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i GEOMATRIX i 5.0 LABORATORY ANALYSIS i Groundwater samples were analyzed for benzene,toluene,ethylbenzene,and xylenes(BTEX)using EPA Method 8240 EPA Method 8020 was previously used for BTEX analysis, however, this method can produce false-positive results for these constituents EPA Method 8240 was selected for BTEX analysis because the possibility of false-positive results for these constituents is eliminated In addition, to evaluate the effects that extraneous material may be having on TPH-D analytical results and to reduce the likelihood of false positive results for TPH-D, three different groundwater samples from each monitoring well were analyzed for TPH-D using modified EPA Method 8015 as follows ' 4. a standard sample, with no preparation, • a sample filtered using a 0 45 micron filter, and 1 • a sample filtered as above and treated with a silica gel cleanup Laboratory services were provided by American Environmental Network of Pleasant Hill, California Analytical data sheets provided by the laboratory are included in Appendix A 6.0 FINDINGS Analytical results for groundwater samples collected by Geomatnx are summarized in Table 2 The analytical results indicate that non-petroleum hydrocarbon by-products of biodegradation present in the ' groundwater likely are resulting in overstated or false-positive results for TPH-D previously reported for groundwater samples collected at the site 1 BTEX were not detected in any groundwater samples collected from the wells TPH-D was not reported above the method detection limit in the groundwater sample collected from MW-2 TPH-Diwas reported in the groundwater samples from wells MW-1 and MW-3 analyzed following the standard procedure for modified EPA Method 8015 ITPH-D was reported in the filtered groundwater samples from wells MW-1 and MW-3, indicating that petroleum hydrocarbon adsorbed onto soil particles and separate-phase petroleum hydrocarbon entrained ' in the samples probably are not a factor In contributing to the reported TPH-D concentration However, TPH-D was not detected in groundwater samples filtered in the field and cleaned up with silica gel prior Ito laboratory analysis, indicating that non-petroleum hydrocarbon by-products of biodegradation were present in the groundwater samples collected from these two wells and are resulting in an overstatement of the TPH-D results j 3 1