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-49- <br />Cumulative Impacts of the Blue Ribbon and Somerset Mines <br />Since all anticipated mining at the Blue Ribbon Mine is within the <br />Hubbard Creek drainage basin, the most significant cumulative impacts <br />of all anticipated mining will be the combined impacts of the Blue <br />Ribbon Mine and Somerset Mine on Hubbard Creek and on the downstream <br />water users. <br />Date collected for the Somerset Mine estimates the annua] yield in <br />Hubbard Creek to be 29,700 acre-feet per year (8% of the mean annual <br />yield of the North Fork of the Gunnison - 340,000 acre-feet per year). <br />The total depletion of the flow in Hubbard Creek due to the combined <br />impacts of the Somerset and Blue Ribbon mines may be 0.09 cfs (39 gpm <br />or 56,160 gpd), 0.07 cfs (31 gpm or 44,640 gpd) coming from inflow <br />measured in the Somerset Mine adjacent to or under Hubbard Creek, and <br />0.02 cfs (8 gpm or 11,520 gpd) coming from withdrawal of water by the <br />Blue Ribbon Mine (this analysis ignores the pumping of mine inflows <br />back into the surface water system). This total depletion amounts to <br />about 0.18% of the average streamflow (49.3 cfs) and 3.9% of the low <br />flow (2.23 cfs) in Hubbard Creek as measured above the Blue Ribbon Mine. <br />Cumulative Hydrologic Effects on Ground Water <br />and Surface Water Resources - Finding <br />An assessment of the probable hydrologic consequences of the mining <br />operation and an assessment of the probable cumulative impact of all <br />anticipated mining in the general area on the hydrologic balance has <br />been made. Pursuant to Rule 2.07.6(2)(c), the Division finds that the <br />Mt. Gunnison mining operation has been designed to prevent material <br />damage to the hydrologic balance outside the permit area. <br />REFERENCES <br />Hamon, W. Russell, 1961. Estimating Potential <br />Evapotranspiration. Journal of the hydraulics Division, ASCE <br />May, 1961: 107-119 <br />National Oceanic and Atmospheric Administration. Climatological <br />Data, Colorado. Ashville, North Carolina. <br />U.S. Army Corps of Engineers, 1960. Runoff from Snowmelt, <br />Engineering and Design Manuals, EM 1110-2-14406. U.S. <br />Government Printing Office, Washington, D.C. <br />U.S. Geological Survey. Some Engineering, and Geologic Factors <br />Controlling Coal Mine Subsidence in Utah and Colorado, <br />U.S.G.S. Professional Paper Number 969, U.S. Department of <br />the Interior, Washington. D.C. <br />- ...,.. <br />,.:' .. K <br />