ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Nitrate Evaluation: The incremental change in nitrate(as nitrogen)concentration in the San Joaquin River due to an increase in WQCF effluent discharged from the current permitted rate(9.87 Data Availability: Manteca WQCF NPDES self-monitoring data from the San Joaquin River at MGD(ADWF))to the proposed rate(27 MGD(ADWF))is slight and below the magnitude of R-1(just upstream of the WQCF discharge)corresponding to dry/below normal water years were change that could be reliably measured in the field. Similarly,the projected increase in nitrate used to calculate an estimated impact of WQCF effluent nitrate(as nitrogen)in the San Joaquin (as nitrogen)mass loading to the river is also slight. A high level of nitrogen removal will be River under critical(600 cfs)and dry/below normal(1250 cfs)river flows at a permitted accomplished through the activated sludge nitrification-denitrification process implemented as discharge of 9.87 MGD(ADWF)and at proposed discharges of 17.5 MGD(ADWF)and 27 one of several treatment process improvements associated with the WQCF upgrade. MGD(ADWF). Improved WQCF treatment processes are projected to produce treated effluent Additionally,projected,median nitrate(as nitrogen)concentrations in the San Joaquin River are having an average nitrate(as nitrogen)concentration of 5 mg/L. well below the Title 22 Primary MCL standard of 10 mg/L. Results: The effect of an increase in WQCF discharge from 9.87 MGD(ADWF)to 27 MGD (ADWF)is appropriately addressed in the receiving water at well-mixed conditions downstream Table 24: Estimated Impact of Nitrate(as Nitrogen)from WQCF Discharge in the San Joaquin of the discharge. During critical and dry/below normal San Joaquin River flow conditions,an River at WQCF R3 increase in WQCF effluent discharge will slightly increase nitrate(as nitrogen)concentration in Nitrate as Nitrogen San Joaquin River Manteca WQCF Effluent the San Joaquin River,relative to its Title 22 Primary MCL criterion,downstream of the R-1 50"%concen.(mg/L)` 2.55 Flowrate(cfs) Flowrate(MGD ADWF) discharge as shown in Figure 18 and Table 24. A slight increase in nitrate(as nitrogen)mass loading to the river is also projected. Projected effluent concen.(mg/L) 5 600 1250 9.87 17.5 27 Est.mass loading(lbs/day) 8,247 17,181 412 730 1,126 Est.downstream R-3 river concentration(mg/L)at 600 cfs 2.61 2.66 2.71 Nitrate as Nitrogen Est.downstream R-3 river concentration(mg/L)at 1250 cfs 2.58 2.60 2.63 `5CP percentile statistic calculated using the following data set: 12 Data Period:January 2002—December 2002;Sample Size,n=12;Percent Detected Data=100% J at 10 SJR Flows E 8 600 cfs 6 1250 cfs c 4 —WQ0 m c 2- 0 U Q 9.87 17.5 27 WQCF Effluent Flow Rate(MGD) Figure 18: Projected Change in San Joaquin River Nitrate(as Nitrogen)Concentration at WQCF R- 3 with increasing WQCF Effluent Flowrate Comparison to Water Ouality Objective: The California Code of Regulation,Title 22 Primary MCL criterion for nitrate+nitrite(sum as nitrogen),incorporated into the Basin Plan by reference,is 10 mg/L. This Title 22 Primary MCL is the appropriate and most stringent water quality objective to apply to nitrate(as nitrogen)in the San Joaquin River. Estimated concentrations of nitrate(as nitrogen)in the San Joaquin River under critical and dry/below normal flow conditions show a slight increase,relative to the Title 22 Primary MCL,with an increase in WQCF effluent discharge from 9.87 MGD(ADWF)to 27 MGD(ADWF). The incremental change in nitrate(as nitrogen)concentration in the river is slight when increasing the WQCF discharge from the current permitted discharge of 9.87 MGD(ADWF)to the proposed 27 MGD(ADWF). Projected,median nitrate(as nitrogen)concentrations in the San Joaquin River are well below the Title 22 Primary MCL standard. City of Manteca Antidegradation Analysis 59 June 2007 City of Manteca Antidegradation Analysis 60 June 2007