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COIARADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale - Page 9. Permit No. CO-0036595. 1 VI. TERMS AND CONDITIONS OF PERMIT b) Instream Waste Concentration (IWC): (Cont.) observed, for Ceriodaphnia sp. water flea and fathead minnows, between the control and any effluent concentration. Should acute toxicity be detected in any effluent concentration less than or equal to the Instream Waste Concentration (IWC) or should a species mortality in any dilution of effluent (including 100X effluent) exceed 50X, the permittee is required to conduce- a series of timely tests to identify and ultimately eliminate or treat the toxicant. The IWC is determined using the following equation: IWC = [Facility Flow (FF)/(Stream Low Flow (annual) + FF)] R 100X Since the acute stream low flow (1E3) for the receiving waters is 0 MGD, the IWC for the permittee is therefore 100X, which represents a wastewater concentration of 100X effluent to OX dilution water. c) Chronic Biomonitoring: The determination as to whether or not an individual facility must conduct chronic SdET testing is dependent upon the ratio of the chronic stream low flow (30 E3) to the design flow of the wastewater treatment plant, as well as the receiving waters classifications. Since the receiving waters are not classified as Aquatic Life Class 1, or Class 2 with inorganic and metal numeric standards, chronic WET testing is oot required at this time. d) Waiver of Requirements: Industrial facilities having simple effluents of consistent quality, ~.+hich can be totally characterized chemically, may request a full or partial waiver of WET testing for the remainder of [he life of the permit, subject to Division approval, if the first four quarters of testing show no pattern of toxicity. The permittee should read the WET testing sections of Part I.A. and I.B. of the permit carefully, and should note that the test methods for the toxicity tests are described in detail in thN Division guidance document, Guidelines for Conducting Sdhole Elfluent Toxicity Tests. This document should be read thoroughly prior to commencing the required WET testing, to ensure that the permittee is aware of the various test conditions that could affect the test results (e.g., sample holding time). 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 II.A.1 of the permit. Such changes shall be reported to the Division immediately. ~ ...