Water temperature as a groundwater tracer in fractured rock

Abstract

Characterization of transport in fractured media is based on observation of the movement of labeled water. Difficulties in labeling water with chemicals include the removal of sample water, residual background concentration, and expensive analytical equipment. These difficulties are avoided with the use of heated (or cooled) water as a groundwater tracer in site characterization. Heated water was successfully used as a tracer in a fractured granite near Oracle, Arizona. The temperature sensing device consisted of 20 thermistors on a down-hole string, distributed over a 62-foot interval. In a three-hole recirculation test, a heat source was placed in a borehole 20 feet from the hole housing the thermistors. A third borehole was pumped with the outflow returned to the borehole containing the heat source. Differential breakthrough of the thermal pulse allowed delineation of flow paths between boreholes.