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' 29 March 2004 • AGE-NC Project No. 97-0327 1 Page 11 of 12 ' • One hydrogeologic unit (Hydrogeologic Unit 1)was informally identified beneath the site extending from the water table at 60 feet bsg to the maximum total depth of the borings. Hydrogeologic unit 1 consists primarily of permeable to semi-permeable, fine to medium ' sand and silty sand with limited minor fine grained material; a slight westward dip in Hydrogeologic Unit 1 was evident in the cross-sections. • Ground water elevations at the site have ranged from approximately 19.31 to 34.74 feet ' below mean sea level since ground water monitoring began in February 2000.Generally,the ground water flow direction has been towards the south-southwest, south and south- southeast. • Distribution of petroleum hydrocarbon contaminants in soil and ground water indicates an initial release/s in the south-end of the former USTs,which then migrated vertically through ' semi-permeable sandy silt media and through more permeable silty fine sand media(V adose zone). At depths between 40 and 45 feet bsg, the contaminants appeared to spread laterally towards the northeast (beneath Fremont Street) and towards the southwest (beneath Oro ' Avenue). • TPH-g was generally detected in water samples collected from well MW-2 at concentrations ' as high 490 gg/l.TPH-d was generally detected in water samples collected from wells MW-1 through MW-4 at concentrations as high as 430 gg/l; however, the highest on site concentration of TPH-d (1,900 gg/l) was detected in a P-8 grab ground water sample ' collected from 51 to 55 feet bsg in June 1999. ` • BTEX compounds were g�,ezfierally detected in water samples collected from well MW-2 at concentrations as high 2 iggd;generally,the concentrations of BTEX compounds in on-site ' ground water monitoring wells MW-1 through MW-4 were below the DHS MCL's for drinking water. ' • Consistent low occurrences of MTBE have been observed in water samples collected at wells MW-1 and MW-2 at concentrations as high as 16 gg/l(by EPA 8260);MTBE concentrations detected in water samples at the site were generally below the MCL of 13 gg/l for drinking ' water. • Consistent low occurrences of 1,2-DCA have been detected in water samples collected from wells MW-1, MW-2 and ,MW-4 at concentrations as high as 6.8 gg/l; 1,2-DCA concentrations detected in water samples at the site were slightly above the MCL of 0.5 µg/1. Except for the initial monitoring event on August 2003,the highest 1,2-DCA concentrations have consistently been in the southernmost wells MW-1 or MW-4 Table 2). The vertical extent and lateral extent of 1,2-DCA are undefined. ' Consistent low occurrences of TBA were generally detected in water samples collected from well MW-2 at concentrations as high as 48 gg/l, which is slightly above the DHS Action