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' 02 September 2003 AGE-NC Project No. 98-0468 _ ' Page 8 of 11 ' S.O. FINDINGS ; The computer-generated CPT lithologic logs were integrated with previous subsurface soil descriptions to construct the subsurface geological model. The.hydrocarb6n impact to ground water and soil was"quantified by laboratory analysis.of the grab ground water and soil samples,,as presented below. 5.1. STRATIGRAPHY ' Based on the findings from the CPT soil soundings, cross sections A-A' was constructed to depict general lithology beneath the site (Figure 3). Predominantly fine-grained soil consisting of silt,clayey silt with a transition north to silty clay and clay were encountered at depths from the near surface to approximately 60 feet bsg. Laterally ' continuous�sand and cemented sand units were encountered at 55 feet to 60 feet bsg in CPT3; at 50 and 70 feet bsg in'CPT1 and at 70 feet bsg in CPTS. Another significant and continuous sand unit was encountered between 65 to 90 feet bsg across the site. Interbedded, fine-grained soil consisting lie of silt,clayey silt,silty clay and clay were encountered at depths between approximately 60 to 70 feet bsg and 90 feet to 105 and.125 feet bsg. CPT computer-generated boring logs are included in Appendix B. Interpretative stratigraphic.cross sections of the hydrogeologic setting at the site is ' depicted in Figure 3. 5.2. . HYDROGEOLOGICAL MODEL, ' Based on the CPT results, AGE has developed a preliminary subsurface model of the sedimentary stratigraphy, comprised of seven informal zones; a vadose(unsaturated) zone and six hydrological units. Hydrological units may be defined as significant vertical intervals of soil having significant ' lateral extent and having similar hydrologic characteristics. (i.e. hydraulic conductivity, transmi§sivity, etc.) over its vertical and horizontal extent. A `flow unit' may be"defined as a hydrological unit characterized by significantly greater hydraulic conductivity values than overlying and underlying units. A flow unit is capable of serving as a preferred migration route,•and could potentially allow migration of large contaminant masses over great distances. ' The model presented is and interpretation of the CPT readings, reflecting soil type'and soil pore pressure.. The-four vertical zones identified are as follows(depths are approximate and can vary by several feet across the site): ' Advanced Gen Environmental,Inc.