ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Manganese (1250 cfs)with increasing WQCF discharge. The incremental change in dissolved manganese concentration in the river is slight when increasing the WQCF discharge from the current Data Availability: Manteca WQCF NPDES self-monitoring data from the San Joaquin River at permitted discharge of 9.87 MGD(ADWF)to the proposed 27 MGD(ADWF)under the critical R-1(just upstream of the WQCF discharge)corresponding to a wet water year were used to flow condition. Projected,median dissolved manganese concentrations in the San Joaquin River calculate an estimated impact of WQCF effluent dissolved manganese in the San Joaquin River are well below the Basin Plan objective. under critical(600 cfs)and dry/below normal(1250 cfs)river flows at a permitted discharge of 9.87 MGD(ADWF)and at proposed discharges of 17.5 MGD(ADWF)and 27 MGD(ADWF). Evaluation: The incremental change in dissolved manganese concentration in the San Joaquin Ideally,an R-1 dissolved manganese data set corresponding to dry/below normal water years River due to an increase in WQCF effluent discharged from the current permitted rate(9.87 would be used for the present analysis,but such a data set was not available. Improved WQCF MGD(ADWF))to the proposed rate(27 MGD(ADWF))manifests as a very slight decrease treatment processes are projected to produce treated effluent having an average total manganese under critical flow conditions(600 cfs)due to the lower effluent concentration of the dissolved concentration of 10µg/L. For the purpose of the current analysis,and to be conservative,all metal relative to the river. No measurable change in the river's dissolved manganese manganese present in WQCF treated effluent is assumed to be in the dissolved form. concentrations are projected during flow conditions representative of dry/below normal water years(1250 cfs)as WQCF effluent discharge increases from 9.87 MGD(ADWF)to 27 MGD Results: The effect on an increase in WQCF discharge from 9.87 MGD(ADWF)to 27 MGD (ADWF). Dissolved manganese mass loading to the river is projected to be slight relative to (ADWF)is appropriately addressed in the receiving water at well-mixed conditions downstream existing in-stream loads. Additionally,projected,median dissolved manganese concentrations in of the discharge. During critical San Joaquin River flow conditions(600 cfs),an increase in the San Joaquin River are well below the Basin Plan objective. WQCF effluent discharge will slightly decrease dissolved manganese concentration in the San Joaquin River,relative to its Basin Plan objective,downstream of the discharge as shown in Table 22: Estimated Impact of Dissolved Manganese from WQCF Discharge in the San Joaquin Figure 16 and Table 22. Estimated river concentrations associated with dry/below normal flow River at WQCF R-3 conditions(1250 cfs)show no measurable change in dissolved manganese concentrations in the San Joaquin River with increasing WQCF effluent discharge. A slight increase in dissolved Manganese,Dissolved San Joaquin River Manteca WQCF Effluent manganese mass loading to the river is also projected. R-1 50"%concen.(µg/L)* 14.3 Flowrate(cfs) Flowrate(MGD ADWF) Projected effluent concen.(µg/L) 10 600 1250 9.87 17.5 27 Manganese,Dissolved Est.mass loading(lbs/day) 46 96 0.8 1.5 2.3 Est.downstream R-3 river concentration(µg/L)at 600 cfs 14.2 14.1 14.0 60 Est.downstream R-3 river concentration(µg/L)at 1250 cfs 14.2 14.2 14.2 J `50'percentile statistic calculated using the following data set: 50 SJR Flows Data Period:November 2005—July 2006;Sample Size,n=10;Percent Detected Data=90 c 40 600 cfs 0 30 1250 cfs 20 —WOO e 10 Q 0 9.87 17.5 27 WQCF Effluent Flow Rate(MGD) Figure 16: Projected Change in San Joaquin River Dissolved Manganese Concentration at WQCF R-3 with increasing WQCF Effluent Flowrate Comparison to Water Quality Objective: The Basin Plan objective for dissolved manganese for the Delta is 50 pg/L,expressed as the dissolved fraction(Basin Plan,Table I11-1). Estimated concentrations of dissolved manganese in the San Joaquin River under critical flow conditions (600 cfs)show a slight decrease,relative to the Basin Plan objective,with an increase in WQCF effluent discharge from 9.87 MGD(ADWF)to 27 MGD(ADWF). No measurable change in dissolved manganese river concentration is projected under drylbelow normal flow conditions City of Manteca Antidegradation Analysis 55 June 2007 City of Manteca Antidegradation Analysis 56 June 2007