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Geological Teclutfcs/a. Page 4 Additional Pilot Test Work Plan Project No.770.2 October 30,2008 Vertical gradients have been calculated for the MW-5/105 &MW-6/106 well pairs during the investigation. Similar to the historical lateral directions, the direction of groundwater in the vertical plane also fluctuates at the site. Both positive and negative vertical gradients have been calculated for the site. The magnitude of vertical groundwater flow direction ranged from—0.02 to 0.01 for the site investigation. — Groundwater elevation in shallow and deep aquifers has increased as much as 15.06 and 15.09 feet since September 2005 respectively. The increasing trend is observed in groundwater elevation since then, so that a daily increase in groundwater elevation is estimated as 0.016 feet/day. Tables 1 & 2 in Appendix A contain the groundwater elevations and gradients recorded for � � 3 s.• the water table and deep wells, respectively. Table 3 includes the well construction d tails. 2.3 Contaminant Distribution v eri"tr y.. Tables 4 through 8 in Appendix A contain the site's historical soil and groundwater da a ( ' Figures 7 and 8 illustrate the soil and groundwater contaminant distribution as superimposed on the two cross-sections A - A' and B — B', respectively.-/The data from the Jul 23, 2008,; '1 T� , groundwater monitoring event and the ctober 2 CPT boreholes are presented in the til V diagrams adjacent to the respective well�scre�enterval 1; � di ; } 2.3.1 Soil !�k' In Figure 7, a column of soil contamination is present under the former UST 04-v e �' excavation/dispenser area. In the vicinity of MW-6/MW-106, no soil contamination was— Ok;;c fid detected and Wm. Hunter & Associates stated no contamination was present in MW-3. GTI previously suggested that the contamination migrated downward to impact the groundwater without less permeable soil layers causing lateral dispersion higher in the column. With the addition of the CPT data, there is a small amount of TPH-D at 50 feet bgs in CPT-2, but clean soils are above and below at 40 and 65 feet bgs, respectively. This contradicts our earlier interpretation. In Figure 8, a similar situation is present. A "stringer" of laterally displaced TPH-D is evident in MW-104 at 55 feet bgs. However, it is noted that this depth is within the historical range of groundwater fluctuations and could be caused by water transport. h)S1` l!S The field geologist noted a strong HC odor at 40 feet bgs and a free product interface at 45.5 feet bgs in boring MW-7. The soil concentration of 9,720 mg/kg TPH-D @ 45 feet bgs corroborates with the free product noted at this depth. It is likely that the geologist had encountered non-aqueous phase liquids (NAPLs) entrained in the silty soil. TPH-D was detected in soil at 55 feet at a concentration of 12,200 mg/kg, then attenuating to 331 mg/kg at 70 feet bgs. Once reaching the groundwater table the diesel contamination spread laterally ,... with the rise and fall of the groundwater table.