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r <br /> ATC Associates Inc Project No 99975 7501 <br /> Figures 5 through 8 illustrate the decline in TPHg and benzene concentrations over the <br /> remediation period for monitoring wells BEI-MW3 and BEI-MW1, respectively <br /> 3 2 Microbial Activity <br /> Operation and maintenance inspections during the remediation period observed an inordinate <br /> amount of bio-mass evident in the groundwater immediately after its extraction This was <br /> ' particularly evident during the initial months after remediation startup, requiring weekly back <br /> flushing of the GAC canisters to remove the accumulated bio-mass This occurrence provided <br /> evidence that the physical and chemical characteristics for bio-degradation in the groundwater, <br /> both above and below the surface, were particularly favorable ATC believes the migration of <br /> fresh oxygenated air and water through the site, as a result of the soil vapor and groundwater <br /> extraction, has effected the destruction of far greater amounts of hydrocarbons, by the process <br /> 1 of enhanced bio-degradation, than have been recovered above ground in the respective SVE and <br /> groundwater carbon treatment units <br /> In the last months of system operation, prior to its shut down in February 2000, the amount of <br /> bio-mass produced had declined to negligible, the result of diminished concentrations of <br /> ' hydrocarbon remaining in the groundwater The significance of known favorable bio-degradation <br /> activity extends beyond the period of active remediation Given the relatively minor <br /> concentrations of petroleum hydrocarbons remaining at the site, it is near certain that the <br /> remaining concentrations will degrade to near non-detectable levels within a relatively short <br /> period of a few years, if that long <br /> 3 3 SVE Radius of Influence Testing <br /> During the December 10, 1998 monitoring event, a soil vapor extraction radius of influence test <br /> was conducted to determine the vacuum influence surrounding the co-extraction well EW-1 As <br /> soil vapor was extracted from EW-1, the vacuum influence away from the well was measured at <br /> three surrounding monitoring wells While pumping 100 cubic feet per minute from EW-1, the <br /> vacuum in the extraction well is only about 3 inches of mercury(39 inches of water) This attests <br /> to the relatively high degree of gas permeability in the soil surrounding the well Using <br /> supersensitive magnahelix vacuum gauges, the most notable vacuum effect was observed in <br /> monitoring well BEI-MW1, located approximately 40 feet from the co-extraction well A <br /> differential of 0 3 inches of water was observed between the vacuum measured in the well and <br /> ambient air pressure The vacuum differential for BEI-MW3, located only about 10-12 feet from <br /> the extraction well was only 0 12 inches of water The vacuum influence between co-extraction <br /> well EW-1 and monitoring well BEI-MW2, located approximately 40 feet apart, was evident but <br />--� eveii siiialier,Irving d differential of 0 01 inLheh of water In summary the results show the SVE <br /> process to have been very effective The probable greatest impact of SVE,however,was through <br /> the enhancement of biological activity as oxygen rich air was drawn through the soil <br /> r <br /> w <br /> r <br /> 3 <br /> r <br />