TECHNICAL EVALUATION OF SOIL REMEDIATION ALTERNATIVES AT THE BUILDING 812 OPERABLE UNIT, LAWRENCE LIVERMORE NATIONAL LABORATORY SITE 300

Eddy-Dilek, C. ; Miles, D. ; Abitz, R.

Savannah River Site (S.C.)

关键词: Decision Making;    Particulates;    Uranium;    Sediments;    Plants;   

DOI  :  10.2172/1043264
RP-ID  :  SRNL-STI-2009-00514
RP-ID  :  DE-AC09-08SR22470
RP-ID  :  1043264

美国|英语

来源: UNT Digital Library

【 摘 要 】

The Department of Energy Livermore Site Office requested a technical review of remedial alternatives proposed for the Building 812 Operable Unit, Site 300 at the Lawrence Livermore National Laboratory. The team visited the site and reviewed the alternatives proposed for soil remediation in the draft RI/FS and made the following observations and recommendations. Based on the current information available for the site, the team did not identify a single technology that would be cost effective and/or ecologically sound to remediate DU contamination at Building 812 to current remedial goals. Soil washing is not a viable alternative and should not be considered at the site unless final remediation levels can be negotiated to significantly higher levels. This recommendation is based on the results of soil washing treatability studies at Fernald and Ashtabula that suggest that the technology would only be effective to address final remediation levels higher than 50 pCi/g. The technical review team identified four areas of technical uncertainty that should be resolved before the final selection of a preferred remedial strategy is made. Areas of significant technical uncertainty that should be addressed include: (1) Better delineation of the spatial distribution of surface contamination and the vertical distribution of subsurface contamination in the area of the firing table and associated alluvial deposits; (2) Chemical and physical characterization of residual depleted uranium (DU) at the site; (3) Determination of actual contaminant concentrations in air particulates to support risk modeling; and (4) More realistic estimation of cost for remedial alternatives, including soil washing, that were derived primarily from vendor estimates. Instead of conducting the planned soil washing treatability study, the team recommends that the site consider a new phased approach that combines additional characterization approaches and technologies to address the technical uncertainty in the remedial decision making. The site should redo the risk calculations as the future use scenario has changed for the site. As a result, the existing model is based on very conservative assumptions that result in calculation of unreasonably low cleanup goals. Specifically, the review team proposes that LLNL consider: (1) Revising the industrial worker scenario to a reasonable maximum exposure (RME) for a site worker that performs a weekly walk down of the area for two hours for 25 years (or an alternative RME if the exposure scenario changes); (2) Revising the ESSI of 2 mg U per kg soil for the deer mouse to account for less than 0.05 of the total ingested uranium being adsorbed by the gut; (3) Revising bioaccumulation factors (BAFs) for vegetation and invertebrates that are based on 100 mg of soluble uranium per kg of soil, as the uranium concentration in the slope soil does not average 100 mg/kg and it is not all in a soluble form; and (4) Measuring actual contaminant concentrations in air particulates at the site and using the actual values to support risk calculations. The team recommends that the site continue a phased approach during remediation. The activities should focus on elimination of the principal threats to groundwater by excavating (1) source material from the firing table and alluvial deposits, and (2) soil hotspots from the surrounding slopes with concentrations of U-235 and U-238 that pose unacceptable risk. This phased approach allows the remediation path to be driven by the results of each phase. This reduces the possibility of costly 'surprises', such as failure of soil treatment, and reduces the impact of remediation on endangered habitat. Treatment of the excavated material with physical separation equipment may result in a decreased volume of soil for disposal if the DU is concentrated in the fine-grained fraction, which can then be disposed of in an offsite facility at a considerable cost savings. Based on existing data and a decision to implement the recommended phased approach, the cost of characterization, excavation and physical treatment of the contaminated materials is roughly estimated to be one third to one fourth of the cost of the current baseline treatment. This is an estimated cost; the actual cost of the project will be sensitive to actual soil/sediment volumes that can be refined with the results from characterization studies. The technical team encourages the site to promote a more holistic approach during remediation of contaminated sediments at Site 300. It is true that the presence of low levels of residual DU on the steep slopes may stress the ecosystem, as it is not possible to block the exposure of resident biota. It is clear that remediation of the primary source areas will reduce potential effects to humans. However, the site should consider that excavation of the slopes will profoundly disrupt the ecosystem and it may take decades to recover.