SITE INFORMATION AND CORRESPONDENCE_CASE 2

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REGIONAL WATER BOARD RESPONSE (SWRCB/OCC File A-1846(a) and A-1846(b)) -9- PETITIONS FOR REVIEW OF Vim,E DISCHARGE REQUIREMENTS `j ORDER NO. R5-2007-0036 (NPOES NO. CA0079154) AND TIME SCHEDULE ORDER NO. R5-2007-0037 CITY OF TRACY, WASTEWATER TREATMENT PLANT would require the implementation of reverse osmosis, while these actions and TMDLs are pending, is inconsistent with the Manteca order. Considering the actions by the Regional Water Board to develop a new salinity policy for the Central Valley and based on the fact that the Discharger could not reasonably b6 expected fo achieve compliance with final salinity WQBELs within the five year life of the Order, on 4 August 2006, Regional Water Board staff recommended for adoption a proposed Order that did not include final WQBELs for salinity. Instead, the proposed Order included an interim performance-based effluent limitation for EC and required the Discharger to implement measures to reduce the salinity in its discharge to Old River. The proposed Order required the Discharger develop and implement a pollution prevention plan for salinity, required an submittal of annual reports demonstrating its efforts to reduce salinity, and established an intermediate salinity goal of 1350 pmhos/cm as EC to be achieved during the permit term. In addition, the proposed Order included a requirement to study the affects of the saline discharge in the South Delta and a reopener provision to allow modification of the permit requirements, if necessary. The Regional Water Board held a lengthy hearing on the proposed Order at the August 2006 Regional Water Board meeting, with salinity issues being the major topic of testimony and Board discussion. The hearing was continued pending a better assessment of the impacts of the discharge on Delta salinity and development of alternative means of regulating salinity for Regional Water Board consideration. The Regional Water Board was concerned with the possible impacts of the discharge without requiring final WQBELs, especially considering the impaired nature of the southern Delta, and directed staff to work with the Discharger, the Department of Water Resources (DWR), and other stakeholders to model the affects of the discharge in the southern Delta. It was suggested that DWR's Delta Simulation Model II (DSM2), which has been used extensively for the South Delta Improvements Project (SDIP), could be used for this purpose. A stakeholder group that included staff from the City of Tracy, Mountain House Community Services District, South Delta Water Agency, CSPA, DWR, and the Regional Water Board was formed to develop appropriate scenarios for running the DSM2 model. The model was run under reasonable worst-case conditions, with temporary barrier operations to evaluate current conditions and with permanent operable gates to evaluate future conditions. Attachment H of the Order R5-2007-0036 provides a detailed description of the modeling scenarios. The DSM2 modeling demonstrated that even under reasonable worst-case conditions the Tracy discharge has limited impacts on the salinity problem in the southern Delta (see Figure 1, below). Furthermore, the Order includes an interim performance-based effluent limitation for total dissolved solids (TDS) that limits the annual mass loading of TDS to current levels. This mass loading limitation will require the EC concentration to decrease as the . discharge flow rate increases, which is expected to occur as the Discharger increases it use of a new, less saline water supply. The DSM2 modeling output predicts reduced EC impacts in the southern Delta as the City of Tracy discharge increases, due to the reduction in the concentration of EC (see Table 2).