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Mr Jeffrey Wong C A M B R I A February 23, 2006 • PREVIOUS WORK 1994 UST Remopal During December 1994, four single-walled, steel USTs (two 10,000-gallon and two 6,000-gallon) and associated product piping were removed Petroleum hydrocarbons were detected in soil samples collected from beneath the former dispenser islands and product piping and in the southeastern half of the UST excavation Fugro West, Inc (Fugro) of Roseville, California performed over-excavation beneath the dispenser area and UST complex and collected additional soil samples One soil sample collected from the bottom of the UST excavation contained 1,000 parts per million (ppm) total petroleum hydrocarbons as gasoline (TPHg), and one soil sample collected from the northern sidewall of the dispenser excavation contained 2 7 ppm TPHg Fugro's April 19, 1995 Underground Storage Tank Closure Report documents the complete results of the UST removal 1996 Soil Borings During February 1996, Enviros, Inc (Enviros) drilled two Geoprobeo borings (GP-1 and GP-2) in the vicinity of the UST complex to investigate the extent of petroleum hydrocarbons detected during the December 1994 tank removal activities Enviros drilled one vertical boring (GP-1) adjacent to the UST complex and one angle boring (GP-2) beneath the UST complex Soil samples collected from the two borings did not contain detectable petroleum . hydrocarbon concentrations, but did contain MTBE at concentrations up to 29 ppm Enviros' May 8, 1996 Soil Boring Installation Report describes this investigation 1999 Soil Borings During January 1999, Shell drilled five soil borings (S13-1 through S13-5) in the vicinity of the UST complex TPHg was only detected in boring S13-3, at a concentration of 3 17 ppm No benzene was detected in any of the soil borings MTBE was detected (by EPA Method 8260) in all borings at concentrations ranging from 0 00807 to 92 9 ppm Groundwater samples were collected from borings S13-3 and S13-4 They contained 46,000 and 6,610 parts per billion (ppb) TPHg, 243 and 63 6 ppb benzene, and 28,000 and 8,050 ppb MTBE, respectively Cambria's June 9, 1999 Site Investigation Report summarizes these results 1999 Borings and Well Installatton During November 1999, Shell drilled four soil borings (GP-3 through GP-6) and installed three groundwater monitoring wells (MW-1, MW-2, and MW-3) The soil borings were drilled in the vicinity of the dispenser islands to determine if this was the source area Analytical data collected from the borings suggest the dispenser islands were not the source area The monitoring wells were installed around the UST complex (Figure 2) Groundwater samples collected from these wells contained TPHg, benzene, and MTBE Analytical data from these wells and previous soil borings drilled in the UST area suggest the USTs are likely the primary source area for petroleum hydrocarbons and MTBE • detected in groundwater beneath this site Cambria's February 10, 2000 Site Investigation/Fourth Quarter 1999 Groundwater Monitoring Report documents the investigation 2