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Hydraulic Conductivity and Storage <br />Hydraulic conductivity (K) of the alluvial aquifer were estimated from published data of <br />similar lithologies in the Denver Basin (USGS, 1989) and EnviroGroup's experience at <br />other sites along the Colorado Front Range. The base-case average K for the alluvial <br />floodplain was simulated at 5x 10-2 cm/sec. The alluvial K value was increased to 1 x 10- <br />cm/sec in a paleochannel located north of the mine as estimated from a regional <br />groundwater well yield map (Shelton, 1975). Based upon published information on the <br />stratigraphic characteristics (Section 2.0), inflow from the claystone terraces to the north <br />and south of the site was represented by assigning a hydraulic conductivity to the <br />claystone/sandstone that was approximately two orders of magnitude lower than the <br />alluvial floodplain sediments (5x 10-4 cm/sec). The specific yield for the aquifer was <br />simulated at 0.20. <br />Recharge <br />Aerial recharge was estimated based on the average annual precipitation of 13 inches per <br />year in the site area (USGS, 1978). Model recharge was simulated at 10% of annual <br />precipitation (1.3 inches/year) for alluvial deposits and at 1.0% of annual precipitation <br />(0.13 inches/year) for the weathered claystone on the terraces north and south of the site. <br />EnviroGroup Limited 6