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COLORADO <br /> Department of Public <br /> •'ori' Health b Environment Water Quality Control Division Fact Sheet, Permit No. C00048939 <br /> B. Parameter Evaluation <br /> 1. Technology Based Limitations <br /> Settleable Solids - In accordance with Colorado Discharge Permit System Regulations, Regulation 61, <br /> 61.8(2)(a)(v), the division may exercise best professional judgment (BPJ) in establishing effluent limits on a <br /> case by case basis for individual permits. For this permit, the division used BPJ to apply the federal ELG for <br /> settleable solids to discharges from outfall 001. This is a new limit for outfall 001, but a compliance schedule <br /> is not applicable to federal ELGs and therefore, the limit is effective immediately. Consistent with the analysis <br /> conducted in the development document for the federal ELG, the division anticipates that the facility will be <br /> able to meet this limit, which is less stringent than the previous TSS permit limitation. <br /> Oil and Grease -The oil and grease limitations from the Regulations for Effluent Limitations are applied as they <br /> are the most stringent limitations. <br /> 2. Water Quality Standards <br /> QH - This parameter is limited by the water quality standards of 6.5-9.0 s.u., as this range is more stringent <br /> than other applicable standards. <br /> Dissolved Arsenic - There is no data available regarding the presence/absence or quantification of this <br /> parameter in the discharge, so a qualitative RP analysis was conducted. As provided in the development <br /> document for the federal ELG, arsenic is detected in discharges from placer mining operations. The mining <br /> process can cause arsenic from arsenic-containing rocks to become soluble due to oxidation of the ore, which <br /> causes arsenic to appear in the discharge. While it is unlikely that dissolved arsenic concentrations in a placer <br /> mine will approach 340 ug/l (the calculated WQBEL), to verify this assumption, a "report"condition has been <br /> added to the permit to characterize the effluent water quality for this parameter. <br /> Total Arsenic-There is no data available regarding the presence/absence or quantification of this parameter <br /> in the discharge, so a qualitative RP analysis was conducted. As provided in the development document for the <br /> federal ELG, arsenic is detected in discharges from placer mining operations. The mining process can cause <br /> arsenic from arsenic-containing rocks to become soluble due to oxidation of the ore, which causes arsenic to <br /> appear in the discharge. While it is unlikely that dissolved arsenic concentrations in a placer mine will <br /> approach 100 ug/l (the calculated WQBEL), to verify this assumption, a "report" condition has been added to <br /> the permit to characterize the effluent water quality for this parameter. <br /> Potentially Dissolved Cadmium - There is no data available regarding the presence/absence or quantification of <br /> this parameter in the discharge, so a qualitative RP analysis was conducted. Metals may occur naturally in <br /> geologic media, such as rock formations, soils, and transportation through groundwater. Mining operations <br /> expose rock to air and water creating a potential for cadmium to be present in elevated concentrations. <br /> Further, as provided in the development document for the federal ELG, cadmium can be present in the <br /> effluent from some placer mine operations. Therefore, monitoring via a "report" requirement has been added <br /> to the permit to characterize the effluent water quality for this parameter. <br /> Potentially Dissolved Trivalent Chromium - There is no data available regarding the presence/absence or <br /> quantification of this parameter in the discharge, so a qualitative RP analysis was conducted. According to the <br /> Agency for Toxic Substances and Disease Registry, chromium in the trivalent form occurs naturally in the <br /> environment. Mining operations expose rock to air and water creating a potential for chromium to be present <br /> in elevated concentrations. Further, as provided in the development document for the federal ELG, chromium <br /> can be present in the effluent from some placer mine operations. Therefore, monitoring via a "report" <br /> requirement has been added to the permit to characterize the effluent water quality for this parameter. <br /> Potentially Dissolved Hexavalent Chromium - There is no data available regarding the presence/absence or <br /> quantification of this parameter in the discharge, so a qualitative RP analysis was conducted. According to the <br /> Agency for Toxic Substances and Disease Registry, hexavalent chromium is produced by industrial processes. <br /> Activities at this site would not produce hexavalent chromium. Therefore a qualitative determination of no RP <br /> has been made for this parameter, and limits and monitoring are not required at this time. <br /> Page 7 of 17 <br /> 4300 Cherry Creek Drive S.,Denver,CO 80246-1530 P 303-692-2000 www.colorado.gov/cdphe/wgcd 4 r;7 <br /> John W. Hickenlooper,Governor I Larry Wolk,MD,MSPH,Executive Director and Chief Medical Officer CO <br /> stez,et.:T. :PP:et peuuEas <br />