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CaEOMATRIX On August 7, 1998, soil borings B3-1, B3-2, and B3-3 were installed and soil samples were ' collected at 5-foot intervals between 10 5 and 40 5 feet bgs No PHCs were detected in the uppermost soil samples collected from 10 to 11 feet bgs, or in the two lowermost samples ' collected at 35 and 40 feet bgs, in any of the three borings PHCs in soils were first detected at 16 feet bgs in boring B3-2, and at 20 feet bgs in B3-1 and B3-3 The highest Ievels of PHCs in ' soils were detected in the sample collected from 15 5 to 16 0 feet bgs in boring B3-2 This sample contained 2,100 mg/kg TPH-g and 8 4 mg/kg benzene ' Uppermost groundwater samples were collected at 12 and 13 feet bgs in borings B3-3 and B3-2, respectively The sample from B3-2 contained trace amounts of PHCs (0 42 micrograms ' per hter [µg/1] benzene), while no PHCs were detected in the sample from B3-3 Groundwater sampled from bonng B3-1 at 22 feet bgs, within the zone of strong petroleum odor, contained ' the highest concentrations of PHCs in groundwater samples, with 1,600,000 gg/l TPH-g The depth-discrete water sample collected from 31 to 35 feet bgs in boring B3-2 contained 2,700 µg11 TPH-g and 60 µg11 benzene, indicating that dissolved phase PHCs are present in the ' coarser grained sediments below the zone of PHC-impacted soils From May 18, 1999 through June 2, 1999, three groundwater monitoring wells were installed within a few feet of corresponding previous soil bonngs All wells were drilled with 8-inch ' hollow-stem auger to depths of 36 to 40 feet to allow installation of 35 feet of well casing Wells are constructed of about 10 feet of blank, 2-inch diameter, schedule 40 PVC casing above 25 feet of 2-inch diameter, 0 02-inch factory-slotted PVC screen The wells have been ' sampled on a quarterly basis and monitoring reports submitted to PHS/EHD Monitoring results are discussed in Section 14, below ' 1.3 SITE HYDROGEOLOGIC SETTING ' The site is located on the delta of the San Joaquin River, approximately 2 mules east of the confluence of the San Joaquin and Calaveras Rivers The subsurface geology consists of a thick sequence of alluvial deposits of late Tertiary to Holocene age, overlying sedimentary rocks of Cretaceous to Tertiary age, which in turn overlie crystalline basement rocks (Bartow and Nilsen, 1990) Data from nearby studies within the Port area indicate a soil profile to a ' depth of about 20 feet bgs consisting of interbedded sands and clays, mostly under reduced conditions (Sierra-Pacific Groundwater Consultants [SPGC], 1994) ' Lithologi c data at Site 3 indicate that, in general, the interval from roughly 13 to 23 feet bgs • Ibeneath the former tanks comprises mostly silt, clayey silt, and clay Silty sand occurs below I 1PROJECR6437 000/6437 Wk Pln Site 3 doe 3 I