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Site History and Previous Investigations
<br />Former Chevron Service Station No. 94054
<br />Between September and December 2006, ARCADIS BBL supervised the installation of nine
<br />groundwater monitoring wells (MW-1A, MW-1B, MW-1C, MW-2B, MW-2C, MW-4B, MW-4C, MW-9B
<br />and MW-9C). Monitoring wells MW-1A, MW-1B and MW-1C were installed near abandoned
<br />monitoring well MW-1. Monitoring wells MW-2B and MW-2C were installed near existing
<br />monitoring well MW-2. Monitoring well MW-4B and MW-4C were installed near existing monitoring
<br />well MW-4. Monitoring well MW-9B and MW-9C were installed in the northbound lane of Franklin
<br />Avenue, across from existing monitoring well MW-9, which is installed in the southbound lane of
<br />Franklin Avenue (ARCADIS BBL, 20070). The greatest concentrations of petroleum hydrocarbon
<br />constituents detected in the soil samples collected during the associated monitoring well
<br />installations were in the soil samples collected from MW-1A at 20.5 feet, MW-1A at 30.5 feet and
<br />MW-1B at 26 feet bgs. TPH-GRO was detected at a concentration of 2,100 mg/kg in the soil
<br />sample collected from MW-1B at 26 feet bgs. BTEX was detected at concentrations of 0.41, 1.1,
<br />19 and 99 mg/kg, respectively, in the soil sample collected from MW-1A at 20.5 feet bgs. MTBE
<br />was detected at a concentration of 0.001 mg/kg in the soil sample collected from MW-1A at
<br />30.5 feet bgs.
<br />Between March and May 2007, ARCADIS BBL supervised the installation of eight soil vapor
<br />probes (SV-1, SV-2, SV-3, SV-4, SV-5, SV-7, SV-8 and SV-9). Soil vapor probes SV-1, SV-2 and SV-3
<br />were installed in a line parallel to the property line, approximately 5 feet south of the former
<br />gasoline UST pit, starting with SV-1 near the western edge of the property and SV-3 near the
<br />eastern edge of the property. Soil vapor probes SV-4 and SV-5 were installed in the former
<br />gasoline UST pit. SV-7 was installed in the northwest corner of the site, SV-8 was installed in the
<br />middle of the site, along the northern edge, and SV-9 was installed in the northeast corner of the
<br />site (ARCADIS BBL, 2007b). The soil vapor probes were sampled; however, tracer gas was
<br />detected at elevation concentrations in all but one sample and subsequently the results were
<br />not evaluated (ARCADIS BBL, 2007b.)
<br />In July 2007, ARCADIS BBL sampled soil vapor probes SV-1, SV-2, SV-3, SV-4, SV-5, SV-7, SV-8 and
<br />SV-9. Petroleum hydrocarbon constituents were not detected the soil vapor samples collected
<br />from the recently installed soil vapor probes. The oxygen, nitrogen, methane and carbon dioxide
<br />concentrations detected in the soil vapor samples collected from SV-1 and SV-3 suggested that
<br />a degree of biodegradation may be occurring at those locations. The soil vapor sampling results
<br />indicated that soil vapor concentrations at the site are below levels of concern (ARCADIS BBL,
<br />2007c).
<br />In May 2008, ARCADIS BBL sampled soil vapor probes SV-1, SV-2, SV-3, SV-4, SV-5, SV-7, SV-8 and
<br />SV-9. The greatest concentration of petroleum hydrocarbon constituents detected in the soil
<br />vapor samples collected during the associated soil vapor probe sampling event was in the soil
<br />vapor sample field duplicate collected from SV-1. TPH-GRO was detected at a concentration of
<br />2,800 micrograms per cubic meter (pg/m3 ) in the soil vapor sample field duplicate collected
<br />from SV-1. 1,2-DCA and MTBE concentrations were not detected above the laboratory MDL in
<br />the soil vapor sample collected during the sampling event. The soil vapor sampling results
<br />indicated that soil vapor concentrations at the site are below levels of concern (ARCADIS, 2008).
<br />In December 2008 and January 2009, ARCADIS supervised the installation of five groundwater
<br />monitoring wells (MW-4D, MW-9D, MW-12B, MW-12C and MW-12D). MW-4D was installed near
<br />monitoring well MW-4, MW-4B and MW-4C. MW-9D was installed near monitoring wells MW-9B
<br />and MW-9C in the northbound lane of Franklin Avenue, across from monitoring well MW-9 which
<br />is installed in the southbound lane of Franklin Avenue. MW-12B, MW-12C and MW-12D were
<br />Stantec
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