs do not include storage costs until 2010 when a repository would first accept spent nuclear fuel and high-level radioactive waste because storage until that point would be required under both the Proposed Action and the No-Action Alternative. The No-Action cost estimate is based on, and consistent with, existing industry experience for dry onsite storage of spent nuclear fuel and high-level radioactive waste. Section 2.2.3 of the Final EIS provides revised cost estimates for the No-Action Alternative.

16. The full quote of the last sentence is:
    "Because these projections are based essentially on best available scientific techniques, DOE focused the assessment of long-term impacts on human health, biological resources, surface-water and groundwater resources, and other resource areas for which the analysis determined the information was particularly important and could establish estimates of impacts." (Draft EIS, p. 2-74)
    The intent of this statement is that DOE assessed all important impacts in the long-term period. No analyses were omitted because of inability to establish an estimate. Some resource areas (such as noise, utilities, and services) were deemed to have no foreseeable impact and no detailed analysis was necessary. DOE realizes that even the full quote is confusing and has, therefore, revised the language in the Final EIS.

17. The value of 2.4 rem listed in the table in Section 2.4.4.1 of the EIS would be the dose to a hypothetical person assuming that exposure would be limited to 100 millirem per year. DOE has added a footnote to the table to include this information. Section 6.2.3.1 contains more information.

18. The statement is correct, and the information in Section 4.1 of the Draft EIS supports the conclusions. However, the paragraph in question was out of place in the Draft EIS. Potential impacts of the transportation of spent nuclear fuel would not be related to thermal load scenarios of the Draft EIS or to the flexible design analyzed in the Final EIS. The paragraph in question has been deleted.

19. The purpose of the bullet in Section 2.4.4.2 referred to in this comment is to identify salient conclusions that can be drawn from the information in the summary table in that section. For this reason, DOE has not included modifications or references to other sections in the Final EIS.

20. DOE believes that it has sufficient information and understanding of the hydrologic setting to adequately determine the potential environmental impacts from the Proposed Action. DOE and others have been evaluating and assessing the hydrologic setting and associated characteristics at the Yucca Mountain site and nearby region for many years. DOE’s site characterization program has been redirected from time-to-time to reflect and accommodate reviews by independent parties, both internal and external to the Department. Nevertheless, it is clear that the regional and site-specific hydrologic setting is complex and uncertainties remain. Additional information would refine DOE’s understanding of, for instance, the regional groundwater flow system, and would further reduce uncertainties associated with flow and transport in the alluvial, volcanic and carbonate aquifers.
    In recognition of these uncertainties, DOE has supported Nye County with its program (called the Early Warning Drilling Program) to characterize further the saturated zone along possible groundwater pathways from Yucca Mountain, as well as the relationships among the volcanic, alluvial, and carbonate aquifers. Information from the performance confirmation program (if Yucca Mountain is approved for a repository) could be used in conjunction with that of the Early Warning Drilling Program to refine the Department’s understanding of the flow and transport mechanics of the saturated alluvium and valley-fill material south of the proposed repository site, and to update conceptual and numerical models used to estimate waste isolation performance of the repository. When DOE published the Draft EIS, only limited information from the Early Warning Drilling Program was available. Since then, however, this program has gathered additional information (see Section 3.1.4.2.1 of the EIS).
    In addition, DOE has installed a series of test wells along the groundwater flow path between the Yucca Mountain site and the Town of Amargosa Valley as part of an alluvial testing complex. The objective of this program is to better characterize the alluvial deposits beneath Fortymile Wash along the east side of Yucca Mountain. Single- and multi-well tracer tests have begun and the results thus far have strengthened the basis of the site-scale saturated flow and transport model. This program is described in Section 3.1.4.2.1 of the EIS.
    Although DOE has improved its understanding of the hydrologic system, uncertainties would remain given the time frame of concern (waste isolation for thousands of years). If the site was approved, DOE would institute a performance confirmation and testing program, elements of which would address the hydrologic system. The purpose of this program would be to evaluate the accuracy and adequacy of the information used to determine whether the repository would be expected to meet long-term performance objectives. The performance confirmation program, which would continue through closure of the repository (possibly as long as 300 years), would offer a means to further understanding of the hydrologic system and reduce uncertainties.

21. DOE has initiated a program to evaluate the hydrologic processes in the saturated zone, particularly the hydrogeologic relationship between the volcanic aquifer, alluvial aquifer, and carbonate aquifer. This is currently being addressed through a cooperative agreement between Nye County and DOE, referred to as the Early Warning Drilling Program. Recent results from this program have been incorporated into this Section 3.1.4.2.1 of the EIS.
    Section 3.1.4.2.2 of the EIS refers to large hydraulic gradient north of the site. Specific information related to the saturated zone and carbonate aquifer can be found in the cited references in Section 12 of the EIS. With regard to the saturated zone and the carbonate aquifer, one well (UE 25p #1) penetrated the carbonate aquifer at Yucca Mountain, another well (NC-EWDP-2DB), along the potential flow path in Fortymile Wash, has penetrated the carbonate aquifer and an upward hydraulic gradient was present. Well NC-EWDP-2DP, along with six additional planned wells, will help characterize the carbonate aquifer system near Yucca Mountain as part of the Nye County Early Warning Drilling Program. Four other wells at Yucca Mountain, as reported by Luckey et al (DIRS 100465-1996), are believed to indicate the potentiometric level in the carbonate aquifer. Elsewhere in the general area, particularly at the southern end of the Nevada Test Site and eastward from the springs in Ash Meadows, the hydraulic relationship between the lower carbonate aquifer and overlying units is well understood (DIRS 101167-Winograd and Thordarson 1975). The very presence of the springs in Ash Meadows demonstrates the fact of an upward hydraulic gradient in the lower carbonate aquifer. Because the lower carbonate aquifer is buried by some 6,000 feet of unconsolidated deposits in the Amargosa Desert west of the springs in Ash Meadows, no wells have been drilled into this aquifer. Claassen (DIRS 101125-1985) presents the hydraulic and hydrochemical evidence of subsurface discharge from the lower carbonate aquifer to the alluvial fill of the Amargosa Desert to the west of Rock Valley Wash. In addition, several investigations have concluded from hydrologic, chemical, and isotopic evidence that the lower carbonate aquifer is the source of the large springs in Furnace Creek Wash (Death Valley). Thus, the understanding of the flow system and hydraulic relationships of the lower carbonate aquifer are based not only on data from well UE 25p #1 at Yucca Mountain, but on a large body of regional hydrologic and chemical evidence collected over the past 40 years.

22. The Draft EIS reported groundwater concentrations and then compared the results to current Safe Drinking Water Act standards for four points of compliance: 5, 20, 30 and 80 kilometers (3, 12, 19, and 50 miles) from the repository. It reported the concentrations for both the mean and 95th percentile of a set of 100 stochastic realizations of the undisturbed case release scenario, which determines the type and quantity of waste released over time. Chapter 5, Appendix I, and the Viability Assessment (DIRS 101779-DOE 1998) discuss this scenario. The Draft EIS reported results for three thermal load scenarios for the peak occurring within 10,000 years after repository closure.
    DOE did not use the concept of representative volume in the Draft EIS because of the nature of the groundwater model, which was the same as that used for the Viability Assessment of a Repository at Yucca Mountain (DIRS 101779-DOE 1998). This model simulates the saturated zone transport as a series of six parallel tubes that follow the general flow of groundwater south through Amargosa Valley to the surface discharge point at Franklin Lake Playa. These one-dimensional tubes have a concentration identified at the repository footprint (that is, all repository footprint water flows through the tubes), a dilution factor characterizes how much dispersion would occur, and a delay factor accounts for sorption. Thus, at the point of compliance the model assumes that groundwater is repository footprint water with a conservative dilution factor and delay time.
    Since publication of the Draft EIS, the Environmental Protection Agency (EPA) and the Nuclear Regulatory Commission finalized their environmental protection and licensing criteria regulations (40 CFR Part 197 and 10 CFR Part 63, respectively), which provide an individual protection standard for the proposed Yucca Mountain Repository.
    For the Final EIS, DOE used the definition of the Reasonably Maximally Exposed Individual (RMEI) from 40 CFR 197.21, which defines the individual as a hypothetical person who could meet the following criteria:
    1. Has a diet and living style representative of the people who are now residing in the Town of Amargosa Valley, Nevada. DOE must use the most accurate projections, which might be 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 in the assessments conducted for Sections 197.20 and 197.25.

    2. Drinks 2 liters (0.5 gallon) of water per day from wells drilled into the groundwater at the location where the RMEI lives.
    The location of the RMEI described in 40 CFR Part 197 would be where the predominant groundwater flow path crosses the southern boundary of the Nevada Test Site which coincides with the southern boundary of the controlled area as defined in the regulation. This point is approximately 18 kilometers (11 miles) from the proposed repository. DOE has concluded that it is not necessary to analyze in the Final EIS a hypothetical individual at locations closer than approximately 18 kilometers to the repository because it is unreasonable to assume that anyone would reside in this area, because:
    • An individual would need to install and operate a water well in volcanic rock at more than 360 meters (1,200 feet) deep to reach the water table at costs significantly above (and likely prohibitive) those that would be incurred several kilometers farther south of the repository where the water tables lies less than 60 meters (200 feet) beneath the surface through sand and gravel. and

    • Locations closer than 18 kilometers (11 miles) are within the controlled area defined in the EPA standard for a Yucca Mountain repository and therefore not in the postclosure accessible environment defined by EPA.

    The updated analysis in the Final EIS estimates potential groundwater impacts reported for the compliance point prescribed in 40 CFR Part 197 [approximately 18 kilometers (11 miles) from the proposed repository]. As part of a comprehensive presentation of impacts, this EIS is charged with providing groundwater impacts for two other important down gradient locations. These are 30 kilometers (19 miles), where most of the current population in the groundwater path is located, and 60 kilometers (37 miles) where the aquifer discharges to the surface (this location is also known as Franklin Lake Playa). This analysis indicates that for the first 10,000 years there would be only very limited releases, attributable to a small number of early waste package failures (zero to three, and possibly as many as five) due to waste package manufacturing defects, with very small radiological consequences (see Table 5-6). For the first 10,000 years after repository closure, the mean and 95th-percentile peak annual individual dose would be thousands of times less than the Environmental Protection Agency standard, which allows up to 15-millirem-per-year dose rates during the first 10,000 years. The peaks would be even smaller at greater distances.
    DOE has revised the definitions of the maximally exposed individual and RMEI in the Final EIS. Chapters 4, 6, and 7 now use the term "maximally exposed individual," and Chapter 5 uses "individual." The individual is the "reasonably maximally exposed individual" defined in 40 CFR Part 197.
    In addition, the Final EIS updated the groundwater protection analyses consistent with criteria provided at 40 CFR 197.30. The results of these analyses are provided in Tables 5-6 and 5-10 of Chapter 5 of the Final EIS and show that both the mean and 95th percentile estimated radionuclide concentrations during the 10,000 regulatory period are thousands of times less than the regulatory limits.

23. Section 3.1.4.2.2 of the EIS indicates that perched water is formed when water percolating down through the subsurface encounters a zone of lower permeability and, as a result, accumulates. Vertical movement of water probably stills occurs, but at a slower rate below the perched water than above. In the tilted strata at Yucca Mountain, the accumulation of perched water must be accompanied by a feature such as a fault to restrict the lateral movement of water. The surface of the perched water then remains at a fairly stable elevation once the inflow and outflow rates are balanced. At Yucca Mountain this is attributed to less infiltration (a drier climate than when most of the perched water accumulated) and/or the elevation of the perched water reaching a point where the lateral restriction changes and the water "spills" out, or it could just reflect a long-term, steady-state condition.
    The commenter is correct that seismic activity could change the rate at which water moves in the unsaturated zone, but it would be much less likely to change the quantity of water moving through the unsaturated zone because quantity is related chiefly to climate. That is, the rate at which water would reach the perched zone might increase for a short period of time as water above it "drained" from the system as a result of increased permeability. But eventually the amount of water reaching the perched water would again be controlled by the amount of water entering the system (that is, infiltration). For either the short-term increase in flux or the long-term climate-driven flux to cause significant "mounding" of the perched water, the seismic activity would have to result in a decreased permeability below the perched zone and/or an extension (lengthening) of the lateral restriction to flow. A scenario of increased perched water elevation is not addressed in the EIS because neither of these conditions would be expected to occur to any significant extent as a result of seismic activity. Compared to the overlying Topopah Spring welded unit, seismic activity might cause less fracturing in the Calico Hills nonwelded unit (the unit causing the perching condition), but it would not be expected to decrease the latter’s permeability. The barrier to lateral flow at faults is believed to be the result of the juxtaposition of a more permeable layer against a less permeable layer caused by the fault displacement. Therefore, to lengthen the barrier, the offset would have to be lengthened. This is an obvious result of displacement, but the greatest displacement in the Yucca Mountain area [32-centimeter (13-inch); Section 3.1.3.3 of the EIS] would be exceeded less than once in 100,000 years. Correspondingly, fault displacement would not be expected to significantly increase the depth of perched water.
    DOE has considered hundreds of "what if" scenarios involving features, events, and processes (FEPs) and how they might affect the long-term performance of the repository. Those scenarios not excluded because of low probability or low consequences or for other reasons were subjected to more detailed analysis and included in long-term performance modeling. This process is documented in DOE’s FEP database and associated documentation. The FEP process does not specifically address "mounding" of the perched water, but it does cover what is believed to be a more realistic scenario; the relatively rapid draining of the perched water due to seismic activity. In this case, were such an event to take place after containers in the repository had begun to degrade, it could result in a fast pulse of contamination reaching the saturated zone. This scenario was excluded from analysis in the long-term performance modeling because it was reasoned that the volume of water associated with the perched system is not great enough to cause a significant "pulse" to the saturated zone.

24. As part of its site characterization activities, DOE has conducted a variety of investigations into the nature of water falling as precipitation on Yucca Mountain and passing through the unsaturated zone to the groundwater beneath. One such study has been to quantify the concentrations of certain radioisotopes in the Exploratory Studies Facility. Isotopes, such as chlorine-36 and tritium, which occur naturally and as a byproduct of atmospheric nuclear weapons testing, serve as indicators of the rate of flow through the unsaturated zone (see Section 3.1.4.2.2 of the EIS for details).
    Results from preliminary studies have identified these isotopes in concentrations that tend to suggest that there are connected pathways through which surface precipitation has percolated to the repository horizon within the last 50 years. However, these isotopes have been found at locations that are generally associated with known, through-going faults and well-developed fracture systems close to the faults at the proposed repository horizon.
    To ensure the correct interpretation of this chemical signal, DOE instituted additional studies to determine if independent laboratories and related isotopic studies can corroborate the detection of elevated concentrations of these radioisotopes. Results of the validation studies to this point have not allowed firm conclusions and, thus, the evaluations continue.
    DOE believes that these findings do not indicate that the Yucca Mountain site should be declared unsuitable for development as a repository. Most of the water that infiltrates Yucca Mountain moves slowly through the matrix and fracture network of the rock, and isotopic data from water extracted from the rock matrix indicates that residence times might be as long as 10,000 years. Furthermore, after excavating more than 11 kilometers (8.4 miles) of tunnels at Yucca Mountain for the Exploratory Studies Facility, DOE determined that only one fracture was moist (there was no active flow of water). This observation has been confirmed in test alcoves that are not subject to the effects of drying from active ventilation.
    Nevertheless, the total system performance assessment incorporates the more conservative water movement data as well as information from other water infiltration and associated hydrogeological studies. As a result of this evaluation, DOE would not expect the repository (combination of natural and engineered barriers) to exceed the prescribed radiation exposure limits during the first 10,000 years after closure.

