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SUPPLEMENTAL SITE INVESTIGATION WORK PLAN South Pointe Property Stockton,California Site Background 2.2 SITE GEOLOGY AND HYDROGEOLOGY The site is located within the Great Valley geomorphic province, a large, elongate, northwest- trending structural trough bounded to the west by the Coast Ranges and to the east by the Sierra Nevada.The Great Valley consists of two long north-south trending valleys connected end-to-end, with the Sacramento Valley to the north and the San Joaquin Valley to the south. The site is located in the northern portion of the San Joaquin Valley. The Sacramento and San Joaquin Valleys have been filled with thick sequences of sediment derived from marine and continental sources. Sedimentary deposits are relatively thin at the valley edges and thicken to more than 25,000 feet in the deepest interior areas. In general, older formations are marine in origin, and younger formations are derived from continental sediments. Younger sediments are being continually eroded, primarily from the Sierra Nevada, and transported to the valleys by downslope fluvial systems. Previous geotechnical and environmental investigations have identified shallow soils beneath the site as consisting of native sandy materials mixed heterogeneously with rubble and debris associated with historical building foundations and similar relics of historical site use. Deeper native soils consist primarily of fine-grained sand to depths of 10 to 15 feet below ground surface (ft bgs). Groundwater has historically been encountered at depths ranging from 8 to 17 ft bgs. Previous environmental investigations associated with the L&M Operable Unit site located south of the subject property have identified an 'A' groundwater zone at 15 to 30 ft bgs and a 'B' groundwater zone at 48 to 53 ft bgs. PREVIOUS SITE INVESTIGATIONS The following sections describe previous environmental investigations at the site. 2.2.1 Geotechnical Assessment - 2006 In September and October 2006, Neil O. Anderson and Associates performed a geotechnical investigation of the site which consisted of advancing 14 exploratory soil borings to depths ranging from 16.5 to 41.5 ft bgs. Encountered materials consisted of loose to well-compacted sandy clay, sandy gravel, and clayey sand mixed with gravel, concrete, and brick debris to depths ranging from 3 to 16 ft bgs. The investigation identified the widespread presence of concrete debris beneath the site, including buried foundations and underground structures, and recommended these materials be removed during site redevelopment and resulting voids filled with appropriate fill. Additionally, onsite native soils were deemed appropriate for use as engineered fill, but that this fill should be free of vegetation and deleterious material. 2.2.2 Environmental Assessment - 2007 Wallace-Kuhl & Associates, Inc. (WKA) performed a site-wide investigation and published the results in the document entitled Subsurface Investigation Report, Stockton Promenade & 2.2