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geohgual rechuucs Inc Page 10 Additional Site Characterization Report Project No 662 2 1 February 20,2004 ' ❑ Clay units were encountered at 24, 34 and 52 feet bgs Like the silts these g y layers are less than 3 feet thick, grey in color and occasionally contain a small percentage of ' sand The deeper clay layers contained black material (organic or magnetite) with prominent iron oxide staining The CPT logs included in Appendix F were reviewed to determine the site lithology The bore log for CPT-4 was compared to log of MW-104 as a relative measure of the correlation between the field logging and CPT methodology The CPT log shows alternating layers of sands, silts and clays with different colors to represent the varying lithologic units sands- yellows & browns, silts- green hues, and clays- blue hues (the complete color key is ' included as Figure 5 in the Gregg report) The CPT methodology results in certain layers identified as stiff or cemented without regard to grain size These units have a dark grey or muted color on the diagrams 1 The field Iogging indicated that the top fifteen feet of MW-104 was primarily sandy The CPT-4 log corresponds well with this data indicating sands, silty sands or sandy silts From ' approximately 17 to 35 feet bgs the field geologist logged alternating layers of sands, silts and clays with no unit exceeding 3 feet in thickness The CPT-4 log also displays the same data, with three prominent sand units (colored yellow and brown) at depths of 21, 25 and 29 Mfeet bgs These three units correlate well with sand units identified by the field geologist at 20, 25 and 28 feet bgs The geologist logged from approximately 35 to 51 feet bgs as sandy and this interval is also depicted on the Gregg log as a prominent brown section (sandy) ' across the same interval A clay section was identified by the field geologist as extending from 51 to 54 feet bgs with a transition back to sand at 54 feet bgs The CPT log shows ' silty clay and clayey silt units across this same interval Based on the above comparison the CPT-4 bore log correlates well with the verified site ' conditions in MW-104 and therefore the rest of the CPT locations were evaluated with a good degree of confidence Figure 2 shows the location of two geologic cross sections developed for the site Figure 3 Geologic Cross Section A—A' shows the site lithology on ' a west to east orientation and Figure 5 Geologic Cross Section B - B' shows the lithology on a southwest to northeast trend The geologic units have been combined into fine grained (silt/clay/silty clay/clayey silt) or coarse grained (sand/silty sand/gravelly sand) units to ' clarify fate and transport of contaminants Note The cross sections were developed using data gathered by different individuals ' utilizing different methodologies Therefore, they need to be looked at as one of several possible interpretations of actual site conditions) In Figure 3 a coarse grained sand unit is present at a depth of approximately 38 --- 48 feet bgs This unit is laterally continuous across the site and all eight CPT logs show variable thickness, brown/yellow sand units at this depth Above and below these sands in both