ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Two characteristics were analyzed to evaluate potential effects of WQCF discharges on dissolved oxygen(DO) concentrations in the San Joaquin River: (1)the change in DO at the Stockton deep water ship channel(DWSC), and(2) an oxygen sag analysis,the minimum DO concentration downstream of the outfall taking into consideration the ambient conditions above the outfall and the characteristics of the WQCF effluent. Because the link between WQCF discharge and the water quality in the DWSC is not direct and is influenced by natural(tides)and anthropogenic (barrier operation,dam releases)mechanisms,the model was run for 6.0, 8.11, and 9.87 mgd discharge conditions and the paired outputs were used to form a regression between the modeled change in DWSC DO corresponding to the change in WQCF load of total ultimate oxygen demand. The regression equation was used to evaluate the future change in DWSC DO due to the proposed project. The analysis showed that for both Phase 1 and 2,the dissolved oxygen concentration in the Stockton DWSC would be greater at the 27 mgd buildout than with the current effluent. The results are shown in Table 4.9-16. The far left column represents the DO concentrations in the SDWSC resulting from nondischarge San Joaquin River and Delta conditions (e.g. temperature,BOD load,tides, export rates, etc.)influencing DO,combined with a WQCF discharge rate of 6 mgd. The subsequent columns represent the same nondischarge conditions,but with WQCF discharging under the currently permitted conditions and flowrate of 9.87 mgd, and the buildout flowrates of 17.5 and 27 mgd. For example, for the same nondischarge conditions, a SDWSC DO concentration of 5.0 mg/l at 6 mgd would actually increase to 5.22 mg/1 at 9.87 mgd, and decrease to 5.11 mg/l at 17.5. It would be almost the same at 27 mgd as at 5 mgd(5.02 vs. 5.00 mg/l,respectively) Table 4.9-16 Modeled Stockton Deep Water Shipping Channel Dissolved Oxygen Amounts (in mg/1) and Change from Currently Permitted Levels 6.0 mgd 9.87 mgd 17.5 MGD(Phasel) 27 MGD(Phase 2) DO in SDWSC DO in SDWSC DO in SDWSC Difference from 9.87 MGD DO in SDWSC Difference from 9.87 MGD 4.00 4.22 4.11 -0.11 4.02 -0.20 5.00 5.22 5.11 -0.11 5.02 -0.20 6.00 6.21 6.11 -0.10 6.02 -0.19 7.00 7.21 7.11 -0.10 7.02 -0.19 8.00 8.20 8.10 -0.10 8.02 -0.18 9.00 9.20 9.10 -0.10 9.02 -0.18 mgd=million gallons per day mg/I=milligrams per liter(parts per million) DO=dissolved oxygen SDWSC=Stockton Deep Water Shipping Channel Source:LWA 2007 The Streeter-Phelps model was used to estimate the dissolved oxygen sag downstream of the WQCF discharge (See Appendix B in LWA 2007 for a detailed description of the model). The results generated from the model were utilized to evaluate the relative impact of increasing the WQCF discharge rate. The minimum DO downstream of the discharge was calculated for the analysis to evaluate the impact of the project above the currently permitted discharge (9.87 mgd). The near field analyses R-1 concentrations of 5.26 mg/l BOD and 0.13 mg/1 as N ammonia were utilized in the DO analyses. The results were not appreciably affected by the seasonality of ammonia and,therefore,the higher summer value was used as a conservative number for the minimum DO analysis. As shown in Exhibit 4.9-5,the incremental change in minimum river DO concentrations is limited to less than 0.1 mg/l between the currently permitted discharge rate of 9.87 mgd and projected build-out of 27 mgd. For both the DWSC DO and minimum DO downstream from the WQCF discharge,the proposed project would not affect DO concentrations by more than 0.2 mg/l. Because the load of biologically oxidizable material carried EDAW DER Hydrology and Water Quality 4.9-46 City of Manteca