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time as the readily dissolvable elements are leached until an equilibrium <br />level is reached. Further discussion of this is found under the Surface <br />Water portion of the Probable Hydrologic Consequences section. <br />Surface Water Effects <br />The majority of runoff from disturbed areas during the mine life will be <br />diverted to Sediment Ponds 005 and 006, prior to release off site. Effluent <br />from Ponds 005 and 006 flows to unnamed ephemeral gulches, and <br />ultimately Dry Creek. Effects of mining on Dry Creek will involve changes <br />in quantity and quality, which are further described below. <br />A negligible acreage affected by the extreme eastern extension of the south <br />area pits and the neck pits between the north and south mining areas will <br />drain to Sediment Pond 009, and eventually to Sage Creek. Measurable <br />effects on Sage Creek water quality or quantity are not projected, due to the <br />small disturbance acreage and the fact that there will be no spoil water flow <br />to the Sage Creek watershed. <br />The mining and reclamation activities will act to change stream channel <br />geomorphologies. Drainage densities and channel frequencies will be <br />reduced; however, Seneca Coal Company has designed and located <br />post-mining drainage channels to minimize the erosive results of the lowered <br />frequencies. <br />During mining operations and until adequate vegetation is established, <br />runoff and erosion rates within the disturbed area will be higher than <br />pre-mining rates. Seneca Coal Company calculated runoff and <br />erosion/sediment yield rates from disturbed areas when designing Sediment <br />Ponds 005, 006 and 009 (Tab 13). Sediment leaving the site will be <br />controlled to meet effluent limits placed upon sediment pond discharges in <br />Seneca Coal Company's Colorado Discharge Permit System permit. <br />Baseline flows in Hubberson Gulch exhibit TSS levels from 5 mg/l to 606 <br />mg/I with an average of 100 mg/1. The total suspended solids increase to <br />Hubberson Gulch that can be attributed to mining is expected to be <br />minimal. Once vegetation is successfully reestablished, the erosion rates are <br />expected to return to the pre-mining level of approximately 140 tons/miZ/yr. <br />Sediment ponds will act to control flood flows from the disturbed area. The <br />ponds will regulate flood discharges, minimizing the impact of the floods. <br />The ponds are not expected to significantly reduce the quantity of runoff <br />water available in Dry Creek. The mine area makes up only a small portion <br />of the Dry Creek watershed (0.9%). <br />The major impact of mining will be the development and subsequent <br />discharge to the surface system of spoils aquifer waters. As each successive <br />29 <br />