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APPENDIX BIRISK BASED CORRECTIVE ACTION TIER 1 AND TIER 2 ANALYSIS <br /> 51TE CLOSURE EVALUATION REPORT <br /> Fortner Beacon Starion No 695 <br /> 900 South Cherokee Lane <br /> moi, California <br /> Delta Project No D093-915 <br /> Page 11 <br /> 7.0 RISK-BASED CORRECTIVE ACTION <br /> The RBCA analysis indicates that current BTEX levels meet the criteria established in the Tier 1 or Tier 2 <br /> analysis The analysis was conducted under guidance from the Standard Guide for RBCA Applied to <br /> Petroleum Release Sites (ASTM, 1995) and Tier 2 Guidance Manual for Risk-Based Corrective Action <br /> (Conner, et al , 1995) <br /> 7.1 Chemicals of Concern - Source Characterization <br /> The following compounds have been identified as chemicals of concern (COC) at the site: BTEX <br /> Appendix I provides chemical characteristics of those compounds (Conner, et al , 1995) The present <br /> extent of these compounds is described in the following sections <br /> 7 1 1 Soil <br />• Removal action conducted at the site since 1985, include free product recovery, soil excavation during <br /> the tank and product line replacement, and operation of a SVE system (July 1991 through February <br /> 1996) The continued remedial actions have removed approximately 125,995 pounds of vapor equivalent <br /> gasoline In March 1996 soil borings SB-1 through SB-6 were installed to characterize the current extent <br /> of impacted soil These borings were installed at locations within the source area(s) and along the <br /> perimeter of the known areas of soil impact (Figure 2) <br /> Table 10 summarizes the analytical results from soil borings SB-1 through SB-6 sampling activities <br /> Samples which contained benzene levels above analytical detection limits were considered in assessing <br /> a representative source concentration of BTEX in the soil for the RBCA analysis In addition, samples <br /> which indicated elevated detection limits were also included in the analysis In total, 12 soil samples <br /> were considered as representative of the source area A statistical fit estimated a representative <br /> concentration for the soil samples that was equivalent to the 95 percent upper confidence limit (UCL) on <br /> the mean This technique will remove anomalies while ensuring that the results are still conservative <br /> This procedure is in accordance with ASTM (1995) and the Tier 2 Guidance Manual (Conner, et at, <br /> 1995) <br /> RPT001 915 <br />