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1 <br /> lie Site Conceptual Model <br /> Frontier Transportation <br />' June 30, 2003 <br /> Page 4 <br /> i <br /> An additional site assessment was performed in 1998 to delineate the lateral extent of <br />' petroleum hydrocarbons identified from the above nine mentioned borings at 9 5' to 11' bg <br /> Monitoring wells MW-4, MW-5, MW-6, and MW-7 identified no detectable concentrations of <br /> TPH-g, BTEX, or MTBE in all soil samples collected from 5'to 25' bg and analyzed(See <br /> Appendix A for soil sample results -The soil sample results indicate that the lateral extent of <br /> impacted soil from 6' to T bg was limited to borings B-I through B-4 only"Furthermore, the <br /> lateral extent of impacted soil from 9 5' to 11' bg via in contact with impacted groundwater does <br /> not extend to MW-4, MW-5, MW-6, and MW-7 r <br /> Another site assessment was performed in 2000 to further deliniate the lateral extent of <br /> petroleum hydrocarbons identified from 9 5' to I f'bg Two borings (lend B-6) and four <br /> monitoring wells (MW-8 through MW-11) were advanced from 20' to 30'bg'Only boring B-6 1� <br /> located within the former gasoline UST excavation pit identified petroleum hydrocarbons �01 � <br /> Concentrations of THP-g, BTEX, and MTBE were first detected in soil collected from B-6 at 10 <br /> bg, the depth of groundwater beneath the site (See Appendix A for soil sample results) Trace&p�r' �' <br /> I levels of BTEX and/or MTBE were detected in soil from 15' to 30'bg in boring B-6 These trace <br /> Ievels may have been detected from impacted groundwater carried down with the auger Samples <br /> collected through this interval may not be representative of soil conditions No other soil <br /> isamples analyzed from B-5, MW-8, MW-9, MW-10, and MW-I 1 identified any detectable <br /> concentrations of THP-g, BTEX, and MTBE-/fhe soil sample results indicate that the lateral <br /> extent of shallow impacted soil from 6' to T bg was exclusively limited to bonngs B-1 through <br /> B-4 -in addition, the lateral extent of TPH-g, BTEX, and MTBE in soil collected from 9 5' to 11' <br /> bg was limited to B-1, B-2, B-3, B-4, MW-IRA, MW-IRB, MW-2RA, MW-2, and MW-Y5-m., 13'6 <br /> IA supplementary site assessment was performed in 2002 to remove additional impacted <br /> soil from the former gasoline UST farm location and determine the vertical extent of petroleum <br /> hydrocarbons identified at depth in boring B-6 A pit 30 feet by 30 feet and averaging 13 feet <br /> deep was excavated near the former gasoline UST farm location Soil samples were collected at 14 <br /> 4' and 12"bg from the excavation pit Laboratory analysis identified low level petroleum 14, <br /> I hydrocarbons at 4' bg and relatively high concentrations of petroleum hydrocarbons at 12'bg(See <br /> Appendix A for soil sample results) Approximately 325 tons of impacted soil was removed for <br /> off-site disposal Three monitoring wells (MW-3R, MW-12, and MW-13) were advanced from <br /> 20' to 40' bg -Monitoring well MW-3R was installed to replace MW-3, which was abandoned <br /> prior to the excavation Monitoring wells MW-12 and MW-13 were advanced to 40 bg to <br /> determine the lateral extent of petroleum hydrocarbons from boring B-6 Soil sample analysis <br /> identified low-level petroleum hydrocarbons at 5'bg in MW-13 exclusively f Elevated <br /> concentrations of TPH-g, BTEX, and MTBE were identified in soil from MW-13 at 10' bg <br /> exclusively Trace levels of BTEX and/or MTBE were detected in soil from 15' to 40' bg in j�Q3V c L <br /> MW-13 Samples collected through this interval may not be representative of soil conditions <br /> 0 �- �� <br />