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Stantec %%P-11 low SECOND QUARTER 2008 GROUNDWATER MONITORING REPORT Background and Previous Work v July 7,2008 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 [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. Visual evidence of chemical V impact was observed to 3.5 feet bgs, where the hardpan layer was encountered. Stantec 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(Ng/L). This constituent is not believed to be sourced from the former ASTs. Well construction details were not available. v 2.3 FEBRUARY 2007 EXCAVATION In February 2007, PG&E contracted with Stantec for the removal of impacted soils observed in the vicinity of the HA-5 soil boring location. Stantec oversaw excavation of approximately 40 yards of petroleum hydrocarbon-impacted soils. Observations made during excavation and analytical results of confirmation soil samples indicated that petroleum hydrocarbon-impacted soils were more laterally extensive than anticipated, and extends to at least 8 feet bgs. The findings of the February excavation work were summarized in Stantec's report entitled, "Results of Soil Removal Action,"dated March 9, 2007 (SECOR, 2007b). 2.4 APRIL AND MAY 2007 INVESTIGATION In April 2007, Stantec completed a multi-phase investigation which included a geophysical 60 survey, a subsurface investigation, and installation of three monitoring wells. The geophysical investigation was performed to identify any remaining USTs or associated piping. No subsurface anomalies consistent with the presence of USTs or related fuel distribution `r equipment were detected during this investigation. Five soil borings (131 through 135) were advanced at locations within, directly adjacent to, and surrounding the February 2007 excavation to observe and characterize soil conditions at depth and to determine the lateral extent of impact. Elevated soil concentrations of total petroleum `, hydrocarbons as diesel (TPHd), motor oil (TPHmo), and gasoline (TPHg)were detected in three of the five borings with maximum concentrations of 620 mg/kg (131 at 21 feet bgs), 6,500 mg/kg (132 at 8 feet bgs), and 2,000 mg/kg (132 at 20 feet bgs), respectively. Petroleum hydrocarbons �., were not detected above laboratory reporting limits in grab groundwater samples collected from soil borings 131 through B5. v r.r is iApg&e\french camp\groundwater monitoring\may 2008 monitoring\qmr rpt_fnl.doc 2.2 4