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COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale - Page 27. Permit No. CO-0027154 VII. PUBLIC NOTICE COMMENTS (continued) EPA Comments -- EPA's comments focused on three areas: metals limitations for stormwater runoff outfalls, the TVS hardness value and chronic WET requirements and limits. Metals Limitations for Stormwater Runoff Outfalls: EPA voiced a concern that BAT limitations for iron wer¢ not restrictive enough for these outfalls and that copper and silver limitations may be needed. They state that their concern is that if discharge occurs 36 to 72 hours after a precipitation event,. the existing limitations may not be protective enough. We refer to Part I.A.2. of the permit, Burden of Proof Recuirements, in which it is stated that the alternate limitations apply only when discharges occur within 48 hours after the end of an event. This correlates with CDMG requirements that permittees dewater ponds within 48 hours to provide adequate containment for subsequent events. The Division believes that discharges from stormwater outfalls normally occur during times of high stream flow, will not adversely impact receiving waters and therefore, typically do not require metals limitations. This has been the position for drafting all coal mining surface runoff permits, including the Colorado General Permit for Coal Mining Facilities (Surface Runoff Only). This facility has even less likelihood than most of causing an impact due to the high hardness previously discussed. ~'VS Hardness: This topic was discussed in the previous section concerning permittee comments. Chronic WET Recuirements: The rationale boiler plate language that states that chronic WET testing may be extended after three years has been added to the permit section that specifies chronic WET requirements. Other Chances -- Stormwater language has been developed by the Division's stormwater group. This language will be incorporated into this permit. The language is similar to that in the general permit for coal mining facilities, but has been modified for this specific site. Additionally, in section IV., a paragraph of discussion aimed at clarifying the permit coverage for various sites in the area operated by CYVCC has been added. Jon C. Kubic February 5, 1993 VIII. REFERENCES A. Colorado Dept. of Health, Water Quality Control Commission. Basic Standa rds and Methodoloeies for Surface Water (3.1.0). Denver: CDH, as revised 8/7/89. B. Colorado Dept. of Health, Water Quality Control Commission. Regulations for E ffluent Limitations (10.1.0). Denver: CDH,. as revised 1/6/86. C. Colorado Dept, of Health, Water Quality Control Commission. $eeulations for t he State Discharge Permit Stem (6.1.0). Denver: CDH, as revised 8/31/89. D. Colorado Dept. of Health, Water Quality Control Commission. Regulati ons for Implementation of the Colorado River Salinity Standards Through the Colorado Di scharge Permit Proeram, (3.10.0). Denver: 1978. E. U.S. Government, Office of the Federal Register, National Archives and Records Administration. Code of Federal Re¢ulations (Part 434). Washington: 1990. F. Charles T. Haan. Statistical methods in hydrology. Ames, IA: 1977. G. William Mendenhall. Introduction to probability and statistics. Nozth Scituate, MA: 1975.