// Frequently Asked Questions

How to Build Confidence in
Karst Characterization?

1. Why are karst sites difficult to characterize?

Karst conditions can change dramatically over short distances. Groundwater flow, contaminant migration, and ground stability may be controlled by a complex network of fractures, conduits, sinkholes, and voids rather than by relatively uniform formation properties. Two nearby borings or wells can therefore encounter entirely different conditions. These features may also be hydraulically connected over long distances, potentially allowing water and contaminants to move rapidly toward springs, wells, surface water, or other receptors. Characterizing the site requires understanding not only where individual features occur, but how they connect within the broader karst system.

2. Why aren’t borings and wells alone enough to characterize karst?

Borings and wells provide direct evidence, but only at the discrete locations investigated. Because controlling karst features may be narrow, irregular, or widely spaced, even a substantial drilling program can miss important pathways or produce an incomplete picture of site conditions. 2D continuous subsurface imaging helps fill the gaps between and beyond isolated data points. When integrated with drilling, it provides the spatial context needed to determine whether observed conditions are isolated or part of a larger connected system—and to develop a better supported conceptual site model (CSM).

3. Does electrical imaging eliminate the need for drilling?

No. Electrical imaging and conventional drilling serve complementary purposes. Imaging provides continuous spatial coverage and helps locate features that isolated borings or wells might miss, while drilling provides the direct evidence needed to confirm interpretations. Using imaging early in the investigation allows confirmation points to be positioned strategically rather than selected with limited knowledge of the subsurface. This improves the likelihood that borings and wells intersect the features controlling site conditions and increases the decision value of data from each location.

4. Does every geophysical anomaly represent a cave or void?

No. Electrical resistivity imaging measures contrasts in subsurface electrical properties, and those contrasts can have multiple potential causes. Anomaly geometry, depth, continuity, and relationship to surrounding geology help evaluate the most likely interpretation. Borings, cores, downhole logging, hydraulic testing, chemistry, and other site data can then be used where appropriate to further evaluate or confirm composition of significant features.

5. Why should karst be evaluated at the regional scale?

Karst groundwater does not necessarily follow property boundaries or simple hydraulic gradients. Recharge may enter through distant sinkholes or losing streams, while groundwater and contaminants may discharge at springs or other receptors at considerable distances from the source or recharge area. A regional-scale evaluation can help identify these larger hydraulic relationships.

6. How does high-resolution characterization of karst reduce project risk?

Appropriately designed high-resolution characterization helps reduce subsurface uncertainties most likely to affect project performance. Identifying controlling features early can reduce the risk of missed contamination, unrecognized migration pathways, unsuitable well locations, ineffective treatment, unexpected groundwater movement, and subsurface conditions that may contribute to ground-instability hazards. A higher-resolution CSM also gives project teams a stronger basis for selecting investigation locations, evaluating receptors, and designing remediation, groundwater-management, or hazard-mitigation measures. This provides a stronger technical basis for decisions and may lower the likelihood of late-stage redesign, schedule delays, and other costly surprises.

7. How can karst-system behavior change over time?

Karst systems can respond rapidly to precipitation, recharge, groundwater levels, pumping, and remediation. Pathways that appear hydraulically inactive under dry or low-flow conditions may become important pathways during storms or periods of elevated groundwater. Monitoring strategies should therefore account for both spatial and temporal variability. Springs, seeps, strategically placed wells, and other discharge points—combined with event-based sampling and temporal electrical resistivity imaging (TERI)—can help capture changing conditions and evaluate whether the CSM and selected project strategy remain appropriate as conditions evolve.
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Madison Culver
Madison Culver, M.Sc.
Staff Geologist / Field Technician
Since joining Aestus in 2024, Madison has performed various project tasks including field data acquisition, data integration and analysis, 2D and 3D visualization, and project report development.

As an undergraduate at Oklahoma State University, Madison utilized electrical resistivity imaging to locate a drilling target for a municipal water well in rural Oklahoma. Her Master’s degree, also from Oklahoma State University, focused on the production and laboratory testing of a novel groundwater tracing particle for use in a sole source aquifer.

Madison previously worked at an environmental consulting firm in Dallas, Texas, where she performed soil/groundwater investigations/reporting, PFAS sampling programs, and Environmental Site Assessments.

Madison is based out of Irving, Texas.
Michelle Lahti
Michelle Lahti, PACE
Administrative Director
Since joining Aestus in 2021, Michelle has supported the CEO and other managers in their day-to-day needs. She also manages human resources and all elements of the many conferences Aestus attends. Michelle works hard to ensure that the needs of stakeholders are addressed in all steps of the business process when working with our clients.
Michelle has a bachelor’s degree in Avionics Engineering Technology from Embry-Riddle Aeronautical University. She also has experience as a small business owner, and over 15 years’ experience as an executive assistant in many different industries. She has her Professional Administrative Certification of Excellence (PACE) through the American Society of Administrative Professionals (ASAP).
Michelle is based out of Wellington, Colorado.
Autumn Town
Autumn M. Town, M.Sc.
Staff Geologist / Field Technician
Autumn performs various project tasks for Aestus, including field data acquisition, data integration and analysis, 2D and 3D visualization, and project report development. Since joining Aestus in 2023, she has helped meet project objectives such as mapping stratigraphy, identifying areas of contamination, and characterizing preferential flow pathways at complex sites across the United States.
As an undergraduate at Oklahoma State University, Autumn utilized electrical resistivity imaging (ERI) to evaluate the hydrogeologic effects of PFAS-containing firefighting foams. While completing her Master’s degree, also at Oklahoma State University, she focused primarily on sedimentology and stratigraphy as she studied the effects of depositional and diagenetic processes on porosity development in a tight gas sandstone reservoir.

