Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPWMA 5. In some cases, subsurface sampling will be conducted by scanning subsurfacesoil cores or borings. In other cases, where buried linear features are suspected, soiltrenching combined with soil screening will be used.• When soil cores are used for sample collection (either specifically for subsurfacecontamination characterization or as part of surface soil characterization work), a downholegamma scan will be conducted by using an appropriate NaI detector (e.g., a 1 in. × 1in. NaI detector with shielding to control gamma flux through the top and bottom of thedetector). Biased samples will be collected from specific subsurface soil intervals thatexhibit the most elevated gross activity levels based on the down-hole gamma scan data.• For locations where systematic or biased surface soil samples are collected, if a 15-cm to1-m soil sample identifies contamination above background levels, then an additionalsample will be collected from the next 1-m-deep interval (i.e., 1 to 2 m) and evaluated todetermine the presence or absence of contamination at depth above backgroundconcentrations. If contamination is encountered in this deeper interval, then samplingmay continue at depth until contamination is bounded vertically.• For locations where systematic or biased subsurface soil samples indicate contaminationis present above background levels, additional sampling locations may be selected tolaterally bound subsurface contamination. The decision to laterally bound contaminationand the sample spacing/configuration required will be location/situation-specific, and willtake into account the original release mechanism, the types of radionuclides encountered,and the levels observed.• In some areas of the WVDP premises, the combination of surface contamination presentpre-WVDP combined with extensive surface reworking by WVDP activities raisesgeneric subsurface soil contamination concerns over larger areas. Examples of thisinclude portions of WMA 5, WMA 3, and WMA 2. In these cases, systematic subsurfacesampling will be conducted with a subsurface core spacing of 20 m. The typical initialdepth of evaluation will be 2 m. This sampling will be coordinated with systematicsurface soil sampling described in Section 6.5.Rev. 1 37