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I <br />Payers featured in the overburden and coals, end will be limited to downgradient portions ~ ~ <br />oii pits where the adjacent units are saturated. Hydraulic conductivities of replaced ~ <br />spoil materials, both vertically e•nd horizontally, will be increased slightly due to the <br />ria LUre of spoil repl acemon t, resulting in similar or slightly higher vertical infiltration <br />rates and higher transmissivitie:o with the resaturated portions of the spoil. Deep <br />nipping where excessive ~:ompac[ion occurs and direct hauling of topsoil where practicable <br />will help ensure that equivalent or greater infiltration rates are maintained. Impac is of <br />the mine spoil and top::oil on vertical infiltration and horizontal ground water floe <br />should be of minimal to negligible significance. <br />Containment of Pit Inflow Pumpage and Impacts on water Ouali[v. All runoff and pit <br />pumpage from disturbed zireas are routed through sedimentation ponds. The ponds will be <br />designed end constructed to impound pit pumpage and runoff from areas disturbed by mining <br />and provide sufficient residence time to ensure the pond discharge water chemistry meets <br />[he effluent requiremen t:s specified in the NPDES permit. Seneca will secure an NPDES <br />permit and establish approved NPDES sites (outfalls) prior to the onset of discharging <br />from the sedimentation ponds. During the proposed life-of-mining, five NPDES ponds will <br />6e established: Ponds 010 and 011 in the Grassy Creek drainage, and Ponds 072, 073, and <br />014 in the Sage Creek drainage. All sedimentation ponds proposed 'for the Yoast Mine will <br />be constructed in accordance with accepted en9 ineering practices. <br />The majority of water to be encountered in the pit (pit inflow) during the first eight <br />years of mining will be pumped to Pond 010, and the majority of any surface water quality <br />impacts as a result of pit pumpage wilt be to Annand Draw. likewise, on the Sage Creek <br />side (last six years of mining), a majority of the pit water will be pumped to Pond 012 in <br />the Y-7 Tributary. Using the following equations developed by Ferreira (1984), iDS <br />increases io the alluvium and streamf low from the pumpage of pit inflow water in both the <br />Grassy and Sage Creek drainages can be calculated. The equation for the computation of <br />chemical load is: <br />L= o x C x 0.0027 <br />where: <br />L = chemical load in tons/day <br />o = flow in cfs <br />C = TDS concentration in mg/L <br />The equation for calculating the resultant TDS from mixing two flows of differing chemical <br />loads is: <br />16 Revised 03/24/95 <br />