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Harding Lawson Associates January 14, 1991 20264,004.02 John Breuner Company Mr. Peter Meier Page 3 compacted backfill material and overlying loading dock. The piping trench backfill was compacted using Whacker equipment. Soil samples were analyzed for total petroleum hydrocarbons(TPH)as diesel and gasoline, and for benzene, toluene, ethylbenzene and xylenes(BTEX). Samples were also analyzed for ethylene dibromide(EDB)and organic lead,because the tank at one time had apparently stored leaded gasoline (as noted on the former dispenser). Review of analytical results indicates that TPH as diesel and gasoline were not detected above laboratory detection limits(10 ppm)in any of the soil samples, with the exception of sample DI-2.5 collected beneath the former dispenser. Gasoline was reported at a concentration of 390 ppm and diesel at a concentration of 37 ppm in this sample. Benzene, toluene, xylenes, and ethylbenzene were not detected above laboratory detection limits (0.025 ppm for benzene and toluene, and 0.075 ppm for xylenes and ethylbenzene)in any of the soil samples, with the exception of 0.065 ppm of toluene reported in sample PP4-3. Organic lead was not detected in any of the analyzed soil samples. EDB was detected in three samples (TS-14, PPI-3, and PP4-3)at concentrations ranging from 0.180 to 0.370 ppm, and was not detected above a detection limit of 0.125 ppm in the other samples. On the basis of H1A's review of LF's November 9, 1989 report, it appears that a limited release of petroleum hydrocarbons has occurred at the site in the vicinity of the dispenser and has impacted the soil in that area. The extent of soil containing petroleum hydrocarbons is unknown at this time. From the absence of TPH as gasoline in samples with detectable concentrations of EDB at the site, it appears unlikely that the EDB is associated with a gasoline release at the site. Since EDB is known to have been used widely in rural areas for agricultural purposes, its introduction into site soils is possibly associated with past agricultural usage in the vicinity. It is not clear after reviewing the Levine-Fricke report if soils from underneath the former dispenser containing elevated concentrations of petroleum hydrocarbons were removed or buried in place. A cursory review of hydrogeologic literature for the Stockton area indicates that the site is located in the San Joaquin Valley groundwater basin, and the depth to groundwater is approximately 60 to 70 feet. The fine grained nature of the native soils, the limited release, and the depth to groundwater of 60 to 70 feet in the site vicinity suggests the threat to groundwater is minimal. PURPOSE AND SCOPE OF WORK The purpose of this investigation is to evaluate the extent of petroleum hydrocarbons in the soil in the former dispenser area. Because the threat to groundwater appears to be minimal, HLA does not propose to perform a groundwater investigation at the site. However, work will be performed to confirm the anticipated groundwater conditions. HLA intends to perform this investigation by completing the following tasks: