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r plume cf dissolved hydrocarbons extended downgradient beyond the limits of the former tank field. 2.3 SOIL VAPOR CONTAMINANT ASSESSMENT On 5 May 1987,EA conducted a soil vapor contaminant assessment(SVGA)at the site,which was by then a vacant,unimproved lot. In vapor sam}les collected fromdetected so is 3 feet below ground ben- zene to 20 ppm and toluene to 25 pp P mor less were measured surface at the northern end of the pump islands. Concentradons of 1 pF in vapor samples collected at 13 oed to�Ite nlanheast fromints at deptlis the tankpit(EA 1987).feet. The indicat- ed plume appeared to have migrated 2.4 GROUNDWATER MONITORING WELLS-EA On 14 and 15 July 1987,to further define the extent of petroleum hydrocarbons in the ground- water,EA drilled and installed four groundwater monitoring wells on the site(see MW4-MW7, Figure 3). Analyses of the soil and water samples indicated that the dissolved petroleum hydro- carbons extended yet farther downgradient and upgradient and that offsite wells would be need- ed. In February 19810, EA installed offsite wells MW8 and 1AW9 across Pershing Avenue (upgradient); MW10 was installed on Rosemarie Lane in April 1988 (downgradient)(see Figure 3). No concentrations of petroleum hydrocarbons greater than detection limits,both TPH as gasoline and BTEX, were measured in soil samples from MW9 and MW10,but soil samples collected from below groundwater from MW8, installed a few feet downgradient from the Shell included station (and upgradient of the subject site),had concentrations of 3,200 mg/kg concentrations of 12, 150,and 260 mg/kg of benzene, toluene,and xylenes,respectively(see Table 1). Because four years of persistent drought have lowered the water table below the screened inter- vals of wells on the site, three deeper monitoringlrecovcry wells (RW l-RW3,Figure 3) were installed on 9-10 May 1990. These wells were installed to provide capacity to extract ground- water and capture the dissolved hydrocarbon plume. Up to 3,700 mg/kg of TPH was found in soil samples collected from well RW l at a depth of 35 feet,below the water table(Table 1). Soil samples collected above the water table contained up to about 20 mg/kg of TPH(RW 3 at 26 feet). 2.5 QUARTERLY GROUNDWATER SAMPLING AND ANALYSIS Since November 1986,EA has been monitoring the wells and sampling groundwater quarterly. Samples of groundwater are analyzed for TP14 (gasoline) by DHS-modified EPA Method 8015 3 c6I1—77794Zrim91/.