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<br />7.3.3 Surface Water Uses <br />Surface waters crossing the Piceance Site are ephemeral and drain directly into <br />Piceance Creek. Therefore, there is virtually no use of on-site surface waters. <br />Surface waters of Piceance Creek, which is a perennial stream, are used for irrigation <br />of agricultural lands. <br />Parachute Creek is perennial and provides irrigation and livestock watering for the <br />surrounding Parachute Creek valley. During the 1980s, development of a reservoir <br />was planned for the Unocal OiI Shale Processing Plant, but it was never constructed. <br />7.3.4 Discharges to Surface Waters <br />There are no planned discharges from the project area to surface waters. Surface <br />water releases could occur in the event of a dam failure or overtopping of <br />ponds/reservoirs during an unusual precipitation event or in the event of a <br />pipeline rupture. <br />7.4 GROUNDWATER <br />7.4.1 Regional Groundwater <br />• Piceance Creek Basin <br />Groundwater in the Piceance Creek Basin comes from infiltration of precipitation at <br />the higher elevations to the east, south, and west of the drainage basin. <br />Groundwater from these higher elevations descends into the deeper portions of the <br />basin and moves laterally toward discharge areas along the lower reaches of Piceance <br />Creek and Yellow Creek. Recharge on the margins of the basin moves downward <br />through the alluvium, the Uinta Formation, and the Parachute Creek Member of <br />the Green River Formation into the upper and middle sections of the Parachute <br />Creek Member. The steady-state recharge-to-discharge rate of 32 cubic feet per <br />second (cfs) results in hydraulic gradients of up to 130 feet per mile in some areas of <br />the basin (Robson and Saulnier 1980). Groundwater recharge into Piceance Creek <br />comes primarily from the shallow alluvial aquifer (Birman 1982, Tait 1982). <br />Most functional groundwater models include three aquifers in the Piceance Creek <br />Basin. These aquifers occur within three principal geologic sequences: the near- <br />surface alluvial aquifer beneath the streams (alluvial aquifer); the Upper Aquifer, <br />which includes the lowermost part of the Uinta Formation and the upper part of the <br />Parachute Creek Member; and the Lower Aquifer, which includes the lower part of <br />the Mahogany Zone down to the top of the Saline Zone (Dissolution Surface). The <br /> <br />American Soda, L.L.P. 'x_17 <br />Commercial Mine Plan <br />August 18, ]998 <br />