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COLORADO DEPARTMENT OFP[/BLlC HEALTHAND ENVIRONMENT, Wnter Qunlity Control Division Rationn[e-Page 5, Permit No. CO-0017146 Totallron, mgA* BAT** 3.5 7.0 Settleable Solids, mUl* N/A 0.5 • Thete parmneters subject to Burden of Proof Requirements as discussed below •* Best Available Technology- npplies to thaseponds already constructed Alternate Limitation Burden of ProofReauirements: In conformance with 40 CFR 434.63, the permittee has the burden of proof when requesting relief from total suspended solids (TSS), total iron and/or settleable solids limitations, as appropriate. Relief shall be granted only when necessary and shall not be granted when the permittee has control over the discharge. The permittee should endeavor to meet the primary limitations whenever possible. Relief is not available for mine drainage. 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 stopped. For snowmeit, to waive TSS and total iron limitations, it u 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 geeater than the !0 year, 14-hour event has stopped. Documentation that the treatment facilities were properly operated and maintained prior to and during the storm event must be submitted with any request for relief. The Division shall determine the adequacy ofproof As part of this determination, the Division shall evaluate whether the permittee could have controlled the discharge in such a manner that primary [imitations 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. Al[ manual pond dewatertng must meet TSS and total iron limitations unless previous approval has been granted for ponds that have no other method of dewatering. Post-Minin¢ Areas: In conformance with 40 CFR 434.50, commencing at the time active mining has ceased and al[ surface areas served by a sedimentad'on pond have been returned to the required contour and revegetation has commenced, applicable discharges may be eligible for past-mining limitations. In most cases, these post-mining limitations shall remain in effect until bond release. The permittee shall notify the Division at the appropriate time so that consideration of permit modifications can be made. Prior to notification and subsequent permit modification, active mining limitations will apply regardless of actual mine status. d. Pollutants Limited by Water Quality Standards: The water quality assessment in Appendix A contains the evaluation of pollutants limited by water quality standards. The mass balance equation shown in Secd'on IV of Appendix A was used to calculate the maximum allowable effluent concentration that could be discharged without causing the water quality standard 'to be violated. A detailed discussion of the calculations for the maximum allowable effluent concentrations for total recoverable arsenic, dissolved cadmium, total recoverable m'valent chromium, dissolved capper, dissolved and total recoverable iron, total mercury, dissolved lead, dissolved manganese, dissolved nickel, dissolved selenium, dissolved silver, and dissolved ainc are provided in Section IY of the water quality assessment contained in Appendix A. The maximum allowable effluent concentrations determined as part of these calculations represent the calculated effluent limits that would be protective of water quality. These are also known as the water quality-based effluent Jimits (WQBELsJ. The Permits Unit evaluated the calculated WQBELs and has made a determination as to whether there is a ` reasonable potential for the facility discharge to cause or contribute to an exceedance of a sheam standard. If there JJ is a reasonable potential for the discharge to contribute to an ezceednnce, effluent limits are included in the permit. A discussion of the reasonable potential evaluation is contained in the paragraphs that follow. Lnst Revised !!/32003 pH, s. u. (minimum -maximum) -6.0 - 9.0--- Total Suspended Solids, mg/1 * 35 70