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' f.\projects\5137\rydcntk.rep <br /> 3.4 Final Excavations and Soil Borings <br /> On February 15, 1991 ESE directed additional excavation with an extended backhoe to <br /> remove the soil containing hydrocarbons. A State-Certified mobile laboratory from Sequoia <br /> Analytical was present onsite to confirm that all soil containing hydrocarbons would be <br /> removed. Fourteen soil samples (2/15/91 Samples S-1 through 5-14 on Figure 3 - Final <br /> ' Excavations and Soil Borings) were collected from the excavation and analyzed on site. <br /> Table 1 shows that these samples contained TPH by 1R concentrations ranging from ND <br /> ' (nondetectable) to 900 mg/kg. The excavation was expanded to the limits of the extended <br /> backhoe, approximately 14 feet deep and 11 feet wide. The excavation extended <br /> approximately 3 feet beneath the building, which was shored by timbers to maintain <br /> structural integrity. As the excavation was expanded beneath the building, two of the <br /> previous soil borings (Bl and 133) were dug out and a one-foot thick layer of oily soil was <br /> noted beneath boring 131 at a depth of approximately 16 to 17 feet. The hydrocarbons <br /> ' appeared to be concentrated in this layer because it was siltier (more permeable) than the <br /> surrounding clays. <br /> ' On February 22, 1991, 6 additional soil borings (Cl through C6 on Figure 3) were drilled <br /> and sampled on the south and north (beneath the building) sides of the excavation to <br /> assess the lateral extent of the oily layer found below boring Bl. Borings C1 through C5 <br /> were drilled to 20 feet below grade. Table 1 shows that soil samples collected from these <br /> ' borings contained Oil and Grease concentrations ranging from ND to 99 ppm. Samples <br /> from the previously noted oily layer between 16 and 17 feet contained Oil and Grease <br /> ' concentrations ranging from ND to 93 ppm. The highest Oil and Grease concentration was <br /> found in the sample from a depth of 6 feet in boring C4. This sample was also analyzed <br /> for other organics and metals. No detectable concentrations of volatile petroleum <br /> hydrocarbons or semivolatile organics were reported. Metals concentrations reported were <br /> - ' below California DHS designated hazardous waste levels. The soil sampling results from <br /> these borings appear to approximately establish the lateral and vertical extent of soil <br /> ' containing significant (greater than 100 ppm) Oil and Grease. <br /> ' 6 <br /> 1 <br />