Transport of Surface-Active Solutes in a Heterogeneous Vadose Zone: Dealing With Limited Data Collection

Realistic modeling of the non-steady state transport of surface-active compounds through unsaturated heterogeneous soils requires representation of the spatial variability in the relationships of soil moisture retention and the unsaturated hydraulic conductivity. In the case of limited resources for site characterization, the question arises as to what type of data to collect and how to best represent these relationships at locations where data are lacking. This study investigates the impact on surface-active solute transport predictions of the collection: 1) of different types of data, air-water retention curves or saturated hydraulic conductivities, 2) at different locations, and 3) of different ways of describing the spatial variability of the data: similar media scaling, Leverett scaling and a categorical-continuous method based on the pore-size distribution index. Based on a series of geostatistically-conditioned realizations, simulations of groundwater flow and contaminant transport were generated utilizing subsets of the soil property measurements from the Las Cruces trench site and compared to simulations utilizing the entire set of soil property measurements from that site. Since preliminary simulations showed that the results were influenced by the flux rate at the land surface, the degree of uncertainty under different infiltration rates was also assessed.