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• SB7 compared to MW2 and MW3 respectively showed the following reductions: TPHg at 96.9% and 99%, Benzene and Toluene complete removal, and Xylenes at 90.5% and 99%. SBS compared to MW2 and MW3 respectively showed the following reductions: TPHg at 98.38% and 99.48%, Benzene, Toluene and Ethylbenzene complete removal, and Xylenes at 96.29% and 99.61%. S136 compared to S133 (highest noted contaminated area) and MW10 respectively, showed the following reductions: TPHg at 99.2% and 96.6%, Benzene, Toluene and Xylenes complete removal. It is felt through vapor extraction and limited over-excavation of the UST area that the source (soil contamination) at this site has been removed and that soils portion of the remedial action efforts has been accomplished and that no further actions are necessary. GROUNDWATER Grab water samples obtained on June 4 and 5, 1997 from soil borings S135, SB6 and SB7 were compared to the historic water samples obtained on December 7, 1988 from S132 and S133, see Table and Charts in CONFIRMATION OF THE EFFECTS OF THE VAPOR EXTRACTION SYSTEM, dated July 31, 1997. Comparing SB3 to SB6 a 93% reduction in the amount of TPHg has been accomplished. Benzene, Toluene and Ethylbenzene have been reduced to below laboratory lower detection limits and Xylenes have been reduced by 99%. Similar reductions can be seen when comparing S132 with S135 and S137, or 92% and 85% for TPHg respectively. While Benzene, Toluene and Ethylbenzene have been reduced to trace amounts. Xylenes have been reduced to 54%and 13% of their original values respectively. Confirmation soil boring S137 was converted into a two inch PVC well MW13. This well along with MW 1, MW2, MW3 and MW 10 is currently being used for vapor extraction. MW2 and MW13 are also used for air sparging (commencing on October 9, 1997). It is anticipated that sparging of these wells will introduce and make available oxygen for biodegradation of the down gradient wells MW8 and MW12. Prior to shutting off the air sparging vapor extraction system on December 8, 1997 MW2 and MW13 along with MW8, MW9 and MW12 were tested for the amount of DO in the groundwater. Sparging had saturated MW2 and MW13 with oxygen, they registered 9.1 and 7.6 mg/L respectively. Upgradient well MW9 contained 4.1 mg/L while downgradient wells MW8 and MW12 contained 1.3 and 1.8 mg/L,. It is unclear at this time if the DO found in wells MW8, MW9 and MW12 is a result of vapor extraction, sparging or the combination of both. What is clear is once the sparging and vapor extraction is turned off, the DO in the groundwater is used up almost immediately, see Figures 6 and 7. 6 R603 Update#50 12/97