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Site History and Previous Investigations
<br />Former Chevron Service Station No. 94054
<br />level set by the California Department of Health Services coupled with the finding that no
<br />domestic well existed between the contaminant source and the municipal well (EA Engineering,
<br />Science, and Technology, Inc., 1987). As part of the investigation a well survey was performed
<br />for the area within a half mile radius of the site. The survey resulted in the finding of four wells
<br />within 2,000 feet of the site. Also as part of the investigation, a water sample was collected from
<br />monitoring wells MW-1, MW-2 and MW-3. The greatest concentrations of petroleum hydrocarbon
<br />constituents detected in the groundwater samples collected from MW-1, MW-2 and MW-3 were
<br />in the groundwater sample collected from MW-1. Benzene, toluene, ethylbenzene and total
<br />xylenes (BTEX) were detected at concentrations of 17,000, 25,000, 2,500 and 16,600 micrograms
<br />per liter (pg/L), respectively, in the groundwater sample collected from MW-1.
<br />In October 1988, all above ground and below ground site features were removed, including five
<br />single walled gasoline USTs (one 2,000 gallon, two 4,000 gallon and two 3,000 gallon), one waste
<br />oil UST (550 gallon), the product line piping, the pump islands and the service station building
<br />(SECOR International Incorporated, 2003). Blaine Tech Services Inc. was present onsite to
<br />document tank removal activities and to collect soil samples from the excavated area. Holes
<br />were observed in the waste oil UST and in both of the 4,000 gallon gasoline USTs. Odor and soil
<br />discoloration was noted in the gasoline and waste oil tank excavations (Blaine Tech Services
<br />Inc., 1988). The greatest concentrations of petroleum hydrocarbon constituents detected during
<br />the UST excavations were in the soil samples collected from beneath the eastern most 3,000
<br />gallon gasoline UST at 13 feet bgs (sample ID #56), beneath the eastern most 4,000 gallon
<br />gasoline UST at 13 feet bgs (sample ID #3A) and beneath the waste oil UST at 11 feet bgs
<br />(sample ID #6). Total petroleum hydrocarbons as gasoline (TPH-GRO) and BTEX were detected
<br />at concentrations of 11,000, 230, 1,100, 320 and 1,670 mg/kg, respectively, in the soil sample
<br />collected from beneath the eastern most 3,000 gasoline UST at 13 feet bgs (sample ID #5B). 1,2-
<br />dichloroethane (1,2-DCA) was detected at a concentration of 0.080 mg/kg in the soil sample
<br />collected from beneath the eastern most 4,000 gallon gasoline UST at 13 feet bgs (sample ID
<br />#3A). Total petroleum hydrocarbons as diesel (TPH-DRO) was detected at a concentration of 9.0
<br />mg/kg in the soil sample collected from beneath the waste oil UST at 11 feet bgs (sample ID #6).
<br />A lead analysis was performed for the soil sample collected from beneath the waste oil UST at 11
<br />feet bgs (sample ID #6); the concentration was recorded as 6.1 mg/kg (Blaine Tech Services
<br />Inc., 1988).
<br />In May 1989, Pacific Environmental Group supervised the installation of 21 soil vapor probes (VP-
<br />1, VP-2, VP-3, VP-4, VP-5, VP-6, VP-7, VP-8, VP-9, VP-10, VP-11, VP-12, VP-13, VP-14, VP-15, VP-16,
<br />VP-17, VP-18, VP-19, VP-20 and VP-21). Soil gas samples were collected from each vapor point
<br />and analyzed for total BTEX concentration. The greatest total BTEX concentration detected was
<br />in the soil gas sample collected from VP-14, at 980 parts per million (ppm) (Terra Vac
<br />Corporation, 1998).
<br />In September 1992, GTI supervised the installation of four groundwater monitoring wells (MW-4,
<br />MW-5, MW-6 and MW-7) and eight soil borings (SB-1, SB-2/SB-2A, SB-3, SB-4, SB-5, SB-6, SB-7 and
<br />515-61. MW-4 was installed along the western edge of the site and MW-5 was installed in the
<br />eastbound lane of Country Club Boulevard, south of the site. Monitoring wells MW-6 and MW-7
<br />were installed in the northbound lane of Franklin Avenue, east of the site. SB-1 was advanced
<br />south-southwest of the former gasoline UST pit. SB-2 was installed southwest of the former
<br />gasoline UST pit and met resistance at approximately 10 feet bgs; SB-2 was abandoned and SB-
<br />2A was then advance next to SB-2 to depth. SB-3 was installed west-northwest, SB-4 was installed
<br />south-southwest and SB-5 was installed south-southeast of the former gasoline UST pit. SB-6 was
<br />Stantec
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