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Passive soil gas survey results may be useful in indicating the presence or absence of VOC <br /> vapors in shallow subsurface soil gas and may provide a qualitative measure of the relative <br /> abundance of VOC vapors in shallow subsurface soil gas, if the gas is present. The sample <br /> results are not quantitative in that the results are reported in ion count concentrations for each <br /> specific VOC species detected and are not quantified on a mass per unit volume basis. <br /> Furthermore, the sample results are not necessarily indicative of the presence of VOC vapors in <br /> deeper subsurface soil gas or of VOCs dissolved in underlying groundwater. <br /> The shallow passive soil gas survey results suggested the presence of both TCE and PCE in <br /> shallow soil gas throughout the northern portion of the City of Lodi including the LNC site <br /> (NERI, 1996; Henshaw, 2001). PCE and TCE were reportedly detected beneath the LNC site. <br /> 4.3 Drive-Point Soil Gas Survey <br /> A shallow (approximately 5 feet bgs) drive-point soil gas survey was conducted by the DTSC <br /> during 1993 to assess potential TCE sources in the northern portion of the city of Lodi. A total of <br /> 117 shallow drive-point soil gas samples were collected in two rounds throughout the City of <br /> Lodi. Approximately 74 drive-point soil gas samples were distributed throughout the northern <br /> portion of the City of Lodi. During the first round of sampling, the volume of soil gas collected <br /> was not measured, so the results were qualitative only and were reported in nanograms. During <br /> the second round, the volume of soil gas collected was measured, and the results were reported <br /> in picograms/liter (URS, 1994; NERI, 1996). The results of these soil gas surveys reported the <br /> possible presence of 1,1,1-TCA, PCE, and TCE in shallow soil gas beneath the LNC facility, <br /> primarily below the northwest corner of the parking lot area(Area D, Figure 7). Low-level <br /> concentrations of 1,1-DCE and 1,1-DCA were also reportedly detected in shallow soil gas in this <br /> same area. <br /> M ain\D:AEnvironmentaI\LN CV\10152007.wpd 17 <br />