Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPcontaminated surface soils with clean cover, removed contaminated surface soils for dispositionelsewhere, and/or re-used contaminated soils as backfill for building foundations or buriedinfrastructure. The sharp change in direct gamma reading results within WMA 1 between 1982and 1991 indicates that there may have been a significant change in contamination status of theimmediate WMA 1 surface.Groundwater flow underneath WMA 1 is expected to be, in general, towards the northeast. Thecore of the North Plateau Groundwater Plume has been steadily migrating in aneasterly/northeasterly direction. There likely are high activity concentrations of less mobileradionculides such as Cs-137 sorbed to soils in the immediate vicinity of the original release. TheLavery Till is expected to have acted as a barrier to vertical Sr-90 migration. Limited soil coresthat include samples from the top of the Lavery Till have confirmed this is the case.There are concerns that the foundation pilings beneath the Process Building may providepreferential flow pathways for vertical migration of contaminated groundwater into andpotentially through the Lavery Till. Presently these pilings are inaccessible for characterization,but as part of the planned decommissioning activities these pilings will be exposed and thepossibility of vertical contaminant migration into the Lavery Till will be evaluated at that time.Figure A.20 shows the current CSM for surface soils. The assumption is that all surface soils inWMA 1 area to a depth of one meter possibly contain contamination above CG w standards.Figure A.21 shows the CSM for soils deeper than 1 m. The assumption is that there is thepotential across WMA 1 for subsurface soils to have impacts greater than background conditions.Figure A.22 shows the CSM for contaminated groundwater beneath WMA 1. The assumption isthat groundwater across WMA 1 has the potential for contamination above background levels.A.8 WMA 1-Specific Characterization Goals• Develop an inventory of buried infrastructure• Evaluate appropriateness of the current list of ROI• Verify absence of additional ROI• Determine level and extent of surface contamination• Identify the presence/absence of subsurface soil contamination• Identify soil waste stream characteristicsRev. 1 A-12