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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Warer Qualiry Control Division
<br />Rationale-Page B, Permit No. CD-0032115
<br />appropriate aquatic life numeric standards, chronic conditions apply. Where the chronic IWC is less than or
<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 IWC for the appropriate discharge point are:
<br />Chronic Low Flow, Facility Design Flow, ,
<br />Discharge Point 30E3, (cjs) (cfs) 1WC, (~)
<br />011, 017, 019, 020, 021, 023 0 varies 100%
<br />The IWCfor this permit is 100%, which represents a wastewater concentration of 100°o effluent to 0%
<br />receiving stream.
<br />However, in addition to the IWC value for determining whether chronic or acute WET testing requirements are
<br />applicable, the classtfu;ation of the receiving stream must be considered. According ra the Colorado Warer
<br />Quality Control Division Biomonitorinr Guidance Document, dated July !, 1993, where the receiving water is
<br />classified aquatic life, class 2 without a[1 of the appropriate aquatic life numeric standards, acute WET testing
<br />is required, regardless of dilution. Since the receiving water is classified as Class 2 Aquatic Life use, but does
<br />not have all of the appropriate aquatic life numeric standards, the Division has determined that acute WET
<br />testing is applicable for this permit (also see following paragraph). Although this segment does have metals
<br />standards, all are based on agricultural use.
<br />iii. Acute WET Limits: The Division has found that discharges of mine drainage and spoils spring water from coal
<br />mines at similar sites have exhibited effluent toxicity. On this basis, the Division believes there is reasonable
<br />potential for the discharge to interfere with attainment of applicable water quality classifications or standards
<br />and therefore, an acute toxicity limit has been incorporated into the permit.
<br />The permittee is required to conduct quarterly monitoring consistent with the frequency specifiuations in the
<br />Colorado Water Quality Control Division Biomonitortn2 Guidance Document. dated July 1, 1993, the results of
<br />which are to be reported as ors LCso, which is the concentration at which SO% or more of the organisms die. If
<br />the LCs° occurs in a concentration of less than or equal to 100% effluent, the permittee is required to comply
<br />with the specifications identified in Part I.A. of the permit.
<br />iv. General Information: The permittee should read the WET testing section of Pan I.A. of the permit carefully.
<br />The permit outlines the test requirements and the required follow-up actions the permittee must take to resolve
<br />a toxicity incident. The perrttittee should read, along with the documents listed in Pan LA.f. the permit, the
<br />Colorado Water Quality Control Division Biomonitorin2 Guidance Document, dated July I, ]993. This
<br />document outlines the criteria used by the Division in such areas as granting reliejfrom WET testing, modifying
<br />test methods and changing test species. The permittee should be aware that some ojthe conditions outlined
<br />above may be subject to change if the facility experiences a change in discharge, as ovYlined in Pan II.A.2. of
<br />the permit. Such changes shall be reported to the Division immediately.
<br />v. Outfalls 001. 002 005. 008. 009. 012, 013. 014. 015. 0l6. 018. 021 and 024: These outfalls, except outfa11001,
<br />consist entirely of surface runoff. Outfa11001 may include French drain water. Because these outfalls consist
<br />of surface nenoffonly and discharge during periods of high stream Jlow, they are not believed to contribute
<br />toxicity. On this basis, WET testing is not a requirement for these outfa[!s. However, the Division reserves the
<br />right to reopen the permit to include WET testing, should facility conditions change or if new information
<br />becomes available.
<br />3. Stormwater Evaluation: Stormwaterfrom active and inactive coal mining sites that has been contaminated by contact
<br />with overburden, raw material, intermediate products, byproducts, finished products or waste products located at the
<br />site is required to be covered by a Colorado Discharge Permit System (CDPS) permit in order to be discharged to
<br />Waters of the State. This coverage may 6e obtained under either a CDPS Industrial Wastewater Discharge Permit or a
<br />CDPS Stormwater Discharge Permit.
<br />The Division understands that all discharges ofstormwaterpass through outfalJs covered under permit CO-0032115.
<br />Any discharges that consist only ofstormwater that have become contaminated as described above, that do not
<br />Last Revised: 3/22/1004
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