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Ms Tammy Hodge CAMBRIA <br /> November 1, 1996 <br /> collected at 8 ft depth from the excavation sidewall in the northeast portion and soil samples collected from <br /> the southern part of the excavation sidewalls did not contain TPHg and benzene, indicating that all significant <br /> hydrocarbon-bearing soil was removed <br /> 1995 Monitoring Wells Installation On March 20, 1995, GTI supervised the drilling and installation of off- <br /> site monitoring wells MW-4 and MW-5, which were installed to a maximum depth of 21 5 ft TPHg and <br /> benzene were not detected in any of the samples from either of these soil bonngs <br /> SITE HYDROGEOLOGY <br /> Regional Hydrogeology. The site is located in the northwest portion of the San Joaquin Valley, on the distal <br /> slope of a Quaternary alluvial fan derived from Coast Range sediments The water quality in the Tracy area <br /> is degraded by intrusion of saline connate water as a result of overdraft of deeper aquifers Shallow ground ' <br /> water is generally poor along the western boundary of the San Joaquin Basin, it is characterized by high <br /> concentrations of dissolved solids (U S Geological Survey Professional Paper 1401-A, 1991) <br /> Local Hydrogeology Subsurface materials beneath the site are predominantly silty clays and clayey silts with <br /> a lens of pebbly sand from about 14 to 18 ft (Attachment C) Ground water was encountered at a depth of <br /> about 10 ft <br /> Boring and Well Logs Boring and well construction logs are included in Attachment C <br /> Cross-Sections No cross-sections have been prepared by previous consultants <br /> Ground Water Depth Depth to water measurements indicate ground water ranges from about 8 to 12 ft deep <br /> (Attachment D) <br /> Ground Water Flow Direction. The ground water flow direction has consistently been northeastward <br /> (Attachment E) <br /> Potential Underground Conduits A sewer was identified at a depth of 2 5 ft by GTI during the installation <br /> of monitoring well MW-5,northeast of the site Though this is in the down gradient direction of ground water <br /> flow, historic depth to ground water has been about 10 ft Therefore, the shallow sewer is not a potential <br /> migration pathway for ground water <br /> 4 <br />