Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPcontaminating subsurface soils between the boundary of WMA 2 and Erdman Brook along thefootprints of Lagoons 2 and 3.The data collection plans for WMA 12 South as described below, do not explicitly address thepossibility of subsurface soil contamination that is overlain by clean soils. The only areas wherethis is believed to be a plausible possibility are along the boundary with WMA 2, resulting fromactivities within WMA 2. Soil sampling to depth will also be taking place in WMA 2 along theboundary with WMA 12 South to address this possibility. If subsurface soil contamination thatextends into WMA 12 South is encountered as part of that effort, sampling will continue intoWMA 12 South until it is spatially bounded.Because both Erdman Brook and Franks Creek are primarily eroding features in this area of thesite, one would not expect to see sediment contamination extending more than one meter into thesubsurface. One would expect to find “bathtub ring” contamination along banks deposited byhigh flows that mobilize and transport contaminated soils and sediments.The limited historical groundwater data available for WMA 12 South show low level tritium andSr-90 impacts, predominately along the border with WMA 2, and to a lesser degree along theborder with WMA 7. Groundwater flow from the boundaries is likely inwards towards the centerof WMA 12 South, with discharges likely occurring to Erdman Brook and Franks Creek.There are no surface soil historical samples within WMA 12 South that exceed surface soil CG wrequirements. However, two surface soil samples (SS-08 and SS-04) come close, and may haveexceeded a Sum of Ratios (SOR) of unity if all 18 ROI had been analyzed. In addition, some ofthe most elevated areas identified by direct exposure readings were not sampled. Based on theexisting data, Figure J.12 indicates where contamination is expected to possibly exist above Phase1 CG w standards in soils, where measurable impacts are not likely to be above CG w standards,and where contamination is very unlikely to be above CG w standards.There is historical evidence of sediments exceeding sediment CG w requirements. Figure J.13shows the portions of Erdman Brook and Franks Creek where sediment CG requirements applyand the likelihood that contamination might be present above sediment CG w requirements. Basedon the very limited data available, Cs-137 appears to be the primary concern in WMA 12 Southsoils and sediments, followed by Sr-90.Rev. 1 J-8