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TRI-STATE GENERATION AND TRANSMISSION ASSOCIATION, INC. <br />HEADQUARTERS: P.O. BOX 33695 DENVER, COLORADO 80233-0695 303-452-6111 <br />July 23, 2015 <br />Mr. Eric Mink <br />Water Quality Control Division <br />Colorado Department of Public Health and Environment <br />4300 Cherry Creek Drive South <br />Denver, Colorado 80246-1530 <br />RE: Updated Notification of Chronic WET Data for Outfalls 007 and 013 <br />New Horizon Mine, CDPS Permit #CO -0000213 <br />Dear Mr. Mink: <br />As noted in our letter dated July 13, 2015, the Whole Effluent Toxicity (WET) testing <br />results for Outfalls 007 and 013 at the Western Fuels — Colorado, A Limited Liability Company <br />(Western Fuels -Colorado) New Horizon Mine (CDPS Permit #CO -0000213) required <br />notification to the Division and accelerated testing. Tri-State Generation and Transmission <br />Association, Inc. (Tri-State) is the parent of Western Fuels -Colorado. Upon further review of the <br />enclosed analytical reports, we are also providing the required notification of WET sublethal <br />results, in accordance with Part I.A.4b. of the permit. <br />Outfall <br />Species <br />Growth or Reproduction Results <br />sublethali <br />IWC <br />NOEC* <br />IC25** <br />007 <br />Fathead minnow <br />(Pime hales romelas <br />60% <br />54.2% <br />100% <br />007 <br />Cerioda hnia dubia <br />1 20% <br />50.1% <br />1000/0 <br />013 <br />Cerioda hnia dubia <br />1 40% <br />1 57.4% <br />1 100% <br />*NOEC means "no observed effect concentration" at which concentration there are no <br />observable adverse effects on the organisms. <br />**IC25 means inhibition concentration causing a 25% reduction in the biological measurement. <br />Based on a review of the lethality and sublethality results, and Seacrest Group's (our <br />third party WET testing laboratory) professional judgment, the most sensitive species for <br />accelerated testing for Outfall 007 is fathead minnow (Pimephales promelas) and for Outfall 013 <br />is Ceriodaphnia dubia. The facility has commenced accelerated WET testing for the most <br />sensitive species for each outfall location to determine if there is a pattern of toxicity. We will <br />report these results to the Division when available. We will also be submitting the initial WET <br />test summaries and chains of custody with the June 2015 Discharge Monitoring Report (DMR) <br />by July 28, 2015. <br />AN EQU41 OPPOR NIN17 ti : AFFiRMA71VF ACTION EMPI OYFR <br />A Touchstone Energy' Cooperative' <br />CRAIG STATION ESCALANTE STATION NUCLA STATION <br />P.O. BOX 1307 P.O. BOX 577 P.O. BOX 698 <br />CRAIG, CO 81626-1307 PREYVITT, NM 87045 NUCLA, CO 8142440698 <br />970424-4411 SOS -972-5200 970-864-7316 <br />