Clarifying Subsurface Risk at Tutu Wellfield in U.S. Virgin Islands

  • October 21st, 2025
  • By Samantha Frandsen
Fractured and Faulted Bedrock

HDR was tasked with designing a remedial strategy for the Tutu Wellfield Superfund Site in St. Thomas, U.S. Virgin Islands (see first image below). The challenge: fractured and faulted volcanic bedrock providing a complex network of high-flux flowpaths for DNAPL and dissolved-phase CVOCs exceeding 200 mg/L which threatened municipal supply wells. Traditional untargeted drilling simply wasn’t enough to map the flowpaths in order to meet clean-up standards and protect the community.

That’s where Electrical Hydrogeology™ came in. Aestus’ team applied our specialty GeoTrax Survey™ electrical resistivity imaging and structured 5-step process to refine the existing CSM.

Key CSM Updates:

  1. Intersecting faults were located and confirmed via targeted drilling to be high-permeability zones that likely accelerate movement of contaminants (pink areas in second image below)
  2. Free-phase DNAPL was successfully located for the first time in site history by drilling areas flagged by electrical imaging
  3. Mapping of the bedrock surface revealed structurally controlled contaminant migration pathways

With the updated CSM, HDR was able to complete remedial design within three months of Aestus’ final report submission, ultimately leading to a more cost-effective and technically robust clean-up that reduced risk to the groundwater dependent community.

Free Phase DNAPL in GeoTrax Survey™ Confirmation Drilling Well
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    Samantha Frandsen
    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. 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.

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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.
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    Grant Eastman
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    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
    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.
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    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.
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    Todd Halihan, Ph.D., P.Gp.
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    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.
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    Stuart W. McDonald, P.E.
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    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.