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Antidegradation Analysis <br />The Antidegradation Rule is found at Rule 31.8. The antidegradation review process at § <br />31.8(3) applies to the review of "regulated activities" with new or increased water quality <br />impacts that may degrade the quality of "reviewable waters." "Regulated activities" means: <br />• Any activities which require a dischazge permit or water quality certification <br />• under federal or state law... <br />Although Segment 3 of the Eagle River is a "reviewable water," the antidegradation review <br />. process does not apply in this case, because the water release is not a "regulated activity." The <br />Water Quality Control Division has determined that the release from the Eagle Park Reservoir <br />does not require a dischazge permit. Nevertheless, an antidegradation type analysis was <br />conducted to satisfy agreements made between CMC and AMG. <br />The initial step in the antidegradation review is the determination as to whether the dischazge is <br />likely to result in significant degradation of the receiving water. The discharge of a potential <br />pollutant can be determined to be insignificant, and hence exempted from antidegradation <br />review, if it passes any one of three approaches: <br />The new or increased flow from the dischazge is very small compared [o the <br />receiving stream (diluted by 100 to 1 or more, determined under low-flow <br />conditions [as defined in Section 31.9]) <br />The new or increased discharge will consume less than 15% of the baseline <br />available increment water quality (baseline available increment is the <br />increment between low-flow pollutant concentration and the relevant water <br />quality standard) <br />• The new or increased discharge causes only temporary or short-term changes <br />in water quality (not available where extended operations having temporary <br />or short-term discharges result in an adverse change in water quality). <br />Even if a new or increased dischazge to a "reviewable" water is found to result in significant <br />degradation by failing all three significance determination approaches outlined above, the <br />discharge can still be approved if it is deemed to be necessary as defined in Section 31.8(3)(d). <br />The following is a significance determination analysis generally following the approach ]aid out <br />in Section 31.8 for the delivery of water from the EPR for the period of record (December 1998 <br />through February 2001). <br />Flow-and-Volume Approach <br />The flow-and-volume significance determination approach considers the degree of dilution <br />occurring in the receiving stream. While this approach is not intended for situations such as the <br />delivery of water from EPR, the flow-and-volume approach is a useful exercise to understand <br />6601631.005 0101 0501 0380 4 <br />\\EOUltlerl Wata\pmjedsV 94]_clirrex\epr report 2.tloc <br />