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Stat1tet � `6
<br /> Site History and Previous Investigations
<br /> Chevron and ARCO Commingled Plume No. CP0034
<br /> February 6, 2009
<br /> In 1998, during the installation of a pay-quick machine, a contractor at the site broke a fiberglass
<br /> product line beneath the southern dispenser island. The broken line was repaired immediately
<br /> and approximately three cubic yards of soil were excavated from beneath the broken product
<br /> line. Soil samples collected after the excavation of the soil contained low levels of petroleum
<br /> hydrocarbons.
<br /> In 1999, one 10,000-gallon, fiberglass gasoline UST, product lines, vapor lines, and dispenser
<br /> islands were removed from the site. Small cracks that appeared to have been created during
<br /> excavation activities were observed in the tank. Soil samples collected from beneath the USTs
<br /> contained maximum GRO, benzene, and MTBE concentrations of 690 mg/kg, 0.692 mg/kg, and
<br /> 0.156 mg/kg, respectively. Soil samples collected beneath the product lines and dispenser
<br /> islands contained maximum GRO, benzene, and MTBE concentrations of 102 mg/kg, 0.298
<br /> mg/kg, and 124 mg/kg, respectively. Di-isopropyl ether, tert amyl-methyl ether, ethyl tert-butyl
<br /> ether, tert-butyl alcohol, and ethanol were reported as non-detect in all soil samples (SECOR,
<br /> 1999).
<br /> One 550-gallon, double-walled, fiberglass waste oil UST was removed from the site in 2002.
<br /> The tank appeared to be in good condition with no holes or cracks. One soil sample was
<br /> collected from the center of the tank pit at a depth of approximately 11 ft bgs. Hexavalent
<br /> chromium, chromium, nickel, zinc, and lead were reported at concentrations of 1.4 mg/kg, 35
<br /> mg/kg, 38 mg/kg, 49 mg/kg, and 12 mg/kg, respectively. All other constituents analyzed for
<br /> were reported as non-detect.
<br /> On June 12, 2007, SECOR staff oversaw WDC perform the destruction of MW-4 in accordance
<br /> with San Joaquin County Environmental Health Department (SJCEHD) requirements.
<br /> Remedial Performance Summary
<br /> A groundwater extraction (GWE) system was operated intermittently from 1984 to 1996. The SVE
<br /> and AS systems were initiated on January 1, 1995 and May 5, 1995, respectively. The SVE
<br /> system is comprised of 14 SVE wells (V-1 through V-12 and E-6) and an Airex Katox 100 catalytic
<br /> oxidizer. The SVE system was shutdown on March 1, 2001, due to low influent concentrations.
<br /> Prior to shutdown, the SVE system removed approximately 4,892 lbs of GRO and 61.3 lbs of
<br /> benzene.
<br /> The AS system consists of eight AS wells (S-1 through S-6, S-8, and S-9) and a 7.5-hp blower
<br /> (MD Pneumatics Model 3202). The AS system was shutdown on April 12, 2007 with the
<br /> approval of SJCEHD.
<br /> 94275 Site History and Previous Investigations.doc 3
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