ND using high-tech aerial method to survey aquifers in area
FARGO — If you see a helicopter towing a large hoop-shaped device about 100 feet above the ground in rural Cass or Richland counties in the next few weeks, don't be alarmed or call the police. It's not a UFO and nobody is spying on you.
It's just a high-tech version of dowsing for water.
The North Dakota State Water Commission is conducting an aerial electromagnetic survey of aquifers in the area to produce high-resolution, three-dimensional maps of groundwater basins that are far more detailed and accurate than old methods could produce.
The technology also allows water managers to more accurately estimate the volume of water contained in aquifers.
"The AEM method is a game-changer in groundwater investigations," said Jon Patch, director of water applications for the State Water Commission. "It's quicker, cheaper, better and safer than conventional methods."
The hoop-shaped device, made of carbon fiber and measuring about 85 feet in diameter, is actually an antenna that sends and receives electromagnetic signals. Those signals penetrate the earth and enable identification of underlying materials, which enables scientists to determine the location of sand and gravel where underground water is found.
The antenna hangs by a cable from the underside of the helicopter. There are two smaller antennas that hang above it. The helicopter flies horizontally, taking a reading every 32 feet or so.
"It's like we're giving the earth an MRI," Patch said. "It's the same technology."
In the past, geologists mapped aquifers by drilling test wells into the ground at different locations and extrapolated the approximate geometry of an aquifer based on what they found.
Such methods were labor-intensive, time-consuming and, as a result, expensive. The maps produced using those methods were also imprecise because the number of wells that could be drilled in an area was limited.
"With test-drilling, it could take years to gather the amount of information that we're now getting in a matter of weeks," Patch said. "The speed and efficiency have increased exponentially."
Aerial electromagnetic surveys were first developed to explore for mineral deposits. The technique was adapted for use in groundwater mapping relatively recently.
North Dakota's Water Commission first used the technique in 2014 near the Missouri River in the western part of the state. Last year, the agency used the technique to survey an area in Stutsman County. That survey actually resulted in the discovery of an aquifer that was previously unknown.
The new survey will begin the week of Nov. 6 and will take about three to four weeks to complete. It will survey an area about eight miles wide from near Gardner on the north to a location south of Wahpeton, and extending about 8 to 10 miles west from the Red River.
Only rural areas will be surveyed because the Federal Aviation Administration prohibits aircraft from flying so low in urbanized areas.
The survey will be conducted in two phases. The first phase will survey along east-west flight paths about 1.2 miles apart. Using data collected in that survey to determine where aquifers are located, a second survey will be conducted along flight paths about one-third of a mile apart to enable more precise mapping.
The Water Commission is contracting with two private companies to conduct the surveys. Ontario-based Geotech will provide the aircraft, antennas, and personnel to conduct the survey. Nebraska-based Aqua Geo Frameworks will provide data processing.