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Mining in the Fish Creek basin began in 1982, in the Cow Camp Creek tributary <br />basin. As mining in this drainage was completed, an azea in another tributary basin <br />of Fish Creek, Bond Creek, was disturbed. Mining activity occured throughout the <br />life-of--mine in this basin. All mining activities have ceased and ongoing <br />reclamation is underway. The effects of mining on the water quality and quantity in <br />each of these surface water basins is discussed below. <br />Grassy Creek Drainage Basin <br />Grassy Creek is a northerly flowing minor tributary of the Yampa River east of <br />Hayden, Colorado. The Seneca II Mine is located about three miles upstream of the <br />confluence with the Yampa River, and includes about 860 acres of disturbed lands <br />within this drainage basin. Surface water monitoring sites aze located above and <br />below the mine to quantify mine-related impacts. Two ponds, NPDES 002 and 003, <br />discharge between these two stations to Grassy Creek. <br />The operator has conducted monitoring of dischazge and water quality at the two <br />surface sites in the Grassy Creek drainage since 1981. At the station above the mine <br />(SW-S2-1) a mean dischazge of 0.47 cubic feet per second (cfs) is characteristic of <br />stream flow during the period June through September, the historic irrigation period <br />in this portion of Routt County. A minimum flow of zero and maximum flow of <br />7.89 cfs has occurred during the period of record up through 2002. June through <br />September TDS concentrations have increased, from a 1987 average of 718 <br />milligrams per liter (mgJl), to a 2002 average of 880 mgfl. <br />Outflow from the Wadge Impoundment (NPDES 002) which, along with the <br />Northwest Impoundment (NPDES 003), is located downstream of site SW-S2-1, is <br />governed by three sources; snowmelt runoff, rainfall runoff and spoils aquifer <br />inflow. During the period June through September for the period of record through <br />2002, a peak flow of 5.64 cfs has been recorded at NPDES 002, minimum flow was <br />zero, and mean flow was 0.25 cfs. These flows are taken from weekly <br />measurements. An increase in TDS concentration has been observed during the <br />period of record, from an average of 2,332 mg/1 in 1987 to an average of 3,760 mg/I <br />for the June through September period in 2002. <br />A second pond which dischazges to Grassy Creek is the Northwest Impoundment <br />(NPDES 003). The June through September mean flow is approximately 0.14 cfs, <br />with a peak flow of 0.88 cfs and minimum flow of zero. June through September <br />TDS concentrations of 1,504 mg/1 were chazacteristic before September 1984, prior <br />to dischazges from atruck-wash facility (which contributes flow to the Northwest <br />Impoundment) using Wadge Impoundment water as a source. Subsequently, as the <br />Northwest Impoundment discharges have increased, June through September TDS <br />has increased to an average of 3,748 mg/1 in the effluent in 2002. <br />22 <br />