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. 09 May 2002 AGE-NC Project No 96-0232 Page 15 of 18 • A release or releases of petroleum hydrocarbons and MTBE occurred from an unidentified source(s)on the site Possible sources,all in the same general area, include impacted soil left in place at the time of the UST replacements, wash-down water from the dispenser area entering the storm drain system, spilled fuel entering the subsurface under the dispenser(s), and/or overfill or a slow release from the USTs or piping currently onsite Available data is suggestive of a release in the UST/dispenser area • Once released to the subsurface,the contaminants rapidly migrated to and impacted shallow ground water at 2 to 20 feet bsg, at which point the contaminants migrated laterally • The subsurface from surface grade to approximately 150 feet bsg is composed primarily of fine-grained soil with intervals of coarse-grained material(sand) The coarse grained material occurs in approximately five intervals above 150 feet bsg that are thought by AGE to form five informal hydrologic units as described above and in AGE's Final Remediation Plan, dated 31 August 2000 Generally, the informal hydrologic units are described as the First Zone from surface grade to 35 feet bsg, the Second Zone from 40 to 60 feet bsg, Rocky's Upper Zone from 65 to 75 feet bsg,the Secondary Aquifer Zone from 85 to 105 feet bsg,and the Primary Aquifer Zone from 130 to 150 feet bsg Ground water below the Primary Aquifer Zone is believed to be non-potable due to high total dissolved solids content • Impacted ground water in the First Zone mixed with ground water in the Second Zone and Rocky's Upper Zone during migration toward the west-southwest There is no well-defined aquitard between the three zones • The low-gradient ground water table was strongly influenced by pumping from the Rocky's Restaurant Domestic Well (RDW-1) which induced migration of MTBE-impacted ground water in the First and Second Zones from the UST/dispenser/storm drain area on the Flag City Chevron site westward toward RDW-1, RDW-1 was abandoned in March 2002 • Impacted ground water in the First and Second Zones migrated vertically to Rocky's Upper Zone, the Secondary Aquifer and Primary Aquifer via mixing in the RDW-1 casing and possibly along the filter pack (Figures 10, 11 and 12) • During non-pumping periods, MTBE-impacted ground water migrated from the well casing and/or filter pack laterally along the coarse-grained members of the lower hydrologic units • Continuous ground water extraction activities from Flag City Chevron site has pulled back some impacted ground water, lowering MTBE concentrations in ground water in the general extraction area, and has prevented additional lateral and vertical migration of impacted ground water Advanced GeoEnvironmental,Inc