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Site History and Previous Investigations
<br />Former Chevron Service Station No. 94054
<br />SP-2, SP-3, SP-4, SP-5 and SP-6 were installed northwest, north, northeast, west, southwest and
<br />south, respectively, of the former gasoline UST pit. The extraction wells were connected to a 40
<br />horsepower (hp) blower and a 600 standard cubic feet per minute (scfm) thermal regenerative
<br />oxidizer. The sparge wells were connected to a 15 hp blower. Full time operation of the system
<br />began on October 26, 2000 and averaged a removal rate of 40 pounds of hydrocarbons per
<br />day (Terra Vac Corporation, 2000).
<br />In June 2001, SECOR International Incorporated (SECOR) performed a well survey for the area
<br />within a one mile radius of the site. The survey included reviewing the California Department of
<br />Water Resources (DWR) files for water wells within a one mile radius of the site and conducting a
<br />door-to-door survey of businesses, commercial buildings and personal residences within a 2,000
<br />foot radius of the site. One additional well, not recorded during either the 1987 EA well survey or
<br />the 1995 Terra Vac well survey, was noted within 2,000 feet of the site; a domestic well located
<br />at 2705 Country Club Boulevard (SECOR International Incorporated, 2002).
<br />In September 2001, SECOR supervised the advancement of direct push borings at six locations
<br />(DP-1, DP-2, DP-3, DP-4, DP-5 and DP-6). Two direct push borings were advanced at each
<br />location, one for soil samples and one for groundwater samples. The DP-1, DP-2, DP-3, DP-4, DP-5
<br />and DP-6 borings were installed along the northern edge of the site, from DP-1 in the northwest
<br />corner to DP-6 in the northeast corner (SECOR International Incorporated, 2002). The greatest
<br />concentrations of petroleum hydrocarbon constituents detected in the soil samples collected
<br />during the associated direct push advancements were in the soil samples collected from DP-3 at
<br />17 feet bgs and DP-6 at 17 feet bgs. Benzene was detected at a concentration of 0.051 mg/kg
<br />in the soil sample collected from DP-6 at 17 feet bgs. Total xylenes were detected at a
<br />concentration of 0.005 mg/kg in the soil sample collected from DP-3 at 17 feet bgs. The greatest
<br />concentrations of petroleum hydrocarbon constituents detected in the groundwater samples
<br />collected during the associated direct push advancements were in the groundwater samples
<br />collected from DP-1 and DP-2. TPH-GRO, BTEX, MTBE and 1,2-DCA were detected at
<br />concentrations of 25,000, 2,500, 480, 490, 2,600, 3 and 61 pg/L, respectively, in the groundwater
<br />sample collected from DP-1. MTBE and tertiary butyl alcohol (TBA) were detected at
<br />concentrations of 3 and 35 pg/L, respectively, in the groundwater sample collected from
<br />DP-2.
<br />In March 2002, SECOR submitted a human health risk assessment to evaluate human health risks
<br />associated with the potential exposure to residual petroleum hydrocarbon chemical levels
<br />detected in groundwater at the site. Human health risks associated with the potential exposure
<br />to residual petroleum hydrocarbon chemical levels in soil were not evaluated because the
<br />operation of the DVE system at the site made the presence of petroleum hydrocarbon related
<br />chemicals in vadose zone soils unlikely. The analytical data procured from the recent
<br />advancements of DP-1, DP-2, DP-3, DP-4, DP-5 and DP-6 was cited as supporting the decision
<br />that petroleum hydrocarbon chemicals in vadose zone soils was unlikely. It was also determined
<br />that shallow groundwater at the site was not a risk for ingestion or dermal exposure and thus the
<br />pathway of interest for a human health risk assessment was vapor intrusion (SECOR International
<br />Incorporated, 2002).
<br />Three areas were evaluated as potentially impacted receptors in the human health risk
<br />assessment: Residential Area 1 (2421 Franklyn Avenue and 2112 Elmwood Avenue), Residential
<br />Area 2 (2120, 2128, 2136 and 2142 Elmwood Avenue) and the site. An approach consistent with
<br />the tiered Risk Based Corrective Action protocol developed by the American Society of Testing
<br />Stantec
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