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APPENDIX BMISK BASED CORRECTIVE ACTION TIER 1 AND TIER 2 ANALYSIS SITE CLOSURE EVALUATION REPORT Former Beacon Station No 695 900 South Cherokee Lane Lodi, California Delta Project No D093-915 Page 15 8.3 Exp2sure to Imnacted Ground Nater S 3 1 Vapors to Ambient Air Ground water at the site is present at approximately 65 feet bsg, thus emissions from ground water are expected to be minimal In addition, since soil is impacted and contains more mass, any emissions will likely result from unpacted soil where vapor partitioning processes are relatively greater S 3 2 Va ars to Enclosed S aces Ground water at the site is present at approximately 65 feet bsg, thus vapors from ground water are expected to be minimal. In addition, since soil is impacted and contains more mass, any vapors will likely result from unpacted soil where vapor partitioning processes are relatively greater S 3 3 Ingestion Ground water has been impacted by petroleum hydrocarbons Although the plume is diminishing, no residential wells have been identified within 250 feet of the site, and the nearest known public well is 2,600 feet away, this exposure pathway was considered to ensure the integrity of the ground water The Tier 1 RBSL model from the Guidance Manual assumes that ground water is from the source area as a drinking water supply The model estimated a RBSL of 9 9 Ag/L which becomes 2 9 µg/L when the 0 29 California Correction Factor is applied The maximum benzene concentration during the last year at the site was detected at 73 µg/L in MW-8 on March 29, 1996. A Tier 2 analysis will be conducted for this exposure pathway with benzene as a COC The RBSL results for ground water are shown in Table 13, and as can be seen, toluene, ethylbenzene, and total xylenes all meet the respective RBSLs The modeling results are presented in Appendix M S 3 4 Discharee to Surface Water The ground water is present at approximately 65 feet bsg and the water elevations are approximately 13 feet below mean sea level For these reasons, discharge to surface water bodies was not considered RPT001 915