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<br />• overlying zone. This is due principally to secondary fracturing and the removal of <br />soluble materials. Within the north-central part of the Piceance Creek Basin, the <br />Lower Aquifer varies from less than 150 feet to 700 feet thick (Robson and Saulnier <br />1980). Based on the core log, the Lower Aquifer is about 375 feet thick at monitoring <br />well 20-1. <br />The direction of groundwater flow in the Lower Aquifer below the Piceance Site is <br />about North 29 degrees East (Daub 1996). Lateral hydraulic conductivity has been <br />reported as 0.5 foot per day for portions of the Lower Aquifer (Robson and Saulnier <br />1980). <br />The transmissivity of the Lower Aquifer is generally less than that of the Upper <br />Aquifer, ranging from less than 402 square feet per day (3,000 gallons per day per <br />foot) at the margins of the basin to 2,680 square feet per day (20,000 gallons per day <br />per foot) in the center of the basin. A transmissivity of 210 square feet per day was <br />measured during a pump test of the Lower Aquifer at the USBM Horse Draw <br />Research Facility (Dale and Weeks 1978). Ina 7-day pump test of the Lower Aquifer <br />conducted at the adjacent lease property to the west of the Piceance Site, <br />transmissivity varied from 280 to 350 square feet per day in four observation wells. <br />Tests indicate that the potential yield of a well tapping the Lower Aquifer may be as <br />much as 1,000 gpm (Wright Water Engineers et al. 1996). <br />• Based on the limited existing data, the storage coefficient of the Lower Aquifer is <br />estimated to be on the order of 10-a (Weeks et al. 1974). Storage coefficient data from <br />a 7-day pump test conducted on the adjacent lease property to the west of the <br />Piceance Site ranged from 2x10-5 to 7x10-5 (Cole et al. 1995). <br />The total estimated groundwater reserves in the Lower Aquifer are estimated at <br />over 2.5 million acre-feet (Coffin et al. 1971). Although large volumes of water are <br />stored in the underground aquifers, the hydraulic conductivity is generally too low <br />to permit continuous operation of high-yielding wells. Throughout the Piceance <br />Creek Basin, water wells open to the Parachute Creek Member yield as much as 1,000 <br />gpm for short periods, although 200 to 400 gpm are typical (Weeks et al. 1974). <br />7.4.2.5 Saline Zone <br />The Saline Zone is the lower confining layer for the Lower Aquifer. The Saline <br />Zone has very low permeability and is free of groundwater. This zone is known for <br />its high resistivity. <br />Parachute Creek Basin <br />The alluvial aquifer system associated with Parachute Creek is largely derived from <br />the Green River and Uinta formations, with some contribution to the streambed <br />• from the Wasatch Formation (ACOE 1985). Groundwater levels in the alluvium of <br />American Soda, L.L.P. 7_21 <br />Commercial Mine Plan <br />August 18, 1998 <br />