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COLORADO DEPARTNE.VT OF PUBLIC HEALTHAND ENVIRONMENT, Water Quntiry Control Division <br />Rntionale -Page 6, Permit No. CO-0044377 <br />f. Colorado Mixin Zone Re ulations: Pursuant to section 31.10 of The Basic Standards and Methodolo ies for Surface <br />ater a mixing zone eterminatian z's required for this permittin& acfzon. T e o ora o zxin one m ementation <br />Wince dated April 2002, identifies the process for determining the meanin imit on t e area impacte y a <br />isc arge to surface water where standards may be exceeded (i. e., regulatory mixing zone . This guidance document <br />provides for certain exclusions from further analysis under the regulation, based onsite-speck conditions. <br />The gguidance document provides a mandatory, stepwise decision-making pprocess for determining t the permit limits wilt <br />not be af~ected by this regulotion. Exclusion, based on Extreme Mixin Xattos, may be ranted ! the ratio of the design <br />flow to t e chronic low flow (30E3)) is greater than 2:1 or if the ratio o~the chronic low f~ow to t e design flow is reater <br />than 20:1. Since the ratio of the low J[ow to the design flow is more than 150:1 for discharges to the North Fork of the <br />Gunnison River (stream segment COGUNFO2), the permittee u eligible for an exclusion from further analysis under the <br />regulation. <br />g. Salini Re ulations: An evaluation of the discharge of total dissolved solids indicates that the Bear Coal #3 Mine does not <br />excee t e t res o d of 1 ton/da or 36s tons/year o salinity as set forth in the Colorado River Salini Standards. In <br />conformance with section 61.8(y2)(1)(i)(A) of the G~lorado Dischar a Permit stem a ations t e permittee has <br />submitted required reports. Therefore, in compliance wit t e o ora o fiver a ini tan ar s and the Colorado <br />Discharge Permit System Regulations, the permittee shall monitor or tota isso ve so i s on a quarterly basis. a~m7es <br />h. Whole Effluent Toxicity (WET) Testing <br />For Outfa11001, acute WET testing is required. (See Part I A of the permit.) <br />,. Pur •cse o WE.T TesTest~n : TF,e Water uality Control Division has established the use a WET testng as a method for <br />i enti ing an controlling toxic disc arges from wastewater treatment facilities. WE testing is being utilized as a <br />means to ensure that there are no discharges ofpo/lutants "in amounts, concentrations or combinations which are <br />harm ul to the beneficial uses or toxic to humans, animals, plants, or aquatic life" as required by Sec[ion 31.11 (1) of <br />the Basic Standards and Methodologies for Sur(aee Waters. <br />ii. In-Stream Waste Concentration /IWCI: Where monitoring or limitations for WET are deemed appropriate by the <br />ivi7 •s~c:ronic in-stream i orlon as represented by the chronic IWC is critical in determining whether acute or <br />chronic conditions shall app! . According to the Colorado Water Ouality Control Division Biamonitoring Guidance <br />Document dated July /, 1993, (ar those dischar es w ere t e c tonic is greater t an o ono t <br />streams a Class I Aquatic Life use or Class ~ Aquatic Life use with all of the appropriate aquatic life numerzc <br />standards, chronic conditions apply. Where the chronic IWC is less than or eoual to 9. / or the stream is not classified <br />as described above, acute conditions apply. The chronic IWC is determined using the joflowing equation.: <br />IWC = [Facility Flow (FF)/(Stream Chronic Law Flow (annual) + FF)j X 100% <br />The flows and corresponding IWC for the appropriate discharge point are: <br /> Disghpr a Poarit"s -Chror3te Low Plow 30E3 i(cfs) <br />~ ~Baci7tly Desi n Floti% `c s ` <br />- <br /> 001 ~ 43 01 <br />0.06 ] <br /> <br />The IWC for this permit is 0.1 %, which represents a wastewater concentration of 0.1 % effluent to 99.9% receiving <br />stream. <br />iii. Acute WET Limits: Due to demonstrated toxicity for Cerioda hnia sp. at Outfall 001 and tom coalmine drainage at <br />severa Simi ar acilities, the Division believes there is reasonable potential for the ischarge to interfere with <br />attainment of applicable water quality classifications or standards. Because of'this condition, the acute toxiczry limit <br />has been previously incorporated into the permit and continues to be effective tmmediaiely. The permittee is required <br />to conduct routine monitoring, the results of which are to be reported as an LCso If the LCs < /00% effluent, the <br />permittee is required to conduct the automatic compliance schedule as identified in Part I B. of tie permit. <br />The permittee is required to conduct quarterly monitoring consistent with the frequency specifications in the Colorado <br />Water Oualirv Control Division Biomonitorin Guidance Document dated July 9, 1993, the results of which arm <br />reported asas a~n:~ne concentration at w :'c 7l°~more of the organisms die. Ijthe LCso occurs in a <br />concentration of Isess than or equal to 100% effluent, the permittee is required to comply with the specifications <br />identified in Part I.A. of the permzt. <br />The discharge ~~om Outfall 001 continually failed the WET test for Cerioda hnia sp. The permittee performed an <br />analysis that showed the source of the toxicity to be salinity. The C~eri~o a~n~ia species is less tolerant to salinity than <br />Daphnia magna. Therefore, Ceriodaphnia will be replaced in future tests with Daphnia ma,g~tnta. Upon this renewal <br />permzt becoming effective, the two test species shall be D~hnia ma na and Pimeohales prome[us (fathead minnow). <br />iv. General Information: The permittee should read the WET testing section of Part I.A. of thepermit carefully. The <br />permitpermit ou~est requirements and the required follow-u actions the ppermittee must take to resolve a toxicity <br />mctdent. The permittee should read, alongg with the documents listed in Part LA.4.a. o the permit, the Colorado Water <br />uality Control Division Biomonitorin Cuidance Document dated July 1, 1993. This document out Inesines t <br />use y t e ivision in suc areas as granting re fie tom WET testing, modifying test methods and changing test <br />s ecies. The permittee should be aware that some of the conditions outlzned above may be subject to change if the <br />facility experiences a change in discharge, as outlined in Part IIA.2. of the permit. Such changes shat! be reported to <br />v. Otrt all 004: Because of the intermittent nature of surface runoff, the fact that discharges occur during high flow <br />peno s and the expected lack of toxicity from this source, WE testing is not a regguiremerzt for outfa 004. The <br />Dzvision reserves the right to reopen the permit to include WET testing, should facility conditions change or if new <br />information becomes avazlable. <br /> <br />