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i COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale - Page 6. Permit No. CO-0000132. VI. TERMS AND CONDITIONS OF PERMIT 1. Water Quality Standard Based Effluent Lim:[tations: a) pH: In the case of pH, the limits are set directly from stream standards, with an allowable range of 6.5-9.0 s.u. b) Metals: Amass balance equation is used to determine the effluent concentrations for those parameters whose limitations are based on the water quality standards. For this facility, the instream limits for Total Recoverable Iron and Total Recoverable Manganese, metals typically found in coal mine effluent, are applicable at discharge point 011. (This is the only point which contains mine water, and thus may have a consistent flow. The other points are only for stoxmwater runoff. For them, since discharge is expected to take place only during or soon after a precipitation event, the mass balance calculation, which utilizes stream low flows, is not applicable.) The mass balance equation is: M3Q3 - M1Q1 M2 Q2 Where: Q1 = Upstream low flow from Part III.B.1 Q2 = Effluent flow from Part II.F Q3 = Combined downstream flow (Q1 + Q2) M1 = Upstream background pollutant concentration M2 = Unknown; effluent pollutant concentration M3 Water Quality Standard For this facility: Ql = 18.1 MGD'~ Q2 0.215 MGD . M1 0.15 mg/1 Total Recoverable Iron (WQ Stn 11152) = 0.024 mg/1 Total Recoverable Manganese (WQ Stn 11152) Mg = 1.0 mg/1 Total Recoverable Iron, chronic = 1.0 mg/1 Total Recoverable Manganese, chronic The calculated limit for Total Recoverable Iron is 72.6 mg/1. This is far greater than the federal limits, and so the stricter limits shall be applied. The calculated limit for Total Recoverable Manganese is 83.2 mg/1. This is far greater than would be expected in the a uent, and so no limits are needed at this Cime. The actual mass balance calculations are i^ the permit file and axe available upon request. *Discharge point 011 discharges to Sanborn Creek, which does not have instream metals limits: However, Sanborn Creek flows several hundred feet to the North Fork of the Gunnison River, which does have instream metals limits. Therefore, the impact on [he North Fork must be examined. The chronic low flow used is for the North Fork, above the confluence with the Fire Mountain Canal.