PRACTICAL APPLICATIONS OF TRACERS IN ENVIRONMENTAL HYDROGEOLOGY AND GROUNDWATER REMEDIATION

Applied tracers, defined as non-natural constituents that are intentionally introduced to a hydrologic system, have been widely used to characterize groundwater flowpaths and estimate velocities, particularly in kart regions. During the past several decades, applied tracers have been used increasingly in research settings to understand solute transport phenomena in fractured rock and porous media aquifers, which has been motivated primarily by environmental concerns related to disposal and release of radioactive and other wastes. However, there are many practical uses for applied tracers in environmental hydrogeology and groundwater remediation. Advances in chemical measurement technology have led to a significant increase in the diversity of constituents used as tracers, permitted quantification of significantly lower tracer breakthrough concentrations, and made high-frequency sampling economically feasible. Consequently, the practical (i.e., non-research) use of tracers in environmental hydrogeology and groundwater remediation is quickly increasing. For example, the spatial distribution of basic aquifer information can be inexpensively obtained using simple single-well tracer tests. Conservative and reactive tracers can greatly aid in the design and evaluation of enhanced bioremediation strategies by providing a reliable way to measure in-situ contaminant decay, electron acceptor/donor utilization rates, and zones of influence. The long-term application of tracers can used to evaluate hydraulic capture and demonstrate containment. For some high-priority sites, phase-partitioning tracers can be used to quantify subsurface volume of nonaqueous phase liquid (NAPL) in support of targeted NAPL-zone remediation activities. Several case studies will be presented and other potential practical applications of tracers in environmental hydrogeology and groundwater remediation will be discussed.