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Mr Darin L Rouse Exxon Company, U S A August 4 1999 Page 2 Cumulative soil samples analytical results collected by Delta during drilling events are summarized in Table I During December 1991, Alton Geoscience advanced 10 soil bonngs (B-1 through B-10) on-site to t depths ranging from 1 1 to 20 5 feet bsg Concentrations of petroleum hydrocarbon constituents were detected in borings B-6 through B-10 ' in Febi nary 1992, Delta installed three additional wells (MW-4 through MW-6) off site each to an approximate depth of 26 5 feet bsg Monitoring wells MW-7 and MW-8 were installed in March 1994 each to a depth of between 20 and 22 feet bsg Monitoring well MW-7 was installed ' on-site, and monitoring well MW-8 was installed off-site Laboratory analyses did not detect concentrations of petroleum hydrocarbon constituents in sod samples submitted from MW-4 through MW-8 hour steel single-wall underground storage tanks at the site consisting of one 1,000-gallon used oil tank one 6,000-gallon regular gasoline tank, one 8,000-gallon premium unleaded gasoline tank, and ' one 10,000-gallon regular unleaded gasoline tank were removed on March 31, 1994 Following removal of the tanks, soil was excavated approximately 2 feet below the UST's into native soil Soil samples were collected from the tank basin Chemical analyses on sod samples detected concentrations of petroleum hydrocarbon constituents During January 1995, Delta advanced five soil borings at the site to depths between 10 and 13 feet ' bsg i wo of the borings were completed as vapor extraction wells VEW-1 and VEW-2 Concentrations of petroleum hydrocarbon constituents were detected in borings VEW-1, VEW-2, and SB-3 During Dc"mber 1995, Delta observed the excavation of the new tank basin at the site Soil samples were collected from the base and side walls of the new tank basin Analytical results ' indicated petroleum hydrocarbon impacted soil within the base of the excavation and the northern section of the excavation The north end of the new tank basin was overexcavated in the direction of the farmer tank basin and vapor extraction well VEW-2 was destroyed during the overexcavation activities Laboratory analyses on soil samples collected from the north end of the new tank basin detected concentrations of petroleum hydrocarbon constituents ' Delta installed vapor extraction well VEW-3 to a depth of 13 feet bsg near former well VEW-2 during May 1997 ' Scope of Work On May 25, 1999, a Delta representative was onsite to oversee Woodward Drilling Company of Rio Vista, California clear eight boring locations prior to drilling The surface of each boring location ' was cut using a concrete and asphalt cutter to provide a clean and neat surface look upon completion of each boring A water pressure wand and vacuum extraction was used to remove the soil from each boring location to a depth between 4 and 8 feet bsg, and each boring was cleared to a diameter two inches larger than the maximum diameter of down hole drilling equipment This method was chosen to prevent damaging any subsurface utilities or structures