USING HEAT AS A GROUNDWATER TRACER FOR AQUIFER CHARACTERIZATION IN A HIGHLY DYNAMIC FLOW ENVIRONMENT

The utility of heat as a groundwater tracer for characterizing the aquifer’s hydraulic conductivity distribution was evaluated at the “Integrated Field Research Challenge (IFRC)” site in Hanford, Washington. The study site is adjacent to Columbia River under highly dynamic flow conditions. Compared to conventional solute tracers such as bromide and tritium, depth-discrete temperature measurement was relatively simple and inexpensive. Using the hydraulic conductivity distribution obtained from the calibration of a solute transport model, the temperature depth profiles and peak arrival times simulated by the heat transport model were in reasonable agreement with field observations. In addition, heat transport can be analyzed conveniently by a conventional solute transport simulator such as MT3DMS due to mathematical equivalence in solute and heat transport processes. The results of this study suggest that heated or chilled water can be used as a cost-effective proxy for solute tracers to improve the characterization of aquifer heterogeneity, especially in the vertical direction. However, a field heat tracer test must be carefully designed and executed to minimize fluid density effects and eliminate sources of noise in temperature data caused by heating during fluid injection and sampling events.