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PARTI Page No. 6 Pernut No.: CO-0047562 g. Toxicity Reopener This permit may be reopened and modified (following proper administrative procedures) to include new compliance dates, additional or modified numerical permit limitations, a new or different compliance schedule, a change in the whole effluent toxicity testing protocol, or any other conditions related to the control of toxicants if one or more of the following events occur: i. Toxicity has been demonstrated in the effluent and the pernu# does not contain a toxicity limitation. ii. The PTUTIE results indicate that the identified toxicant(s) represent pollutant(s) that maybe controlled with specific numerical limits and the permi# issuing authority agrees that the control of such toxicants through numerical limits is the most appropriate course of action. iii. The PTUTIE reveals other unique conditions or characteristics, which, iu the opinion of the permit issuing authority, justify the incorporation of unanticipated special conditions in the permit. 4. Storm Exemption - Tacilities Permitted to Discharge If, as a result of precipitation or snowmelt, a source with an allowable discharge under 40 CFR part 440 has an overflow or excess discharge of effluent which does not meet the limitations of 40 CFR part 440, the source may qualify for au exemption from such limitations with respect to such discharge if the following conditions are met: a) The facility is designed, conshucted and maintauted to contain the maximum volume of wastewater which would be generated by the facility during a 24-hour period without an increase in volume from precipitation and the maximum volume of wastewater resulting from a 10-year, 24-hour precipitation event or treat the maximum flow associated with these volumes. In computing the maximum volume of ~vastezvater which would result from a 10-year, 24-hour precipitation event, the facility must include the volume which would result from all areas contributing runoff to the individual treatment facility, i.e. ,all runoff that is not diverted from the active mining area and runoff which is not diverted from the mill area. b) The facility takes all reasonable steps to maintain treatment of the wastewater and minimize the amount of overflow. c) The facility complies with the notification requirements of 40 CFR 122.60 (g) and (h). The storm exemption is designed to provide an affirmative defense to an enforcement action. Therefore, the operator has the burden of demonstratiug to the appropriate authority that the above conditions have been met. In addition, if a discharge occurs as a result of the 10-year, 24-hour storm volume being exceeded and the permittee wishes to claim an exemption from technology based effluent limitations, the permittee shall submit, within 5 days of the said discharge, documentation that the facility was maintained to contain or treat the previously specified volumes. The pernuttee must also submit documentation of the storm event, including the precipitation recorded at the closest official precipitation gauge station (or the pemuttee's own gauge), the volume of runoff produced and the steps taken to maintain treatment and T ,n•niin;~e the amount of overflow. For claiming a storm water exemption, the permittee must also adequately demonstrate that all reasonable management, containment, and treatment options have been optimally utilized. The storm event exemptions are only applicable for the following parameters at this facility, which are based upon Federal BAT/BPT limitations: Total Suspended Solids Chemical Oxygen Demand Total Recoverable Zinc Dissolved Radium 226 30-day average limitation for Total Radium 226. All data/documentation required by the section which can not be reported on applicable discharge monitoring report forms (DMRs) shall be reported in a letter as an attachment to the DMR. Submittal of documentation of containment, maintenance and precipitation records above does not exempt the permittee from the notification requirements of Part II.A.4. of this pemut.