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ethylbenzene, and xylenes (BTEX) by EPA Method 8020 The samples were also analyzed for <br /> methyl t-butyl ether (MTBE) by EPA Method 8020 <br /> IThe analytical results for the samples collected on 18 April are presented in boldface type in <br /> Table 1, along with previous data The laboratory analytical report and chain-of-custody <br />' documentation are included as Appendix B <br /> Detectable concentrations of TPH-g in the samples ranged from 63 ,uglL (MW 1) to 78,000 µg/L <br />' (RW3) Detectable benzene concentrations ranged from 5 5 ,ug/L (P2) to 5,100 µg/L (RW3) <br /> The concentration of TPH-g in the sample collected from MW8, located adjacent to the Shell <br /> service station and upgradient of the site, was 43,000,uglL MTBE was detected in samples from <br />' wells MW3, IW 1, and RW2 at concentrations of 17 ug/L, 38 bcglL, and 74 kcgIL, respectively <br /> Groundwater sample analytical results are shown in Figure 1 <br />' Petroleum hydrocarbon concentrations in the extracted soil vapor have decreased significantly <br /> since the startup of the vapor extraction and treatment (VET) system at the site, suggesting <br />' considerable progress in the remediation of the vadose zone As can be seen in Figure 4, the <br /> monthly monitoring of TPH-g concentration in the extracted soil vapor entering the VET system <br /> oxidizer indicates a 20-fold decline since startup The monthly monitoring of benzene <br /> concentration in the extracted soil vapor entering the VET system oxidizer indicates a more <br /> drastic decline of two orders of magnitude since startup (Figure 4) During the current quarter, <br /> petroleum hydrocarbon concentrations in the extracted soil vapor entering the VET system <br /> oxidizer have remained near the values observed during the previous quarter 88-140 µglL for <br /> TPH-g and 0 18-0 86 gg/L for benzene <br />' 2.1 WSPA STUDY <br />' Exxon RS 7-3942 is included in the Western States Petroleum Association (WSPA) Purging <br /> Study The normal sampling schedule will resume next quarter <br /> The WSPA study is being conducted to assess the significance of purging in obtaining <br /> representative samples of groundwater Both pre-purge and post-purge samples are collected <br />' from selected groundwater monitoring wells, following a WSPA-approved protocol prepared by <br /> SECOR International, to determine if there is a statistically significant difference in hydrocarbon <br /> concentrations between pre-purge and post-purge samples The analytical results provided in this <br />' report are from post-purge samples Analytical results for pre-purge samples are provided in the <br /> laboratory report, but are not included in this quarterly report <br />' Laboratory analytical results and chain-of-custody documentation are provided in Appendix B <br />' WP61 73942Q496 TX 5 2 <br />