Tracing Groundwater Flow by Mise-à-la-masse Measurement of Injected Saltwater

Abstract

Conventional use of the mise-à-la-masse method is limited to the study of the conductive mineralized deposits but can also be applied to engineering and environmental studies. This paper deals with an experiment that was carried out in the dam site of Middle Marsyangdi Hydroelectric Project to study the flow direction and velocity of groundwater around two boreholes. Concentrated salt solution was injected continuously at the rate of [Formula: see text] into the boreholes below the water table. The potential field of the current electrode at the borehole was monitored on the surface. For both boreholes, analyses were carried out by the equipotential line method, which uses the time and the distance traversed by the equipotential lines to determine velocity of the groundwater. This experiment demonstrates that the mise-à-la-masse method is useful to find the velocity and flow direction of the groundwater. The experiment can also be conducted in a metal-cased borehole. The experiment also shows that the placement of the remote current electrode has effects on the calculated velocity. The method provides reliable results if the monitoring is carried out for injection at shallow depths, most likely less than [Formula: see text].