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COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale -Page 13, Penrti[ No. CO-0043648 T1te facility is designed, constructed and maintained to contain tJte maximum vo[unte of wastewater stored and corttairted by rite jaciliry during normal operating conditions wirltout an increase in volume from precipitation and the maximum volume of wastewater resulting from a 10-year, 24-hoar precipitation event. In comptuing dte maximum volume aJ wastewater whicit would result from a 10-year, 24-/tour precipitation evert[, rite facility must include the volume which would result from al[ areas contributing runoff to the Valley Leach Facility (i.e., all runoff not diverted from the active raining area). For the purposes ojthis permit, the 10-year 24-hour rairtjall depth has been determined to be 2.4 incites. ii) The permittee takes all reasonable steps to minimize the discharge. iii) Aft notification requirements of rite permit are complied with, including those listed below. The permittee has submitted injorntation, bout in comments to the Water Quality Control Division and to rite State Division of Minerals and Ceo[ogy, indicating tl:a! rite jaciliry is designed, constructed and tvi[l be maintained to contain [he water volumes described above. However, verbal notification shall be given to the Division within 24 hours of rite occurrence of any discharge from the Valley Leach Facility that may qualify for the exemption. Then, a report mast 6e submitted wit/tin 5 days of the said discharge, documenting that the jaciliry was maintained to contain rite previously specified volumes. The permittee must also submit documentation of the storm event, including rite precipitation gouge station (or the permittee's awn gauge), the volume of runoff produced and rite steps taken to maintain treatment and minimize the amount of overflow. All data/documentation required by this section w/rich can riot be reported on applicable discharge monitoring report forms (DMRs) shat! 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 any other notification requirements ojthis permit. d. Storm Exemption From Federal E(fluertt Limitations for Best Professional Judgement) and Water Quality Standard Based Limits -Discharge Points 002A. 003A and 004A If, as a result of precipitation or snowme[t, discharges from any of the above points violate limitations based on federal ELG's, Best Professional Judgement, or water quality standard based limits, ti:e discharge Wray qualify for an exemption from such limitations if t/te following conditions are met: 1) The foci/iry is designed, constructed and maintained to contain dte rnazimunt 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 n 10-year, 24-!tour precipitation event or treat the maximum flow associated with these volumes. In computing the maximum volume of wastewater whicit would result from a 10-year, 24-hour precipitation event, the jaciliry must include the volume which would result front all areas contributing runoff to the individual treatment facility, i. e., al[ runoff that is nor diverted from the active mining area and runoff which is not diverted from the mill area. For the purposes of this permit, the IO-year 24-hour rainfall depth has been determined to be 2.4 inches. ii) Tite permittee takes a!1 reasonable steps to maintain treatment ojthe wastewater and minimize the amount of overflow. iii) Al[ notification requirements of dte permit are complied with, including those listed below. If Ute pernittee intends to use the 10-year, 24-hour storm exemption, a report must be submitted within 90 days after the effective date of tftis permit, documenting tiro[ rite facility is designed, constructed and will be maintained to contain the water volumes described above.