High-Resolution Quantification of Groundwater Flux Using a Heat Tracer: Laboratory Sandbox Tests

Groundwater flux is the most critical factor controlling contaminant transport in the aquifer. High-resolution information about groundwater flux and its variability is essential to properly assessing and remediating contamination sites. Recently, we developed a new thermal method that has shown considerable promise for obtaining such information in an efficient fashion. This new approach is based on the previously proven concept of using a heat tracer to track groundwater movement and the development of fiber optic distributed temperature sensing technology for high-resolution temperature measurement (cable wrapping). Results of an initial field application indicated that heat-induced temperature profiles are very consistent with the hydraulic conductivity data from the same location, providing new insights into subsurface flow variations at the site. However, the relation between the thermal profiles and groundwater flux is only qualitative; a quantitative analysis is highly desirable in order to obtain a more definitive relationship between the heating-induced temperature increase and groundwater flux. In this work, a sandbox was constructed to simulate a sand aquifer, and a series of heat tracer tests are performed under different flow rates and heat inputs. By analyzing the temperature responses among different tests, we will develop a quantitative temperature-flux relationship, which can be used for the new thermal approach to directly predict groundwater flux under different field conditions.