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basins. Drainage densities and channel frequencies will be reduced, and channel <br /> gradients will be slightly increased in some areas;however, the operator has designed and <br /> located post-mining drainage channels to minimize erosion. <br /> Sediment leaving the site is controlled to meet effluent limits placed upon sediment pond <br /> discharges in SPL's Colorado Discharge Permit System permit. The total suspended solids <br /> increase to Hubberson Gulch that can be attributed to mining is projected to be minimal. <br /> Once vegetation is successfully reestablished, the erosion rates are expected to return to <br /> the pre-mining level of approximately 140 tons/mil/yr. <br /> Sediment ponds will act to control flood flows from the disturbed area. The ponds will <br /> regulate flood discharges, minimizing the impact of the floods. The ponds are not <br /> expected to significantly reduce the quantity of runoff water available in Dry Creek. <br /> The major impact of mining will be the development and subsequent discharge to the <br /> surface system of spoils aquifer waters. As each successive pit is reclaimed in the <br /> Wadge and Wolf Creek/Sage Creek mining areas, a spoils aquifer will begin to develop. <br /> The water necessary to recharge these aquifers will be derived from precipitation,overland <br /> flow, and discharge from the Williams Fork formation overburden and the coal seams <br /> being mined. <br /> The backfilled pits in and of themselves will display unconfined conditions; however, <br /> the pits will be underlain by relatively confining units. <br /> As water enters the reclaimed areas,it will tend to migrate through the spoils toward the <br /> lowest point in the pit. While some of this water may be lost to the walls, the major <br /> portion of it will stay in the pit, as the permeability of this material is greater than that of <br /> either the walls or the floor. It is projected that the water quality of spoil aquifers at the <br /> Seneca IIW Mine site will approximate that at the nearby Seneca II Mine. The Seneca II <br /> Mine spoil aquifers exhibit elevated levels of total dissolved solids,magnesium, <br /> manganese, molybdenum, and sulfate. <br /> As the aquifer is developing, the water will be of slightly poorer quality than the <br /> above assumptions, but as the more easily leached constituents are lost, the quality <br /> should approximate that at the former Seneca II Mine. Analysis of spoils water from the <br /> former Seneca II Mine indicates that this magnesium-calcium sulfate water has elevated <br /> levels of sulfate and magnesium. TDS values vary between 2,200 and 4,000 mg/l. <br /> Eventually,water at Seneca IIW Mine will begin to discharge to the surface as the water <br /> elevation exceeds the ground level or when sufficient head is developed. <br /> The primary impact of Seneca IIW mining operations (including south extension <br /> operations)on surface water quality will be an increase in total dissolved solids (TDS) <br /> concentration resulting from the occurrence of spoil springs after backfilled spoil in the <br /> mine pits has become saturated. The projected impacts on each of the affected drainages <br /> near the permit area are summarized below. <br /> Hubberson Gulch <br /> SPL predicts spoil springs in the Seneca IIW South Area will increase TDS in Hubberson <br /> Gulch upstream from the Pond 006 drainage from 676 mg/1 to 1,787 mg/I. This <br /> prediction was calculated from mean discharges and mean TDS concentrations for June - <br /> September data for the entire period of record. This projection exceeds the Division's <br /> Page 26 of 37 <br />