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- SEP - 27 - 04 03 : 54 PM BF ' INC . 760 3 8572 PM03 Migration of free phase gasoline product has been identified immediately northwest of the building as identified in MW- 13 , The contaminant concentration increases significantly from east to west in the excavation extending from Industrial Drive 40' east of the building to edge of the prefabricated, moveable structure. Gasoline, BTEX and MTBE increased by one to two orders of magnitude from the east side samples, ENS and ESS , collected at 14' bgs (beneath groundwater) to the northwest side sample, WNS, also collected at 14' bgs adjacent to the building wall. Contamination concentrations in soil samples collected 4' beneath the water table in WNS identified 2,500 ppm TPH-gasoline, 12207 ppm BTEX and 26 ppm MTBE. The two eastside samples collected at 14' bgs identified TMgasoline at 810 ppm, BTEX at 30 ppm and MTBE at 11 ppm . It is proposed that the prefabricated building be moved and excavation be completed under the building to remove the majority of the gasoline product layered under the water. Excavation will extend as needed under the building based upon the significant increase from the east side of the excavation in a westerly direction to the edge of the building. TPH-gasoline, BTEX and MTBE concentrations identified at 10' bgs in soil samples collected immediately above the groundwater in monitoring MW- 13 identified apparent free phase concentrations of TPH-gasoline at 700 ppm, BTEX at 115 ppm and MTBE at 37 ppm, MW- 13 is approximately 10' west and 10' north of the movable building. The identification of increasing free phase gasoline beneath the water as the building is approached in a westward direction and the identification of floating free phase product northwest of the building confirm that the free phase source of contamination is migrating under the movable shed. Groundwater samples collected in MW- 1 and MW44 west of the building also identify significant dissolved phase gasoline product concentrations in an elliptical shaped westward plume migrating under the building and extending westward to MW-9 hydraulically down gradient of the source area, CSI proposes immediate excavation prior to long term clean up to remove the layered free phase contaminants providing a driving head for significant plume expansion, at least 260' laterally and unknown vertically . It is estimated that removal of majority the tree phase product inverted under the water and in the groundwater will require an excavation approximately 30 ' north to south and extending approximately 60 ' from the eastern edge of the free phase source to the point of attenuation of the source . The property owner supports that the pre-fabricated steel shed adjacent to the west side of the free phase gasoline and oxygenate plume be moved northward during excavation. A mobile laboratory will be operated on site to confirm visual observation of the excavation of this inverted LNAPL layer. The identification of surging sands during advancement of well MW44 to 40' bgs and the significant concentrations of gasoline, aromatics and oxygenate beneath the groundwater support that migration can be occurring in numerous permeable zones as discussed in our past meeting.