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COLOR9D0 DEY:1 RTMENT OF PUBLIC HEALTH AND ENVIRON,LIENT, W'uter Qtrahry Control Drvrsiorr Rationale - Amenrbnent No 1. Page 7, Pennu Nn. CO-0000221 4) Generaf hr(onnntion. 7):e pennittee should read dre acute WET resting section in Part I A 4. of the • pernnt for infonnatinn upplicahle to drew new discharges Pte permit outlines the te~'1 regttirm:ents and the required follow-up ncuo+rs the pennittee nurst take to resolve a mxiciry incrdent. The permittee should read, along with the documents listed in Part 1. ,a. 4. a. oJthe pernnt, the Co(orndo Wnter~uality Control Division Bianorrirorittg Guidance Document dated July I, /993. This donurtent mulines the criteria used by the Division in such areas as granting relief front WET testing, modifying test medrods and changing test species. The pennittee should be mvnre drat some of the conditions mulined above may be subject to change if the facility experiences a change in discharge, as outlined in Part 1/.,1.2 of the permit. Such changes shall 6e reported to the Division immediately. 5) Ecem tiori jot Surface Rirnr~ Only - Out/nll 015: The discharges from outjall 0/5 corrtmn surface runoff solely nnrl do not cornam toxic pollutants in tonic mnomus. On this basis, WET testing i.r oat a requirement jot this outjall. However, the Division reserves the right to reopen the pernnt to include WET testing, should facility conditions change or iJnew utfornmtiort becomes available. 6) Species Chmtge jot Outjall 005: TFte perntittee requested that, for outjall 005, fire test species be changed jrorrt Ceriodaphnta sp. to Daphnia magna. They submitted supporting laboratory data demonstrating that high salinity caused test jaiheres with Ceriodapthnia, while Daphnia rnngnn pressed in concurrent tests on nvo instances in July /993. TStis change is approved. Pan /.A.4.a. of the permit is amended to reflect this change. B. Monitoring Effluent Monitoring: EfJluenr monitoring for the new outfnlls will 6e required as shown in Tables VI-4 and V!- 5. Refer to the permit for locations of monitoring points. • Nloniroring_Frequencv Reduction: The pennittee requested that the monitoring frequency jot all ou[falls excep( 003 be reduced to monthly jot the three parameters for which weekly monitoring is rzow required (p H, oil & grease and Jlow). They asked that the weekly frequency remain far outjall 003 because it receives flow from the shop area artd r/te tnrck wash and the quality may be more variable. Tate other ou[falls primarily receive surface runoff from disturbed and undisturbed areas. The pennittee cites problems accessing remote areas where many of these otttfnlls are located (even in good weather 6ecatae there are no roads), the lack of noncompliance with these field parameters, and the cost of sampling and analysis as the primary reasons for this request. The pernri[tee provided data ort complrance for existing ottrfalls from 1930 through 1998. Outfalls 002, 005, 008, 009, 0/0 and 011 Itad no pH eccursiorts during this period. Ottrfall 004 had sic excursions out of 727 measurements. The excursions occurred between /984 and 1987 and were attributed to algae. Outjall 006 /tad 8 escursions, all occurring irr 1990 and 1991. These excursions were also attributed to algae. None of the exceedences were attributed to the sources directly. Only outjall 003, which receives flow frwn the truck wash system, ltas experienced any oil and grease excursions. T]iis were prior to /991. lnsrallation of oil booms prevent! future occurrences. None of the oatfalls !rave or /tad flow limitations. The Division is applying this request to the currently authorized o«tfa/ls. The pennittee will install rerrtate monitoring equipment for fio+v and pH at dre new o«tfalls 012 through 0I7. This wit! enable them to fidfill the weekly monitoring requirement. However, it still would be difficult for there to access these sites on a weekly basis to make visual oil and grease observations. So, they will mstalt and maintain oit booms at these ourfalls. On this basis, the oil and grease monitoring frequency will be drnnged to mauhly. The flow to these ponds rs panmrily surface nmoff from disnvbed and undisturbed areas. The Ca(orado Division ojhlinernls and Geology (CDh/C) spennhst assigned ro Ihts mine complec has utdicated that there • simufd be no flow that would cause mi upset resulting m unusual effluent qunhry. The CDMG has no objectiar m a monaonng frequenn~ reduction.