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' 02 September 2003 AGE-NC Project No. 98-0468 ' Page 6 of 1 I MTBE was detected indiscrete groundwater samples collected from 55 feet bsg,approximately 100 ' feet down gradient from the former UST. The down-gradient lateral' .extent of petroleum hydrocarbons is limited by wells MW-7 and MW-8. ' During the last sampling event in April 2003, TPH-g was detected in ground water samples MW-6 and: MW-8 at concentrations of 290 µg/1 and 140 µgll, respectively. BTEX compounds.were not ' detected in any of the ground water samples.MTBE was detected in water-table-well samples MW-4 and MW-6 at concentrations 16 µg/1 and 120 µg/l, respectively. MTBE was also detected in deep- screened-well samples MW-9 and MW-10 concentrations of 80 ltg/l and 28 gg/l, respectively. ' Ground water data and analytical ground.water monitoring well data are included in Tables 3 and 4. 4.0. PROCEDURES On 17 July 2003, two soil boring (CPT1 and CPT2) were advanced on=site .(Figure 2). CPT ' technology was utilized at each boring location. Lithologic data was collected from the initial CPT boring and an immediately adjacent twin boring was then advanced to collect grab ground water • samples from selected depths. i ' 4.1. CPT LITHOLOGIC INVESTIGATION The CPT investigation utilized a 25-ton truck-mounted CPT drill rig equipped with 1.50-inch ' diameter hollow-stem rods. A hydraulic ram was utilized to advance a cone penetrometer tip attached to the hollow-stem rod assembly to total depth in each soil-boring. CPT1 was located at monitoring wells MW-4,MW-6 and soil boring SB8 and advanced to a depth of 125 feet bsg. CPT2 i ' was located north of monitoring well MW-10 and advanced to a depth of 105 feet bsg. At each boring location,the soil.parametersof cone penetrometer tip resistance, sleeve friction and pore water pressure were continuously measured as the cone penetrometer was advanced to.depth. Utilizing the soil parameters, the Hogentogler Co. computer program interpreted general lithology types based on the CPT Soil Behavior Classification System (Robertson, P.K., Campanella, R.G, ' Gillespie, D, and Greig, J., 1986).and displayed the interpreted lithologies on a continuous CPT boring log. The CPT interpretive logs are presented in Appendix B. ' Rinseate generated during drilling activities was containerized in properly labeled DOT-approved 55-gallon drums and'was stored on-site in an area lacking public access. The CPT soil borings were backfilled over their entire depth range with.a bentonite/Portland cement grout mix. ' Advanced GeoEnvironMental,Inc.,