What is the HTEM aquifer mapping project?

We are using the latest airborne electromagnetic survey technology, helicopter time-domain electromagnetics (HTEM), to see deep into the subsurface and get a picture of our aquifers that we have never had before. You may see a helicopter towing a large hoop hanging from a cable, which is a device that uses electromagnetics to create images of the subsurface. The information we collect from this process will help us to create a 3D picture of what the aquifers look like as deep as 1,000 ft (300 m) underground.

Why is my county doing this?

This project is a big step forward for the Champaign, Ford, Iroquois and Vermillion County communities in better understanding their water resources. Water quantity, quality, recharge and security is an important focus for the Champaign County board, local authorities, industry bodies and communities. This project provides support and security to public health and local economies. Water security is critical for community sustainability, community health and economic security. This project implements rapid and state of-the-art science-based technology that is widely accepted globally as the best method for mapping aquifers similar to those in Champaign, Ford, Iroquois and Vermillion Counties. This advanced technology is a safe and cost-effective way for these counties to get precision imaging below ground.

This project will provide a critical scientific basis for ensuring water-supply security to prepare for possible public health problems or economic stresses in the future.

What information will my county learn from the HTEM aquifer mapping project?

The Scientific Surveys of the Prairie Research Institute (PRI) have studied the Mahomet Aquifer for decades, and they have built a robust, historic knowledge base of this water resource along with powerful predictive models of its sustainability. However, this project will give scientists and the public the most cutting-edge scientific information to even better improve that robust knowledge base and help scientists develop one of the most detailed understandings of an aquifer resource in the world. The HTEM survey will fill gaps of geologic knowledge and show details of the aquifer at a resolution we have never seen before. We can literally look down to 1,000 ft deep in the subsurface at the highest resolution of geophysical data ever obtained within the aquifer.

Figure 1. 2D cross-section showing interpreted HTEM data collected in Champaign County during the first phase of the Mahomet Aquifer mapping project.

Figure 1 shows an example of data collected via helicopter (and interpreted by scientist at the PRI) in Champaign County in 2023 during the first phase of the Mahomet Aquifer mapping project. HTEM results like this help us to map the geology under the earth’s surface, allowing us to determine the extent of the Mahomet Aquifer and other shallow aquifer materials present in the subsurface. This information will ultimately help PRI scientists greatly improve estimates of long-term sustainability, which include addressing questions regarding groundwater recharge and water quality. This mapping effort will be the framework to develop a groundwater-management plan to enable resilient and sustainable management of our only groundwater resource.

Don’t you already have all this information?

Over many decades, scientists at the Prairie Research Institute (PRI) have invested vast human and financial resources to improve our scientific understanding of the complex Mahomet aquifer system. As a result, this aquifer is one of the most rigorously studied aquifers in the Midwest United States, which includes many historic geologic mapping and groundwater flow modeling projects. These studies by PRI scientists have included traditional methods such as exploratory drilling, ground-based geophysics and surface-mapping of soils. These data are key to our current understanding of the aquifer. However, the data are relatively sparse compared to data from regional studies of the aquifer, and therefore, the majority of the Mahomet aquifer remains largely unexplored and unknown. This airborne aquifer mapping project will not only significantly advance PRI’s ability to holistically image and characterize the aquifer at system-wide scales and depths, but it will also include the resolution needed for local understanding of the system.

Who will perform the HTEM mapping?

This mapping effort is supported through a grant from Champaign County for the study of the Mahomet aquifer and will be conducted by the Prairie Research Institute (PRI) at the University of Illinois. A specialty airborne geophysical survey company, SkyTEM, under contract with PRI, will perform the HTEM survey to acquire the data. SkyTEM has been conducting HTEM surveys since 2003 and operates worldwide.

What is SkyTEM?

SkyTEM is a company with airborne electromagnetic survey technology designed by the Danish Government and universities specifically for efficient and effective mapping of groundwater resources.

