The use of fluorocarbon tracers to monitor the movement of water in unsaturated porous media : column study and computer model

Abstract

A major problem associated with monitoring the velocity of water in unsaturated porous media is the difficulty of removing samples of the pore water at different times for analysis. A possible solution to this problem is to use volatile fluorocarbon tracers which are transported in a soluble form, yet can be measured in a gaseous state, thus eliminating the difficult process of extracting liquid samples from soils with high matric suction. The three fluorocarbon tracers used to investigate the suitability of a volatile tracer method were bromochlorodifluoromethane, chlorodifluoroethane and sulfur hexafluoride. Five laboratory column experiments were conducted to determine under what conditions volatile tracers would give reliable estimates of water flow rates. The Discrete State Compartment computer model was used to interpret the laboratory data, thereby allowing a more accurate estimate of water travel times in unsaturated media.