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1.0 INTRODUCTION- This NTRODUCTIONrThis report has been prepared by Upgradient Environmental Consultants (Upgradient) for Apache Plastics L P (Apache) to document the momtonng and remedial activities that have taken place at its facility since October 1995 The work described here has been performed under contracts 94116 (Vapor Extraction Monitoring) and 95004 (Groundwater Momtonng) These activities are discussed separately in the following sections i2.0 BACKGROUND 2.1 Location and Setting The Apache Plastics manufacturing plant is located in a mixed commerciallresidential neighborhood in ' east-central Stockton (Figure 1) Topography in the area is flat, at a surface elevation of 22 feet above sea level The site is underlain by discontinuous beds of medium to fine-grained alluvial sediment ranging in grain size from sand to silt Finer-grained beds of silty clay are interbedded at various depths ' (0-15 feet, 35-40 feet, and below 65 feet) 2.2 Soil and Groundwater Contamination ' Gasoline was,detected in the soul following the removal of a 1000-gallon underground storage tank (UST) from the building in August 1988 (Figure 2) Subsequent investigative work by Western Geologic Resources (WGR) and Remediation Services, Inc (RSI) indicated that total petroleum hydrocarbon concentrations as high as 13,000 mg/kg were present at a depth of 40 feet, and concentrations exceeding 1,000 mg/kg extend more than 25 feet in all directions from the UST ' excavation) Contaminated groundwater was encountered in the first monitoring well that was installed (MW-1, subsequently destroyed during road construction) and six additional groundwater moritonng wells were drilled and sampled Gasoline was detected in some of these during sampling several years i ago, but drought conditions in recent years have lowered the water table and the wells went dry In 1991 2.3 Soil Remediation ' To remediate the soil contamination beneath the site, Apache elected to use in-situ vapor extraction after a 1992 feasibility test performed by RSI showed this method to be effective at the site RSI installed trwo wells in a side-by-"side configuration within the former tank excavation (Figure 2) Both wells are completed with blank 2-inch-diameter PVC casing that is open at the bottom end to allow vapor inflow The shallow well is bottomed at 35 feet, and the deep well is bottomed at 60 feet The wells are mannfolded at the Surface to an internal combustion engine destruction unit manufactured by VR Systems of Anaheim, California 2