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COLORADO DEPARTMENT OFPUBLICHEALTHAND ENVIRONMENT, Water Quality Control Division Rationale-Page 8, Permit No. CO-0031115 equal io 9.1, or the stream is not classified as described above, acute conditions apply. The chranic IWC is determined using the following equation: IWC = (Facility Flow (FF)/(Stream Chronic Low Flow (annual) + FF)J X 100% The flows and corresponding IWCfor the appropriate discharge point are.• ' Chronic Low Flow, Facility Design Flow, a Discharge Point 30E3, (cfs) (cjs) IWC' (~) 011, 077, 019, 010, 021, 013 0 varies 100% The IWCfor this permit is 10D%, which represenu a wastewater concentration of 100% effluent to 0% receiving stream. However, in addition to the IWC value for determining whether chronic or acute WET testing requirements are applicable, the classification of the receiving stream must be considered. According to the Colorado Water OualiN Control Division Biomonitorin2 Guidance Document dated July 1, 1993, where the receiving water is classified aquatic life, class 1 without all of the appropriate aquatic life numeric standards, acute WET testing is required, regardless of dilution. Since the receiving water is classified as Class 1 Aquatic Life use, but does not have all of the appropriate aquatic life numeric standards, the Division has determined that acute WET testing is applicable for this permit (also see following paragraph). Although this segment does have metals standards, all are based on agricultural use. iii. Acute WET Limiu: The Division has found that discharges of mine drainage and spoils spring water from coal mines at similar sites have exhibited eQ7uent toxicity. On this basis, the Division believes there is reasonable potential for the discharge to interfere with attainment of applicable water quality class~cattons or standards and therefore, an acute toxicity limit has been incorporated into the permit. The permittee is required to conduct quarterly monitoring consistent with the frequency specifications in the Colorado Water OualiN Control Division Biomonitorinp Guidance Document. dated July 1, 1993, the resulu of which are to be reported as an LCsP, which is the concentration at which 50% or more of the organisms die. If the LCsa occurs in a concentration of less than or equal to 100% effluent, the permittee is required to comply wish the specifications identified in Pan I.A. of the permit. iv. General Information: The permittee should read the WET testing section of Part I.A. of the permit carefully. The permit outlines the test requirements and the required follow-up actions the permittee must take to resolve a toxicity incident. The permittee should read, along wish the documenu listed in Part I.Af the permit, the Colorado Water OualiN Control Division BiomonitorinQ Guidance Document. dated July 1, 1993. This document outlines the criteria used by the Division in such areas as granting reliefjrom WET testing, modifying test methods and changing test species. The permittee should be aware that some of the conditions outlined above may be subject to change if the facility experiences a change in discharge, as outlined in Part ILA.1. of the permit. Such changes shat] be reported to the Division immediately. v. Outfalls 001 001. 005. 008. 009. OI2. 013. 014. 075. 016. 018. 011 and 024.• These ovrjalls, except ourfal7 001, consist entirely of surface runoff. Outfa11001 may include French drain water. Because these outfalls consist ojsurJace runoff only and discharge during periods of high stream flow, they are not believed to contribute toxicity. On this basis, WET testing is not a requirement for these outfalls. However, the Division reserves the right to reopen the permit to include WET testing, should facility conditions change or ifnew information becomes available. 3. Stormwater Evaluation: Stormwater from active and inactive coal mining sites that has been contaminated by contact with overburden, raw material, intermediate producu, byproducts, finished products or waste producu located at the sire is required to be covered by a Colorado Discharge Permit System (CDPS) permit in order io be discharged fo Waters of the State. This coverage may be obtained under either a CDPS Industrial Wastewater Discharge Permit or a CDPS Stormwater Discharge Permit. The Division understands that a71 discharges ofstormwater pass through outfa]ls covered under permit CO-0032115. Any discharges that consist only ofstormwater that have become contaminated as described above, that do not discharge through the outfalls for permit number CO-0031]15 must be covered by a Stormwater Discharge Permit. Last Revised: 4J2912DD4