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are rich in kerogen, these horizons contribute to an increase in the bicarbonate concentration through sulfate reduction in the presence of the organic material in the oil shale, a process which reduces the sulfate concentration and increases the bicarbonate concentration (Robson and Saulnier, 1981). Black Sulfur Gulch, south of Ryan Gulch, has springs which emanate hydrogen sulfide likely derived from this geochemical process (Saulnier, 1978). Robson and Saulnier (1981) and Saulnier (1978) present iso-concentration maps and point-concentration maps of groundwater quality in the Upper Aquifer, as reflected in the concentration of total dissolved solids. These data were largely drawn from data in Welder and Saulnier (1978), Weeks and Welder (1974), Dale and Weeks (1978), and Ficke, Weeks, and Welder (1974). Welder and Saulnier (1978) present hydrologic and water-quality data collected during the drilling of 24 test holes in Piceance Creek Basin by the USGS. The 24 test holes were drilled in paired sets with one well open to the "A Groove Aquifer" and one well cemented in the Mahogany Zone and then left open to various thicknesses of the Lower Aquifer. The pattern of groundwater quality reflected in the data collected during drilling and the analyses of groundwater samples from these test holes indicates a general increase in dissolved solids from south to north in the basin. Analyses of groundwater samples from Uinta Formation sections of some of these wells indicate that the Uinta Formation portion of the Upper Aquifer may have a higher dissolved-solids concentration than the Parachute Creek Member portion of the Upper Aquifer (Saulnier, 1978). The area of the American Soda Yankee Gulch lease is near to the USBM exploratory boreholes drilled in Horse Draw, just south of Yankee Gulch and the American Soda lease. Projections from these data indicate that the Upper Aquifer in this area has an undisturbed groundwater quality with an estimated dissolved solids concentrations ranging from 1000 to 1500 mg/L. Recent groundwater samples from wells within the American Soda lease property (Agapito, 1999) indicate some groundwater in this area with dissolved- solids concentrations signifrcantly higher than indicated by Robson and Saulnier (1981) and Saulnier (1978). In particular samples from the recently recompleted 20-1 welt indicate dissolved-solids concentrations of greater than 50,000 mg/L. Well 20-1 is an exploratory borehole drilled and cored in 1966 through the saline- mineral zone containing soluble halite (NaCI) and Nahcolite (NaHC03) to a total depth of 2084 feet below ground surface (bgs) (Nielsen, 1997). The hole has surface casing to a depth of 803 feet in the Upper Aquifer. After resource evaluation, well 20-1 was reported to be filled with drilling mud from the total depth in the saline zone through the upper part of the hole (803 - 2084 ft bgs). Well 20-1 was thus completed open hole with drilling mud from below the Lower Aquifer, including the zone possibly containing dissolved solids derived from the saline minerals below the dissolution surface, through the A- Groove part of the Upper Aquifer. Upon re-entry of well 20-1 in 1997, no Sentemher 7 1999