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MW C.S. KA 140. 16.31.01 May 24, 1931 Page 3 F d4' samples. TPH as diesel was detected only in the soil sample from Boring 184 (130 mg/kg). All soil samples indicated motor oil concen—traAjons ranging from 1.1 mg/kg to 440 mg/kg. A water sample taken by, lowe lrI0 al),Oiler thio %lh the cqntet of the auger in ebri+ng:B 1 revealed a motor oil oon entcaliion of 900 M /L. The cantainination appeared to be a result of asphalt contained in the fill near the former tank and product lines. IPh sio r laic . nd M. 'dw elo i 0 - The subject site is located on the:Biehop Tract in San Joaquin County at the very northern end of Stefani Lane off Eight Mile Road. The site is bordered to the north by Telephone Cut , Stough, which is part of the San JoaqumRiver deltasstem, and in all otherlSacramento Y directions by cultivated fields. Surface elevation on site is approximately ten feet above sea level. Local terrain is relatively flat with very little relief across the site. The site is underlain by approximately ten feet of imported fill material. Native soils that f underlie the fill consist of Quaternary peat and marsh deposits. These deposits are composed of decaying fresh-water plant remains and fine-grained, very organic rich marsh deposits with 3 minor amounts of clay and silt. Ground water beneath the site is expected to be unconfined and approximately ten feet below ' grade. The ground water flow direction beneath the site is under tidal influence and is highly variable. FIELD INVESTIGATION Excavation of Former Tank Area u .. Excavation consisted. of removing approximately 21.5 cubic yards of soil from the vicinity of the former 8000-gallon tank to a depth of 14 feet below grade with an excavator. The soil removed was stockpiled onsite for later sampling. A one-foot thick concrete hold-down slab was encountered at a depth of 12 feet. The hold-down slab was removed by breaking it up with a backhoe mounted air-hammer. After removal of the concrete slab, soil samples (E1 1 through E5) were immediately collected from the sidewalls and bottom of the excavation at. depths of approximately 13 to 14 feet. Ground water was observed infiltrating into the a;