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COLORADO DEPARTMEM OF PUBLIC NE1L7Fl AND ENVIRONMEM. Water Qaa[ity Control Division <br />Amendment No.3 - Rationale. Page 2. Permit No. CO-0038T76 <br />!/I. PURPOSE OF AMENDMEM <br />D+is arrtetdmenr addresses a concern from the permittee in a least dated 3larch 28, 1997. 7S+ey indicarrd the need jar the <br />•, otujaU 013 gjluent Jlow to be increased to 2,000 gpm. During recent mining operations, a geographical fault war <br />encountered that brought a very large wLrtne of water into the mine. the mine workings were flooded for a period ojrime. <br />the permirtee pumped out shit water ro wriout point/ on the site jot ttoroge and ultimate discrarge including an <br />utderground vault treated by past mining and cutting reaGng pads. Becoate of rhir large new water soura, the permirtee <br />has increased water pumping txipabiliry ro 2.000 gpm to accommodate the current 1k`v's and any future flows as well as allow <br />them to discharge the acrumularrd water, l)re permit has not beat previoresty ev+alrtattd for this volume ojwa~er. 7lis <br />action incorporates this evaluation and turrurwrizts the Division's conehcrians. <br />/V. EVALUATION OF IMPACT ON PERMIT CONDI170NS BECAUSE OF HIGHER FLOW <br />A. Effluent Limita6ans and Monitoring Regrdrtmerus <br />Ourfall 0I3 dvcharges to Lone Pine Gulch, a tributary w rbe North Fork of rlu Gunnison River. I7u Doty impact <br />needing consideration ar this time is whetho the inoeared flow changes the Gmirations jar iron. <br />Lone Pine Gulch bas no meralr aandmds and the chronic tow flow for Lone Pine GulrJty zero. On this basis, the <br />evaluation must consider the pouibk impact an the North Fork ojthe Gunnison River. The North Fork has a chronic <br />water quality standard for total recovrrobk iron of 1.0 mg/l atd the chronic tow flowrs 4! cfs. To daermine whether <br />water quality bared limitations arc neoeuary for iron, dre mast balance formula dettribed in derail in region VI.A.2 of <br />the renewal rotlonale Barad February l6, 1995 it ute+i A brief dertription of this protest follows. <br />The mass balance equattonv: <br />Ms . MfQr- MiQr <br />Qa <br />r -.` <br />Whale <br />Q ~ Upstream low flow (41 cfs) <br />Qr ~ Mau»tum dudrarge Jlow (4.3 cfs) <br />Qt ti CarllbinCd doWM1RTCQIn flow (Qr t Q~ <br />Mr ~+ Upstream badeground poUrrtant conanmuion (unknown -assume zero) <br />Mr ~ Unbwwn; Mtsdmum allowable ejJluart pollutant concenrrarion calculated using mats balarttx equation <br />Mt y Mau»rum downstream allowable pollutant concentration (WQS for IR iron of 1.0 mg/lJ <br />The resulting (imttationv l0.1 mg/l. Drir value is btgher than the federal egGrent guideline based limitations of 3.5/7.0 <br />mg/l dtm currattly apply to this outfalL On this basis, no dtartge in the permit u necessary to acaommadare an efrU+ent <br />flow from outfaQ 013 of 2,000 gpm (4.S cfs). <br />71st/ evaluation danonrrrares that the permittee tsn dutharge flaws aP ro 2,000 gpm (1.88 MGD or 4.3 efsJ from aurfaQ <br />0/3 with no change in dre efrluent Umitationr imputed via previout amadmau no. Z If the permiaee fads the need in <br />t/te future to drscharge above 2.000 gpm, a new rcqum and evahrarion will be necessary. Because this action doer not <br />dwttge any permit limitations or other conditions, it it conriderrd a minor modification oat subject to public notieG <br />Jort G Rabic <br />April 29, 1997 <br />• <br />