ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Near and Far Field Dilution Analysis of Manteca Discharge October 2006 using two discharge cases: the first with the current side bank discharge, and the second, a preliminary design diffuser. Both cases were run for different river flow conditions and with different discharge rates to simulate SIP critical conditions (SWRCB, 2005). Model Description The finite element representation of the San Joaquin River used for the Manteca near field dilution modeling extends from the gage at Vernalis to the bifurcation at the head of Old River as shown in Figure 1. The model includes one-dimensional cross-sectionally averaged sections at the upstream and down stream ends and a two-dimensional depth- averaged section extending from below Mossdale Bridge to just upstream of the outfall. Details of the entire 2-D section of the finite element mesh are shown in Figure 2, and the immediate vicinity of the outfall is shown in Figure 3 and Figure 4 with the side bank discharge and with the diffuser, respectively. Three-D views of the network, colored by depth, are shown in Figure 5 and Figure 6 with the side bank discharge and the diffuser, respectively,where the lines show the projection of the individual element on the channel bottom and the shaded areas show the shape and location of cross sections that are referenced below. The bridge piers appear as holes in the networks. For the side bank discharge simulations, effluent is input to the first two elements of the side bank discharge channel, as shown in Figure 7. For the diffuser simulations, effluent is input to the 16 elements making up the diffuser(Figure 8). The diffuser is 140 feet long, located in the deepest section of the channel on the eastern side of the San Joaquin River, extending out from the location of the existing side bank discharge. Diffuser elevations follow the existing channel contours. 2