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• • Geologita[Tecknicslitc. Page 4 Geoprobe Investigation Project No. 425.2 September 18,2008 Sample W4.35xlOE-6 BSS-2 @ 18' BSS-2 @ 20' BSS-2 @ 28' 7 BSS-2 @ 30' 6 1.4 Contaminant Distribution The soil and groundwater mass balance calculations were presented in GTI's "Soil Excavation Report" dated January 28, 2002. In summary - approximately 11,632 lbs. of TPH-g was estimated in the calculations, and according to the excavation contaminant mass removal calculations, approximately 4,900 lbs. (42%) of TPH-gasoline was removed with soil excavation. Therefore, about 6,700 lbs. of TPH-g has not been removed. 1.5 Zone Divisions The aquifer is divided into four zones (Zones A through D) defined by the screen intervals of the sixteen monitoring wells associated with the site. (Table 1) • Zone A includes monitoring wells screened between 5 and 22-feet bgs (MWs: 1 —8) • Zone B includes monitoring wells screened between 32 and 35-feet bgs (MWs: 2X, 101, 105, 106, SW-101, SW-102) • Zone C includes monitoring wells screened between 45 to 49.5-feet bgs (MWs: 102, 107,201) • Zone D is represented by MW-202 screened between 79 and 81.5-feet bgs (MW-202) 2.0 PROPOSED INVESTIGATION In an attempt to better define the horizontal and vertical extent of plume migration on the north side of the site GTI proposes to install up to 15 direct push boreholes to a depth of 40 ft bgs (Figure 2) and test both soil at different depths and groundwater for gasoline based contaminants. By looking at the TPH-G plume shown in Figure 3 it can be seen that the contour generated using the Surfer Package can't be reliable since we don't have any data on the north side of the site between MW-2 and the two wells on the north side of Durham Ferry Road (MW-6 and MW-7). Figure 3 shows the distribution of TPH-G in the shallow zone (Zone A) while MW-6 and MW-7 have been non-detect for the whole site history and MW-2 has been the most contaminated well. The contours on the north side of the site are all the result of interpolation between these three points and can be questioned in the regard that MW-2 contamination plume might simply be an isolated pocket of contamination. To clarify this, a geo-probe investigation at the site is required.