// Frequently Asked Questions

Leveraging GeoTrax Survey™ for Direct Push HRSC

1. Can GeoTrax Survey™ be used before direct push HRSC?

Yes. Even with direct push HRSC tools (MIP, HPT, UVOST, TarGOST, etc.), investigations are still essentially “blind” without GeoTrax Survey™ guidance. Key site features such as vertical preferential flow paths and LNAPL zones can be missed if HRSC is used alone.

2. Can GeoTrax Survey™ be used where direct push rigs encounter refusal?

Yes. GeoTrax Survey™ is independent of lithology, so refusal is not an issue. Aestus can image through bedrock without added cost, even when use of direct push drilling methods is not possible due to hard lithology.

3. Do GeoTrax Survey™ and direct push HRSC replace the need for conventional sampling?

No. Both methods are qualitative in the sense that they do not provide precise contaminant concentrations in soil and groundwater. Therefore, conventional sampling and analytical laboratory analyses may still be required, depending on site conditions and regulatory requirement.

4. How does the resolution of GeoTrax Survey™ compare to direct push HRSC?

Direct push HRSC generally provides higher vertical resolution, while GeoTrax Survey™ offers continuous lateral coverage. The results typically correlate well and together provide a more complete understanding of subsurface conditions. For example, HRSC can confirm high-permeability zones which GeoTrax Survey™ can then connect across the site.

5. How do GeoTrax Survey™ and direct push HRSC results compare overall?

Historically, both methods generally agree in terms of identifying impacted zones, but GeoTrax Survey™ often provides more context. For example, one energy firm compared GeoTrax Survey™, Laser-Induced Fluorescence (LIF), and soil samples and found that LIF sometimes produced false positives where GeoTrax Survey™ and soil borings showed no contamination. These false positives were viewed as a potential liability.

As another example, the image below provides a comparison of GeoTrax Survey™, TarGOST® (Tar-Specific Green Optical Screening Tool), and a traditional soil boring at a former tie treatment facility.
  • The GeoTrax Survey™ images were able to map the vertical/horizontal extents of DNAPL related impacts across the imaging domain – impacted zones correlated with the more moderately electrically resistive anomalies (i.e., orange zones)
  • Soil Boring 5 confirmed that there was a higher saturation of oil in the center of the orange zones (i.e., in the strongest part of the anomaly)
  • TarGOST (TG) log detects shown below in orange graphical plots generally occurred within the same electrical anomalies, but the higher TarGOST® reflectance was generally limited to the top of Aestus’ orange anomalies (NOT supported by the soil boring)..
TARGost FAQ GeoTrax Survey™ Image
Resistive drilling targets at a previously remediated gasoline site. The 5 shallow borings were all nondetect for impacts, while the resistive targets were sampled and were impacted (Halihan et al., 2005).
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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 Sate 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.