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Cyanide Evaluation: The incremental change in total cyanide concentration in the San Joaquin River due <br /> to an increase in WQCF effluent discharged from the current permitted rate(9.87 MGD <br /> Data Availability: Manteca WQCF NPDES self-monitoring data from the San Joaquin River at (ADWF))to the proposed rate(27 MGD(ADWF))is slight and below the magnitude of change <br /> R-1(just upstream of the WQCF discharge)corresponding to dry/below normal water years were that could be reliably measured in the field. Similarly,the projected increase in total cyanide <br /> used to calculate an estimated impact of WQCF effluent total cyanide in the San Joaquin River mass loading to the river is also slight. Additionally,projected,median total cyanide <br /> under critical(600 cfs)and dry/below normal(1250 cfs)river flows at a permitted discharge of concentrations in the San Joaquin River are well below the CTR freshwater chronic objective of <br /> 9.87 MGD(ADWF)and at proposed discharges of 17.5 MGD(ADWF)and 27 MGD(ADWF). 5.2 pg/L. <br /> The treatment plant's new UV disinfection process is projected to produce treated effluent <br /> having an average total cyanide concentration of 1 pg/L. Table 20: Estimated Impact of Total Cyanide from WQCF Discharge in the San Joaquin River at <br /> Results: The effect of an increase in WQCF discharge from 9.87 MGD(ADWF)to 27 MGD WQCF R3 <br /> (ADWF)is appropriately addressed in the receiving water at well-mixed conditions downstream Cyanide,Total San Joaquin River Manteca WQCF Effluent <br /> of the discharge. During critical and dry/below normal San Joaquin River flow conditions,anm Flowrate(cfs) Flowrate(MGD ADWF) <br /> increase in WQCF effluent discharge will slightly increase total cyanide concentration in the San R-1 50 %concen.(µg/L)* 0.28 <br /> Joaquin River,relative to its CTR objective,downstream of the discharge as shown in Figure 14 Projected effluent concen.(µg/L) 1 600 1250 9.87 17.5 27 <br /> and Table 20. A slight increase in total cyanide mass loading to the river is also projected. Est.mass loading(lbs/day) 1 2 0.08 0.15 0.23 <br /> Est.downstream R-3 river concentration(µg/L)at 600 cfs 0.30 0.31 0.33 <br /> Cyanide,Total Est.downstream R-3 river concentration(µg/L)at 1250 cfs 0.29 0.30 0.30 <br /> *50"percentile statistic calculated using the following data set: <br /> Data Period:January 2002—December 2002;Sample Size,n=12;Percent Detected Data=25 <br /> 6 <br /> J <br /> ar 5 SJR Flows <br /> 3 <br /> 0 4- 600 cfs <br /> 3 iiiiiiin 1250 cfs <br /> 2 —WQO <br /> c 1 <br /> 0 <br /> U <br /> 0- <br /> 9.87 17.5 27 <br /> WQCF Effluent Flow Rate(MGD) <br /> Figure 14: Projected Change in San Joaquin River Total Cyanide Concentration at WQCF R-3 with <br /> increasing WQCF Effluent Flowrate <br /> Comparison to Water Ouality Obiective: The CTR freshwater chronic objective for total <br /> cyanide as it applies to the San Joaquin River is 5.2 pg/L. The CTR total cyanide objective is <br /> not hardness dependent as are some other CTR metals objectives. Estimated concentrations of <br /> total cyanide in the San Joaquin River under critical and dry/below normal flow conditions show <br /> a slight increase,relative to the CTR objective,with an increase in WQCF effluent discharge <br /> from 9.87 MGD(ADWF)to 27 MGD(ADWF). The incremental change in total cyanide <br /> concentration in the river is slight when increasing the WQCF discharge from the current <br /> permitted discharge of 9.87 MGD(ADWF)to the proposed 27 MGD(ADWF). Projected, <br /> median total cyanide concentrations in the San Joaquin River are well below the CTR freshwater <br /> chronic objective. <br /> City of Manteca Antidegradation Analysis 51 June 2007 City of Manteca Antidegradation Analysis 52 June 2007 <br />