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COLORADO DEPARTMENT OF HEALTH, Water Quality Cuntro[ Division Rationale -Page 22, Perntit No. CO-0043648 However, in addition to the /WC value for determining whether chronic or acute WET testing requirements are applicable, the classification of [he receiving stream must be considered. According to the Colorado Water Oualitv Control Division Biomonitorine Guidance Document, dated July 1, 1993, chronic WET resting is required for facilities where the receiving stream has a Class 1 Aquatic Life use or Class 2 Aquatic Life use with all of the appropriate aquatic life numeric standards; otherwise, acute WET testing is required. Since this receiving water is clashed as Class /Aquatic Life use, the Division has determined that chronic WET testing is applicable for this permit (see following paragraph). cJ Chronic WET Limitations: /j airy discharge from point 007A occurs, it will likely contain cyanide. Pursuant to section 6.9.2. (5J of the Regulations for State Dischnree Permit System (5 CCR 1002-21, the Division believes [here is reasonable potential for the discharge to interfere with attainment of applicable water quality classifications or standards. Because of this condition, the chronic limit has been incorporated into the permit and becomes effective immediately. The permittee it required to conduct routine monitoring. The results of the testing are to be reported on Division approved forms. The permiaee will be required to conduct a statistical derivation on the data, looking for any statistically sign cant difference in toxicity between the control and the effluent concentrations. This set cf calculations will look at the full range of tonicity (lethality, growth and reproduction). !f a level of chronic tonicity occurs, such that there is a statistically sign cant difference in the lethality (at the 95°~ confidence level) between the control and any effluent concentration less than or equal to the lnstream Waste Concentration (/WCJ, the permittee will be required to follow the automatic compliance schedule ident~ed in Part /. B. of the permit, if the observed toziciry is due to organism lethality. Only ezceedance of the limitation specked in Part 1. A.2 will trigger the requirement for conducting the automatic compliance schedule ident~ed in Part I.B. ojthe permit. ljthe toziciry is due to differences in the growth of the fathead minnows or the reproduction of the Ceriodaphnia, no immediate action on the part of the permittee will be required. However, this incident, along with other WET data, will be evaluated 6y the Division and may form the basis for reopening the permit and including additional WET limits or other requirements. dJ General /nformntion: The permittee should read the WET testing sections ojPart 1. A. and I.B. of the permit carefidly. 77te permit outlines the test requirements and the required follow-up actions the permitree must take to resolve a toziciry incident.. The perminee should rend, along with the documents listed in Pnrt /. B of the permit, the Colorado Water Quality Control Division Biomonirorine Guidance Document, dated July !, 1993. 7hir document outlines the criteria used by the Division in such areas as grunting relief from 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 lI.A.1 of the permit. Such changes shall be reported to the Division inmrerlinteh~. 7. Stortnwnter Stormwater permitting requirements, for discharges consisting of storrnwnter only, have been and will contimte to be implemented through a separate individual ,eronnwnter permit. 8. Best Mnnneement Practices The permirtee .shall take all reasonable precautions to prevent any point source discharge of process water or cond~ined procccs water/stormwater that may reach surface waters of the State, which may be associated with the Cresson Mine Project. TT~e permittne shall insure that the excavation, movement and placement of any mine tailings or other materiair that ought be contaminated with cyanide or other environmental pollutants is carried out in a manner x•hich will avoid any discharge of pollutants to surfirce waters of the State.