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H. ICnoil, 5/1811995, Page 2 of 4 ' r - and depth. The r levels between monitoring points is a reflection of differing point locations p vacuum response at all monitoring points verifies that the VES zone of influence is sufficient for remediation of the former UST area The consistency of vacuum levels over r time suggests that the system has achieved a state of equilibrium and that the zone of vacuum influence is not increasing with continuing system operation. r The system was shut down several times during the operational period due to normal maintenance activities, system adjustments, and carbon change-out episodes The total shutdown time was approximately 2-weeks during the three month operational period. rSystem off-gas sampling has been performed weekly from startup to satisfy air permit Y 9 requirements (effluent samples), and to establish and verify a reduction of volatile organic compound (VOC) concentrations within the extracted soil gas (influent samples). All samples have been analyzed for total petroleum hydrocarbons (TPH) within the gasoline range by Modified EPA Method $015, and for benzene-toluene-ethylbenzene-xylene ' (BTEX) by Modified EPA Method 8020. All samples collected between startup and January 3, 1995, were transported to and ' analyzed by Capitola Technologies in Capitola, California. A continuing reduction of soil vapor VOC concentrations has been observed during the reporting period The maximum TPH-gasoline level of 667.7-ppm observed at startup has decreased to a low of 48.6-ppm on January 30, 1995. On January 5, 1995, the site operator left the employ of the equipment supplier, On-Site r Technologies, and began Automated Environmental Services of Modesto, California. He continued to perform the O&M activities at the site. As a result of the company change, soil vapor samples collected after January 10, 1995, were transported to and analyzed by Trace Analysis Laboratory, Incorporated, in Hayward, California. The Trace Analysis results were higher by an apparent factor of four with respect to the previous Caprtola r results. Samples were sent to Trace Laboratories, Capitola Technologies, and a third laboratory, Superior Precision Analytical, Incorporated, in Martinez, California, on January 30, 1995, rto evaluate laboratory performance and correlation. There appears to be no correlation between the sample results from the three laboratories. This may be due to the laboratories preparing their samples using differing protocols, using differing petroleum rstandards for calibrating their gas chromatographs, calculating their results using differing computer programs, and presenting their data in differing units. The data from the January 30, 1995, samples and from one additional planned duplicate sampling event will be rfurther evaluated to determine if correlations exist between the separate laboratories, and to identify factors that may be causing the differing data values between laboratories. There is no laboratory certification program for vapor analysis in California, and no rstandard accepted practices or protocols for preparation and analysis of vapor samples. r t-rbe WN,1i�od EaRb Comp�Y' r