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Former Beacon Station No 12474 June 7,2005 Stockton California Results of Additional Groundwater Assessment • RESULTS OF ADDITIONAL SITE INVESTIGATION Soils encountered during drilling of groundwater monitoring wells MW-13 through MW-17 consisted mainly of interbedded clay, silt and silty sand These soil types are correlated with the existing data as shown in two cross sections trending north-south (A-A'), and northwest- southeast (B-B') on Figure 2 The cross sections are shown on Figures 3 and 4 Analytical results indicate no TPHg, BTEX or fuel oxygenates concentrations in soil samples collected from the monitoring well MW-13 through MW-17 borings as summarized in Table 1 Two soil samples collected from the monitoring well MW-I5 boring at 92 5 and 124 feet bsg contained near-reporting limit concentrations of DCA No other DCA concentrations were reported in soil samples Groundwater samples have been collected from monitoring wells MW-13 through MW-17 on a quarterly basis since second quarter 2004 as summarized in Table 3 Concentrations of dissolved petroleum hydrocarbon as gasoline in groundwater were reported only in MW-14 and MW-17 after well development Hydrocarbon concentrations in groundwater samples from monitoring wells MW-13 through MW-17 have been generally near or below reporting limits No concentrations of DCA have been reported in groundwater samples collected from monitoring wells MW-13 through MW-17 UPDATED SITE CONCEPTUAL MODEL The site conceptual model (SCM) is used to develop hypotheses regarding the Iocation and movements of hydrocarbons in soil and groundwater Additionally, descriptive evaluations are developed to identify the potential impacts by hydrocarbons in the site environment to human health or beneficial uses of groundwater This SCM consists of descriptions of the site physical and hydrogeological conditions, the source, nature and extent of the environmental impacts, and hypotheses of the fate and transport of petroleum hydrocarbons in site soil and groundwater, and potential sensitive receptor exposure pathways AddtnlGWassmnt Protect No 1474 15 6 HORIZON ENVIRONMENTAL INC.