Mexican Hat, Utah (UMTRA Site)

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The former Mexican Hat mill and tailings site covered approximately 95 hectares (235 acres) and is located on Navajo Nation land at Halchita, Utah, about 2.4 kilometers (1.5 miles) southwest of Mexican Hat, Utah. Before remedial action, the site contained two adjacent piles of tailings. One covered 10 hectares (25 acres) and the other covered 19 hectares (48 acres). The site also contained seven mill buildings and associated debris, a concrete pad, contaminated soil, and wind-blown material.

FACILITY MISSION

The mission of the Mexican Hat mill site was to provide uranium for the United States Government. The source of contamination was the residual tailings that remained after the milling process extracted the uranium. Texas-Zinc Minerals Corporation built the Mexican Hat plant in 1957 and operated it under a lease with the Navajo Nation until 1963, when it was sold to Atlas Corporation. Atlas operated the mill for two years and shut it down in 1965. When the Atlas lease expired in 1970, control of the site reverted to the Navajo Nation.

The Environmental Management program is responsible for cleaning up surface- and ground-water contamination at the UMTRA sites. The Uranium Mill Tailings Radiation Control Act designated the residual radioactive material found at this site for cleanup and stabilization. The Act directed the Environmental Protection Agency to promulgate standards (Code of Federal Regulations Title 40, Part 192) and the Department of Energy to perform the cleanup. It also assigned the Nuclear Regulatory Commission to oversee and certify the cleanup and license the completed disposal cell. The affected Tribes will participate in decisionmaking.

Pursuant to the Uranium Mill Tailings Radiation Control Act, the Department of Energy entered into a Cooperative Agreement in 1983 with the Navajo Nation. The agreement outlines the roles and responsibilities of each party. The Department of Energy pays 100 percent of all costs (assessment and remediation) when the UMTRA site is on Indian land. In addition, the Department of Energy is responsible for paying 100 percent of the Tribe's costs. The Nuclear Regulatory Commission concurred on the original agreement and is required to concur on all major modifications.

FUTURE USE

The Mexican Hat disposal site is located on Navajo Nation land. However, the long-term surveillance of the disposal cell is the responsibility of the Department of Energy through a Custodial Access Agreement between the Navajo Nation and the Federal Government. Provisions of the Custodial Access Agreement will allow the Department to have permanent access to the disposal cell and will likely include restrictions, as necessary, to protect the public health, safety, and the environment.

ENVIRONMENTAL RESTORATION

Surface remedial action has been completed and the source of contamination has been stabilized. However, residual milling-related contaminated ground water remains.

Surface Project

Remedial action under the UMTRA Surface project began at the site in 1988 and was completed in February 1995. Remedial action involved consolidation of approximately 2 million cubic meters (2.6 million cubic yards) of residual radioactive material in place at the bottom of what is now the Mexican Hat disposal cell, followed by placement of approximately 703,152 cubic meters (925,200 cubic yards) of residual radioactive material from the Monument Valley site in Arizona, for a total of approximately 2,647,080 cubic meters (3,483,100 cubic yards) of residual radioactive material. Eleven vicinity properties were remediated concurrently with site remediation activities. This report assumes that the Nuclear Regulatory Commission will certify the site in February 1997 and license the disposal cell in March 1997.

Major Surface Project Milestones

TASK	COMPLETION DATE Fiscal Year
Publish the Revised Remedial Action Plan	1996
Nuclear Regulatory Commission Issues General License	1997
Transfer to Grand Junction Projects Office's Long-Term Surveillance and Maintenance Program	1997

The Mexican Hat Remedial Action Plan outlines the necessary tailings and contaminant distribution and remediation. The revised Remedial Action Plan, which requires Nuclear Regulatory Commission concurrence, will be published in December 1995. The UMTRA Surface Project will conduct surveillance and maintenance of the disposal cell after completion of remedial action and prior to its transfer to the Grand Junction Projects Office's Long-Term Surveillance and Maintenance program in FY 1997.

Ground-Water Compliance Project

The Department is developing a Programmatic Environmental Impact Statement pertaining to all 24 UMTRA sites. For a discussion of the Programmatic Environmental Impact Statement, see the UMTRA program narrative in the New Mexico section of this report. Site-specific National Environmental Policy Act documentation will be developed to propose an appropriate ground-water compliance strategy and reasonable alternatives for the Mexican Hat site once the Programmatic Environmental Impact Statement is completed.

This report assumes a strategy of demonstrated compliance, with additional characterization and the application of supplemental standards based on limited-use of ground water. For all types of ground-water compliance strategies, once the Nuclear Regulatory Commission determines the site to be in compliance with Subpart B of the Environmental Protection Agency Standards and it is certified, no additional long-term surveillance or monitoring will be conducted.

The following milestone dates have been established for planning purposes.

Ground water is present in two units beneath the site, the Halgaito Shale Formation and the Honaker Trail Formation. There is no ground-water contamination in the Honaker Trail Formation. The ground water in the shallower zone, the Halgaito Shale, is contaminated. It occurs over a limited area and ground water in this formation is primarily the result of tailings seepage. Controlled by fracture orientation, ground water within the Halgaito Shale flows east at an approximate rate of 9 meters (30 feet) per year. Ground water in the Halgaito Shale Formation exceeds the Environmental Protection Agency maximum concentration limits for several constituents, including chromium, molybdenum, net gross alpha, nitrate, and uranium. This contaminated ground water does not affect domestic wells.

Direct Program Management/Support

Program management supports management efforts for the National Environmental Policy Act process, site characterization and licensing, public information/participation, applicable state and federal regulator costs, quality assurance audits, program and management support for the technical assistance contractor, special studies, document control, technical assistance contractor site and technical management, cost and schedule controls, planning and preparation of the federal budget, and the Environmental Management Progress Tracking System.

FUNDING ESTIMATE

The following table presents estimated funding information for the Mexican Hat site.