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- 26 - <br />1 <br />' .The high flow frequency data is from Figures H2 and H3. Frequency analysis of <br />data from a period of record shorter than 10 years and estimating frequencies of <br />hydrologic events greater than twice the record length are not usually recommended <br />A detailed analysis of the surface water hydrology is contained in section 2,04.7(2). <br />' Station No. 09084600 is approximately 0.5 mi. upstream of the permit area, It will be <br />' referred to as station 600 for the remainder of the permit. <br />, Surface water quality data for Fourmile Creek on file with USGS is included in <br />~ <br />' Table H3. Samples for these analyses were taken near Station 600. According to <br /> these analyses, Fourmile Creek is moderately hard (total hardness is CaC o3, 142), has <br />' a very small concentration of dissolved solids (electroconductivity, 281 micromhos/cm), <br />' is basic (pH, 8.8), and has good buffer capacity (alkalinity, 157). All of these are <br /> indications of very high quality water. The USGS has no records of groundwater <br />' chemical analysis in this area. <br /> Ground water is pumped from the Sunlight Mine below the level of Fourmile Creek <br />' to permit continued expansion of the mine downdip along the D seam. A limited <br /> quality analysis of this mine water has been made by the operator (Table H.4). <br />' <br /> The principal aquifers in the area are the sandstone and coal beds. Where the <br />' sandstone units are coarser grained or more fractured, they are the more productive <br /> aquifers. Coal beds are aquifers where they are highly fractured. <br />i -' Previous mining operations at the Sunlight Mine (known also as the Fourmile Mine a <br />~ <br />I few years ago) removed an estimated half of the coal to within an estimated average <br />1 <br /> of 150 feet below the surface along dip. Current mining is removing a reported 200 <br />_, tons per month and produces an estimated average of fifteen to thirty galllons per <br /> minute of ground water discharge, allowing access to the coal below the ground water <br />-, level. Water level in the mine is approximately 100 ft. below Fourmile Creek. <br /> The Sunlight Atine and Permit Area is in the Carbondale field in the Unita coal <br /> <br /> region of the Piceance Basin in western Colorado (Figures G.1 and G.2). The coal is in <br />_1 <br />T <br /> <br />~, I) <br />