Pipeline Brings Water Through a Mountain

Arkansas pipeline project features the longest tunnel bore of its kind in North America

Pipeline Brings Water Through a Mountain

Hot Springs Water Utilities crew members at the utility shop in Hot Springs.

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A $155 million project that will provide the city of Hot Springs, Arkansas, with an additional water source by the end of 2025 features about 30 miles of pipeline — including a section that passes through almost a half-mile-long microtunnel bored through nearby Blakely Mountain.

Started in fall 2022, the Hot Springs Water Supply Project is by far the largest water-utility project in the city’s history. It will bring up to 15 million gallons per day of water from Lake Ouachita, a roughly 40,000-acre lake — the state’s largest — that’s located about 15 miles northwest of the city and was created by the Blakely Mountain Dam, says Monty Ledbetter, the city’s utilities director.

That allocation was negotiated by the Mid-Arkansas Water Alliance, a nonprofit coalition of regional communities and water utilities, with the United States Army Corps of Engineers in 2017.

Two bond issues — one for $110 million and one for $45 million — are funding the project. Revenue generated by ratepayers will pay off the bonds.

“The city needs an additional water source because we’ve reached our capacity more than once,” says Ledbetter. “In 2012, we reached our maximum capacity 56 times during a very dry period and since then we’ve reached it at least once a year.

“If it stays dry, we’ll probably hit our maximum again this year.”

Shortage spurs search

By state mandate, a water shortage technically occurs when a community reaches 80% of its maximum allocation, which occurred in Hot Springs in 2010, 2011, 2012 and 2022. The first shortage spurred city officials to start searching for another water source.

“Multiple alternatives were considered in the planning process with respect to location of the new intake, a new treatment plant and the route of the transmission mains associated with the project,” Ledbetter explains. “One option was to pump water over Blakely Mountain, for example, or pump water from Lake Ouachita into another lake, Lake Ricks.

“It was an extremely complicated decision process.”

Expected population growth also factored into the need for another water source, he notes. (The city’s population currently stands at a little more than 38,000 people, but the system supplies water for around 98,000 consumers in the city and two other communities.)

Droughts that now occur more frequently also played a role.

“During dry spells, we really see the needle move when everyone’s water sprinklers kick in,” Ledbetter says.

The city’s primary source of water is upper Lake Hamilton, a 7,200-acre reservoir created by the Carpenter Dam, located on the Ouachita River near the southeast part of the city. The river flows along the west and south sides of the city.

The city’s allocation of water from Lake Hamilton is 30 mgd. Nearby Lake Ricks provides a secondary source with a 6 mgd allocation, but it’s not used very often because it’s an unreliable water source, Ledbetter says.

The utility operates two water treatment facilities, the Ouachita Water Treatment Plant on the northwest side of the city and the Lakeside Water Treatment Plant, located about a mile north of Hot Springs. But the Lakeside plant will likely be “mothballed” within the next few years, he says.

A boring topic

The key component of the project is the 2,600-foot-long, 61-inch-diameter bore through Blakely Mountain, a 1,132-foot-tall ridge composed of various types of sandstone and shale and located near the Blakely Mountain Dam. Michels Corp., a global construction company based in Milwaukee, was hired to do the bore, which is the longest of its kind in North America using direct and steerable pipe-thrusting technology, according to Michels officials.

Drilling through a mountain may seem like a lot of extra work and expense. But it was the best option because Lake Ouachita is at a higher elevation than Hot Springs. As such, water can travel via gravity from an intake 40 feet below the lake’s surface to a new treatment plant under construction 17 miles south, on the southeast side of Hot Springs, Ledbetter says.

“That will save us millions of dollars in pumping costs during the life expectancy of the new treatment plant,” he says. “All we have to operate is a valve that controls the flow of raw water.”

The pipeline from Lake Ouachita will have to traverse portions of sprawling Lake Hamilton twice; those sections will be made of 42-inch-diameter concrete pipe that will run along the bottom of the lake, Ledbetter explains.

“We won’t have to anchor it down because the walls of the pipe are five inches thick,” Ledbetter says.

The rest of the pipeline is made from spiral-welded steel that’s 48 inches in diameter. The annular space between the pipeline and the 63-inch-diameter bore will remain unfilled except for the first 40 feet of each end, which will be filled with grout to secure the line, he explains.

From the plant, another pipeline will carry treated water for 13 miles. At that point, it will tie into the south end of the city’s water distribution system.

So far, so good

The bore through Blakely Mountain started in October 2022, while pipeline construction and work on the new treatment plant began in August 2021. The estimated completion date for the entire project is late 2025, Ledbetter says.

Aside from a small delay in the boring process caused by harder-than-expected rock and associated problems, the project generally is on schedule, he notes.

But no matter when it’s completed, Ledbetter is happy to see more than a decade of consideration and planning come to fruition.

“We are literally building the future for Hot Springs,” he says. “It will provide the water that Hot Springs needs for the next half century.

“Yes, it’s a lot of money and it’s hard to get approval for a project of this size and with such a large price tag, but the bottom line is that our board of directors and the community understood the need for it and provided outstanding support.

“If Hot Springs is going to continue to grow, we had to do this.”


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