ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

Home Browse Search

Table 4.9-13 Estimated Impact of Total Aluminum from WQCF Discharge in the San Joaquin River at WQCF R-3 Aluminum Total San Joaquin River Flowrate Manteca WQCF Effluent Flowrate (cubic feet per second) (million gallons per day) R-1 50th%concen.(pg/1)l 785.1 Projected effluent concen.(µg/1) 150 600 1250 9.87 17.5 27 Est.mass loading(lbs/day) 2,539 5,290 12.3 21.9 33.8 Est. downstream R-3 river concentration(µg/1)at 600 cfs 769.3 757.6 743.7 Est. downstream R-3 river concentration(µg/1)at 1,250 cfs 777.4 771.6 764.5 '50th percentile statistic calculated using the following data set: Data Period:January 2002—September 2004;Sample Size,n=14; Percent Detected Data= 100% Source:LWA 2007 The City prepared a WER study(City of Manteca 2007) and submitted the results of this study to the RWQCB. The results of the study recommended a WER of 22.7 for direct adjustment of the chronic objective(i.e., 22.7 times the current objective of 87µg/1)resulting in an effluent limit of 1,975 gg/1 for aluminum would be acceptable and sufficiently protective of the beneficial uses of the San Joaquin River. This WER would also be applicable to the corresponding acute objective. The WQCF discharge at full buildout(27 mgd)would have an average daily total aluminum concentration of 150 gg/1 at the point of discharge,which is substantially below the effluent limit identified in the WER study. Although the RWQCB has not adopted a new effluent limit for aluminum as of the date of publication of this EIR, available science indicates that effluent limits substantially greater than the proposed discharge concentrations under the project would be sufficiently protective of the beneficial uses of the San Joaquin River. Because the project's discharge concentrations of aluminum would be substantially below discharge concentrations shown by available scientific studies to be protective of water quality,the project would result in less-than-significant aluminum impacts. IMPACT Hydrology and Water Quality—Effects of Proposed Project Discharges on Electrical Conductivity 4.9-7 Concentrations in Receiving Waters.Because the project would result in minor increases in EC in the San Joaquin River at full buildout(27 mgd)and effluent concentrations would be below established EC water quality objectives during agricultural and nonagricultural seasons, the project would not result in significant EC water quality impacts. Therefore, the project's near-field EC impacts would be less than significant. Manteca WQCF NPDES self-monitoring data from the San Joaquin River at monitoring location R-1 (just upstream of the WQCF discharge) corresponding to dry/below normal water years were used to calculate an estimated impact of WQCF effluent electrical conductivity(EC)in the San Joaquin River under critical(600 cfs) and dry/below normal(1,250 cfs)river flows at the existing permitted discharge of 9.87 mgd and at proposed discharges of 17.5 mgd and 27 mgd. Due to the seasonal EC objectives contained in the Sacramento–San Joaquin Delta Basin Plan, available EC data were divided into two groups for the purpose of the present near-field analysis: April through August data set with a seasonal objective of 700 umhos/cm;(micromhos per centimeter– the standard measure of electrical conductivity in freshwater)and September through March data set with a seasonal objective of 1000 umhos/cm. 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 Board decisions and water quality control plans do not mention or consider treated effluent discharges as a source of salinity in the southern Delta(SWRCB 2005). The incremental change in near-field EC (measured at R-3, see Exhibit 4.9-1)in the San Joaquin River resulting from an increase in WQCF effluent discharged from the current permitted rate (9.87 mgd)to the proposed rate EDAW DER Hydrology and Water Quality 4.9-36 City of Manteca