ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Table 28: Summary of Peak Percent Cross Section with greater than 1°F Comparison to Water Quality Objectives: The thermal plume from the 9.87 MGD(ADWF) Temperature Differential for Fall Critical Water Year Flowrates for Side Bank discharge does not comply with all objectives of the Thermal Plan. The analysis of the thermal Discharge at 27 MGD(ADWF)(RMA 2006) plume reveals that the temperature differential between the effluent and the river may slightly Reduction from Peak exceed 20 OF for brief periods,but utilizing timed discharge during periods of low river flow a 1 Background effluent cross-sectional OF differential is limited to less than 25%of the river's cross section. Additionally,there is a San Joaquin River Discharge temperaturei'i area impacted by limited zone where the temperature differential exceeds 4 OF. However,the fisheries analysis of temperature(°F) temperature(°F) (°F) 1°F or more the thermal plume revealed that there would be no significant impact on sensitive fish species 62 65 11 19.0% and the impact would be limited to avoidance behavior of migrating salmonids(LWA,2006a). 62 66 10 28.2% A request to evaluate objective 5 A.La as monthly average,and an exception limited to objective 62 67 9 35.1% S.A.Lc is being sought to provide relief and allow compliance with the Thermal Plan. 62 68 8 39.7% For the side bank discharge,increasing the WQCF discharge rate above 9.87 MGD(ADWF)will result in the 1 OF temperature differential over less than 25%of the cross section provision of the (1) WQCF Effluent Temperature 76°F thermal plan to be exceeded. As the discharge rate is increased the zone of water greater than 4 OF above ambient river temperature grows laterally and vertically;and extends further For the case of a diffuser,the differential between the ambient river and centerline of the fully downstream. To meet the Thermal Plan objectives,the WQCF effluent would need to be cooled developed plume can be calculated from the differential between the discharge and ambient river to within 3-4 of of the ambient river. temperatures and the in-plume dilution(RMA,2006). The procedure is detailed in Appendix A. Potential diffuser designs likely would extend greater than 25%of the channel width. Without The required effluent temperature differentials above the ambient river temperature to meet the 1 additional cooling of the WQCF effluent,utilizing a diffuser will cause exceedance of both the 1 OF temperature above ambient over less than 25%of the cross section objective in the Thermal OF temperature differential over less than 25%of the cross section,and the 4 OF differential Plan for the WQCF project flowrates are listed in Table 29. anywhere in the river. If the WQCF effluent is cooled to within 5 OF of the ambient,the 1 OF temperature differential over less than 25%of the cross section will be met,but a small footprint Table 29: Maximum Increment between Effluent Discharged via Diffuser and where the plume is developing will exceed the 4 OF temperature differential objective. By Ambient River Temperature for a 1°F Differential between Thermal Plume and the cooling the effluent to within 4 OF of the ambient river,the discharge would meet all objectives Ambient River(RMA 2006) of the Thermal Plan. Maximum Temperature Evaluation: The Thermal Plan objectives are slightly exceeded for the currently permitted Minimum Initial Dilution Increment(Taff—Tup,tr,,,,)(°F) Flowrate (parts river water per 1 part for 1°F increase over<25% discharge of 9.87 MGD(ADWF);however,an evaluation of the impacts of the thermal plume (MGD ADWF) wastewater) cross-section reveals that there are no significant impacts of the plume and a limited exception is being sought 9.87 11 12 for the WQCF. Increasing the effluent flowrate will increase the thermal plume,resulting in exceedance of both the 1 OF temperature differential over less than 25%of the cross section,and 17.5 6 7 4 OF differential anywhere objectives in the Thermal Plan. Because the Thermal Plan objectives 27 4 5 are exceeded,the characteristics of the WQCF plume need to be evaluated for the level of impact on aquatic life. If the plume is found to not impact the aquatic life within the San Joaquin River, then an exception to the Thermal Plan will be required. If the plume is determined to impact While the assumption of a fully developed plume will not affect the analysis for the 1 OF aquatic life in the San Joaquin River,then the City is prepared to design,construct,install,and temperature differential between the centerline of the plume and the ambient river for a cross operate a cooling tower that cools treated effluent prior to its discharge into the San Joaquin section,the 4 OF temperature differential would have to be met at the diffuser to comply with the River. The cooling tower would be confirmed to perform at final design specifications prior to Thermal Plan. As the analysis reveals,to meet the 1 OF temperature differential over 25%of any operation of the WQCF at the proposed expanded capacity. Implementation of a cooling tower transect,the effluent would need to be cooled to within 5 OF of the ambient river;to ensure the would act to sufficiently reduce the modeled thermal impacts of the WQCF's non-cooled temperature in the plume drops to within 1 OF of the ambient over the short distance required to effluent plume resulting in no significant adverse thermal effects on fisheries and aquatic fully develop the plume. If it can be shown that a maximum 5 OF difference between the resources as a result of the planned increase in WQCF discharge capacity from the current discharge and ambient river does not impact aquatic life,a Thermal Plan Exception to objective permitted rate(9.87 MGD(ADWF))to the proposed rate(27 MGD(ADWF)). c.would be required. Either a Thermal Plan Exception could be sought,or the effluent could be cooled to within 4 OF of ambient river temperature,resulting in compliance with all objectives of the Thermal Plan. City of Manteca Antidegradation Analysis 69 June 2007 City of Manteca Antidegradation Analysis 70 June 2007