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TABLE 17-17 • <br />Ground Water Quality Impact Computational <br />Approach and Flow Values <br />1. Hydraulic gradients were measured from potenti ometric surface maps <br />2. Hydraulic conductivities were based on the geometric mean of aquifer tests performed <br />in the respective aquifers <br />3. Cross sectional areas of flow for bedrock units were calculated using the maximun <br />length of aquifer measured near the crop lines times 60 feet for the overburden and <br />11.8 feet for the Wadge <br />4. Alluvial cross sectional areas were calculated using the saturated thickness <br />assumptions listed below and widths taken from the Alluvial Valley Floor map (Exhibit <br />16-2) <br />5. Mean TDS values for the bedrock aquifers were used and mean June-September TDS values <br />for the alluvial aquife rs were used <br />6. Spoil discharge to the bedrock aquifers was mixed in a 1:1 ratio with bedrock water <br />7. Pit areas measured are shown in Table 17-16 • <br />8. Spoil discharge to the 006 alluvial aquifer was mixed 50 percent spoil flow with SO <br />percent alluvial aquif er flow and a 2.5 foot increase in saturated thickness was <br />assumed since vertical K values should be si gnificantly lower than horizontal K <br />values <br />9. Saturated thicknesses i n the Hubbe rs on Culch, Watering Trough Culch, and Dry Creek <br />alluvial aquifers were assumed to the 100 percent of the alluvial thicknesses as most <br />of the monitoring wells indicate that water is <2.5 feet from ground surface. <br />10. The volume of new allu vial flow at each point in the alluvial system was calculated <br />as the total premining flow minus the confluent tributary flow above that point. <br />Flow Values for Overburden, Wadge, and Alluvial Aquifers <br />Aquifer Desiana ti on K (ft/day) I (ft/ft) A (ftz) 0 (cf s) <br />North pit overburden 0.05 0.145 165,1:0 0.0139 <br />Central pit overburden 0.05 0.10 932,643 0.054 <br />North pit Wadge 0.01 0.15 32,474 0.00057 <br />Central pit Wadge 0.01 0.11 71,555 0.00091 <br />North pit Spoil Spoil flow into the overburden and Wadge Coal aquifers • <br />Central pit Spoil is governed by the same aquifer characteristics as listed <br /> above <br /> 42 <br />