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' Mr. Dan Barber Project OF90-002.02 October 28, 1992 Page 2 BACKGROUND Exploratory soil boring BH-1 was drilled at the supply yard north of tank E in March 1990, prior to the removal of the tank in March 1991. The exploratory soil boring location is shown on Drawing 1. Total petroleum hydrocarbons as diesel (TPHD) was detected at a concentration of 2,900 milligrams per kilogram (mg/kg) in the soil sample collected from this boring at a depth of 10 feet. When tank E was excavated, a confirmation soil sample was collected and analyzed for total petroleum hydrocarbons as gasoline and benzene, toluene, ethylbenzene, and total xylenes; however, the sample was not analyzed for TPHD. Since the confirmation sample was not analyzed for TPHD, there remained a question whether the soil beneath and adjacent to the tank contained diesel. FIELD ACTIVITIES AND OBSERVATIONS To determine whether diesel remained in the soil beneath and adjacent to the tank, on August 17, 1992, Teichert excavated the fill material from the former excavation using a backhoe. Approximately 2 feet of clean sandy gravel fill were encountered ' near the surface just below the concrete pad covering the former excavation. Below this imported fill were approximately 8 feet of loose native material. This material was reported by Teichert to be soil which was originally excavated from around the tank and placed back in the excavation following the removal of the tank. This native material had no visual or olfactory evidence of petroleum hydrocarbon impact. At a depth of 10 feet, hard native soil was encountered, indicating the limit of the original excavation. Teichert overexcavated the sidewalls of the north edge of the ' excavation, beyond where soil boring 131-1-1 had been drilled. This area was overexcavated since the analytical results for the soil sample from the boring indicated diesel impact to soil at a depth of 10 feet. The native soil encountered at the bottom ' and sidewalls of the excavation had no visual or olfactory evidence for diesel impact, so confirmation soil samples were collected. Some product odor was detected in the shallow soil at a depth of approximately 1 to 2 feet. This odor was found to be limited to a thin clay layer, approximately 0.1 to 0.2 foot thick, located between the asphalt and the underlying sand fill. This clay was ' stained gray and had a strong product odor. To determine the origin of this material, Telchert removed the asphalt north of the original excavation where the product seemed to be more highly concentrated. In excavating this area and an additional area ' east of the excavation, the impacted clay layer was found to be continuous. Since the clay appeared continuous, and since it was underlain by fill sand, it was concluded that the clay was placed as a base for the asphalt, and that it was probably saturated with a heavy petroleum hydrocarbon product consistent with standard asphalt placement procedures. piOV9010900020.2aw