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Pittsburg and Midway Coal Company Edna Mine Water Quality Assessment CO-0032638 <br />scT = o. ~s x ~wQs-BWQ~ + BWQ <br />Where, <br />WQS = water quality standard (chronic standazd or, in the absence of a chronic standard, <br />the acute standard) <br />ADBACs aze then determined by re-calculating the mass-balance equation using the SCT in place of <br />the water quality standard, as in the following equation: <br />ADBAC = <br />Where, <br />SCT x Q3 - M, x Q <br />Qz <br />QI =Upstream low flow (lE3 or 30E3) <br />Qz =Average daily effluent flow (design capacity) <br />Q3 =Downstream flow (Q, + Qz) <br />M~ =Ambient existing water quality concentration (From Section fl) <br />SCT =Significant concentration threshold <br />When Q~ is equal to zero, Qz equals Q3, and therefore the following equation results: <br />ADBAC =SCT <br />The SCTs and ADBACs for pollutants of concern were calculated and are set forth in Tables A-11 <br />and A-12 for Outfall 004 and Outfall 007, respectively. Note that SCTs and ADBACs were not <br />determined for total mercury at either outfall because impacts were not determined, as previously <br />discussed. <br />Table A-12 <br />SCTs and ADBACs for Potential Pollutants of Concern at Outfall 007 <br />Pollutant 'SCT .- ' :-M:t': Q~(cfs) Q'z ~rfs)' -Q;f'.(cfs) ADBfIC s <br />Fe, TR (ug/I) 238 130 0.25 4.0 4.25 245 <br />Mn, Dis (ug/1) 477 13 0.25 4.0 4.25 506 <br />Appendix A twQn Ba vers~o~ a-s enuy Page 17 of 19 Last Revised September 2, 2005 <br />