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The Shelard Grop STS Project No. 94039-XA July 10, 1987 Page 2 except in the area of the highest deflection of 150 feet of the native soils feet had HNU deflections • foundation subcut excavation. The ppm was observed in the upper 2 in test pit 2. Native soils at 17 of 1 to 2 ppm. The petroleum product which was encountered appears to be the result of a spill which occurred at the site during the time that the area was used as a gas service station. The con- figuration of the spill appears to indicate that leakage occurred in a relatively small area, migrating vertically through the existing fill soils on -site until native soil and groundwater was encountered at a depth of approximately 15 feet. The petroleum product appears to be confined to a relatively small area. Petroleum product has been attenuated in the soils and no free product was observed. It appears that significant biodegradation of the petroleum product has been occurring. Previous site evaluations at this location included Subsur- face Exploration and Geotechnical Engineering Evaluation Report dated October 14, 1986; Chemical Analysis of a Soil Sample, which was noted to have faint chemical odors, report dated November 6, 1986; and an Air Photo Evaluation of the site, report date,J March 9, 1987, STS File 194039. Copies of portions of these reports are included for your review. The premise that the petroleum contamination is of limited extent is evident by the soil borings which were conducted at the site. No areas of gross contamination were identified in any of the test borings. Chemical testing performed on a sample obtained from boring 2 confirms the fact that the contamination in these borings is minor. It is estimated that a total of 300 to 400 cubic yards of soil contaminted with petroleum product exists in this area. Based upon the examination of the site conditions we recom- mend that the contaminated soils present at the site be remediated in the following manner. o Excavate the contaminated soils with HNU deflections greater than 10 parts per million. o Land spread these soils in thin lifts in the area of the proposed parking lot. The soils should be disked periodically in order to assist in volatilizing the petroleum product. 0 Soils will be compacted and become part of a fill sec- tion beneath the asphalt parking area once HNU deflec- tions of less than 10 ppm are obtained. The asphalt parking lot will minimize infiltration of water through these soils and minimize any impact due to leaching of the contaminants from them.