Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPIn the case of WMA 2, the southern side of the excavation will be sloped at an angle ofapproximately 45 degrees from the floor to the land surface. Along the west, north, and east sidesof the excavation, the excavation floor will extend to the slurry wall.For both WMA 1 and WMA 2, remedial support data collection will begin as the excavationsapproach their design extent (i.e., when excavation is within 2 ft of the design surface). Thereason for starting remedial support data collection at this point is to provide information on thecontamination status of soils immediately above the till. In the case of WMA 1, these data will beused to assist in determining which foundation pilings are of potential concern. In the case ofWMA 1 and WMA 2, these data are expected to provide insights into where contamination mightextend deeper into the till. The assumption is that contamination within the till would likely beoverlain by soils with much higher activity concentrations.The initial round of remedial support data collection will consist of complete coverage by scanswith a FIDLER detector for the floor of the excavations. The FIDLER has sufficient sensitivityfor identifying Cs-137 at its subsurface CG w value, is well-suited for excavation work (i.e.,relatively insensitive to shine from excavation walls or adjacent facilities), and is capable ofdetecting other low-energy gamma emitting radionuclides such as Am-241 and U-238 atrelatively low levels if they are present. Scans will be logged as they progress by using surveyinginstrumentation capable of three-dimension locational control to less than 1 ft in accuracy and theresulting data (measurements results and coordinates) recorded electronically. Scan data will berecorded in a manner that identifies the excavation surfaces to which they apply. Scan data willbe mapped and reviewed for completeness and for indications of gross activity results notconsistent with background. At its subsurface CG w value, Cs-137 will have a FIDLER responsesignificantly greater than background. However, the primary contaminant of concern at thebottom of the excavations will likely be Sr-90, which will not be detectable directly by grossgamma activity scans. It is possible, though, that Sr-90 may be commingled with other slightlyelevated radionuclides with activity concentrations detectable by a FIDLER that would flag areasas potentially of concern.Since a deep subsurface background reference area will likely not be available prior to theinitiation of WMA 1 and WMA 2 excavations, the initial round of scanning results will also beused to identify a portion of the excavation surface that appears to be at background conditions.This area will be systematically sampled with six soil samples collected across the area to a depthRev. 1 55