Conceptual Site Model - Argonne National Laboratory

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