2012-01-06_PERMIT FILE - C1982057 (24)

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As described in Tab 7 (Hydrologic Description), natural ground waters at the Seneca II-W Mine contain high concentrations of dissolved minerals and solids. The resaturation of spoil materials will augment the natural ground water recharge system; however, the quality of ground water in the spoil will not be 411 similar to the premining water quality in this unit. Analysis of the impact of spoil material (Tab 17) indicates that the ground water recharged by the spoil water will affect the quality of the ground water. In general, the dissolved solids content of the ground water is expected to increase to a level greater than the baseline TDS level. In the II-W South area, TDS increases possible are 41 % (3,640 mg/L) in the overburden aquifer and 255% (2,733 mg/L) in the coal aquifer. SCC does not anticipate the transfer of ownership or use of any ground water wells completed in units within the Seneca II-W complex. All boreholes, wells, shafts, and auger holes will be cased and/or sealed to prevent possible ground water degradation through the mixing of ground water and/or surface water that could occur within the borehole. A specific plan for sealing of boreholes, exploration holes, auger holes, wells, and shafts is contained in Tab 'IS, Hydrologic Reclamation Plan. Ground Water Quantity. Typical backfilling methods primarily involve the use of dozers and scrapers (see Tab 20, Backfilling and Grading). Studies by Rahn (1976) and VanVoast and Hedges (1975) indicate that replaced spoil materials display greater porosities and hydraulic conductivities due to the increased void space, regardless of how the spoil is backfilled in the pits. Spoil backfilling using the methods described in Tab 20 (Backfilling and Grading) will ensure the eventual resaturation of the disturbed areas (pits), and thus minimize the adverse effects of mining on ground water flow. The Seneca II-W complex is located in an area that has a climate yielding 16 to 22 inches of annual precipitation. Evapotranspiration rates in the region are relatively high (see Tab 7, Hydrologic Description). The infiltration rate of precipitation through the loamy topsoil and spoil is estimated to be slow to moderate. Slow infiltration rates are common for this area and for this climate since the majority of recharge to local aquifers occurs from the gradual infiltration of snowmelt water. Overburden and topsoil handling, reconditioning, and revegetation methods outlined in Tab 21 (Minesoil Reconstruction) and Tab 22 (Revegetation Plan) will maximize the potential for establishing reclaimed areas that yield infiltration rates and capacities equal to or greater than premining soil hydraulic conditions. Reseeding and mulching of redistributed topsoil in a timely manner will augment the retention and eventual downward movement of soil moisture. Since the texture of the replaced topsoil is generally a sandy loam to clay loam, the infiltration rate through the topsoil will be moderate. Deep ripping of final graded spoil where severe compaction exists, followed by topsoil placement and disking will enhance the infiltration potential of the reclaimed materials. Ground water accumulating in significant amounts in the mining pits will be removed by pumping the • water to those sediment ponds designed to have the prescribed minimum volume for the 10-year, 24- hour storm event. Design criteria for the ponds is described in Tab 13 (Facilities), and it includes plans 2 1 Revision 9/98