Jessica Meyer, Ph.D., assistant professor at the University of Iowa, is giving the keynote presentation, “Do You Know Where Your Aquitards Are? A Case for Hydraulically Calibrated Geology as the Foundation for Robust CSMs of Contaminated Fractured Rock Systems” at the upcoming 2019 NGWA Conference on Fractured Rock and Groundwater, September 23-24 in Burlington, Vermont.
Meyer is an assistant professor in the Department of Earth and Environmental Sciences and recently shared her insights on what is needed to construct a sufficiently robust conceptual site model (CSM) as well as key concepts about fractured rock hydrogeology.
NGWA: Can you tell us how you became interested in understanding the relationship between the hydraulic and geologic structure of the subsurface?
Meyer: The relationship between the hydraulic and geologic structure of the subsurface is essentially captured by hydrostratigraphy. I became interested in hydrostratigraphy when, as part of my master’s degree, my supervisors told me that the first thing I needed to do was define the hydrostratigraphy of the site where I was doing my research. I have an undergraduate degree in geology, so I have an understanding of how many other types of stratigraphy are defined but was uncertain how to go about delineating hydrostratigraphic units. So, I looked in all the introductory textbooks for guidance. I thought there would be a key piece of data or a defined process. I was surprised to discover that these books all explained how important hydrostratigraphy was to groundwater studies, but none actually provided any concrete guidance on how to define it. Hydrostratigraphy seemed like an interesting topic to research and fortunately my supervisors provided me with an amazing opportunity to pursue it at contaminated rock sites across North America. From that point on, I’ve been hooked.
NGWA: The conference is focused on what is needed to construct a sufficiently robust CSM. What do you see as the most critical ingredients for CSMs of contaminated fractured rocks?
Meyer: As hydrogeologists, we are trying to understand complex physical/chemical/biological processes evolving in both space and time in the subsurface. Our sampling and measurement methods typically only provide information about a tiny fraction of the subsurface volume we are interested in understanding, making interpretations and conclusions from these data sets nonunique and poorly suited to supporting predictions. I think the key to overcoming this challenge lies in collecting multiple, independent, high-resolution data sets focused on the processes controlling both flow and transport. This style of data has the greatest potential to identify data and knowledge gaps and constrain our interpretations and uncertainty.
NGWA: As a field-based physical hydrogeologist and professor, what are some of the key concepts about fractured rock hydrogeology that you teach your students?
Meyer: I think there are two critical things to teach students about fractured rock hydrogeology (as a starting point). First, groundwater velocities are many times larger in fractured rock than in porous media. This is a really critical concept because we are taught that groundwater moves slowly in our introductory hydrogeology courses that are typically focused on porous media. Second, students need to have an intuitive appreciation for the influence of diffusion in any system where hydraulic conductivity contrasts are large, whether it’s in fractured rock or porous media. As a field-based hydrogeologist, I also think that it’s really important to provide students with exposure to what the rocks actually look like so they can appreciate/internalize the scales of heterogeneity. I think this is best accomplished by looking at outcrop in person but can also be facilitated with good photos or hands-on experience with cores.
NGWA: One of your interests is in advancing understanding of bedrock aquitards. Can you tell us a little bit about that?
Meyer: Aquitards often don’t receive too much attention because the focus is on the units that supply water and readily transport contaminants. But I’m really interested in what flow systems look like in different geologic/hydrogeologic settings and aquitards have a huge influence on the three-dimensional geometry of flowpaths. Most of our conceptual and mathematical models represent aquitards as units with low hydraulic conductivity in all directions. Shallow sedimentary rock aquitards are of particular interest to me because they can exhibit large anisotropy in hydraulic conductivity due to the characteristics of their fractures. I don’t think we fully understand the impact of this anisotropy on the transport of natural solutes (which is important to understanding groundwater ages/residence times) or contaminants.
NGWA: What is your overall view of the future of addressing contaminants in fractured rock?
Meyer: Bedrock aquifers are some of our most important water supply units globally and that importance will only increase as our population continues to grow and climate change influences both the distribution of people and water resources on the planet. I think coping with this challenge will require a combination of approaches, including advancing characterization techniques so water resource development can be very targeted to minimize risk of existing contaminant issues rather than abandoning whole aquifers, taking advantage of — and facilitating — the natural remediation occurring in these systems, and continuing to develop innovative active remediation techniques. Overall, it’s very exciting and motivating to be a part of such a rapidly advancing field of research.
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NGWA thanks Meyer for her time in answering these questions and in being the keynote presenter at the 2019 NGWA Conference on Fractured Rock and Groundwater.