Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPF.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 leakreleased an estimated 200 gallons of radioactive nitric acid with approximately 93 Ci Sr-90(DOE 2009 Table 2-17).F.4.3Other Known and Suspected ReleasesF.4.3.1Sewage Treatment System ContaminationPotentially Affected Media:Potentially Affected WMAs:subsurface soil, groundwater, sediment1, 6, 12 (Erdman Brook)Historically, the Process Building (in WMA 1) was connected to the Old Sewage Treatment Plantvia an underground wastewater line. A 1970 to 1971 investigation of unexpected tritium andgross beta contamination in Erdman Brook led to the discovery of contamination in the sanitarysewer system. It was discovered that the underground wastewater line had failed near thesouthwest side of the Process Building. The resultant leak allowed contaminated groundwater inRev. 1 F-6