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I AUGEAS Corporation California Natural Products Problem Assessment Report June, 1991 1.0 SUMMARY Augeas Corporation was retained by Dr. Cheryl Mitchell, an owner of California Natural Products of Lathrop, California,to assess specific environmental concerns stemming from the leakage of fuel from an underground product line.The 18-inch long product line connected a 2,000-gallon twin-compartment above-ground gasoline storage tank to a pump and dispenser located adjacent to the tank. Although the gasoline compartment of the tank had not been used since 1985, the tank pump and associated product lines were not moved until July 26, 1990. Subsurface contamination was fust suspected when an engineering firm conducted a routine geotechnical core boring survey to determine soil compaction in preparation for the erection of a new grain silo. t : The California Natural Products property,which is currently being leased from W.Pat Mitchell,consists of approximately 14 acres of land in Section 26,Township 1 South,Range 6 East,in southern San Joaquin r • County(Figure 1).The property is owned by Mr.Pat Mitchell,and his wife,Cheryl Mitchell; the property has been in the Mitchell family since 1948. Figure 2 is a plot plan of the developed portion of the property in the vicinity of the former 2,000-gallon twin-compartment tank. The remainder of the property is irrigated pasture and is unaffected by the leakage. Since the fuel storage tank was above ground, a tank excavation report was not prepared. However,a groundwater and soil contamination assessment workplan was prepared and submitted to the San Joaquin County Health Department in early August, 1990. Near-surface soils in the vicinity of the former tank contain levels of adsorbed gasoline. Since soil may retain residual levels of gasoline of up to 0.5 gal/fe, it is conceivable that hundreds of gallons of gasoline may still be contained in the soil. For this reason, an assessment of the areal extent of soil contamination was completed to evaluate the magnitude of the problem. Figure 3 shows the location of soil borings, monitoring wells and an oval-shaped area of contamination over 240 feet long by 180 feet wide, comprising approximately 31,200 ft'The contaminated zone begins at a depth of approximately five feet and extends downward to the water table, generally at a depth of 15 feet below the surface. • a 2