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Manan o UP0198 PaIGIS 6 C-0 0 �3.�3 Qenzeo�e 6r� S�fil c�a�c� �roe�aac��w�c�p Concentrations of benzene increased with depth from 22 feet bgs to 40 feet legs to from a range of 0.019 ppm to 13 ppm. At 45 feet bgs to concentrations decreased to 0.14 ppm to 0.11 ppm, 0.011 ppm and noes-detectable Oevels identified at 48, 59, & 63 feet bgs, respectively. 4 l'ae highest levee of TCLP benzene was 460 ppm at 40 fret {bgs. 'TCLP Benzene decreased with depth to 3.2 ppm, 1.7 ppm, and non-detectable at 45, 59, and 6�3 feet bgs, respectively. The remaining seven (y) soil samples collected and analyzed for TCLP benzene from 63 to 100 feet bgs yielded non-detectable results for leachability. This indicates that the benzene is not leachable to the groundwater. Benzene was identified in the groundwater grab sample, at 4.3 ppb, indicating that the benzene reached the groundwater by leaching through the vertical soil profile via ¢another migratory pathway, by cross contamination of the bailer during its dece down the center of the hollow-stem auger, or by vapor phase migration. 4.0 SOOd S4° A 41GMG°PO V the top 30 feet of the borehole encountered predominantly sandy clays and clayey sands. From 30 to 42 feet, the soil was composed of a silty sand. 3e0ow the silty sand, from 42 to 60 feet bgs was a sandy silt which graded into a silt. Ot appears that the reason the highest concentrations of gasoline constituents have accumulated on top of the soli, within the more porous and pemeable silty sand. On effect, the eighteen (18) foot Chock silt prayer has played a major roll in the prevention of the vertical migration of contaminants to groundwater. On light of the fact that the silt payer is so thick relative to the small areal extent of the subject site, we can conclude that it is laterally continuous. A relatively dry sandy silt was identified between 87 and 100 feet bgs and was used as the representative soil medium for the lateral fate and transport of benzene in groundwater. 5.0 OP'VQFACQ 8M MARMV rJAU122 SMPPIN C^I'MLS A door to door well search was performed on .duly 11, 1998 in order to confirm the well locations as indicated by the driller supply well logs previously collected at the State Department of Water Resources and to identify any supply wells in the vicinity of the subject site which are not documented (See Figure 2 for supply welO location asap) & (See Appendix C for weil driller logs). One undocumented well was identified at the Lockeford School and another at the Lockeford water tower (See Figure 3 for photos of • undocumented supply wells). Both of the undocumented wells are located closer to the subject site than any of the other wells identified during the