Hydrogeology of the Bird's Nest Aquifer, Uintah County, Utah

Abstract

The Uinta Basin of northeastern Utah contains a large portion of the United States' oil-shale reserves. Two tracts on the eastern side of the basin, designated U-a and U-b, have been leased by the federal government for oil-shale development. The Bird's Nest Aquifer is the principal water-bearing zone in the area. At the tracts aquifer permeability is principally due to solution of nahcolite crystals, while to the west primary porosity of sandstone and tuffs is more important. In the vicinity of the Oil Shale Lease Tracts the aquifer is recharged by a perennial stream, Evacuation Creek, and by another source, probably upward leakage from deeper aquifers. The Evacuation Creek recharge water contains above 3,000/1 dissolved solids and has a sodium-sulfate composition. The water derived from the other recharge source contains less than 2,000 mg/1 dissolved solids and has a sodium-bicarbonate composition. Ultimate discharge of the aquifer is to the Green River. Percolation of water through retorted oil shale residue produces leachate with very high dissolved solids, sodium, sulfate, strontium, selenium, fluoride, and potentially carcinogenic organic compounds, but low permeability rocks above the aquifer reduce the danger of aquifer contamination by leachate originating from surface spent-shale disposal dumps.