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Unit <br />Maximum <br />(ft/day) <br />Minimum <br />(ft/day) <br />Geometric <br />Mean <br />(ft/day) <br />No. of <br />Data <br />Points <br />No. of <br />Wells <br />Valley fill <br />1.96E +02 <br />1.44E -03 <br />3.26E +01 <br />16 <br />9 <br />F sandstone <br />5.24E -02 <br />7.87E -03 <br />1.76E -02 <br />6 <br />6 <br />F/G sequence <br />1.98E -01 <br />4.28E -04 <br />3.88E -02 <br />18 <br />18 <br />1 <br />-A= Walsh <br />Environmental Scientists and Engineers. 1.1C <br />Regional recharge and discharge <br />Recharge to units of the Williams Fork Formation and the Trout Creek Sandstone occurs <br />along the outcrops on the south, east, and west margins of the basin, from the saturated <br />valley fill in the streams channels, and via seepage from overlying units in the southern <br />areas (WMC 2005). Recharge is probably highest on the south side of the basin in the <br />Danforth Hills, which, because of their elevation, tend to have lower average <br />temperatures, more precipitation, and more snow than other potential recharge areas. <br />Discharge occurs where the steeply- dipping north limb of the syncline is dissected by <br />streams and along the northern portions of the stream channels. The elevation of the <br />Collom, Straight, Williams and Good Spring drainages where they cross the north limb of <br />the syncline is about 6,500 feet. <br />Along the southern reaches of the stream channels, the deeper units of the Williams Fork <br />Formation (down to the I coal sequence) are observed to outcrop. The stream channels <br />cut through successively higher units from south to north on the south limb of the <br />syncline. The valleys provide drainage for the shallower coal and sandstone units. As a <br />result of these conditions, the southern portion of the groundwater basin consists of a <br />sequence of perched groundwater zones. In general, the groundwater levels occur within <br />the respective water - bearing units. Conditions in the southern part of the project area are <br />therefore relatively similar to those in the existing ColoWyo Mine. Perched groundwater <br />zones in the upper coal seams are expected to be encountered in the Collom Mine, but <br />with a greater magnitude and frequency of sustained inflows than at the ColoWyo Mine <br />as a result of the greater drainage area and the greater recharge rate. <br />On the north side of the basin, the Williams Fork units outcrop along the steeply upturned <br />north limb of the Collom Syncline. Units of the Williams Fork are also exposed along the <br />stream valleys. Groundwater in the northern area appears to discharge into the valley fill <br />of the incised drainages. <br />Hydraulic Conductivities <br />Hydraulic conductivities results from well tests indicate that the most permeable bedrock <br />units are within the F/G sequence (WMC 2005). The sandstone units have lower <br />permeabilities than the coal seams. Table 5 summarizes the range and geometric mean of <br />hydraulic conductivities for specific units of interest in the Collom lease area. The coal <br />seams have average hydraulic conductivities ranging from approximately 0.187 to 0.039 <br />feet/day. The highest hydraulic conductivities were observed in the Fab and G seams. <br />The sand units have average hydraulic conductivity values ranging from a high of <br />approximately 0.008 feet/day (F sandstone) to 0.0017 feet for the H sandstone. <br />Table 5 Hydraulic Conductivities' <br />P PROW( I \t do* %.. MIBR t.% Pnul PI ]I•. .F:\ (ollom05 01 .w• ,I■•■ <br />32 <br />