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1 5 2 Groundwater Sampling and Anal sm On June 21, 1993, Aegis personnel collected groundwater samples from the five accessible wells at the site The samples were collected according to the Aegis SOP ' included in Appendix A, and submitted under chain-of-custody to Pace incorporated of Novato, California, a state-certified analytical laboratory The samples were analyzed for ta) TPH-G by modified EPA Method 8015, and, b) BTEX by modified EPA Method 8020 ' Laboratory analytical reports did not indicate petroleum hydrocarbons in any of the five ' wells sampled on June 21, 1993 The recent and historical analytical results are summarized in Table 3 The analytical reports and chain-of-custody form are included in Appendix C Figure 7 shows the well locations and sampling results 6 0 CONCLUSIONS ' The data derived from recent site activities has demonstrated that soil vapor extraction has reduced petroleum hydrocarbon concentrations in the soil Although petroleum ' hydrocarbon constituents were present from 16 to 36 feet below grade in SB-9, no benzene was detected This indicates the success of vapor extraction in removing the more volatile and mobile hydrocarbon compounds Since June 1991, groundwater analytical results have not indicated the presence of petroleum hydrocarbons in any of the monitoring wells During this time, the groundwater elevation has fluctuated from approximately 39 to 45 feet, corresponding to depths ranging from approximately 54 to 61 feet below grade The groundwater elevation has been within this zone since 1988 The vertical fluctuation of the groundwater does not appear to have had an impact on groundwater duality No TPH-G was present in soil samples collected every five feet from 36 feet below grade to groundwater at 57 feet below grade The soil boring results indicate at least a 15-foot thick interval (41 to 56 feet below grade) of mostly silty soil containing nondetectable TPH-G and less than 0 04 ppm BTEX concentrations exists immediately above the water table Also, the proximity of the clean soil borings indicates limited lateral extent of petroleum- impacted soil IBased on the above observations, Aegis believes the remaining petroleum hydrocarbons present in the vadose zone are immobile and localized, and do not present a threat to groundwater Therefore, Aegis recommends no further remedial action or monitoring and believes the site should be considered for closure 93 0056 QMR 4