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COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division <br />Rationale - Page 16. Permit No. CO-0027154 <br />VI. TERMS AND CONDITIONS OF PERMIT <br />A. Effluent Limitations (continued) <br />As mentioned at the start of this discussion, the total recoverable (TR) <br />manganese limitation for outfall 019 is applicable to the flow-weighted <br />mean effluent concentration of outfalls 001, 005 and 007. This mean is <br />calculated using the following formula: <br />M019 - (0001)(M001) + (0005)(M005) + (0007)(M007) <br />Q019 <br />Where: M019 - Calculated flow weighted mean concentration for outfall 019; <br />0001 - Maximum daily flow during period for outfall 001; <br />M001 - Effluent concentration for outfall 001; <br />Q005 - Maximum daily flow during period for outfall 005; <br />M005 - Effluent concentration for outfall 005; <br />0007 - Maximum daily flow during period for outfall 007; <br />M007 - Effluent concentration for outfall 007; <br />Q019 - Combined maximum daily flow for outfalls 001, 005 and 007. <br />The TR manganese monitoring frequency is weekly. The permittee should <br />collect TR manganese samples as required from outfalls 001, 005 and 007, <br />then determine the maximum daily flow during the previous week. These <br />data shall be used in the above formula to determine the flow-weighted <br />mean for the week. The 30-day average concentration shall be determined <br />using a normal arithmetic mean of all weekly results per calendar month. <br />Because actual silver effluent concentrations are so much lower than the <br />potential limitations for outfalls 001 and 007 (see table in section VII), <br />no limitations are being imposed for these two outfalls in this permit. <br />However, routine monitoring will be required to assess future levels. <br />Effluent levels for outfall 005 have exceeded the chronic limitation of <br />0.003 mg/1. For this reason, silver limtiations are being imposed for <br />outfall 005. <br />Zinc was previously limited at outfalls 005 and 007; however, the <br />receiving water no longer has a zinc standard, so a limitation is <br />unnecessary. Further, if limitations were specified to protect the next <br />downstream segment, the limitations would be much higher than past actual <br />and future expected effluent concentrations. Thus, zinc limitations are <br />not included in this renewal permit. <br />3. Regulations for Effluent Limitations: The Regulations for Effluent <br />Limitations (10.1.0), apply to the conventional pollutants. For this <br />facility, the limitation for Oil and Grease is based on this regulation. <br />4. Discussion of Limitations - Salinity: The Regulations for Implementation <br />of the Colorado River Salinity Standards Through the Colorado Discharge <br />Permit Program, (3.10.0) address the discharge of total dissolved solids <br />(TDS) to the Colorado River Basin. It 1s a requirement of this regulation <br />that all discharges into the Colorado River basin be monitored for TDS (or <br />electrical conductivity where a correlation has been approved by the <br />Division) on a routine basis. Also, as part of this regulation, a report <br />is necessary when total loadings from any facility exceed one ton/day or <br />350 tons per year. Please aee section VI.C.2. for further information. <br />