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Appendix B AdvancedGeo <br /> AGE Project No. 99-0559 Environmental <br /> Page 12 of 12 <br /> representing a smear zone of contamination and/or the continual vertical migration <br /> of petroleum hydrocarbons at a rate faster than the water table can dissolved <br /> petroleum hydrocarbons. <br /> • TPH-g and BTEX compounds were also detected in deeper groundwater samples <br /> collected from wells near the former UST area, inexplicable increasing or <br /> remaining at stable concentrations with depth, nearly 180 feet bsg at the former <br /> UST area. The vertical and the lateral extent of TPH and BTEX has not been <br /> defined by sample collected in the former UST area, yet low concentration of TPH <br /> and BTEX are present south of the former UST area at well MW-6. <br /> • The dissolved MTBE has migrated west of the former UST area in the shallow <br /> water table and migrated northwest under Waterloo Road. The vertical migration <br /> of dissolved MTBE has been reduced by the advective forces of significant <br /> groundwater hydro stratigraphic flow units, particularly at a depth of 100 feet bsg, <br /> yet the dissolved plume of MTBE extends well beyond the site and nearly one-half <br /> of a mile west of the site. <br /> • The general combination of free phase petroleum product and a long duration of <br /> contamination in the environment likely has generated a vertical diffusion, which <br /> likely equal or exceeds the lateral migration distance of the dissolved MTBE west <br /> of the site. <br />