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i <br />' CRAPTERTHREE Affected Environment <br />In a grab sample collected at 95 feet bgs during drilling of alluvial monitoring we1121-2, <br />concentrations of sulfate (335 mg/I), iron (4.50 mg/1}, and manganese (0.910 mg/1) exceeded <br />Colorado groundwater standards. <br />Subsequent sampling of monitoring we1121-2 shows that several chemical parameters exceeded <br />Colorado groundwater standards. These include chloride (1,047 mg/1), sulfate (550 to 900 mg/1), <br />chromium (0.061 to 0.102 mg/]), iron (0.5 to ] 0 mg/1), and manganese (0.065 to 0.91 mg/1). <br />Upper Aquifer <br />' The Upper Aquifer is generally defined as the saturated zone that includes the lower, saturated <br />portion of the Uinta Formation and the upper Pazachute Creek Member of the Green River <br />Formation down to the top of the Mahogany Zone. The depth to groundwater in two American <br />Soda monitoring wells (20-5 and 20-8) completed in the Uinta Formation was about 105 and 158 <br />feet bgs, respectively. Although wells 20-5 and 20-8 did not penetrate the entire Upper Aquifer <br />sequence, the total saturated thickness of the Upper Aquifer at the Piceance Site, based on <br />information from neazby wells (i.e., we1120-1) and core holes, is approximately 650 feet. It <br />should be noted that most of American Soda's wells aze located close to each other on the side <br />slope (i.e., elevations of approximately 6,200 feet msl) of a tributary drainage to Piceance Creek. <br />Depth to groundwater in upland areas of the ]ease block at elevations of about 6,500 feet msl is <br />expected to be 350 to 450 feet bgs. <br />Based on static groundwater elevations measured on September 21, 1998, in well 19-2 (6,145.86 <br />feet msl), well 29-3 (6,103.66 feet msl), we1120-5 (6,098.52 feet msl), and well 2-10 (6,142.00 <br />feet msl), the potentiometric surface is located in the upper portion of the Uinta Formation at the <br />Piceance'Site. Groundwater flow in the Upper Aquifer below the Piceance Site is generally to <br />the east northeast at 80 degrees azimuth (Daub ] 996). The horizontal hydraulic gradient is <br />' approximately 0.0096 feet per foot. <br />American Soda conducted a pumping test on well 20-8 (Upper Aquifer) at a maximum sustained <br />rate of I50 gpm with an associated drawdown of 266 feet. Agapito's analysis of the test <br />indicated a transmissiviry of 1,500 gallons per day (gpd/fl) (Agapito 1997). <br />Much of the groundwater in the Upper Aquifer system is classified as a sodium bicazbonate type, <br />with sulfate as a major anion. Generally, concentrations of dissolved soiids increase with aquifer <br />depth and in a northerly direction. TDS content ranges from 400 to 2,000 mg/1. Calcium, <br />magnesium, and sulfate concentrations are generally greater in the Upper Aquifer than in the <br />Lower Aquifer, while sodium, bicazbonate, and fluoride are higher in the Lower Aquifer. <br />Groundwater quality data collected during drilling of American Soda solution mining we1120-3, <br />monitoring well 20-5, and water supply well 20-8, indicate TDS concentrations in the Uinta <br />Formation ranged from 944 to 2,980 mg/1 at depths from 357 to 650 feet bgs in the Uinta <br />Formation. <br />Salinity increases rapidly as the A-Groove is approached, with TDS concentrations in excess of <br />10,000 mg/1 in the lowest parts of the Upper Aquifer (Steigers 1997a, Steigers 1997b). A water <br />quality sample taken just above the A-Groove at a depth of 8] 1 feet bgs at solution mining well <br />20-3 had a TDS concentration of 15,900 mg/1(Steigers 1997a, Steigers 1997b). The TDS data <br />Groundwater 3-19 <br />