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' 27 October 2003 <br /> • AGE-NC Project No 98-0450 <br /> ' Page 4 of 17 <br /> ' 2 3 2 Site Stratigraphy <br /> Silty clay was generally encountered from a depth of approximately 5 feet to 30 feet or 40 feet bsg <br /> ' across the site Light colored sand was encountered at a depth of 30 feet bsg in the former dispenser <br /> area and at 40 feet bsg in the former UST area The sand body thickness Increased as viewed from <br /> south to north under the former UST <br /> Silty clay was encountered at a depth of 45 feet bsg in the dispenser area(boring SB7) and silty clay <br /> was not encountered until a depth of 55 feet bsg under the former UST excavation Silty clay was <br /> ' only encountered in the soil samples collected north of the site <br /> Soil borings are depicted in Appendix A Based upon soil samples submitted for geotechnical <br /> ' analysis,fine sand encountered below approximately 30 to 35 feet bsg has a permeability of 2X10 5 <br /> cm/sec and an average porosity of 40% The total percentage of organic material calculated from the <br /> ' soil sample analyzed was 1 3% A stratigraphic cross sections of soils at the site with analytical <br /> results of soil samples is depicted in Figure 3 <br /> ' • 2 3 3 Extent of Petroleum Hydrocarbon-Impacted Soil <br /> ' Laboratory results of soil samples analyzed are summarized in Tables 1 and 2 <br /> • TPH-g and BTEX were detected at high concentrations below the former USTs TPH-g and <br /> ' BTEX compounds in soil are delineated toward the southwest and south by analytical data <br /> from soil samples collected from soil borings BMW-5 and S137 <br /> ' • The vertical extent of the soil impacted by petroleum-hydrocarbons was delineated to depths <br /> above 60 feet in the former UST area and above 40 feet bsg in the former dispenser island <br /> area However, fuel additives were not limited to depths of less than 40 feet bsg,based on <br /> ' soil analysis from the western end of the former northern dispenser island(SB5) <br /> • Benzene was detected in the greatest concentrations below in soil the former UST area <br /> Significant benzene concentrations were also detected below the former northern dispenser <br /> ' island at depths of 25 feet bsg to 35 feet bsg <br /> • The greatest concentrations of MTBE were detected in soil below the former USTs at depths <br /> of 15 feet bsg to 30 feet bsg MTBE was detected in soil samples from SB1, SB4, SB5, S136 _ <br /> and SB7 The highest concentration, 9,200 gg/kg, was detected at a depth of 30 feet bsg in <br /> the former UST area in soil boring SB4 <br /> Advanced GeoEnvironmentul,Inc <br /> 1 <br />