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i ..� November 2,2001 Quik Stop Station No.076k r , } Stockton California Work Plan for-Soil and Groundwater Investi ation located 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. REGIONAL AND LOCAL HYDROGEOLOGY The site is situated in the central portion of the Great Valley Geomorphic Province otherwise known as the Central Valley of California. The Central Valley consists of-two broad, topographically distinct, alluvial valleys:'the Sacramento Valley in the north; and the San Joaquin Valley in the south. These two valley s'hmeet in the area of the inland delta formed by the confluence of the San Joaquin and Sacramento Rivers. Stockton is situated in the northern San Joaquin Valley just east of and adjacent to the San Joaquin/Sacramento River delta system. The Great Valley geomorphic province is an elongate nortliwest-trending asymmetric structural trough filled with a thick sequence of marine and non-marine sediments ranging in age from Jurassic to Holocene. Great Valley sediments generally thin to zero towards the adjacent ,Sierra Nevada and Coast Ranges provinces and are predominantly underlain by the westward continuation of Sierran granitic and metamorphic rocks. The Coast Ranges are underlain, in part, by folded and faulted sedimentary rocks equivalent to intervals'found at depth in the Great Valley stratigraphic sequence. 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 and are generally underlain by consolidated marine rocks. Surface sediments in the site area are generally Pleistocene to Holocene alluvial and plains deposits. Shallow native soils at the site have been classified as clayey silt. 7076wp 11-01.doc Project No.7076.12 2 HORIZON ENVIRONMENTAL INC.