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5-3 Groundwater Remediation The existing on-site monitoring and recovery system installed by GR and EMCON should be retained and utilized. No additional on-site monitoring or recovery wells are necessary. The permit required for discharging the water pumped by the recovery system into the RWCF sanitary sewer system should be renewed. Conversations with the RWCF personnel indicate that renewal of the discharge permit and continued pumping should not be a problem, as long as hydocarbon constituents in the water are below combustible levels. Soil Remediation Based on the soil and groundwater conditions at the site, two possible soil remediation techniques are discussed below. Both are considered to be applicable and feasible alternatives, but in situ aeration is recommended as the most effective means of soil remediation. ARCO and BC will evaluate the method which will be the most effective at the site. In-Situ Aeration. An in-situ aeration system is recommended as the most effective means of eliminating hydrocarbon vapors from the soil, as well as the groundwater beneath the site. It would consist of a system of vertical, manifolded, vapor extraction wells connected to a single vacuum system. The vacuum system would be located in the northwest corner of the site, as far as possible from residential areas. The vapors recovered through the system would be incinerated, adsorbed through carbon adsorption, or discharged directly to the atmosphere. An aeration permit must be obtained from the San Joaquin County Air Pollution Control District. Soil Flushing. An alternative to in situ aeration is soil flushing . This method involves using water to "flush" hydrocarbons out of the soil into the groundwater system. This method would be effective at this site because of the silty to sandy soils, the shallow groundwater , and the functioning recovery system. Additional Investigative Work In addition to the groundwater and soil remediation, the following investigative work is recommended for the site. Work Plan and Permits. Prior to performing additional investi- gative work at the site, a detailed work plan should be prepared in accordance with San Joaquin County requirements. Necessary permits would be obtained for drilling, encroachment, discharge, and aeration purposes. A work plan for additional investigative work is included as Appendix G.