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Y Mr.Darin L.Rouse Exxon Company,U.S.A. April 22, 1999 Page 2 collected from MW-1 through MW-3 did not detect concentrations of petroleum hydrocarbons. Cumulative soil samples analytical results collected by Delta during drilling events are summarized in Table 1. During December 1991, Alton Geoscience advanced 10 soil borings (B-1 through B-10) on-site to depths ranging from 11 to 20.5 feet bsg. Concentrations of petroleum hydrocarbon constituents were detected in borings B-6 through B-10. Soil sample analytical results are summarized in Table 2. In February 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 during 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 soil samples submitted from MW-4 through MW-8. Four 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 soil samples detected concentrations of petroleum hydrocarbon constituents. Analytical results are presented in Table 3, and sample locations are illustrated in Figure 3. During January 1995, Delta advanced five soil borings at the site to depths between 10 and 13 feet bsg. Two 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. Cumulative soil sample analytical results collected by Delta during drilling events are summarized in Table 2. During December 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 former tank basin and vapor extraction wells 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. Soil sample analytical results for sample collected within the new tank basin are summarized in Table 4. Delta installed vapor extraction well VEW-3 to a depth of 13 feet bsg near former well VEW-2 during May 1997. Results for soil samples are summarized in Table 1. Prouosed Scone of Work To assess residual petroleum hydrocarbon constituents in soil and ground water Delta proposes to install two additional ground water monitoringwells each to a depth of 20 feet bsg and soil borings each to a depth sg of 30 feet . a props _ wells will be screened across the water table. T e s i :F t