Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPresults was the opposite of 1982 – areas closer to the Process Building had lower valuesthan areas more distant. A possible explanation is the construction activities in WMA 5that were taking place resulting in displaced and/or covered surface soil nearer to theProcess Building, and the potential for run-off of contaminated surface soils towards thedrainage features that border WMA 5 to the north.• Soil sample data have been collected for WMA 5 that are available in ELIMS. FigureE.12 shows the locations of surface soil samples and soil cores with subsurface soilsamples. GPBG0208, MWPTW-1, and MWPTW-2 were completed in 2008. The NPseries cores were completed in 1994. All other sampling was done in 1993. Figure E.12also shows the Cs-137 and Sr-90 results for surface samples from these locations whensurface samples were collected. Surface contamination is scattered throughout WMA 5,with observed activity concentrations likely controlled by historical activities that havemodified surface features in this area. In the subsurface there was evidence of Sr-90impacts that extended along the southeastern border of WMA 5 and that extended west atleast to beneath the footprints of Lag Storage Buildings 3 and 4.• Groundwater sample data also have been collected for WMA 5 that are available withinELIMS. Figure E.13 shows the locations of groundwater data collection color-coded bySr-90 results. Figure E.14 shows the locations of groundwater data collection color-codedby tritium results. These locations are a mixture of GeoProbe locations wheregroundwater samples were collected at a specific point in time, monitoring wells with alimited duration of sampling events, and monitoring wells with extensive samplinghistories. The detection limits for Sr-90 and tritium varied widely among ELIMSsamples. 10 pCi/L and 500 pCi/L were selected as thresholds for Sr-90 and tritium,respectively, because based on ELIMS data results above these activity concentrationswere consistently above method detection limits and so indicative of contaminationimpacts rather than simply measurement error.In general, Sr-90 and tritium groundwater impacts are present in the eastern half of WMA5, although in some cases at levels close to detection limits. The Sr-90 activityconcentrations, in general, increase as one moves from west to east in WMA 5. In theeastern corner of WMA 5, groundwater impacts likely reflect the North PlateauGroundwater Plume.Rev. 1 E-9