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_pg_ <br />Presently, 242 acres in the permit area drain into the sediment ponds. The <br />storage in ponds decreases the flow of Grassy Creek and takes some water out <br />of the system by evaporation in the ponds. Post-mining and reclamation <br />requirements call for removal of all the ponds except for Pond 6 which will be <br />left as a stockpond. Pond 6 will receive drainage from 101 acres. Some water <br />will be lost to the surface water system due to storage and evaporation in the <br />pond. <br />The pond has a maximum storage capacity of only 2.95 acre/feet. Therefore, <br />any impact to surface water quantity will be negligible. <br />Cumulative Hydrologic Impact Assessment - Summary and Findings <br />A. Surface Water <br />In January of 1983, the Colorado District of the U.S. Geological Survey, Water <br />Resources Division, was contracted by the Division to model the cumulative <br />effects of all anticipated mining in the general area of the Upper Yampa River <br />Basin. The USGS adapted an existing surface water quality model for use in <br />this area, and calibrated the model using data from water years 1976 to 1981. <br />The Division provided estimates of the short-term and long-term effects of <br />mining which were added to the model to predict the cumulative effect of <br />mining in the general area. Model output (monthly discharge, dissolved solids <br />concentration, and dissolved salt load) was obtained for four geographical <br />locations; lower Middle Creek, lower Fish Creek, lower Trout Creek, and the <br />Yampa River at the Hayden gaging station. <br />The effects of mining prior to 1981 were included in the USGS data used to <br />calibrate the model. Therefore, the effects of mining after 1981 needed to be <br />estimated and specifically added to the model. These effects were estimated <br />by the Division using information obtained from the mine permit applications <br />on file with the Division. Scenarios were developed which included both the <br />direct and indirect surface water effects. (Indirect surface water effects <br />result from the interaction of surface water with affected ground water <br />systems.) <br />Mining effects were divided into short-term effects and long-term effects. <br />These time frames are relative to the life of the mining operation. <br />Short-term effects include surface and ground water effects that would occur <br />during the mining operation and for a short time following reclamation, such <br />as discharge from sediment ponds, discharge from underground mine workings, <br />and the discharge of affected waters from shallow ground water systems. The <br />natural flow patterns of the affected ground water systems are disrupted by <br />mining, and surface and ground water is mixed. Increased evaporation losses <br />from the sediment ponds are assumed to be offset by increased runoff from <br />disturbed areas. <br />