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Near and Far Field Dilution Analysis of Manteca Discharge October 2006 <br /> Summary <br /> Near field and far field dilution analysis of the Manteca discharge has been completed <br /> using local and Delta-wide versions of the 2-D depth-averaged models RMA2 and <br /> RMA 11. <br /> Near Field <br /> Near field dilution simulations were performed for three river flow rates, three discharge <br /> rates and two outfall scenarios. San Joaquin River flow rates analyzed were the 1Q10 of <br /> 564 cfs, representing Acute conditions, the 7Q10 of 615 cfs, representing Chronic <br /> conditions, and the harmonic mean of 2,015 cfs,representing Human Health conditions. <br /> Observed tide at Old River at Head was used for the downstream tidal boundary. The <br /> Acute and Chronic simulations used the July 1-17, 1992 tide, and the November 20— <br /> December 5, 2001 tide was used for the Human Health simulations. Discharge rates <br /> analyzed were the current permitted rate of 9.87 MGD, and proposed discharge levels of <br /> 17.5 MGD and 27 MGD. Timed discharge was required for the Acute and Chronic <br /> simulations due to the low river flow rates. The flow rate for the Human Health <br /> simulations was sufficiently high to allow continuous discharge. All of the flow— <br /> discharge combinations were analyzed with a side bank outfall and with a 140' long <br /> diffuser. Dilution along plume centerlines was analyzed for each flow and discharge <br /> scenario. <br /> For the Acute side bank discharge scenarios, there is virtually no dilution at the outfall, <br /> and at 10,000 ft downstream of the discharge, dilution is approximately 37:1 for the 9.87 <br /> MGD simulation, 21:1 for the 17.5 MGD simulation, and 13:1 for the 27 MGD. For the <br /> Acute diffuser scenarios, the lowest dilution occurs at approximately 700 feet <br /> downstream of the diffuser. For the 9.87 MGD simulation, the lowest dilution is <br /> approximately 11:1, for the 17.5 MGD simulation 6:1 and for the 27 MGD simulation <br /> 4:1. The side bank outfall and diffuser plume centerline concentration profiles are <br /> essentially identical beyond about 2,000 feet from the discharge point. <br /> For the Chronic side bank discharge scenarios, there is limited dilution at the outfall, and <br /> at 10,000 ft downstream of the discharge, dilution is approximately 16:1 for the 9.87 <br /> MGD simulation, 9:1 for the 17.5 MGD simulation, and 6:1 for the 27 MGD. For the <br /> diffuser scenarios, the lowest dilution occurs at approximately 4,100 feet downstream of <br /> the diffuser. For the 9.87 MGD simulation, the lowest dilution is approximately 12:1, for <br /> the 17.5 MGD simulation 6:1 and for the 27 MGD simulation 4:1. At 10,000 ft <br /> downstream of the discharge, dilution is the same as for the side bank scenario. The side <br /> bank outfall and diffuser plume centerline concentration profiles only differ significantly <br /> within about 5,000 feet of the discharge point. <br /> For the Human Health scenarios there is virtually no dilution at the outfall, and at 10,000 <br /> ft downstream of the discharge, dilution is approximately 134:1 for the 9.87 MGD <br /> simulation, 75:1 for the 17.5 MGD simulation, and 47:1 for the 27 MGD. For the <br /> diffuser scenarios, the lowest dilution occurs at the diffuser. For the 9.87 MGD <br /> simulation, the lowest dilution is approximately 69:1, for the 17.5 MGD simulation 3 8:1 <br /> and for the 27 MGD simulation 25:1. At 10,000 ft downstream of the discharge, dilution <br /> is approximately 126:1 for the 9.87 MGD simulation, 71:1 for the 17.5 MGD simulation, <br /> ii <br />