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Report:Groundwater-quality Monitoring—July 14-15,1006, 7500 West Eleventh Street, Tracy, CA. Page 4 selected groundwater-quality monitoring wells. The historical record of LNAPL thickness measured in the array of floating product monitoring wells is presented in Table 3. 1.4.3 Testing of Water in Potable Water-sLapply Wells At the direction of the SJCEHD, the quality of water in six potable water-supply wells in the neighborhood of the Navarra Site was first analyzed in April 2004. Over time, the number of wells sampled has been reduced. Currently, two potable water-supply wells are being monitored. Those are the well at the Casa Mendoza Restaurant at 7500 West Eleventh Street and the well at the former Suburban Propane facility at 23901 S. Chrisman Road. As is documented in Table 4, no analytes of concern have been detected in any samples recovered from any of the potable water-supply wells located in the neighborhood of the subject property. 1.4.4 Evaluation of Natural Attenuation In addition to the groundwater-quality monitoring round that was conducted in February and March 2005, an extensive program of field testing, laboratory analysis and geochemical and engineering studies was completed to investigate the progress of natural - attenuation processes that are reducing the contaminant load in groundwater beneath the v Navarra Site. That work demonstrated that there is strong primary and secondary evidence that natural attenuation is aggressively reducing contaminant concentrations in the subsurface and that those processes alone will be sufficient to adequately remediate the groundwater within a reasonable time, which is estimated to be on the order of 10 to 20 years (The San Joaquin Company Inc. 2006b). 1.5 Geology and Hydrogeology The subject property and the surrounding area are situated on level terrain on the distal, ism 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. 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 ~ SJC