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' Quik Stop Market No 76 October 28,2003 Stockton California Results of Additional Groundwater investigation Mount Diablo Baseline and Meridian The Quik Stop station facilities, as shown on Figure • 2, include a station building in the eastern portion of the site, two unleaded gasoline USTs Iocated in the northern portion of the site, and a gasoline dispenser island located in the southwestern portion of the site Product piping and dispensers were located over and adjacent to the former USTs Fill and turbine ports were situated at the southern ends of the former USTs SITE HYDROGEOLOGY The site is situated in the central portion of the Great Valley Geomorphic Province of California Generally unconsolidated to poorly consolidated alluvial, fluvial and lacustrine deposits of Miocene to Holocene age comprise the upper portion of the stratigraphic sequence of the Great Valley province Surface sediments in the site area are generally Pleistocene to Holocene alluvial and plains deposits Site soils to approximately 60 feet below surface grade (bsg) are predominantly silt with variable clay and sand fractions, and . minor silty sand The site is located in the San Joaquin River hydrologic basin Groundwater, as measured in July 2003, is approximately 64 feet bsg According to the SJCEHD, the regional groundwater flow is generally southwestward to southeastward BACKGROUND In October 1998, two gasoline USTs (former USTs on Figure 2), product lines and dispensers located above and adjacent to the USTs were excavated and removed from the site The UST basin was excavated to a depth of 12 feet below surface grade (bsg) Five soil samples were collected from beneath the former USTs at depths of 14 to 16 feet bsg Horizon documented the UST removals, and soil analytical results in Tank Closure Report dated February 8, 1999 • 076AddGWmvestgtn10-03 doc 2 ProjectNo 7079 14 HORIZON ENVIRONMENTAL