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The majority of pit inflow waters will be contained by Ponds 005 and 006; little or no pit pumpage will <br />be received by Pond 009. Therefore, any surface water quality impacts as a result of pit pumpage will <br />be to Dry Creek. Using equations presented by Ferreira (1984), the resulting TDS concentration (DSC) <br />of Dry Creek due to pit inflow discharges can be calculated. These equations are explained in detail in <br />the portion of this Tab titled "Potential Impact of Replaced Spoil on Ground Water Quality". <br />As previously stated, the highest yearly pit inflows for both the overburden and Wadge coal will occur <br />in year 2001. These aquifers will produce an estimated 4,806,953 gal/year (0. 02 cfs) during year 2001 <br />as pit inflows. The overburden and Wadge coal aquifers have mean TDS values of 2,582 and 885 mg/l, <br />respectively (see "Ground Water Chemistry" section of Tab 7, Tables 7-15 and 7-17). A weighted <br />average (based on relative inflow rates) for these aquifers combined is 2,741 mg/l. Therefore, the <br />chemical load in tons/day (L) for pit inflow waters discharging to Dry Creek during the year 2001 is: <br />L = 0.02 x 2,741 x 0.0027 = 0.148 tons/day <br />Dry Creek has an average TDS value of 1,048 mg/1, and its mean discharge for the time period June - <br />September (low -flow irrigation season) is 1.50 cfs. Therefore, the chemical load of Dry Creek is: <br />L = 1.50 x 1,048 x 0.0027 = 4.244 tons/day <br />Using the chemical load values derived above, and mean flow values for Dry Creek and the pit <br />discharges (expressed in acre-feet), the resultant dissolved solids concentration for Dry Creek is: <br />DSC = (0.148 + 4.244)/(0.04 + 2.98) x 0.00136 = 1,071 mg/l <br />A TDS value of 1,071 mg/1 due to pit inflows discharging to Dry Creek represents a 2.0 percent increase <br />over the premining Dry Creek average value of 1,048 mg/1. This impact represents a worst-case <br />scenario since year 2001 has the highest pit inflows, and the calculations assume that all pit inflows will <br />discharge to Dry Creek without infiltration losses to the alluvium. <br />Impact of Spoil Water Quality on the Ground and Surface Water Quality This section contains a <br />determination of the Probable Hydrologic Consequences of the existing and <br />17 12/07/16 <br />