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Kennedy/Jenks Consultants
<br /> As a result, a more comprehensive investigation was undertaken, as detailed in the Soil
<br /> Sampling Workplan (IC, 1993a). The workplan, which received verbal approval from the
<br /> Regional Board, proposed to overlay a 150-foot by 150-foot grid on OU-1 to determine locations
<br /> for 36 surface soil samples (0.5 to 1.0 feet bgs) (S-1 to S-36) and nine shallow boring locations
<br /> for collection of surface soil samples and underlying soil samples (1.0 to 1.5 feet and 1.5 to
<br /> 2.0 feet bgs). All samples were analyzed for total lead only. Concentrations of lead ranged from
<br /> 5.3 to 3,120 mg/kg in the surface samples; 10.6 to 3,520 mg/kg in the mid-boring samples; and
<br /> 7.4 to 882 mg/kg in the deepest samples (Appendix D). Using these data, the volumes of soil
<br /> onsite with lead concentrations above possible action levels of 1,000 mg/kg, 500 mg/kg and
<br /> 174 mg/kg were estimated at 1,500, 3,500 and 9,500 cy, respectively.
<br /> At the request of Southern Pacific, IC conducted a risk assessment, as summarized in the
<br /> report, Derivation of a Soil Action Level for Lead(IC, 1993b). Using the lead exposure model
<br /> developed by DTSC, action levels for residual lead in soil were determined based on the most
<br /> conservative (protective) assumptions for future land use, including residential use of the
<br /> property, children as receptors, and children's consumption of home-grown produce. The result
<br /> was a mean soil action level for lead of 241 mg/kg.
<br /> The risk assessment results were transmitted to the Regional Board as an attachment to the
<br /> Workplan for Further Site Characterization (IC, 1993c). This workplan indicated that Southern
<br /> Pacific was seeking approval from the City of Tracy Planning Department for redevelopment of
<br /> the Railyard, and the City required concurrence from the San Joaquin County Public Health
<br /> Services (County) that site conditions were acceptable for residential use; the County in turn
<br /> requested approval from the Regional Board. As a result, Southern Pacific prepared the
<br /> workplan for the Regional Board identifying all steps necessary to fully characterize site soils,
<br /> exposure risk due to soils, groundwater quality, and potential for soil constituents to impact
<br /> groundwater quality. Potential remedies to eliminate any impacts would then be evaluated, and
<br /> the preferred and approved remedy would be implemented. The workplan noted which steps
<br /> had been completed to date and defined tasks to resolve the remaining data gaps in the
<br /> characterization. The workplan also indicated that Southern Pacific would remove the soil
<br /> containing lead at concentrations above the Title 22 Total Threshold Limit Concentration (TTLC)
<br /> of 1,000 mg/kg.
<br /> The Regional Board provided comments on the workplan, including a request that the
<br /> 241 mg/kg soil action level for total lead be used. IC responded on behalf of Southern Pacific
<br /> that the value derived with DTSC's lead exposure model was overly conservative for use as the
<br /> remediation goal, and the 500 mg/kg goal was more appropriate (IC, 1994a). The Regional
<br /> Board then agreed to provide conditional approval of the workplan, contingent upon DTSC's
<br /> approval of the 500 mg/kg goal. However, as documented in the Site Remediation
<br /> Report/Workplan (IC, 1994b), when Southern Pacific, the Regional Board and DTSC met to
<br /> discuss the issue on 27 July 2004, DTSC did not agree to accept a 500 mg/kg as a cleanup
<br /> goal protective of human health. As a result, a final soil cleanup level was not set, but
<br /> 500 mg/kg was established as a soil cleanup level protective of groundwater (IC, 1994b).
<br /> The workplan was implemented as documented in the Site Remediation Report/Work plan
<br /> (IC, 1994b). Specifically, an additional groundwater sample was collected from MW-1 for metals
<br /> analysis (MW-2 was also designated for sampling but could not be located at that time), and
<br /> further soil sampling was conducted for analysis of general minerals, pH, lead and chromium.
<br /> Soil sampling included collection of 35 surface soil samples (0.0 to 0.5 feet bgs) and 30 soil
<br /> Remedial Investigation Work Plan Page 4
<br /> Former Tracy Railyard, Tracy, California
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