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The analytical results for the samples collected on 8 August are presented in boldface type in Table 1, along with previous data The laboratory analytical report and chain-of-custody documentation are included as Appendix B Detectable concentrations of TPH-g in the samples ranged from 450 4g/L(MW4) to 58,000,ug/L (RW3) Detectable benzene concentrations ranged from 4 4 ,ug/L(MW4) to 4,200,ug/L (RW3) The concentration of TPH-g in the sample collected from MW8, located adjacent to the Shell service station and upgradient of the site, was 46,000/..tg/L MTBE was detected in samples from wells MW2, MW4, and MW9, at concentrations of 6 8 ug/L, 7 4 4glL, and 230,uglL, respectively Groundwater sample analytical results are shown in Figure 1 3. SOIL VAPOR EXTRACTION AND TREATMENT SYSTEM A vapor extraction system (VES) has been operating at the site since May 1994 The system extracts soil vapor from the vadose zone through seven wells (V 1, V2, V4, MW2, MW3, MW5, and MW6) and destroys hydrocarbons with an oxidizer The system is augmented with air spargmg equipment that infects air below the water table through infection wells [WI and IW2 The oxidizer was converted from thermal to catalytic operation in May 1995, following a steady decline in extracted soil vapor concentrations, as shown in Tables 2 and 3 The decline in extracted soil vapor concentrations has continued since the conversion to catalytic operation During the current quarter, oxidizer influent samples contained TPH-g concentrations from 60 pg/L to below the method detection limit (mdl) of 10 jig/L, and benzene was detected from 3 9 gg/L to below the mdl of 0 050,ugIL 4. WORK PROPOSED FOR NEXT QUARTER Groundwater elevations will be measured and groundwater samples will be collected in November 1996 The samples will be analyzed for TPH-g, BTEX, and MTBE Because of the proximity of wells IW 1 and MW4, well P 1 is sampled only twice a year Similarly, because of the proximity of wells IW1 and RW2, well MW2 is sampled only twice a year On the same basis, well MW 1 is sampled only twice a year, because of its proximity to well P2 Because concentrations of petroleum hydrocarbons in wells MW 12 and MW 13 have been consistently below method detection limits for at least the last six quarterly sampling events, those wells will only be sampled once a year Next quarter, in November 1996, the following wells will be sampled MW2 through MW10, recovery wells RW I through RW4, piezometers P1 and P2, and infection well IW 1 Submerged vapor wells V2 through V4 will be sampled if there is no sheen present W P61-13942QS%TX 3 2