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,,.. Report: Groundwater-quality Monitoring—October 27,2003: 7500 West Eleventh Street, Tracy, Cit. Page 3 former locations of the fuel pump islands are also shown on Figure 2. At the same time that the tanks were removed from the site, soil heavily affected by fuel hydrocarbons was excavated from beneath the pump island area and 521.25 tons of that material were disposed off-site at a permitted facility. In addition, some 2,000 gallons of floating product and affected groundwater were removed from the subsurface by pumping from a tank pit into a vacuum truck, which was used to transport it to a permitted recycling .., facility (Dietz Irrigation 1999a). An initial phase of site characterization work was completed in May 2000. It included the ,�,.. installation of seven groundwater-quality monitoring wells (Nos. MW-1 through MW-7) at the locations shown on Figure 2. An extended phase of site characterization was initiated on March 25, 2002; it included the installation of an additional eight �- groundwater-quality monitoring wells, numbered MW-3A, MW-3B, MW-8 through MW-12, and MW-12A. It was completed on April 11, 2002, with a round of groundwater sampling and analysis that encompassed all 15 groundwater-quality monitoring wells by y then extant on the site (The San Joaquin Company, 2002c). 1.4 Geology and Hydrogeology The subject property and the surrounding area are situated on level terrain on the distal, northern slope of an alluvial fan. The shallow underlying alluvial sediments are of AW Quaternary to Recent age. The site and the immediately adjacent property along the south side of West Eleventh Street and the west side of Chrisman Road have been extensively excavated and backfilled during prior filling station construction and remodeling, utility installation, and highway expansion. Beneath the paving and fill, the soils are composed of alluvial materials consisting of interbedded clays, silts and sands. These materials have been deposited in a complex lenticular form composed of relatively low permeability clays and silty clays inter- bedded with permeable silts and sands. The sizes of individual permeable lenses vary from relatively large features having considerable areal extent to small, localized lenses of limited extent and thickness. In some instances, these lenses merge into each other to form semi-continuous permeable strata within the less permeable clayey material. In the neighborhood of the 7500 West Eleventh Street site it is estimated that these alluvial �. materials are some 100 ft. thick. The stratigraphy described above is typical of the alluvial fan upon which Tracy and the surrounding area are situated. Beneath the alluvial sediments are the poorly sorted clays, silts sands and gravels of the Tulare Formation that were primarily derived from the Inner Coast Range hills that rise along the west side of the San Joaquin Valley. The Tulare Formation is separated into two members, the Upper Tulare Formation and the Lower Tulare Formation. Both members of the Formation are, on the regional scale, moderately to highly permeable and yield moderate to large quantities of water to wells. The Upper Tulare Formation is separated from the Lower Tulare Formation by the low-permeability, lacustrine Corcoran v sic