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S ECOR - Mr. Michael Infurna San Joaquin County Environmental Health Department March 27, 2007 Page 2 of 8 groundwater. The findings of the investigation were presented in the SECOR document entitled, "Results of Limited Phase 11 Investigation,"dated February 14, 2006. May 2006 Investigation Following the December 2005 investigation, additional information was obtained by SECOR indicating that the older steel ASTs were not located at the ConVault location that was the subject of the 2005 investigation. The older ASTs were reportedly located in a nearby structure identified historically as the heavy equipment storage shed. In May 2006, SECOR completed an additional subsurface investigation in the vicinity of the storage shed. Soil sample locations are illustrated on Figure 2. Using hand tools, seven soil borings were advanced to depths of approximately 3.3 to 3.8 feet bgs, where each of the soil borings encountered the hardpan layer. Thirteen soil samples were collected from representative depths above the hardpan and submitted for chemical analysis. The findings of the investigation were presented in the SECOR document entitled, "Results of Second Limited Phase 11 Investigation,"dated August 2, 2006. Soil samples from four soil borings advanced in the vicinity of the former equipment storage shed and from two step-out borings advanced east of the shed, reported only very low concentrations of diesel-range hydrocarbons (up to 17 milligrams per kilogram or mg/kg). Soil samples from soil boring HA-5, advanced approximately 10 to 15 feet southwest of the shed, reported elevated concentrations of gasoline-, diesel-, and motor oil-range hydrocarbons, and detectable concentrations of ethylbenzene and total xylenes. Impacts were observed to 3.5 feet bgs, where the hardpan layer was encountered. SECOR also sampled an adjacent domestic well which supplies the PG&E facility. The only constituent detected was 2,2-dichloropropane, which was reported at a concentration of 1.3 micrograms per liter (pg/L). This constituent is not believed to be sourced from the former ASTs. Well construction details were not available. February 2007 Excavation In February 2007, PG&E contracted with SECOR for the removal of impacted soils observed in the HA-5 soil boring location. SECOR oversaw excavation of approximately 40 yards of petroleum hydrocarbon-impacted soils. Observations made during excavation and analytical results of confirmation soil samples indicate that petroleum hydrocarbon-impacted soil is more laterally extensive than anticipated, and extends to at least 8 feet bgs. The findings of the February excavation work was summarized in SECOR's report entitled, "Results of Soil Removal Action"(March 2007). I:\PG&E\French Camp\additional 2007 investigation\work plan\2007 Investigation Work Plan_Final.doc March 27,2007 Project No.050T.50351.01