Measurements and modeling of tracer transport in a sandy soil

A physically-based dual-porosity model of water and solute transport under transient field conditions was used to simulate³H transport in seven undisturbed monoliths of a coarse-textured sand under bare soil conditions over a period of 15 months. A double-tracer application of³H and³⁶Cl was performed to test whether sidewall flow occurred in this experimental set-up. The objectives of this study were: to identify any impacts of preferential flow in this type of soil, to quantify³H losses from the soil due to evaporation, and to assess the suitability and relative behavior of³H and³⁶Cl as tracers of water. The model input parameter values were obtained by a combination of direct measurements and model calibration. One domain flow simulations of water flow and tracer concentrations in seepage agreed fairly well with those observed, indicating convective-dispersive behavior in this sandy soil. From the observed tracer and water balance for the entire observation period, the recovery of³H and³⁶Cl in seepage was 33 and 91% respectively, with 67% of the applied H lost by evaporation. Both³H and³⁶Cl broke through in seepage simultaneously, showing that³⁶Cl is equally suitable as a tracer of water as³H. The double-tracer test showed that sidewall flow did not occur.