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. d _. . <br />LJ <br />The basic water balance, including evapotranspiration and the <br />partitioning of precipitation into aurface runoff and infiltration, is <br />expected to remain unaffected by mining in the post-mining period after <br />reclamation is complete. A small increase in surface runoff ie predicted for <br />the West Ridge area as a result of proper reclamation. Subsurface runoff will <br />penetrate the depth of the spoils and seep downdip into Trout Creek. The <br />concentration of dissolved solids in this seepage is expected to be 3000 mg/1 <br />compared to the pre-mining estimate of 570 mg/1 on the Moffat Area. The mean <br />annual concentration of TDS in combined surface and subsurface runoff from <br />both the mine and undisturbed lands on the Moffat Area is estimated at 2290 <br />mg/1. The corresponding number before mining is estimated to be 541 mg/1. <br />The post-mining TDS concentration in drainage from West Ridge is expected to <br />be 2828 mg/1 as compared to the pre-mining value of 2122. Because the mean <br />`icy annual volume of runoff from the land to be mined is very small relative to <br />~`\\` the mean annual discharge of Trout Creek, the elevated TDS levels in the mine <br />'\ drainage will caus~t can annual TDS concentration in Trout Creek to <br />• ~y increase by about~2 mg/1 b sed on the predictive model as described in <br />' Section 2.5.3.5. <br />~,~ 4.5.9 O896RV71TION9 <br />r ~ <br />The data and analyses contained in this section of the report relate <br />specifically to the proposed surface mining area known as the Edna Mine. The <br />work reported herein is part of a more extensive, study that includes areas to <br />the west, and north of the Edna Mine. <br />1.5.4.1 etroam Ploq Rogimo <br /> Rydrologic Sottiag - The Edna Mine is located in the Colorado River <br /> Basin and constitutes a portion of the Trout Creek drainage basin located <br /> southwest of Steamboat Springs, Colorado. As shown in Exhibit 2.5-1, the <br /> Trout Creek watershed is comprised of a catchment area that contributes <br /> directly to Trout Creek and three major tributary watersheds; Fieh Creek, <br /> Foidel Creek and Middle Creek. The head waters of the Trout Creek watershed <br />• are near Mt. Orno in Garfield County and the drainage point is the confluence <br /> Mid-term '94 2.5-2 September 15, 1994 <br />