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Final AOC 65 Interim Removal Action Report
Section 4 - Conclusions and Recommendations
PCB levels were detected in a characterization subsurface soil sample (CS-SB20) taken from borings west of building 90, and in a sample (AOC65-SB03) collected during a previous investigation. Since these levels are above background (non-detect for organics), it is not possible to attain closure for the soils portion of AOC-65 based on the data collected following the IRA. Since there is also uncertainty regarding whether closure could ever be attained for AOC-65 soil unit given the VOCs remaining in the soil gas underlying the Building 90 slab, closure attainment of AOC-65 soils will need to be delayed until additional remediation by SVE can be performed.
Confirmation soil samples indicate that several metals constituents, including cadmium, chromium, copper, zinc, and lead, are present at concentrations well above background levels in soils surrounding Building 90. These results suggest that metals should remain COCs for AOC-65. Based on the metals concentrations found above background levels and the detection of PCB contamination in soils, attaining closure of the site under RRS1 cannot be demonstrated.
Due to the uncertain nature of remaining PCB contamination and the presence of metals concentrations above background levels at AOC-65, closure of site surface soils under RRS1 has not been demonstrated. Closure of the site surface soils will likely need to be eventually pursued in conjunction with closure of the subsurface soils underneath Building 90 following successful implementation of SVE to remediate soils underlying the building slab. No additional remediation other than the SVE planned under the building slab and throughout the western side of Building 90 should be implemented under the risk reduction rules. Evaluation of the site for closure under Texas Risk Reduction Program (TRRP) should be considered upon transfer of all non-closed sites to the TRRP program in 2004.