EXAMINING THE INFLUENCE OF ENHANCED HYDROGEOLOGIC KNOWLEDGE ON STRUCTURAL UNCERTAINTY IN THREE-DIMENSIONAL RECONSTRUCTIONS OF GLACIGENIC SEDIMENT

Three-dimensional (3D) hydrogeologic representations of the subsurface focus on the spatial distribution and interconnectedness of hydrogeologic units inferred from lithology, primary and secondary structures, fluid chemistry, hydraulic head, and hydraulic conductivity data, in addition to other data sources. These conceptual models are guided by a hydrogeologic framework developed from depositional environment interpretations and may form the basis for numerical groundwater flow modeling. Although sophisticated 3D interpolation software and numerical efficient of modeling codes enable parameterization and simulation of complex systems, the availability and quality subsurface data limits the modeled complexity. Uncertainty in the distribution and geometries of subsurface units between field data points may be reduced through the inclusion of stratigraphic knowledge in the interpolation process.

To explore the influence of enhanced (hydro)geologic understanding on framework development, three conceptual block models were constructed for glacial sediment associated with ice marginal deposition. Unit volumes were generated using: 1) associations based on sediment texture, b) an imposed conceptual framework on genetically-linked, texturally similar sediment, and 3) an imposed framework on genetically-linked, texturally similar sediment with the addition of control points. Increasing amounts of “expert” knowledge is incorporated into each model, moving from a model developed solely on the available data, through the inclusion of regional stratigraphic knowledge, and furthered with additional inferences based on expected facies associations. The distribution and interconnectedness of sediment were interpolated across the study area using interpolation algorithms in a 3D software environment.

The resulting hydrogeologic unit geometries were evaluated for plausibility given the established glacial history of the area and error associated with the interpolation. The influence of hydrogeologic knowledge on output unit distributions and the resulting structural uncertainty was investigated by comparison of unit distributions and geometries, relative unit volumes, and fit of the top of unit elevations to borehole observations across the three conceptual block models.