ARCHIVED REPORTS_FEASIBILITY STUDY AND CORRECTIVE ACTION PLAN

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Stockton s wastewater discharge permit in effect trades one environmental issue for another. For the reasons discussed, discharge of treated groundwater to the sanitary sewer is not a viable option. Land Disposal: Disposal of treated groundwater to land under General Order #R5-2003-004 (General Order) was also considered. The General Order's TBA discharge limit is 12 µg/L, which is similar enough to less than 5.0 µg/l, that the same treatment design and operational issues associated with sanitary sewer disposal also apply to land disposal. Green house gas emissions are lower for the land disposal option since wastewater treatment plant capacity is not being consumed. However, all the other elements remain the same. The electrical usage, travel and transport to maintain operation, and waste disposal (carbon) is still considered excessive and not environmentally sustainable. The General Order requirements to install a disposal area monitoring network and the associated monitoring requirements increase the carbon footprint of this option even further. For the reasons discussed, discharge of treated groundwater to land is not a viable option. Re-Injection: The third option considered was re-injection of treated groundwater back into the center of the contaminant plume. Under this scenario, CRA would request approval of discharge limits higher than those listed under RWQCB General Order#R5-2008-0149 (waste discharge requirements [WDR]) in consideration of background contaminant levels. It has already been determined through correspondence (electronic correspondence dated January 16, 2009 from RWQCB staff) with the RWQCB that permit limits under the General Order are not negotiable. Therefore, site-specific WDR would be necessary to allow negotiation of site-specific discharge limits. To determine the injection rate for a well penetrating an unconfined aquifer, the "Theis equation' for non-equilibrium flow was used3. Site-specific data were used in the calculations that were generated from the DPE pilot test. The calculations show an injection rate of approximately 3 gpm per well. Theoretically, 14 injection wells would be needed to return the design withdrawal of 40 gpm to the aquifer. However, actual recharge rates are seldom equal to theoretical calculations due to various factors such as water quality, turbidity, water temperature, biological buildup, 3 Driscoll,F.G.,1986. Groundwater and Wells,Johnson Division,St.Paul,Minnesota pp.218,771-772 241725(33) 15 CONESTOGA-ROVERS&ASSOCIATES