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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division Rationale -Page 9, Permit No. CO-0032115 Table VI-0 - Effluent Limitations for Dutfalls 003, 006 and 014 Discharge Ismitations Maiimum Conctalratians Parameter 30.Dav Ave. Daily Mar. Rationale Flow, MGD Report Report Design Capacity Settleable Solids, ml/P N/A 0.5 Federal Effluent Guidelines Oil and Grease, mg/t N/A 10 State EfJluem Regulations DH, s. u. (minimum-maximum! N/A 6.5-9.0 Water Quality Standards Total Suspended Solids, Total Jron and Settleable Solids limitations are subject ro burden of proof requirements -see section VI.A.2.bl• 2. Discussion of Effluent [.imitations a) Reeulations for EiTluem Limitations: The Regulations for Effruem Limitations (10.1.0), apply to the conventional pollutants. For this facility the limitation jor Oil and Grease is based on this regulation. 6) Water Quality Standards: The only parameter in this permit for which water quality standards (WQS) apply is pH. The water quality standards of 6.5 to 9.0 s.u. are more stringent than the state eJ)Tuent standards of 6.0 to 9.0 s. u., thus the WQS based limita[ions, equal [o the standards, shall apply. c) Aop[icable Federal Elfluem Guidelines and Standards: The federal guidelines which apply to this type ojfaciliry are found under 40 CFR 434, titled Coal Mining Point Source ERTuent Guidelines. The limitations which apply are shown in the following !able. Table VI-5 - Federal Standards (40 CFR 434) Parameter : limitations '3o Dav Avz . Daily: Maz. .:...:.... .:.::::.:.. pH, s. u. (minimum -maximum) --6.0 - 9.0-- Tatal Suspended Solids, mg/P• 35 70 Total Iron, mg/P• BAT++ 3.5 7.0 NSPS++• 3.0 6.0 Settleable Solids, mP/P+ N/A 0.5 7lrerc paramrterr rubjca to Burden of Proof RrquirrmrNt, rce ntv recrion •• But Awilab(c 7echnotogy - appuer !o (hare pondr already contrrurrrd ••• New Source Performance Standardr - apph'rr to (hart ponds conttrutrrd offer S/4/84 Alternate Limitation Burden o/ Proof Requirements: /n conformance with 40 CFR 434.63, the permittee has the burden of proof when requesting relief from total suspended solids (13'S), total iron and/or settleable solids limitations, as appropriate. The intent of this regulation is ro afford relief only when needed due ro a volume of water generated by a specific storm event, it is not imended to be automatically applied to al! discharges caused by precipitation, nor to be used to discharge iblumes in excess of that generated by the storm event. On this basis, relief shall be grained only when necessary and shall not be granted when the permirree has con[roI over the discharge, enabling them to meet the primary limitations. The permittee should endeavor to meet the primary limitations whenever possible. Because monua! dewatering can be accomplished os time and conditions permit, all monual dewarering shall be required (o meet the primory limitations. Pit dtwatering is not eligible for alternate 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 1n sudr a manner that primary limitations could have been met. For rainfall, to waive TSS and total iron limitations, it is necessary to prove that discharge directly resulted from a specific even[ and occurred through automatic dewattring devices within 48 hours after measurable precipitation has stopped. In addition, to waive settleable solids limitations, it is necessary to prove that an event greater than the magnitude ojthe 10-year, 24-hour event occurred.