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y Stantec ,,, <br /> SECOND QUARTER 2008 GROUNDWATER MONITORING REPORT <br /> Background and Previous Work <br /> L July 7,2008 <br /> � 2.0 Background and Previous Work <br /> The Site has been used by PG&E as a general construction yard for pipeline crews since the <br /> late 1950s and was purchased by PG&E in 1991. In June 2005, Stantec performed a Phase I <br /> Environmental Site Assessment (Phase I ESA) at the Site (SECOR, 2005). The Phase I ESA <br /> determined that in 1995, PG&E removed one concrete AST from the Site. The AST was a <br /> ConVault-style tank consisting of separate vessels for storage of diesel and gasoline. <br /> According to on-site PG&E employees, the ConVault had reportedly replaced older steel ASTs <br /> used for storing and dispensing fuels. <br /> bw The following sections summarize subsurface investigations performed to date by Stantec. <br /> 2.1 DECEMBER 2005 INVESTIGATION <br /> L <br /> In December 2005, Stantec completed a limited subsurface investigation to evaluate soils <br /> beneath the former ConVault and steel ASTs for the presence of fuel hydrocarbons. The <br /> locations of the former ConVault AST and soil sample locations are illustrated on Figure 2. <br /> Minor concentrations of diesel- and motor oil-range petroleum hydrocarbons were detected in <br /> shallow soils to 2 feet below ground surface (bgs), and soluble fractions of these constituents <br /> were not present at or above the method reporting limits. Shallow soils consisted of silts and <br /> clays, underlain by a 'hardpan' layer at approximately 3.5 feet bgs. Based on the low chemical <br /> concentrations, lack of reportable soluble fractions, and fine-grained soil types, Stantec <br /> concluded that the reported impacts had a very low potential to migrate to groundwater. The <br /> findings of the investigation were presented in the Stantec document entitled, "Results of <br /> Limited Phase 11 Investigation,"dated February 14, 2006 (SECOR, 2006a). <br /> 2.2 MAY 2006 INVESTIGATION <br /> Following the December 2005 investigation, additional information was obtained by PG&E and <br /> Stantec indicating that the older steel ASTs were not located at the ConVault location that was <br /> the subject of the 2005 investigation. The older ASTs were reportedly located in a nearby <br /> structure identified historically as the `heavy equipment storage shed.' In May 2006, Stantec <br /> v completed an additional subsurface investigation in the vicinity of the storage shed. Soil sample <br /> locations are illustrated on Figure 2. Using hand tools, seven soil borings were advanced to <br /> depths of approximately 3.3 to 3.8 feet bgs, where each of the soil borings encountered the <br /> �• hardpan layer. Thirteen soil samples were collected from representative depths above the <br /> hardpan and submitted for chemical analysis. The findings of the investigation were presented <br /> in the Stantec document entitled, "Results of Second Limited Phase II Investigation,"dated <br /> �+ August 2, 2006 (SECOR, 2006b). <br /> r <br /> is iApg&e\french camp\groundwater monitoring\may 2008 monitoring\gmr rpt_fnl.doc 2.1 <br /> 4 <br />