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Remedial Action Plan RE: 425 W. Larch Street, Tracy, CA October 1 , 2008 W&A Project No, FMI-08-001 Page 9 of 11 soil vapors and groundwater are removed from the subsurface, they are partitioned in an air/water separator. The hydrocarbon-laden vapors and groundwater are then channeled to separate treatment systems. Soil vapor is typically treated with a thermal or catalytic oxidizer; groundwater is typically treated using GAC vessels prior to discharge under a sewer or storm drain permit. As previously discussed, a pump test has shown that wells screened across fine-grained soils (5 to 20 feet bgs) could sustain a pumping rate of 2 gpm with an ROI of approximately 25 feet. This data appears to indicate that subsurface conditions may be favorable for the application of DPE. Given the ability to attain higher groundwater extraction rates in wells screened from 5 to 20 feet bgs, which may allow for air movement through the smear zone, DPE may be very effective. W&A anticipates installation of two new wells and use of existing wells to complete DPE at the site. Based on W&A' s experience implementing DPE technology at similarly impacted service stations, the time-frame to mitigate subsurface petroleum hydrocarbon impact can vary from approximately 3 to 4 years. The cost for design, construction, implementation, operation and maintenance (for a 3 year period) of a DPE system, and groundwater monitoring for an additional 3 years, is estimated to be approximately $583 ,000, assuming adequate power is readily available to install and operate the system. 5.6 Chemical Oxidation (using Ozone) Chemical oxidation involves injection of oxidants such as ozone (03), hydrogen peroxide, potassium permanganate, etc. into the subsurface using specially designed wells or regular groundwater monitoring wells. These oxidants break down the petroleum hydrocarbons to carbon dioxide (CO2) and water. Some of the unreacted or residual oxidant breaks down to oxygen (02) that can dissolve into groundwater, thereby aiding in bioremediation of petroleum hydrocarbons. The performance of these chemical oxidation technologies, similar to bioremediation processes, varies from site to site depending on local hydrogeologic conditions and the nature and concentration of contaminants. Chemical oxidation via 03 sparging involves injecting air combined with 03 into the subsurface using dedicated, specially designed, injection wells. Ozone sparging is typically conducted using dedicated 03 sparge units, and commercially available 03 generating systems are capable of producing 1 to 5 pounds of 03 per day. The performance of insitu chemical oxidation systems is dependent on the effective deliveryof 03 to areas of concern, and this in tum is dependent on subsurface lithology. The geologic conditions in the saturated interval in which 03 wells would be installed (about 22- 24 feet bsg) appear to have low permeability and therefore may not be favorable to 03 injection technology and transportation of ozone to the contaminant. However, given the concentrations of GRO benzene and MTBE and the fluctuating groundwater levels that appear to have created a smear zone within the soil, we believe that chemical oxidation is an implementable and potentially effective remediation option for the site, W&A recommends bench scale and pilot scale testing. WINEFIELD L ASSOCIATES, INC. J INV1PON"f*TAk AND 5nrr77 CONSULTANTS