Using multiple environmental tracers to quantify fieldscale hydrodynamic

Using multiple environmental tracers to quantify field-scale hydrodynamic dispersion and reduce parameter uncertainty in reactive transport models Casey Kleppel, MSc Student - Geosciences Department, University of Montana Introduction Understanding how groundwater and contaminants propagate through an aquifer system due to complex subsurface heterogeneous structure is critical in developing models that more accurately simulate true subsurface systems. The main source of uncertainty within all groundwater transport models is in the implementation of parameter values that accurately characterize the system. Reducing uncertainty by quantifying the parameter of hydrodynamic dispersion is essential in long-term predictions of subsurface waste migration. Research Question Can multiple environmental tracer concentrations sampled over a limited number of times quantify field-scale values of hydrodynamic dispersion? Results: Conclusions • Ratios of CFCs/SF 6 concentrations show a distinct input peak in our synthetic aquifer similar to Tritium concentration peaks. • Initial investigation into 2 D synthetic flux averaged ratio heterogeneous models compared to homogeneous ratio models display a best-fit single full-field value of hydrodynamic dispersion. 100 meters Break through curves – Synthetic Aquifer at 50 m Methods We generate a series of synthetic aquifer fields to model spatial variability using known atmospheric tracer datasets to determine if a single, unique value of dispersion can be applied field-wide. Break through curves of tracer concentrations, and ratios thereof, through our synthetic aquifers over time are fit to curves produced through our heterogeneous truth model. Break through Curves – Synthetic Aquifer at 100 m • While this method works for the fluxed average concentration ratio in the 2 D plane, this method does not work for the average resident concentration ratios. • Further development of 3 D synthetic aquifers will provide intuition into how these environmental tracers move through real world subsurface conditions. • Broader Impacts This new method of utilizing multiple environmental tracers over a limited time series could be an easy, inexpensive, and effective solution in quantifying fieldscale hydrodynamic dispersion and reduce parameter uncertainty in groundwater and contamination transport models. Average Resident Concentration: Acknowledgments • Dr. W. Payton Gardner, Department of Geosciences Flux Averaged Concentration: • Dr. Michael Hofmann, Department of Geosciences • Dr. Jon Graham, Department of Mathematical Sciences