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CtologtcalTeclrxtcsluc Page 8 Revised Site Conceptual Model Report Project No.507.2 April 3,2008 GeoProbe Borings GP-4 and GP-5 *' On February 28, 2008 two shallow 30 ft GeoProbe borings were installed to further defile the site. The subsurface in the vicinity of GP-4 is characterized by: ❑ At 5 feet bgs brown, slightly moist,very fine grained, silty clay was present. a At 10 feet bgs brown, slightly moist, very fine to fine grained sandy clay was encountered. ❑ Brown moist clay was found at 15 bgs. ❑ The clay was underlain by clayey sand present at 20 feet bgs. This grey, moist soil contained a strong petroleum odor. ❑ At 25 feet bgs dark blue/grey, moist silty clay was encountered, again with a strong petroleum odor. ❑ At 30 bgs a dark grey, moist, clayey silt was encountered, again with a strong petroleum odor. The subsurface in the vicinity of GeoProbe GP-5 is characterized by: ❑ At 5 feet bgs and again at 10 feet bgs,brown, moist, very fine grained sandy clay was present. ❑ At 15 feet bgs a black, moist to wet sandy clay was encountered. ❑ A clayey sand present at 20 feet bgs underlay the clay. This grey, moist soil of L- varying grain size contained a strong petroleum odor. ❑ At 25 feet bgs dark blue/grey, moist silty clay was encountered, again with a strong petroleum odor. ❑ At 30 feet bgs dark grey, moist clayey silt was encountered, again with a strong petroleum odor. J6. As expected, the subsurface in the vicinity of GeoProbe 4 and 5 is dominated by clay sediments, with a clayey sand unit at approximately 20 feet below ground surface. Figures 4, 6 and 8 provide a geologic interpretation of the units observed in the borehole logs; see Figure 3 for Cross Section locations. Note: The cross sections were developed using data gathered by different individuals utilizing different methodologies. Therefore, they need to be booked at as one of several possible interpretations of actual site conditions.) The cross sections include lithologies divided into fine grained units (slits and clays) and LM coarse grained units (sands). This is particularly true in the vicinity of the three continuously cored borings SB-7 through SB-9 that were advanced at the site on rune 30, 2006. The purpose of these three boreholes was to determine if sandy or silty soils are present that have not been detected previously due to the 5 foot sampling interval used in the past. The results of that investigation showed that there are sandy units in shallow soils and the cross sections show sandy soils at 15 -- 35 feet although some thin clay units are present. Photographs included in GTI's September 5, 2006 "Additional Site Characterization Report" are reiterated below: V