ARCHIVED REPORTS_DRAFT - PHASE I REMEDIAL INVESTIGATION REPORT

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Kennedy/Jenks Consultants approval of the 500 mg/kg goal. However, as documented in the Site Remediation Report/Workplan (IC 1994b), when Southern Pacific, the Regional Board and DTSC met to discuss the issue on 27 July 2004, DTSC did not agree to accept a 500 mg/kg as a cleanup ' goal protective of human health. As a result, a final soil cleanup level was not set, but 500 mg/kg was established as a soil cleanup level protective of groundwater (IC 1994b). The workplan was implemented as documented in the Site Remediation ReportlWorkplan (IC 1994b). Specifically, an additional groundwater sample was collected from Well MW-1 for metals analysis (Well MW-2 was also designated for sampling but could not be located at that time), and further soil sampling was conducted for analysis of general minerals, pH, lead and chromium. Soil sampling included collection of 35 surface soil samples (0.0 to 0.5 feet bgs) and 30 soil samples from 10 shallow borings (two samples from 0.0 to 0.5 feet bgs; eight samples from 0.5 to 1.0 feet bgs; and ten samples each from 1.5 to 2.0 feet and 2.5 to 3.0 feet bgs). Total lead concentrations in soil samples from this investigation (and prior data) were used to prepare isoconcentration maps with 500 and 1,000 mg/kg contours. The soil volume with total lead concentrations greater than 500 mg/kg was estimated at 2,400 cy. Results of other analyses included detection of soluble lead in 20 of 41 soil samples, all at concentrations below the Title 22 Soluble Threshold Limit Concentration (STLC) of 5.0 mg/l. Other soluble metals (barium, cadmium, copper, mercury and zinc) were also detected at concentrations below their respective STLCs. In the groundwater sample, VOCs and TPHd were not detected, but a TPH hydrocarbon mixture was detected at a concentration of 66 micrograms per liter (pg/1). Based on �• all of the analytical results obtained to that date, the document included a workplan for soil excavation and disposal. In April 1995, DTSC required that the soil remediation goal be lowered to 220 mg/kg based on the assumption that the property would be used for residential development following soil remediation and sale of the property by Southern Pacific (Terranext 1996b). Excavation began in July 1995, and 9,900 cy of soil was transported offsite for disposal. An additional 15,600 cy of soil was stockpiled at the eastern end of the OU-1. Soil test pits were dug to assess the extent of remaining affected soil. Seven of the 12 outermost soil test pits indicated in situ concentrations of lead in soil exceeding the soil cleanup levels of 220 mg/kg total lead and 0.015 mg/I soluble lead using a distilled water leaching agent. Based on these findings, it was concluded that a substantial volume of soil remained to be excavated to meet a 220 mg/kg goal. As a result, Southern Pacific decided to cancel the sale and redevelopment of the property. No further excavation was conducted, but restoration of OU-1 proceeded with Regional Board approval. Stockpiled soil was stabilized by a proprietary process, tested to confirm that lead concentrations were less than the 1,000 mg/kg TTLC and the 5.0 mg/I STLC values for lead, and returned to the excavation. Additional clean fill material was imported and placed on top of the stabilized soil. Following completion of the excavation, stabilization and backfilling, an additional four groundwater monitoring wells were installed within areas of former or residual lead-impacted soil. The six wells (including Well MW-2, which was now accessible) were monitored quarterly, and reports dated September 1996 through March 1997 did not show dissolved lead in samples from any of the wells, during any quarter (Terranext 1997). As a result, monitoring was discontinued and a no further action determination was requested from the Regional Board. The Regional Board's response was not available in the background files reviewed by Kennedy/Jenks during preparation of this Report. DRAFT Phase I Remedial Investigation Report Page 5 Former Tracy Railyard, Tracy, California g:lis-groupladminl ob10510565777.18_uprr109-reportstri rpMeddoc