25. DOE has started a program to evaluate the hydrologic processes in the saturated zone, particularly the hydrogeologic relationship between the volcanic aquifer, alluvial aquifer, and carbonate aquifer. This is currently being addressed through a cooperative agreement between Nye County and DOE, referred to as the Early Warning Drilling Program. Recent results from this program have been incorporated into this Section 3.1.4.2.1 of the EIS.
    With regard to the saturated zone and the carbonate aquifer, one well (UE 25p #1) penetrated the carbonate aquifer at Yucca Mountain, another well (NC-EWDP-2DB) along the potential flow path in Fortymile Wash penetrated the carbonate aquifer and an upward hydraulic gradient was present. Well NC-EWDP-2DP, along with six additional planned wells, will help characterize the carbonate aquifer system near Yucca Mountain as part of the Nye County Early Warning Drilling Program. Four other wells at Yucca Mountain, as reported by Luckey et al (DIRS 100465-1996), are believed to indicate the potentiometric level in the carbonate aquifer. Elsewhere in the general area, particularly at the southern end of the Nevada Test Site and eastward from the springs in Ash Meadows, the hydraulic relationship between the lower carbonate aquifer and overlying units is well understood (DIRS 101167-Winograd and Thordarson 1975). The very presence of the springs in Ash Meadows demonstrates the fact of an upward hydraulic gradient in the lower carbonate aquifer. Because the lower carbonate aquifer is buried by some 6,000 feet of unconsolidated deposits in the Amargosa Desert west of the springs in Ash Meadows, no wells have been drilled into this aquifer. Claassen (DIRS 101125-1985) presents the hydraulic and hydrochemical evidence of subsurface discharge from the lower carbonate aquifer to the alluvial fill of the Amargosa Desert to the west of Rock Valley Wash. In addition, several investigations have concluded from hydrologic, chemical, and isotopic evidence that the lower carbonate aquifer is the source of the large springs in Furnace Creek Wash (Death Valley). Thus, the understanding of the flow system and hydraulic relationships of the lower carbonate aquifer are based not only on data from well UE 25p #1 at Yucca Mountain, but on a large body of regional hydrologic and chemical evidence collected over the past 40 years.

26. Section 3.1.4.2.2 of the EIS refers to the large hydraulic gradient north of the Site. An expert elicitation panel addressed this feature and narrowed its likely cause to two theories: (1) flow through the upper volcanic confining unit or (2) semi-perched water. The consensus of the panel favored the perched-water theory. Whatever the cause, the experts were in agreement that the probability of any large transient change in the configuration of this gradient is extremely low (DIRS 100353-CRWMS M&O 1998). DOE has initiated a program to evaluate the hydrologic processes in the saturated zone, particularly the hydrogeologic relationship between the volcanic aquifer, alluvial aquifer, and carbonate aquifer. This is currently being addressed through a cooperative agreement between Nye County and DOE, referred to as the Early Warning Drilling Program. Recent results from this program have been incorporated into Section 3.1.4.2.1 of the Final EIS.

27. The reference from which DOE extracted this information does not correlate water-level fluctuations with proximity to Fortymile Wash. The Draft EIS mentioned this only because Fortymile Wash is an area of periodic recharge, which could have a local, temporary affect on the elevation of groundwater (see Section 3.1.4.2.2 of the EIS). The reference to the wells’ proximity to Fortymile Wash has been removed.

28. The washes listed in the comment are tributaries to Fortymile Wash, and Fortymile Wash is a tributary to the Amargosa River. Because they are tributaries, the EIS text acknowledges that these washes might be classified as "waters of the United States." At present, there has been no formal designation of these drainage channels. Without such a designation, DOE believes that it is appropriate in the EIS to continue to indicate that these washes might be classified as waters of the United States. The Department will continue to coordinate with the Army Corps of Engineers regarding any possible future designation of these or other affected washes.

29. Section 3.1.4.1.1 of the EIS discusses surface water in the region of Yucca Mountain and indicates that groundwater discharges to the channel of the Amargosa River near the community of Beatty, Nevada. The purpose of this discussion is only to identify areas along the river channel where surface water exists on a regular basis. It is not to identify the source of the groundwater that supplies the flow; this information is included in the discussion of regional groundwater in Section 3.1.4.2.1 of the EIS (which includes Figure 3-13). In the discussion of Basins in Section 3.1.4.2.1, the description of the Pahute Mesa-Oasis Valley groundwater basin indicates groundwater outflow is southward to the Amargosa Desert. The flow arrow shown in Figure 3-13 of the Draft EIS at the south end of the Pahute Mesa-Oasis Valley basin points southward toward Amargosa Desert and shows the groundwater pathway to be beneath the community of Beatty. Accordingly, groundwater discharged in the area of Beatty comes from the Pahute Mesa-Oasis Valley basin.

30. DOE revised its socioeconomic baseline projections and estimated impacts for the Final EIS incorporating population data available from the State of Nevada and local communities. The revisions include an estimated baseline projection to 2035 for the socioeconomic parameters considered in the EIS. In the Final EIS, the estimated population distribution within 80-kilometers (50-miles) of the repository is also based on projections to 2035 utilizing information available from State and local sources. The allocation of individuals to a particular sector within the 80-kilometer area was based upon surveys conducted in 2000. Figure 3-25 of the EIS provides the population distribution for 2035.

31. The Environmental Protection Agency recently published an age-specific risk factor of 5.75 chances in 10 million per millirem for fatal cancer (DIRS 153733-EPA 2000). However, DOE currently uses the value of 5.0 and 4.0 chances in 10 million per millirem for fatal cancer for members of the public and workers, respectively, as recommended by the International Commission on Radiological Protection (DIRS 101836-ICRP 1991). When recommending these risk factors, the International Commission on Radiological Protection also expressed the desirability, for purposes of radiation protection, to use the same nominal risk factors for both men and women and for a representative population with wide ranges in age. The Commission stated that although there are differences between the sexes and populations of different age-specific mortality rates, these differences are not so large as to necessitate the use of different nominal risk factors. However, the higher risk factor for members of the public compared to that recommended for workers accounts for the fact that children comprise a relatively large part of the population and are more sensitive to the effects of radiation (cancer induction) than adults. Although the embryo-fetus is more radiosensitive (with a radiation risk factor about two times that for the whole population) it is protected by the body of the mother and comprises a small part of the overall population. Pregnant women are not unduly radiosensitive, especially to low levels of radiation.
    Both the Agency and DOE recognize that there are large uncertainties associated with these risk factors, as expressed by the National Council on Radiation Protection and Measurements comment on the result of their uncertainty analysis in the risk coefficients that " … show a range (90 percent confidence intervals) of uncertainty values for the lifetime risk for both a population of all ages and an adult worker population from about a factor of 2.5 to 3 below and above the 50th percentile value" (DIRS 101884-NCRP 1997). The Department believes that the 15-percent difference in these risk factors is well within other uncertainties and would provide little additional information to the decisionmaking process that this document informs. For these reasons, DOE will continue to use risk factors recommended by the International Commission on Radiological Protection in their National Environmental Policy Act documents.

32. Appendix K of the EIS cites reference documents that include the details of the dose calculations. Information on these documents is available at DOE Reading Rooms and on the DOE Internet site (http://www.ymp.gov).

33. The EIS sections cited by this comment identify potentially affected waterways and groundwater characteristics pertaining to the 77 commercial and DOE generator sites. Sections 7.2.1.3 and 7.2.2.3 discuss the potential hydrologic impacts associated with the No-Action scenarios.
    With regard to transportation, Sections 3.2.2.1.3 and 3.2.2.2.3 of the EIS provides information on hydrology related to transportation corridors within Nevada. Table 3-37 and 3-39 present surface-water resources and groundwater basins, respectively, along the candidate rail corridors. Table 3-58 and 3-59 do the same for candidate heavy-haul truck routes. For Nevada transportation, potential impacts to hydrology from construction and operations are presented throughout Chapter 6. For example, see Section 6.3.2.2.1. The analyses are based on an identification of surface-water resources within the 400-meter (0.25-mile) corridor for each alternative and outside the corridor, but within 1 kilometer (0.6 mile). Designated groundwater basins are identified.
    DOE does not specifically analyze a transportation accident, such as a spill, involving contamination of surface water or groundwater because the casks are designed to be watertight and spent nuclear fuel and high-level radioactive waste are not easily dispersed in water. While small particles could be generated by the impact forces of an accident, and driven out of a shipping cask by a severe fire, the amount of contamination that could ultimately enter groundwater would be much lower than that which would initially enter surface waters. Factors such as soil sorption of radionuclides, rate of flow into recharge areas, dilution by rain water and surface water, dilution by the large volume of groundwater, and delay associated with infiltration would mitigate and greatly reduce any contamination that could occur. Therefore, water pathway contamination, including subsequent contamination of food and natural resources, would not be a significant contributor to the radiological risks of transporting spent nuclear fuel. DOE has, however, identified potential mitigation measures for surface water and groundwater from the construction and operation of transportation systems. See Sections 9.3.3.1 and 9.3.3.2 of the EIS.

34. DOE agrees with this comment and recognizes the potential need for Section 404 permitting. Section 11.2.2 of the EIS discusses this potentially applicable requirement. As indicated in Section 11.2.2, DOE may need to obtain a permit from the U.S. Army Corps of Engineers if the repository or the transportation facilities requires the discharge of dredge or fill materials into waters of the United States.

35. DOE concurs with this suggestion. Cross-references to Chapter 5 have been added to Section 4.1.3.3 to avoid confusion between short-term preclosure effects and long-term performance after closure.

36. In the analysis of long-term performance, breaches of the containers were not treated as separate scenarios but rather the result of modeling a number of features, processes, and events that then lead to various types of container breaches. As such then, there are no expected scenarios for container breaches. The impacts to groundwater result directly from the overall scenarios considered: nominal or "undisturbed" scenario, volcanic events, and human intrusion. These are clearly differentiated in the Draft EIS and the Final EIS with regard to groundwater impacts. Container breach is merely a process that is component to these broader scenarios. The Final EIS points out that general corrosion is a primary process for failure driving the dose results for the whole post-10,000-year period. Section I.5.1 of the Final EIS discusses waste package failures versus time and discusses the modes of failure and the relationship to the annual dose history.

37. DOE does not specifically analyze a transportation accident, such as a spill, involving contamination of surface water or groundwater because the casks are designed to be water tight and spent-nuclear fuel and high-level radioactive waste are not easily dispersed in water. While small particles could be generated by the impact forces of an accident, and driven out of a shipping cask by a severe fire, the amount of contamination that might ultimately enter groundwater would be much lower than that which would initially enter surface waters. Factors such as soil sorption of radionuclides, rate of flow into recharge areas, dilution by rain water and surface water, dilution by the large volume of ground water, and delay associated with infiltration would mitigate and greatly reduce any contamination that might occur. Although DOE’s analyses in Chapter 6 take into account the proximity of surface waters and ground water basins (see Section 6.3.2.2.1 of the EIS as an example), water pathway contamination, including subsequent contamination of food and natural resources, would not be a significant contributor to the radiological risks of transporting spent-nuclear fuel. Analyses performed in previous EISs (see Section 1.5.3 and Table 1-1) have consistently shown that the airborne pathway has the greatest potential for exposing large numbers of people to radioactive material in the event of transportation accident resulting in the release of radioactive materials. DOE has, however, identified potential mitigation measures for surface water and groundwater from the construction and operation of transportation systems. The reader is referred to Sections 9.3.3.1 and 9.3.3.2.
    While DOE believes the information presented in these sections of the EIS are sufficient to assess the relative merits of the alternatives, the Department acknowledges additional environmental reviews would be required to assess the potential impacts of such things as specific alignments through a transportation corridor.

38. Section G.2.3.2 of the EIS discusses releases of noble gases from spent nuclear fuel in repository surface facilities in more detail. Releases of noble gas radionuclides could occur at any commercial nuclear reactor sites that handle spent nuclear fuel. Such releases are documented in annual and semiannual environmental reports and published in a Nuclear Regulatory Commission summary, Radioactive Materials Released from Nuclear Power Plants (DIRS 155108-Tichler, Doty, and Lucadamo 1995).
    Krypton and other noble gases do not accumulate in environmental or biological media and, therefore, present little hazard to humans or the environment. Radon is somewhat different because of its decay products, but so little radon is released from spent nuclear fuel that it is almost immediately indistinguishable from naturally occurring radon in the environment. As stated in Section 4.1.4.2 of the EIS, estimated doses to plants and animals would be small and impacts from those doses would be unlikely to affect the population of any species because the doses would be much lower than 100-millirad-per-day. The International Atomic Energy Agency has stated that there is no convincing evidence that chronic exposures of 100 milliard per day will harm plant or animal populations. Neither of these noble gases is typically monitored in biologic communities because the potential for impact is so small.

39. DOE would consider providing escape ramps from trenches, including ponds and basins, as a mitigation measure (see Section 9.2.3.2 of the EIS).

40. The loss of a small number of tortoises along roads and at the repository site would not affect the long-term survival of the local or regional population of desert tortoises. Tortoises are widespread throughout the region and large tracts of undisturbed tortoise habitat surround Yucca Mountain. Research at Yucca Mountain during site characterization confirms that activities similar to those proposed would have little effect on adjacent populations (DIRS 104294-CRWMS M&O 1999). Only five Desert Tortoise deaths have been attributed to site characterization activities. The rate of tortoise mortality would remain comparable to that observed during site characterization because the amount of traffic would be similar. Under the legal-weight truck scenario, the repository would receive about 40 shipments a day of supplies, materials, and equipment (Section J.3.6.1 of the EIS), and up to six shipments of spent nuclear fuel or high-level radioactive waste (Section J.1.2.1 of the EIS). During site characterization, the daily average number of vehicles passing traffic counters in 1993 and 1994 was between 40 and 55 (DIRS 104294-CRWMS M&O 1999). DOE and the U.S. Fish and Wildlife Service have completed consultation on the potential effects of repository construction, operation, and monitoring and closure on threatened and endangered species. In its Biological Opinion, the Fish and Wildlife Service concluded that these actions would not jeopardize the continued existence of the Mojave population of the desert tortoise. That Opinion includes an unlimited take provision of tortoises along roads at Yucca Mountain, in part because deaths due to vehicles are anticipated to be infrequent. (See Appendix O of the EIS for the Biological Opinion.) Section 4.1.4 of the Final EIS has been modified to better explain the conclusion that the Proposed Action would not affect the tortoise population.

