Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPAs originally deposited, surface soil activity concentrations should have decreased towards thenorth, away from WMA 1. However, the surface features of many areas within the WVDPpremises have been reworked significantly since the release; as a result, the current spatial anddepth distribution of soil contamination may be significantly different than the original footprint.In addition, the surface soil contamination likely has been naturally spread by erosion and runoffinto surface drainage features; this phenomenon may have enlarged the area impacted bydeposition, although detailed data regarding this effect are not available (DOE 2010Section 3.11.5).Finally, other releases from the Process Building stack may have produced minor impacts. Theseother releases include the 1968 failure of a dissolver off-gas system filter, resulting in 0.28 Ci ofparticulate activity, and the 1968 failure of a vessel off-gas system filter, resulting in the March1968 releases to exceed the monthly allowance by 15 percent (DOE 2010 Section 3.11.5).C.4.2North Plateau Groundwater PlumePotentially Affected Media: subsurface soil, groundwater, sedimentPotentially Affected WMAs: 1, 2, 3, 4, 5, 6Several releases have contributed to a contaminated groundwater plume originating in the area ofthe Process Building (in WMA 1). The plume is expected to have migrated towards the northeast,and to have remained within the WVDP premises. There likely have been groundwater seeps todrainage features, resulting in sediment contamination; these sediment impacts may extendbeyond the WVDP premises. WMAs 1, 2, 3, 4, 5, and 6 likely are affected. Because this area issituated on the North Plateau, the area of contamination is known as “the North PlateauGroundwater Plume.” The predominant mobile contaminant in this plume is Sr-90.The major contribution to the plume occurred in 1968. (Other potential contributing releases arepresented in Sections A.4.3, B.4.3, C.4.3, and E.4.3.) Radioactive acid leaked into the subsurfaceat the southwest corner of the Process Building when Line 7P-240-1-C in the Off-Gas OperatingAisle (within the Process Building) failed. The leakage drained down to the underlying Off-GasCell and the adjacent southwest stairwell, then apparently flowed through an expansion joint inthe concrete floor of the Off-Gas Cell and migrated into the underlying sand and gravel. The leakRev. 1 C-6