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Report. Groundwater-quality Monitoring—October 17,2004, 7500 West Eleventh Street, Tracy, CA. Page 4 po 4 t3' $ that analyte actually present in that groundwater sample. By April 11, 2002, it was clear that floating product was present in the surface of the -7. It continued to be present at various apparent groundwater in Monitoring Well MW F thicknesses up to 0.58 ft. until an LNAPL-purging program in that well was initiated on November 8,2003. As part of the further extension of the site characterization program in ; April 2004, five floating product monitoring wells were installed at the locations shown on Figure 2 to investigate the down-gradient extent to which LNAPL may have migrated in the interior of the plume of affected groundwater emanating from the 7500 West Eleventh Street property. The thickness of floating product in those five wells was checked at that time and tests were also made to detect the presence of LNAPL on the water table in groundwater-quality monitoring wells MW-7, MW-13 and MW-14. The same array of wells was again checked for the presence of floating product on July 26, � 2004 and on October 27, 2004. The historical record of LNAPL thicknesses measured in the array of floating product monitoring wells is presented in Table 3. At the direction of the SJCEHD, the quality of water in six potable water supply wells in the neighborhood of the Navarra Site was analyzed in April 2004. Second and third rounds of sampling and analysis of the water produced from those wells were conducted j on July 27 and October 28, 2004. The results of those three sampling rounds are recorded t. in Table 4. ^� 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 { 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. 1 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 � is 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 r Tulare Formation that were primarily derived from the Inner Coast Range hills that rise sic