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- ' Former Beacon Station No. 12474 March 18,2002 Stockton, California Problem Assessment Report/Corrective Action Plan L U corner of the site to provide lateral definition. Two soil borings (B-5 and B-6) were drilled • at the north end of the two dispenser islands and were completed with three nested soil vapor extraction wells, VW-11213, and VW-41516, respectively. Soil analytical data for soil borings B-5 and B-6, and monitoring wells MW-6 through MW-9 are contained in Appendix A. Gasoline-range hydrocarbons were reported in soil and groundwater samples collected during the previous investigations. Depth to groundwater has generally risen from approximately 80 feet below surface grade (bsg) in 1993 to approximately 59 feet bsg in 2001. Quarterly monitoring in February 2002 indicated an average groundwater depth of approximately 58 feet bsg, an eastward to southward groundwater flow direction under a shallow gradient of approximately 0.001. In October 1999, Horizon advanced five soil borings which were completed as monitoring wells MW-10, MW-11, MW-12 (soil boring B-7), vapor extraction well VW-7 (soil boring B-8), air sparge well AS-1 (soil boring B-9). Soil analytical data for soil borings B-7 ithrough B-9, and monitoring wells MW-10 and MW-11 are contained in Appendix A. Horizon has performed aquifer, soil vapor extraction and air sparge tests at the site to evaluate soil and groundwater remedial alternatives. Horizon documented remedial testing results in Report of Remedial Testing (Horizon, 1997a) dated 26 August 1997 and Vapor Extraction/Air Sparge Test Report dated 18 January 2000 (Horizon, 2000a). Test results indicate the methods are feasible soil and groundwater remedial alternatives. Quarterly groundwater monitoring has been performed at the site since December 1993. Tabulated historical groundwater monitoring data from December 1993 through 1997 are contained in Appendix B. Groundwater monitoring data from March 1998 through February 2002 are summarized in Table 1. • 474PARCAP3-02.doc 3 Project No. 1474.23 HORIZON ENVIRONMENTAL INC.