ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Electrical Conductivity Electrical Conductivity(Sept.-Mar.) Data Availability: Manteca WQCF NPDES self-monitoring data from the San Joaquin River at R-1(just upstream of the WQCF discharge)corresponding to dry/below normal water years were 1200 used to calculate an estimated impact of WQCF effluent EC in the San Joaquin River under > 1000 critical(600 cfs)and dry/below normal(1250 cfs)river flows at a permitted discharge of 9.87 t— SJR Flows MGD(ADWF)and at proposed discharges of 17.5 MGD(ADWF)and 27 MGD(ADWF). 800 600 cfs Improved WQCF treatment processes are projected to produce treated effluent having an average 0 600 1250 cts EC of 825µmhos/cm. Eapp- _WQC` Results: The effect of an increase in WQCF discharge from 9.87 MGD(ADWF)to 27 MGD v 200 (ADWF)is appropriately addressed in the receiving water at well-mixed conditions downstream w 0 of the discharge. Due to the seasonal EC objectives contained in the Basin Plan,available 9.87 17.5 27 ambient EC data were divided into two groups for the purpose of the present near-field analysis: WQCF Effluent Flow Rate(MGD) an April through August data set,and a September through March data set. During critical and dry/below normal San Joaquin River flow conditions,an increase in WQCF effluent discharge will produce a minor increase in EC in the San Joaquin River downstream of the discharge Figure 9: Projected Change in San Joaquin River Electrical Conductivity at WQCF R-3 during during April through August relative to its seasonal objective of 700µmhos/cm,and will September through March with increasing WQCF Effluent Flowrate produce a slight increase in EC in the river during September through March relative to its seasonal objective of 1000µmhos/cm. These incremental increases in river EC observed when Comparison to Water Ouality Objective: The Basin Plan for the Delta establishes seasonal evaluating the April through August(agricultural season)and September through March(non- EC objectives in the San Joaquin River and southern Delta of 700µmhos/cm(April–August) agricultural season)time periods are shown in Figure 8 and Table 14,and Figure 9 and Table and 1000µmhos/cm(September–March). Estimated EC in the San Joaquin River under critical 15,respectively. and dry/below normal flow conditions shows a minor increase during April through August relative to the 700µmhos/cm objective,and a slight increase during September through March Electrical Conductivity(Apr.-Aug.) relative to the 1000µmhos/cm objective,with an increase in WQCF effluent discharge from 9.87 MGD(ADWF)to 27 MGD(ADWF). Under both seasonal EC objective scenarios(see Figure 8 800 and Figure 9)the projected median EC in the San Joaquin River is well below the seasonally- 700- relevant Basin Plan EC objective. r+^600 SJR Flows o E Evaluation: Salinity control issues in the Delta have been reviewed and addressed by the State c0 500 ri 600 cfs Water Board as far back as 1991,as described in the 1991 Delta Plan(SWRCB,1991). 0 400 ri 1250 cfs Subsequent State Water Board analyses of elevated salinity in the southern Delta presented in the E 300 WQO 1995 Bay-Delta Plan(SWRCB,1995)and Revised Water Right Decision 1641(SWRCB,2000) 13 200 conclude that salinity problems in the southern Delta are the result of many inter-related w 100 0 litconditions,including water diversions upstream of the Delta,water diversions within the Delta 9.87 17.5 27 for export and local use,high levels of salinity in irrigation return flows discharged to the Delta waterways and tributaries,groundwater inflow,seasonal flow variation,and tidal conditions. WQCF Effluent Flow Rate(MGD) Although discharge of treated wastewater to the Delta or its tributaries under an NPDES permit can marginally affect EC in the southern Delta,previous State Water Board decisions and water quality control plans do not mention or consider treated effluent discharges as a source of salinity Figure 8: Projected Change in San Joaquin River Electrical Conductivity at WQCF R-3 during April through August with increasing WQCF Effluent Flowrate in the southern Delta(SWRCB,2005). In regard to the present analysis,the incremental change in EC in the San Joaquin River due to an increase in WQCF effluent discharged from the current permitted rate(9.87 MGD(ADWF)) to the proposed rate(27 MGD(ADWF))is minor during the months of April through August (agricultural season)relative to the 700µmhos/cm objective,and slight during the months of September through March(non-agricultural season)relative to the 1000µmhos/em objective. City of Manteca Antidegradation Analysis 41 June 2007 City of Manteca Antidegradation Analysis 42 June 2007