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Mountain Coal and Beaz Coal Water Quality Assessment CO-0038776 and CO-0044377 <br />It is the standazd approach of the WQCD to perform amass-balance check to determine if fecal <br />coliform standards are exceeded. WQCD procedure specifies that checks are conducted using only <br />the chronic low flow as set out in Section III. Using the mass-balance equation provided in the <br />beginning of Section IV, the background concentration contained in Section II, and the in-stream <br />standazds for fecal coliform shown in Section II, checks for fecal coliform were conducted. The <br />effluent flow, Qzi reflects the design flow from Outfa11004 and Internal Outfa11007 in the respective <br />calculations. The data used and the resulting calculations of the allowable dischazge concentration, <br />M2, are set forth below. <br />North Fork o the Gunnison River <br />Parameter Q t (cfs) Q Z (cfs) Q s (cfs) MI (#/100 <br />ml) M3 (#/100 <br />ml) MZ (#/100 <br />ml) <br />Fecal Coliform 43 0.28 43.28 4 200 30,300 <br />Outfa11007 <br />Parameter Q~ (cfs) Qz (cfs) Q j (cfs) M~ (#/100 <br />ml) Mj (#/100 <br />ml) Mz (#/100 <br />m!) <br />Fecal Coliform 43 0.016 43.016 4 200 526,950 <br />Metals: Metals may occur naturally in rock azound coal seams. Earth disturbances, such as mining <br />operations, expose rock to air and water creating a potential for these elements to be present in <br />elevated concentrations. Thus, arsenic, cadmium, copper, chromium, iron, lead, manganese, <br />mercury, nickel, selenium, silver and zinc, which have been identified as pollutants potentially <br />present in mine water dischazges, aze evaluated in this assessment. According to the Agency for <br />Toxic Substances and Disease Registry, chromium in the trivalent form occurs naturally in the <br />environment whereas hexavalent chromum is produced byindustrial processes. Tzdustrial processes <br />at this facility would not generate hexavalent chromium and therefore the evaluation for chromium is <br />limited to the trivalent form. <br />Using the mass-balance equation provided in the beginning of Section IV, the low flows provided in <br />Section III, the background concentrations contained in Section II, and the in-stream standards for <br />metals shown in Section II, assimilative capacities were calculated. The effluent flow, Qz, reflects <br />the combined design flow of 0.28 cfs resulting from Mountain Coal WWTFs Outfalls 004 and 016 <br />and Beaz Coal WWTF Outfa11001, thereby resulting in the calculation of an allowable dischazge <br />concentration, M2, applicable to all three outfalls. The data used and the resulting calculations of the <br />allowable dischazge concentrations, Mz, aze set forth in Table A-9 for chronic assimilative capacities <br />and in Table A-10 for acute assimilative capacities. <br />Appendix A Page 15 of 20 Last Revised 3/9/2004 <br />