ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Temperature The finite element representation of the San Joaquin River used for the Manteca thermal modeling extends from the gage at Vernalis to the bifurcation at the head of Old River. The Preparation of the 2000 Draft Environmental Impact Report for the WQCF Phase III/IV model includes a one-dimensional cross-sectionally averaged section from the upstream Expansion Project(EDAW,2000),revealed that the WQCF effluent would not comply with all boundary near Vernalis to above the river bend upstream of the WQCF outfall,a three- objectives of the Water Quality Control Plan for Control of Temperature in the Coastal and dimensional section extending from just upstream of the outfall to below Mossdale Bridge,and Interstate Waters and Enclosed Bays and Estuaries of California(Thermal Plan;SWRCB,1972) two-dimensional depth-averaged sections downstream of Mossdale Bridge to Old River. A short under some conditions. Because the WQCF outfall is an existing discharge in the tidally 2-D section also transitions between the upstream 1-D section and the 3-D section. influenced reach of the San Joaquin River,Section 5.A of the Thermal Plan applies to the discharge and stipulates the following: The model was used to evaluate three critical seasonal scenarios:Fall,Winter,and Spring for the critical dry and below normal river flowrates. During these periods anadromous fish are in the (1) Elevated temperature waste discharges shall comply with the following: river,either migrating upstream as adults or emigrating downstream as juveniles. Because there a. The maximum temperature shall not exceed the natural receiving water is no clear most critical condition for evaluating the thermal impact of the WQCF plume,all temperature by more than 20°F. three of the conditions identified above have been evaluated. The heat budget component of the b. Elevated temperature waste discharges either individually or combined model was calibrated separately for each of the periods as each season has significantly different with other discharges shall not create a zone,defined by water meteorological conditions. (LWA 2006b) temperatures of more than 1°F above natural receiving water temperature, Results: The winter condition resulted in the plume with the largest area of elevated which exceeds 25 percent of the cross-sectional area of a main river temperatures. The modeled thermal plume from the side bank outfall for the winter critical channel at any point. condition corresponding to the currently permitted capacity(9.87 MGD(ADWF))and the c. No discharge shall cause a surface water temperature rise greater than 4°F ultimate project capacity(27 MGD(ADWF))are shown in plan view in Figure 21 and for above the natural temperature of the receiving waters at any time or place. transects downstream of the discharge in Figure 22. Because of the increased discharge flows associated with the project,the thermal plume will be larger and in addition will not comply with In general,the WQCF effluent is warmer than the San Joaquin River,and if evaluated on a objectives a.,b.,or c.of the Thermal Plan. A summary comparison between the thermal plumes monthly average,objective a.of the Thermal Plan is met for the WQCF discharge. Because the from the 9.87 MGD(ADWF)and 27 MGD(ADWF)conditions is listed in Table 27. effluent is warmer than the receiving water,objectives b.and c.of the Thermal Plan are not necessarily met within the WQCF plume. By operating under a timed discharge during periods Table 27: Summary of Percent Cross Section Elevated 1°F or more of low river flow to discharge only on the outgoing tide,the thermal plume will meet objective b. during Winter Dry Water Year Flowrates(RMA 2006) of the Thermal Plan. However,the temperature difference between the discharge and the river may exceed objective c.of the Thermal Plan. Pursuant to General Water Quality Provision 4 of Distance %cross-sectional area elevated more than V F the Thermal Plan,the City is pursuing a limited exception to specific Thermal Plan water quality downstream of discharge(ft) 9.87 MGD(ADWF) 27 MGD(ADWF) objectives for the permitted discharge rate of 9.87 MGD(ADWF)(LWA,2006a). The current thermal analysis is expanded to evaluate the thermal impacts of 17.5 MGD(ADWF)and 27 25 7 15 MGD(ADWF)WQCF discharges on the San Joaquin River. Additionally,the case of a diffuser 125 8 35 discharge is modeled as a means of evaluating the impact of modifying the treatment plant's 250 9 41 outfall. 450 16 47 Modeling Approach: A three-dimensional,hydrodynamic RMA-10 model of the river run in 1,000 22 48 the vicinity of the WQCF discharge is used as the basis for the evaluation. The model simulates 1,500 00) 51 atmospheric heat exchange using the meteorological data from nearby monitoring sites as inputs, (1) Worst case plume resulting from timed discharge release,at maximum cross sectional and has been calibrated and validated using historic data and recent field measurements. The area,plume has yet to reach 1,500 m. hydrodynamic simulation is influenced by density gradients produced by differences in water temperature and other parameters(e.g.,EC,suspended sediment),and incorporates a heat budget algorithm to simulate heat transfer across the air-water interface. The three-dimensional RMA- 10 analysis provides a detailed description of the effluent plume based on the complex geometry of the San Joaquin River in the vicinity of the Manteca discharge(including,sharp bend 100 ft upstream of discharge,Railroad Bridge,Mossdale Bridge,and variable bathymetry and varying water surface elevation),and the fundamental physics that effect hydrodynamic behavior. City of Manteca Antidegradation Analysis 65 June 2007 City of Manteca Antidegradation Analysis 66 June 2007