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COLORADO DEPARTMENT OF HEATH, Winer Qursliq; Division Rntimrnle - Pnge 5, Permit No. CO-0043648 measurement flume. Storm water flows that n:ay enter the sedimentation pond and flow to OOIA include local runofffrom the revegetated toe been of the VLF, rwrofffrom re-located Highway 67, and rwrofffrom the stornr water control measures to the south rind east of the VLF. Outfa11005B-This ou[fall will be used for arryprecipitation-caused discharges from the VLF which mny occur either as a result of the annual precipitation frilling on the VLF exceeding the annual evaporation or as a result ofa singleprecipitation event causing the 10 year, 24-hour storm intensity to be exceeded. No specific overflow outfnll has been cmtstructed. In the unlikely event there is a need to direct flows from the VLF into Arequa Gulch because of extreme precipitation conditions, some form offluid management strategy will have to be implemented. The Division will not include Outfall OOSA in this renewal permit based on the unknown nature of the quality of the discharge once the VLF liners are pierced; revised water quality standards for,4requa Gulclt and Cripple Creek that tnay be adopted in the future by the Commission; and other regulatory requirements that may be adopted in the future. III. WATER QUALITYASSESSMENT The Water Quality Control Division's Assessment Unit has performed an assessment ofthe stream standards, low flow data, and ambient strewn data and determined the assimilative capacities ofArequa Gulch and Cripple Creekfor the pollutants ofconcern. This information is in Appendix A to this rationale. The Division's Permits Z1nit has reviewed the assimilative capacities and determined the appropriate venter quality bused permit limitations, which can be found in Tables VI- I mid VI-2 of the rationale. IV. FACILITYDESCRIPTION A. Industry Description 1. Type ofhrdustry - T17is facility is an open pit-cyanide heap leach gold mining operation. The project consists of the Cresson Mine Wrens, the VLF, the Adsorption, Desorption, and Recovery Facility, the crusher, OSAs, artd arrcillnry areas. Reclamation of the mine site includes backfilling of some mined areas, detoxification of the ore in the VLF, breaching the VLF liner, contouring, and revegetation of disturbed areas. 2. Potential Sources of Pollutants -The potential sources ofthe pollutants that mny be discharged nt Outfn11001A are cyanide cmnpounds and n:e[als in the water that flows to the sedimentation pond. 3. Chemicals Used -Other than the potential pollutants discussed above, no other chemicals which mny be stored at the »:ine site are likely to be present in quantities or used in a manner which would pose a risk of being discharged ro waters of the State. This is described further in CC&V's Emergency Response Plan. B. Wastewater Treahnent Descripton The trenhr:entfaciliryforOutfa1100]Aconsistsofasedimentationpond. Currently,twopondsforapassivelimestonesystent are operated as an "experimental" water quality tnnnagetnent practice. These are located itntnediately upsrren»t of the sedimentation por:d (See Figure 4). For Outfa11005B, if n discharge were to occur, the most likely approach would involve the controlled release ofjlowsfrotn the External Storage Pond("ESP')toAreguaGu[ch. The ESPhasacapaciryof20mi1liongallansandnsystemforreducing weak acid dissociable cyanide ("CtVwad) concentrations. Transfer of venter from the ESP to Arequa Gulch could be accomplished using n pumpback pipeline. The sump for the pumpback would be used to direct flows from the pipeline into Arequn Gulch at Outfa11005B, as shown in Figures 4, S, and 6 ofthe Penntt. Only minor changes (e.g., removal ofcheck valves, disconnection ofputnps) to the putnpback system would be required to accotnmodnte flows frotn the ESP. An alternative would involve laying a temporarypipeline from the VLF over the Phase II toe berm to Arequa Gulch. Due to elevation change from the crest to the base of the toe bean, siphonir:g and gravity flow would be possible. Existing tiptop, geotextile, or liner material already in the area would be used alone or in combination to dissipate energy nt the outlet of the pipe. Monitoring systems within the VLF would allow ample time to implement either of these alternatives. Flows under either alternative would enter one of the BMPs in the uppermost reaches ofArequa Gulch before passing through Outfn11005B, which is below Outfall OOIA.