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Geosyntec <br /> consultants <br /> 2. SITE BACKGROUND <br /> 2.1 Location and Historical Use <br /> The Site is located at 1904 West Charter Way, Stockton, California. The Site occupies <br /> approximately 4.2 acres in a predominantly industrial area west of the City of Stockton, California <br /> (Figure 1). A residential neighborhood borders the Site to the east, an undeveloped parcel borders <br /> the Site to the south, and parcels located immediately west and north of the Site are used for <br /> industrial purposes. The San Joaquin River and Stockton Regional Wastewater Disposal Ponds <br /> are located approximately 3,000 and 3,500 feet west of the Site, respectively. <br /> The Site was used from 1955 to 1993 for storage and distribution of agricultural chemicals, <br /> including pesticides,herbicides, soil fumigants, and fertilizers containing nitrogen and other plant <br /> nutrients (Geomatrix, 2005). This entailed the use of structures including a multi-purpose <br /> building,tank farms,storage bunkers and wash racks(Geomatrix,2005 and Apex,2018). Gasoline <br /> and diesel fuel, used to fuel delivery trucks,were stored in underground tanks near the east side of <br /> the multi-purpose building and were removed in 1990 (Geomatrix, 2005). The Site is currently <br /> vacant and fenced around its entire perimeter. Concrete slabs and structural foundations for other <br /> former Site infrastructure remain in some areas of the Site. <br /> 2.2 Hydrogeology <br /> The Revised Contingency Plan summarized previous investigations which indicated that the Site <br /> is underlain by interbedded, relatively continuous, thin layers of sand, silt and clay to a depth of <br /> about 150 feet below ground surface(ft bgs),the maximum depth of investigation beneath the Site. <br /> Based on the findings from these investigations,three water-bearing zones have been identified in <br /> the vicinity of the Site; these water-bearing zones are referred to as the shallow, intermediate and <br /> deep zones. <br /> The shallow zone (referred to as the A zone in the MRP) is present between approximately 20 and <br /> 40 ft bgs and consists of a relatively continuous fine- to medium-grained sand that bifurcates into <br /> two layers toward the south and west of the Site. The shallow zone is overlain by primarily fine- <br /> grained materials. The intermediate zone(referred to as the B zone in the MRP)is present between <br /> approximately 70 to 90 ft bgs and consists of very fine-grained to silty sand. The deep zone is <br /> present between approximately 115 and 135 ft bgs and consists of interbedded clayey sand, silty <br /> sand, and sand. <br /> Groundwater levels in the shallow and intermediate zones vary seasonally at the Site with levels <br /> declining during the summer months and recovering during the winter months. Groundwater level <br /> data for the past 10 years of monitoring show that the water level in the shallow zone varied <br /> seasonally between depths of about 5 and 15 ft bgs. The direction of horizontal groundwater flow <br /> in both the shallow and intermediate zone is generally easterly (Geomatrix, 2005). <br /> 2.3 Results of Previous Investigations and Site Remedial Activities <br /> Results from previous Site investigations indicate that constituents of concern (COCs) related to <br /> the past operations at the Site have been detected in the shallow and intermediate zones. No COCs <br /> were detected in samples from the deep zone; therefore, no further investigations have been <br /> Work Plan for Vapor Intrusion Investigation 2 July 30,2021 <br />