Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPwould expect groundwater to move from the northern and southern boundaries towardsthe center of the WMA, and from west to east.J.6 Planned Phase 1 DP ActivitiesThere are no planned Phase 1 decommissioning activities for WMA 12 South.J.7 Conceptual Site ModelBased on the available information, the conceptual site model (CSM) for WMA 12 South is asfollows. No environmental releases of contamination within WMA 12 South are believed to haveoccurred. However, environmental media within WMA 12 South have been affected to somedegree by releases elsewhere at the WVDP site. This has resulted in surface soil contaminationfor at least portions of WMA 12 South (as evidenced by historical direct gamma surveys andlimited soil samples), potential subsurface contamination along the northeastern boundary ofWMA 12 South along WMA 2, and also in more significant streambed sediment contaminationresulting in releases of contaminated water from the Lagoon 3 discharge weir. In the case of thelatter, Erdman Brook has the bulk of these impacts. The impacts increase as one movesdownstream to the WVDP fence line, likely due to historical releases from WMA 2.Contamination in stream sediments is significant enough that eastern portions of Erdman Brookhave been designated radiological control areas by WVDP (see Figure J.1)In addition, historical activities within WMA 7 may have led to the release of contaminated soilsinto drainage features that crossed into WMA 12 South. The radiological control area defined forWMA 7 does currently extend into WMA 12 South (see Figure J.1).Because there have not been significant historical soil disturbance activities for the majority ofWMA 12 South, subsurface soil contamination is not expected to be present in most of the area.The exceptions to this is an area immediately adjacent to WMA 2 that appears to have been apush-out area active in 1960s, and that exhibited elevated gamma readings in 1990-1991. Anysoil contamination present is expected to be limited to surface soils (i.e., top one meter of soils)with the possible exception of soils immediately adjacent to WMA 2 along the historical wastestorage lagoons. Also, within WMA 2, Lagoons 2 and 3 are unlined. Contaminated groundwatermay have migrated through the subsurface with discharge via seeps to Erdman Brook, potentiallyRev. 1 J-7