Measurements, modeling, and interpretation of contaminant fate and transport in porous media. Investigations include mechanistic studies of colloid mobilization, retention, and transport in saturated and unsaturated porous media; quantification of agglomeration and transport potential of manufactured nanoparticles in porous media; colloid stability and transport in soil as affected by soil properties especially clay and organic matter contents; effect of land application of wastes on fate and transport of microorganisms.