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COLORADO DEPARTAIENT OF EALTH, Water Quality Control Division • <br />Rationale -Page 4, Permit No. CO-0024562 <br />The flows and corresponding !WC's jar the appropriate discharge points are: <br />,. , <br />'::; t~roiric.Zow Flow,30gi; Faaliij Destgrs F/ow; .. ; .: ' <br />Discharge Point..;:., :...'.:.:: : (cIs) ..::..:..:: :. :: :`. (cjs) :; ::.. :. I-VC, (96) <br />001 6.8 4.0 37.0 <br />002 6.8 6.0 46.9 <br />In addition to the IWC vdue jar determining whether chronic or acute WET testing requirements are <br />applicable, the classification ojthe receiving stream must be considered. According to the Colorado <br />Water Oudity Control Division Biamonitorine Guidance Document dated !dy 1, 1993, chronic WET <br />testing is required jor facilities where tic receiving stream has a Class 1 Aquatic L(~e use or Class 2 <br />Aquatic L(fe use with all ojdu appropnate aquatic l(fe numeric standards; otherwise, acute WET <br />testing is required <br />Since this receiving water is class(~ed as Class I Aquatic L{'fe use and the IWC's jor both discharge <br />points are greater than 9.1%, the Division has determined that chronic WET testing is applicable jor <br />this permit (see jolloxing paragraph). <br />3) Chronic WET Limitations: The Mining Company has detected signifttant tonicity in the effluent and <br />has not been able to identify any spec{/ic pollutant that may be the cause. Pursuant to section 6.9.2. (S <br />of the Re¢ulattans for State Discharee Permit Svslem (5 CCR 1002-2). the Division believes there rs <br />reasonable potential jor the discharge to interfere with the attainment ojappGcabk water quality <br />classjfications ar standards. Because oJthLs condition, the chronic limit has been incorporated into the <br />permit. <br />The original permit aUawed a three year period before the WET limit (acute) was to become effective ors <br />April I, 1995. This amendment wiU joUow the same schedule, wrth the amended permit specifying that <br />the chronic WET limit will become effective April 1, 1995. <br />Prior to the chronic limit becoming effective, the permittee is required to conduct routine monitoring. <br />The results of the testing are to be reported on Division approved forms. The permittee will be required <br />to conduct two types of statLstical derivations on the data, oru looking jor any statistically signf/icant <br />difference in laxleity between tht control and the e,(/luenl concentrations and the second identj~ying the <br />IC2S, should one exist. Both sets ojcalculations will look at the juU range ojtoxicity (lethality, grawrl: <br />and reproducion). Ija level ojchronic toxu:tty occurs, such that there is a statistically sigdfuanl <br />difference in the lethality (at the 95°6 corEJ'idence level) between the control and any e,()'luent <br />concentralian less than or equd to the Instream Waste Concentration (IWC) and (j the lethdity IC2S < <br />the IWC, Jhe perminee will be required to joUow the automatic compliance schedule rdennfied in Part <br />I.B. ojthe permit, j~the observed toxicity is due 10 organism lethality. Once the chronic lethdity <br />limitation becomes effective, only exceedance ojthe limitation specified in Part LA.1. will trigger tl:e <br />requirement jor conducing the automatic compliance schedule identified in Part I.B. of the permit. <br />Prior to and after the limitation becomes effective, {(the toxicity is due to differences in the growth of <br />the fathead minnows or the reproduuion ajlhe Ceriodaphnia, no immediate scion on the part ojthe <br />permittee wiU be required. However, this incident, long with other WET data, wiU be evduated by the <br />Division and may form the basis jor reopening the permit and including additional WET limits or other <br />requiremems. <br />