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Ms. Tammy Hodge CAMBRIA November 1, 1996 Work Chronology The following is a chronology of work performed at the site including dates, consultants, previous activities and summaries of analytical results. This chronology is based on a review of reports prepared by previous environmental consultants. 1991 Tank Tightness Test., On December 3, 1991,a tightness test of the 550-gallon waste oil tank carried-out by Tanknology indicated a leak. The tank was subsequently pumped out and removed from service. 1992 Waste Oil Tank Removal: On January 8, 1992,a 550-gallon,single-walled steel waste oil tank located north of the station building was removed by Wendt Construction (Wendt) of Lodi, California. Samples collected from the over-excavation in the tank pit at a depth of 11.5 ft contained total petroleum hydrocarbons as gasoline(TPHg)at a concentration of only 3.6 parts per million (ppm),total petroleum hydrocarbons as oil (TPH-o)at 20 ppm and xylenes at 0.0068 ppm. Ground water was encountered at a depth of 12 ft in the tank excavation. TPHg and TPHo were detected at 7,300 and 1,000 parts per billion (ppb), respectively, in the ground water sample (Attachment B). 1992 Soil Boring and Monitoring Wells Installation: In November 1992, Groundwater Technology,Inc. (GTI)drilled soil borings SB-1 through SB-6. Borings SB-1 through SB-3 were drilled to a depth of 11.5 feet (ft). Soil borings SB-4 through SB-6 were drilled to a depth of 21.5 ft and were completed as monitoring wells MW-1 through MW-3. A maximum of 3,400 ppm TPHg was detected at 5 ft depth in SB-2. Benzene was detected at a maximum concentration of 7.4 ppm in SB-2 at 10 ft depth. Lead was detected at a maximum concentration of 6 ppm at 10 ft depth soil samples in SB-4 and SB-6. 1993 Gasoline Storage Tanks Removal. In July 1993, the three gasoline storage tanks were removed by Golden West Builders of Livermore, California. Five additional tanks located along Adams Street were encountered during this excavation and were subsequently removed. TPHg and benzene were detected at 3,900 and 6.1 ppm,respectively, in a soil sample collected at a depth of 10 ft underneath the known 10,000- gallon tank removed from the northern portion of the tank pit(Attachment B). A maximum of 260 ppm total petroleum hydrocarbons as gasoline (TPHd) was detected beneath the known middle 10,000-gallon tank. Water samples collected at the bottom of the excavation contained TPHg and benzene at 34,000 and 3,200 ppb, respectively. 1993 Over-Excavation: In July 1993,Touchstone Developments excavated additional soil in the northern and southern part of the previous tank excavation along Adams Street. TPHg and benzene were detected at a maximum concentration of 110 and 0.16 ppm, respectively, at a depth of 8 ft in a confirmation sample 3