41. In general, the uncertainty approach used in the EIS uses realistic ranges of values for inputs and, where possible, acknowledges the uncertainty. In some instances, conservative assumptions are necessary to avoid the possibility of understating the potential impacts of the proposed Yucca Mountain Repository.
    An interesting outcome of a full uncertainty analysis of a system such as the proposed repository is that the use of "expected values" (for example, averages) for all parameters does not actually predict the expected outcome very well. Because of the skewed aspect of many input parameters to the models (a reflection of the real nature of the underlying data), the results predicted using only mean values actually produce a low-probability occurrence, usually in the 90th percentile or above of the outcomes predicted in a full stochastic assessment. Thus, it is more reasonable to perform a full stochastic assessment and report the expected outcome in terms of the statistics computed from the results. DOE did this in the EIS by reporting the mean outcome and the tail probability (95th percentile). However, the EIS has been revised to more clearly and more fully discuss both the modeling uncertainties and the degree of conservatism in the modeling.

42. Chapter 5 and Section 8.3.1 of the EIS now include analyses of atmospheric releases of radon-222 to the time of peak dose.

43. Chapter 5 and Section 8.3.1 of the EIS now include analyses of atmospheric releases of radon-222 to the time of peak dose.

44. Chapter 5 and Section 8.3.1 of the EIS now include analyses of atmospheric releases of radon-222 to the time of peak dose.

45. The referenced statement in Section 5.5 of the Draft EIS is an error. There was no global population calculation performed for the Draft EIS. The statement has been removed.

46. The overview of the screening process in the Draft EIS referred to a process detailed in Appendix I. DOE believes that Appendix I provided sufficient detail for a full understanding of what was done. In the updated analysis presented in the Final EIS, a different screening process was used due to design changes. This new screening process is detailed in Appendix I and cross-referenced in Chapter 5 of the Final EIS. The discussion in Final EIS Appendix I was designed to provide as clear and comprehensive explanation as possible.

47. The intent of Section 5.2.3.4 of the Draft EIS (Sections I.2.2 and I.2.8 of the Final EIS) is to describe the process models and radionuclide movement tendencies. Section 3.1.4.2.1 provides aquifer and pathway information.

48. DOE recognizes that additional data would further define the flow system and reduce uncertainties about the interactions among the alluvial, volcanic, and carbonate aquifers in the saturated zone. DOE has initiated a program to evaluate the hydrologic processes in the saturated zone, particularly the hydrologic relationships between the volcanic aquifer, alluvial aquifer, and carbonate aquifer. This is currently being addressed through a cooperative agreement between Nye County and DOE, referred to as the Early Warning Drilling Program. Recent results from this program have been incorporated into Section 3.1.4.2.1 of the Final EIS.
    It is correct that only one well penetrates the lower carbonate aquifer at Yucca Mountain. Four other wells at Yucca Mountain, as reported by Luckey et al (DIRS 100465-1996), are believed to indicate the potentiometric level in the carbonate aquifer. Additional wells are being drilled to characterize the carbonate aquifer system near Yucca Mountain as part of the Early Warning Drilling Program. One of the wells drilled under this program, which is about 19 kilometers (12 miles) south of the repository site, also penetrated the carbonate aquifer and shows an upward gradient at that location.
    With regard to the comment on Ash Meadows, groundwater that infiltrates through Yucca Mountain does not discharge at the Devils Hole Protective Withdrawal or in Ash Meadows. The elevation of the water table in the Devils Hole/Ash Meadows area is about 64 meters (210 feet) higher than the water table in the Amargosa Desert to the west and south. This east-to-west decline in the elevation of the water table indicates that groundwater from the carbonate rocks beneath the Devils Hole Hills flows westward across Ash Meadows toward Amargosa Desert--not the other way around. Therefore, contaminants from Yucca Mountain could not discharge at springs in Devils Hole and Ash Meadows nor contaminate the aquifer.

49. This comment identifies the infiltration rates for the high and intermediate thermal loads. The amount of infiltration, or flux, that would go through the proposed repository would vary based on the thermal loads being considered. Sections 5.4.1, 5.4.2, and 5.4.3 of the Draft EIS address the high, intermediate, and low thermal load scenarios, respectively. For each scenario, the footprint of the repository (that is, the size of the repository perpendicular to downward moving infiltration) expands to a larger size to support the lower waste loading. With the high thermal load scenario, the waste would be tightly packed and an estimated 27,000 cubic meters (22 acre-feet) of water would infiltrate through the repository. An estimated 31,000 cubic meters (25 acre-feet) of water would go through the repository under the intermediate thermal load scenario. With a low thermal load repository, the waste would be spread out and an estimated 57,000 cubic meters (46 acre-feet) of water would infiltrate through the repository. The same concept is applicable to the higher-and lower-temperature operating modes, which influence the size of the underground emplacement and, therefore, the estimated quantity of water that would infiltrate.

50. Section 5.7.2 of the Final EIS presents dose history curves for the volcanic scenarios showing the mean and 95th-percentile curves along with lines for the nominal case for comparison to results for various volcanic disturbance scenarios and the undisturbed waterborne release results.

51. This is a valid point. The sentence in question is confusing and has been deleted from the EIS.

52. Thank you for your comment.

53. DOE thanks the Environmental Protection Agency for its input. Information presented in Section M.5.1 of the EIS provides additional information related to emergency response planning and Section M.6 provides additional information on financial assistance programs.

54. If the Yucca Mountain site was approved for development of a repository, shipping routes would be identified at least 4 years before shipments began and Section 180(c) assistance would be made available approximately 4 years prior to shipments through a jurisdiction (see Section M.6 of the EIS). In accordance with 10 CFR 73.37(a)(7), actual route selection and submission to the Nuclear Regulatory Commission would occur 1 or more years before a route’s use for shipment (see Section M.3.2.1.2 for more information). At this time, many years before shipments could begin, it is impossible to predict with a reasonable degree of accuracy which highway route or rail lines DOE would use. In the interim, states and tribes may designate alternative preferred highway routes, and highways and rail lines might be constructed or modified. Therefore, for purposes of analysis in this EIS, DOE identified representative highway routes in accordance with U.S. Department of Transportation regulations, which require the use of preferred routes (Interstate System highway, beltway or bypass, and state or tribal designated alternate route) that reduce time in transit (see Figure 6-11). DOE identified rail lines based on current rail practices, as there are no comparable Federal regulations applicable to the selection of rail lines for shipment of radioactive materials (see Figure 6-12).
    In response to public comments, DOE has included, state maps of representative highway routes and rail lines it used for analysis in Appendix J of the EIS (see Section J.4). Section J.4 includes potential health and safety impact estimates associated with shipments for each state through which shipments could pass.

55. Because of the public’s interest in transportation, DOE has added to this EIS Appendix M and maps and tables that show the analyzed routes and estimated health and safety impacts for each state through which the shipments would pass. Appendix M provides general background information about transportation-related topics, such as transportation regulations (Section M.2), transportation operations (Section M.3), cask testing (Section M.4), and emergency response (Section M.5).
    DOE has issued a draft Request for Proposals requiring the Regional Servicing Contractor to prepare a transportation plan that describes the Contractor’s operational strategy and delineates the steps it would implement to ensure compliance with all regulatory and other DOE requirements. This includes identification of proposed routes and associated routing considerations, coordination and communication with all participating organizations and agencies, including other Regional Servicing Contractor(s), DOE, state, Native American tribal, and local governments, and interactions with appropriate Federal and state organizations. The route and mode determinations would be interactive. If, during the course of the mode or route determinations, one of the previously determined factors changed, the site-specific mode and route analysis would be reevaluated to ensure consistency.

56. The Conformity Review discussions have been updated in all sections. Conformity Review results are summarized in Section 6.3.1.1 of the EIS for the mostly legal-weight truck scenario, in Section 6.3.2.1 for the mostly rail scenario, and in Section 6.3.3.1 for the heavy-haul truck scenario. The Conformity Review was focused on with levels of carbon monoxide and particulate matter (PM₁₀), for which the Las Vegas air basin has been classified as being in "serious nonattainment." Since the Draft EIS was published, the mostly rail scenario has been selected by DOE as the preferred transportation option. The Conformity Review found that more detailed analyses (that is, a Conformity Determination) would be required for the construction phase of a branch rail line in the Valley Modified Corridor, if that rail corridor was selected. The other corridors would not present a conflict with the General Conformity requirements for carbon monoxide and PM₁₀. Emissions for constructing a branch rail line in the Valley Modified Corridor are estimated in the Conformity Review to be up to 145 metric tons (160 tons) per year (160 percent of the General Conformity threshold level) for carbon monoxide, and up to 120 metric tons (130 tons) per year (190 percent of the General Conformity threshold level) for PM₁₀.
    The carbon monoxide emissions within the nonattainment area would result from fuel use by the construction vehicles and vehicle emissions from commuter and supply traffic to the Yucca Mountain site. The PM₁₀ releases would include the emissions from disturbing the ground and from fuel combustion of the construction equipment. Dust abatement measures (for example, water applications) would reduce fugitive dust PM₁₀ emissions by 70 percent. The emissions estimates could be reduced further by lengthening the construction time or more detailed task planning to reduce the production of emissions.
    Emissions from a branch rail line in the Valley Modified Corridor into the nonattainment area would occur during the much longer operations phase, as the locomotive passed through the nonattainment area on its way to the Yucca Mountain site. However, operations phase emissions would not exceed the General Conformity threshold levels. The estimated operations emissions for a branch rail line in the Valley Modified Corridor would be 81 percent of the carbon monoxide General Conformity threshold level and less than 3 percent of the PM₁₀ General Conformity threshold levels.
    In addition, the Conformity Review compared the Valley Modified Corridor carbon monoxide and PM₁₀ release estimates to the Nevada carbon monoxide and PM₁₀ State Implementation Plans (DIRS 156706-Clark County 2000; DIRS 155557-Clark County 2001). The construction phase Valley Modified carbon monoxide emissions estimates would be less than 0.2 percent of the total daily carbon monoxide inventory emitted into the nonattainment area. The construction phase Valley Modified PM₁₀ emissions estimates would be less than 0.08 percent of the daily and annual PM₁₀ inventory emitted into the Las Vegas Valley air basin.

57. DOE defined "dose risk" in a text box in Section 6.1.1 of the EIS as follows:
    "Dose risk is the sum of the products of the probabilities (dimensionless) and the consequences (person-rem) of all potential transportation accidents."

58. DOE and the U.S. Fish and Wildlife Service (see Appendix O of the EIS) have concluded that the loss of a small number of tortoises along roads and at the repository site would not affect the long-term survival of the local or regional population of desert tortoises. Tortoises are widespread throughout the region and large tracts of undisturbed tortoise habitat surround Yucca Mountain. Research at Yucca Mountain during site characterization confirms that activities similar to those proposed would have little effect on adjacent populations. The rate of tortoise mortality would remain comparable to that observed during site characterization because the amount of traffic would be similar. Under the legal-weight truck scenario, the repository would receive about 40 shipments a day of supplies, materials, and equipment (Section J.3.6.1 of the EIS), and six shipments of spent nuclear fuel or high-level radioactive waste (Section J.1.2.1). During site characterization, the daily average number of vehicles passing traffic counters in 1993 and 1994 was between 40 and 55 (DIRS 104294-CRWMS M&O 1999). The U.S. Fish and Wildlife Service has authorized an unlimited take of tortoises along roads at Yucca Mountain during repository construction and monitoring and closure in part because deaths due to vehicles are anticipated to be very infrequent (see Appendix O). Section 4.1 has been modified to better explain the conclusion that the Proposed Action would not affect the tortoise population.

59. As is typical for deterministic analyses such as those performed to evaluate No-Action Scenarios 1 and 2, the EIS analysis used best estimate single-input values to produce a best estimate result. As is also typical with these analyses, a separate analysis (semi-quantitative) addressed the uncertainty associated with the input values and assumptions and provided an assessment of the effects these uncertainties could have on the model results (see Section K.4 of the EIS for details).
    However, for Scenario 2 the analysis provided a range of best estimate impact values between regions for collective, as well as individual, impacts (see the tables in Section K.3.1 of the EIS). This was done to illustrate the importance of environmental transport human exposure (exposed population) parameters. Also under this scenario, a range of accident impacts was provided for high and low populations. Under Scenario 1, impact ranges were not developed because all collective and individual impacts were extrapolated from information provided by the Nuclear Regulatory Commission’s environmental assessment of the Calvert Cliffs Independent Spent Fuel Storage Installation (DIRS 101898-NRC 1991).
    As stated in Section K.4 of the EIS, DOE attempted to quantify a range of uncertainties associated with mathematical models and input data, and estimated the potential effect these uncertainties could have on collective human health impacts. By summing the uncertainties discussed in Sections K.4.1, K.4.2, and K.4.3 of the EIS where appropriate, DOE estimated that total collective impacts over 10,000 years could have been underestimated by as much as 3 or 4 orders of magnitude. However, because there are large uncertainties in the models used for quantifying the relationship between low doses (that is, less than 10 rem) and the accompanying health impacts, especially under conditions in which the majority of the populations would be exposed at a very low dose rate, the actual collective impact could be zero.
    On the other hand, impacts to individuals (human intruders) who could move to the storage sites and live close to the degraded facilities could be severe. During the early period (200 to 400 years after the assumed loss of institutional control), acute exposures to external radiation from the spent nuclear fuel and high-level radioactive waste material could result in prompt fatalities. In addition, after a few thousand years onsite shallow aquifers could become contaminated to such a degree that consumption of water from these aquifers could result in severe adverse health effects, including premature death. Uncertainties associated with these localized impacts relate primarily to the inability to predict accurately how many individuals could be affected at each of the 77 sites over the 10,000-year analysis period. In addition, the uncertainties associated with localized impacts would exist for potential consequences resulting from unusual events, both manmade and natural. Therefore, as discussed in Section K.4 of the EIS, uncertainties resulting from future changes in natural phenomena and human behavior that cannot be predicted, process model uncertainties, and dose-effect relationships, when taken together, could result in overestimating or underestimating the impacts by as much as several orders of magnitude relative to the values listed in Section K.3.

60. DOE referenced 40 CFR Part 61 primarily because it provided a direct comparison to an air quality emission standard. Since publication of the Draft EIS, the Environmental Protection Agency promulgated Public Health and Environmental Radiation Protection Standards for Yucca Mountain, Nevada, at 40 CFR Part 197, which included an annual dose limit to a member of the public of 15 millirem (40 CFR 197.4). In accordance with requirements of the Energy Policy Act, the Nuclear Regulatory Commission subsequently promulgated Yucca Mountain licensing criteria, which includes a Preclosure Public Health and Environmental Standard at 10 CFR 63.204 of 15 millirem per year to a member of the public. The appropriate sections of the EIS (including those mentioned in Chapter 8) have been updated to reflect a comparison to the recently promulgated standard of 15 millirem.

