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fluid-filled shaft in 40-ft sections (Cox, 1979; Utter and Hawkins, 1978). However, this operation would have maintained a overpressured condition in the shaft throughout the 66-day casing installation period. Under this condition, permeable sections of the Upper and Lower Aquifer would have been subject to invasion of the saline fluid in the shaft due to the overbalanced condition. After the shaft liner was installed, the liner was stage cemented by pumping cement down the annulus. However, Cox (1979) indicates that the cementing operations achieved only limited success, possibly due to the presence of external stiffening rings around the 40-ft sections of the liner and the fact that there were brecciated permeable horizons and dissolved mineral sections behind the shaft liner. Initial test holes drilled though the shaft liner encountered water under pressure in several horizons. Given this scenario, it is likely that the groundwater in the brecciated Lower Aquifer was subject to degradation from the saline drilling fluid and/or saline water from the dissolution zone being forced up the annulus during liner installation. The estimated distance from the shaft to well 29-4 is about 3200 ft. Using the same data as used for nearby well D-1, injected fluid could have traveled approximately 4000 ft northeastward from the USBM shaft in the 22 years since its construction. Thus, the saline water observed in samples from the Lower Aquifer in well 29-4 (Table 1) may have been derived from a 22-year old saline- water plume emanating from the USBM shaft. In addition, drilling-fluid water- quality data collected during the drilling of monitor well 29-4 indicates that groundwater encountered in this well was relatively fresh (less than 2000 µS/cm) and in the range of groundwater quality presented in Dale and Weeks (1978), until the borehole entered the "B-Groove" aquifer. Thus, a contamination plume migrating from the USBM shaft in Horse Draw may have degraded the quality of groundwater in the Lower Aquifer. As was described for the Upper Aquifer, the groundwater quality of the Lower Aquifer beneath and in the vicinity of the Yankee Gulch lease appears to be anomalous relative to the pattem of groundwater quality in the Lower Aquifer in Piceance Creek Basin presented in Robson and Saulnier (1981) and Saulnier (1978). Although the structural geology of the area indicates that there may be fracturing connecting the Upper and Lower Aquifers in the vicinity of the Yankee Gulch lease (Snyder and Terry, 1977), the examples presented above indicate that there is also the likelihood that the somewhat anomalous groundwater quality in the area has been affected by a number of anthropomorphic practices such as inter-aquifer well completions, disposal-well operations, and the sinking of the USBM experimental shaft in Horse Draw. Summary The hydrogeology of the area in the vicinity of the Yankee Gulch lease is both characteristic and anomalous with respect to the accepted pattern of the occurrence of groundwater and groundwater quality in Piceance Creek Basin Sentamber 7. 1999