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Stantec
<br /> Site History and Previous Investigations
<br /> Stockton Charter Way Commingled Plume No. CP0057
<br /> November 15, 2011
<br /> In July 1996, four soil borings (B-22 through B-25) were advanced and converted into vapor
<br /> extraction wells (VW-10 through VW-13). TPHg and benzene were detected in soil samples
<br /> collected during the removal activities at concentrations up to 730 and 0.22 mg/kg, respectively.
<br /> In July and August 2000, Delta Environmental Consultants, Inc. of Rancho Cordova, California
<br /> (Delta) contracted Woodward to install five groundwater monitoring wells (MW-1B,
<br /> MW-1C, MW-8, MW-8B, and MW-8C). TPHg, benzene, and MTBE were detected in soil
<br /> samples collected during the installation activities at concentrations up to 100, 0.719, and 0.266
<br /> mg/kg, respectively. These activities are summarized in the Delta Soil and Groundwater
<br /> Investigation Report dated November 22, 2000.
<br /> Between September and November 2005, URS Corporation of Sacramento, California (URS)
<br /> contracted Woodward to destroy wells VW-2 through VW-6, VW-9, VW-12, VW-13, and MW-4.
<br /> In November 2005, URS contracted Woodward to install four groundwater monitoring wells
<br /> (MW-9 through MW-12) to further define the lateral extent of petroleum hydrocarbon-impacted
<br /> groundwater beneath the property. In addition, 17 dual-completion soil vapor extraction
<br /> (SVE)/air sparge (AS) wells (EW-1/SP-1 through EW-17/SP-17) and five AS wells (SP-18
<br /> through SP-22) were installed to complete the treatment system well network. TPHg, benzene,
<br /> and MTBE were detected in soil samples collected during the installation activities at
<br /> concentrations up to 3,700, 49, and 0.0064 mg/kg, respectively. These activities are
<br /> summarized in the URS Remedial System Installation Report dated November 15, 2006.
<br /> Between December 2005 and August 2006, URS excavated trenches, laid and connected
<br /> tubing to the AS wells and the injection system, and conducted general system installation
<br /> activities. The SVE/AS system was started on October 17, 2006. The system was installed
<br /> without changes to the original design.
<br /> A groundwater monitoring and sampling program has been in place at this property since May
<br /> 1992.
<br /> Remedlation Activities
<br /> A waste oil underground storage tank (UST) was formerly located in the northeastern corner of
<br /> the property. The waste oil UST was reportedly removed on November 18, 1986.
<br /> In July 1992, RESNA performed a SVE test on the property to evaluate the feasibility of SVE as
<br /> a remediation alternative for the vadose zone. These activities are summarized in the
<br /> RESNA Vapor-Extraction Test Results dated December 18, 1992.
<br /> In February 1996, EMCON observed American Construction and Environmental Services as
<br /> they performed the removal of two 6,000-gallon, single-walled, steel USTs; one 8,000-gallon,
<br /> single-walled, steel UST; one 10,000-gallon, single-walled, fiberglass UST; associated product
<br /> piping; and dispensers. The two 6,000-gallon USTs historically contained regular leaded and
<br /> mid-grade unleaded gasoline. The 8,000-gallon UST historically contained premium leaded and
<br /> supreme-grade unleaded gasoline. The 10,000-gallon UST historically contained regular
<br /> unleaded gasoline. Twelve soil samples (TS-1 through TS-6 and P-1 through P-6) were
<br /> collected during removal activities. TPHg, benzene, and methyl tert-butyl ether (MTBE) were
<br /> detected in soil samples collected during the removal activities at concentrations up to 12,000,
<br /> Stockton Charter Way Site History and Previous Investigations.doc 2
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