61. The maximally exposed individual dose values in Table 8-22 of the Draft EIS are the integrated doses over the period of closure; six years each for the high and intermediate thermal-load scenarios and 15 years for the low thermal-load scenario. In Table 8-28 of the Final EIS (the table that corresponds to Table 8-22 of the Draft EIS), the closure period for the Inventory Modules ranges from 12 to 23 years for the higher-temperature and lower-temperature repository operating modes.

62. The Department has revised the table to include the information on gross alpha concentration in Table 8-49 of the Final EIS.

63. As indicated in Section 8.3.2.1, information on Greater Confinement Disposal on the Nevada Test Site is from the Final Environmental Statement on the Nevada Test Site and Off-Site Locations in the State of Nevada (DIRS 101811-DOE 1996). DOE included the description as it appears in the Nevada Test Site Final EIS, but DOE did not base its analysis on this description. Rather, the Department relied on the analyses in the Nevada Test Site EIS for input to Chapter 8. The Department acknowledges, however, that transuranic radionuclides are a part of the category of Greater Confinement Disposal, with americium isotopes as one example. The discussion in Section 8.3.2.1 of the Final EIS includes the presence of transuranic radionuclides in this category.

64. As indicated in Section 8.3.2.1, information on Greater Confinement Disposal on the Nevada Test Site is from the Final Environmental Impact Statement on the Nevada Test Site and Off-Site Locations in the State of Nevada (DIRS 101811-DOE 1996). The designation of "major known isotopes or wastes" is intended only to give the reader a broad sense of what would be included in the appropriate waste category and does not affect the analysis in this EIS. The Department relied on the analyses in the Nevada Test Site EIS for input to Chapter 8. As a consequence, DOE did not repeat the detailed composition of the radioactivity at the Nevada Test Site in this chapter.
    A footnote to Table 8-53 in the Final EIS clarifies that the table is intended for information purposes only.

65. In response to this comment, DOE has reexamined the discussion of waste subject to Greater Confinement Disposal and has modified Section 8.3.2.1.2 of the EIS to indicate that there is no credible mechanism for the long-term release of materials from the Greater Confinement Disposal to the accessible environment.
    The material subject to Greater Confinement Disposal is placed in boreholes that are approximately 37 meters (120 feet) deep; the waste itself is no closer than approximately 21 meters (70 feet) to the surface. DOE has reviewed previous analyses at the Nevada Test Site and has concluded that there is no credible pathway for long-term release of materials by resuspension of nonvolatile radionuclides because the material is sufficiently far below the surface. In addition, evapotranspiration exceeds precipitation in this region and this, coupled with the fact that the boreholes are sufficiently above the water table, indicates that there is no credible scenario for the Greater Confinement Disposal material to enter the groundwater.

66. As the Environmental Protection Agency notes, the Draft EIS evaluated the preliminary design concept described in the Viability Assessment of a Repository at Yucca Mountain (DIRS-101779-DOE 1998) for repository surface facilities, and disposal containers (waste packages). It also evaluated the plans for the construction, operation and monitoring, and closure of the repository. DOE recognized before it published the Draft EIS that plans for a repository would continue to evolve during the development of any final repository design and as a result of any licensing review of the repository by the U.S. Nuclear Regulatory Commission. The design evolution is evaluated in the Supplement to the Draft EIS and integrated into the Final EIS. The Supplement to the Draft EIS incorporates new information, including an improved understanding of the interactions of potential repository features with the natural environment, the addition of design features for enhanced waste containment and isolation, and evolving regulatory requirements. The design will continue to evolve in response to additional site characterization information, technological developments, and interactions with oversight agencies. Section 2.3.4 of the Supplement describes the design modifications (engineered barrier designs) including the addition of drip shields and refined waste packages.
    With regard to the design process, DOE is moving forward with a final design but acknowledges, as noted above and as documented by the Supplement to the Draft EIS, the design could further evolve. The updated design information presented in the Supplement was carried forward to the Final EIS. However, DOE believes the design has progressed to a point that it provides a reasonable basis for estimating the range of potential short- and long- term impacts that would likely result from any final design.

67. As noted by the EPA, DOE has consulted, and will continue to consult, with tribal governments as sovereign entities that possess authority and responsibility for Native American territory. A major objective of these consultations is to ensure that the EIS addresses the full range of Native American cultural and technical concerns related to the Proposed Action. Moreover, in these consultations DOE makes every effort to avoid compromising the interests of individual tribes and, thus, to minimize conflicts between tribes and tribal groups or other local (nontribal) government entities.
    Native Americans have expressed general concern about the impacts of the candidate rail corridors, heavy-haul truck routes, and intermodal transfer station locations. Consistent with its trust responsibilities, DOE does not intend to take action, make decisions, or implement programs without consulting affected tribal governments. In all cases, project decisions will incorporate input from affected tribes.
    DOE prepared the EIS in accordance with Section 2 of the Nuclear Waste Policy Act of 1982, which defines affected Indian Tribes as "…any Indian Tribe—(A) within whose reservation boundaries a monitored retrievable storage facility, test and evaluation facility, or a repository for high-level waste or spent nuclear fuel is proposed to be located; and (B) whose federally defined possessory or usage rights to other lands outside the reservations boundaries arising out of congressionally ratified treaties may be substantially and adversely affected by locating such a facility: Provided that the Secretary of Interior finds, upon the petition of the appropriate government officials of the Tribe that such effects are both substantial and adverse to the tribe." For this EIS, "Native American" means "Indian" or "American Indian."

68. In response to public comments, DOE has revised Figures 2-25 and 2-26 of the EIS to show Federally recognized tribal lands located along highway and rail routes that could be used for national transportation.

69. DOE has maintained a Native American Interaction Program with 16 tribes and one organization since the mid-1980s. Tribal representatives are named by their respective tribes to sit on a DOE-funded, self-organized committee called the Consolidated Group of Tribes and Organizations, whose charter is to present their respective tribal concerns and perspectives to the Department. The Group meets twice per year and participates in field trips to Yucca Mountain to impart cultural resource protection information and to become more aware of the studies being conducted. While the Group does not support the potential use of Yucca Mountain as a repository, they have agreed to be involved in an honest and participatory process. DOE will continue to support the Group and Native American Interaction Program while carrying out the mission of characterizing the Yucca Mountain site. The DOE also supported an American Indian Writers Subgroup process in the preparation of a report that provides Native American perspectives on the repository to be used in writing the EIS. The Native American Interaction Program is described in Section 3.1.6.2.1 of the EIS. The Native American view of the affected environment is described in Section 3.1.6.2.2 of the EIS and the impacts from the Proposed Action are discussed in Chapter 4 of the EIS. Section 4.1.5.2 of the EIS addresses the Native American viewpoint with regard as to how the proposed project would affect cultural resources in the Yucca Mountain area. Section 4.1.13.4 of the EIS discusses the Native American perspective regarding the proposed repository and the surrounding region. These beliefs have been documented in American Indian Perspectives on the Yucca Mountain Site Characterization Project and the Repository Environmental Impact Statement (DIRS 102043-AIWS 1998), which has been sent to the commenter.

70. The Department of the Interior’s expressed policy is that its bureaus receive National Environmental Policy Act documents through a coordinated distribution from its Office of Environmental Policy and Compliance. In addition, DOE will send a copy of the Final EIS directly to the Bureau of Indian Affairs as recommended.

71. Chapter 5 and Appendix I of the EIS describe environmental consequences (primarily potential groundwater impacts) from the long-term performance of the repository. Section 5.4 of the EIS contains information on the radiological impacts on human health, and Section 5.6 examines the consequences from chemically toxic materials during the first 10,000 years after closure. Environmental Protection Agency regulations (40 CFR Part 197) and Nuclear Regulatory Commission regulations (10 CFR Part 63) require that DOE demonstrate that releases from the repository would not exceed limits specified in those regulations over a 10,000-year period. DOE recognizes that some radionuclides and potentially toxic chemicals would, after long periods, eventually enter the environment outside the repository. Nevertheless, modeling of long-term repository performance indicates that the combination of natural and engineered barriers would keep doses resulting from such releases below the regulatory limits established by 40 CFR Part 197 and 10 CFR Part 63.
    Nevada water-quality regulations (Nevada Administrative Code 445A.119-225), discussed in Section 11.2.2 of the EIS, are not applicable to the long-term performance of the repository. These regulations specify water-quality standards that the Environmental Protection Agency and the State regulate by issuing permits for point-source discharges and runoff to maintain water quality. Section 4.1.3 of the EIS discusses the impacts to surface-water and groundwater hydrology during construction, operation and monitoring, and closure of the proposed repository. DOE does not anticipate any point-source discharges, but has concluded that repository operations would result in minor changes to runoff and infiltration. DOE would comply with all applicable permit conditions.

72. Thank you for your comment.

73. Chapter 5 and Appendix I of the EIS describe environmental consequences (primarily potential groundwater impacts) from the long-term performance of the repository. Section 5.4 of the EIS contains information on the radiological impacts on human health, and Section 5.6 examines the consequences from chemically toxic materials during the first 10,000 years after closure. Regulations established by the Environmental Protection Agency (40 CFR Part 197) and the Nuclear Regulatory Commission (10 CFR Part 63) require that DOE demonstrate that doses resulting from releases of radionuclides from the repository would not exceed limits specified in those regulations over a 10,000-year period. DOE recognizes that some radionuclides and potentially toxic chemicals would, after long periods, eventually enter the environment outside the repository. Nevertheless, modeling of long-term repository performance indicates that the combination of natural and engineered barriers would keep such releases below the regulatory limits established by 40 CFR Part 197 and 10 CFR Part 63.
    Nevada water quality regulations (Nevada Administrative Code 445A.119-225), discussed in Section 11.2.2 of the EIS, are not applicable to the long-term performance of the repository. These regulations specify water quality standards that the Environmental Protection Agency and the State regulates by issuing permits for point-source discharges and runoff to maintain water quality. Section 4.1.3 of the EIS discusses the impacts to surface water and groundwater hydrology during construction, operation and monitoring, and closure of the proposed repository. DOE does not anticipate any point-source discharges, but has concluded that repository operations would result in minor changes to runoff and infiltration. However, DOE does not anticipate any impacts from the repository on watering of livestock without treatment, habitat for fish and other aquatic life existing in a body of water, the suitability of the water for propagation of wildlife and waterfowl without treatment, or any unique ecological or aesthetic value of the water. DOE would comply with all applicable permit conditions.

74. Chapter 5 and Appendix I of the EIS describe environmental consequences from the long-term performance of the repository. Regulations established by both the Environmental Protection (40 CFR Part 197) and the Nuclear Regulatory Commission (10 CFR Part 63) require that DOE demonstrate that doses resulting from releases of radionuclides from the repository would not exceed limits specified in those regulations over a 10,000-year period. DOE recognizes that some radionuclides and potentially toxic chemicals would, after long periods, eventually enter the environment outside the repository. Nevertheless, modeling of long-term repository performance indicates that the combination of natural and engineered barriers would keep such releases well below the regulatory limits established by 40 CFR Part 197 and 10 CFR Part 63.
    The State of California Water Quality Standards are not directly applicable to discharges of groundwater to the surface. Water quality standards established by the Environmental Protection Agency and the states are regulated by the issuance of permits for point-source discharges and runoff to maintain water quality. Section 4.1.3 discusses impacts to surface-water and groundwater hydrology during construction, operation and monitoring, and closure of the proposed repository. DOE does not anticipate any point-source discharges, but has concluded that repository operations would result in minor changes to runoff and infiltration. DOE would comply with all applicable permit conditions.

75. The cited regulations are not directly applicable to the long-term performance of the proposed Yucca Mountain Repository. Regulations established by both the Environmental Protection Agency (40 CFR Part 197) and the Nuclear Regulatory Commission (10 CFR Part 63) require that DOE demonstrate that releases from the repository would not exceed limits specified in those regulations over a 10,000-year period. DOE recognizes that some radionuclides and potentially toxic chemicals would, after long periods, eventually enter the environment outside the repository. Nevertheless, modeling of long-term repository performance indicates that the combination of natural and engineered barriers would keep doses resulting from such releases well within the regulatory limits established by 40 CFR Part 197 and 10 CFR Part 63.
    The concentration of radionuclides at the chief discharge point (Franklin Lake Playa) after 10,000 years would not be deleterious to human heath (see Section 5.4) or to the health of plants or animals (see Section 5.9). Concentrations of radionuclides downgradient from Franklin Lake Playa (farther away from Yucca Mountain) after 10,000 years would be even lower.

76. Under Waste Acceptance System Requirements Document (DIRS 110306-DOE 1999), RCRA-regulated high-level radioactive waste would not be accepted for disposal at the Yucca Mountain repository. DOE is aware that the high-level radioactive waste at both the Idaho National Engineering and Environmental Laboratory and the Hanford Site contains listed hazardous wastes that would have to be "delisted" by the Environmental Protection Agency and the appropriate States. The Department would have to petition the Environmental Protection Agency to delist the waste. Petitions to the relevant states could also be required. DOE would work with the states and the Environmental Protection Agency to ensure they have the information they need to evaluate the delisting petitions.
    DOE high-level radioactive waste also exhibits certain characteristics of hazardous waste (specifically corrosivity and toxicity) prior to treatment. The treated waste would not exhibit any of the characteristics of a hazardous waste. Characteristic hazardous wastes do not require a petition and rulemaking by the Environmental Protection Agency to exit the hazardous waste system, although the Department would need to have supporting data and information to demonstrate that the characteristics have been removed from the treated waste form.
    DOE has revised the discussion in Chapter 11 of the Final EIS to clarify these questions.

77. The table in question appears in Section I.3.2 of the Final EIS. A footnote has been added to the table to show that the high-level waste form that would be disposed of in the proposed repository would not exhibit the Characteristic of Toxicity as measured by the Toxicity Characteristic Leaching Procedure. Section 11.2.4 discusses listed waste that would have to be delisted prior to emplacement in the repository. Waste shipped to the repository would not be regulated as hazardous waste under the Resource Conservation and Recovery Act.

78. Asbestos is not used in the manufacture of nuclear fuel, nor is it contained in high-level radioactive waste. Polychlorinated biphenyls (PCBs) are not used in the manufacture of nuclear fuel. While some high-level radioactive wastes are contaminated with PCBs, detectable levels of PCBs are unlikely to remain in the vitrified high-level radioactive waste forms. Therefore, the Toxic Substances Control Act, its implementing regulations, and regulations governing disposal of asbestos (or PCBs) are not applicable to the proposed repository.

79. DOE approved Order 435.1 after it issued the Draft EIS. As a result, it has included DOE Order 435.1 in the Final EIS table (Section 11.3), and has deleted the reference to DOE Order 5820.2A.

80. DOE has revised Table 11-1 of the EIS to include a discussion of the Yucca Mountain-specific radiation standards at 40 CFR Part 197 that would govern surface and subsurface operational activities at the repository. These new standards implement the general requirements of 40 CFR Part 191 for the proposed Yucca Mountain Repository.

