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This decision document presents the selected interim remedial action for Operable Unit (OU) Ill surface water and ground water at the Monticello Mill Tailings Site (MMTS) in San Juan County, Utah. The selected interim remedial action was chosen in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act as amended by the Superfund Amendments and Reauthorization Act of 1986 and, to the extent practicable, with the National Oil and Hazardous Substances Pollution Contingency Plan (NGP). This decision is based on the administrative record for this site. The State of Utah concurs with the selected interim action. The selected alternative for the interim remedial action for OI Ill surface water and ground water at the MMTS is Alternative 2-implementing institutional controls, continuing Millsite dewatering and treatment of excavation water and surface runoff, continuation of ongoing monitoring efforts, and evaluation of a permeable reactive treatment (PeRT) wall through the use of a pilot-scale treatability study. The PeRT wall is an enhancement to the interim remedial action. This remedial action is only an interim measure. If monitoring results indicate that the interim remedial action is not achieving the objectives of preventing exposure to and reducing contaminants in contaminated ground water, other alternatives will be evaluated from the OU Ill feasibility study. The final remedy for the site surface water and ground water will be documented in the final Record of Decision (ROD) for OU Ill.


PB98-964407 EPA S41-R98-106