ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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the reserve portion of the TMDL allocations. The reasonable potential for the DO objectives to be exceeded is not significantly affected by the project. Sacramento River Manteca WQCF Effluent Contribution to Far-Field Delta Locations at confluence with American River The percent contribution(by volume)of WQCF effluent is calculated for several points of interest within the Sacramento-San Joaquin River Delta for both critical and dry/below normal water years as a measure of the potential effect that increasing WQCF discharge capacity might have in the far-field. Furthermore,the percent WQCF effluent contributions are used in conjunction with historic Delta water quality data and historic Manteca effluent data to estimate the incremental change in Delta water quality with increases in WQCF discharge. Modeling Approach: A two-dimensional,depth averaged,finite element model of the Delta extending from Martinez at the downstream end,up the Sacramento River to the American River confluence,and up the San Joaquin River to Vernalis(RMA 2006)is used to perform far-field dilution analysis simulations. The boundary conditions of the model include 15-minute tidal inputs at Martinez;historical daily inflows for the Sacramento River,San Joaquin River, Cosumnes River,Mokelumne River,Yolo Bypass,and other inflows(e.g.Calaveras River, French Camp Slough,etc.);historical exports at Delta Mendota Canal(DMC),Contra Costa at Old River,Contra Costa at Rock Slough,the North Bay Aqueduct,Clifton Court used by the State Water Project(SWP);and inflows and withdrawals by Delta Islands. Additionally, historical operations of the operable gates and temporary barriers are included in the far-field delta model. The model domain is presented in Figure 26,and detailed in"Near and Far Field Dilution Analysis of the Manteca Wastewater Discharge"(RMA 2006). O Model simulations evaluating the WQCF operating under the timed discharge schedule with daily average discharge rates of 9.87,17.5,and 27 MGD(ADF)are used to determine the Martinez W incremental impacts of the project within the Delta. Model results are tracked at six locations within the Delta as indicated in Figure 27. Simulations for nominal San Joaquin River flowrates of 600 cfs and 1,250 cfs were performed to evaluate critical and dry/below normal water years, respectively. Results: The minimum and maximum calculated WQCF effluent contributions for six selected locations within the Delta are listed in Tables 35 and 36 corresponding to critical and dry/below normal water years,respectively. In general,the further away from the WQCF the far-field site is located,the lower the percent contribution of WQCF effluent,and as WQCF discharge San Joaquin River Manteca outfall increases,so does its percent contribution at far-field locations. The calculated WQCF percent at Vernalis contribution exceedance plots are presented for six selected Delta locations in Figures 28 through 33. For example,from Figure 28,less than 0.5%of the water at the State Water Project Clifton Court intake will be of WQCF origin for 70%of a critical water year;and for 85%of a Figure 26: Finite Element Mesh of Simulated Waterways for Far-Field Simulations(RMA 2006) dry/below normal water year at a WQCF discharge rate of 27 MGD(ADWF). Lower WQCF discharge results in lower percent contributions of WQCF effluent at far-field locations. Comparison to Water Quality Objectives:There are no established objectives for the percent contribution a wastewater treatment facility's effluent can make within waters of the Delta. Evaluation: Even under critical water year conditions and a WQCF discharge rate of 27 MGD (ADWF),the percentage of water of Manteca origin is less than 1%most of the time(greater than 70%of the time)at selected Delta locations,with the sole exception of the Stockton Turning Basin. City of Manteca Antidegradation Analysis 79 June 2007 City of Manteca Antidegradation Analysis 80 June2007