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L Former Beacon Station No. 12474 March 18,2002 Stockton,California - Problem Assessment Report/Corrective Action Plan L 7.2 Vapor Extraction Test A four-hour vapor extraction test (VET) was performed on December 9, 1999. Vapors were extracted from vapor extraction wells VW-I (screened interval 50 to 65 feet bsg) and VW-2 (screened interval 37 to 47 feet bsg). Monitoring wells VW-4, VW-5 and VW-7 were monitored for induced vacuum influence. Tabulated field data and analytical results are contained in Appendix E (Table 1). On the basis of field and laboratory results, it appears that vapor extraction is a feasible alternative for soil remediation. Field and laborztory data indicated that higher TPHg mass extraction rates are achievable from vapor extraction well VW-2. Estimates of radii of influence are in excess of 30 feet while extracting from both vapor extraction wells VW-1 and VW-2. It is expected that flow rate and vacuum influence characteristics for vapor extraction wells VW-4 and VW-5 would be similar to vapor extraction wells VW-1 and VW-2. A figure showing estimated radii of influence for the nested vapor extraction well . groups VW-INW-2 and VW-4NW-5 are contained in Appendix E. The locations of the vapor extraction wells appear to be adequate to remediate hydrocarbon-impacted soil beneath and along the north side of the existing dispenser islands. 7.3 Air Sparge Test On 14 December 1999, an eight-hour air sparge test (AST) was performed on air sparge well AS-1 (screened 70 to 75 feet bsg). Injection air flow rate, and pressure responses in vapor extraction well VW-1 and monitoring wells MW-2 and MW-3 were monitored during the AST. Tabulated air sparge test field data are contained in Appendix E (Table 2). The concentration of dissolved oxygen (DO) increased in well MW-2 from 0.9 to 1.6 ppm, a 77% increase during the 8-hour test. Well AS-1 did not recharge for 45 minutes after the completion of air sparging, therefore a groundwater sample could not be collected for DO . measurement. The field data obtained from the AST suggest that air sparging is a feasible 474PARCAP3-02,doc 12 Project No. 1474.23 HORIZON ENVIRONMENTAL INC.