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' 23 December 2005 . AGE-NC Project No 95-0103 ' Page 5 of 7 3 2 3 Natural Attenuation - Geochemical and Geophysical Results ' Geochemical arameters were generally consistent between on-site and off-site wells duan the A g Y g October 2005 monitoring and sampling event • The pH values were almost stable or equal between all wells monitored (6 355-6 713) ' Conductivity varied across the site Highest values were found In offsite well MW-2 (2,424 µmho/cm)and in the plume area at well VE-1 (2,269 µmho/cm) Lowest values were found in the northern plume area at well VE-6 (1,616 µmho/cm) and eastern plume area at well ' MW-4(1,847 µmho/cm) Alkalinity was highest at off-site well MW-2(860 milligrams per liter mg/1)and lowest within the down gradient edge of the plume at well EW-1 (590 mg/1) Redox and dissolved oxygen measurements were significantly greater than detected during ' the purging process and not reliable when comparing the sample set The highest DO value was reported from well MW-2 at 6 62 mg/l, north and upgradient of the plume area However,the lowest DO values were down gradient of the former release area(EW-1 2 03 ' mg/1) and at the former UST site (VE-6 2 61 mg/1) • Nitrate and sulfate values were highest off-site at well MW-3 (2 2 mg/l, and 230 mg/l, respectively) and MW-2 (2 1 mg/1 and 240 mg/l,respectively) The lowest concentration of 10 nitrate was detected at EW-3, at 160 mg/l, while the lowest concentration of sulfate was at offsite well MW-5 at 1 1 mg/l ' Ferrous Iron, carbon dioxide, nitrite, and sulfide were not detected in the samples • The remaining metals and Ions detected In the water samples do not significantly vary In ' concentrations between the wells However,some elements were reduced In the core area of the plume and generally TOC was elevated within the core areas (EW-3 7 1 mg/1 and MW-2 1 1 mg/1) Additionally, COD was only detected on the site In the core of the ' petroleum release area ' The expressed assimilative capacity (EAC) for the ground water at the site was estimated to be 18 3 mg/l (difference In concentrations between background and areas of highest BTEX contamination - see Appendix D) The typical EAC for successful loss of contamination In the ' aquifer has been depicted above 300 mg/1, however, because of the simplifications of the estimate, only empirical field data(analytical data) can be relied upon to reflect contaminant degradation and mass reduction As with all estimates of mass loss, EAC does not represent actual subsurface reactions The hydrocarbon analytical results of current and previous monitoring well samples are summarized ' in Tables 2 and 3 ' Advanced GeoEnvironmental,Inc 1