81. This comment is correct. DOE has modified the definition of "controlled area" in the Glossary (Chapter 14) to be consistent with 40 CFR Part 197.

82. DOE agrees with this recommendation and has included this change in the EIS Glossary.

83. In EIS Glossary, DOE has modified the definition of institutional control to include the distinction between active and passive control.

84. DOE has revised these definitions in the Final EIS. Chapters 4, 6, and 7 now use the term "maximally exposed individual," and Chapter 5 uses "receptor." The receptor is equivalent to both the "reasonably maximally exposed individual" defined in the Environmental Protection Agency’s regulations at 40 CFR Part 197. This change reflects the regulatory definitions and requirements for long-term performance recently promulgated by both agencies.

85. The text and reference cited in this comment do not appear in the Final EIS.

86. The reference format that DOE used in the EIS is consistent with document traceability requirements the Department established for the Yucca Mountain Project. The Environmental Protection Agency report number is part of the reference text.

87. Section J.1.4.2.1 of the EIS contains a discussion of accident severity categories, conditional probabilities, and release fractions. Figure J-9 shows the values for pressurized-water and boiling-water reactor spent nuclear fuel, respectively.

88. Both No-Action scenarios assume that the onsite storage facilities would remain under effective institutional control for the first 100 years. This means that they would be monitored and maintained with repairs being made as necessary to ensure the integrity of the dry storage canisters. DOE recognizes that the weather-protection structures (metal buildings for DOE below-grade storage vaults and reinforced concrete storage modules for commercial spent nuclear fuel), as currently constructed, would not likely remain intact for the 100-year institutional control period without major repairs. Therefore, the Department assumed that a major repair effort would occur 50 years into the 100-year period (see the figure in the introduction to Chapter 7 of the EIS). For purposes of analysis, DOE assumed this major repair effort to require 50 percent of the manpower and materials required to completely replace the facilities. Collective occupational radiation doses were estimated to be 72 and 118 person-rem for the Proposed Action and Module 1 scenarios, respectively (see DIRS 104596-Orthen 1999). Although not reported separately, these impacts have been included in the short-term (first 100 years) impacts for both scenarios, as discussed in Sections 7.2.1 and 7.3.2 of the EIS.
    Although the analysis assumed that under institutional control the storage facilities would be maintained and repaired as necessary, Sections K.4.1.1 and K.4.3.1 of the EIS discuss the uncertainties associated with maintenance of institutional control and uncertainties associated with environmental degradation and corrosion rates along with their potential impacts on the reported results. As stated in Section K.4.1.1, premature failure of effective institutional controls could result in an earlier release of radioactive materials to the accessible environment. However, this scenario would probably increase overall impacts by no more than a factor of 2.

89. DOE agrees that there is some limited potential for a criticality event to occur in degraded spent nuclear fuel canisters. However, DOE believes the discussion in Section K.2.5.2 of the EIS includes the appropriate level of analysis and qualitative description of probability. There are many uncertainties and speculative processes involved in the hypothetical scenario that assumes no effective institutional control after approximately 100 years, as well as the sequence of events that could occur within that scenario. DOE does not believe it is possible to establish defensible probabilities for this No-Action accident scenario or the components of the scenario described in this comment that could lead to potential criticality during extended periods of dry storage with no institutional control (Scenario 2 of the No-Action analysis). Other factors that the analysis would have to quantify to estimate those probabilities would be different climatic conditions around the country, the different types of commercially available dry storage configurations, the range of burnup in the spent nuclear fuel, and the initial enrichment of the fuel.
    Rather than specific probability analyses of the impacts associated with this No-Action scenario, the EIS provides qualitative descriptions of the relative likelihood of criticality events. First, the EIS states that criticality could be possible (in degraded storage canisters) if other conditions were met simultaneously. Those other conditions are a configuration that would allow water to enter but not drain out of the storage canister and fuel containing sufficient fissionable atoms to allow criticality. The second condition would depend on initial enrichment and burnup of the fuel. The EIS also states that a small amount of the spent nuclear fuel would be likely to have the appropriate enrichment burnup combinations, which could enable criticality to occur. Three types of criticality events were acknowledged as possible with only the most energetic type having potential to produce large impacts. That event is possible, but highly unlikely. It could happen only if sufficient amounts of fissionable material were brought together suddenly into a critical configuration. The more likely possibility would be for water to build up around degraded fuel elements. If fissions began to occur, the water would boil away and the criticality would stop. As noted in Section K.2.5.2 of the EIS, even the most energetic criticality would be unlikely to exceed the impacts associated with an aircraft crash onto a degraded dry storage module as evaluated in Section K.2.5.1. Therefore, DOE believes that further quantification of the probability of such an event would not provide useful information or be defensible.

90. As noted in the comment, DOE indicated in the Draft EIS its intention to evaluate updated designs in the Final EIS. Design updates were first presented and evaluated in the Supplement to the Draft EIS issued in May, 2001 and then integrated into the Final EIS. The Supplement to the Draft EIS presents new information, including an improved understanding of the interactions of potential repository features with the natural environment, the addition of design features for enhanced waste containment and isolation, and evolving regulatory requirements. The design will continue to evolve in response to additional site characterization information, technological developments, and interactions with oversight agencies.
    With regard to the design process, DOE is nearing a final design but acknowledges, as noted above and as documented by the Supplement to the Draft EIS, the design could further evolve. However, DOE believes the design has progressed to a point that it provides a reasonable basis for estimating the range of potential short- and long- term impacts that would likely result from any final design.

 

 

 

 

RESPONSES TO U.S. ENVIRONMENTAL PROTECTION AGENCY
COMMENTS ON THE SUPPLEMENT TO THE DRAFT EIS
(Comment Document 10231)

1. The Final EIS includes this Comment-Response Document, which identifies and addresses each of the comments received on both the Draft EIS and the Supplement to the Draft EIS. In response to public comments, DOE modified the Final EIS in a variety of ways, including clarifications or changes to the text, updating information, and modifying analyses. The Department considered comments on the Draft EIS in preparation of the Supplement to the Draft EIS (which were appropriately carried forward to the Final EIS). In part, for example, the comments received on the Draft EIS influenced DOE’s description of the Science and Engineering Report design elements presented in the Supplement. The Supplement was limited in scope to "aspects of the design that have changed since DOE issued the Draft EIS" (which did not include transportation).
   Consistent with Council and Environmental Quality and DOE regulations, the Department did not release the Comment-Response Document before issuing this Final EIS or hold hearings on the Comment-Response Document or this Final EIS.

2. In response to public comments, DOE modified the Final EIS in a variety of ways, including incorporation of the flexible design (introduced in the Yucca Mountain Science and Engineering Report and the Supplement to the Draft EIS), clarifications or changes to the text, updating information, and modifying analyses. DOE believes that the environmental impacts presented in the Final EIS for the flexible design (and its associated operating modes) bound reasonably foreseeable actions.
   In June 2001, DOE conducted three public hearings on the Supplement to the Draft EIS to provide the public with opportunities to comment on the Project’s latest plans for design and operation. In September and October 2001, the Project conducted hearings on key documents that were released in advance of a potential Site Recommendation [theYucca Mountain Science and Engineering Report (DIRS 153849-DOE 2001) and the Preliminary Site Suitability Evaluation (DIRS 155734-DOE 2001)].
   Upon issuance of the Final EIS, the public will have the opportunity to examine the Comment-Response Document and the Department’s response to the public’s comments. This approach is consistent with regulations issued by the Council on Environmental Quality and DOE’s implementation procedures at 10 CFR 1021.
   Should the Secretary of Energy recommend Yucca Mountain to the President, however, the recommendation would be accompanied by several supporting documents including the Final EIS and its Comment-Response Document. In the event Yucca Mountain was authorized and the project moved forward, DOE would submit a License Application to the Nuclear Regulatory Commission. The Nuclear Regulatory Commission’s licensing process would afford the public additional opportunities to review and comment on the specific design elements of the Yucca Mountain repository. In the event that DOE incorporated additional design modifications subsequent to the submittal of a License Application, the Nuclear Regulatory Commission’s licensing process would provide additional opportunities for the public to comment on the repository.

3. After DOE issued the Supplement to the Draft EIS in May 2001, both the Environmental Protection Agency standards at 40 CFR Part 197 and the Nuclear Regulatory Commission licensing criteria at 10 CFR Part 63 were promulgated. In addition, in 2001 DOE promulgated its 10 CFR Part 963 guidelines to be consistent with the adopted EPA standards and the NRC licensing criteria. The estimated impacts presented in the Final EIS fully consider, and provide comparisons with, the final standards as promulgated. DOE has modified Chapter 11 of the EIS to include the final regulations.

4. A postclosure monitoring program is required by 10 CFR Part 63. This program would include the monitoring activities that would be conducted around the repository after the facility was closed and sealed. The regulations require that a license amendment be submitted for permanent closure of the repository [10 CFR 63.51(a)(1) and (2)]. This amendment must specifically provide an update of the assessment for the repository’s performance for the period after permanent closure, as well as a description of the program for postclosure monitoring. This program would include continued oversight to prevent any activity at the site that posed an unreasonable risk of breaching the geologic repository’s engineered barriers; or increasing the exposure of individual members of the public to radiation beyond allowable limits. The details of this program would be defined during the processing of the license amendment application for permanent closure. Deferring a description of this program until the closure period would allow for the identification of appropriate technology including technology that could become available in the future.

5. The description in the Supplement to the Draft EIS should have read: Other support facilities planned for the North Portal Operations Area include basic facilities for personnel support, warehousing, security, and transportation (motor pool). Section 2.1.2.1.1 of the Final EIS reflects this clarification.

6. To avoid compromise, details of physical security plans are typically not made available to the public. However, DOE believes that security for the spent nuclear fuel surface aging facility would be similar to that required for existing commercial Independent Spent Nuclear Storage Facilities currently licensed by the Nuclear Regulatory Commission. At a minimum, security controls would include positive control on ingress and egress at the facility, as well as periodic surveillance by security personnel. Detailed security requirements for all areas of the proposed repository, including the fuel aging facility, would be included in the construction and operating license approved and issued by the Nuclear Regulatory Commission.

7. The flexible design does include monitoring of the exhaust air and the ability to filter the exhaust stream if radioactive contamination was detected. The design would comply with applicable health and safety requirements.

8. The Final EIS is based on the flexible design described in detail in the Science and Engineering Report (DIRS 153849-DOE 2001). Thermal management of the proposed repository would involve complex, nonlinear relationships among many parameters of the repository system [see the Science and Engineering Report (DIRS 153849-DOE 2001) for further discussion]. The major determinants of the peak temperatures are the age of the fuel at emplacement, the linear heat load along each drift, and the ventilation period after emplacement. By keeping the drift spacing constant, the overall feasibility of the various repository operating modes can be evaluated. The analysis presented in the Science and Engineering Report supports the environmental impact conclusions in the EIS. The Science and Engineering Report recognizes that the thermal load or areal mass loading can be varied also by the liner thermal load (which was done in the Science and Engineering Report), the drift spacing (which was not done in the Science and Engineering Report), or both. By varying the fuel age, waste package spacing, and ventilation, DOE has considered the major factors that would affect temperature variations in the repository. As noted in both the Science and Engineering Report and the Supplement to the Draft EIS, future studies could include variations in drift spacing. At present, DOE does not expect the conclusions drawn from the analysis in the Final EIS to change substantially as a result of variations in drift spacing versus waste package spacing.

9. As mentioned in Section 2.4 of the Supplement to the Draft EIS, uncertainties in future funding or the order of waste shipments might require the repository to be developed in a sequential manner, such as constructing the surface and subsurface facilities in portions or "modules." This approach would incorporate "lessons learned" from initial work into subsequent modules, reduce the initial construction costs and investment risk, and potentially increase confidence in meeting the schedule for waste receipt and emplacement. The intent of this discussion was not to imply that uncertain funding would increase confidence.

10. The information and analyses used to estimate the reasonably maximally exposed individual doses are provided in Appendix H. National Emission Standards for Hazardous Air Pollutants (40 CFR Part 61) are applicable only to routine or permitted releases. They do not apply to accidents. Since publication of the Draft EIS, the Environmental Protection Agency promulgated Public Health and Environmental Radiation Protection Standards for Yucca Mountain, Nevada, at 40 CFR Part 197, which included an annual dose limit to a member of the public of 15 millirem (40 CFR 197.4). In accordance with requirements of the Energy Policy Act, the Nuclear Regulatory Commission subsequently promulgated Yucca Mountain licensing criteria, which includes a Preclosure Public Health and Environmental Standard at 10 CFR 63.204 of 15 millirem per year to a member of the public. The appropriate sections of the EIS (including those mentioned in Chapter 8) have been updated to reflect a comparison to the recently promulgated standard of 15 millirem.

11. The flexible design presented in the Supplement to the Draft EIS was carried forward to the Final EIS analyses.

12. Golder Associates, Inc., developed both GoldSim (the integrating software used for the Supplement to the Draft EIS and Final EIS) and RIP (the software used for the Draft EIS). GoldSim is a new generation of the RIP program, not an entirely different program. The differences have more to do with user interface convenience and the mechanics of data handling than with the actual modeling. Nevertheless, as part of the production, delivery, and documentation of GoldSim, Golder Associates validated that program against RIP by running similar cases in both. Thus, differences in the integrating software caused no differences between the Draft EIS, the Supplement to the Draft EIS, and the Final EIS.

13. The modeling for the Supplement and the Final EIS for long-term performance analysis includes improved coupling of these processes over the essentially uncoupled versions used for the Draft EIS. Section I.2.3 of the Final EIS and the documents referenced in that chapter discuss these models.

14. As reported in Nuclear Waste Fund Fee Adequacy: An Assessment (DIRS 153257-DOE 2001), the nuclear waste fund investments had a market value of $8.5 billion as of September 30, 1999. The analysis in the report found that the current fee of 1 mil (one tenth of 1 cent) per kilowatt hour charged to generators of commercial spent nuclear fuel was adequate to cover projected disposal expenses (including costs associated with packaging and transportation) and recommended that the fee remain unchanged.
    Section 302 of the Nuclear Waste Policy Act of 1982 specifies that funding for disposal of commercial spent nuclear fuel is provided by payment of fees to the Secretary of Energy by the generators of electricity from nuclear power plants. Equivalent amounts are paid by the Federal Government to cover similar costs associated with disposal of spent nuclear fuel or high-level radioactive waste generated or owned by the United States. Utility fees and Federal appropriations are required to be sufficient to offset expenditures associated with repository studies; transportation; and operations and closure of a repository, as determined by an annual review by the Secretary of Energy. In the event that future generations decide that the potential repository should remain open for an extended period (up to 300 years or more), the fee structure could require modification. The statement, about "uncertain funding," was intended to be in the context of funding requirements for those activities (in the relative near-term leading up to the ability to receive and emplace waste (if the site was recommended and approved), and was not intended to reflect doubt about funding once the facility, if approved, became operational.

