2002-05-13_PERMIT FILE - C1981018 (2)

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• COLOBADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale - Page 5. Permit No. CO-0038024. VI. TERMS AND CONDITIONS OF PERMTT b) Inatream Waste Concentration (IWC): (Cont.) acute tozicity be detected in any effluent concentration less than or equal to the Inetream Waste Concentration (IWC) or should a species mortality in any dilution of effluent (including 1005 effluent) ezceed SOS, the permittee is required to conduct a series of timely tests to identify and ultimately eliminate or treat the tozicant. The IWC is determined using the following equation: IWC ~ [Facility Flow (FF)/(Stream Low Flow (annual) + FF)) R 1002 Using the facility design flow of 0.29 MGD and the acute stream low flow (lE3) of 0 MCD, the IWC for this outfall is therefore 100X (i.e., no pattern of acute to:icity demonstrated in any effluent concentration less than or equal to 1002). c) Relationship to EPA Requirements: The Regulations for the State Discharge Permit System on biomonitoring call for several approaches on limits which are objectionable to EPA. In an effort to maintain continuity of the permit issuance process, EPA and Colorado have agreed to a temporary accommodation which calls for the imposition of monitoring and a series of triggered . responses for control of WET if detected rather than immediate WET limits for selected Colorado permits. (The biomonitoring language in the permit has been revised to conform to that agreed to by EPA. It does not include any additional requirements for the permittee.) These selected permits are limited to those facilities that have no known tozicity problem or potential for tozicity. A mandatory reopener clause will be placed in this permit which calls for the imposition of limits in three years in those cases where a real or potential WET problem has been established. Occurence of toaicito during the fourth and fifth years calls for the immediate introduction of limits. This approach is in conformance with the objective of the Region VIII NPDES WET Control Program in that, under both approaches, limits will be in effect is three yeazs where there is a tonicity problem. The reference in the reopener clause to federal regulations directs that such limits must conform to applicable federal regulations in effect at that time. d) Chronic Hiomonitoring: The determination as to whether or not an individual facility must conduct chronic WET testing is dependent upon the ratio of the chronic stream low flow (30E3) - 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 I3fe Class 1, or Class 2 with inorganic and metal numeric standards, chronic WET testing • is not required at this time at 024.