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1 ' 25 February 2005 AGE-NC Project No 01-0827 ' Page 8 of 10 ' of xylene The BTEX concentrations have also declined to non-detect levels or at levels below concern or maximum contaminant limits, since July 2003 The last well sample from well MW-6 was non-detect for hydrocarbons Cross sections showing the vertical distribution of hydrocarbon- impacted ground water are presented in Figures 5 and 6 Laboratory analysis has also detected the fuel additives, methyl tert butyl ether (MTBE), 1,2-dichloroethane (1,2-DCA) and randomly di-isopropyl ether (DIPE), tert butanol (TBA), ethyl tertiary-butyl ether (ETBE) and tertiary-amyl methyl ether (TAME) The following fuel additives have been detected constantly 1 • MTBE in well VW2d at concentrations as high as 120 gg/1 (31 December 2002) and currently is detected near 16 gg/1, while MTBE was previously steadily detected in well ' MW-1 and VW-5d at low concentration, these well samples are currently non detect for MTBE, ' • 1,2-DCA in monitoring wells MW-1 and vapor well VW-1,VW-2d and VW-d5, 1,2-DCA is currently non-detected in the sample from the wells,the last detection of 1,2-DCA was in the August 2004 sample of VW-2d at a concentration of 6 4 µg11, '• • Occasional occurrences of DIPE, TBA, and/or TAME detection have no longer been regularly documented IThe lateral extent of the dissolved petroleum hydrocarbon plume is defined toward the east by well VW-3, west by well MW-5, south by well MW-3 and north by well MW-4 The plume is locally ' undefined northeast of the well RW-1,due to low detection in samples from that well The dissolved pet for eum hydrocarbon plume is currently vertically defined near the former UST release and vertically at location of the highest soil contamination by well MW-6, screened from 60 feet to ' 65 feet bsg ' 6.0. SITE CONCEPTUAL MODEL ' Based on the data collected to date from soil borings and ground water monitoring wells, AGE has developed a site conceptual model for the release,migration and distribution of the contaminants in the subsurface as described below Release(s) of petroleum hydrocarbons occurred from the on-site USTs The only hydrocarbon impacted UST removal sample was collected from UST#1, collected in April 1987 The UST #1 removal reportedly occurred at the location of vapor well VW-2d, which coincides with the significant petroleum hydrocarbons detected in soil from boring B 10 samples collected at 15 feet •ti bsg The high detections of petroleum hydrocarbons in soil samples from boring B16, indicates a Advanced GeoEnvzronmentsl,Inc