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Quik Stop Station No 39 September 23,2005 Stockton,California Results of Additional Subsurface_Investigation I RESULTS OF ADDITIONAL SUBSURFACE INVESTIGATION U Soils encountered in the monitoring well borings consisted predominantly of interbedded and laterally gradational silty sand, sandy silt with minor silt and clayey silt The clayey silt, encountered in the three borings between depths of 52 and 62 feet bsg, appears to be laterally continuous between the monitoring well MW-4, MW-5 and MW-6 borings First groundwater encountered during drilling was noted at approximately 62 feet bsg Static groundwater levels in the completed monitoring wells were measured at approximately 51 feet bsg The clayey silt layer appears to act as a semi-confining unit Analytical results of soil samples collected during drilling of monitoring well MW-4, MW-5 and MW-6 borings are summarized in Table 1 No petroleum hydrocarbon analytes were reported in any soil sample Analytical results of the initial groundwater samples collected from monitoring wells MW-4, MW-5 and MW-6 and subsequent site groundwater monitoring data for first, second and . third quarters 2005 are summarized in Table 2 No petroleum hydrocarbon analytes were reported in the initially collected groundwater samples or those collected for third quarter 2005 Reported concentrations of TPHg and toluene in groundwater samples collected for first and second quarter 2005 are considered spurious No DCA was reported in any sample SENSITIVE RECEPTOR SURVEY Horizon conducted a sensitive receptor survey for the area within a 2,000-foot radius from the site The sensitive receptor survey included identification of natural surface water bodies, a Department of Water Resources (DWR) Well Completion Report file review and a r physical survey of the area to identify land use Topographic and street maps were reviewed for identification of naturally occurring surface water bodies The purpose of the survey is to • 7039rpt9 05 Project No 7039 16 6 HORIZON ENVIRONMENTAL INC.