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). H. KLEINFELDER & ASSOCIATES <br /> select soil samples will be delivered under chain—of—custody to a <br /> state/EPA certified laboratory. The remaining soil samples will be <br /> retained in refrigerated storage for future reference or analysis. After <br /> 30 days unused samples will be returned to the sampling site. <br /> 3.2 QUALITATIVE FIELD SCREENING <br /> A Photovac TIP using a photoionization detector (PID) will be used to <br /> screen each soil sample. The PID field screening of the soil samples <br /> should provide a qualitative indication of the presence of petroleum <br /> hydrocarbons. The PID measures total ionizable compounds in air in parts <br /> per million by volume (ppmv) in relation to a select standard. The <br /> standard proposed for this investigation will be a 25 or 50 ppm benzene <br /> calibration gas. Calibration will be performed prior to use in the <br /> field. <br /> Selection of soil samples to be submitted for chemical analysis will be <br /> based on the PID results. The screening procedure will consist of <br /> scraping the top soil layer collected in the tube to expose fresh soil and <br /> scanning the vapors emitted from the soil. The vapor reading will be <br /> noted and evaluated at the completion of the field investigation to select <br /> samples for chemical analyses. The sample with the highest PID reading <br /> from each sampling location will be submitted for chemical analysis. <br /> 27:712-2 4 <br />