2001-06-04_REVISION - M1977493 (2)

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ER_WB1), and from the EPR Outlet, and these data can be used for this type of analysis. The analysis consists of five separate steps: • Determine the chronic aquatic life water quality standard for Segment 3, from Rule 33, Classifications and Standards, Colorado River Basin, Eagle River sub-basin. • Determine the baseline concentrations (low-flow period) of potential pollutants in the water above the Outfall (Station ER_Al). • Derive the significant concentration threshold by determining the difference (subtraction) between the chronic standazd for each potential pollutant and the baseline water quality concentration, calculating 15% of the difference between the chronic standard and the baseline concentration for the East Fork, and adding this value to the baseline concentration. • Determine the average concentration of potential pollutants in the East Fork downstream of the EPR Outfall and above the confluence with the South Fork (Stations ER_B 1 and ER_WB 1) during the period when the EPR is discharging. • Compare the average concentrations of potential pollutants at the downstream East Fork stations to the significant concentration threshold. If the significant concentration threshold (as derived in this analysis) is greater than or equal to the average concentration in the East Fork downstream of the EPR Outlet, a conclusion of insignificant degradation is supported. Results of the antidegradation analysis indicate that the none of the potential pollutant concentrations in the East Fork are above the significant concentration threshold (as derived in this analysis) at either of the downstream stations Station ER_B1 or ER_WB1 (Table 5). )n addition, potential pollutant concentrations in the EPR Outlet are significantly below the chronic aquatic life water quality standazds (Table 5). These results indicate that delivery of water from the EPR does not result in significant degradation in the East Fork of the Eagle River. Temporary or Short-Term Discharge Approach The temporary or short-term discharge significance determination approach is available for discharges that are of a temporary nature, or of a limited duration but not temporary. This approach is not available to discharges that have an adverse affect on the water quality of the receiving stream, even if the discharges aze limited in duration but will occur over extended periods. The water deliveries from the EPR are not temporary-they are expected to continue into the future during every fall, winter, and spring. Deliveries from the EPR occur on demand and are continuous during many of the fall, winter, and spring months. In considering the number of days when water is delivered from EPR during the period of record, deliveries occurred on no 6601631.005 0101 0501 0380 \\b0ultlerl\tlatabrojecls\194]_clima~Aepr report 2.tloG