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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division Amendment No. 4-Rarionale. Pare No. 3. Permit No. CO-0032115. 022 1 •+ +^ 0.70 1.03 023 1 +• •• 0.53 0.91 024 1 •• ++ 0.25 0.52 • No discharge has been reported for the most recent two year period. *• These ponds have not been placed into service yet. Ponds are designed to treat the !0-year, 24-hour equivalent volume to applicable standards, not necessarily to contain that volume. This is reflected in some pond volumes that are less than the applicable 10.year, 24-hour event volumes. III. RECE/i7NG STREAM A. Identification, Qasstflcadoa and Startda-ds 1. Identifcaton: Outfall 021 discharges to East Middle Fhane Gulch, outfall 022 discharges to Deal Gulch, outfall 023 discharges to East Flrone Gulch, and outfal! 024 discharges to West Horse Gulch. These receiving waters are tributary to the Yampa River and are within segment 3a, Lower Yampa/Green River sub-basin, Lower Colorado River basin. 2. C7as~cation: Segment 3a is designated as Use Protected and is classified for the following uses: Recreation, Class 2; Aquatic Lfe, Class 2 (wn»rtJ; Agrictdtrtre. 3. Numeric Standards: The standards which have been assigned in accordance with the above classifications can be found in the C7assificarions and Numeric Standards for the Lower Colorado River Basin, Regulation No. 37 (S CCR ]002-37J, as amended July 74, 1997, and effective August 30, 1997. /t should be Hated that this facility does not discharge pollutants which ore limited by water quality standards with the exception of pH, for which the standard is 6.3 to 9.0 s.u. The segment has ro metals standards or standards for other parameters applicable to this site. B. Reteiving Water Data 1. Quantity. Acute and Q[ronic Low Flows: Since a!! receiving waters are intermittently flowing gulches, the !ow flows are 0 cfs and the while eeluent tariciry (WET) testing IWC is 100'% for the applicable outfalls (027 and 023). >V. PURPOSE OF AMENDMENT In a letter dated July 7, 1999, the perntittee requested that the permit be modified to add three new outfal/s. In a second letter dated July 24, 2000, the pernrittee requested that a faarth new outfall be added New outfalls 021 and 023 serve primarily to capture and treat surface runoff, and may receive same mine water from dewatering of the surface mining operation. OutfalLs 022 and 024 serve to capture and treat surface runoff. The permit already cortrains e, jJluent [imitarions and monitoring requirements that are applicable for these new discharges. Part I.A.I. (6J specifies eahtent Gmitarians that are applicable for outfalls 022 and 024. Parr I.A.I. (cJ specifies ejJluent limitations that are applicable for ou[falls 021 and 023. In addition, Part LA.2. ,Anne WET Testing, applies to outfaUs 02l and 023, subject to certain a-emprians (see the ne# paragraph). Part LB.7. (aJ specifies monitoring requirements that arc applicable f»r otafaUs 021 and 024. Para LB.l. (bJ specifies monitoring requirements that are applicable for outfa!!s 021 and 023. The basis for these effluent limitations and matitoring requirements is stated in previous rationales to this permit. These rodonales are parr of the permit files and available for inspection to any interested parries.