Abstract

The uranium mill tailings at the Green River, Utah, UMTRA Project site are being stabilized in a mostly below-grade disposal cell adjacent to the inactive mill site. The intent of the remedial action is to protect human health and the environment from potential hazards associated with the tailings. The disposal site is underlain by approximately 20 feet of Quaternary-age pediment sands and gravels, and 180 feet of Cretaceous-age sandstones, siltstones and limey shales. The flow of ground water near the site is complex, and is controlled by the presence of joints and fractures in bedrock and the local dip of the strata. In general, ground water flows west from the disposal site toward the Green River. The quality of ground water beneath the site is generally poor, with concentrations of total dissolved solids ranging from 2,000 to 9,000 milligrams per liter. Contamination as gross alpha activity, molybdenum, nitrate, selenium, uranium, and ammonium is present in the ground water beneath the old tailings pile, which is in the floodplain of Brown’s Wash, a tributary to the Green River. Two main components of the Green River disposal cell will protect ground water. These are: (1) a very low permeability clay infiltration barrier compacted above the tailings to limit the flux of moisture through the tailings and into ground water, and; (2) six feet of clean, selected buffer soils compacted beneath the tailings to retard the movement of contaminants to ground water from the overlying contaminated materials.