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10 INTRODUCTION <br /> ' This report has been prepared by Upgradient Environmental Consultants (Upgradient) for Apache <br /> Plastics L P (Apache) to document the monitoring and remedial activities that have taken place at its <br /> facility since December 1995 The work described here has been performed under contract 96004 <br /> 20BACKGROUND <br /> 2.1 Location and Setting <br /> ' The Apache Plastics manufacturing plant is located in a mixed commercial/residential neighborhood in <br /> east-central Stockton (Figure 1) Topography in the area is flat, at a surface elevation of 22 feet above <br /> sea level The site is underlain by discontinuous beds of medium to fine-grained alluvial sediment <br /> ranging in grain size from sand to silt Finer-gramed beds of silty clay are interbedded at various depths <br /> (0-15 feet, 35-40 feet, and below 65 feet) <br /> ' 2.2 Soil and Groundwater Contamination <br /> ' Gasoline was detected in the soil following the removal of a 1000-gallon underground storage tank <br /> (UST) from-the building in August 1988 (Figure 2) Subsequent investigative work by Western <br /> Geologic Resources (WGR) and Remediation Services, Inc (RSI) indicated that total petroleum <br /> hydrocarbon concentrations as high as 13,000 mg/kg were present at a depth of 40 feet, and <br /> concentrations exceeding 1,000 mg/kg extend more than 25 feet in all directions from the UST <br /> excavation Contaminated groundwater was encountered in the first morutonng well that was installed <br /> ' (MW-1, subsequently destroyed during road construction) and six additional groundwater monitoring <br /> wells were drilled and sampled Gasoline was detected in some of these during sampling several years <br /> ago, but drought conditions in 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 elected to use in-situ vapor extraction <br /> after a 1992 feasibility test performed by RSI showed this method to be effective at the site RSI <br /> ' installed two wells in a side-by-side configuration within the former tank excavation (Figure 2) Both <br /> wells are completed with blank 2-inch-diameter PVC casing that is open at the bottom end to allow <br /> vapor inflow The shallow well is bottomed at 3 5 feet, and the deep well is bottomed at 60 feet The <br /> ' wells are <br /> marufolded at the surface to an internal combustion engine destruction unit manufactured by VR <br /> Systems of Anaheim, California -- <br /> I' 2 <br /> 1 <br /> 1 <br />