Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPthe northern wall of the WMA 1 excavation cannot compromise the structural integrity of theHLW Tanks in WMA 3.Within those constraints, one goal of the two excavations is to remove subsurface contaminationthat exceeds the subsurface CG requirements derived by and contained in the Phase 1 DP.To verify that the planned excavation footprints do, in fact, address subsurface contaminationabove CG w requirements, subsurface sampling will take place along the planned footprintboundaries for WMA 1 and WMA 2. The sampling strategy defining the lateral extent of theWMA 1 and WMA 2 excavations has the following components:• Continuous soil cores will be collected with a spacing of 10 m for locations along sheetpile wall footprints and 20 m for locations along slurry wall footprints, with intact soilcores retrieved. Soil cores will include at least 1 m of the underlying Lavery Till. Thereason for the 10 m spacing along sheet pile wall footprints is to provide a reasonableprobability that contamination with a significant subsurface spatial extent is identified.“Significant extent” is defined as subsurface contamination that may extend more than 10m beyond the proposed excavation footprints; the assumption is that if this is the case, thecontamination would have extended along the excavation boundary at least as long. In thecase of slurry walls, contamination is assumed to be present on the side opposite theexcavation; in this case the spacing is driven by geotechnical design needs for those walls(e.g., depth to till). For both sheet pile and slurry walls, the proposed spacing may bemodified in response to field conditions if those are different from initial assumptions.For example, in the case of the slurry wall, if significant variation in the depth to theLavery Till was found from core location to core location, the spacing might be reducedto better capture the variations in Lavery Till depth.• For each core location from sheet pile wall footprints and from the southern boundary ofthe WMA 2 excavation, a down-hole gamma scan will be performed with an appropriateNaI detector to the extent practicable. Each hole will extend beneath the water table;consequently, usable down-hole gamma scan data will likely not be available for the fulldepth of the core. Each core will also be scanned ex situ for gamma and gross betaactivity by using an appropriate detector.Rev. 1 41