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IMPACTS ON SURFACE AND GROUNDWATER <br />During 1984 and 1985 the mine bench was stabilized by rebuilding the mine bench with <br />an engineered fill of underground coal mine waste. Rock underdrains were placed in <br />and under the coal mine waste to channel spring water and seepage from the coal mine <br />waste fill. For the period June 1985 through November 2007 the following underddrain <br />statistics area provided. The north underdrain has averaged 0.06 gpm with an average <br />conductivity of 2383 umhos/cm. The middle underdrain has averaged 0.005 gpm with <br />an average conductivity of 1291 umhos/cm. The south underdrain has averaged 0.14 <br />gpm with an average conductivity of 4742 umhos/cm. These low flows would have <br />minimal impact on the quality of water in Hubbard Creek. The maximum conductivity <br />measured at an underdrain was 6400 umhos/cm. <br />The primary concern with regard to the underground coal mine waste is the impact on <br />Hubbard Creek from water that seeps through the pile. The pile encompasses an area <br />of about 5 acres. A worst case scenario would be in the case the average rainfall <br />during a year (16.94" ref. PAP page 47) all percolated through the pile. In this case 7 <br />acre feet, at a conductivity of 6400 umhos/cm would reach Hubbard Creek and the <br />downstream receiving waters. The data on the conversion between conductivity and <br />TDS for this site is limited. If it assumed that 6400 umhos/cm equates to a TDS of <br />6400 mg/I, then the 7 acre feet that percolates through the pile would contribute <br />approximately 60 tons of salt to Hubbard Creek during the year. The Colorado <br />Department of Health considers mine discharges of less that 350 tons per year (1 ton <br />per day) to be no salt discharge. Therefore this worst case estimate of 60 tons per year <br />is considered to be an insignificant contribution of salt to the downstream receiving <br />waters. <br />Another way to analyze the impact on Hubbard Creek is to analyze how the addition of <br />7 acre feet of relatively high conductivity water impacts the quality of water in Hubbard <br />Creek. It is estimated that Hubbard Creek discharges 24,700 acre feet per year (ref. <br />page 43). Introduction of 7 acre feet per year with a conductivity of 6400 into a 24,700 <br />acre feet per year discharge with a conductivity of 150 increases the conductivity of <br />Hubbard Creek about 1.7 umhos/cm. Clearly this 1.7 umhos/cm increase is an <br />insignificant impact to Hubbard Creek and the downstream receiving waters. <br />An increase in the conductivity measurements in downstream Hubbard Creek would <br />indicate an increased salt load. Quarterly conductivity measurements in lower Hubbard <br />1 of 3 7/08