ARCHIVED REPORTS_DRAFT - PHASE I REMEDIAL INVESTIGATION REPORT

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Kennedy/Jenks Consultants ' Section 5: Results 5.1 Geology and Hydrogeology The soil stratigraphy can be observed on the boring logs included in Appendix A and on the trench logs included in Appendix B. Over most of the Railyard, the upper 12 feet of soil typically consisted of a yellowish brown silt or fine sandy silt. Layers of well-graded sand were commonly observed in borings in AOI 10 below about 12 feet bgs, and a lens of gravel was observed in the easternmost trench in OU-5. During the recent investigation activities, groundwater was typically encountered at depths of about 13 feet bgs to 15 feet bgs in OU-2, and at slightly deeper depths in western OU-5. The shallow groundwater sampled in this investigation appears to be unconfined. The magnitude and direction of the groundwater gradient is uncertain because no monitoring wells are currently ' located at the former Railyard. However, past groundwater gradient maps of the OU-1 area indicated the gradient had a north to northwest direction (RMC Lonestar 1992; Terranext 1996a, 1996c, 1997). The distribution of the hydrocarbons in groundwater in the western portion of ' OU-5 suggests that the gradient direction may be west to northwest. 5.2 Analytical Results Analytical results and comparison values are presented in Table 5 through Table 14. The analytical data reports are included in Appendix C. Comparison values provided in the tables include the Preliminary Remediation Goals (PRGs) established by the U.S. Environmental Protection Agency, California Human Health Screening Levels established by the California Environmental Protection Agency (CHHSLs), and in OU-1, ' the former remediation goal for lead in soil. PRGs and CHHSLs are health-risk based concentrations that can be used as guidelines to evaluate whether remedial measures at a site are warranted. Both commercial/industrial values and residential values are presented in the tables. ' 5.3 Operable Unit 1 As described in Section 2, OU-1 encompasses the area where remediation of soil containing lead was previously conducted and where lead may still remain in some soils. Accordingly, soil samples collected in OU-1 were analyzed for total and soluble lead. No groundwater samples were collected from OU-1. ' Analytical results from soil samples are summarized in Table 5. For comparison, the commercial and residential PRGs for lead (800 mg/kg and 150 mg/kg, respectively), and the commercial ' and residential CHHSLs for lead (3,500 mg/kg and 150 mg/kg, respectively) and the 1995 soil remediation goal of 220 mg/kg of lead are presented in Table 5. Concentrations of total lead in • surface samples are shown on Figure 5. DRAFT Phase I Remedial Investigation Report Page 22 ' Former Tracy Railyard, Tracy, California g:1is-groupladminljob10510565777.16_up«109-reportstri rpMext.doc