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' 08 August 2005 • AGE-NC Project No 98-0534 " , ' Page 14 of 15 investigation of the former UST area,yields 318 yards of impacted soil with a volume of 2 3 gallons ' of petroleum (TPH) In the remaining impacted soil at the site (Appendix F) The estimated distribution of dissolved MTBE concentrations is depicted in plan view in Figure 8 -' ' The dissolved volume-mass calculation using the data collected from the most recent ground water monitoring event demonstrates that a mass of 0 14 kilograms or 0,3'lbs of dissolved MTBE remains near the former UST area(Appendix G) r►l-"' b G ' 6.0. DISCUSSION AND CONCLUSIONS Based on data collected during site assessment and ground water monitoring events,AGE concludes I • In August 2000, the gradient in the area of the former USTs was calculated to be 0 003'ft/ft in southwest flow direction, in December 2000,the gradient was calculated to be 0 003 ft/:ft' ' in a south-southeast to southwest flow direction, in May 2001, the gradient was calculated to be 0 007 ft/ft' in a south-southeast to southwest flow direction, in January 2002, the gradient was calculated to be 0 009 to 0 01 ft/ft in a northernly flow direction, in June 2002, • the gradient was calculated to be 0 009 to 0 01 ft/ft In a northeastern flow direction, in October 2002,the gradient was calculated to be nearly flat,in January 2003,the gradient was calculated to be 0 0063 ft/ft in a northeast flow direction and 0 0052 ft/ft in a southwest flow direction, in October 2003, the gradient was calculated to be 0 002 ft/ft in a southwestern flow direction and in February 2004, the gradient was calculated to be 0 02 ft/ft in a northwest flow direction The final ground water monitoring event demonstrated a northern ground water flow direction at a gradient of 0 017 ft/ft The flow direction at the site has been ranged from north-northwest to south-southwest during this investigation ' Concentrations of petroleum hydrocarbons have decreased in MW-1 through MW-8 to non-detectable concentrations between the August 2000 and February 2004, since then ground water monitoring events, initial elevated petroleum hydrocarbon concentrations in ' ground water encountered during tank removal and soil boring activities were not detected u in quarterly ground water monitoring samples Monitoring well MW-9,screened from 60 feet to 65 feet bsg at the former UST release area was non detect for hydrocarbons and fuel additives for three consecutive monitoring events The lack of high concentrations during quarterly monitoring indicates the initial elevated concentrations were due to minor releases ' of petroleum hydrocarbons as a result of contractor error, product spillage, during tank removal Field notes from the geologist on site during removal activities indicate product spilling from UST during removal The dissolved hydrocarbon plume appears to be well- defined, low in concentration and stable The dissolved MTBE has been laterally defined at concentrations near water quality objectives and are limited to within the boundaries of the • site Table 4 summarizes analytical results for all ground water samples collected at the site 1 Advanced GeoEnvironmental,Inc