ARCHIVED REPORTS_FEASIBILITY STUDY AND CORRECTIVE ACTION PLAN

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influence determined through testing and the coverage required in the three source areas, a DPE system would require 17 DPE wells. Based on this number of DPE wells, the total DPE system flow equates to a maximum 68 gpm (average 40 gpm assumed), which would require treatment and disposal. CRA evaluated three water disposal options for the proposed DPE system: sanitary sewer discharge, land disposal, and re- injection. Sanitary Sewer Discharge. The local Publicly Owned Treatment Works is owned and operated by the City of Stockton and includes both the wastewater collection system and wastewater treatment plant. A City of Stockton wastewater discharge permit is required for discharging treated groundwater to the sanitary sewer. Shell held a City of Stockton wastewater discharge permit for the former (now dismantled) groundwater treatment system at the subject site. However,treated groundwater has not been discharged to the sanitary sewer in several years. The discharge from the former treatment.system was not compliant with the TBA and lower explosive limit requirements of the discharge permit. It was determined that this treatment system could not comply with the permit requirements in its then current condition or with any upgrades. Therefore, the treatment system was shut down and off-hauling of untreated groundwater was initiated. CRA has stopped operation of other remediation systems for Shell in the City of Stockton as they also cannot comply with the City of Stockton wastewater discharge permit requirements. The City of Stockton wastewater discharge permit requires that treated groundwater not contain TBA (with a detection limit of 5.0 µg/L) or other oxygenates. TBA treatment technologies are limited and very expensive, especially at the higher flow rates expected at this site. Although it may be technically feasible to design a treatment system that can comply with this TBA discharge limit, the cost would be excessive if the design is based on non-detect TBA (which cannot be guaranteed). Furthermore, continuous operation would likely be disrupted routinely in order to maintain compliance with this discharge limit. Since DPE requires sustained dewatering of saturated soils for effective vapor extraction, these operational disruptions would cause recovery of the groundwater table and re-saturation of soils. This would reduce the effectiveness and increase the cost of DPE by lengthening the operational duration. Lastly, a treatment system designed for these parameters would not be an environmentally sustainable approach based on the excessive electrical usage,travel and transport to maintain operation, and waste disposal (carbon consumption and sewer or wastewater treatment plant capacity). These elements result in exorbitant greenhouse gas emissions. The design and operation of a DPE system to comply with the City of 241729(33) 14 CONESTOGA-ROVERS&ASSOCIATES