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COLORADO DEPARTMENT OF PUBLIC HEALTHAND ENVlRONMEhT, Water Quality Control Division <br />Rationale-Page 7, Permit No. C0.0017l46 <br />equal to 9.1, or the stream is not classified as described above, acute conditions apply. The chronic IWC is <br />determined using the following equation: <br />IWC = [Facility Flow (FF)/(Stream Chronic Low Flow (annual) + FF)J X 100% <br />The flows and corresponding IR'Cfor the appropriate discharge point are: <br />Discharge Poinu Chronic Low Flow, Facility Design Flow, IWC, (a/o) <br />30E3, (cfs) (cfs) <br />001 +002+016 135 0.91 0.39% <br />The IWC for this permit is 0.39%, which represents a wastewater concentration oj0.39% effluent to 99.61% <br />receiving stream. <br />iii. Acute WET Limits: The Division has found that discharges of mine drainage from coal mines have exhibited <br />effluent toxicity. On this basis, the Division believes there is reasonable potential for the discharge to interfere <br />with attainment of applicable water quality classifications or standards and therefore, an acute toxicity limit <br />previously existed and has been incorporated into the renewal permit. <br />The Roadside Mine (North and South Portals) WWTF has conducted acute toxicity testing for several years and <br />has demonstrated that at a concentration of'100% effuent the samples are not lethal to 50% ojthe organisms. <br />Thus, the facility has demonstrated that it can meet an acute toxicity limit of LCsa >I00%, and this limit will be <br />effective immediately. <br />The permtttee is required to conduct quarterly monitoring consistent with the frequency specificatiorss in the <br />Colorado Water Oua[ity Control Division Biomonitorin2 Guidance Document. dated July 1, 1993, the results of <br />which are to be reported as an LCso-, which is the concentration at which 50% or more of the organisms die. If <br />the LCsa occurs in a concentrarion of less than or equal to 700% effluent the permittee is required to comply <br />` ~ with the spec cations identified in Part I.A. of the permit. <br />As previously established, monitoring point "RSMW" shall continue for WET testing. This point shall consist <br />of a single composite sample comprised ojgrab samples from Outfalls 001, 001 and 016, as applicable, and <br />proportioned to flow. _ <br />iv. General Information: The permtttee should read the WET testing section of Part I.A. of the permit carefully. <br />The permit outlines the test requirements and the required follow-up actions the permtttee must take to resolve <br />a toxicity incident. The perminee should read, along with the documents listed in Part I.A. of the permit, <br />including the Colorado Water Ouality Control Division Biomonitorine Guidance Document. dated July 1, 1993. <br />This document outlines the criteria used 6y the Division in such areas as granting relief from WET testing, <br />modifying test methods and changing test species. The permtttee should be aware that some of the conditions <br />outlined above may be subject to change if the facility experiences a change in discharge, as outlined in Part <br />ILA.1. of the permit. Such changes shall be reported to the Division immediately. <br />3. Stormwater: Stormwater discharge permits are required for active and inactive coal mining facilities as covered under <br />Standard Industrial Classification (SIC) Code 12. <br />Division records indicate that Snowcap Coal Co, Inc. has coverage for stormwater discharges from the Roadside Mine <br />(North and South 'Portals) under a General Stormwater Discharge Permit number COR-040175. Stormwater <br />permitting issues jor this mine will be handled separately by the Division's Stormwater Unit, although this permit may be <br />reopened at a later date to incorporate stormwater provisions, if deemed appropriate. <br />4. Economic Reasonableness Evaluation: Section 25-8-503(8) of the revised (June 1985) Colorado Water Quality Control <br />Act required the Division to "determine whether or not any or all of the water quality standard based effluent limi[ationr <br />are reasonably related to the economic, environmental, public health and energy impacts to the public and affected <br />J persons, and are in furtherance of thepolicies set forth in sections 25-8-/91 and 25-8-104." <br />The Colorado Discharge Permit Svstem Rezulan'ons Regulation No. 61, further define this requirement under 61.11 and <br />state: "Where economic, environmental, public health and energy impacu to the public and affected persons have been <br />Last RevireAr /1/3/2003 <br />