ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Near and Far Field Dilution Analysis of Manteca Discharge October 2006 Table 3 Summary of peak cross-sectional area impacts resulting from four different discharge temperatures for fall,historical low flow,intermittent side bank discharge simulations. Background Reduction Peak cross- San Joaquin Discharge from sectional River temperature observed area Date temperature (o F) effluent impacted by (° F) temperature 1° F or more (° F) October 4 61 65 11 22.5% October 4 61 66 10 29.7% October 4 61 67 9 37.3% October 4 61 68 8 41.3% October 3 62 65 11 19.0% October 3 62 66 10 28.2% October 3 62 67 9 35.1% October 3 62 68 8 39.7% Diffuser Temperature simulations were performed only with side bank discharge. Diffuser discharge was not examined. The diffuser distributes effluent across a wider portion of the channel,but at higher dilution than the side bank discharge. The difference between the two discharge types is illustrated in Figure 27. This plot shows dilution across the channel width for side bank and diffuser discharge, 27 MGD Acute simulations at the time and location(800' downstream of diffuser) of minimum dilution for the diffuser case. Twenty-five percent of the channel cross-section with the minimum dilution is shown for each case. For the side bank discharge case, the lowest dilution is along the eastern bank, whereas for the diffuser, the lowest dilution is towards the middle of the channel. We can evaluate the diffuser discharge based on the following. • We have assumed that the diffuser will be designed such that the vertical effluent distribution is nearly uniform a short distance downstream from the diffuser. • Acute dilution computed for the diffuser represents the minimum dilution (maximum impact). • Minimum dilution occurs approximately 800' downstream of the diffuser for the Acute scenario, however travel time over 800' is short so that heat exchange is not a significant issue. 32