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flow rather than infiltration. The amouttt of surface runoff will depend <br />upon many factors including storm intensity and duration, antecedent soil <br />moisture conditions, permeability and infiltration capacity of the soil <br />and overburden cover, topography, and the amount and type of vegetation <br />cover. <br />In performing the water balance calculations, runoff coefficients of 0.25 <br />(April through August), 0.20 (September and October) and 0.0 (November <br />through April) were used. It was assumed that little or no runoff will <br />occur when the monthly precipitation does not exceed one inch (i.e., the <br />runoff coefficients for those months will be zero). These coefficients <br />approximate those used in the rational formula for various surface con- <br />• ditions. By applying these coefficients to mean monthly precipitation, <br />an estimate of "mean monthly surface runoff" was calculated. Although <br />this method will in most cases underestimate surface runoff, it was felt <br />that ignoring the surface runoff totally would result in a misleading <br />assessment of the water balance. -Table 2.7-23 presents the average <br />monthly surface runoff. <br />2.7.6.4 Ground-4later Bechar <br />Aquifers at the Trapper Mine site are recharged by direct infiltration <br />through the thin soils and by flora losses from the intermittent streams <br />when they are flowing. Most of the infiltrating recharge is from snowmelt, <br />and the rate of infiltration is probably very slow. The Yampa River may <br />recharge its alluvial aquifer at some times. The Upper Unit of the <br />Williams Fork Formation probably receives recharge through- <br />2-528 <br />