 

 

RESPONSES TO U.S. NUCLEAR REGULATORY COMMISSION
COMMENTS ON THE DRAFT EIS
(Comment Document 1898)

1. DOE has an ongoing program to address Nuclear Regulatory Commission comments on the Viability Assessment and other technical issues, largely as they have been translated into its comprehensive listing of scientific modeling issues in the Commission’s Issue Resolution Status Reports (see, for example, DIRS 135160-Bell 1996; DIRS 154605-NRC 2000). Not all technical issues raised by the Commission are closed, but DOE has made and will continue to make a good faith effort to address each issue to the extent practicable. As reported in the Final EIS, the Department has made a number of modifications to the design of the repository and to the Total System Performance Assessment model that address Commission concerns. As of September 2001, the Key Technical Issues have all been declared "Closed-Pending" by the Commission.
   DOE has made a similar best effort to address the status of model validation and data quality assurance. The Department recognizes that it needs to apply a rigorous and effective quality assurance program, and that doing so will be crucial to demonstrating the validity of findings and analyses in any License Application. In response to previous Nuclear Regulatory Commission comments in this area, DOE has established a schedule for achieving quality assurance goals by the time of the License Application, if Yucca Mountain is found suitable and approved for development of a repository. DOE has met interim quality assurance goals for the Site Recommendation phase.
   In the September 6, 2001, Quarterly Meeting with the Nuclear Regulatory Commission, DOE outlined the transition plans for the respective quality assurance programs which would support becoming a licensee. The Commission indicated further evaluation of implementation of these plans would take place in approximately 6 months.

2. In the Final EIS, DOE has identified and analyzed a higher-temperature operating mode and a range of lower-temperature operating modes. Chapter 2 and other related sections of the Final EIS have been revised to reflect this refinement in design selection, which basically is an establishment of design fundamentals such as drift layout, drift spacing, depth and location of emplacement areas, and location of ventilation raises. The Final EIS describes a design for the repository with variations on the operating mode. The key parameters defining the operating mode are package spacing, drift temperatures, length of active ventilation, and age of the fuel being emplaced. The range of variances in these parameters basically determine the extent of the repository design that will be utilized for the emplacement of the 70,000 metric tons of waste and fuel; the higher-temperature operating mode would require only the main central segment of the repository; several of the lower-temperature operating modes would use that segment and the western extension, while the "ultra" low-temperature operating modes would require use of the entire planned initial design. In this way, DOE has focused its analysis on a more clearly defined proposal, and demonstrated that the environmental impacts of the construction and operation of the proposed repository would not be likely to exceed the upper range of the estimated impacts. Tables in Chapter 2 of the EIS demonstrate the bounding nature of the flexible operating modes within construct of a fixed design.

3. The Final EIS addresses the relevant technical issues DOE received in comments from the Nuclear Regulatory Commission relative to specific technical issues and the Viability Assessment of a Repository at Yucca Mountain (DIRS 101779-DOE 1998).

4. In the Draft EIS and the Supplement to the Draft EIS, DOE analyzed a variety of scenarios that offer a range of options for implementing the Proposed Action to construct, operate (including transportation) and monitor, and eventually close a repository at Yucca Mountain. These scenarios, which reflect potential design considerations, waste packaging approaches, and modes for transporting spent nuclear fuel and high-level radioactive waste to the Yucca Mountain site, considered the range of the environmental impacts likely to result from the Proposed Action.
   In the Final EIS, DOE has identified and analyzed a range of operating modes from higher- to lower-temperature. The lower-temperature analytical scenario considered six cases. Chapter 2 of the EIS and other related sections of the Final EIS have been revised to reflect this refinement in design selection, which basically is an establishment of design fundamentals such as drift layout, drift spacing, depth and location of emplacement areas, and location of ventilation raises. The Final EIS describes a design for the repository with variations on the operating mode. The key parameters defining the flexible operating modes are package spacing, drift temperatures, length of active ventilation, and age of the fuel being emplaced. The range of variances in these parameters basically determine the extent of the repository design that will be utilized for emplacement of 70,000 metric tons of heavy metal of spent nuclear fuel and high-level radioactive waste; the higher-temperature operating mode would require only the main central segment of the repository; the lower-temperature operating mode could use that segment and the western extension, and could possibly require use of the entire available emplacement area. DOE has focused its analysis on a more clearly defined proposal, and demonstrated that the environmental impacts of the construction and operation of the proposed repository would not be likely to exceed the upper range of the estimated impacts.
   DOE believes that the information in the EIS on the potential direct, indirect, and cumulative impacts that could result from the Proposed Action is sufficient. This belief is based on the level of information and analysis, the analytical methods and approaches used to represent conservatively the reasonably foreseeable impacts that could occur, and the use of "bounding assumptions" if information is incomplete or unavailable and if uncertainties exist.
   For the same reasons, DOE believes that the EIS provides the information necessary to make decisions on the basic approaches to transporting spent nuclear fuel and high-level radioactive waste (such as mostly rail or mostly truck shipments), as well as the choice between alternative rail corridors in Nevada. However, follow-up implementing decisions, such as the selection of a specific alignment in a corridor, the specific location of an intermodal transfer station, or the need to upgrade heavy-haul truck routes, would require field surveys, State and local government consultations, environmental and engineering analyses, and National Environmental Policy Act reviews.

5. Since the issuance of the Draft EIS, the Department has continued to evaluate actions in the region of influence that could pose a potential cumulative impact. As a result of these reviews, the Department identified several new actions for which information was not available for the Draft EIS. These actions come from several agencies and private companies. For instance, Section 8.1.2.2 of the Final EIS contains an expanded discussion of the Timbisha Shoshone Homeland Act, along with possible implications to groundwater rights. Chapter 8 also contains discussions of other actions by the Bureau of Land Management (e.g., the Ivanpah Cargo Airport, the Moapa Paiute Energy Center); these actions were considered when evaluating the cumulative impacts for the technical discipline areas.
   As part of the updated analyses, the Department has expanded the land-use discussion in Chapter 8 to address specifically the known actions that have been identified since the publication of the Draft EIS. Where possible, the Department has identified changes in land use along with estimates of area to be disturbed and possible impacts with other actions in the area. In addition, all discipline areas (for example, biological resources and cultural resources) were reviewed to ensure that the appropriate level of discussion was included to address the potential cumulative impacts of all the actions. However, not all actions could be evaluated to the same level of detail because information was not always available to allow an in-depth evaluation.

6. DOE believes that the EIS adequately analyzes the environmental impacts that could result from the Proposed Action. This belief is based on the level of information and analysis, the analytical methods and approaches used to represent conservatively the reasonably foreseeable impacts, and the use of bounding assumptions where information is incomplete or unavailable, or where uncertainties exist. The use of widely accepted analytical tools, latest reasonably available information, and cautious but reasonable assumptions offer the most appropriate means to arrive at conservative estimates of transportation-related impacts.
   For the reasons discussed above, DOE believes that the EIS provides the environmental impact information necessary to make certain broad transportation-related decisions, namely the choice of a national mode of transportation outside Nevada (mostly rail or mostly legal-weight truck), the choice among alternative transportation modes in Nevada (mostly rail, mostly legal-weight truck, or heavy-haul truck with use of an associated intermodal transfer station), and the choice among alternative rail corridors or heavy-haul truck routes with use of an associated intermodal transfer station in Nevada. DOE has identified mostly rail as its preferred mode of transportation, both nationally and in Nevada. At this time, however, the Department has not identified a preference among the five candidate rail corridors in Nevada.
   If the Yucca Mountain site was approved, DOE would issue at some future date, a Record of Decision to select a mode of transportation. If, for example, mostly rail was selected (both nationally and in Nevada), DOE would identify a preference for one of the rail corridors in consultation with affected stakeholders, particularly the State of Nevada. In this example, DOE would announce a preferred corridor in the Federal Register and other media. No sooner than 30 days after the announcement of a preference, DOE would publish its selection of a rail corridor in a Record of Decision. A similar process would occur in the event that DOE selected heavy-haul truck as its mode of transportation in Nevada. Other transportation decisions, such as the selection of a specific rail alignment within a corridor, would require additional field surveys, State and local government and Native American tribal consultations, environmental and engineering analyses, and appropriate National Environmental Policy Act reviews.
   In this EIS, DOE has used computer models it has used in previous EISs and other studies. These models are widely accepted by the national and international scientific and regulatory communities. For instance, DOE selected the RADTRAN 5 computer program to estimate radiological impacts to populations from incident-free transportation and from accidents. RADTRAN, which was originally developed by Sandia National Laboratories in the late 1970s, has been used in many other previous DOE EISs, and it has undergone periodic review and revision. In 1995, an independent validation review of RADTRAN 4 (immediate predecessor to RADTRAN 5) demonstrated that it yielded acceptable results when compared to "hand" calculations. More recently, an independent review found that RADTRAN 5 overestimates the measured radiation dose to an individual from moving radiation sources.
   To ensure that the EIS analyses reflect the best latest reasonably available information, DOE has either incorporated information that has become available since the publication of the Draft EIS or modified existing information to accommodate conditions likely to be encountered over the life of the Proposed Action. For example, the analysis in the Draft EIS relies on population information from the 1990 Census. In this Final EIS, DOE has scaled impacts upward to reflect the relative state-by-state population growth to 2035, using 2000 Census data.
   Although the EIS analyses are based on the best latest reasonably available information and state-of-the-art analytical tools, not all aspects of incident-free transportation or accident conditions can be known with absolute certainty. In such instances, DOE has relied on conservative assumptions that tend to overestimate impacts. For instance, DOE assumed that the radiation dose external to each vehicle carrying a cask during routine transportation would be the maximum allowed by U.S. Department of Transportation regulations. Similarly, DOE assumed that an individual, the "maximally exposed individual," would be a resident living 30 meters (100 feet) from a point where all truck shipments, or 200 meters (660 feet) from a point where all rail shipments would pass. Under these circumstances, the maximally exposed individual would receive a dose of about 6 millirem from exposure to all truck shipments, and a dose of about 2 millirem from exposure to all rail shipments (6 millirem represents an increased probability of contracting a fatal cancer of 3 in 1 million). Although it can be argued that individuals could live closer to these shipments, it is highly unlikely that an individual would be exposed to all shipments over the 24-year period of shipments to the repository, even though DOE incorporated this highly conservative assumption in the analysis.

7. At present, DOE does not have definitive information on specific tracts of land or community elements that the Proposed Action could affect, so it is premature to identify specific mitigation measures categorically. If the repository was approved, however, DOE would have discussions with potentially affected units of local government and consider appropriate support and mitigation measures. DOE would also continue its ongoing interactions with Native American tribes. In addition, specific mitigation measures could be part of a Mitigation Action Plan or similar plan, such as terms and conditions to Biological Opinions from the U.S. Fish and Wildlife Service and Nuclear Regulatory Commission licensing conditions. DOE, in submitting an application to construct and operate a repository, would identify relevant mitigation measures to the Commission for its consideration, and could reasonably expect a comprehensive set of mitigation measures or conditions of approval to be part of any licensing process. At this time, DOE has not decided whether to prepare a Mitigation Action Plan. As described in Chapter 9 of the EIS, DOE intends to commit to reasonable management actions required to mitigate potential adverse environmental impacts. The Department would develop mitigation actions in cooperation with potentially affected units of local government.
   Section 116(c)(2)(A)(i) and (ii) of the NWPA state that "the Secretary shall provide financial and technical assistance to the State of Nevada and any affected unit of local government…to mitigate the impact on such State [Nevada] or affected unit of local government of the development of [a] repository and the characterization of [the Yucca Mountain] site." Such assistance can be given to mitigate likely "economic, social, public health and safety, and environmental impacts." Within that broad framework, neither Section 116 nor any other provision of the NWPA limits the impacts that are subject to assistance under Section 116 to the environmental impacts considered in this EIS. This section also allows payments to the State of Nevada and to any affected unit of local government equal to taxes they would have received if the activity was performed by a non-Federal entity.
   Under the NWPA, the Section 116 impact assistance review process and the Yucca Mountain Repository EIS process are distinct from one another, and the implementation of one would not depend on the implementation of the other. Thus, the provision of assistance under Section 116 would not be limited either by the impacts identified in this EIS or by its findings on such impacts. A decision to provide assistance under Section 116 would be based on an evaluation of a report submitted by an affected unit of local government or the State of Nevada pursuant to Section 116 to document likely economic, social, public health and safety, and environmental impacts. Similarly, Section 180(c) of the NWPA requires the Secretary of Energy to provide technical assistance and funds for training public safety officials of appropriate units of local government and Native American tribes through whose jurisdictions DOE would transport spent nuclear fuel and high-level radioactive waste.
   Mitigation measures discussed in the EIS include those for water use (Sections 9.2.3 and 9.3.3), cultural resources (Sections 9.2.5 and 9.3.5), biological resources (Sections 9.2.4 and 9.3.4); and public health and safety (Sections 9.2.6 and 9.3.6). Chapter 9 discusses impacts in addition to the areas mentioned in this comment. Conversely, DOE has generally not proposed mitigation measures in areas where analyses did not identify consequential impacts. In some instances, an analysis might reveal impacts for which there would be no practical mitigation measures. Decisionmakers would consider the unmitigated consequences in weighing the need for the project against the potential for adverse consequences.
   With regard to this comment’s example of mitigative measures for Native American interests, DOE supported the preparation of the American Indian Writers Subgroup document (DIRS 102043-AIWS 1998) and used it as a primary reference to the EIS (see Sections 3.1.6.2.2 and 4.1.13.4). DOE would include avoidance of significant archaeological sites as a mitigative action where feasible. If avoidance was not feasible, a data recovery effort would preserve the archaeological data. In addition, DOE would implement Section 180(c) of the NWPA, which requires the Secretary of Energy to provide technical assistance and funds for training public safety officials of appropriate units of government and Native American tribes through whose jurisdictions transportation of spent nuclear fuel and high-level radioactive waste would occur. The training would cover procedures for safe routine transportation and for dealing with emergency response situations.
   Since issuing the Draft EIS, DOE has continued to evaluate design features and operating modes that would reduce uncertainties in or improve long-term repository performance, and would improve operational safety and efficiency. The result of the design evolution process was the development of the flexible design (which the Supplement to the Draft EIS called the Science and Engineering Report Flexible Design). Although this design focuses on controlling the temperature of the rock between the waste emplacement drifts (as opposed to areal mass loading) the basic elements of the Proposed Action to construct, operate and monitor, and eventually close a geologic repository at Yucca Mountain remain unchanged.
   DOE would monitor impacts during the construction and operation of the repository. A postclosure monitoring program, required by 10 CFR Part 63, would include monitoring activities around the repository after closure. The regulation requires submittal of a license amendment for permanent closure of the repository [10 CFR 63.51(a)(1) and (2)]. This amendment must provide an update of the assessment for repository performance for the period after permanent closure, as well as a description of the program for postclosure monitoring. This program would include continued oversight to prevent any activity at the site that posed 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. The details of this program would be defined during the processing of the license amendment for permanent closure. Deferring final development of this program until the closure period would enable a more complete understanding of the circumstances of the repository at closure and incorporation and use of new technologies that could become available by closure.

