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The major impact of mining will be the development and subsequent dischazge to surface system of spoils 9quifer waters. As each successive pit is reclaimed, a spoils aquifer will begin to develop. The water necessary to recharge this aquifer will be derived from precipitation, overland flow, and discharge from the Williams Fork formation overburden and the Wadge coal. The backfilled pits in and of themselves will display unconfined conditions,~owever~ the pits will be surrounded on the sides and be underlain by relatively confining units. The underlying material will be even more confining than the sides. As water enters the reclaimed areas it will tend to migrate through the spoils toward the lowest point in the pit. While some of this water may be lost to the walls., the major portion~of it will stay in the pit, as the permeability of this material is greater than that of either the walls or the floor. It is projected that the water quality of spoil aquifers at the Seneca II-W Mine site will approximate that at the neazby Seneca II Mine. The Seneca II Mine spoil aquifers exhibit elevated levels of, total dissolved solids, magnesium, manganese, molybdenum, and sulfate. Complete water quality analyses of two spoils aquifer wells are published in the Seneca II Mine 1984 Annual Hydrology Report, Appendix B. As the aquifer is developing, the water will be of slightly poorer quality than the above assumptions, but as the more easily leached constituents are lost, the quality should approximate that at Seneca fI Mine. Analysis of spoils water from the Seneca II Mine indicates that this magnesium-calcium sulfate water has elevated levels of sulfate and magnesium. TDS values vary between 2,200 and 4,000 mg/l. Eventually, water at Seneca II-W Mine will begin to dischazge to the surface as the water elevation exceeds the ground level or when sufficient head is developed. This dischazge may be contained in a sediment pond, or may flow into the unnamed gulch along the access road. The primary impact of Seneca II-W and Seneca II-W South Area mining operations on surface water quality will be an increase in total dissolved solids (TDS) concentration resulting from the occurrence of spoil springs after backfilled spoil in the mine pits has become saturated. The projected impacts on each of the affected drainages near the permit area are summazized below. Hubberson Gulch Seneca Coal Company projects spoil springs in the Seneca II-W South Area will increase TDS in Hubberson Gulch upstream from the Pond 006 drainage from 676 mg/f to 1,739 mg/1. This prediction was calculated from mean discharges and mean TDS concentrations for June -September data for the entire period of record. Seneca II-W Findings Document 31 November 3, 1999