ARCHIVED REPORTS_DRAFT - PHASE I REMEDIAL INVESTIGATION REPORT

Home Browse Search

Kennedy/Jenks Consultants • Based on these results, an additional 14 surface soil samples (SS-1 to SS-14) were collected in the vicinity of Well MW-1 and analyzed for total lead (IC 1992b). The goal of this effort was to delineate the extent of lead at concentrations greater than a proposed action level of 500 mg/kg ' (the project files contain no record that approval of this goal was sought from the Regional Water Quality Control Board [Regional Board] or DTSC). Lead was detected at concentrations ranging from 120 to 1,600 mg/kg, and it was concluded that additional sampling would be required to characterize the extent of the lead. As a result, a more comprehensive investigation was undertaken, as detailed in the Soil Sampling Workplan (IC 1993a). The workplan, which was reported by IC to have received verbal approval from the Regional Board, proposed to overlay a 150-foot by 150-foot grid on OU-1 to determine locations for 36 surface soil samples (sample depths of 0.5 to 1.0 feet bgs) (S-1 to S-36) and nine shallow boring locations for collection of surface soil samples and underlying soil samples (1.0 to 1.5 feet and 1.5 to 2.0 feet bgs). All samples were analyzed for total lead only. Concentrations of lead ranged from 5.3 to 3,120 mg/kg in the surface samples; 10.6 to 3,520 mg/kg in the mid-boring samples; and 7.4 to 882 mg/kg in the deepest samples. Using these data, the volumes of soil onsite with lead concentrations above possible action levels of 1,000 mg/kg, 500 mg/kg and 174 mg/kg were estimated at 1,500, 3,500 and 9,500 cy, respectively. At the request of Southern Pacific, IC conducted a risk assessment, as summarized in the report, Derivation of a Soil Action Level for Lead(IC 1993b). Using the lead exposure model developed by DTSC, as described in DTSC's 1992 document entitled Assessment of Health Risks from Inorganic Lead in Soil— Supplemental Guidance for Human Health Multimedia Risk Assessments of Hazardous Waste Sites and Permitted Facilities, action levels for residual lead in soil were determined based on the most conservative (protective) assumptions for future land use, including residential use of the property, children as receptors, and children's consumption of home-grown produce. The result was a mean soil action level for lead of 241 mg/kg. The risk assessment results were transmitted to the Regional Board as an attachment to the Workplan for Further Site Characterization (IC 1993c). This workplan indicated that Southern Pacific was seeking approval from the City of Tracy (City) Planning Department for 1 redevelopment of the Railyard, and the City required concurrence from the San Joaquin County Public Health Services (County) that site conditions were acceptable for residential use. The County in turn requested approval from the Regional Board. As a result, Southern Pacific prepared the workplan for the Regional Board identifying steps necessary to fully characterize site soils, exposure risk due to soils, groundwater quality, and potential for soil constituents to impact groundwater quality. Potential remedies to address any impacts would then be evaluated, and the preferred and approved remedy would be implemented. The workplan noted which steps had been completed to date and defined tasks to resolve the remaining data gaps in the characterization. The workplan also indicated that Southern Pacific would remove the soil containing lead at concentrations above the Title 22 Total Threshold Limit Concentration (TTLC) of 1,000 mg/kg. The Regional Board provided comments on the workplan, including a request that the 241 mg/kg soil action level for total lead be used. IC responded on behalf of Southern Pacific . that the value derived with DTSC's lead exposure model was overly conservative for use as the remediation goal, and the 500 mg/kg goal was more appropriate (IC 1994x). The Regional Board then agreed to provide conditional approval of the workplan, contingent upon DTSC's DRAFT Phase I Remedial Investigation Report Page 4 Former Tracy Railyard, Tracy, California g:lis-group\admin\jobk0510565777.18—uprr\09-reportslri rplllext.doc