Bromide Tracer Migration in Highly Weathered Soil.

Anionic tracers, such as bromide (Br^-), are generally considered to be transported in a conservative manner (i.e., R ≤ 1) due to their electrostatic repulsion from soil clays possessing a net-negative surface charge. To test the perception in acidic soil condition, a series of batch and column experiments were conducted with the subsurface soil obtained from Savannah River Site (SRS), representing typical of highly weathered soils from the Atlantic Coastal Plain. The clay fractions of the soil were mainly kaolinitic, with small amounts of hydroxy-interlayered vermiculite and relatively large amount of free-Fe oxides. Tritiated water (³H₂O) was used to compare the breakthrough behavior of Br^- under acidic condition. Under the saturated column condition, Br breakthrough was significantly retarded compared to ³H₂O breakthrough. Interestingly enough, the breakthrough of corresponding cation of Br was also retarded. The observed experimental results were simulated with sorption of Br^- and cation exchange model using PHREEQC-2 transport modeling code for further investigation.