DOE OSTI2013
Lower Three Runs is a large blackwater stream that runs through the eastern and southern portion of the Savannah River Site. The Lower Three Runs watershed includes two SRS facility areas: P Area (P Reactor) and R Area (R Reactor) that provided effluent discharges to Lower Three Runs. During reactor operations, effluent discharges were well above natural (pre-industrial) or present day stream discharges. The watershed contains a 2,500-acre mainstream impoundment (PAR Pond), several smaller pre-cooler ponds, and a canal system that connects the pre-cooler ponds and discharges surface water to PAR Pond. From the PAR Pond dam, Lower Three Runs flows approximately 36 kilometers braiding through bottom-land/flood-plain forests before it enters the Savannah River. About eight kilometers downstream from the PAR Pond dam, the SRS boundary narrows (termed the Lower Three Runs tail) providing a limited buffer of DOE property for the Lower Three Runs stream and associated flood-plain. Previous screening characterization efforts revealed Cs-137 contamination in the sediment/soils of the flood-plain. As a part of the American Recovery and Reinvestment Act stimulus package, a comprehensive characterization effort was executed on the sediment/soils of the Lower Three Runs tail flood-plain providing a comprehensive look at the contaminant signature of the area. As a follow-up to that characterization, a regulatory decision Core Team, comprised of members of the South Carolina Department of Health and Environmental Control, Environmental Protection Agency - Region IV, and DOE, conducted negotiations on a risk-based approach to address the level of contamination found in the tail flood-plain as an early action that provided a long-term solution to exposure scenarios. For evaluation purposes, the adolescent trespasser was selected as the most likely human receptor for the Lower Three Runs tail portion because of the natural attractiveness of the area for recreational activities (i.e., hunting, fishing, hiking etc.) and access from public property. Exposure of the adolescent trespasser to Cs-137 contaminated sediment/soil at concentrations greater than 23.7 pico curies per gram have been calculated to result in an unacceptable cancer risk (> 1 x 10{sup -4}). Comparing the characterization sampling results conducted in 2009 with the benchmark concentration of 23.7 pCi/g, identified elevated risk levels along three sampling areas in the Lower Three Runs tail portion. On January 5, 2012, it was agreed by the core team that a Removal Action in the Lower Three Runs tail was to be conducted for the identified soil/sediment locations in the three identified areas that exceed the 1 x 10{sup -4} risk (23.7 pCi/g) for the adolescent trespasser receptor. The addition of Land Use Controls following the Removal Action was appropriate to protect human health and the environment. A systematic screening matrix was initiated at the identified hot spots (i.e., sampling points with Cs-137 activities greater than 23.7 pCi/g) to identify the limits of the excavation area. Sediment/soil within the defined removal areas would be excavated to the depth necessary to achieve the cleanup goal and disposed of in a CERCLA Off-Site Rule approved disposal facility. It was agreed that this removal action would adequately reduce the volume of available Cs-137 in the Lower Three Runs tail and consequently residual activities of the Cs-137 would decay over time reducing the amount of Cs-137 available in the tail which would curtail risk. The Land Use Controls consist of installation of an additional seven miles of fencing at major road crossings, utility easements, and at areas that showed a higher probability of access. In addition, signs were placed along the entire SRS perimeter of the Lower Three Runs tail approximately every 200 feet. Sign posts included both a No Trespassing sign and a Contaminant Warning sign. The project initiated a subcontract for both the removal action and the installation of fencing and signs on May 1, 2012. All field activities were completed by July 26, 2012. The project excavated and disposed of over 2700 cubic yards of contaminated sediment/soil, erected approximately seven miles of fence and placed over 2,000 signs demonstrating DOE's commitment to protect human health and act as a good neighbor to residents in the area. (authors)
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