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1 .0 INTRODUCTION <br /> This report has been prepared by Upgradient Environmental <br /> Consultans (Upgradient) for Apache Plastics L.P (Apache) to <br /> document the monitoring and remedial activities that have taken <br /> place at its facility since September, 1994 . The work described <br /> here has been performed under contracts 94116 (Vapor Extraction <br /> Monitoring) , 95004 (Groundwater Monitoring) , and 95016 (Waste <br /> Disposal ) . These activities are discussed separately in the <br /> following sections . <br /> 2 .0 BACKGROUND <br /> 2 . 1 Location and Setting <br /> The Apache Plastics manufacturing plant is located in a mixed <br /> commercial/residential neighborhood in east-central Stockton <br /> (Figure 1) . Topography in the area is flat, at a surface elevation <br /> of 22 feet above sea level . The site is underlain by discontinuous <br /> beds of medium to fine-grained alluvial sediment ranging in grain <br /> size from sand to silt. Finer-grained beds of silty clay are <br /> interbedded at various depths (0-15 feet, 35-40 feet, and below 65 <br /> feet) . <br /> 2 .2 Soil and Groundwater Contamination <br /> Gasoline was detected in the soil following the removal of a 1000- <br /> gallon underground storage tank (UST) from the building in August <br /> 1988 (Figure 2 ) . Subsequent investigative work by Western Geologic <br /> Resources and Remediation Services, Inc. (RSI ) indicated that total <br /> petroleum hydrocarbon concentrations as high as 13, 000 mg/kg were <br /> present at a depth of 40 feet, and concentrations exceeding 1, 000 <br /> mg/kg extend more than 25 feet in all directions from the UST <br /> excavation. Contaminated groundwater was encountered in the first <br /> monitoring well that was installed (MW-1 , subsequently destroyed <br /> during road construction) and six additional groundwater monitoring <br /> wells were drilled and sampled. Gasoline was detected in some of <br /> these during sampling several years ago, but drought conditions in <br /> recent years have lowered the water table and the wells went dry in <br /> 1991. <br /> 2 .3 Soil Remediation <br /> To remediate the soil contamination beneath the site, Apache <br /> elected to use in-situ vapor extraction after a 1992 feasibility <br /> test performed by RSI showed this method to be effective at the <br /> site. RSI installed two wells in a side-by-side configuration <br /> within the former tank excavation (Figure 3 ) . Both wells are <br /> completed with blank 2--inch-diameter PVC casing that is open at the <br /> bottom end to allow vapor inflow. The shallow well is bottomed at <br /> 35 feet, and the deep well is bottomed at 60 feet. The wells are <br /> manifolded at the surface to an internal combustion engine <br /> 2 <br />