DELTA — Unseen by human eyes, two gigantic storage chambers have been created in recent months in Millard County.

A highly unusual construction project — the first of its kind in the West — is transforming a buried deposit of salt into an enormous underground storage facility for propane and butane.

Ultimately, the huge, invisible project — if its backers' ambitions are met — could play a big role in how energy is stored and even generated in Utah.

Most of what they've accomplished is literally impossible to see because it's a half-mile underground where storage space is relatively cheap to construct.

"Above-ground tanks are extremely expensive," said Tiffany James, vice president of Magnum Development.

The company is developing the project on state school trust land near the Intermountain Power Project a few miles north of Delta.

A big drilling rig bored down 3,000 feet deep into an enormous natural deposit of salt. The caverns were created through a process known as "solution mining."

For months, Magnum pumped in streams of water to dissolve the salt, creating two caverns so big they'd be skyscrapers if they were above ground. Each is about 200 feet wide and close to 900 feet high, a huge amount of storage space for liquids and gases at a cost far less than above-ground storage tanks.

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"You don't have the same kinds of above-ground maintenance, weather corrosion, all these types of things," James said. "You drill a well, you have a cavern, you maintain a wellhead. So it's very minimal infrastructure that way. It's a lot cheaper."

As the mining water is pumped back out of the cavern, a solution emerges that's totally saturated with dissolved salt. In fact, the water is a briny fluid six times saltier than the ocean.

Magnum built a 156-acre pond to contain the brine. It's the most visible aspect of the huge project, company officials said. The huge reservoir is lined to prevent leaks. Eventually, Magnum officials expect to sell the salt, possibly for wintertime highway applications.

The natural salt deposit 3,000 feet below ground is about 1 mile thick and 3 miles wide. Magnum officials say the enormous body of salt could ultimately be honeycombed with as many as 100 storage caverns. And that, in turn, could attract a variety of business opportunities.

"As you look across the country where other bodies of salt like this exist, a lot of economic development has followed right behind it," said Magnum Development CEO Craig Broussard.

Salt cavern storage facilities are common in coastal areas near the Gulf of Mexico, but this is the first of its kind west of the Rockies.

The Millard County salt deposit was discovered in the 1970s by a wildcat oil and gas drilling operation. Until now, the salt bed has never been commercially exploited.

Magnum Development crews installed a short railroad spur that will allow rail cars to deliver products to the storage facilities. The immediate plan is to pump about 3 million barrels of energy-rich butane and propane into the manmade storage caverns.

The real economic promise is the possibility of more caverns. Magnum originally planned to create three caverns for storing natural gas. Each chamber would have been the size of a buried Empire State Building.

A slump in natural gas prices put that idea on hold. Magnum officials hope to revive that concept in coming years, particularly if — as expected — the coal-burning Intermountain Power Plant remodels itself into a natural gas facility.

Another Magnum concept has drawn enthusiastic support from environmental groups: a storage facility for renewable energy from the wind and the sun. The idea is to build a cavern that works like a battery. When extra electricity is available from wind or solar farms, the power would be used to compress air and pump it into the ground. When more electricity is needed, the compressed air would be released through turbines that generate electricity.

"Think wind, think solar, think the sun not shining or the wind not blowing," Broussard said. "This is a great way to store that energy below the ground, release it 'on peak' when you need it, and be able to regulate that flow."

Magnum's more ambitious plans are geographically linked to a plan by the Intermountain Power Agency to recraft its power project as a regional energy hub, feeding energy from a variety of renewable and non-renewable sources into the national electricity grid. Intermountain Power officials have not said if they expect Magnum to store natural gas for the power plant.

Some of Magnum's ideas depend on unpredictable future energy markets. But the company is betting there's a market now for cheap storage, out of sight in the salt bed.

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