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estimated from data developed by tl~e U.S. Forest Service for <br />similar topographical conditions or can be calculated from the <br />• following equation: <br />ET = P - R - U + QSg <br />An approximate hydrologic budget within the Orchard Valley Mine <br />area was calculated for the Steven's Gulch drainage basin. Any <br />impact from the proposed mining would initially effect this <br />drainage and it is the only drainage basin to have available <br />information pertinent to ground water table at this time. A <br />similar calculation will oe developed for the East F.oatcap drain- <br />age uasin at a later date. <br />Steven's Gulch 47ater Budget <br />Ti,e Steven's Gulcti drainage is monitored at a station located <br />near the entrance road to the Orchard Valley Mine. A Parshall <br />flume (SW-5) was installed at this point in 1978 and later <br />replaced about 150 feet upstream in 1581. The drainage area at <br />this point is about 3.96 square miles. The streambed upstream <br />from this point is deeply incised into the surrounding rocks and <br />the stream due to the steep gradient, and geological conditions <br />did not develop any significant accumulation of streambed <br />deposits. About 1.5 miles upstream of the monitoring point, the <br />Steven's Gulch gradient is much flatter and the stream laid <br />deposits wree developed to a greater degree. In this area where <br />• the stream laid deposits are about 250 feet wide and up to 97 <br />feet deep, a C47I well field was developed. Therefore, certain <br />parameters necessary for tl~e Steven's Gulch basin hydrologic bud- <br />get are know for the lower reaches (flow and precipitation moni- <br />tored near the existing mine) and certain parameters (snowpack <br />and ground water levels) are measures at the Steven's Gulch well <br />field. <br />However, even with this existing data it was possible to develop <br />a hydrologic oudget for the upper portion of Steven's Gulch, <br />using certain assumptions and extrapolations. <br />A hydrologic uudget for the Steven's Gulch at the CWI well field <br />location (drainage basin = 2.53 sq, mi.) for the year 1983 is <br />presented in the following table. <br /> <br />2 <br />