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Mountain Coal and Bear Coal Water Quality Assessment CO-0038776 and CO-0044377 <br />• Dissolved Zinc acute = 379 <br />• Dissolved Zinc chronic = 382 ug/1. <br />Ammonia: Ammonia is present in the aqueous environment in both ionized and un-ionized forms. <br />It is the un-ionized form which is toxic and which is addressed by water quality standards. The <br />proportion of total ammonia present in un-ionized form in the receiving stream is a function of the <br />combined upstream and effluent ammonia concentrations, and the pH and temperature of the effluent <br />and receiving stream, combined. <br />The Colorado Ammonia Model (CAM) is a softwaze program designed to project the downstream <br />effects of ammonia and the ammonia assimilative capacities available to each dischazger based on <br />upstream water quality and effluent discharges. To develop data for the CAM, an in-stream water <br />quality study must be conducted of the upstream receiving water conditions, particularly the pH and <br />corresponding temperature, over a period of at least one yeaz. <br />There were no data available for the North Fork of the Gunnison River near the Mountain Coal <br />WWTFs that could be used as adequate input data for the CAM. Therefore, the WQCD standard <br />procedure is to rely on default values for the allowable chronic concentrations of in-stream total <br />ammonia, which are provided in the Colorado Total Maximum DailyLoad and WasteloadAllocation <br />Guidance and the CDPS Summary of Rationale General Permit for Domestic Wastewater Treatment <br />Facilities that Discharge to Receiving Waters with a Chronic Low Flow: Design Flow Ratio of <br />'100:1 or Greater. Note that acute values are not provided in these sources and thus aze not evaluated <br />as part of this assessment, <br />Using the mass-balance equation provided in the beginning of Section IV, the acute and chronic low <br />flows set out in Section III, the ammonia existing quality concentration shown in Section II, and the <br />in-stream standards found in the Colorado Total Maximum Daily Load and Wasteload Allocation <br />Guidance and the CDPS Summary of Rationale General Permitforpomestic Wastewater Treatment <br />Facilities that Discharge to Receiving Waters with a Chronic Low Flow: Design Flow Ratio of <br />100:1 or Greater for M3, assimilative capacities for chronic total ammonia were calculated. The <br />effluent flow, Q2, reflects the design flow from Outfa11004 and Internal Outfa11007 in the respective <br />calculations. The data used and the resulting calculations of the allowable discharge concentration, <br />Mz, aze contained in Tables A-11 and A-12. <br />Appendix A Page 18 of 20 Last Revised 3/9/2004 <br />