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Firestone Store #3573 400 North El Dorado Street, Stockton, Caldorma October 25, 1995 VES Quarterly Report and Request for Closure-4589 Page 5 of 14 33 Analytical Results/Trends Vapor stream sampling and analysis was performed weekly throughout SVES operation to identify the level of TPH-G and BTEX concentrations within the soil vapor, and to establish the trend of TPH-G and BTEX concentration reduction over time Laboratory analytical results from the first quarter of operation can be reviewed in the monitoring report sent to San Joaquin County on May 18, 1995 (First Quarter Monitoring Report, Appendix 7 6) Analytical results from the second quarter of operation are tabled in Section 2 0 of this report While all samples were analyzed for BTEX, benzene is the compound of primary regulatory concern, therefore it is the only BTEX compound for which concentration trends and residual levels have been evaluated The following evaluations of TPH-G and benzene concentration trends are based on laboratory results from Capitola Technologies ' 3 3.1 TPH-Gasoline ' The TPH-G Concentration Graph on Page 6 was created using a visual best-fit curve through the plotted data points As demonstrated by the curve, the maximum TPH-G level of 667 7-ppm (observed at startup on November 4, 1994) decreased rapidly over the first month of operation The TPH-G vapor concentration fell below 100-ppm in mid-December 1994 and remained below that level throughout the remainder of system operation TPH-G concentrations remained relatively stable (48 6-to 82 0-ppm)throughout the three month period from mid-December 1994 through the primary system shutdown on March 24, 1995 Since there is no discernable trend of TPH-G concentration reduction during this operational period, reduction of TPH-G concentrations in soil vapor is believed to have reached an asymptotic state during this time Fallowing the shutdown period for subsurface equilibration (March 24 through April 21 , 1995), the system was re-started to investigate for elevated VQC concentrations that may have resulted from the dormant period A sample collected during startup of the SVES following the shutdown period displayed a decreased TPH-G concentration of 27 1-ppm when compared with the pre- shutdown sample result of 56 9-ppm TPH-G results for the following three weeks remained below the pre-shutdown levels RYAN-MU UWY, INCORPORATED Denver Fnvu+oumenl Conshmetion Management Los Angeles