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i 28 February 1997 AGE-NC Project No 95-0144 n Page 4 of 20 In January 1996, two in-situ air sparging wells (IAS-I and TAS-2)were installed at the site An in- situ air sparging (IAS) pilot test was performed'at the site in February 1996 Increased induced = pressure, organic vapor, ground water elevation and dissolved oxygen were generally measured at monitoring wells throughout the test Procedures and results were summarized in the Corrective ' Action Plan -February 1996 prepared by AGE Cross sections A-A' and B-B' (Figures 3 and 4) illustrate the encountered soil profile and the ' ~estimated extent of impacted soil in the vicinity of USTs No 3 through 6 Impacted soil is also present below the current ground water table, due to historic fluctuations of ground water elevations at the site Analytical results of all soil samples collected at the site are summarized on Tables 1 through 3 ' Quarterly ground water monitoring has been performed on 17 occasions between January 1991 and February 1997 as surnmarized in various quarterly reports Petroleum hydrocarbons have not been detected m samples collected from monitoring wells MW-8 or MW-18 Only low concentrations of ' hydrocarbons were detected in MW-I 1 and MW-12 during the October 1995 monitoring event Low concentrations of TPH-g and TPH-d were detected in MW-13 during the last three monitoring events Low hydrocarbon concentrations have been detected intermittently m MW-2, MW-4 and MW-5 since installation Concentrations have shown a general decrease in wells MW-2 and MW-4, while concentrations have shown a recent increase in well MW-5 Petroleum hydrocarbons have ' been detected in samples collected from MW-1, located adjacent to the former USTs location during each sampling event _ 'The estimated extent of impacted ground water in the vicinity of USTs No 3 through 6 is illustrated on Figure 5 Recent depth to ground water data is summarized on Table 4 Analytical results of water ' samples from the monitoring wells, and Geoprobe "hydropunch" sampling are summarized on Tables 5 through 7 ' Several additional sites with potentially impacted ground water are located up-gradient and cross- E gradient to the site However, based upon samples collected from the site and information rovided w by the PHS-EHD, the plumes from these sites do not appear to have impacted the subject site 4.0. POTENTIAL IMPACT ON NEARBY SURFACE AND GROUND WATER I Typically, ground water would represent the migration medium for contaminants over significant distances Sites that are located in up-gradient or equi-gradient(cross-gradient) directions from the < subject property are not likely to be negatively impacted by the subject property Since the Deep Water Channel is approximately 400 feet up-gradient of the site, impacted water at the site does not