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• I3 November 1997 AGE-NC Project No 95-0128 Page 4of5 In February 1997,a soil sample was also subjected to physicochemical and microbiological analyses It was found that while physicochemical conditions appeared to be suitable, suitable organisms for reduction of gasoline compounds were absent, possible due to biotoxic conditions caused by high petroleum contamination concentrations or the presence of biotoxic metals These findings indicated that natural attenuation of that petroleum hydrocarbons on the site through biologic activity is not occurring at a significant rate and is not likely to unless site conditions are appropriately modified The details of this work will be presented in a later report APPLICABILITY OF THE WORK PLAN ADDENDUM TO THE CURRENT SITUATION Figure 7 shows the estimated extent of the soil and ground water plumes, and the locations of existing and proposed extraction wells and sparge points Figures 2 and 3 show the soil compositions, TPH-g concentrations and existing screened intervals of most wells on the property If the work plan addendum (-%NPA) is approved, impacted soil between approximately 20 feet and 35 feet bsg can be effective addressed and remediated by the vapor extraction portion of the WPA, . as the soil is coarse grained It is reasonable to assume that the coarse grained soil and ground water lying between 35 feet and 40 feet bsg can be effectively addressed by spargrng and vapor extraction The effectiveness of spargmng on the impacted fine grained soil below 40 feet bsg may be in doubt due to the one permeability value obtained for the interval, but it seems reasonable to assuine that ground water coming into contact with the air sparge stream will be stripped of the more volatile hydrocarbons,thereby reducing the dissolved mass By removing the hydrocarbon mass in the coarse grained soil and reducing the hydrocarbon mass in the ground water in the finer grained soil, it is intuitive that the overall hydrocarbon concentration in ground eater will be reduced and the plume of dissolved hydrocarbons will be stabilized and probably will contract Hydrocarbons left in the fine y grained soil should have little additional effect on ground water as the forces of adhesion and adsorption that make it difficult to sparge the soil also retards dissolution of the hydrocarbons into the ground water It is not anticipated that oxidation of iron dissolved in ground water will cause significant fouling of sparge points CONCLUSIONS AND RECOMMENDATIONS It is the belief of AGE that if the CAP had been approved and put into effect when ground water was at 50 feet bsg, most of the subsequent hydrocarbon impact on ground water would have been . prevented At the present time,at least 10 feet of coarse grained vadose zone soil and 5 feet of coarse soil and ground water in the saturated zone can be easily and effectively addressed by the VRA The