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'S 07 May 2004 AGE-NC Project No 98-0534 a ' Page 12 of 14 'detectable concentrations in aWg/l tonng wells as of 06 February 2004,TPH-d has decreased from ' a maximum concentration of In MW-4 to non detectable concentrations in all monitoring wells as of 23 January 2003, benzene was detected on only one occasion at a concentration of 0 62 µg/1 in MW-6, toluene has decreased from a maximumcork r�a,t�o°n of 1 5 µg/1 in MW-4 to non - ' detectable concentrations in all monitoring wells as of , Q02, MTBE has decreased from a maximum concentration of 350 µg/1 in MW-6 to non detectable concentrations in all monitoring wells as of 06 February 2004,TBA has decreased from a maximum cgnccnt r �ation of a�µg/1 in MW- 6 to non detectable concentrations in all monitoring wells as of 02 0 e and ETBE has decreased from a maximum concentration of 24 µg/1 in MW-6 to non detectable concentrations in �yy ' all monitoring wells as of;P41;_Jtme 2002 No other petroleum constituents of concern were detected from the ground water momtonng events ' Analytical results of ground water samples are summarized in Table 2 General lithology is depicted in cross sectional view in Figure 5 Selected soil sample locations and ' the estimated extent of petroleum-impacted soil beneath the site are depicted in cross sectional view in Figure 6 The estimated distribution of adsorbed TPH-g concentrations is depicted in plan view in Figure 7 The estimated distribution of dissolved TPH-g concentrations is depicted in plan view �u � �� lie in Figure 8 When the data collected at the site is plotted in both plan view and cross sectional view, oy` the apparent volume of petroleum impacted soil beneath the site is approximately 341 cubic yards (Appendix D) I An adsorbed 1 - so bed vo ume mass calculation using the data collected during UST removal and investigation of the former UST area, yields 341 yards of impacted soil with a volume of 2 31 gallons of petroleum (TPH) in the remaining impacted soil at the site (Appendix D) 6.0. DISCUSSION AND CONCLUSIONS Based on data collected during site assessment and groundwater monitoring events,AGE concludes - In August 2000, the-gradient 1n the area of the former USTs was calculated to be 0 003.f/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 Icalculated 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 Advanced GeoEnvironmeatal,Inc r ' f