ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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FAR-FIELD METHODOLOGY Modeling Approach DWSC DO: To evaluate the DO concentrations in the DWSC due to the proposed project,the modeling approach of the 2000 Draft Environmental Impact Report for the The far-field water quality effects of the currently permitted WQCF design capacity(9.87 MGD WQCF Phase III/IV Expansion Project(2000 DEIR;EDAW 2000)was extended to consider the (ADWF))and the proposed WQCF design capacity phased increases of 17.5(ADWF)and 27 increased discharge of the current proposed project. The DO simulations performed for the 2000 MGD(ADWF)are calculated using a mass balance model in conjunction with a hydrologic DEIR were designed to determine the expected change in conditions in the ship channel and model of water movement through the Sacramento-San Joaquin River Delta(RMA,2006). turning basin. To investigate DO,a dynamic link-node modeling system was used to calculate the impact of increasing WQCF plant capacities and level of treatment on DO in the DWSC. In Far-Field Analysis and Results the analysis,the base case effluent condition for the modeling was 6.0 MGD(ADWF)with 20 The fraction or percentage of WQCF effluent present at various locations within the Delta was mg/L for BODS and 22 mg/L as N ammonia. Two phases were considered for the Manteca modeled in order to provide an indication of the far-field impacts of the proposed project on expansion:8.11 MGD(ADWF)plant capacity and 9.87 MGD(ADWF). Both cases included Delta water quality. Six locations within the Delta(see Figure 3 and Figure 27)were chosen as advanced treatment resulting in effluent concentrations of 20 mg/L for BODS and 2.0 mg/L as N far-field sites for the evaluation of water quality impacts due to increased WQCF discharge. for ammonia. The incremental change in DO was calculated by sequentially running the model Sites were selected to provide pre-and post-project water quality estimates at several drinking for the base case and the two phases;and subtracting the DO results for the DWSC. To recreate water export locations and the DWSC. Due to the limited availability of concurrent water the regression model the concentrations and flows used in the 2000 DEIR are represented here. quality data sets at the various Delta locations of interest,only EC,nitrate,DOC,and DO were The differences in loading between the 2000 DEIR and the discharge scenarios are used to selected for far-field analysis. EC is a useful water quality parameter because it serves as a calculate the expected difference in DWSC DO. surrogate for salts,while nitrate and DOC are constituents of concern for the treatment of In the analysis,the predicted differences in DWSC DO concentrations were due to the drinking water. To estimate far-field EC,nitrate,and DOC concentrations,the Delta hydrologic differences in loading of oxygen-affecting compounds from the two effluent flowrates. For the model is used to calculate the percent contribution of WQCF effluent at the various Delta model,investigators assumed a BODS to BOD„it factor of 2.5. The investigation did not model locations. DO is treated separately from the other constituents in the current analysis because the the nitrogen cycle explicitly. Instead,an assumed ammonia-to-BOD„tt factor of 4.57 was applied physical transfer of oxygen from the atmosphere and the biological consumption of oxygen in the model. during respiration greatly affect the concentration of DO. DO can not be considered conservative,and the area of greatest concern for this parameter is the DWSC. The calculated In the 2000 DEIR,the difference in DWSC DO was calculated in response to increasing Manteca effluent fractions facilitate the use of a mass balance model to estimate changes in the selected effluent discharge rates from 6.0 to 8.11 MGD(ADWF),and from 6.0 to 9.87 MGD(ADWF). water quality parameters due to an increase in WQCF discharge. Historic Delta water quality The 6.0 MGD(ADWF)baseline case corresponds to conditions before nitrification- data and historic Manteca effluent data are then used to estimate water quality in the Delta under denitrification was operational at the WQCF. For the 6.0 MGD(ADWF)case,the concentration two WQCF discharge scenarios:17.5 MGD(ADWF)and 27 MGD(ADWF). of BODutt was 151 mg/L due to the ammonia concentration of 22 mg/L as N typical of the discharge. For the 8.11 and 9.87 MGD(ADWF)cases,the conversion factors allowed the total Dissolved Oxygen Manteca effluent BODutt concentration to be calculated as BODutt=20 mg/L(2.5)+2.0 mg/L Two important aspects of DO in the San Joaquin River should be analyzed as WQCF discharge (4.57)=59.1 mg/L. Under the present analysis,current and projected WQCF effluent will have to the river increases:(1)the change in DO at the DWSC,and(2)the minimum DO average BODS of 7 mg/L and ammonia of 1.5 mg/L as N,allowing the total ultimate oxygen concentration downstream of the outfall,considering the ambient conditions above the outfall demand to be calculated as BODuit=7 mg/L(2.5)+1.5 mg/L(4.57)=24 mg/L. Combining the and the characteristics of the WQCF effluent(i.e.an oxygen sag analysis). BOD.It concentration with the effluent flowrate yields the load of total ultimate oxygen demand discharged to the San Joaquin River. The effluent load of total ultimate oxygen demand DO concentrations in the DWSC are historically subject to severe depression under low river discharged by the WQCF is presented graphically as a function of ADWF in Figure 23. As seen flow conditions that may result in a DO concentration below the minimum objective of 5 mg/L. in the figure,WQCF treatment improvements have drastically reduced the load of total ultimate In January 2005,the Central Valley Regional Water Quality Board(Regional Water Board) oxygen demand to the river,with the load discharged under the projected build-out flowrate of adopted a Total Daily Maximum Load(TMDL)for DO in the Stockton DWSC. Because of 27 MGD(ADWF)being less than the load discharged prior to nitrification-denitrification of the sufficiently large data gaps leading to an unresolved linkage analysis,the TMDL was adopted effluent when the discharge flowrate was 6.0 MGD(ADWF). with a phased implementation allowing the needed field and modeling studies to be performed From the near-field analysis,the San Joaquin River at RI BOD5 is 5.26 mg/L and the summer by December 2009 before revisiting the waste load and load allocations for specific sources. and winter ammonia concentrations are 0.13 and 0.08 mg/L as N,respectively. The The minimum DO concentration downstream of the WQCF outfall is important to investigate corresponding total ultimate load carried by the San Joaquin River upstream of the WQCF is because the full expression of oxygen demand,with the deepest sag in DO concentrations,is 92,600 lb/d in the summer and 91,100 lb/d in the winter for the dry/below normal river flowrate potentially far downstream from the WQCF. of 1,250 cis. City of Manteca Antidegradation Analysis 71 June 2007 City of Manteca Antidegradation Analysis 72 June 2007