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ATC Associates Inc. <br /> 1117 Lone Palm Avenue, Suite 201 <br /> Modesto,California 95351 <br /> 209-579-2221 <br /> r ASSOCIATES i N c. fax: 209-579-2225 <br /> Vr <br /> unleaded gasoline. Groundwater was encountered in the UST excavation at approximately seven <br /> feet below ground surface (bgs). Laboratory analyses of two samples of groundwater collected <br /> 6.0 from within the excavation indicated the groundwater had been impacted by petroleum <br /> hydrocarbons. <br /> �.• On March 29 and 30, 1988, Kleinfelder supervised the installation of three monitoring wells <br /> (MW1, MW2, and MW3) at the site and conducted a sensitive receptor survey. Based on <br /> Kleinfelder's Groundwater Assessment Report dated April 12, 1988, petroleum hydrocarbons <br /> were not detected at or above laboratory reported detection limits in the groundwater samples <br /> collected from MW1, MW2, or MW3. The groundwater flow direction was reported to be <br /> toward the north. <br /> V <br /> On April 19, 1988, an additional monitoring well, MW4, was installed north of the former UST <br /> basin. Based on Kleinfelder's Additional Monitoring Well report dated April 22, 1998, <br /> petroleum hydrocarbons were detected in the groundwater sample collected from MW4 on April <br /> 19, 1988. The groundwater flow direction was reported to be toward the northwest on April 20, <br /> 1988. <br /> In April 1988, the open excavation associated with the former USTs was expanded by excavating <br /> petroleum impacted vadose zone soils As reported in Kleinfelder's Soil Removal Report dated <br /> May 3, 1988, approximately 350 to 400 cubic yards of soil were excavated from April 25 to 28, <br /> 1988. Laboratory analyses of soil collected from the sidewalls of the enlarged excavation <br /> indicated low concentrations of petroleum hydrocarbons remained at the south and southeastern <br /> portion of the excavation. <br /> 11.0 On February 26, 1993, Parker Environmental Services (P.E.S.) advanced seven soil borings <br /> (131-11 through 131-17). Soil samples were collected from each boring and a groundwater sample <br /> was collected from each boring except BH7. Petroleum hydrocarbons were detected in soil <br /> 11.0 samples collected from all the borings except BH1 and BH3. Petroleum hydrocarbons were <br /> detected in each groundwater sample. Water levels measured at the site on March 2, 1993, <br /> indicated the groundwater flow direction was to the southeast. Refer to the P.E.S. Interim Report <br /> on Subsurface Investigation Work at Cheaper! # 37 dated April 20, 1993, for additional <br /> information. f <br /> `'' From July to October 1995, P.E.S. conducted subsurface investigation activities that included <br /> installing four additional monitoring wells (MW5 through MW8) and advancing 14 hand <br /> augured soil borings (B8 through B21). Borings B15 through B21 were advanced off-site to the <br /> `r west, southwest, and south. Groundwater was encountered at approximately 6.5 feet bgs. Soil <br /> and groundwater samples were collected from B8, B10 through B18, B20, B21, and MW5 <br /> b" through MW7. A groundwater sample was also collected from MW8. Petroleum hydrocarbons <br /> were detected in all soil samples except for the samples collected from MW5 through MW7, B14 <br /> 2 ATC Associates Inc. <br /> S:\Environmental\25847.0037\Work Plan additional vert-hor delineationTH2.doc <br /> 9 <br />