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Mr.Michael Infurna,SJCEHO April 7,2006 <br /> Well Installation Work Plan <br /> Palisades Station No. 835,Stockton,CA <br /> Page 4 <br /> predominately observed on-site, and southeast groundwater flow directions are <br /> predominately observed east of the site, in the vicinity of Ryde Avenue. Given the <br /> historical groundwater flow direction, the 7-11 facility #14117 appears to be situated <br /> immediately upgradient of the site. <br /> Extent of Petroleum Hydrocarbon Impact to Groundwater <br /> Shallow groundwater in the eastern portion of the site is impacted with dissolved <br /> petroleum hydrocarbons. The dissolved petroleum hydrocarbon impact appears to extend <br /> east-southeast from the former UST and fuel dispenser area, across Ryde Avenue to the <br /> vicinity of wells MW-4 and MW-8. TPHG, benzene, MTBE, and TBA concentrations <br /> for well samples collected during the fourth quarter 2005 monitoring and sampling event <br /> are depicted on Figure 7. <br /> Based on the findings of the September 2005 CPT investigation,_ dissolved petroleum <br /> hydrocarbon impact extends to at least FWW of the site, at <br /> concentrations that generally decrease with depth. Depth discrete groundwater samples <br /> below this depth were not attempted, as fine grained soils that do not appear to represent <br /> TPHG, benzene, <br /> MTBE, and TBA concentrations for samples collected from borings CPT-1 through <br /> CPT-4 are included on geologic cross section B to B' (Figure 6). <br /> Well MW-7, which is situated in the southwestern corner of the Palisades property, is <br /> also impacted with petroleum hydrocarbons. Given the historical groundwater flow <br /> direction in the site vicinity, well MW-7 is immediately downgradient of 7-11 station <br /> #14117. Stratus has previously stated that the petroleum hydrocarbon impact in the <br /> southwestern portion of the Palisades property appears to have originated from the 7-11 <br /> facility. <br /> Remedial Actions <br /> It is our understanding that Exxon replaced the site USTs and product delivery lines in <br /> December 1995 and January 1996. The new USTs were placed in a different cavity than <br /> the former UST complex (see Figure 2). The soil excavated from the new UST cavity area <br /> (an estimated 700 cubic yards) was impacted with petroleum hydrocarbons and <br /> subsequently removed from the site. An additional 62 cubic yards of soil (estimate) was <br /> excavated and removed in order to place the current product delivery lines and fuel <br /> dispensers. Delta submitted a report titled Soil Excavation and Sampling Results in May <br /> 1996 to document the excavation and sampling activities. <br /> KAUSA Gasoline\0835\Work Plans\palisades835 workplan2006.doc STRATUS <br />