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COLORADO DEPARTMENT OF HEALTH. Water Quality Control Division <br />Rationale -Page 9. Permit No. CO-0038024 <br />Samples shall be taken at the effluent discharge points. Salinity requirements are included in Part I.A.4. <br />of the permu. <br />eJ Whole Effluent Tosicirv fWE17 Testine For outfalis 004, 023, 024 and 026, acute WET requirements <br />apply. (See Parts LA and LB ojthe permit.) <br />IJ Puroosc f WET Testing: The Water Quality Control Division has established the use of WET testing <br />as a method for rdentrfying and controlling toxic discharges from wastewatn treatment fac!litiu. WET <br />testing rs being utilized as a means to ensure that three are no discharges of pollutants 'in amounts, <br />concentrations or combinations which are harmful to the beneficial uses or toxic to humans, animals, <br />plates, or aquatic life' as required by Section 3.1.11 (1 J of the Basic Standards and Methodologies for <br />Surface Waters. <br />2J Instream Waste Concentration //R'Cl: R'hert monitoring or limitations for WEI' are deemed <br />appropriate by the Division, chronic rostrum dilution as represented by the chronic IWC is critical in <br />dttermrning whether acute or chronic conditions shall apply. For those discharges where the chronic <br />)WC is greater than (>J 9.196, cluonic conditions apply, where the IWC is lest than or equal to (5J <br />9.1 acute conditions apply. The chronic IWC is daerndned using the follmving equation <br />IWC = jFacitiry Flow (FF)/(Stream Chronic Low Flow (annual) + FF)] X 100`% <br />The flows and rnrresponding IWCfor the appropriate discharge poLu are: <br />Discharge. Point Chrome Low; Flaw, 'FaaTtty Dengn Flow, /WC (96) <br />30E3. (cIs) . leis) <br />004, 023, 024 and 026 0 varies 700 <br />The IWC for this permit is 10096, which represems a wastewater concentration of 100'% effluent to <br />0% receiving stream See the following paragraph for additional criteria in determining whether <br />acute or chronic requirements apply. <br />3J Acute WET l.rmitations: The Division considers the aquatic life classifuation and uses of the receiving <br />water in determining whether acute or chronic WET requirernetus are imposed Because the <br />receiving water is classed aquatic life class 2 with no appropriate aquatic life numeric standards, <br />acute requirements apply to this discharge instead of chronic requirements. The potemial for tosicity <br />in coal mine drainage is demonstrated by a growing Division data base of WET test failures, including <br />several failures at this facility. On this basis, as required under section 6.9.2(5) of the Regulations <br />for the State Discharge Permit Svstem. the Division fords there is reasonable potemial for the <br />discharges from outfalLs 004, 023, 024 and 026 to interfere with attairuneru of applicable water quality <br />class fuations or standards. Because of this condition, the acute limitation has been incorporated into <br />the permit. Because the permiaee has been performing acute WET monitoring for five years under the <br />previous permit, the acute limrtation xdll become effective immeduuely. The permittee is required to <br />conduct routine monitoring, the resulu of which art to be reported as an LC,~ If the LC„ 5 100`% <br />ejJluent, the permittee is required to conduct the automatic compliance schedule as identified in Part <br />I.B. of the permit. The resulu of the resting are to be reported on Division approved forms. <br />