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7-Eleven/Stockton February 1990 5 w Also, during October and November of 1986, three additional monitoring wells were installed off site (MW-10 through MW-12) to obtain further dissolved-plume definition. Underground piping was connected to MW-12 in order to allow it to be used as a Pumping well to intercept dissolved hydrocarbons in the event that migration was detected approaching the Tomato Growers, Association (TMG) domestic well. This well (MW-12) has not been used as a pumping well to date. Initially, the groundwater recovered by pumping was treated by carbon adsorption prior to being discharged 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 the installation of two new monitoring wells (MW-13 and MW-14) . The monitoring well locations were selected to evaluate the origin of sporadic hydrocarbon contamination detected in samples from domestic wells which are located upgradient of the site. Work in February 1987 also included the installation and activation of a soil-vent remediation system. The soil-vent system was installed to address the adsorbed and vapor phases of contamination in the - vadose-zone soils. This system consists of four vapor-extraction points connected to a high-vacuum blower and manifolded to a vapor-phase, activated-carbon adsorption system. From late 1986 to early 1988, a prolonged decline in the regional water-table elevation occurred due to abnormally arid conditions in the Stockton area. As a result, the groundwater yield from the groundwater-pumping wells was reduced. To improve the recovery volume, a new recovery well (RW--1) was installed on W February 1, 1988. At the same time, the remediation/abatement system underground lines and electrical systems were upgraded. GROLINDLVATER TECHNOLOGY.INC.