ARCHIVED REPORTS_PRELIMINLARY SUBSURFACE INVESTIGATION

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Preliminary Subsurface Investigation City of Stockton, former Western Pacific Railroad Property, Stockton, CA May 27, 1992 W0601.11) ' 6.2 Groundwater Laboratory analysis recorded priority pollutant metals above method detection limits in the groundwater samples collected from wells MW-1 through MW-3. None of the levels detected exceeded the Total Threshold Limit Concentration values as listed in Title 22 of the California Code of Regulations; however, one sample contained concentrations of selenium (WPRR-MW3) above the State Primary Maximum Contaminant Level (MCL). No volatile or semi-volatile ' organics were detected in any of the samples analyzed by EPA method 8240 and 8270, respectively. The laboratory results for the water samples are presented in Table 4. Laboratory reports, chain of custody documentation, and laboratory QA/QC data, are included in Appendix H. 6.2.1 Wells Located on Adjacent Sites The seven new monitoring wells and two existing wells at the Banner Island property were sampled on March 18 and 19, 1992 (Figure 2). This site is located directly southeast of the former WPRR property and subsurface investigations were conducted concurrently at both sites. Laboratory analysis recorded priority pollutant metals above method detection limits in the groundwater samples collected from wells BI-MW1 through BI-MW9. Although none of the levels detected exceeded the Total Threshold Limit Concentration values as listed in Title 22 of ' the California Code of Regulations, some of the samples contained concentrations of arsenic (BI- MW4 and 8), barium (BI-MWI), chromium (BI-MW1 and 2), and selenium (BI-MWI, 4, and 8) above the respective State Primary Maximum Contaminant Levels (MCL). These include selenium, the same metal that exceeded its MCL at the former WPRR site. The only volatile organic detected was acetone ( 120 parts per billion, ppb) in well BI-MW4. R041392.SAV 11 1