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' 21 June 2002 AGE-NC Project No 99-0624 ' Page 3 of 6 3.0. RESULTS ' The CPT lithologic data interpretation was Integrated with previous subsurface soil descriptions to ' refine the subsurface geologic model,the hydrocarbon impact to ground water and soil were assessed by laboratory analysis of the grab ground water and soil samples, as presented below ' 31 STRATIGRAPHY ' Based on the computer-interpreted data acquired from the CPT soil borings and soil composition data acquired in previous borings(Figure 2),cross sections A-A' and B-B' were constructed,which depict general hthology beneath the site (Figures 3 and 4) The site stratigraphy suggests an overall ' coarsening upwards sequence Below 85 feet below surface grade(bsg)to total depth(100 feet bsg), the sediments are dominantly stiff fine-grained sediments,with several thin,discontinuous clay and silt Iayers In the zone from 20 feet to approximately 85 feet bsg,the cross sections generally depict ' thin, laterally continuous, mostly cemented sand layers, ranging in thickness from approximately 1 foot to approximately 5 feet, intercalated with fine-grained sediments, the frequency of occurrence of the sand layers appeared to increase upwards as well as towards the south and east The upper 20 ' feet of soil generally consist of alternating silty to gravelly sand layers which fines upward to silts in the upper 7 feet ' Copies of the computer-generated CPT boring logs are included in Appendix A ' 3 2 HYDROGEOLOGIC MODEL Based on the CPT results and comparison with soil descriptions from borings previously advanced I on the site, AGE has developed a preliminary subsurface model of the site soil stratigraphy comprised of eight informal zones - a vadose (unsaturated) zone and seven hydrologic units I Hydrologic units may be defined as significant vertical intervals of soil having significant lateral extent and having similar hydrologic characteristics(I e hydraulic conductivity,transmissivity,etc ) over Its vertical and horizontal extent A `flow unit' may be defined as a hydrologic unit characterized by significantly greater hydraulic conductivity values than the 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 interpretational and will be modified as more data is collected The eight vertical zones identified are as follows(depths are approximate and can vary by several feet across Ithe site) Advanced GeoEnvi ron mental,Inc