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COLORADO DEPAR77NENI' OF PUBLIC HEALTH AND ENVIRONMEM, Water Quality Corurol Division Rationde -Page S, Pamir No. CO-0044776 Table VI-2 -Federal Standards (40 CFR 434) Parameter Limitatioru . 30 Day Avg .. Daily Max pH, s. u. (minimum -maximum) -6.0 - 9.0-- Total Suspended Solids, mg/P' 35 70 Total Iron, mg/P~ (NSPS**) 3.0 6.0 Settleable Solids, mP/e" N/A 0.5 ^ These parameter subject to Burden of Proof Requirements (available for surface runoff only -see next section) ** New Source Performance Standards -applies to those facilities constructed after S/4/84 Alternate Limitation Burden of Pro Requirements: Irt confornurnce with 40 CFR 434.63, the permittee has the burden of proof when requesting relief from total suspended solids (I'SS), total iron and/or settleable solids limitations, as appropriate, for discharges of surface runoff Relief shall be granted only when necessary and shall not be granted when the permittee has control over the discharge. The permittee should endeavor ro meet the primary limitations whenever possible. Relief is nor available for mine drainage alone, nor when the majority of a discharge consists of mine drainage. O For rainfall, to waive TSS and total iron limitations, it is necessary to prove that discharge occurred within 48 hours after measurable precipitation has stopped. In addition, to waive settleable solids limitations, it is necessary to prove that discharge occurred within 48 hours after precipitation greater than the 10-year, 24-hour event has slopped. For snowmelt, to waive TSS and total iron limitations, it is necessary to prove that discharge occurred within 48 hours after pond inflow has stopped. In addition, to waive settleable solids limitations, it is necessary to prove that discharge occurred within 48 hours after pond inflow volume greater than the 10-year, 24-hour event has stopped. Should a precipitation event or snowmelt occur, the permittee shall submi[ adequate proof in order for an exemption to 6e claimed, Weather station data should be submitted where appropriate. Documentation that the treatment facilities were properly operated and maintained prior ro and during [he storm event must be submitted with any request for relief. Additionally far outfall 002. the perminee must demonstrate that the majori(~of the discharge,fpr which the exemotion is claimed consists of surface runoff. Said proof shall be submitted as an attachment to the Discharge Monitoring Report (DMR) for the appropriate period. The Division shall determine the adequacy of proof. As part of this determination, the Division shall evaluate whether the permittee could have comrolled the discharge in such a manner that primary limitations could have been met, whether proper sediment storage levels were maintained and the ponds had sufficient water and sediment capacity for the storm event plus other relevant factors. A![ manual pond dewatering must meet TSS and total iron limitations unless previous approval has been granted for ponds that have Bp pl)1~ method of dewatering. For ponds with automatic dewatering snucrures, only discharges through these structures are eligible jot the exemption. c) Calculation of Water Qualirv Based ;~renr Limitations: Because ourfall 002 may contain mine drainage, a mass balance equation was used to determine the effluent concentrations that would not violate the allowable in-stream concentrations defined by the water quality standards for the Nonh Fork of the Gunnison River. The mass balance equation is: MJ . M~Qr - MrQr Qr