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Ms. Tammy Hodge CAMBRIA November 1, 1996 SOIL AND GROUND WATER INVESTIGATIONS Hydrocarbon Distribution in Soil The highest TPHg concentration detected in soil was 3,900 ppm at 10 ft depth in the northern portion of the gasoline tank pit. An additional 1.5 ft of soil was over excavated. Confirmation samples at a depth of 11.5 ft contained TPHg and benzene at a concentration of 460 ppm and 0.98 ppm, respectively. The highest benzene concentration detected in soil was 7.4 ppm at a depth of 10 ft in soil boring SB-2, cross gradient of the gasoline tank pit,near Adams Street. Soil at this depth is predominantly clayey silt. TPHd were detected at a maximum concentration of 260 ppm in the northern part of the tank pit. This soil was also over-excavated an additional 1.5 ft. Confirmation soil samples collected at 11.5 ft in this excavation did not contain TPHg and benzene. Oil and Grease(O&G)and total lead were detected at a concentration of 280 ppm and 12 ppm, respectively, in the waste oil tank pit at a depth of 10 ft. This soil was subsequently over-excavated and confirmation soil samples collected from the excavation sidewalls at a depth of 11.5 ft did not contain O&G and lead. No hydrocarbons were detected at any depth in any of the soil borings for the monitoring wells. Therefore, the distribution of hydrocarbons in soil has been defined. Based on the soil analytic data, it may be inferred that hydrocarbons in soil are confined to a small area on the eastern side of the former gasoline tank pit TPHg Concentration in Ground Water (Down Gradient Well MW-1) 2m _ Hydrocarbon Distribution in Ground Water a ° o ,wa The highest historic TPHg concentration detected in the o 500 monitoring wells was 2,400 parts per billion (ppb) in 0LLLf well MW-1 in December 1992. Maximum benzene was 4—wemli also detected in September 1994 at a concentration of]1 — � ppb in MW-1. As shown in the adjacent graphs,TPHg concentrations in wells MW-1 and MW-2,the only wells TPF§concentration in Ground Water Pile Gradient Well MW-2) with detected hydrocarbons,have steadily dropped since om the wells were installed in 1992. Methyl-tertiary butyl a 800 ether(MTBE)was detected at a maximum concentration a �o _ 4m of 51 ppb in MW-1 on November 21, 1995. Monitoring wells MW-2,MW-3 and MW-5 define the up gradient, 0 WT m T m cross gradient and down gradient extent of hydrocarbons ° y of aLL ur $ E u, zs � in ground water to non-detectable levels. THa— 5