2018-04-23_REVISION - M2007031 (4)

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COLORAD .Q j Department of PubliOc 71%' Health b Environment Water Quality Control Division Fact Sheet,Permit No. C00048939 compliance with the limitation and consistent with Division initiatives for mercury, quarterly effluent monitoring for total mercury at low-level detection methods will be required by the permit. Dissolved Metals / Potentially Dissolved For metals with aquatic life-based dissolved standards, effluent limits and monitoring requirements are typically based upon the potentially dissolved method of analysis, as required under Regulation 31, Basic Standards and Methodologies for Surface Water. Thus, effluent limits and/or monitoring requirements for these metals will be prescribed as the "potentially dissolved"form. TR Trivalent Chromium For total recoverable trivalent chromium, the regulations indicate that standard applies to the total of both the trivalent and hexavalent forms. Therefore, monitoring for total recoverable chromium will be required. VIII. DISCUSSION OF STORMWATER-ONLY, NON-NUMERIC EFFLUENT LIMITATIONS, TERMS and CONDITIONS- Outfall 002 This renewal permit contains requirements for stormwater discharges from the facility that are necessary to protect waters of the state. These requirements resulted from a comprehensive review of stormwater provisions for mining and non-mining sectors in existing CDPS permits, and coordination with the Division of Reclamation, Mining and Safety (DRMS). A. Narrative Water Quality Effluent Limitation This permit section contains the narrative effluent limitation that 'discharges authorized under this permit must be controlled as necessary to meet applicable water quality standards.' Consistent with other recently issued stormwater discharge permits, the division used this WQBEL language as it directly relates stormwater discharge quality to water quality standards. As provided in the permit, the division expects that compliance with the other conditions in the permit will control discharges as necessary to meet applicable water quality standards, but requires the permittee to take corrective action if the permittee becomes aware, or the division determines, that the authorized discharge causes or contributes to an exceedance of applicable water quality standards. For such cases, the division also included a provision in the permit that allows it to modify the permit to add site-specific terms and conditions as necessary to control discharges to meet water quality standards. B. Technology-based Effluent Limitations 1. Practice-based Effluent Limitations The effluent limitations contained in this permit are located in a section separate from the Stormwater Management Plan, thereby differentiating effluent limitations from other terms and conditions of the permit. Practice-based effluent limits (PBELs)are technology-based effluent limits, which are required for all CDPS permits. The PBELs correspond to the required levels of technology-based control (BPT, BCT, BAT) for various discharges under the Colorado Water Quality Control Act. The PBELs identified in this permit are applicable to stormwater-only discharges, to address potential impacts to receiving water quality from such discharges. a. Minimize Exposure - the renewal permit defines the term "minimize" to provide the permittee with a clear expectation for the level of performance of control measures implemented to achieve the practice-based effluent limits that require the permittee to"minimize" pollutants. For such practice- based effluent limits, the term minimize means to "reduce and/or eliminate to the extent achievable using control measures (including best management practices)that are technologically and economically practicable in light of best industry practice." Page 10 of 17 � 4'H 4300 Cherry Creek Drive S.,Denver,CO 80246-1530 P 303-692-2000 www.cotorado.gov/cdphe/wqcd * \C C John W.Hickenlooper,Governor I Larry Wolk,MD,MSPH, Executive Director and Chief Medical Officer CO y