Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPA.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. The plume is expected to have migrated towards the northeast, and to haveremained within the WVDP premises. There likely have been groundwater seeps to drainagefeatures, resulting in sediment contamination; these sediment impacts may extend beyond theWVDP premises. WMAs 1, 2, 3, 4, 5, and 6 likely are affected. Because this area is situated onthe North Plateau, the area of contamination is known as “the North Plateau GroundwaterPlume.” 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 (DOE2009 Table 2-17).A.4.3Other Known and Suspected ReleasesA.4.3.1Wastewater Line LeakPotentially Affected Media:Potentially Affected WMAs:surface soil, subsurface soil, groundwater1, 2, 3, 4, 5, 6 (North Plateau Groundwater Plume)In 1967, the wastewater line to Tank 7D-13 (Line 7P-160-2-C) leaked an unknown amount ofradioactive wastewater during transfer from the tank. This release occurred near the south side ofthe Process Building. In 1974, the area around Tank 7D-13 was excavated to repair a sanitarysewer line. Radioactive groundwater and soil were encountered in the excavation. An exposurerate of 200 mR/hour beta-gamma was measured in the excavation and groundwater leakage intoRev. 1 A-5