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The Lower Aquifer may be from 300 to 800 feet thick (Saulnier, 1978). Beneath <br />the American Soda Yankee Gulch lease, the Lower Aquifer is approximately 400 <br />feet thick. The Lower Aquifer water quality becomes more saline near the <br />dissolution zone with dissolved solids concentration approaching 100,000 mg/L <br />possible in the northern Piceance Creek Basin (Saulnier, 1978). The Lower <br />Aquifer area with the most naturally saline groundwater lies along a fracture zone <br />in the northern part of the basin where there is natural saline groundwater <br />discharge as described in Saulnier (1978). Robson and Saulnier (1981) and <br />Saulnier (1978) indicate that the undisturbed groundwater in the LowerAquifer in <br />central Piceance Creek Basin and in the area beneath the Yankee Gulch lease <br />may contain from 1000 to 1500 mglL concentrations dissolved solids, except in <br />the zone immediately above (variably several tens of feet) the dissolution surface <br />where dissolved-solids concentrations may exceed 50,000 mg/L (Welder and <br />Saulnier, 1978; Saulnier, 1978). <br />Data from groundwater samples collected since 1997 from American Soda wells <br />at and up-gradient of the Yankee Gulch lease (Agapito, 1999) also indicate that <br />Lower Aquifer groundwater has a higher dissolved solids concentration than <br />indicated by Robson and Saulnier (1981) and Saulnier (1978). However, the <br />dissolved-solids-concentration iso-concentration contours in Robson and <br />Saulnier (1981) and Saulnier (1978) do not indicate sample points from the <br />Yankee Gulch lease, but from the Horse Draw USBM site approximately 1/2 to <br />3/4 mile south of the lease. Recent data and events occurring after the collection <br />of the data in the USGS reports and Saulnier (1978) indicate that events and <br />processes extraneous to the Yankee Gulch lease may have contributed to <br />degradation of lower Aquifer groundwater. <br />Recent groundwater samples from wells within the American Soda lease <br />property indicate some groundwater with dissolved-solids concentrations <br />significantly higher than indicated by Robson and Saulnier (1981) and Saulnier <br />(1978). In particular Lower Aquifer samples from the 20-1 and 20-3 wells <br />indicate dissolved-solids concentrations of greater than 50,000 mg/L. As <br />discussed above, well 20-1 likely has created a plume of saline groundwater. <br />Over the 28 years that the well was abandoned, this could also be the source of <br />the elevated dissolved-solids concentrations (i.e. greater than reported in USGS <br />sample analyses) observed in wells in the immediate vicinity (less than 500 ft) of <br />20-1, such as found in well 20-3. <br />Another example of a relatively a recent disturbance to Lower Aquifer water <br />quality near the Yankee Gulch lease may be seen just north of the lease area. <br />From 1971 to 1973, Shell Oil Co. conducted in situ soluble-mineral and oil-shale <br />extraction experiments in the saline zone of the Parachute Creek Member (Prats, <br />et al, 1977). These experiments produced millions of gallons of saline waste <br />water high in concentrations of sodium and bicarbonate. In conjunction with <br />Sentamher Z 1999 <br />