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'S r e� The wells were surveyed after completion under the direction of GTI. Wellhead elevations used in gradient calculations are those reported in the GTI report of 21 August 1987. Gradient direction from the most recent gauging is shown on the 4- All data from the gauging potentiometric map of Figure and surveying is presented in Table 9. 2.6 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 i i; 5/8-inch-diameter steel probes into the soil at 1l 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 injected into a Phot 10550 portable gas chromato- � .�. "graph for '.analysis. The Photovac t0S50 .is a-programmable,. inte fgrating gas chromatograph with a ph otoioni bian dlPTD1 [. I The instrument was calibrated with standards consisting of 10 ppm benzene and 10 ppm toluene in air. 3 roximatel 20 feet) soil gas ? . On 23 and 24 November.1987, deep, (app Y samples. were collected from six locations on (V1-V6, Figure .. 5,' and monitoring well headspace samples were taken from the. -five _. .: - -....__ - monitoring wells A follow-up investigation for the ;presence o'f -- ` i shallow hydrocarbon levels was conducted on 22 December .1987. Shallowsamples were collected from five locations (V7-V11 , Figure 5 ) - ,.M e2.5/71050/8--89/txt 10 NV KGF - I.Y