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w Migration of free phase gasoline product has been identified immediately northwest of the building as demonstrated in MW- 13 . The contaminant concentration increases /� > significantly from east to west in the excavation extending from Industrial Drive 40 � � 0 nld //ll I of the building to edge of the prefabricated, moveable structure. Gasoline, BTEX an 9qd MTBE increased by one to two orders of magnitude from the east side samples, EN ! � 1• l � /� ESS, collected at 14 ' bgs (beneath groundwater) to the northwest side sample, WNS 'V collected at 14' bgs adjacent to the building wall . Contamination concentrations in s "� #� / /t Z , xj samples collected 4' beneath the water table in WNS identified 2,500 ppm TPH-gas( h77'ef 1 ,207 ppm BTEX and 26 ppm MTBE. The two eastside Samples collected at 14 ' bg; are qv identified TPH-gasoline at 810 ppm, BTEX at 30 ppm and MTBE at I 1 ppm. @F S o Q Excavation will extend as needed under the building based upon the results of additie„a, testing proposed in this interim RAP . 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 hi y )kJ ppm, BTEX at 115 ppm and MTBE at 3) Vppm. MW- 13 is approximately , - n 10' north of the building. The identification of increasing free gasoline beneath the water as the building is approached in a westward direction and the identification of M4e 1 .3 I© + floating free phase product northwest of the building confirm that the free phase sour, h coni'•. % ¢ �a % contamination is migrating under the building. /77/rJ / �o JVVE Groundwater samples collected in MW- 1 and MW- 14 west of the building also identih7iV1 d 16 , significant dissolved phase gasoline product, concentrations in an elliptical shaped_ /ort- _ ! Jdp �p westward plume migrating under the building and extending westward to MW-9 y1rT"- —i-�• hydraulically down gradient of the source area. M16C % as ltd Y Y o y3i7u- t 32 r--7 @ + t 9 , The identification of surging sands during advancement of well MW- 14 to 40' bgs � 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. Lateral advective migration om ssolved MTBE at concentrations greater than 1 , 000 ppm, extends approximately 60 feet westward from the source in the first water. It is proposed that three additional monitoring wells be advanced to 20' bgs further delineate shallow contamination migration. As identified in site-wide cross sections A-A' and B- B ' , see June 2004 RAP, the soil lithology identified is predominately described as heterogeneous clay with coarse-grained channeling. 1 It is proposed that a direct push 2"-diameter slotted monitoring well be advanced to 20 ' bgs to assess contamination of the first aquifer. Proposed well locations are shown on the attached Site Layout Map. IIS BEA proposes expedited implementation of this partial RAP to provide data necessary for cost benefit analysis comparing groundwater sparging, monitoring intrinsic r\ I biodegradation or soil vapor extraction.