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Weekly bio-venting of MW-8 and MW-12 are being conducted by Lawrence Tank Testing Currently the groundwater is too high, no slotted casing is exposed above groundwater at MW12 to conduct bio-venting As of December 9, 1998 the 2 hour once a week bio-venting of MW-8 has removed a calculated 5 62 pounds of gasoline range hydrocarbons and a total of 543 pounds of hydrocarbons as gasoline and CO2 The average flow rate is 50 8 cfm, with a vapor stream consisting of TPHg of 0 01 mg/L and CO2 at 1 5%, see Table 3 and Appendix E Summary SOIL Confirmation soil sample borings S134, S135, SB6 and SB7 were drilled and sampled (June 1997) near previous sample boring SBI, SB2 and SB3 (December 1988), see Figure 3 Charts were developed to show the reduction comparisons of the soil sample results, see previous report CONFIRMATION OF THE EFFECTS OF THE VAPOR EXTRACTION SYSTEM, dated July 31, 1997, Table 2 for results No MTBE was noted in any of the soil samples The following four comparisons are from the 50 foot depth, which is the depth of the historic highest concentrations 1 SB4 compared to SBI showed a 99 7% reduction of gasoline range hydrocarbons (TPHg), complete removal of benzene and toluene, and a 99 8%reduction of the xylenes 2 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% 3 SB5 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% 4 S136 compared to SB3 (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, that through vapor extraction and limited over-excavation of the UST area, the source (soil contamination) has been removed and the soil portion of the remedial action efforts has been accomplished GROUNDWATER Grab samples of the water were obtained on June 4 and 5, 1997 from soil borings SB5, SB6 and SB7 These water samples were compared to the historic water samples obtained on December 7, 1988 from SB2 and SB3, 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% 7 8603 Update#E54/CLOSURE 3 12198