8. DOE determined that it is not necessary to examine the composition of the general population residing along existing spent nuclear fuel and high-level radioactive waste transportation corridors before DOE can reasonably conclude that there would be no disproportionately high and adverse impacts to minority and low-income populations from the transportation of radioactive materials. In addition, as described in Chapter 6 of the EIS, incident-free transportation and the risks from transportation accidents (the maximum reasonably foreseeable accident scenario would have 2.3 chances in 10 million of occurring per year would not present a large health and safety risk to the population as a whole, or to workers or individuals along national transportation routes. The low effect on the population as a whole also would be likely for any segment of the population, including minorities, low-income groups, and members of Native American tribes.
   In response to comments, DOE also considered locations at which individuals could reside nearer to the candidate rail corridors and heavy-haul truck routes in Nevada as a way of representing conditions that could exist anywhere in potentially affected communities. For purposes of analysis, DOE assumed that a maximally exposed individual could reside or work as close as 4.9 meters (16 feet) to a potential heavy-haul truck route and 30 meters (98 feet) to a rail corridor. During the 24-year period of repository operations, if every shipment of spent nuclear fuel and high-level radioactive waste passed by these maximally exposed individuals, the would receive an estimated dose ranging from about 2 millirem (increased fatal cancer probability of 1 in 1 million) for rail shipment to about 29 millirem (increased fatal cancer probability of 2 in 100,000) for heavy-haul shipments.
   These exposures would be well below those received from natural background radiation, would not be discernible even if corresponding doses could be measured, and would not add measurably to other impacts that an individual could incur. For comparison, the lifetime likelihood of an individual incurring a fatal cancer from all other causes is about 1 in 4.
   However, the Final EIS examines the composition of the population along candidate rail corridors in Nevada. Selecting among alternative new routes may offer opportunities to avoid high and adverse impacts that would fall disproportionately on low-income or minority populations relative to the general population that would not be present when considering existing transportation corridors. Therefore, even though the health effects from exposure to radioactive materials from transportation activities would not implicate environmental justice concerns in selecting new routes, other factors such as the impacts of the construction and use of a newly created route on land use, socioeconomics, noise, air quality, and esthetics may vary by location. In response to comments, DOE has updated and refined information germane to the environmental justice analysis. For example, the EIS now includes additional and more detailed mapping and information that describes the proximity of tribal lands to rail corridors in Nevada. Section 6.3.4 of the Final EIS presents the analysis of environmental justice impacts in Nevada.

9. Federal Reserve Water Rights are noted in the footnote to Table 3-11, but are not quantified because they are not directly comparable to water appropriations authorized by the State of Nevada. As stated in the Final Environmental Impact Statement for the Nevada Test Site and Off-Site Locations in the State of Nevada (DIRS 101811-DOE 1996), the Federal Reserve Water Rights position is that the Nevada Test Site is "…entitled to withdraw the quantity of water necessary to support the NTS missions." The Nevada Test Site EIS does not quantify or limit these rights, except for their purpose, and the repository EIS concurs with this view. With respect to identifying committed water resources, the repository EIS is obligated to identify cumulative impacts of other Federal and non-Federal actions. Chapter 8 discusses the past, present, and foreseeable future actions and associated water demands. In this manner, the EIS does indirectly identify quantities of water expected to be associated with reserved water rights (that is, if their impacts would be cumulative with those of the Proposed Action).
   The purpose of Table 3-11 of the Draft EIS and its associated text is not to suggest that ample water is available. The intent is only to describe existing groundwater resources and use in the region of Yucca Mountain. DOE agrees that average withdrawals do not tell the entire story when looking at groundwater resources and their availability. This is the reason that both water appropriations and estimates of perennial yield are also shown in the table. In addition, DOE understands, though not expressed in the EIS, that the State Engineer must consider factors in addition to those shown in the table when considering requests for water appropriations.
   Chapter 8 of the EIS describes the cumulative impacts of groundwater use by the Nevada Test Site, Nellis Air Force Range, and the proposed repository. Additional text has been added to Section 8.2.3.2 to better address other uses of groundwater in the area. As identified in Section 4.1.3.3, the peak projected annual water demand for the proposed action [360,000 cubic meters (290 acre-feet)], when combined with projected demand from the Nevada Test Site [350,000 cubic meters (280 acre-feet)], would approach, but would not exceed, the lowest estimate of perennial yield for the western two-thirds of the Jackass Flats hydrographic area [720,000 cubic meters (580 acre-feet)]. The corresponding discussion in Section 4.1.3.1 of the EIS (impacts from performance confirmation) is intentionally brief because of the relatively small annual water demand projected for that phase of the project. The evaluation in this section compares projected water demand to the perennial yield estimates and shows them to be minor. The addition of the Nevada Test Site demand would still put projected water withdrawals well below the lowest estimates of perennial yield, which were not mentioned.
   With respect to the wide range of perennial yield figures identified for hydrographic area 227a, an explanation of the origin and basis for each of these numbers is beyond the scope of the EIS. A partial answer is that estimates of recharge are difficult and vary widely in this area where evapotranspiration is high and quantities of surface water are low. An order of magnitude difference between recharge estimates for the same study area is not unusual in the literature. The source of the perennial yield information presented in Table 3-11 of the Draft EIS is in a footnote to the table. The cited source identifies the studies from which the perennial yield values are taken and discusses those studies. The EIS recognizes that the Nevada Division of Water Planning uses an estimate of perennial yield that is not totally consistent with those listed in Table 3-11. Tables 3-35 and 3-43 of the Draft EIS both include a footnote indicating that the Nevada Division of Water Planning uses a combined perennial yield of 30 million cubic meters (24,000 acre-feet) for hydrographic areas 225 through 230. This estimate was not used in the tables because it has not been divided into the individual areas. DOE thought it important to give estimates and discuss perennial yield based on these smaller areas, so it used the best available data (on an individual hydrographic area basis). DOE believes that the EIS considers a wide range of perennial yield values, particularly for hydrographic area 227a (Jackass Flats), and that this is appropriate and conservative. The fact that the Nevada Division of Water Planing uses different values for some of the committed resources is due to the use of a more recent reference in the EIS (DIRS 103406-NDWP 1992).
   As indicated above, Chapter 8 of the EIS discusses other (nonrepository) water demands in the Yucca Mountain region. However, Section 4.1.3.3 does clearly indicate that there would be an ongoing Nevada Test Site water demand from the same hydrographic area from which the Yucca Mountain Site Characterization Project would be withdrawing water. This section does not mention water demands for the Nellis Air Force Range because there are no demands in this hydrographic area. It does discuss the potential for overdraft of this hydrographic area. This hydrographic area (227a – Jackass Flats) is not an isolated basin. It receives water both from the surface (recharge from precipitation) and as underflow from upgradient areas. It also loses water as underflow to downgradient areas. As described in the EIS, withdrawing only slightly more water than the low estimate of perennial yield (which is based solely on recharge from local precipitation) would be unlikely to cause a depletion of the reservoir because of the higher quantities estimated to be moving through as underflow. However, it would probably result in a minor shifting of the general groundwater flow patterns to compensate. Since the publication of the Draft EIS, two groundwater modeling efforts have been completed to simulate the effects of the projected water demands by the repository on the groundwater flow system. The Final EIS has been modified to discuss the results of these efforts, which are consistent with the general impacts discussed above.
   As indicated above, effects of overdrafting within Jackass Flats are discussed in this EIS and modifications have been added to the Final EIS to address the results of applicable modeling efforts. With respect to the Amargosa Desert, Section 4.1.3.3 of the EIS states that water demand associated with the proposed repository would have only a small impact on water availability in Amargosa Desert. That is, actual or potential overdrafting of groundwater in the Amargosa Desert would be attributed predominantly to pumping in that area and would not be substantially affected by the amount of water needed to support the repository. Accordingly, possible impacts from overdrafting in Amargosa Desert are not discussed in the EIS. Overdrafting at Yucca Flat is not described in the EIS because it does not have a direct connection to the Proposed Action. Figure 3-13 of the Draft EIS shows that Yucca Flat is within the Ash Meadows Groundwater Basin and the direction of groundwater flow from there is toward Frenchman Flat and eventually to the Ash Meadows area and, if remaining as underflow, to the Amargosa Desert. This is consistent with the State of Nevada report Water for Nevada (DIRS 103016-State of Nevada 1971), which shows no groundwater inflow to this hydrographic area (area 159 – Yucca Flat), but does show its groundwater outflow going to Frenchman Flat, which also receives underflow from adjacent areas. The Nevada Test Site withdraws water from Frenchman Flat (hydrographic area 160), but at quantities far below its perennial yield (DIRS 101811-DOE 1996). Based on this picture of groundwater flow conditions, overdrafting at Yucca Flat would be expected to result in very localized conditions, probably not even extending far into Frenchman Flat because the combined water use for these two areas (Yucca and Frenchman Flats) is only a small fraction of their combined perennial yield [1.8 million cubic meters (1,400 acre-feet) of peak annual water demand versus 16,350 acre-feet of perennial yield (DIRS 101811-DOE 1996)]. Any affects on the groundwater flow from Yucca Flat overdrafting would surely be lost by the time groundwater flow reaches the southern end of the Amargosa Desert where impacts could be cumulative with those of the Proposed Action. Accordingly, Chapter 8 discusses impacts of the total water demand and cumulative impacts from the Nevada Test Site and the Proposed Action and does not address noncumulative issues that are internal to the Test Site.

10. The EIS identified a land withdrawal area in Section 3.1.1.3 to comply with regulations issued by the Nuclear Regulatory Commission concerning land ownership and control for a repository at Yucca Mountain (10 CFR Part 63). The safety of the repository requires DOE to demonstrate with a reasonable expectation that the long-term performance of the repository can meet the environmental radiation-protection standards established by the Environmental Protection Agency (40 CFR Part 197). Essentially all of the land identified for withdrawal (that is, about 229 out of 230 square miles) is Federal land. About 1 square kilometer at the southern end is private land. There is no State land or tribal land within the withdrawal area. If Congress withdrew the land for a repository as discussed in Section 4.1.1.1 of the EIS, it could specify conditions for other land uses as part of the withdrawal. The land withdrawal could eliminate currently existing opportunities for multiple use, including recreation, mineral exploration and mining. Because the lands within the withdrawal area do not have unique characteristics that have historically attracted the public, and because large tracts of public land occur nearby, DOE believes that the impacts to people who use this land would be negligible. DOE acknowledges in the EIS that Native Americans consider the intrusive nature of the repository to be an adverse impact to all elements of the natural and physical environment.

11. The statement in the Draft EIS on page 5-47, "There is considerable uncertainty in the estimates of soil temperature increases due to uncertainties in the thermal properties of the soil…" is misleading. There are some uncertainties in the thermal properties of the soil but these do not cause "considerable uncertainty" in the estimates of soil temperature increase. DOE has revised the text of the EIS to reflect this. While the Department acknowledges that some uncertainties exist in thermal properties of Yucca Mountain soils, the EIS modeling effort used the best available information for predicting average soil temperature increases. The model did not use the weekly to monthly soil temperatures to which the commenter refers because the time scale "could not be used to accurately estimate the soil thermal conductivity" (DIRS 103618-CRWMS M&O 1999). Rather, it used only hourly soil temperature measurements, which allowed the use of diurnal fluctuations to estimate the thermal diffusivity of the soil and provided a calibration for the thermal diffusivities modeled for wet, dry, and nominal soils. The thermal diffusivity obtained from the hourly soil temperature measurements was similar to that estimated for soils under wet conditions. Therefore, the thermal diffusivity estimated for dry soil represents a conservative value on predicted soil temperature increase, and the "available data suggest very modest temperature rises due to repository heat effects" (DIRS 103618-CRWMS M&O 1999). DOE has revised the EIS to clarify the reasons why dry soil thermal conductivity provides a conservative prediction of soil temperature increase. Temperature changes used to evaluate impacts were based on dry soils, and therefore cover the range of possible effects of soil warming on desert tortoises and other biological resources.
    As described in Section 5.9 of the EIS, based on these conservative calculations, the predicted increase in soil temperature at the shallow depth at which tortoises lay eggs would be very small compared to the range of natural variation in soil temperatures at Yucca Mountain (DIRS 105031-CRWMS M&O 1999) and the range of temperatures at which desert tortoise eggs have been successfully incubated. This small change in temperature, therefore, should have no adverse affect on tortoise eggs. Because of this and the small size of the affected area [about 3 square kilometers (740 acres)], DOE believes that impacts to the desert tortoise from heat generated by the proposed repository would be minimal.

12. DOE does not believe that quantitative analysis is either missing or required to conclude that the Proposed Action would have little effect on biological resources at Yucca Mountain. As stated in Section 4.1.4 of the EIS, the most important impacts of repository construction and operation on desert plants and animals would be the disturbance of about 3 to 7 square kilometers (about 800 to 1,700 acres) of land and the continuation of traffic and human presence. These activities would occur in a region with few other disturbances and would affect species that are common and widespread throughout the region. DOE based the conclusion that the Proposed Action would have little effect on desert tortoises on detailed site-specific research on the tortoise populations at Yucca Mountain during site characterization. That research confirmed that activities similar to those proposed have little effect on adjacent populations. DOE has modified Sections 4.1.4.1 and 4.1.4.2 of the EIS to better explain its conclusions about impacts to desert tortoises.
    The withdrawal of land surrounding the repository would protect a substantial area near the edge of the range of the tortoise from potential stressors that could occur if the land in the withdrawal area was developed for other uses.

13. The Final EIS presents the baseline information for economic measures to 2035. The intent of the cited statement in Section 4.1.6.2.1 is that there would not be a significant decline in the economy due to the closure of the repository. It does not indicate that individual workers might not be absorbed into the local economy fully using their "repository skills." This would be no different than the closure of any workplace, such as a manufacturing facility, where displaced employees might have to change occupations or move, although the impacts to the local economy might be small.

14. This comment takes issue with Section 6.3.2.2.1 of the EIS, which indicates "[t]he projected length of the corridor – 513 kilometers (319 miles) – is the most important factor for determining the number of workers [560] that would be required." Because DOE based the identification of the alternative corridors on a range of factors including land ownership, engineering, and terrain or steepness of grade, the length of the corridor inherently reflects of the weighing and balancing of these other factors. As a consequence, the length of a branch rail line would influence the number of workers required and worker productivity because of the engineering requirements and possible routing constraints in the initial layout of the corridor.
    With regard to the socioeconomic analyses in which the cited statement appears, the number of workers is the fundamental parameter for estimating other potential changes to the economy such as Gross Regional Product, disposable income, and State and local spending.

