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CHAPTERFIVE Draft EIS Reuislons Formation down to the top of the Mahogany Zone. The depth to groundwater in two American Soda monitoring wells (20-5 and 20-8) completed in the Uinta Formation was about 105 and 158 feet bgs, respectively (Table 3.4-11. Although wells 20-5 and 20-8 did not p~:netrate the entire Upper Aquifer sequence, the total saturated thickness of the Upper Aquifer at the Piceance Site, based on information from neazby wells (i.e., we1120-1) and core holes, is approximately 650 feet. It should be noted that most of American Soda's wells are located closf: to each other on the side slope (i.e., elevations of approximately 6,200 feet msl) of a tributary drainage to Piceance Creek. Depth to groundwater in upland azeas of the lease block at elevations of about 6,500 feet msl is expected to be 350 to 450 feet bgs. Based on static groundwater elevations measured on September 21, 1998, in well 19-2 (6,145.86 feet msl), well 29-3 (6,103.66 feet msl), well 20-5 (6,098.52 feet msl), and well 20-10 (6,142.00 feet msl), the potentiometric surface is located in the upper portion of the Uinta Formation at the Piceance Site. Groundwater flow in the Upper Aquifer below the Piceance Site is generally to the east northeast at 80 degrees azimuth (Daub 1996). The horizontal hydraiilic gradient is approximately 0.0096 feet per foot (50.7 feet per mile). Wells completed in the Uinta Formation yield as much as 300 gym, althougliyields of less than 100 ~m aze more common (Weeks et al. 1974). Tests of the Upper Aouifer at the U.S. Bureau of Mines (USBMI Horse Draw Mine Research Facility located immediately south of the project yielded an averaee dischazee of 280 gpm for 900 minutes, with a drawdown of approximately 10 feet (Dale and Weeks 19781. During American Soda's air drillingof water supply well 20-8, which provides water for the experimental test cavity operation, the boreholf: was dry down to a depth of 162 feet bes, indicatine that no perched zones were encountered. Firom 162 feet bes to approximately 420 feet bgs, water production steadily increased from 0 gpm to about 60 gpm. At 420 feet bgs, water production rose rapidly to 250 gpm, and, at a total delrth of 560 feet bgs in the Uinta Formation, estimated water production increased to 400 epm. The static water level in the borehole after drilline was 160 ft bgs (Aeapito 19971. ~J American Soda conducted a pumping test on we1120-8 (Upper Aquifer) at a maximum sustained rate of 150 gpm with an associated drawdown of 266 feet. Agapito's analysis of the test indicated a transmissivity of 1,500 gallons per day (gpolft) (Agapito 1997). Much of the groundwater in the Upper Aquifer system is classified as a sodium bicarbonate type, with sulfate as a major anion. Generally, concentrations of dissolved solids increase with aquifer depth and in a northerly drrection within the basin. TDS content ranges froos 400 to over 9_~0~99A mg/1. Calcium, magnesium, and sulfate concentrations aze generally greater in the Upper Aquifer than in the Lower Aquifer, while sodium, bicazbonate, and fl uoride aze icall higher in the Lower Aquifer. American Soda completed and sampled two wells (wells 20-5 and 20-81 in the Upper Aquifer. Table 3.4-2 presents a summary of the analytical results for these wells. Ra~H analytical data aze contained in Appendix K. TDS concentrations measured durine 1997 and 1998 for wells 20-5 and 20-11 raneed from 676 to 3,276 me/1, with a combined mean value for the two wells of approximately 1,840 me/I. Well 20-5 is screened at 632 to 642 feet bes, and we1120-8 is screened at 534 to 554 feet bes (Table 3.4_11. 5-12