The Department of War has made a considerable investment in detailed Environmental Sequence Stratigraphy (ESS) studies for installations with soil and impacted groundwater. The main deliverable of these ESS studies is typically a set of maps and intersecting subsurface cross-sections depicting detailed stratigraphy. In addition to providing a useful conceptual framework, these ESS sections can be the basis for a detailed numerical groundwater flow model. The objective of this study was to detail an efficient methodology for translating ESS studies into functional numerical groundwater flow models using models constructed at three demonstration sites for illustration and testing.

This project did not involve the development of new technology; rather, it focused on leveraging existing, state-of-the-art geologic modeling software and MODFLOW graphical user interfaces to enhance the translation of ESS studies into functional numerical models.

Examples of the Flexibility of Unstructured Grids 
(Top: Unstructured Gridding of a Valley Fill Aquifer; 
Bottom: Unstructured Grid of a Buried Channel)

To create and run large, stratigraphically complex MODFLOW models in earnest, the best performance was achieved by using unstructured grids/MODFLOW-Unstructured Grid with the SAMG+ parallel multigrid solver, which must be purchased as an optional add-on for any of the commercial MODFLOW modeling programs. There does not appear to be a viable methodology to create the models without an intermediate step of creating surfaces (“structural contours”) constraining key stratigraphic horizons. The principal monetary cost of modeling is labor; these costs could be reduced significantly if these surfaces were generated by the stratigrapher performing the ESS study, or by a geologist with substantial knowledge of the site.  

The tools used in this project were found to be incompletely implemented in the software that was used. The developers of these programs were appreciative of the opportunity to test their software with these more complex stratigraphic models, and this project has driven numerous improvements in Groundwater Modeling Systems, Groundwater Vistas, Visual MODFLOW FLEX, and Leapfrog. The larger groundwater modeling community should profit from these software improvements. (Project Completion - 2025)