Presentation Type
Poster Presentation
Category
STEM (science, technology, engineering, mathematics)
Abstract/Artist Statement
We investigate methods to reduce uncertainty in the conceptual-physical structure of groundwater flow and transport models using naturally occurring environmental tracers. We take a novel approach to assess this uncertainty by calibrating hydrogeologic models derived from alternate conceptualizations of subsurface structure using environmental tracer data and reactive transport code. From borehole data at a site near Riverton, Wyoming, two deterministic conceptual models based upon different hypotheses of the physical structure were created. In the first model, two permeable stratigraphic layers are separated by a continuous silty-clay confining unit. In the second model, the two permeable stratigraphic layers are separated by a discontinuous confining unit with lens-like deposits. Both alternatives use the known thickness at borehole locations; the continuous layer assumes the mean thickness where unknown; and the extent of lens-like deposits is approximated by correlation lengths collected from geostatistical software. These conceptual models are translated into numerical code MODFLOW 2005 and assigned common site-specific boundary conditions. For each alternative, MT3DMS was used to simulate transport of chlorofluorocarbons (CFC’s), Sulfur-hexafluoride (SF6) and tritium (3H) concentrations through the subsurface. The difference between simulated concentrations of each alternative can be compared to the analytical detection limit, where differences greater than approximately 5% would indicate that these natural tracers can be used to elucidate uncertain geologic structures of this type. With these tools, hydrogeologists and forecast analysts can better assess uncertainty of alternate subsurface conceptualizations and confidently make informed decisions.
Mentor Name
Payton Gardner
Video Presentation
Evaluating the use of Environmental Tracers to Reduce the Conceptual-Geologic Uncertainty of Hydrogeologic Models
We investigate methods to reduce uncertainty in the conceptual-physical structure of groundwater flow and transport models using naturally occurring environmental tracers. We take a novel approach to assess this uncertainty by calibrating hydrogeologic models derived from alternate conceptualizations of subsurface structure using environmental tracer data and reactive transport code. From borehole data at a site near Riverton, Wyoming, two deterministic conceptual models based upon different hypotheses of the physical structure were created. In the first model, two permeable stratigraphic layers are separated by a continuous silty-clay confining unit. In the second model, the two permeable stratigraphic layers are separated by a discontinuous confining unit with lens-like deposits. Both alternatives use the known thickness at borehole locations; the continuous layer assumes the mean thickness where unknown; and the extent of lens-like deposits is approximated by correlation lengths collected from geostatistical software. These conceptual models are translated into numerical code MODFLOW 2005 and assigned common site-specific boundary conditions. For each alternative, MT3DMS was used to simulate transport of chlorofluorocarbons (CFC’s), Sulfur-hexafluoride (SF6) and tritium (3H) concentrations through the subsurface. The difference between simulated concentrations of each alternative can be compared to the analytical detection limit, where differences greater than approximately 5% would indicate that these natural tracers can be used to elucidate uncertain geologic structures of this type. With these tools, hydrogeologists and forecast analysts can better assess uncertainty of alternate subsurface conceptualizations and confidently make informed decisions.