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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division Rationale — Page 8, Permit No. C00036251 uranium will apply to all outfalls. These limitations are the same as those contained in the previous permit for outfalls OO1A and 002A. v. COD — A Federal ELG exists for COD for 100 mg/1, 30 -day average limitation and 200 mg /1 daily maximum. These limitations are the same as those contained in previous permits except the last issued permit, which eliminated this requirement without specific reasons. These limitations have been included in this permit, for Outfall OO1A and Outfall 002A. vi. Total Zinc - The RP analysis discussed below resulted in no RP for the zinc WQBEL at outfall 002A, however, the Federal ELG limits of 500 /1000 µg/1 for 30 -day average /daily maximum for total zinc, will apply to all outfalls. These limitations are the same as those contained in the previous permit for outfalls OO1A and 002A. vii. - The pH limitation specified in the ELG is not the most stringent and thus is not used as discussed below. b. Regulation 62: Regulations for Effluent Limitations — These Regulations include effluent limitations that apply to all discharges of wastewater to State waters. These regulations are applicable to the discharge from the Cotter Corporation JD -7 and JD -9 Mines' WWTF. i. Oil and Grease — The oil and grease limitations from the Regulations for Effluent Limitations are applied as they are the most stringent limitations. These limitations are the same as those contained in the previous permit and are imposed effective immediately, for Outfalls OO1A, OO1B, 002A, 002B and 002C. ii. Total Suspended Solids — The limitation for TSS in Regulation 62 does not apply as a Federal ELG exists for this parameter. 2. Water Quality Regulations and Guidance Documents a. Water Quality Assessment — The WQA contains the evaluation of pollutants limited by water quality standards. The mass balance equation shown in Section IV of the WQA was used for most pollutants 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 radium 226 +228, and metals is provided in Section VI of the WQA. The potential WQBELs determined as part of these calculations represent the calculated effluent limits that would be protective of water quality. 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. b. Antidegradation — The unnamed tributaries of East Paradox Creek and Bull Canyon to the Dolores River are Use Protected, therefore, antidegradation review is not required, pursuant to Section 31.8 of The Basic Standards and Methodologies for Surface Water.