Monitoring of water flow and solute transport through the unsaturated zone using a large-diameter borehole

A Method for monitoring water flow and solute transport through the unsaturated zone is of crucial necessity for early detection of threats to ground water. A method developed by Ukrainian hydrogeologists in the 1970s involves a borehole of a large enough diameter for a person to enter, that provides the possibility of installing monitoring equipment, and enables collecting undisturbed sediment blocks and samples of pore water and gas. Practically, tensiometers and vacuum lysimeters are installed at various levels in the borehole walls. They provide high quality sampling and measurements, and enable determining parameters of unsaturated water flow and solute transport and their temporal and spatial variability. The method was tested at several locations. Selected results from two sites, showing the temporal and spatial distributions of capillari pressure and solute concentrations, are presented. The results exhibit the difference between lateral variation in water flow and solute transport characteristics. The accuracy and representativeness of the measurements were tested against the mutual interaction between the various instruments installed in the borehole walls. Monitoring using the large-diameter boreholes provides the possibility of early detection of threats to ground water under areal contamination inputs, and of quantitative prediction of its future trends.