| Chemical and microbiological groundwater contaminants such as NAPL's and Cryptosporidium Parvum oocysts, resulting from industrial and agricultural activities, are threatening human health and the environment. This research explores the transport of contaminants from the soil surface to groundwater, through the vadose zone, by preferential flow. Experiments involving preferential transport of NAPL's and Cryptosporidium were carried out.; To study the transport of NAPL's, a light transmission method is developed to measure the fluid contents of the whole flow field in transient, three-phase, oil-water-air systems based on the hue and intensity of light transmitted through a slab chamber. Water content and hue are uniquely related over a large range of fluid contents. Liquid content (water plus oil) is a function of both hue and light intensity. The air content is obtained by subtracting the liquid content from the sand porosity. The light transmission method was applied to unstable flow of water into partially oil-saturated sand in a two-dimensional slab chamber.; The transport of oocysts through the subsurface is investigated by performing experiments, in vertical columns filled with sand and glass beads, under conditions known to foster fingered flow, and on undisturbed soil columns subjected to macropore flow. To investigate the influence of gas-water interfaces on the retention and transport of oocysts, modifications of the hydrodynamical conditions in the sand columns are performed by varying the rainfall intensity, and by making the sand water-repellent or creating artificially water-repellent barriers at two different depths. All the columns are subjected to artificial rainfall and are allowed to reach steady-state; then, feces from contaminated calves are applied to the surface, along with a Cl-- tracer, and rainfall is continued at the same rate. The breakthrough of oocysts and Cl--, monitored in the effluent, demonstrates the importance of preferential flow on the transport of oocysts, while the spatial distribution of oocysts suggests a close relationship between oocyst retention and the extent of gas-water interfaces. |
