ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Appendix B: Streeter-Phelps Dissolved Oxygen Where H is calculated in meters for the desired flowrate,Q expressed in cfs. The average cross sectional velocity is calculated using a nominal channel width of 100 meters as follows: Analysis u-Q-(0.02832m�,) Using the Streeter-Phelps model,the float time downstream to where the minimum DO will 100•H occur can the calculated using the equation as follows(Tchobanoglous and Schroeder,1985): Performing the above calculations allows the calculation of the critical deficit,D.,as follows: 21 1"[k, 1-D,(k2-k) if� k2 1-D;(k2-k�� D; © if O"=0 >1 O. k -k k kL; k kL; D�= k Le else "= 0 if k(1-D,(k� k�1<1 k2 J The minimum DO is then calculated as follows: Where O;,is the float time in days to the location of minimum DO concentration. The variables DOS,;,,=130_-D, Di and Li are the combined river and discharge initial DO deficit and ultimate oxygen demand, respectively. The deficit is the difference between the oxygen saturation concentration for the river temperature and the estimated DO concentration of the mixed river and effluent. Values for oxygen saturation are a function of temperature and are from Tchobanoglous and Schroeder (1985). The variables k and k2 represent the decay rate of BOD constituents and the reaeration rate,respectively. The BOD decay rate at 20°C of 0.10 1/d is the value determined for the San Joaquin River in Chen and Tsai(2002). The temperature dependence of the decay rate is represented as an Arrhenius relationship using the theta value of Chen and Tsai(2002)as follows: kT=k,o.1.04(T-20) Where kT is the decay rate at a desired temperature,T(in°C),given the decay rate at 20°C,k2o. The reaeration rate for the San Joaquin River is determined using the empirical formula from Tchobanoglous and Schroeder(1985)as follows: 294(D,r uy' k2= Hx Where the average depth and cross sectional velocity are represented as H and u,respectively. The molecular diffusivity of oxygen at a given temperature,Dir,is calculated as follows: Dir =Dim.1.037(T-20) Where Dip =1.760.10'm2/d(Tchobanoglous and Schroeder,1985). The bathymetric and flowrate transect data collected for the Thermal Plan Exception analysis (LWA,2006a)is used to determine relationships between San Joaquin River flowrate and the average depth and cross sectional velocity. The river depth is estimated using a Manning's equation developed using the data collected for the Tbermal Plan Exception analysis(LWA, 2006a),and is as follows: H=2.0• Q 1,412 City of Manteca Antidegradation Analysis 127 June 2007 City of Manteca Antidegradation Analysis 128 June 2007