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COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale -Page 17, Permit No. CO-0034142 In the event the background concentration was reported as total recoverable and the most stringent criteria was based on the potentially dissolved method of analysis, background concentrations were assumed to be zero. Similarly, if the background rnnceMation xns reported as potentiah~ dissolved and the most stringem criteria was based on a total recoverable method of analysis, background concentrations were also assumed to be zero. Table Vl~ dots the maxvnum effluent concentration of pollutants that could be discharged from Outfalir 003, 022, and 024. For Outfalis 003, 022, and 024, metair effluent limitations west calculated using a rnaxinut»t flow of 6.28 efs (4.06 MGD) for off three outfalLs, the metals standards Iisted in section III.A.3. of this rationale, the annual chronic and acute low flows for the Williams Fork River Gsted in section JII.B.2. and upstream concentrations provided by the permiute in Table 111-3. Based on a comparison of the calculated e,Qluem limitations in the Table Vi'~ and the reported concentrations in each of the outfalis that was submitted by the permittee iri the application jot renewal, no additional warn quality-based effluent limitations, with the exception of iron and zinc which had been lirtited in the previous permit, were incorporated in the proposed permit. .9ppendix A to this rationale contains the data submitted by the permittee. The previous permit had total recoverable iron and total recoverable zinc limitatrons at Outfalis 003, 022, and 024. Since the calculated effluent limitations far potentially dissolved iron were less than zero, the receiving stream is not attaining the water quality criteria for potentially dissolved iron. Therefore, potentially dissolved iron limitations will be set at the water quality criteria (0.3 mg/IJ. Similarly, the calculated cffiueru limitation for zinc was based upon the potemially dissolved ruthod of analysis since the most stringent for zinc is based upon the potentially dissolved method of analysis. Water quality-based e_Qluem lrmitations were calculated assuming a maximum flow from the No. 6 Mine of 394 gpm Using this flow and the standard, based upon a potentially dissolved method of analysis, the monthly average ejjlueru conceruration is 0.9 mgp and maximwn allowable efJluem concentration is 0.92 mg/l. Since monitoring data show that Cyprus has not had d~ulty complying with the previous fora! recoverable zinc permit lirtit, this limit is retained in the proposed permit to insure that there is no backsliding ojegluem quality. In the evem the facility has problems complying with the total recoverable zinc limit due to an increase in flow from the No.6 Mine, the permit may be reopened to evaluate a less stringent zinc limit. d. Antidegrndation -Since the Williams Fork River it classified as Use Protectrd, an antidegradation review is not required pursuant to section 3.1.8(I)(bJ of The Basic Standards and rNethodologies for Surface Water. Since this permiaing action will not resuU in an increase in arty efJluem concentration limit or effluent flow limit for the outfalis that discharge to the Yampa River, the Yampa River it not a "reviewable water", pursuant to section 3.1.8(3J(aJ of The Basic Standards and Methodologies ibr Surface Water, bared upon a finding of no increased water quality impact. e. Salinity Regulations: In compliance with the "Regulations for lmplememation of the Colorado Salinity Standards Through the CDPS Permit Program', the perminee shall monitor for total dissolved solids on a quaner[y basis. Samples shall be taken at the effluem discharge point(s). .Salinity requirements are included in Part I, Section B.3 of the permit.