2017-05-11_PERMIT FILE - C1981012 (18)

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In TRIM COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division Fact Sheet- Page 13, Permit No. C00000906 stopped. In addition, to waive settleable solids limitations, it is necessary to prove that the discharge occurred during the precipitation event, or within 48 hours after precipitation greater than the 10 -year, 24-hour event has stopped. For snowmelt, to waive TSS and total iron limitations, it is necessary to prove that the discharge occurred during pond inflow from the snow melt event, or within 48 hours after pond inflow has stopped. In addition, to waive settleable solids limitations, it is necessary to prove that the discharge occurred during pond inflow from the snow melt event, or within 48 hours after pond inflow volume greater than the 10 -year, 24-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 from primary limitations. The division shall determine the adequacy of proof. As part of this determination, the division shall evaluate whether the permittee could have controlled 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. All manual pond dewatering must meet TSS and total iron limitations. b. Regulation 62: Regulations for Effluent Limitations - These Regulations include effluent limitations that apply to all discharges of wastewater, except stormwater, to State waters. These regulations are applicable to the discharge from outfall 001. 2. Numeric Water Quality Standards The WQA contains the evaluation of pollutants limited by water quality standards. The mass balance equation shown in Section VI of the WQA was used, where applicable, to calculate the potential water quality based effluent limitations (WQBELs), M2, that could be discharged without causing the water quality standard to be violated. A detailed discussion of the calculations for the maximum allowable concentrations for the relevant parameters of concern is provided in Section VI of the Water Quality Assessment developed for this permitting action. The maximum allowable pollutant 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 limits (WQBELs). Both acute and chronic WQBELs may be calculated based on acute and chronic standards, and these may be applied as daily maximum (acute) or 30 -day average (chronic) limits. In order to ensure protection of uses on the receiving stream and downstream segments, effluent limits for both the receiving stream and downstream segment were considered when developing permit limitations. For outfall 001, effluent limits were determined for the Middle Fork of the Purgatoire River and for the mainstem of the Purgatoire River downstream. When the same standards apply to both segments, the more stringent limit is selected to ensure uses on both segments are protected. The applicable limitations developed in the WQA are included in Table VII -2.