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Four monitoring wells, GD-1, GD-1(2), GF-1 arxi GZ-1, have been completed in the Twentymile <br />Sandstone. Well GD-1, which served the Trapper Mine office and related facilities, produced about <br />75 gallons per minute (gpm). The GD-1 well exper'~enced productbn problems in October 1991 and <br />was replaced by GD-1 (2) well. GD-1 is currently aback-up well with a pumping capacity of 12-15 <br />gpm. At the time of installation the GD-1 well Indbated a transmisslvlry of about 77 to 65 gallons per <br />day per loot (gpolh). This value appears to be anomabusly bw arxi may reflect problems wRh <br />completion of the well. II the Twentymile Sandstone Is assumed to be 100 feet thick, the resulting <br />permeability (based on a transmissHity of 77 to 85 gpd(tt) is approximately one gallon per day per <br />square foot (gpd/ft~. This value Is probaby much bwer than the actual value for this unit. Corner- <br />sations with bcal well drillers have Indk;ated that large-diameter Twentymile Sandstone wells In the <br />Big Bottom area or near the axis of the syncline normaly produce approximatey 500 gpm. The <br />Twentymile Sandstone probably has a permeability near 50 gpd/itz, Transmissivity values for this unit <br />are probaby about 5,000 gpd/ftz. The GD-1 (2) well is estimated to have a pumping capacity of <br />• approximately 75 gpm. <br />Upper Unit of Williams Fork Formation <br />The Upper Williams Fork as a whole Is an aquitard. Some of the individual strata, such as coals and <br />sandstones, behave as aquifers. Ground water occurs In perched aquifers, confined aquifers, and <br />water table aquifers within the Upper Williams Fork. <br />Twenty wells have been drilled to define the aquifer units M the Upper Williams Fork, see Woodward- <br />Thodinnson (1975), Colder (1976) and Settergren (1979), refer to Table 2.7-20. The variable aquifer <br />properties of <br />---------1-- -- -~-~--- - - <br />