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A.7TORNEY-CLIENT PRIVILEGE 2.0 SUMMARY OF PREVIOUS INVESTIGATIONS 2.1 RISK ASSESSMENT SUMMARY In May, 1993, ChemRisk® submitted to S3CPHS a baseline risk assessment for the Site which assessed (1) the potential for chemical migration through soil to groundwater and (2) the magnitude of any potential Site-related exposures and potential health risks associated with current Site conditions Using environmental fate and transport modeling, it was demonstrated that the petroleum hydrocarbons had only limited migration potential in Site soil Over a 99-year period, tetradecane, used as a conservative surrogate chemical, migrated less than one foot ChemRisO concluded that the petroleum hydrocarbons will not impact the groundwater beneath the Site There were therefore no complete exposure pathways at the Site It was recommended that the petroleum hydrocarbons present in soil beneath the Santa Fe Railway Company Site can safely remain in place because they do not pose a threat to either groundwater resources or human populations No further investigations are necessary and additional groundwater monitoring at the Site is unnecessary, 2.2 SOIL SAMPLING AND ANALYSIS Six rounds of soil sampling have been completed Soil from beneath the Site was sampled and analyzed in January 1988, August 1989, January 1991, May 1991, December 1992, and April 1993 The first round of sampling included analyses for (1) total petroleum hydrocarbons (as diesel) (2) benzene, (3) toluene, (4) ethylbenzene, (5) xylenes, (6) halogenated volatile organics, and (7) polychlonnated biphenyls (PCBs) As halogenated volatile organics PCBs, and BTEX were not detected in the preliminary samples, subsequent samples were analyzed only for TPHd, gasoline and in some instances, BTEX. The results of the soil sampling are presented in Tables IA and 1B Figure 2-1 presents the sampling locations and summarizes the results Figures 2-2 to 2-4 illustrate the vertical and lateral extent of contamination as characterized during the soil sampling investigation of May 1991 TPHd as high as 6,900 ppm was detected during the initial sampling round Subsequent investigations reported TPH,, concentrations as high as 7,400 ppm in a sample taken at a depth of I1 0-I2 0 feet (B-5) In the third round of sampling which included samples taken during monitoring well installation, TPH, was less than 1 0 ppm (the reporting limit) In the May 1991 sampling event, a concentration of 4,300 ppm of TPHd was identified in a sample taken at a depth of 15 5 to 16 0 feet The primary purpose of the final two rounds of soil sampling was for partitioning studies to simulate the movement of TPHd These investigations are discussed below in Section 3 0 1 G�iymLMONTEICLOSURE SMMiOeM7t 7 002 2