Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPcolor-coded by Sr-90 results. Figure D.13 shows the locations of groundwater datacollection color-coded by tritium results. These locations are a mixture of GeoProbelocations where groundwater samples were collected at a specific point in time,monitoring wells with a limited duration of sampling events, and monitoring wells withextensive sampling histories, all from the sand and gravel unit overlying the Lavery Till.The detection limits for Sr-90 and tritium varied widely among ELIMS samples. 10pCi/L and 500 pCi/L were selected as thresholds for Sr-90 and tritium, respectively,because based on ELIMS data results above these activity concentrations wereconsistently above method detection limits and so indicative of contamination impactsrather than simply measurement error.In general, Sr-90 and tritium groundwater impacts are present in the southern portion ofWMA 4. The Sr-90 and tritium activity concentrations, in general, decrease as one movesto the east and north. However, there is insufficient groundwater data from the northernportion of the WMA 4 to definitively state that groundwater impacts do not exist in thatportion of WMA 4.D.6 Planned Phase 1 DP ActivitiesThere are no planned Phase 1 decommissioning remediation activities for WMA 4.As a separate activity, DOE has installed a permeable treatment wall to address the North PlateauGroundwater Plume south of the CDDL, in WMA 2. The North Plateau Groundwater Plume andthis treatment wall are discussed in more detail in Appendix B.D.7 Conceptual Site ModelBased on the available information, the conceptual site model (CSM) for WMA 4 is as follows.No environmental releases of radioactive contamination within WMA 4 are believed to haveoccurred. However, environmental media within WMA 4 have been affected to some degree byreleases elsewhere at the WVDP site. These impacts include air deposition contamination onsurface soils at least along the western and southern portions of WMA 4, contamination in ditchesresulting from erosion and sedimentation from other contaminated portions of the site and fromthe discharge of contaminated groundwater, and groundwater contamination beneath at least theRev. 1 D-6