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' hn KLEI NFELDER The following TPH concentrations were detected in the remaining four samples (4 of 14). Sample Depth TPH-Gasoline TPH-Diesel Number feet Location m k (mg/kg) 1 #3 11.5 South wall of 10,000 19 98 tank excavation #6 22 West wall of 10,000 6,000 1,100 ' tank excavation #7 11.5 West wall of 10,000 27,000 9,100 tank excavation ' #11 16 Middle to northern end 23,000 2,000 of 500 gallon tank excavation TPH contaminated soil was excavated in the vicinity of the three removed tanks until ' petroleum hydrocarbons were non-detect or low over most of the excavation area. However, elevated TPH concentrations remained at two locations (location #6-7 and location #11). Based on the results of the 14 soil samples, the open excavation was backfilled. ' Nor-Cal retained Emcon Associates to install and sample a single ground water monitoring well. The monitoring well was located at the approximate center of the backfilled excavation area of the three tanks. The intent of the well was to sample ground water directly beneath the removed tanks (the area likely to be impacted by the vertical ' migration of petroleum hydrocarbons) rather than installing three ground water monitoring wells around the perimeter of the excavation. ' Monitoring well MW-1 was installed on May 28, 1991. Ground water was encountered at a depth of 69 feet. Two soil samples (17.5 and 41 feet) and one water sample were submitted for analyses. TPH-Diesel, TPH-Gasoline and BTEX concentrations were not detected in the soil samples analyzed from MW-1 with the exception of 0.1 mg/kg benzene detected in ' the 41-foot sample. TPH-Gasoline and benzene were detected at 100 ;Ug/l and 1.6 ,ug/l - respectively in the water sample collected from MW-1. r FR1-92-15 Page 4 of 21 Copyright 1992 Kleinfelder, Inc.