When
Where
2026 GSA Birdsall-Dreiss Lecturer, Dr. Michael Sukop, Florida International University, will present his lecture on Friday, March 6, 2026, time and location to be confirmed.
Abstract
The Biscayne Aquifer of southeastern Florida supplies water to approximately 6 million people. It is a Pleistocene eogenetic carbonate karst unconfined aquifer characterized by meter-thick strata of dense networks of 2-cm burrow ichnofossil touching vugs and bedding plane conduits. The porosity of the burrowed zones can be 50% or more and the rock can be difficult or impossible to core. The large pores and high porosity likely result in non-Darcian flow under quite low gradients (>10-5) and contribute to extremely high hydraulic conductivities (Ks) that are challenging to quantify. While numerous arguments can be made against efforts to quantify a hydraulic conductivity of karstic rocks, enhanced understanding of the operative processes has fundamental value and may ultimately enable higher fidelity flow and transport modeling.
Multiple independent lines of investigation have been followed to address these challenges, and some consistent results are emerging. Standard petrophysical laboratory measurements yield exceptionally low Ks (~10-5 m s-1) probably due to intrinsic limits of the tests. The K of similar intensely burrowed zone rocks has been shown to be ~15 m s-1 through high viscosity glycerol laboratory measurements on a 0.1 m diameter 3-D printed epoxy core created from computed tomography data collected from an outcrop sample. This is consistent with analytical Poiseuille flow solutions for a 2-cm pipe yielding K ~102 m s-1. Lattice Boltzmann flow modeling corroborates the experimental results. Other Lattice Boltzmann results on smaller samples yield K estimates approaching 50 m s-1. The Lattice Boltzmann simulations of flow in the 0.1 m core were extended to a Reynolds number of approximately 100 and reductions in the apparent hydraulic conductivity were used to fit a Forcheimer model. Subsequent laboratory measurements using water and flows with Reynolds numbers in the range of 1,000 to to 10,000 were exceptionally well predicted by the Forcheimer model.
Lattice Boltzmann modeling of flow was applied to an atypically large 0.4 x 0.4 x 17-m block of the aquifer that was simulated geostatistically and conditioned on high resolution borehole imaging data. The estimated K was 50 m s-1. Slug tests in the Biscayne Aquifer frequently show underdamped oscillatory responses indicative of inertial flow conditions. A literature search shows that the results of analyses of any underdamped slug tests never exceed K values of ~0.1 m s-1. Careful aquifer tests on the Biscayne Aquifer conducted and published in the 1950s and 1990s yielded minimum estimates of the high end of the K range of the Biscayne Aquifer of 0.1 to 0.2 m s-1.
These disparate results demand explanation. The agreement of laboratory and Lattice Boltzmann results at the 0.1 m scale suggests that the K of the burrowed zones is well constrained in the 10-50 m s-1 range. Simple thickness-weighted averaging of these Ks for a number of 1 and 2 m thick burrow zones observed in a 16 m thick portion of the aquifer suggests that the overall K would be about 5-25 m s-1. The older aquifer tests are inconclusive and new aquifer tests are prohibitive if not impossible to conduct conclusively. The slug test analyses yield unexpectedly low Ks; further examination of the standard approaches for analysis of oscillatory slug tests seems needed. Standard petrophysical laboratory measurements are not appropriate for these rocks.
Bio
Michael Sukop is professor of hydrogeology in the Department of Earth and Environment and the Institute of Environment at Florida International University in Miami, where he has taught and conducted research since 2003. He is a Fellow of the Geological Society of America, a licensed professional geologist, and a certified hydrogeologist in California.
He principally works on groundwater issues in Southeast Florida, including saltwater intrusion, septic systems, injection wells, and groundwater inundation. He has expertise in groundwater and solute transport modeling especially as they apply to seawater intrusion and the physics of the Biscayne Aquifer. He co-authored Version 4 of the popular SEAWAT model for seawater intrusion. He is author and co-author of 2 books on Lattice Boltzmann computational fluid dynamics modeling. Publications are listed here: https://scholar.google.com/citations?user=xFIZLe4AAAAJ&hl=en
He and his students have leveraged the United States Geological Survey’s Urban Miami-Dade Surface-Groundwater Model in a number of studies, including for the U.S. Army Corps of Engineers and the Florida Building Commission, and for the estimation of septic discharge fate. They are building applications to estimate flooding from short-term groundwater rises in response to rainfall events and evaluating the potential impacts of widespread use of injection wells for stormwater disposal. His team is currently implementing the coastal subsurface monitoring network for Southeast Florida (https://coastal-subsurface.fiu.edu/).