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installed in existing ground water monitoring wells or installed as a slurry in borings drilled below the water table Using ORCs to remediate the hydrocarbons in ground water typically requires 1 or more years, and depends on site conditions and water quality objectives Although conclusive field studies have not been completed, ORCs may reduce MTBE concentrations in ground water Cost-Effectiveness Because ORCs do not require system operation or maintenance, remediation using ORCs is easy and inexpensive The cost effectiveness of ORC installation for MTBE is unknown Recommendation- Because the objective is to safely and cost-effectively decrease hydrocarbon concentrations in ground water, oxygenation using ORCs appears to be a cost-effective and appropriate remedial technique for this site Cambria recommends installing ORCs in perimeter site wells to remediate the dissolved hydrocarbon plume in conjunction with periodic ground water extraction in the source area near the former tank complex Ground water extraction (GYVE) should move ground water from the perimeter of the site toward and through the source area After hydrocarbons have been removed from the source area near the old tank complex, ORCs may also be installed in source area wells Continued monitoring of DO, hydrocarbon, and MTBE concentrations will evaluate the effectiveness of ground water oxygenation using ORCs Ground Water Extraction System Installation This alternative uses GWE to remove contaminated ground water from the subsurface with above ground treatment of the influent stream and discharge of treated water to either sanitary or storm sewer This technology has been shown to be generally ineffective at mass removal and restoration of ground water quality objectives, and is typically implemented only when hydraulic control of a ground water contaminant plume is required, as with an MTBE problem in ground water that is flowing offsite The pump test showed that GWE should be able to provide hydraulic control across the site, even at a relatively low pumping rate Some underground piping was installed during the tank removal activities from wells RW-1 and MW-5 to the back of the station building to allow for easier system installation Cost-Effectiveness Although this alternative does not cost effectively remediate dissolved hydrocarbons, the alternative could provide migration control to prevent MTBE from spreading offsite The costs of system installation are relatively high - on the order of $40,000 to $50,000, and the discharge alternatives, which should have a large impact on the system costs, are not clear at . this time The City of Stockton Municipal Utilities Department is in the process of developing standards for discharge of MTBE to the local wastewater treatment plant 240-0783 22