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2 . SITE INVESTIGATIONS <br /> 2 . 1 PREVIOUS INVESTIGATION <br /> r <br /> On 24 July 1986, during the excavation of the fuel storage tanks <br /> by American Management Corporation, hydrocarbons were detected in <br /> the soil and ground water within the tank excavation. A follow- <br /> up investigation was continued by Harding Lawson Associates <br /> (HLA) . That investigation consisted of drilling, soil sampling, <br /> installation of three monitoring wells, analysis of samples, and <br /> r <br /> a final report. The HLA investigation confirmed that some <br /> hydrocarbons were present in the ground water. The results of <br /> ` the HLA investigation are summarized in Table 2 . <br /> 2 . 2 SOIL VAPOR CONTAMINANT ASSESSMENT <br /> r The SVCA at this site consisted of the collection of soil vapor <br /> samples from 14 points for on-site analysis. The site was <br /> divided into a 40-foot grid, and additional points were placed to <br /> r <br /> refine plume definition. <br /> Prior to collection of each sample, a vacuum pump was used to <br /> purge previously collected vapor from the probes to ensure that <br /> r soil vapor samples collected were not contaminated. The vacuum <br /> pressure reading on the purging apparatus was recorded. This <br /> vacuum pressure is related to the soil ' s gas permeability and is <br /> useful in data interpretation. The samples were collected <br /> through a septum with a microsyringe and injected into a Photovac <br /> IOS50 chromatograph for analysis. <br /> r The Photovac lOS50 is aortable <br /> p programmable, integrating gas <br /> chromatograph with a photoionization detector ( PID ) . The PID is <br /> �. a nondestructive flow-through detector that uses high energy <br /> ultraviolet radiation as its ionization source. The high energy <br /> L radiation ionizes compounds, generating an energy increase in the <br /> r 11 <br />