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L A) 15 April 2004 AGE-NC Project No 99-0559 Page 2of13 2 1 ON-SITE ASSESSMENT AND MONITORING WELL INSTALLATION On 14 to 17 December 1999, AGE advanced four soil probe borings at the site Probe borings were advanced in the area surrounding the current UST locations to maximum depths of 62 feet below surface grade(bsg) On 25 and 26 January 2000,four groundwater monitoring wells(MW-1 through MW-4)were installed at the site The most intensely fuel component-impacted(methyl-tertiary butyl ether MTBE) soil was in the area of borings B2,MW-2, and MW-3 at depths as great as 65 feet A significant mass of hydrocarbons was present in the vicinity of well MW-2 from 15 feet to 65 feet bsg and to a lesser degree south of the former USTs, in the area of well MW-3, from 45 feet bsg to 65 feet bsg Approximately six inches of free-product has been regularly observed in well MW-2 The highest concentrations of dissolved total petroleum hydrocarbons quantified as gasoline(TPH-g) and MTBE have been documented in the area of the former UST and approximately 75 feet southwest of the suspected release MTBE has been detected in samples from well MW-2 at concentrations as high as 310,000 microgram pre liter (µg/1) TPH-g and benzene have been most recently detected in samples from well MW-2 at concentrations of 220,000 µg/l and 32,000 µg11, respectively Samples from each of the four wells currently contain MTBE and benzene above 4,500 µg/l and TPH-g at concentrations greater than 26,000 µg/1 (Table 1) Laboratory analysis of ground water samples collected from two monitoring wells on the northern and eastern property boundaries appeared to show that dissolved petroleum hydrocarbons extent off- site ffsite The vertical and lateral extent of impacted ground water at the site was not defined,further more increasing concentrations of dissolved hydrocarbons in the ground water monitoring wells indicate off-site migration of contaminants The mass of dissolved hydrocarbons and MTBE is significant and required off-site assessment and immediate interim remediation In April 2001 three paired soil borings(CPT-1, CPT-2 and CPT-3) were advanced on-site, at each boring location, hthologic data was collected from the initial CPT boring, then an immediately adjacent twin boring was advanced to collect grab ground water samples from selected depths Soil borings CPT-1, CPT-2 and CPT-3 were advanced vertically to maximum depths of approximately 155 feet below surface grade(bsg), 162 feet bsg and 158 feet bsg,respectively CPT1 was advanced at the western edge of the site, CPT2 was advanced adjacent to the UST release, and CPT3 was advanced along the southern edge of the site Generally, the subsurface of the site Is comprised of alternating thick intervals of fine-grained material and thin to thick coarse-grained units Based on the CPT data, AGE identified six hydrogeologic units (HU1 through HU6), defined as bodies of rock or sediment that has hydrogeologic characteristics(i e hydraulic conductivity,pore pressure,etc )that make them distinct • Advanced GeoEnvkronmental,Inc