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1 19 February 2002 AGE-NC Project No 95-0109 ' Page 5 of 6 • Based on the CPT results and comparison with soil descriptions from borings previously ' advanced on the site, AGE has developed a preliminary subsurface model of the site soil I stratigraphy comprised of four informal zones, a 'vadose (unsaturated) zone and three ' hydrologic units (HU1, HU2 and HU3) The vadose zone extends from surface grade to ' approximately 55 feet bsg HU1 extends from 55 feet to 64 feet bsg on-site and vanes to 69 feet bsg toward CPT-3 The soil consists of moderate to high pore pressure cemented sand, s ' silt, silty sand, and undefined stiff fine grained material, thin low pore pressure intervals occur south of the site HU2 extends from 64 to 99 feet bsg on-site and vanes from 69 to 96 feet bsg at CPT-3 HU2 soil consists of gravelly sand and sand on-site (CPT-1 and CPT-2) ' with increasing silt south of the site(CPT-3),the unit has very low pore pressure on-site with development of intercalated high and low pore pressure intervals at CPT-3 HU3 extends from 99 to 140 feet bsg on-site and vanes from 96 to 140 feet bsg off-site (CPT-3), the bottom of the unit is not well defined The soil consists predominantly of fine grained soil with laterally discontinuous sand intervals, pore pressures vary from moderate to high, but ' exhibit limited lateral continuity of specific high or low pressure intervals, pore pressures become more variable at CPT-3, varying from low to high AGE believes the high pore pressure intervals encountered in the CPT borings generally retards the vertical migration of ' contaminants Hydrologic units are depicted in cross sectional view A-A'(Figure 4) • Low concentrations of TPH g were detected in the water samples collected from HU2 and HU3 Low concentrations of benzene were detected only in the water samples collected from CPT-2 in HU2 Low concentrations of toluene,ethylbenzene and total xylenes were detected in samples collected from HU2 and very low concentrations of toluene, ethylbenzene and total xylenes were detected in HU3 Fuel additives were not detected at or above laboratory reporting limits in the ground water samples Constituents of concern detected in ground' water samples collected during the CPT investigation are depicted in cross sectional view A-A '(Figure 4) L S.O. RECOMMENDATIONS Based on the findings from this investigation, AGE concludes • Continued uarterl' ground water monitoring of the shallow well network on-site the next q Y�' g , quarterly ground water monitoring event is tentatively scheduled for March 2002 • Installation of an additional shallow-screened monitoring well to assess the lateral extent of 1,2-DCA-impacted ground water in HU1 as outlined in the approved AGE-prepared IAdditional Site Assessment Work Plan - September 2,001 dated 24 September 2001 • F I s Advanced GeoEnvironmental,Inc i I