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i Figure 10 summarizes TPHG, benzene, MTBE, and TBA concentrations for samples collected from monitoring wells during the first quarter 2005, by ET1C Engineering and the consultant representing the 7-11 facility More recent results of quarterly well sampling at 7-11 Station #14117 were not available to Stratus at the time of a September 2005 review of SJCEHD files Figure 11 presents TPHG, benzene, MTBE, and TBA concentrations for samples collected from the site by Stratus personnel in September 2005, during completion of the third quarter 2005 groundwater monitoring and sampling event At the time of the third quarter 2005 well sampling event, the highest concentration of TBA (280,000 µg/L) was reported for the sample collected from well VEW-3 TPHG and MTBE concentrations at well VEW-3 were reported below elevated laboratory reporting limits (250 µg/L) TPHG (640 4g/L), MTBE (1,100 µg/L), and TBA (2,400 µg/L) were reported at off-site well MW-8 Relatively low concentrations of MTBE (1 6 pg/L to 150 µg/L) were reported for wells MW-1 through MW-4, MW-7, MW-9, and VEW-1 Benzene was not reported in any of the groundwater samples collected during the third quarter 2005 sampling event The lateral extent of TPHG, TBA, and MTBE impact to groundwater does not appear to be fully characterized east, southeast, and northeast of the site Based on the results of hydropunch groundwater samples collected at the CPT boring locations, MTBE and TBA concentrations in groundwater decrease significantly below approximately 25 feet bgs TBA and MTBE concentrations at boring CPT-2 declined from 270,000 µg/L and 3,400 pg/L, respectively (15 feet bgs), to 5,400 µg/L and 190 µg/L, respectively (38 feet bgs) MTBE and TBA impact to groundwater extends to approximately 52 feet bgs in the eastern portion of the site, in the vicinity of borings CPT-1 through CPT-3 Groundwater samples deeper than 52 feet bgs were not attempted in the eastern portion of the site, as fine grained soils were generally logged by CPT from approximately 55 to 80 feet bgs The vertical extent of petroleum hydrocarbon impact to groundwater may not be fully characterized in the southeastern portion of the property Well MW-7, and borings CPT-5 through CPT-7, are situated in the western portion of the Palisades property, immediately east (downgradient) of the 7-11 facility Maximum concentrations of 88 1 µg/L (MTBE) and 11,800 µg/L (TBA) have been reported in historical samples collected from well MW-7 TBA was reported for the samples collected from boring CPT-5 at 21 feet bgs (23 µg/L) and 28 feet bgs (580 µg/L), and boring CPT-6 at 23 feet bgs (1,400 µg/L) Benzene was reported in the samples collected from boring CPT-5 at 28 feet bgs (3 1 µg/L), CPT-6 at 59 feet bgs (0 74 µ/L), and boring CPT-7 at 30 feet bgs and 47 feet bgs (1 9 µg/L) Based on our understanding of the site hydrogeology and the known distribution of hydrocarbons in the subsurface, the petroleum hydrocarbon impact observed at well MW-7, and borings CPT-5 through CPT-7, likely has originated from the 7-11 facility Groundwater analytical data at the CPT-i through CPT-4 boring locations, and historical results from sampling of well VEW-3 (2001 to 2005), indicate that the highest concentrations of dissolved petroleum hydrocarbons are situated within first encountered groundwater in the eastern portion of the site, immediately adjacent to the former USTs and eastern pump island, and the current UST complex Groundwater monitoring wells are not currently in place to constrain and fully evaluate petroleum hydrocarbon concentrations in the eastern portion of the K\USA Gasoline108351Reportslusa835-scm-assessment report doc Page 10 STRATUS