ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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minor when increasing the WQCF discharge from the current permitted discharge of 9.87 MGD Total Suspended Solids(TSS) (ADWF)to the proposed 27 MGD(ADWF). Data Availability: Manteca WQCF NPDES self-monitoring data from the San Joaquin River at Evaluation: The incremental change in BOD concentration and mass loading in the San Joaquin R-1(just upstream of the WQCF discharge)corresponding to a wet water year were used to River due to an increase in WQCF effluent discharged from the current permitted rate(9.87 calculate an estimated impact of WQCF effluent total suspended solids(TSS)in the San Joaquin MGD(ADWF))to the proposed rate(27 MGD(ADWF))is minor. Additionally,treatment River under critical(600 cfs)and dry/below normal(1250 cfs)river flows at a permitted process upgrades including a high-rate activated sludge process and tertiary filtration in discharge of 9.87 MGD(ADWF)and at proposed discharges of 17.5 MGD(ADWF)and 27 accordance with Title 22 standards and UV disinfection conforming to National Water Research MGD(ADWF). Ideally,an R-1 TSS data set corresponding to dry/below normal water years Institute(NWRI)guidelines will produce effluent concentrations of BOD less than 10 mg/L. would be used for the present analysis,but such a data set was not available. Improved WQCF The associated consumptive oxygen demand downstream of the WQCF discharge due to BOD treatment processes are projected to produce treated effluent having an average TSS inputs is addressed in the Far-Field Analysis and Results section of this report in a discussion of concentration of less than 10 mg/L. For the purpose of the current analysis,and to be far-field DO impacts. conservative,future TSS effluent concentration was considered to be 10 mg/L. Table 11: Estimated Impact of Biochemical Oxygen Demand from WQCF Discharge in the San Results: The effect of an increase in WQCF discharge from 9.87 MGD(ADWF)to 27 MGD Joaquin River at WQCF R-3 (ADWF)is appropriately addressed in the receiving water at well-mixed conditions downstream of the discharge. During critical and dry/below normal San Joaquin River flow conditions,an Biochemical Oxygen Demand(BOD) San Joaquin River Manteca WQCF Effluent increase in WQCF effluent discharge will slightly decrease TSS concentrations in the San Mossdale 50"%concen.(mg/L)* 5.26 Flowrate(cfs) Flowrate(MGD ADWF) Joaquin River downstream of the discharge as shown in Figure 6 and Table 12. A slight Projected effluent concen.(mg/L) 7 600 1250 9.87 17.5 27 increase in TSS mass loading to the river is also projected. The use of wet water year TSS data Est.mass loading(lbs/day) 17,011 35,439 576 1,022 1,576 may have imparted a slightly high bias to the calculation of downstream,estimated TSS Est.downstream R-3 river concentration(mg/L)at 600 cfs 5.30 5.34 5.37 concentrations in the San Joaquin River,indicating that actual future TSS concentrations measured during dry/below normal water years in the San Joaquin River might show slightly Est.downstream R-3 river concentration(mg/L)at 1250 cfs 5.28 5.30 5.32 lower,relative concentrations than presently estimated. *50"percentile statistic calculated using the following data set: Data Period:October 2000-October 2001;Sample Size,n=10;Percent Detected Data=100 Total Suspended Solids(TSS) 25.6 caJ E 25.2 SJRRows 24.8 ■600 cfs ■125,c fs c � 24.4 c 0 v 24.0 9.87 17.5 27 WQCF Effluent Flow Rate(MGD) Figure 6: Projected Change in San Joaquin River Total Suspended Solids Concentration at WQCF R-3 with increasing WQCF Effluent Flowrate Comparison to Water Quality Objective: The Basin Plan's narrative objective for suspended material states: "Waters shall not contain suspended material in concentrations that cause or adversely affect beneficial uses." City of Manteca Antidegradation Analysis 35 June 2007 City of Manteca Antidegradation Analysis 36 June 2007