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<br />• <br />• Aquifer.) The data from the Upper and Lower Aquifers are generally consistent <br />with previous water quality data observed. <br />7.4.4.1 Alluvial Aquifer <br />Alluvial groundwater in the Piceance Creek Basin is classified as a sodium <br />bicarbonate type. Concentrations of dissolved solids in the alluvium range from 470 <br />mg/1 to as high as 6,720 mg/I and average close to 1,750 mg/1 over the entire basin <br />(Weeks and Welder 1974). Water quality data collected from American Soda's <br />Alluvia( Aquifer monitoring well 21-2 reflect a TDS level of 1,540 mg/1 at the <br />Piceance Site (see Table 7-4). In general, the water quality of the Alluvial Aquifer is <br />more similar to that of the Upper Aquifer than to that of the Lower Aquifer. Higher <br />TDS levels downstream toward the White River are attributable mainly to <br />irrigation water returns, groundwater inflow, and the concentrating effect of <br />evapotranspiration (Weeks et al. 1974). <br />7.4.4.2 Upper Aquifer <br />Much of the groundwater in the Upper Aquifer system is classified as a sodium <br />bicarbonate type, with sulfate as a major anion. Generally, concentrations of <br />dissolved solids increase with aquifer depth and in a northerly direction. TDS <br />content ranges from 400 to 2,000 mg/1. Calcium, magnesium, and sulfate <br />• concentrations are generally greater in the Upper Aquifer than in the Lower <br />Aquifer, while sodium, bicarbonate, and fluoride are higher in the Lower Aquifer. <br />Groundwater sampling in the central Piceance Creek Basin near the Piceance Site <br />indicates that Upper Aquifer water tends to be asodium-sulfate-bicarbonate type <br />typically containing about 500 to 600 mg/1 TDS. Water quality data collected during <br />drilling of American Soda water supply well 20-8, solution mining well 20-3, and <br />monitoring well 20-5 (Tables 7-2, 7-3, and 7-4, respectively) indicate TDS levels in the <br />Uinta Formation ranging from 944 to 1,260 mg/1 at depths of 357 to 650 feet. <br />A USDW is considered to have TDS concentrations less than 10,000 ppm. Water <br />quality data collected while drilling solution mining well 20-3 indicate that the <br />USDW is restricted to the Uinta Formation at this site, i.e., down to depths of 700 to <br />750 feet. Conductivity measurements taken in the field after every 30 feet of drilling <br />showed that water quality deteriorated significantly between 694 feet depth <br />(conductivity 1,500 Nmhos/cm) and 758 feet (conductivity 12,000 }lmhos/cm). <br />Salinity increases rapidly as the A-Groove is approached, with TDS values in excess <br />of the 10,000 ppm USDW limit in the lowest parts of the Upper Aquifer (Steigers <br />1997a, Steigers 1997d). A water quality sample taken just above the A-Groove at a <br />depth of 811 feet below surface at the solution mining well 20-3 site recorded a TDS <br />level of 15,900 mg/1 (Steigers 1997a, Steigers 1997d). <br /> <br />American Soda, L.L.P. 7_26 <br />Commercial Mine Plan <br />August 18, 1998 <br />