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During mining operations and until adequate vegetation is established, runoff and erosion rates within the disturbed area will be higher than pre-mining rates. Seneca Coal Company calculated runoff and erosion sediment yield rates from disturbed areas when designing all sediment ponds. (Tab 13). Sediment leaving the site will be controlled to meet effluent limits placed upon sediment pond discharges in Seneca Coal Company's Colorado Discharge Permit System permit. Baseline flows in Hubberson Gulch exhibit TSS levels from 5 mg/I to 606 mg/I with an average of 100 mg/I. The total suspended solids increase to Hubberson Gulch that can be attributed to mining is expected to be minimal. Once vegetation is successfully reestablished, the erosion rates are expected to return to the pre-muting level of approximately 140 tons/mi'/yr. Sediment ponds will act to control flood flows from the disturbed area. The ponds will regulate flood discharges, minimizing the impact of the floods. The ponds are not expected to significantly reduce the quantity of runoff water available in Dry Creek. The mine area makes up only a small portion of the Dry Creek watershed (0.9%). The major impact of mining will be the development and subsequent discharge to the surface system of spoils aquifer 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, however 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 nearby 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 [I Mine. Analysis of spoils water from the Seneca Seneca II-W Findings Document 31 June 15, 2001 Permit Renewal No. 3