Conceptual Site Model - Argonne National Laboratory
Conceptual Site Model - Argonne National Laboratory Conceptual Site Model - Argonne National Laboratory
WVDP Phase 1 CSAPD.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 (DOE2009 Table 2-17).D.4.3Other Known and Suspected ReleasesThere are no known or suspected releases that originated within WMA 4. Debris and wasteplaced in the CDDL was supposed to have been free of radioactive contaminants.D.5 Existing DataExisting data sets for this area include:• In 1982 static direct exposure readings were collected across the WVDP premises(WVNSCO 1982). Figure D.9 shows these data. At the time, the greatest WMA 4impacts were apparent along the western and southern portions of WMA 4.Rev. 1 D-4
WVDP Phase 1 CSAP• In 1990 and 1991 a second static direct exposure measurement program was conductedacross the WVDP premises (WVNSCO 1992). In the case of WMA 4, this effortprovided systematic coverage of its area on a 10-m grid. It used differentinstrumentation/protocols than the 1982 study, so the results are not quantitativelycomparable. However, the 1990-1991 data collection effort did provide insights intosurface soil contamination across WMA 4 (Figure D.10). Impacts were more pronouncedand widespread across WMA 4 in this data set, indicating additional impacts may haveoccurred since the prior 1982 survey.• There have been several historical soil/sediment sampling activities in WMA 4.Environmental monitoring via soil/sediment sampling has taken place since 1991 to thepresent at location SNSWAMP (Figure D.1). Soil and sediment samples were alsocollected in 1993 as part of the RFI. Finally, in 2008, a fairly intensive sampling programwas conducted in the ditch portions of WMA 4 to support planned remediation activitiesfor the North Plateau Groundwater Plume. Table D.1 summarizes the amount of soil dataavailable for the 18 Radionuclides of Interest (ROI).Figure D.11 shows soil/sediment sampling locations and provides surface Cs-137 and Sr-90 results for those locations with surface soil samples or sediment samples. The bulk ofhistorical data collection has focused on ditches and so provides little information aboutthe contamination status of soils in the rest of the WMA 4 area. The historical samplingdid find Cs-137 and Sr-90 contamination in most samples that included some well abovesurface soil CG w standards in surface sediments/soils associated with the ditches. Theobserved Cs-137 is likely due to a combination of surficial deposition and consolidationof contamination within ditch sediments through erosional processes. The observed Sr-90contamination is likely tied to contaminated groundwater discharges to the ditches. TheSS/SB-PRB series samples from the ditch along the west side of the CDDL onlymeasured gross alpha and gross beta; for many of these samples gross beta activity wassignificantly elevated above background indicating likely Sr-90 contamination.• There is a significant amount of groundwater data collection from the southern portion ofthe WMA 4 area, linked to historical efforts to characterize Sr-90 contamination ingroundwater in that area. Figure D.12 shows the locations of groundwater data collectionRev. 1 D-5
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WVDP Phase 1 CSAPD.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 (DOE2009 Table 2-17).D.4.3Other Known and Suspected ReleasesThere are no known or suspected releases that originated within WMA 4. Debris and wasteplaced in the CDDL was supposed to have been free of radioactive contaminants.D.5 Existing DataExisting data sets for this area include:• In 1982 static direct exposure readings were collected across the WVDP premises(WVNSCO 1982). Figure D.9 shows these data. At the time, the greatest WMA 4impacts were apparent along the western and southern portions of WMA 4.Rev. 1 D-4