ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

Home Browse Search

Iron (ADWF)to the proposed 27 MGD(ADWF). Projected,median dissolved iron concentrations in the San Joaquin River are well below the Basin Plan objective. Data Availability: Manteca WQCF NPDES self-monitoring data from the San Joaquin River at R-1(just upstream of the WQCF discharge)corresponding to a wet water year were used to Evaluation: The incremental change in dissolved iron concentration in the San Joaquin River calculate an estimated impact of WQCF effluent dissolved iron in the San Joaquin River under due to an increase in WQCF effluent discharged from the current permitted rate(9.87 MGD critical(600 cfs)and dry/below normal(1250 cfs)river flows at a permitted discharge of 9.87 (ADWF))to the proposed rate(27 MGD(ADWF))manifests itself as a slight decrease under MGD(ADWF)and at proposed discharges of 17.5 MGD(ADWF)and 27 MGD(ADWF). critical and dry/below normal flow conditions due to the lower effluent concentration of the Ideally,an R-1 dissolved iron data set corresponding to dry/below normal water years would be dissolved metal relative to the river. Dissolved iron mass loading to the river is projected to be used for the present analysis,but such a data set was not available. Improved WQCF treatment slight relative to existing in-stream loads. Additionally,projected dissolved iron concentrations processes are projected to produce treated effluent having an average total iron concentration of in the San Joaquin River are well below the Basin Plan objective of 300µg/L. 50µg/L. For the purpose of the current analysis,and to be conservative,all iron present in WQCF treated effluent is assumed to be in the dissolved form. Table 21: Estimated Impact of Dissolved Iron from WQCF Discharge in the San Joaquin River at WQCF R-3 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 Iron,Dissolved San Joaquin River Manteca WQCF Effluent of the discharge. During critical and dry/below normal San Joaquin River flow conditions,an R-1 50t0%concen.(µg/L)* 61.5 Flowrate(cfs) Flowrate(MGD ADWF) increase in WQCF effluent discharge will slightly decrease dissolved iron concentration in the Projected effluent concen.(µg/L) 50 600 1250 9.87 17.5 27 San Joaquin River,relative to the Basin Plan objective,downstream of the discharge as shown in Est.mass loading(lbs/day) 199 414 4.1 7.3 11.3 Figure 15 and Table 21. A slight increase in dissolved iron mass loading to the river is also projected. Est.downstream R-3 river concentration(pg/L)at 600 cfs 61.2 61.0 60.8 Est.downstream R-3 river concentration(µg/L)at 1250 cfs 61.4 61.3 61.1 *50"Percentile statistic calculated using the following data set: Iron,Dissolved Data Period:November 2005—July 2006;Sample Size,n=10;Percent Detected Data=60 400 J 300 SJR Flows c 600 cfs 0 200 1250 cfs c —WQO u 100 c 0 U 0 9.87 17.5 27 WQCF Effluent Flow Rate(MGD) Figure 15: Projected Change in San Joaquin River Dissolved Iron Concentration at WQCF R-3 with increasing WQCF Effluent Flowrate Comparison to Water Ouality Objective: The Basin Plan objective for dissolved iron for the Delta is 300µg/L,expressed as the dissolved fraction(Basin Plan,Table III-1). This Title 22 Secondary MCL is the appropriate and most stringent water quality objective to apply to iron in the San Joaquin River. Estimated concentrations of dissolved iron in the San Joaquin River under critical and dry/below normal flow conditions 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). The incremental change in dissolved iron concentration in the river is slight when increasing the WQCF discharge from the current permitted discharge of 9.87 MGD City of Manteca Antidegradation Analysis 53 June 2007 City of Manteca Antidegradation Analysis 54 June 2007