15. The EIS evaluated potential impacts from a regional volcanic eruption. Section H.2.1.3 of the EIS concludes that 3 centimeters (about 1.2 inches) is the maximum thickness of tephra (solid material; ash) from a "regional volcanic eruption, which is more likely," that could be deposited on repository facilities. Analyses to date indicate that such an event would not affect structures such as the Waste Handling Building, where DOE would process casks.
    The EIS analysis used a thickness-versus-distance curve from Miller et al. (DIRS 152166-1982). This curve shows that ash from the Long Valley Caldera/Mono-Inyo Volcanic area [about 250 kilometers (155 miles) west of Yucca Mountain] would deposit about 1 centimeter (0.4 inch) of ash at the proposed repository. The same volume of material from an eruption in the closer Coso Volcanic Field [about 150 kilometers (93 miles) southeast of Yucca Mountain] would deposit 2 to 3 centimeters (0.8 to 1.2 inches) of volcanic ash at the repository (DIRS 102889-Perry and Crow 1990).

16. Supporting analyses or references related to issues in this comment are available in the Environmental Baseline File: Archaeological Resources (DIRS 104997-CRWMS M&O 1999). That document includes a bibliography of cultural resource reports that contain specific details requested by the commenter. These documents are available from the Yucca Mountain Project Public Reading Room. DOE believes the level of information provided in the EIS is sufficient for decisionmakers to understand the issues and potential for impacts on archaeological and cultural resources.
    Archaeological field studies in support of the Yucca Mountain Project have been conducted since 1982 by the staff of the Desert Research Institute. Based on project needs during this period, several methodologies have been employed to characterize and protect archaeological sites and data. These include (1) use of existing archaeological data from previous projects, (2) intensive archaeological field surveys and limited subsurface testing, (3) preactivity surveys at areas ahead of planned ground-disturbing activities for areas lying outside of the acreage surveyed under the previous category, (4) data recovery, (5) random sample unit surveys for larger tracts outside the withdrawal area, and (6) archaeological site monitoring to assess changes to significant sites over time.
    Specific field methods and techniques employed at Yucca Mountain are outlined in the following documents:
    1. Programmatic Agreement Among the United States Department of Energy, The Advisory Council on Historic Preservation and the Nevada State Historic Preservation Officer for the First Nuclear Waste Deep Geologic Repository Program, Yucca Mountain, Nevada. (DIRS 157145-Gertz 1988)
    2. Research Design and Data Recovery Plan for Yucca Mountain Site Characterization Project (DIRS 103196-DOE 1990)
    3. Environmental Field Activity Plan for Archaeological Resources (DIRS 103198-YMP 1992)
    4. Branch Technical Procedures: Field Archaeology (DIRS 157150-DRI 1990)
    In addition to these generic documents, several project-specific individual research designs have been prepared for individual field survey, testing, and data recovery efforts undertaken by the Desert Research Institute. Copies of these documents are available from the Desert Research Institute, DOE, and the State Historic Preservation Officer.
    DOE used the combined information derived from implementation of the methods noted above to provide the summarization for the EIS. While precise figures (number of acres) have not been compiled for the entire land withdrawal area, all areas associated with the repository site that have either been disturbed by past site characterization activities or that are proposed for disturbance during repository construction and operation have been inventoried for archaeological resources. Archaeological data for other parts of the larger withdrawal area have received varying levels of archaeological study, ranging from random sample unit surveys to intensive coverage associated with preactivity activities away from the repository site. In some instances, known archaeological site data also are derived from surveys conducted by other agencies and/or projects (for example, Bureau of Land Management, Nellis Air Force Base, and the Nevada Test Site) on lands not currently managed by the Yucca Mountain Project.
    All of the historic sites discussed in Section 3.1.6 of the EIS are associated with non-Native American occupation and use of the area. Section 3.1.6.2.2 discusses historic-period Native American sites, which are documented in the Native American resource document prepared by the Consolidated Group of Tribes and Organizations’ American Indian Writers Subgroup (DIRS 102043-AIWS 1998).

17. The Draft EIS methodology for estimating source concentrations was detailed in Appendix I on pages I-15 to I-18 (Section I.3.2.3.1). This section describes in detail how the values in Tables I-11 and I-12 were developed using the EQ3/6 software. The values in Tables I-11 and I-12 were then used to develop the screening information in Table I-13 as explained in section I.3.2.3.2 (pages I-18 to I-19). This screening process determined which elements required more rigorous analysis (taking into account many other mitigating processes). Chemicals eliminated in the screening process demonstrated such low potential concentrations, in these calculations, that more rigorous analysis (which would account for additional mitigating processes) was unnecessary to establish there would be no significant impacts. In the screening analysis, EQ6 simulations of the reaction of the solution resulting from corrosion with the host rock demonstrated that nearly all the dissolved nickel would precipitate (resulting in a concentration of only about 0.0001 milligram per liter) upon contact with the crushed tuff invert (see Draft EIS Table I-12 and accompanying discussion). For this reason, nickel was not considered further in the impact analyses. Detailed analysis for those chemicals not screened out are described in Section I.6 of the Draft EIS. This material was referred to in Chapter 5 of the Draft EIS on page 5-39.
    The Final EIS analyzes the new waste package design (Alloy-22 outer shell with stainless-steel sleeve). The new analysis conservatively assumes the nickel reaction with tuff would not take place. As detailed in Section I.6 of the Final EIS, bounding calculations (not taking into account many mitigating processes) still indicate a nickel concentration producing only a small fraction of the oral reference dose for nickel.

18. These sections differed because some addressed exposure of workers during working hours, while others addressed the continuous exposure of members of the public. Sections 3.1.8.2 and F.1.1.6 are specifically concerned with the potential exposure of workers. Radon concentrations at points of exposure within the repository and several kilometers from repository ventilation exhaust are considerably different. The use in the Draft EIS was consistent and appropriate.
    The Final EIS uses more recent repository radon flux information that has become available since the Draft EIS was published. This new information has replaced much of the information used as the basis of estimates in the Draft EIS. Dose estimates to subsurface workers from radon decay products now use Working Level estimates made for the flexible design (DIRS 154176-CRWMS M&O 2000). Section F.1.1.6 of the Final EIS describes these dose estimates. Working Level estimates can be converted to estimates of dose using a published conversion factor (DIRS 103279-ICRP 1994). Dose estimates for members of the public are also based on new estimates of radon release from the repository, which take advantage of new analyses of ventilation and radon flux from the repository walls (DIRS 150246-CRWMS M&O 2000; DIRS 154176-CRWMS M&O 2000). Section 4.1.2 reports revised dose estimates for the public from radon.
    Information was not available for the Draft EIS to take into account the effect of heating of the emplacement drift walls by the waste packages. The analyses noted above have addressed the effect of heating (DIRS 154176-CRWMS M&O 2000), and the Final EIS takes this factor into account. All analysis scenarios for the Draft and Final EIS account for the effects of different repository sizes or volumes. A larger repository has a correspondingly larger radon release. However, the radon flux from repository walls and total radon release is not directly proportional to the total repository volume. Radon flux and release depend on the specific characteristics of the repository, including the relative quantity of larger-diameter excavations such as access mains, 5.5-meter (18-foot)-diameter excavations such as emplacement drifts, and smaller excavations such as ventilation raises. Radon release also depends upon the project phase, and whether or not a specific excavation would have a concrete liner (which would reduce radon flux).
    The statement in Section 4.1.7.3.1 of the Draft EIS that radiological health impacts in the "surface" facilities are independent of thermal load scenarios is unrelated to subsurface radon release. The bulk of dose to surface workers is due to handling of spent nuclear fuel, which depends on the facility throughput, (that is, 63,000 metric tons of heavy metal for the Proposed Action). The dose contribution from radon released from the subsurface is negligible. These statements remain correct for the Flexible Design evaluated in the Final EIS. Additional clarification on the contribution of subsurface radon to workers doses has been added.
    Sections G.2 and F.1.1.6 have been extensively revised in the Final EIS to present the new information noted above, as have the corresponding impacts in Sections 4.1.2 and 4.1.7.

19. DOE recognizes that neither No-Action scenario is likely to occur (see Section 2.2 and the introduction to Chapter 7 of the EIS). However, they were identified to provide a basis for comparison to the Proposed Action and because they reflect a range of potential impacts that could occur from the continued storage of material at these sites. For example, the impacts associated with the first 100 years of effective institutional control (either Scenario 1 or Scenario 2 of the No-Action Alternative) enable a direct comparison to the impacts of the Proposed Action during the first 100 years after closure of the repository. For purposes of analysis and to be consistent with the Proposed Action, Scenario 2 does not assume credit for institutional control after approximately 100 years. Under this scenario storage facilities and spent nuclear fuel and high-level radioactive waste would degrade, and radioactive material would eventually enter the accessible environment. This assumption is based upon a review of generally applicable Environmental Protection Agency regulations for the disposal of spent nuclear fuel and high-level radioactive waste (40 CFR Part 191) and the National Academy of Sciences review of standards for the proposed Yucca Mountain Repository (DIRS 100018-National Research Council 1995). Each of these references generally discounts the consideration of institutional control for longer periods of performance assessments for geologic repositories.
    Section K.4.1.1 of the EIS discusses the uncertainties associated with changes in societal values that could lead to the loss of institutional controls. Although these conditions might be difficult to imagine happening in the United States, they are not unlike what has occurred recently in the former Soviet Union and Germany prior to the end of World War II. The evaluation of Scenario 2 was not included in the EIS as a scare tactic. In fact, DOE took extreme care to avoid overestimating any impact from the No-Action Alternative. By intentionally using a realistic best estimate modeling approach (see Section K.1) and by not including all potential human exposure pathways (see Section K.3.1), DOE concludes that the impacts of such a scenario might have been underestimated by several orders of magnitude (Section K.4).

 

 

RESPONSES TO U.S. NUCLEAR REGULATORY COMMISSION
COMMENTS ON THE SUPPLEMENT TO THE DRAFT EIS
(Comment Document 10248)

1. In the Draft EIS and the Supplement to the Draft EIS, DOE analyzed a variety of scenarios and implementing alternatives that it could deploy to construct, operate and monitor, and eventually close a repository at Yucca Mountain. The purpose of these scenarios and implementing alternatives, which reflect potential design considerations, waste packaging approaches, and modes for transporting spent nuclear fuel and high-level radioactive waste to the Yucca Mountain site, was to: (1) provide the full range of potential environmental impacts of the Proposed Action and No-Action Alternative; (2) reflect potential decisions, such as the mode of transport, that the EIS would support; and (3) retain flexibility in the design of the repository to maintain the ability to reduce uncertainties in or improve long-term repository performance, and improve operational safety and efficiency. The design and operation enhancements presented in the Supplement have been carried forward to the Final EIS.
   Many of the issues relating to how a repository would be operated and how the spent nuclear fuel and high-level radioactive waste would be packaged would be resolved only in the context of developing the detailed design for a possible license application. DOE cannot predict with certainty how it would eventually resolve these issues. However, to enable an improved understanding of the potential environmental impacts from a more specifically defined Proposed Action, DOE has identified its preferred alternatives, simplified aspects of the Proposed Action, and modified its analyses and presentation of information to illustrate the full range of potential environmental impacts likely to occur under any foreseeable mode of transportation, or repository design and operating mode. Thus, for example, DOE has identified rail as its preferred mode of transport both nationally and in Nevada, and demonstrated through analysis that the mostly truck and mostly rail national transportation scenarios provide the full range of environmental impacts.
   In the Final EIS, DOE has identified and analyzed a range of operating modes from higher- to lower-temperature. Chapter 2 of the EIS and other related sections of the Final EIS have been revised to reflect this refinement in design selection, which basically is an establishment of design fundamentals such as drift layout, drift spacing, depth and location of emplacement areas, and location of ventilation raises. The Final EIS describes a design for the repository with variations on the operating mode. The key parameters defining the flexible operating modes are waste package spacing, length of active ventilation, and waste package loading (principally the age of the fuel being emplaced). The range of variances in these parameters basically determine the extent of the repository design that will be utilized for emplacement of 70,000 metric tons of waste and fuel; the higher-temperature operating mode would require only the main central segment of the repository, several of the lower-temperature operating modes would use that segment and the western extension, while the "ultra" low-temperature operating mode would require use of the entire planned initial design.

2. In the Draft EIS, DOE evaluated a preliminary design based on the Viability Assessment of a Repository at Yucca Mountain (DIRS 101779-DOE 1998) that focused on the amount of spent nuclear fuel (and associated thermal output) that DOE would emplace per unit area of the repository (called areal mass loading). Areal mass loading was represented for analytical purposes in the Draft EIS by three thermal load scenarios: a high thermal load of 85 metric tons of heavy metal (MTHM) per acre, an intermediate thermal load of 60 MTHM per acre, and a low thermal load of 25 MTHM per acre. DOE selected these analytical scenarios to represent the range of foreseeable design features and operating modes, and to ensure that it considered the associated range of potential environmental impacts within the framework of a design the central feature of which was areal mass loading.
   Since DOE issued the Draft EIS, it has continued to evaluate design features and operating modes that would reduce uncertainties in or improve long-term repository performance, and improve operational safety and efficiency. The result of the design evolution process was the development of the flexible design that was evaluated in the Supplement to the Draft EIS and is evaluated in this Final EIS. This design focuses on controlling the temperature of the rock between the waste emplacement drifts (as opposed to areal mass loading) by varying other parameters such as the heat output per unit length of the emplacement drift and the distances between waste packages. Within this design framework of controlling the temperature of the rock, DOE selected these lower- and higher-temperature operating modes to represent the range of foreseeable design features and operating modes, and to ensure that it considered the associated range of potential environmental impacts (DOE recognizes that many of the short-term impacts tended to increase over those discussed in the Draft EIS).
   In this Final EIS, DOE varied design parameters to create scenarios to illustrate lower- and higher-temperature operating modes in such a way as to provide the range of potential environmental impacts. Furthermore, to not underestimate the environmental impacts that could result from implementing any of the lower- or higher-temperature operating modes, DOE has relied on conservative, yet realistic, assumptions when uncertainties remain.

3. In this Final EIS, DOE has updated and expanded the description of the flexible design and associated facilities, as well as performed a complete analysis to describe the range of potential environmental impacts that could occur under the Proposed Action. The tables in Section 2.4 of the Final EIS demonstrate the bounding nature of the flexible operating modes within the construct of a fixed design.

4. In the Supplement to the Draft EIS total worker years are used as a primary impact indicator for occupational health and safety impacts. As noted on page 3-1, "The Department used the ratio of primary impact indicators to specific impacts in the Draft EIS to determine the Supplement impact estimates." Therefore, in the analysis the base ratio of involved (including radiation workers) workers to noninvolved (including general employees) workers was the kept the same as for the Draft EIS. The exposure [dose] levels used were the same as described in Appendix F of the Draft EIS. The total dose to each of these worker populations was changed accordingly for the total length flexible design being considered as compared to the Draft EIS high thermal load scenario. The additional time needed for repository monitoring and maintenance was included in the Supplement estimates. A complete analysis of worker impacts under the flexible design operating modes is presented in Section 4.1.7 of the Final EIS. Section 4.1.7.5 shows that over the duration of the project construction, operation and monitoring, and closure phases the dose to the maximally exposed worker is about the same as shown for the thermal load scenarios in the Draft EIS.

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