Autumn is based out of Tulsa, Oklahoma.
Morgan Love
Morgan Love, M.Sc.
Senior Project Geologist
Morgan has been a part of the Aestus team since 2012. She supports all aspects of data integration for Aestus in 2D and 3D space, including modeling of geophysical, geochemical, and geologic data. She also performs geophysical data processing and develops quality control and automation protocols to ensure data integrity.

Prior to Aestus, Morgan used her environmental geology undergraduate degree working for a water resource company, a geosciences software company, and a seismic data acquisition company. She holds a Master's Degree in Computer Information Systems.

Morgan is based out of Fort Collins, Colorado.
Grant Eastman
Grant Eastman
Equipment Manager / Field Technician
Grant maintains all our equipment and vehicles at a firehouse ready status in order for the field team to be ready to mobilize at moment’s notice. He also troubleshoots any technical issues that come up as well as being a member of the field team.

Grant graduated from Colorado State University with a degree in Watershed Science. After graduating he completed 8 years of military service with the Colorado Army National Guard, including two deployments to the middle east. Before joining Aestus, he was a senior technician building custom automation equipment and wire harness mockups for aerospace companies.

Grant is based out of Milliken, Colorado.
Samantha Frandsen
Samantha Frandsen, M.Sc, P.Gp.
Hydrogeophysicist / Project Manager
Since joining Aestus in 2018, Samantha has performed all aspects of the Aestus project lifecycle, including acquisition field work, processing of geophysical data, data integration, 3D visualization, and reporting. As project manager, she oversees a variety of projects completed at complex sites across the United States and strives to help our clients efficiently leverage Aestus’ high-resolution GeoTrax Survey™ data to improve understanding of subsurface conditions.

Prior to her time with Aestus, she earned her Bachelor’s degree (magna cum laude) in Physics from the University of Richmond and taught high school physics as a Teach for America corps member. She then completed her Master’s degree (Distinction) in Exploration Geophysics at the University of Leeds in the UK. For her thesis, she utilized several different geophysical techniques to characterize the subsurface remains of a former gasworks facility for which she was awarded the GETECH award for best overall performance in the Independent Project and the Association for Industrial Archaeology’s Dissertation Award.

When she’s not investigating what’s below the ground, Samantha enjoys exploring all the above-ground fun her Stateline (South Lake Tahoe), NV home has to offer via trail running, mountain biking, and snowboarding.

Samantha is based out of Stateline, Nevada.
Michael McNair
Michael McNair
Project Geologist / Field Team Leader
Michael has worked on a variety of project types using Aestus’ electrical hydrogeology techniques to help Aestus’ clients succeed relative to characterization of contaminated sites, evaluating geohazards, municipal water well exploration, and monitoring subsurface changes over time. Michael currently manages Aestus’ field operations to collect high quality subsurface electrical imagery (GeoTrax Survey™) at rural, urban, and industrial sites with complex logistics. When not in the field, Michael is a key member of Aestus’ reporting team and leads or assists with 2D/3D data integration, QC, data interpretation, and reporting.

Michael previously worked at an environmental consulting firm in Dallas, Texas, where he performed soil/groundwater investigations in the field and subsequently developed reports. Michael earned a Bachelor of Science in Geology from Baylor University.

Michael is based out of Orlando, Florida.
Todd Halihan
Todd Halihan, Ph.D., P.Gp.
CTO/Data Interpretation Lead
Todd’s focus at Aestus centers on subsurface characterization using electrical hydrogeology and sustainable water supply. He is also a professor and the Sun Company Clyde Wheeler Chair in Hydrogeology at Oklahoma State University. He was the National Ground Water Association’s 2018 McEllhiney Lecturer and he is a founding member of the NGWAU program for groundwater outreach and education.

Dr. Halihan is the recipient of the American Institute of Hydrology’s C.V. Theis Award winner. He is also a professional geophysicist (CA), professional driller (OK) and a PADI divemaster.

Todd is based out of Stillwater, Oklahoma.
Stuart McDonald
Stuart W. McDonald, P.E.
CEO/Project Executive/Contracting
Stuart has dedicated over 20 years of his career overseeing the development of Aestus with the goal of empowering clients worldwide to gain more certainty in subsurface issues to make better technical decisions and save time and money on their projects. He has been involved in managing hundreds of projects for Aestus in the USA, Europe, Asia, and South America.

Stuart spent the first decade of his career as an environmental consultant primarily with Canonie Environmental and Harding Lawson Associates and gained experience performing cradle to grave site characterization and remediation work on high profile Superfund and other projects. This experience was the genesis of founding Aestus in 2001 as it became clear that the environmental industry needed more data density and more certainty for optimal decision-making on projects.

Stuart is based out of Loveland, Colorado.