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15 May 2009 <br /> AGE-NC Project No. 95-0103 <br /> Page 2 of 6 <br /> • The letter states "A reasonable estimate of residual contaminate mass in soil and ground <br /> water"'.A multiple decade set of ground water and ground water data is available for the site. <br /> Some data has been made available following active ground water remediation <br /> (air-sparging)/soil vapor extraction and ground water extraction. The dissolved mass has <br /> been presented in the past and soil evaluation for residual soil contamination was also <br /> presented. However, the most recent ground water and current soil data were used to <br /> calculate the following values. The current dissolved mass has been calculated at 0.75 <br /> gallons of total petroleum hydrocarbons as gasoline,based on the last sampling event from <br /> monitoring wells and remediation well samples. The current adsorbed mass has been <br /> calculated at 38.98 gallons of total petroleum hydrocarbons as gasoline, based on the last <br /> sampling event from extraction well samples and soil borings. <br /> • The letter states "A demonstration that natural attenuation processes are affecting the <br /> contaminates". A review of the historical soil and ground water demonstrates declined <br /> concentration.The dissolved plume is not moving,even in the absence of effective hydraulic <br /> controls or active air-sparging to deplete the intensity of the mass on-site. The dissolved <br /> plume has not moved north to well MW-2,east to well MW-7 nor west beyond well MW-3, <br /> likely due to advection combined with diffusion and the retardation of the dissolved plume <br /> by soil and clean ground water off-site.The plume has migrated south on-site and southwest <br /> off the site;specifically to the location of well MW-5. Well MW-5 was installed to monitor <br /> the predominate migration direction of the dissolved plume,southwest.However,the plume <br /> migration has been retarded by years of active remediation and well MW-5 was remediated <br /> by natural attenuation; well outside the reached of mechanical remediation. <br /> In December 1998, water samples from wells MW-3, MW-4 and vapor well VE-6 were analyzed <br /> for bio-enumeration and physicochemical characterization by A. Keith Kaufinan, M.S. All three <br /> water samples were found to have concentrations of inorganic components sufficient to support a <br /> microfauna for bioremediation. Nitrogen, potassium and phosphates were at sufficient levels to <br /> support a microfauna for bioremediation for undetermined time period.The sample set contain two <br /> samples from on site wells with low to moderate microbiological populations as biodegraders(wells <br /> MW-4 and VE-6),while the off-site well sample contained no biodegraders.Wells MW-4 and vapor <br /> well VE-6 contained select biodegrading populations ofbacteria at concentrations of 88%and 14%, <br /> respectively. Hydrocarbon concentrations may not be high enough to stimulate the selective <br /> biodegrader populations to accelerate natural attenuation. Under the present circumstances,natural <br /> attenuation by bioremediation is not likely to occur off site with no biogegraders and low oxygen <br /> content. <br /> Based on the information from the site, a population of biodegrading micro-organisms exists that <br /> may promote degradation of the hydrocarbons on the site. In the off-site sample analyzed, these <br /> organisms were not detected. These populations may be encouraged due to the addition of oxygen <br /> Advanced GeoEnvironmentai,Inc. <br />