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APPENDIX BRISK BASED CORRECTIVE ACTION TIER 1 AND TIER 2 ANALYSIS, SITE CLOSURE EVALUATION REPORT Former Beacon Station No 695 900 South Cherokee Lane Lodi, Califontia Delta Project No D093-915 Page 16 9.0 'ITER 2 EVALUATION A Tier 2 evaluation was performed because the Tier 1 RBSLs for the vapors to enclosed spaces and ground water ingestion exposure pathways and it was expected that the SSTL to be developed under the Tier 2 evaluation would be more cost effective than remediation to Tier 1 RBSLs 9.1 Va rs to Enclosed Spaces The same model used for the RBSL calculation(Appendix J) was used for the SSTL evaluation, however, some of the input parameters were changed to account for site specific features The distance to the receptor was changed to 100 feet to account for the separation between the impacted soil and the building on-site In addition, most likely exposure (ML.E) factors were used instead of the Reasonable Maxi num Exposure(RME) factors used in estimating RBSU The MLE factors were used in accordance with the American Industrial Health Council(1994)and EPA(1992)guidelines As stated in Appendix J(Conner, . et al , 1995) this model is very conservative in assuming a 1 percent open crack space in the foundation and a low air exchange rate The open crack space was changed to 0 1 percent for a one foot foundation and the air exchange rate was doubled. The results are in Appendix M The results of the model indicate a SSTL of 4 3 mg/kg for benzene When this value is multiplied by 0 29, the resulting SSTL is 12 mg/kg benzene The representative benzene concentration is 0 97 mg/kg benzene, thus indicating that the site is within SSTLs for this exposure pathway 9.2 Ground Nater Ingestion E Benzene concentrations in both soil and ground water are above RBSLs under the assumption that ground water on the site will be used as a drinking water supply Since the ground water on the site will not be used for drinking water, SSTIs were estimated to determine the applicable clean-up level A sensitive receptor survey was performed and indicated that no residential drinking water wells existed within 250 feet of the site A municipal water well was identified at a distance 2,600 feet downgradient RPT001 915