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N ATC Associates Inc. 1 117 Lone Palm Avenue, Suite 201 \\V•// Modesto, California 95351 209-579-2221 A 660CIATES INC . Fax: 209-579-2225 respect to petroleum hydrocarbon vapors. The vapor extraction wells are screened from 10 to 40 feet bgs. The actual radius of influence associated with each vapor extraction well varies depending on subsurface geologic conditions, the extent and distribution of hydrocarbon-impacted soil , and site- specific operating conditions of the vapor extraction system. The estimated radii of influence associated with VEl through VE4, based on the 2005 pilot test, are presented in Figure 7. 9.2 System Design Specifications 9.2.1 Vapor Extraction System The proposed soil vapor extraction system will utilize existing vapor extraction wells VE1 through VE4 (Figure 3). The extraction system will be operated tinder similar conditions as the previously conducted pilot tests to achieve similar results. Each vapor extraction well will be incorporated into the vapor extraction Avell network, howevcr their respective use (duration, episodic cycling, etc.) will be evaluated based upon vacuum response and vapor concentrations. The estimated removal rate of TPH observed during the long term pilot test using VE2 as the extraction well was approximately 8.3 pounds per hour. Thermal oxidation will be employed as the method of off-gas destruction. Removal rates will be the greatest during the first several months of system operation and will exceed the allowable emission limit without off-gas treatment. Subsurface piping will direct extracted vapor from the extraction wells to a nearby remediation compound (Figure 8). Components of the vapor extraction system located in the remediation compound wilt ' include the following: a thermal catalytic oxidizing tout containing a vapor extraction blower, a flow indicator that measures extracted airflow, a condensate separator to remove entrained droplets of moisture, associated piping, control valves, pressure gauges, flow inters, instrumentation and controls. The remediation compound wW and equipment will be surrounded by fencing to preclude public access. Based on ATC ' s experience at similar sites and the results of the pilot tests, a 250 elfin thermal catalytic oxidizer would be sufficient to operate the vapor extraction component of the system and remediate the off-gas. The vacuum blower on the unit would create a maximum vacuum of 14 inches of mercury and an airflow rate of 250 standard cubic feet per minute. The thermal oxidizer on the Ludt would operate at a minimum temperature of approximately 1 ,400 degrees Fahrenheit and have a destruction efficiency of 95% to 99%, The equipment will be staged on a trailer designed for temporary use. 9.2.2 Remediation System Layout Components of the vapor extraction system will be located in an enclosed compound in the northwestern portion of the site depicted on Figure 8. A network of subsurface piping will be used to convey recovered soil vapor from the four extraction wells to the remediation compound as shown on Figure 9. Piping will be installed at an estimated depth of two feet bgs. Well vaults will SVE System Design Plan ATC Associates Inc. Stockton City Tani Page 9