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URS Operating Services,Inc. • ARR for ESUClimax <br /> START,EPA Region Vlll Revision: 0 <br /> Contract No.68-A'5-0031 Date: 04/1998 <br /> Pa5e 5 of 37 <br /> Quaternary deposits at the CM site consist of detrital sand, gravel, and boulders originating <br /> from glacial, alluvial, and landslide activity. These deposits are approximately 50 to 100 <br /> feet in thickness,are primarily located in drainages in the valley bottoms, and underlie the <br /> area comprised by the CM tailings ponds (State of Colorado,Office of the State Engineer, <br /> Division of Water Resources(CDWR) 1993; USGS 1974). <br /> Groundwater may be found locally in fractured areas of the bedrock; however,groundwater <br /> movement along fault zones within the bedrock is generally believed to be inhibited by the <br /> presence of low permeability clayey gouges in the faults(CMC 1980). Any groundwater <br /> flow within the Paleozoic sedimentary units is impeded in areas in which movement along <br /> the Mosquito Fault has brought impermeable Precambrian crystalline rocks into contact with <br /> the Paleozoic units. The Quaternary deposits present in the CM site area may be of <br /> sufficient permeability and saturation locally to yield useable quantities of groundwater to <br /> wells. Groundwater is found from 50 to 100 feet below ground surface (bgs) in the <br /> Quaternary deposits. Hydraulic conductivity of the Quaternary deposits ranges from 10' <br /> to 10'centimeters per second(cm/sec)(CDWR 1993;Office of the Federal Register 1990). <br /> 3.3.2 Hydrolow <br /> The CM site is located at the headwaters of the Arkansas River, the Eagle River, and <br /> Tenmile Creek(USGS 1970a; USGS 1983). Tenmile Creek has a mean annual flow rate <br /> of 101 cubic feet per second(cfs)at Frisco, Colorado(USGS 1996). Water from Tenmile <br /> Creek is collected in Dillon Reservoir approximately 12.1 miles north-northeast of the CM <br /> NPDES discharge to Tenmile Creek. Site drainage to the headwaters of the Eagle and <br /> Arkansas Rivers is captured and pumped to the Tenmile Creek drainage(CMC 1993). <br /> 3.3.3 Climate <br /> The CM site is located in a semiarid climate zone. Most of the precipitation is in the form <br /> of snow and associated spring runoff. The mean annual precipitation, as totaled from the <br /> University of Delaware (UD) database, is 11.7 inches. The net annual precipitation, as <br /> calculated from precipitation and evapotranspiration data obtained from UD, is 3.7 inches <br /> 75-51 119.00 <br /> F:\START\CLIMAX\Final.ARR\CLIMAX.TXf.wpd:bas <br />