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impact of Replaced Spoil Material on Ground Water Flow and Recharge Capacity <br />Tab 17-1 provides a review of the potential impacts of spoil material on ground water flow and <br />recharge for the Seneca II-W area. The topsoil and overburden characteristics are nearly identical <br />between the Seneca II-W and Seneca II-W South areas. Therefore, it is speculated that the impacts of <br />spoil on ground water flow and recharge will be similar, that is not to diminish the horizontal or vertical <br />permeabilities of the aquifer materials las discussed in Section 17-1 of the existing permitl. No <br />significant impacts to ground water flow or changes to the infiltration rates are expected and the <br />ground water system is expected to return to nearly its original (pre-mining) state upon final <br />reclamation. <br />Containment of Pit Inflow Pumpage and Impacts to Water Quality <br />Runoff and pit pumpage from the disturbed areas will be routed through sedimentation ponds, <br />which will be designed and constructed to provide sufficient residence times to ensure that <br />suspended solids concentration in pond effluent meets requirements specified in NPDES Permit <br />No. CO-000022. Three NPDES ponds, Ponds 015, 016 and 017, will contain runoff and pit <br />pumpage from the Seneca II-W South mining area. All ponds will be constructed in accordance <br />with accepted engineering practices. <br />The majority of pit inflow waters will be contained by Ponds 016, 016a and 017, located in the <br />Hubberson Gulch drainage, a tributary to Dry Creek. Pond 016a will be apre-treatment pond <br />constructed immediately upstream of Pond 076, and will be used to contain stormwater runoff <br />generated by the 10-year, 24-hour storm event in the Sage CreeklWolf Creek mining area. Since <br />it is apre-treatment pond it does not need to be included in the NPDES permit. Little or no pit <br />pumpage will be received by Pond 015, located in the Sage Creek drainage. Therefore, <br />predicted surface water quality impacts as a result of pit pumpage will be predominantly <br />restricted to Dry Creek. Using equations presented in Tab 17-1 of the existing permit, the <br />resulting total dissolved solids ITDS) concentration expected in Dry Creek runoff due to pit <br />inflow discharges can be calculated. <br />As indicated above, the highest yearly pit inflows contributed by the Wadge ground water <br />system will occur in year 2001. Combined discharge from the overburden and coal aquifers into <br />the pits is estimated to reach approximately 3,854 gal/day (0.006 cfsl during year 2001. The <br />Wadge coal aquifer, in the vicinity of the South area, has a period of record (through 2001) <br />mean TDS value of 815 mg/I (utilizing data from well WW41• Because no monitoring wells were <br />completed in the Wadge overburden within the South area, Seneca II-W Wadge overburden <br />ground water chemistry data were used in this discussion. The Wadge overburden aquifer in the <br />Seneca II-W area has a premining (years 1982 through 1989) mean TDS value of 2,582 mg/I <br />(utilizing wells WOV2, WOV14, WOV15, WOV17 and WOV 181. The estimated chemical load in <br />tons/day ILI for Wadge pit inflow waters discharging to Dry Creek during the year 2001 were <br />calculated as follows: <br />96 Revised 1/02 <br />