Sean Simmonds stood in front of an airplane on the tarmac at Louisiana Regional Airport near Gonzales and turned its large propeller by hand several times, moments after the engine had just been shut off.
Like wiping the Cessna 208B’s brow past the finish line of a long, focused run over rugged terrain, Simmonds said he was cooling the engine down at the day’s end.
Simmonds, a flight mechanic, and the rest of his crew with a U.S. Geological Survey contractor had spent much of a recent Friday flying the Cessna and towing a special, bomb-shaped sensor over the Baton Rouge, New Orleans and Lafayette areas to “see” deep into the ground.
The crew with Xcalibur Multiphysics has been conducting aerial surveys of underground water resources important for agriculture in Louisiana. The USGS wants to better understand their geology, how the aquifers are being used and the impact of saltwater intrusion, agency scientists said.
The flights, which made it to south Louisiana in early November, are part of larger USGS studies underway since 2017 to analyze the Mississippi River Alluvial Plain aquifer, important areas on that shallow aquifer’s fringes, and the Chicot Aquifer in southwest Louisiana.
“It’s all about understanding groundwater resources and, to some extent, groundwater quality, where as you go south, we see more saline water,” said Burke Minsley, a USGS research geophysicist based in Denver, Colorado.
The aerial survey work in Louisiana, which is expected to be finished as early as mid-December, has stretched across parts of seven states from southern Missouri and Illinois to Lake Charles and the mouth of Mississippi River. The flights don’t include the drinking water source for Baton Rouge, the Southern Hills aquifer, which has its own saltwater intrusion problems.
Once finished, the Xcalibur plane and other USGS contractors’ planes or helicopters will have surveyed a combined 100,000 square miles of territory, an area slightly bigger than the entire state of Oregon. It will have flown a straight-line distance of 50,000 miles, equivalent to a little more than two trips around planet, USGS scientists said.
The plane, which is ringed by a thick wire, sends signals into the ground and an electromagnetic sensor called a “receiver bird” towed behind the plane picks up signals the subsurface reflects back, measuring the earth’s electrical conductivity.
From those returned signals, USGS scientists say they can help tell what the aquifer’s geology is up to 1,000 feet deep, where the water might be and whether it may have higher salinity levels.
The information will help fill in the gap in the geological understanding — what the USGS calls “connecting the dots” — of what lies in-between the thousands of water, petroleum or other wells drilled across the region through the years.
The aerial surveying is hardly a monotonous ride on cruise control.
The crew is flying an east-west and sometimes north-south grid across the landscape. Staying on track requires a four-person crew in the tight confines of the Cessna — a pilot, a co-pilot, the mechanic, Simmonds, and a fourth person to manage the data collection and the towed sensor.
Pilot Grant Bourne said maintaining the consistent heading, speed and elevation for hours at time can be tiring work.
The plane flies its specified survey line at the relatively low and often turbulent height of around 400 feet in the air. The crew must also watch out for the sensor, which is being towed about 200 feet above the ground a few hundred feet behind the plane, and the threat of lightning.
“Yeah, it is pretty hard work, so you’re not getting too bored,” he said.
Bourne estimated a recent Friday flight, which lasted from about 7 a.m. to 3:30 p.m. with one refueling, covered nearly 560 miles over the Baton Rouge and New Orleans areas and part of Lafayette.
Bourne and his crew, who work for a Spanish company that uses the airplane to find oil and minerals like gold, are on their second year in the USGS project. This year, they have been in Louisiana about three months.
They had been working out of Monroe until a few weeks ago, when they shifted down to the Gonzales-area general aviation airport south of Interstate 10.
With all his time over Louisiana, Bourne said the amount of activity on the state’s waterways has really been a notable sight. Radio towers have been a problem in parts of northern Louisiana, northwestern Mississippi and southwestern Tennessee.
“Towers, you seem to have a lot of towers,” Bourne said.
That’s no stray observation.
The plane and its tow “bird” are flying below the tops of the towers and their radiating guy wires. So the craft must be steered to avoid them.
Minsley and other USGS officials said the aerial survey work is being combined with well and other data to create hydrological models of the aquifers so people can better manage the water sources.
The Mississippi River Alluvial Plain aquifer, for instance, is the third most-pumped aquifer in the nation, with 9 billion gallons per day drawn from the underground source for agriculture. It serves as the supply for one of nation’s most important agricultural regions, the USGS says.
The continued withdrawals have led to major groundwater declines in the Mississippi and Arkansas deltas and other parts of the aquifer.
The Chicot aquifer, which is used for rice, soy bean, corn and crawfish farming, as well as residential and industrial uses in southwest Louisiana, also suffers from groundwater depletion and salt water intrusion.
Three earlier phases of the aerial survey work had already been finished by March and produced information on those parts of the groundwater resources, but analysis on the final batch of data in south Louisiana won’t be finished until late 2022.
If you look up, you might just catch the Xcalibur plane and its tow bird overhead.
Part of the Cessna’s path includes flying the length of rivers. The lower Mississippi from Baton Rouge south remains on the to-do list, possibly in the next week or so.