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r 7-Eleven/Stockton 4 May, 1989 1985, five additional monitoring wells were installed (MW-5, YW- 6, MW-7, MW-8, and MW-9) , and sampling of the monitoring wells and nearby domestic wells was initiated. These preliminary hydrogeologic investigations identified gasoline adsorbed within the vadose-zone soil, and dissolved within the groundwater, concentrated as free-phase product, and volatilized as vapors. The discovery of free product within MW-1 and MW-4 prompted the initiation of a groundwater remediation/abatement program. Initial work involved periodic hand bailing of free product as requested by the San Joaquin Local Health District. In early July 196£, a small-diameter double-pumping system was installed in MW-4 to control the continued migration of free product and to collect product from the well. In late October 1986, two additional pumping wells (PW-1 and PW-3) were installed to -`-' improve control over plume migration and provide for remedial clean up of the free product and dissolved contamination. In addition to the pumping wells, groundwater from MW-4 was pumped to the treatment compound upon detection of free product in this 4 well. The contaminated groundwater recovered by these methods was treated by carbon filtration prior to discharge to the -- sanitary sewer system. In February 1987, the carbon filtration system was replaced by an air-stripping tower. Additional work conducted in February 1987 included installation of two new monitoring wells (MW-13 and MW-14) . The monitoring well locations were selected to evaluate the origin of sporadic contamination in domestic wells which are located up gradient of the site. Work in February 1987 also included the installation and activation of a soil-ventilation system. The - soil-ventilation system was installed to address the adsorbed and vapor phases of contamination in the vadose-zone soils. This �iROUND 1AUR TECIM11AIGY.INC.