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01 October 2013 <br />AGE Project No. 99-0559 <br />Page 5 of 6 <br />Groundwater flow directions remained generally consistent in HU1/HU2, HU3/HU4, <br />and HU6; slight variations in flow direction were observed in HU5. <br />The dissolved MTBE plume in first water table wells extends southwest of the UST <br />release and increases in concentration at wells MW-4 and MW-5A; MTBE continues <br />to be non-detect below the laboratory detection limit in well MW-1 and was non- <br />detect in well MW-6A during the September 2013 sampling event. TBA was <br />detected at elevated levels (as high as 5,800 pg/I in MW-3) in samples collected <br />from wells MW-2, MW-3, and MW-4 during the September 2013 sampling event. <br />Concentrations of dissolved TPH-g, benzene, and MTBE in HU1/HU2 wells MW-2, <br />MW-3, and MW-5A have increased over the past three sampling events after <br />deceasing significantly following the January 2009 event. However, concentrations <br />are still significantly below the levels detected prior to 2009. Concentrations of <br />dissolved TPH-g, benzene, and MTBE in HU1/HU2 wells MW-1, MW-4, and MW-6A <br />have remained stable over the previous three sampling events. <br />MTBE was detected in wells MW-5B, MW-6B, and MW-7B at a depth of 100 feet <br />bsg during the September 2013 event. <br />The lateral extent of shallow, impacted groundwater towards the west and <br />southwest, down-gradient of the UST area, has been defined. However, elevated <br />concentrations of dissolved MTBE have migrated off-site. <br />The vertical extent of impacted groundwater at the former UST area has been <br />defined. Historically, the vertical extent of dissolved plume is defined southwest of <br />the USTs by wells MW-5E and MW-9, and further southwest of the site by well <br />MW-10. TPH and BTEX plumes extend to deeper HUs near the property boundary <br />at well MW-7; yet were not detected in well MW-5 at significant concentrations. <br />Generally, concentrations of TPH-g, BTEX and MTBE in the most impacted shallow <br />wells have been significantly remediated; the current concentration is 90% less than <br />the typical concentration and the current concentration is 99% less than the <br />maximum concentration. <br />Concentrations trends within wells, established in the upper water table, declined <br />considerably since the initiation of active soil vapor extraction; further have <br />considerably declined over the past two years. However, dissolved MTBE and TBA <br />appear to have the potential for off-site migration and dispersion. <br />Advanced GeoEnvironmental, Inc.