Heavy rain was triggering unexpected changes in airflow deep inside the Sanford Underground Research Facility, leaving engineers with more questions than answers. After gathering new data and digging into previous research, they discovered that falling water inside a mine shaft was temporarily pushing air through the underground ventilation system.
Keeping an underground facility running safely isn’t just about solid rock and sturdy tunnels. Engineers also have to manage a constant flow of fresh air while removing groundwater and rainwater that seep below the surface. Both systems are essential, and at SURF in South Dakota, they turned out to be connected in a surprising way.
The mystery started a few years ago when engineers noticed that parts of the ventilation system behaved differently during major rainstorms. The South Dakota Science and Technology Authority reported that airflow sometimes slowed down or even briefly reversed, something the team couldn’t explain at first.
Rain Was Changing The Airflow Underground
Jason Connot, a mining engineer who has worked at SURF since 2019, was among the first to notice the unusual pattern.
“We noticed our fan would go haywire at 5 Shaft. Some areas would show reduced or even reversed airflow during large rain events,” Connot said.
Normally, fresh air enters the underground facility through two intake shafts before leaving through two exhaust shafts. One of those exhaust routes, known as 5 Shaft, has another job when heavy rain hits. If more water enters the facility than the pumping system can handle, the extra water is sent down the shaft into a deep underground pool before being pumped back to the surface.
The connection between that water and the changing airflow wasn’t obvious. Engineers could see the effect happening, but they didn’t know what was causing it.
New Sensors Helped Reveal the Answer
The breakthrough came after SURF installed Maestro airflow sensors on the 2000 Level. The new equipment gave engineers a much clearer picture of how air was moving through the underground workings.
As mentioned in the press release, published inSanford Underground Research Facility website, the investigation had already received an important clue from Steve Gabriel, then a science teacher at Spearfish High School, and his students. They built and installed airflow monitors that recorded an unexpected increase in airflow during a test of the shaft deluge system on the 4850 Level.
“We felt that airflow increase on the 4850 Level during that test. That’s what made the correlation and triggered everything,” Connot said.
The team began to suspect that the falling column of water inside 5 Shaft was acting like agiant piston, pushing air through the ventilation network as it dropped.
A study published in Mining, Metallurgy & Explorationdescribes similar effects in large municipal sewer systems. Connot and colleagues from South Dakota Mines adapted those fluid dynamics equations to match SURF’s underground layout, and the results closely matched what engineers had been measuring.
“When we added our numbers and parameters to the model, everything came out spot on,” Connot said. “You would not think the weight of water droplets could move so much air.”
A Safer Way to Work Underground
The findings aren’t limited to rainstorms. Engineers also use large amounts of water in certain emergency situations, including underground fires.
“If there’s ever a fire, mining engineers will sometimes turn a valve on up top and just dump water down the shaft. Knowing this can change the air flow is critical information for everyone. We tested this, we’ve seen it occur,” Connot said.
The research is already helping SURF better predict how its ventilation system will respond when large volumes of water enter the shaft. Bryce Pietzyk, the facility’s director of underground operations, said the work allows engineers to adjust ventilation controls before airflow changes become a problem.
