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<br />A TWO-DIMENSIONAL MODEL OF THE TROUT CREEK SANDSTONE SIMULATING THE <br />EffECTS OF PUMPAGE ON STREAM FLOWS, SENECA IIW AND YOAST MINE S1TES <br />Introduction <br />The U.S. Geological Survey's finite-difference, ground-water flow <br /> <br />model, MODFLOW (McDonald and Harbaugh, 1984), was used to simulate the <br />effects of long-term well pumpage from Peabody's Seneca IIW and Yoast mine <br />properties on local and regional surface flow. Two proposed water supply <br />wells, one at each mine site, will provide potable water for mine <br />operation needs. Each well was estimated to pump water from the Trout <br />Creek sandstone at a constant rate of 35 gpm for a period of approximately <br />15 years for the Seneca IIW well (from year 1990 to 2004) and 9 years for <br />the Yoast well (from year 1996 to 2004). The model's focus was to <br />simulate ground-water flow in this unit and its interaction with surface <br />flow. <br />Within a ten-mile radius of both mine sites, the Trout Creek <br />sandstone crops out in several major drainages: at the head of Hubberson <br />Gulch, three places along Sage Creek, one place in Grassy Creek, two <br />places in Fish Creek, four places along Trout Creek, one place in Middle <br />Creek, and in two places along the Yampa River (Figure 1). It was <br />necessary to determine the amount of stream loss that may occur in these <br />areas from long-term pumpage in order to evaluate potential impacts to <br />surrounding water-resource users and to accurately estimate stream <br />replacement water volumes. <br />The Trout Creek sandstone is the uppermost member of the In es <br />r 1 <br />formation and is a prevalent marker bed in the region <br />8333003.004 <br />1 <br />The fine-grained <br />C;nnTranc ins <br />