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• The majority of pit inflow waters will be contained by Ponds 005 and 006; little or no pit pumpage will be received by Pond 009, Therefore, any surface water quality impacts as a result of pit pumpage will be to Dry Creek. Using equations presented by Ferreira (1984), the resulting TDS concentration (DSC) of Dry Creek due to pit inflow discharges can be calculated. These equations are explained in detail in the portion of this Tab titled "Potential Impact of Replaced Spoil on Cround Water Ouali ty", As previously stated, the highest yearly pit inflows for both the Overburden and Wadge Coal will ear 2007. These aquifers combined will produce an estimated 4,806,953 ~I~~ gal/d y (.02 cf s) ring year 2001 as pit inflows. The Overburden and Wadge Coal aquifers ~,J ave mean S values of 2,582 and 885 mg/1, respectively (see "Ground Water Chemistry" L,~~..~ section of Tab 7). A weighted average (based on relative inflow rates) for these aquifers /f~ ~~ ~~ combined is 2,741 mg/1. Therefore, the chemical load in tons/day (L) for pit inflow "I' waters discharging to Dry Creek during the year 2001 is: L = 0.02 x 2,741 x 0.0027 = 0.748 tons/day Dry Creek has an average TDS value of 1,048 mg/1, and its mean discharge for the time • period June-September (1orv flow/irrigation season) is 1.50 cf s. therefore, the chemical load of Dry Creek is: l = 1.50 x 1,048 x 0.0027 = 4.244 tons/day Using the chemical load values derived above, and mean flow values for Dry Creek and the pit discharges (expressed in acre-feet), the resultant dissolved solids concentration (DSC) for Dry Creek is: ~ 0,14 7~~/,W`~ DSC = 4.244 ~__ = 1,071 mg/1 ' I ( 1 vT _ ' ~y~ ~ 9,>~ q ~ (0.04 + 2.98) x 0.00136 up (I/l(v/{/(~V`G(J ~ ~d0l~ A TDS value of 1,071 mg/7 due to pit inflows discharging to Dry Creek represents a two percent increase in the premising Dry Creek iD5 average value of 1,048 mg/l. This impact represents a worst case scenario since year 2001 has the highest pit inflows and the calculations performed above assume that all pit inflow waters will discharge to Dry Creek without infiltration losses to the alluvium. . Impact of Spoil Vla ter Quality on the Ground and Surface Water Quality. This section contains a determination of the Probable Hydrologic Consequences of the existing and 17