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27 October 2003 <br /> • AGE-NC Project No 98-0450 <br /> Page 10 of 17 <br />' By the end of 2002, the maximum dissolved hydrocarbon concentrations in ground water were <br /> detected in monitoring well BMW-4 at the former UST excavation,maximum BTEX concentrations <br /> were also detected in BMW-4, and at concentrations that are below the DHS' Primary Maximum <br /> Contaminant Levels (MCL) for drinking water <br /> MTBE was detected in two ground water samples(BMW-2 and MW-5)dawn-gradient of the former <br /> UST location, only sample MW-5, at a concentration of 14 µg/1,was significantly above the DHS' <br /> Secondary MCL of 5 µg/1 Trendlines plotted on a graph of MTBE concentration versus time for <br /> wells BMW-2 and BMW-5 showed declining trends from initiation of monitoring in 1998 to the <br /> ' present, however, the MTBE trendlines showed a more steeper decline at a better than 80% <br /> correlation from August 1999 to the present The consistent decline in MTBE concentrations since <br /> ' August 1999 may be due in part to SVE remediation beginning in August 2000 (Appendix B) <br /> 5 0. CONFIRMATION SAMPLING AND ANALYSES <br /> In order to assess the progress/success of remediation via in-situ air-sparging and soil-vapor <br /> ' extraction,confirmation soil samples from the USTs and northern dispenser areas were collected and <br /> analyzed in October 2002,confirmation grab ground water samples were collected in June 2003 to <br /> define the down-gradient extent of contaminated ground water, a confirmation ground water <br /> ' monitoring event was conducted in August 2003, and soil vapor samples were collected and <br /> analyzed for rebound in soil-vapor concentrations on 02, 03 and 18 September 2003 <br /> 5 1 CONFIRMATION SOIL SAMPLING AND ANALYSIS <br /> ' On 25 October 2002, two soil probe borings (CB 1 and CB2) were advanced at the site to collect <br /> confirmation soil samples in order to assess the progress of soil-vapor extraction, one boring(CBI) <br /> was advanced in the former UST excavation near well BMW-4 and the other boring (CB2) was <br /> ' advanced at vapor well VW-1, at the former dispenser area(Figure 2) The borings were advanced <br /> to a total depth of 35 feet below surface grade(bsg)utilizing a van-mounted Geoprobe 5400 direct- <br /> push probing unit equipped with 1 25-Inch diameter probing rods, the probing unit advances soil <br /> probe borings using a hydraulic hammer to drive soil and ground water sampling tools to specified <br /> depths The subsurface soil profile, vapor wells and confirmation borings traces with sample results <br /> ' are illustrated on cross-sections A-A' in Figure 5 <br /> • <br /> Advanced GcoEnvironmental,Inc <br />