Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPUnderstanding where subsurface soil contamination is present and its extent is important for thefollowing reasons. First, outside of the WMA 1 and WMA 2 excavations, Phase 1 FSS protocolscan be applied only to surface soils where there is confidence that deep or subsurfacecontamination is not present. Second, Phase 2 decision-making requires knowledge of the natureand extent of subsurface soil contamination. With the exception of the North PlateauGroundwater Plume in the North Plateau, data on the nature and extent of subsurface soilcontamination within the WVPD premises are very limited.Subsurface contamination has several potential sources. The first is contamination resulting fromthe presence of buried infrastructure. In this case, contamination at depth could have resultedfrom leaking infrastructure that carried contaminated waste, from the use of contaminated soils asbackfill when infrastructure was installed (particularly pertinent to infrastructure installed afterthe 1968 releases from the Process Building main stack that resulted in surface soil contaminationassociated with the cesium prong), and from the potentially preferential flow pathways buriedinfrastructure provides to contaminated groundwater. A second source is contamination that wasburied by WVDP/NFS activities. A prime example is the original outfall ditch in WMA 6 thatwas covered to control exposure to contaminated sediments. A third source is the migration ofcontaminated groundwater through the subsurface. The principal example of this is the subsurfacecontamination that currently exists beneath portions of WMA 2 and WMA 4 resulting from therelease of contaminated liquids beneath the Processing Building in WMA 1.CSAP data collection will verify the presence/absence of subsurface soil contamination where itis considered a potential concern, and will provide data to determine its extent when it isencountered. The strategy for investigating subsurface soil contamination has the followingcomponents:• Initial conceptual site models will be established for each of the WMAs that identify,based on existing information, areas within WMAs where subsurface contamination issuspected to be present. The appendices to the CSAP provide initial conceptual sitemodels for each of the WMAs. Historical information pertinent to these initial conceptualsite models include the presence/absence of buried infrastructure, evidence of surface soildisturbance in historical aerial photographs, anecdotal evidence of releases that may haveresulted in subsurface soil contamination, and subsurface soil and groundwater data setsthat contain radionuclide results.Rev. 1 35