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' GealogicalTec/acccslnr Page 9 Site Characterization Report ' Project No 724 2 May 9,2006 • ' 3.3 Contaminant Mass Estimate Calculations The contaminant data gleaned during this and previous field efforts will be presented in a forthcoming Site Conceptual Model (SCM) report 4.4 CONCLUSIONS AND RECOMAMNDATIONS ' Based on our interpretation of the data collected over the course of this subsurface investigation, GTI have reached several conclusions These conclusions are based on the premise that the data we considered, although incomplete, are representative of actual site ' conditions We acknowledge that there may be undiscovered conditions, which would upon their consideration, change our interpretation and thus our conclusions Our recommendations are based on our knowledge of site conditions, and on the state and limitations of subsurface investigative technology ' 4.1 Conclusions • The geology of the site consists primarily of alternating layers, lenses and interstratified beds of clays, silts and sands Significant units containing gravels are absent ' • Groundwater flow trends northeast to east a High levels of BTEX and TPH-G are present in the groundwater of all six on-site shallow and intermediate monitoring wells (MW-1 through MW-6) ' * The soil contamination above the water table appears to be hrmted in lateral extent to the areas directly within 15 feet of the former dispenser island • The residual soil TPH-G contamination in the vadose zone and sorbed hydrocarbons below the water table continues to provide a source for dissolved hydrocarbon groundwater plume • The groundwater plume contamination is stratified with the main mass of contaminants having migrated to a depth of 45 to 70 ft bgs • Sandy units below 60 — 65 feet below grade may be acting as a preferential pathway ' for contaminant migration to the northeast of the site as depicted in Figure 6 • The low levels of contaimnation in well MW-101 and lack of contaminants in MW- 201 suggests that these wells define the vertical linut of the plume beneath the site t • The plume boundary has been defined by the advancement of the CPT borings The down gradient extent of the plume probably attenuates to tion-detect levels within 50 feet of the CPT locations ' • The detections of THP-G in the northern two Shell Stations suggest that a co-mingled plume is present 1