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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division Amendment No. 1 -Rationale. Page 4, Permit No. CO-0032638 Alternate Limitation Burden o(Proo(Reguirements: In conformance with 40 CFR 434.63, the permirree has the burden of prooj when seeking relief from total suspended solids (TSS), total iron and/or settleable solids (SS) limitations jot surface runofjonly. Relief may be granted jot each discharge occurrence only when necessary and shall not be granted when the pennittee has control over the discharge. The permirree should endeavor to meet the primary linritarions whenever possible. The permirree will need to show that exceedence of the applicable linritarions was caused by precipitation and no other source and that the discharge was beyond their control. The permirree Iran the burden of proof when seeking reliejjrom fora! suspended solids (TSS), total iron and/or settleable solids (SS) limitations. Outjall 001 is eligible. Outfalls 004 and 007 are eligible jot relief only when the ecceederrce is caused by precipitation. Demonstration is necessary. 1) 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 linritarions, it is necessary to prove that discharge occurred within 48 hours after precipitation greater than the 10-year, 24-hour event has stopped. 2) For snownrelt 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 permirree shall submit adequate proof in order jot an exemption to be claimed. Said prooj shall be submitted as an attachment to the Discharge Monitoring Report (OMR) jot the appropriate period. The Division shall determine the adequary of prooj As part of this determination, the Division shall evaluate whether the pennittee could have controlled the discharge in such a manner that primary limitations could have been met. All manual dewatering of the ponds shall meet TSS and total iron limitations. c) Pollutants Limited by Water Quality Standards: Outfall 007 contaius mine drainage and/or spoils spring water. This may result in discharge at any time. Therefore, water qualiry-based effluent limitations nrusr be carsidered. The calculated water qualiry-based effluent limitations are presented in Table V-3. For those parameters shown in Table V-! that are limited by Water Quality Standards, the mass balance equation shown in V.A.2. was used ro calculate the allowable effluent limitations that would not cause the water qualiry standards ro be violated jot the discharge. These limitations are shown as the values jot Mr in Table V-3. The values jot Q, is set at /0, the value jot Q1 is set at I • thus the value jot Q~ is ! l (for both chronic and acute limitations). The value Jor Mr has been set at zero (see section 1/.8.1.) and the values jot M, vary depending on r/re applicable water quality standards (M~. These values for M, are shown in Table V-3 along with the calculated effluent limitations (M~ jot outfal! 007. Table V-3 -Summary of Mass Balance Calculations Parameter Stream Standard, (M3), Effluent Concentration, (M2), Acute/Chronic Acute/Chronic Arsenic (1'R), ug/P 50/N/A 550/N/A Cadmium (PD), ug/P 4.82/1.3/ 53/l4 Copper (PD), ug/P 21.06/13.82 230//50 Iron (TR), ug/P N/A/1000 N/A/11000 /ton (PD), ug/P N/A/300 N/A/3300 Lead (PO), ug/P 128.67/5.04 1420/55 Manganese (I7t), ug/P N/A/1000 N/A/11000 Manganese (PD), ug/P N/A/50 N/A/SSO Mercury (Total), ug/P N/A/0.01 N/A/0.11