The technology has been used commercially since 2003 to map large aquifer systems in countries including Denmark, Netherlands, India, USA, Canada and Australia. SkyTEM’s airborne technology is able to measure subtle changes between aquifer materials (e.g., sand) and non-aquifer materials (e.g., clay) at and below the ground to depths of nearly 1,000 feet. Thus, it is a valuable technology for defining aquifer boundaries and characteristics.

More information about SkyTEM can be found at www.skytem.com.

What does the SkyTEM helicopter look like?

helicopter towing geophysical equipment
Figure 2: A SkyTEM helicopter towing geophysical equipment in preparation for data acquisition.

Figure 2 shows what the SkyTEM helicopter and the geophysical equipment look like. The helicopter will fly between 100 and 150 miles per hour (160-240 km/h) in parallel lines 2,100 ft (650 m) apart and at an altitude of 100-250 feet (30-75 m). The geophysical equipment is suspended under the helicopter and will be about 115 ft (35 m) above the ground.

Where will the SkyTEM helicopter fly?

The SkyTEM helicopter will fly along transects across Ford, Iroquois, and Vermillion Counties. Those transects are shown as yellow lines on the map below (Figure 3), and are located within the jurisdiction of Ford, Iroquois, and Vermillion Counties. The helicopter will not fly over buildings, dense infrastructure and/or populated areas due to FAA rules. Furthermore, the presence of steel in buildings and infrastructure disturbs the electromagnetic response of the SkyTEM technology. The helicopter will fly along these pre-planned flight paths at 2,100 ft (650 m) spacing, relatively low to the ground at 100-250 ft (30-75 m) above the surface. Therefore, as the helicopter passes any given location, it will be visible for just a short period of time.

Figure 3: Map showing the study area in Champaign, Iroquois, Ford and Vermillion Counties, with the flight lines (yellow and green lines) spaced at 2,100 ft (650 m) apart. The helicopter will not fly over the areas without yellow lines, e.g., over the towns of Champaign, Urbana and Savoy, because they are highly populated with dense infrastructure.

Does the mapping present any risks?

The magnetic field generated by the SkyTEM system is not a risk to humans, animals, or infrastructure. A person or animal standing on the ground would experience magnetism similar to someone standing next to a typical home, and the process is actually safer than watching an LCD or plasma TV, or even blow-drying your hair. The magnetic field exposure for someone riding on an electric train is approximately 100 times stronger than what a person on the ground would experience from HTEM mapping.

The SkyTEM system will be flown at a fast speed of 100-150 miles per hour (160-240 km/h)., but the helicopter will be operated by experienced pilots who are specially trained for the low-level flying while towing equipment required for the geophysical surveys. The company works directly with the FAA to ensure flights are safe and in accordance with U.S. law.

Will farm animals be frightened?

The noise from the helicopter has been described as the equivalent to a truck going past on a highway, and it lasts for around two to four minutes. The helicopter will fly back and forth across the county in gridlines, so it will then return near a given location approximately 30 minutes later, but at a distance of about 2,100 ft (650 m) away.

During other SkyTEM projects, most animals are unfazed by the helicopter, but some younger animals could be frightened. Horses could be frightened in some instances. However, some surveys conducted close to farms have reported no issues with horses or any other animals.

If you are concerned about the effect helicopter flights might have on you or your animals (particularly horses), email kemwaks@illinois.edu or phone 217-265-0528. Project leaders can let you know the flight information and times and locations of when the helicopter will be expected in your area.

Will the new map help with other non-science issues?

No. This is a scientific program concerned with subsurface geology and aquifer mapping. Information from this project will only be used to build scientific interpretations and maps that will guide sustainable groundwater-management decisions.

Are there privacy concerns?

No. The SkyTEM survey will only collect electromagnetic information about the geology beneath the helicopter. No pictures, videos, or any other measurements are collected.