Inside Minnesota’s underground natural gas storage facility

From the surface, there’s little to suggest that something remarkable is happening hundreds of feet below the ground in Waterville — but Thomas Coffman knows differently. 

Beneath the southern Minnesota landscape is the only natural gas storage facility in the state, capable of storing billions of cubic feet of natural gas. 

The facility, operated by CenterPoint Energy, is inspected by the Department of Public Safety’s Office of Pipeline Safety (OPS) every year. 

“People hear ‘natural gas storage’ and may picture a big tank,” said Coffman, OPS chief engineer. “But with underground storage, we’re looking at a completely different type of facility. There are wells, underground formations, pressure and a lot of systems working together to safely store and deliver that gas when Minnesotans need it.” 

It’s a reminder that pipeline safety is not always about what you can see. 

Unlike the tanks many people picture when they hear “natural gas storage,” the Waterville facility does not store natural gas as a liquid. 

The gas is stored underground in a porous rock formation, where layers of rock and natural pressure help contain it. During periods when demand is lower, natural gas can be injected into the storage field. When demand rises — particularly during Minnesota’s cold winters — gas can be withdrawn, processed and sent into the pipeline system. 

That’s very different from liquefied natural gas, or LNG, which is natural gas cooled to extremely low temperatures until it becomes a liquid. Turning gas into a liquid dramatically reduces its volume, allowing LNG to be stored in specialized tanks aboveground and transported where needed. 

That complexity is why inspections matter. 

OPS inspectors examine records, procedures, equipment and field conditions to make sure operators are meeting state and federal pipeline safety requirements. Minnesota law specifically directs the Office of Pipeline Safety to inspect records and procedures related to the design, construction, testing, operation and maintenance of pipeline facilities. 

For Minnesotans, much of that work happens quietly — and that’s the point. 

“When you turn up the heat on a cold Minnesota morning, you probably aren’t thinking about what happened hundreds of feet underground to make sure that natural gas was available,” Coffman said. “Our job is to make sure the systems behind that energy supply are being operated safely and that potential problems are identified before they become emergencies.” 

At the Waterville facility, the most important parts of the inspection may be the things the public will never see: the records reviewed, the questions asked, the equipment examined and the safety practices verified. 

It’s a lot of work beneath the surface — literally — to help keep Minnesota safe.