GENERAL43250 - Laserfiche WebLink

Home Browse Search

(Welder and Saulnier, 1978; Weeks et al., 1974; Dale and Weeks, 1978; Robsor and Saulnier (1981); and Saulnier (1978). Groundwater is found in the Upper and Lower Aquifers in the bedrock, and in the alluvium. In general, groundwater quality in the bedrock aquifers in the Piceance Creek Basin ranges from 800 to 1500 mg/L in the central part of the Piceance Creek Basin including the area of the Yankes Gulch lease. However, the water quality of the Upper and Lower Aquifers may be affected by natural and artificial processes which can alter the quality of groundwater and render it more saline than would otherwise be expected given the data presented in basinwide water-quality evaluations by the USGS (Welder and Saulnier, 1978; Robson and Sauinier (1981); and Saulnier (1978). It appears that the area of the Yankee Gulch lease and immediately upgradient from the lease has been subjected to inter-aquifer contamination by fluids which are non-representative of groundwater in the Upper and Lower Aquifers (Figures 3 and 4). The following processes and events have likely created sources for inter-aquifer communication. Well 20-1 was drilled in 1966 to the saline zone to investigate oi! shale and sodium minerals. During drilling the hole was open from the A Groove to the dissolution zone, then plugged to an indeterminate depth, most likely in the Lower Aquifer and filled with mud and abandoned according to standard practice at that time. During recompletion in 1997, it appeared that the hole was open to both the Lower and Upper Aquifers. The history of well 20-1 indicates that it was, and remains, a source of inter-aquifer contamination for 31 years, the effects of which are seen in wells completed and/or producing water in the vicinity of well 20-1. • A Shell Oil Co. in situ oil-shale and soluble-mineral extraction experiment near the mouth of Horse Draw, just south of the Yankee Gulch lease, operated from at least 1971 to 1973 and the project employed a Lower Aquifer disposal well which discharged several million gallons of waste water with a specific conductivity exceeding 50,000 µS/cm to the Lower Aquifer. Given the porosity, permeability, potential for upward flow, and gradient of the Lower Aquifer in this area, it appears likely that the contamination plume from this disposal well has reached the Yankee Gulch lease and the area of monitoring well 21-3. The USBM experimental Horse Draw mine consisted of a bored 10-ft diameter shaft to a total depth of 2371 feet bgs. The open shaft acted as a borehole promoting inter-aquifer flow. The shaft was bored through the saline zone with a full column of saline polymer drilling fluid which remained in an overpressured condition in the open shaft during the 66-day shaft liner installation. It is likely that a plume of saline water has migrated from the shaft and was encountered during the drilling of monitoring well 29-4. Stormwater discharge from the American Soda retention ponds may have contributed to a temporary elevation of dissolved solids in the alluvium in the Sentamher 7. 1999 10