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1 � <br /> of 0 .3, the pore velocity of ground water underneath the site <br /> would be <br /> ! V = Ki/n = 10_3 m/s x 0.004/0.3 <br /> 1.3 x 10-5 m/s = 225 feet year <br /> i <br /> 2.1.2 Chemical Contamination <br /> There have been three onsite and one offsite investigations .into <br /> potential hydrocarbon contamination at the Stockton site. On 30 <br /> January 1987, Blaine Tech Services (BTS 1987) sampled subsurface <br /> soils during the removal of the underground storage tanks (Figure <br /> 5) . Except for samples 119 and 414 (these arf. at locations 1 and <br /> 4, at depths of 19 and 14 feet) , all of the samples were analyzed <br /> by Thermo Analytical Inc. (Flay 1987a, b) for benzene, toluene, <br /> xylene, and total petroleum hydrocarbons. The results of these <br /> analyses are given in Table 3. In addition to the above-named <br /> compou'Zds, the sample taken from the waste oil tank pit (Client <br /> id #4, Table 3) was analyzed for polychlorinated biphenyls (PCB) <br /> and for 25 halogenated volatile hydrocarbons. None of these <br /> compounds were detected (Flay 1987a) . <br /> In addition to soil samples, and at the same locations, BTS <br /> (1987) measured vapor concentrations in the gasoline tank field <br /> during the tank removal. Neither the instrument used nor type of <br /> measurement reported were identified; the results were reported <br /> as parts per million (ppm) vapor: <br /> Location 1 119 2 218 3 318 <br /> Concentration (ppm) 550 450 4,000 6,000 6,000 1, 500 <br /> The second investigation of onsite contamination was done by <br /> Groundwater Technology, Inc. (GTI 1987) . On 18 March 1987, GTI <br /> installer; three monitoring wells surrounding the area %f the <br /> former tank field (Figure 5) . Soil samples were taken for <br /> i <br /> 10 <br />