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1 ' Site Conceptual Model . Frontier Transportation June 30, 2003 ' Page 3 4 Within predominantly clay from approximately 10' to 25'bg along B-B' in monitoring wells MW- ' 2 and MW-3 See Appendix B for cross sections and boring/well construction logs First subsurface water was encountered at depths from JA'to k ' bg during tank removal to ' and monitoring well installation at this site in 1995 and 1996 Since then, shallow subsurface water has been encountered beneath the site between 6' and 10' bg The most recent data ' collected in April of 2003 identified the flow of groundwater in a generally western direction- beneath the site (See Appendix C for groundwater gradient) The hydraulic gradient has been relatively flat historically(approximately 0 002 ft/ft) A Rose diagram was generated from ' groundwater flow data from March 1998 through December 2002 The diagram identified that groundwater historically flows west or southwest beneath the site See Appendix C for Rose diagram ' 4.0) EXTENT OF SOIL CONTAMINATION ' Soil sample results from the 1995 UST removal identified petroleum hydrocarbons exclusively in the northeast excavation pit where gasoline was stored 'Four soil samples were collected from the pit bottom (8 5'bg) and identified TPH-g between 9,800 mg/Kg to 4,700 mg/Kg'�aind BTEX between 1,007 mg/Kg to 1,354 mg/Kg(See Appendix A for soil sample results) Laboratory analysis indicates that the gasoline USTs were the source of impacted soil in J the excavation pit bottom I , . The site assessment performed in 1996 f used on delineation of the source, the farmer gasoline USTs Borings B-1 through B-4 and onitoring wells MW-1 through MW-3 were advanced to various depths up to!)W'b Lab(ratory analysis identified low level concentrations of TPH-g (�P mg/Kg) and BTEX ( 0 f g/Kg) in those soil samples collected from shallow depths (6' tWof 7' bg) MTBE was identified at a maximum of 30 5 mg/Kg at 6' bg in boring B-2 located the former USTs' Soil samples collected from 9 5' to 11' bg, the approximate depth to groundwater, identified relatively high concentrations of TPH-g, BTEX, and MTBE J Concentrations of TPH-g were observed from 1,300 mg/Kg to 104 mg/Kg, BTEX from 259 2 mg/Kg to 5 23 mg/Kg(and MTBE from 110 mg/Kg to c0 625 mg/Kg(See Appendix A for soil sample results) Laboratory analysis indicates that most of the shallow impacted soil has been removed during UST excavation Borings B-1 through B-4 were located 2 feet to 18 feet away from the UST removal pit and identified low level petroleum hydrocarbons from 6' to 7'bg Ye. Moreover, the elevated TPH-g, BTEX, and MTBE concentrations from the capillary fringe and saturated zone (9 5' to 11' bg) indicate that petroleum hydrocarbons have migrated through the soil and impacted the shallow groundwater The contact between impacted groundwater and soil is the source of the lateral extent of TPH-g, BTEX, and MTBE identified in soil collected from B-1, B-2, B-3, 13-4, MW-1 RA, MW-1 RB, MW-2RA, MW-2, and MW-3 at 9 5' to 1'1' bg No soil samples we'r'e, rA nal zeal--frr),,,. kA k)- .a Sal a )00-f%lox S r�1YS� i11t� � �� bo 3 5 w � bam Gti�Fx y s� pe,�i-rQ I tij n,, t4yX ��u�n we,6 fin ,