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�1E4�OgfCa�TtC/IIICS!/« Page 11 Revised Site Conceptual Model Report € Project No.507.2 April 3,2008 events. The magnitude of vertical "groundwater flow direction ranged from-0.0003 to 0.0072 { for the site investigation, which is similar to the horizontal gradient. Table 5 in Appendix A contains the groundwater elevations and gradients recorded for the " water table ,aquifer. Table 6 shows the calculated vertical gradients for MW-9/109 ` shallow/deep Ewell pair. Table 7 includes the well construction details. 2.5 Contaminant Distribution 2.5.1 Vadose Zone The drawings`in Figures 5, 7 & 9 illustrate the soil andoundwater contaminant ant distribution , as superimposed on cross sections A - A', B - B' and C - C'. The soil data in these figures were obtained at the time of the borings' installation (1995 -2008) and the groundwater data are from sampling activities conducted during the groundwater monitoring event of February { 11,2008. The historical fluctuations of the water table are also shown in the sections. In Figure 5, there islittleevidence fIPH-G-soil-contamination'ab� - `Y ove the water table.; Tlus situation was caused by a lack of laborat- 'data from obviousl - x -� - ry y impacted core areas (for example near.SB-7). In June 2006 the field geologist noted a strong gasoline odor in soils starting at 6 ft in boring SB-7 with organic vapor readings (OVM) of 21 - 136 ppm. Likewise, soils from 1999 boring SB-3 were noted with gasoline odor at 5-- 10 ft with OVM readings of 18-23. In Figure 7 there is little soil contamination above the water table except in the location of borings MW-9' GP-2 and SB-109.109. In Figure 9, there is little soil contamination above the water table, except in the location of SB-109/MW-1.09. The data from-the recent`Geo1 r0'6e 4-and-5 confirms.this, and-indicates'little soil'contaminatioii'frornrt the water table to-an elevation of_30 ft below ground-surface: Boring SB-1 was placed in the vier,i of the former UST excavation as shown in Figure 2. Since soil samples from SB-1 were clean at 15 ft the source -of the release appears to be associated with piping or dispenser's rather than the UST itself. The presence of gasoline impacted surface soils in the alley between the site's two buildings suggests that the UST dispenser was in this location or adjacent to one of the buildings. The TPH-G concentrations in soil attenuate laterally with distance and depth from this core of the soil plume. 2.5.2 Groundwater { s As stated above, Figures 5, 7 and 9 illustrate the February 11, 2008 monitoring event groundwater contaminant distribution as superimposed on cross sections A - A', B -B' and C - C'. The groundwater data are presented in the diagrams adjacent to the respective well's screened interval. a' -- _._ . i The TPH-G distribution_in the-shallow wells is illustrated in Figure 11, <Well MW-9 contain the lu hest concentration 114 000' ` (. µg/l).,of detected contaminants in the sfiallow aquifer. The plume attenuates laterally away'"from this well to the locations of wells MW-4, MW-5