MONITORING OF WATER-FLOW AND SOLUTE TRANSPORT THROUGH THE UNSATURATEDZONE USING A LARGE-DIAMETER BOREHOLE

A method for monitoring water flow and solute transport through the un saturated zone is of crucial necessity for early detection of threats to ground water. A method developed by Ukrainian hydrogeologists in th e 1970s involves a borehole of a large enough diameter for a person to enter, that provides the possibility of installing monitoring equipme nt, and enables collecting undisturbed sediment blocks and samples of pore water and gas. Practically, tensiometers and vacuum lysimeters ar e 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. Selec ted results from two sites, showing the temporal and spatial distribut ions of capillary pressure and solute concentrations, are presented. T he results exhibit the difference between lateral variation in water f low and solute transport characteristics. The accuracy and representat iveness of the measurements were tested against the mutual interaction between the various instruments installed in the borehole walls. Moni toring using the large-diameter boreholes provides the possibility of early detection of threats to ground water under areal contamination i nputs, and of quantitative prediction of its future trends.