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fti 1 Gradient directions from the gauging data collected over the last two years are shown in Figure 1 and Figures C-1 through C-9. 3.6 SOIL VAPOR CONTAMINANT ASSESSMENT EA conducted a soil vapor survey (SVCA) at former Exxon RS 7-1050 on 23 and 24 November and- 22 December 1987. An SVCA is a field method of collecting samples of soil vapor and analyzing them for petroleum hydrocarbons with a portable gas chromatograph. Sam- ples of soil vapors at Exxon RS 7-1050 were collected by driving 5/8-inch-diameter steel probes into the soil at 11 locations. A vacuum pump .was used to purge .several probe-volumes of vapor from the probes, thus: ensuring that the samples were representative of ;,'' the vapors contained in the soil. The vapors were extracted from the probes with` a microsyringe through a septum in the vacuum pump and in into a Photovac 16550. portable gas chromato I graph .for analysis. The Photovac 1OS50is d programmable, inte- grating gas chromatograph with aphotoionization detector (PID). The .instrument was calibrated with standards consisting of. 10. ppm benzene and 10 ppm toluene in air. _ On 23 .and 24 November 1987., deep (approximately .20 feet) soil .gas samples were collected from six locations .on the. site (V.i-V6,. Figure 7;, and monitoring well headspace samples were,.taken .from the five monitoring wells. A follow-up investigation for the presence of shallow hydrocarbon levels was conducted on 22 December 1987. Shallow samples were collected from five' loca tions (V7-Vii , Figure. 7) . No.,si g nificant hydrocarbon concentrations were detected in any 'of the...samples collected in. the course of: the SVCA. The highest - concentrations were: seen;in. the` headspace sample's from the muni- 1 toying wells. The .results of .the SVCA analyses are.presented in Tables 3 and A. e35/.7..1050/2-90/tx 25 ( MIMM_ err}