This Remedial Action Plan (RAP) has been developed to serve a two- fold purpose. It presents the activities proposed by the Department of Energy (DOE) to accomplish long-term stabilization and control of the residual radioactive materials (RRM) from Monument Valley Arizona, and Mexican Hat, Utah, at the Mexican Hat disposal site. It also serves to document the concurrence of both the Navajo Nation and the Nuclear Regulatory Commission (NRC) in the remedial action. This agreement, upon execution by DOE and the Navajo Nation and concurrence by the NRC, becomes Appendix B of the Cooperative Agreement. This document has been structured to provide a comprehensive understanding of the remedial action proposed for the Monument Valley and Mexican Hat sites. It includes specific design and construction requirements for the remedial action. Pertinent information and data are included with reference given to the supporting documents. Appendices A, B, and C are provided as part of this document. Appendix A presents regulatory compliance issues, Appendix B provides details of the engineering design, and Appendix C presents the radiological support plan.

Portions of the final Remedial Action Plan (RAP) for the Green River site, Volumes 1 and 2, Appendix B of the Cooperative Agreement No. DE-FC04-81AL16257, March 1991 (DOE, 1991) have been modified. The changes to the RAP are designated as RAP Modification No. 2. These changes have been placed in a three-ring binder that will supplement the original RAP (DOE, 1991), and include the following: addendum to the Executive Summary; Section 3.5 (Ground Water part of the Site Characterization Summary); Section 4.0 (Site Design); Section5.0 (Water Resources Protection Strategy Summary); Appendix D.5 (Ground Water Hydrology); and Appendix E (Ground Water Protection Strategy). In addition to these revisions, there have been editorial changes that clarify the text, but do not change the meaning. Also, certain sections of the document, which are included in the submittal for ease of review and continuity, have been updated to reflect the final ground water protection standards and the current UMTRA Project format and content of RAPs.

This Remedial Action Plan (RAP) has been developed to serve a dual purpose. It presents the series of activities that is proposed by the US Department of Energy (DOE) to stabilize and control radioactive materials at the inactive Phillips/United Nuclear uranium processing site designated as the Ambrosia Lake site in McKinley County, New Mexico. It also serves to document the concurrence of both State of New Mexico and the US Nuclear Regulatory Commission (NRC) in the remedial action. This agreement, upon execution by the DOE and the state and concurrence by NRC, becomes Appendix B of the Cooperative Agreement.

This document provides the modifications to the 1988 Remedial Action Plan (RAP) of the contaminated materials at the Monument Valley, Arizona, and Mexican Hat, Utah. The text detailing the modifications and attachments 1 through 6 are provided with this document. The RAP was developed to serve a two-fold purpose. It presents the activities proposed by the Department of Energy (DOE) to accomplish long-term stabilization and control of the residual radioactive materials (RRM) from Monument Valley, Arizona, and Mexican Hat, Utah, at the Mexican Hat disposal site. It also serves to document the concurrence of both the Navajo Nation and the Nuclear Regulatory Commission (NRC) in the remedial action. This agreement, upon execution by DOE and the Navajo Nation and concurrence by the NRC, becomes Appendix B of the Cooperative Agreement. This document has been structured to provide a comprehensive understanding of the remedial action proposed for the Monument Valley and Mexican Hat sites. It includes specific design and construction requirements for the remedial action. Pertinent information and data are included with reference given to the supporting documents.

This Remedial Action Plan (RAP) has been developed to serve a two-fold purpose. It presents the series of activities which are proposed by the U.S. Department of Energy (DOE) to accomplish long-term stabilization and control of radioactive materials at the inactive uranium processing site located near Monument Valley, Arizona It also serves to document the concurrence of both the Navajo Nation and the U.S. Nuclear Regulatory Commission (NRC) in the remedial action. This agreement, upon execution by DOE and the Navajo Nation and concurrence by NRC, becomes Appendix B of the Cooperative Agreement.

Modifications to the water resources protection strategy detailed in the remedial action plan for the Green River, Utah, disposal site are presented. The modifications are based on new information, including ground water quality data collected after remedial action was completed and on a revised assessment of disposal cell design features, surface conditions, and site hydrogeology. The modifications will result in compliance with the U.S. EPA proposed ground water standards (52 FR 36000 (1987)).

The DOE proposes to achieve compliance with the proposed EPA groundwater protection standards (Subparts A and B of 40 CFR 192) by meeting the EPA maximum concentration limits (MCLs) or background concentrations for designated hazardous constituents in groundwater in the uppermost aquifer (alluvium/weathered granodiorite) at the point of compliance (POC) at the Lowman disposal site near Lowman, Idaho. The proposed remedial action in conjunction with existing hydrogeological conditions at the Lowman site will ensure sufficient protection of human health and the environment. The DOE has concluded that the EPA groundwater protection standards will be met at the POC because, with the exception of antimony, none of the hazardous constituents that exceed laboratory method detection limits within the radioactive sand pore fluids were above the proposed concentration limits. The DOE has demonstrated that antimony will meet the proposed concentration limits at the POC through attenuation in subsoils beneath the disposal cell and by dilution in groundwater underflow. The Lowman processing site is in compliance with Subpart B of 40 CFR 192 because statistical analyses of groundwater samples indicate no groundwater contamination.

The DOE proposes to achieve compliance with the proposed EPA groundwater protection standards (Subparts A and B of 40 CFR 192) by meeting the EPA maximum concentration limits (MCLs) or background concentrations for designated hazardous constituents in groundwater in the uppermost aquifer (alluvium/weathered granodiorite) at the point of compliance (POC) at the Lowman disposal site near Lowman, Idaho. The proposed remedial action in conjunction with existing hydrogeological conditions at the Lowman site will ensure sufficient protection of human health and the environment. The DOE has concluded that the EPA groundwater protection standards will be met at the POC because, with the exception of antimony, none of the hazardous constituents that exceed laboratory method detection limits within the radioactive sand pore fluids were above the proposed concentration limits. The DOE has demonstrated that antimony will meet the proposed concentration limits at the POC through attenuation in subsoils beneath the disposal cell and by dilution in groundwater underflow. The Lowman processing site is in compliance with Subpart B of 40 CFR 192 because statistical analyses of groundwater samples indicate no groundwater contamination.