[en] The experiment reported here is an expansion of studies of dispersive processes in an unconfined sand aquifer on the property of Chalk River Laboratories near Twin Lake, covering a 270 m flow path between the injection well and the groundwater discharge area. Previous experience had shown that the use of a non-reactive tracer that emits moderate-energy gamma rays provides much more information than can be gleaned from tracers that require actual water sample collection. At the time of this experiment non-reactive gamma-emitting tracers with half-life long enough to undertake the 270 m experiment had not been developed. Tritium was used so some information on large-scale dispersion phenomena could be collected and instrumentation would be properly placed for a subsequent experiment that would use a gamma-emitting tracer. Because of the scoping character of the experiment, only limited data were collected. The experiment involved the controlled injection of a relatively large (60 m³) volume of water labelled with tritiated water, and the subsequent tracking of the slug during natural gradient convective transport to the discharge area. This paper describes the hydrogeologic setting and the experimental and analytical methods, and presents and discusses the findings. (L.L.) (8 refs., 11 figs., tab.)