2010-12-09_REVISION - C1982057 - Laserfiche WebLink

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The majority of runoff from disturbed areas within the original permit area during the mine life will be diverted to Sediment Ponds 005 and 006, prior to release off site. Effluent from Ponds 005 and 006 flows to unnamed ephemeral gulches, and ultimately Dry Creek. The majority of runoff from disturbed areas in the south extension area during mine life will be diverted to the Sediment Pond 016/016A series or to Sediment Pond 017, prior to discharge. Effluent from the ponds will flow into Hubberson Gulch, and ultimately Dry Creek. Effects of mining on Hubberson Gulch and Dry Creek will involve changes in quantity and quality, which are further described below. A negligible acreage affected by the extreme eastern extension of the south area pits and the neck pits between the north and south mining areas will drain to Sediment Ponds 009 and 015, and eventually to Sage Creek. Measurable effects on Sage Creek water quality or quantity are not projected, due to the small disturbance acreage and the fact that there will be no spoil water flow to the Sage Creek watershed. The mining and reclamation activities will result in changes to the geomorphic characteristics of ephemeral stream channels within the 005, 006, 016 and 017 drainage basins. Drainage densities and channel frequencies will be reduced, and channel gradients will be slightly increased in some areas; however, the operator has designed and located post-mining drainage channels to minimize erosion, with riprap specified where warranted. 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/l to 606 mg/l with an average of 100 mg/1. 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-mining level of approximately 140 tons/mil/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 in the Wadge and Wolf Creek/Sage Creek mining areas, a spoils aquifer will begin to develop. The water necessary to recharge these aquifers will be derived from Seneca II-W Findings Document 41 C1982057 Permit Renewal No. 5 December 9, 2010