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1 1.2.4 Phase 4 - Groundwater and Soil Sampling in Vicinity of Tank A 1b Due to the presence of impacted soil in the vicinity of Tank A, on August 2 and 3, 1989 AEMC ' conducted a Soil Contamination Assessment in accordance with guidelines outlined by PHS/EHD This assessment consisted of one continuously cored soil boring (EX-1) to 45 feet below ground surface (bgs) and four soil sampling borings (BH-1 through BH-4) in the vicinity ' of the Tank A excavation to define the vertical and horizontal extent of impacted soil (Figure 2) Low concentrations of toluene were present in all of the four soil sampling borings to a depth of 42 feet bgs Groundwater was encountered beneath the site at approximately 42 feet bgs Toluene concentrations in soil samples collected from these bonngs ranged from 0 210 ppm to ' non-detect TPH-diesel, TPH-gasoline, benzene, ethylbenzene and xylenes were not present in these soil samples Table 2 summarizes soil sample analytical results from this sampling event. Groundwater samples were collected from EX-1 and BH-4 at approximately 42 feet bgs ' Laboratory results of the groundwater analyses indicate that gasoline hydrocarbons had not impacted groundwater However, a concentration of 1,000 micrograms per liter (gg/L) of total ' lead was detected in the groundwater sample collected from EX-1 Table ") lists groundwater sample analytical results from this sampling event I.Z5 Phase 5- Over Excavation of Tank A On April 4, 1990, the former Tank A excavation was over excavated to 25 feet bgs and impacted soil was stockpiled on the surface for aeration Improper sampling techniques observed by a PHS/EHD staff member present during soil sample collection rendered the sample results invalid The excavation was backfilled A composite soil sample was collected from the stockpile on May 14, 1990 This sample did not contain detectable concentrations of BTEX There is no documentation in the file as to the disposition this stockpiled soil During recent site visits in May 1996, no soil stockpile was present 9.Z 6 Phase 6 - Soil Boring and Groundwater Monitoring Well Installation On July 2, 1990, AEMC completed the installation of three groundwater monitoring wells (MW- 1 through MW-3) and one soil boring (SB-1) The soil boring was placed at the east end of the ' former Tank A excavation to verify the presence of clean backfill Soil samples were collected from MW-1 through MW-3 and SB-1 during drilling The highest concentration of toluene detected was 0 077 ppm at a depth of 15 feet bgs m MW-1 TPH-gasoline was detected in SB-1 _ 3