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Near and Far Field Dilution Analysis of Manteca Discharge October 2006 <br /> and 46:1 for the 27 MGD, similar to the side bank scenario. The side bank outfall and <br /> diffuser plume centerline concentration profiles differ for the two cases down to the <br /> location where the model transitions to 1-D (approximately 5,400 ft), at which point the <br /> concentrations become fully mixed across the channel cross-section. <br /> Thermal Analysis <br /> The model used for the current study was used previously to simulate temperature for the <br /> Thermal Plan Exception study(LWA, 2006). The temperature simulations were <br /> performed using the 3-D version of the model with a side bank discharge. <br /> Results from winter low flow condition simulations indicate that the maximum channel <br /> cross-sectional area impacted by over P F with the side bank discharge is 21% for the <br /> 9.87 MGD discharge rate and 51% for the 27 MGD discharge rate. <br /> Sensitivity analysis runs were performed for the fall historical low flow intermittent, 27 <br /> MGD discharge to determine the amount of effluent cooling that would be required under <br /> this flow rate. Results indicate that a reduction of approximately I P F would be required <br /> to reduce the cross-sectional area impacted by more than P F to less than 25%. The <br /> required effluent temperature reduction results in a 2.5°F differential under critical <br /> conditions. <br /> Temperature simulations were not performed with a diffuser outfall, however near field <br /> diffuser simulation results for Acute conditions can be used to estimate differentials <br /> between effluent and background river temperatures that would maintain less than 25% <br /> of the channel cross-section below 1°F. For any discharge, the maximum allowable <br /> temperature differential between effluent temperature and background river temperature <br /> would equal the minimum Acute dilution plus one. For the Acute conditions analyzed in <br /> this report, this results in maximum temperature differentials of 12°F for the 9.87 MGD <br /> discharge, 8°F for the 17.5 MGD discharge and 5°F for the 27 MGD discharge. <br /> Far Field <br /> Far field tracer simulations were performed for a critically dry year(October 1991 <br /> through September 1992) and a normal dry year(January through December, 2002) with <br /> three discharge rates: the current permitted rate of 9.87 MGD, and proposed discharge <br /> levels of 17.5 MGD and 27 MGD. For each scenario, effluent contribution was analyzed <br /> at six key locations including the Clifton Court intake, DMC intake, Contra Costa intake <br /> at Rock Slough, Contra Costa intake on Old River, San Joaquin River at Light 18 and the <br /> Stockton Turning Basin. <br /> During the 1991 — 1992 simulation, the lowest peak effluent contributions occur at <br /> Contra Costa intake in Rock Slough where the maximum effluent contribution for the <br /> 9.87 MGD case is 0.2%, for the 17.5 MGD case is 0.3%, and for the 27 MGD case is <br /> 0.5%. <br /> The highest peak effluent contributions occur at the Stockton Turning Basin where the <br /> maximum effluent contributions is 3.2% for the 9.87 MGD case 3.7% for the 17.5 MGD <br /> case, and 5.7% for the 27 MGD case. <br /> iii <br />