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r <br /> IL <br /> by methods described in the 1985 edition of "Guidelines for Addressing Fuel Leaks" prepared <br /> �- by the California Regional Water Quality Control Board, San Francisco Region. <br /> Analytical results (Table 1) indicated low levels of PHCs detected beneath the four tanks. No <br /> benzene was detected in any of the soil samples, and most PHCs (maximum of 120 mg/kg <br /> TPHg) were detected along the west side of the excavation, beneath Tank #4. PHCs were <br /> detected in four of nine samples collected along the pipeline. Trace amounts of toluene, <br /> xylene, and ethyl benzene were detected in the sample approximately 120 feet west of the <br /> former tanks. Higher levels of PHCs including 0.55 mg/kg benzene and as much as 140 <br /> �- mg/kg TPHg were detected near and beneath the former dispenser island where discolored soil <br /> and petroleum odors were noted during the pipeline removal. <br /> 2.3 GEOLOGIC AND HYDROLOGIC CHARACTERISTICS <br /> V <br /> The subject site is located on the delta of the San Joaquin River, approximately 2 miles east <br /> of the confluence of the San Joaquin and Calaveras Rivers. The subsurface geology consists <br /> of a thick sequence of alluvial deposits of late Tertiary to Holocene Age, overlying sedimentary <br /> rocks of Cretaceous to Tertiary age, which in turn overlie crystalline basement rocks (Bartow <br /> and Nilsen, 1990). Based on data from nearby studies within the Port area, the soil profile <br /> at the site to a depth of about 20 feet bgs consists of interbedded, sands and clays, mostly <br /> under reduced conditions (Sierra-Pacific Groundwater Consultants [SPGC], 1994). <br /> Data from nearby studies indicates that the current depth to groundwater in the vicinity ranges <br /> from about 5 to 10 feet bgs (SPGC, 1998, and EMCON, 1998). Seasonal fluctuations in the <br /> water table appear to range from about 3 to 5 feet, with some as much as 6 to 9 feet. <br /> Historically, water levels in this area have risen as much as 8 feet since 1994. Tank removal <br /> inspection records for Port sites (dating back to 1987) indicate that no groundwater was <br /> encountered during excavation or soil resampling to a depth of as much as 16 feet bgs. <br /> Groundwater flow directions in the vicinity of the site appear to be variable, ranging from west <br /> �- northwest to east southeast. Flow direction changes may be due to tidal influences produced <br /> by the deep water channel to the north and the San Joaquin River to the west and southwest <br /> of the Port area. <br /> 3.0 PROPOSED SCOPE OF WORK <br /> The proposed scope of work includes advancing three borings in the vicinity of the USTs and <br /> two borings in the vicinity of the dispenser, using the Geoprobe direct-push method, and <br /> 3 ssitns U9TiKV-WPK <br /> BOYAJIAN & ROSS, INC. <br /> Environmental Scientists & Engineers <br />