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1.0 EXECUTIVE SUMMARY Stratus Environmental, Inc. (Stratus), on behalf of Beasley and Associates, L.P., has prepared the following Well Installation and Destruction Report and Site Conceptual Model Update (SCM Update) for the Former Apache Plastics Facility, located at 2050 East Fremont Street, Stockton, California (see Figure 1 and Figure 2). This SCM Update was prepared pursuant to a request from San Joaquin County Environmental Health Department(SJCEHD). The subject site is situated within a mixed residential and commercial neighborhood in east- central Stockton. Extruded plastic piping was formerly manufactured at the property. A 1,000- gallon gasoline underground storage tank (UST) was installed beneath the northern portion of the Apache Plastics building in 1976. The UST and associated product dispensing system was removed in 1992. The site building has been subdivided for use as an ACE Hardware Store, indoor boat/recreational vehicle storage, and office space. Assessment of subsurface petroleum hydrocarbon impact was initiated at the site in 1989. Groundwater beneath the site is impacted with gasoline range organics (GRO), benzene, toluene, ethylbenzene, and xylenes (BTEX), tertiary butyl alcohol (TBA), and 1,2-dichloroethane (1,2-DCA). Impact to groundwater extends to at least 120 feet below ground surface (bgs), and is monitored by a well network with screening intervals above 70 feet bgs, 85 to 90 feet bgs, and . 94 to 120 feet bgs. Relatively high concentrations of dissolved petroleum hydrocarbons and 1,2- DCA remain near the former UST area. Impact does not appear to extend off-site east-southeast (downgradient) of the site. Based on our understanding of the extent of impact and the distance of known water supply wells from the site, it appears unlikely that petroleum hydrocarbons originating from the former Apache Plastics facility threaten off-site water supply wells. Depth to groundwater has ranged from approximately 42 feet bgs (2001) to 69 feet bgs (1990) since monitoring was initiated in 1989. According to SJCEHD personnel, groundwater in the area surrounding the site was measured as low as approximately 110 feet bgs in 1979. Groundwater was observed at approximately 45 to 47 feet bgs during the second quarter 2006. Groundwater flow beneath the site has generally been calculated to be towards the southeast and east at low gradients. A soil vapor extraction system (SVES) was operated at the site from June 1994 through June 1997. Remediation using the SVES was terminated at this time due to increases in groundwater levels beneath the site. Petroleum hydrocarbons were extracted from wells situated near the former UST and fuel dispensing area. An estimated 16,200 pounds of GRO were reportedly removed from the subsurface by the SVES. Based on the results of soil samples collected from recently advanced boring MW-13, concentrations of petroleum hydrocarbons remaining in vadose zone soils (above 40 feet bgs) situated near the former UST are very low. Petroleum hydrocarbon impact to soil and groundwater has also been reported at a former service station property located at 2085 East Fremont Street, immediately north of the site. GRO, BTEX, methyl tertiary butyl ether (MTBE), TBA, ethanol, 1,2-DCA, and 1,2-dibromoethane (EDB) impact have been reported beneath this property. Based on historical monitoring well K;\Apache P]astics\Reports\apache-scm-assessment report2006.doc Page 1 5TRAWS