Engineering a Better System

Growing Midwestern community lays the groundwork for water infrastructure expansion and improvement

Engineering a Better System

Nick Borns, principal engineer for water at the City of Sioux Falls, South Dakota, stands with a work crew behind him on a job site in Sioux Falls. (Photography by Jay Pickthorn)

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Sioux Falls sits in the southeast corner of South Dakota. The Big Sioux River flows through the city, giving the city its name and giving residents a picturesque park setting where the water cascades down a series of rocky outcrops on its way south to a rendezvous with the Missouri River.

The water Nick Borns works with every day doesn’t have the eye appeal of the city’s waterfalls but as long as the water flows through the city’s water mains without undue leakage and arrives at faucets on demand, Borns is satisfied. The utility of water can be beautiful, too.

Borns is Sioux Falls’ principal engineer for water. As such, he is responsible for developing and executing the capital program for the city’s water treatment plant and distribution system. He and his team have been busy during the eight years since he moved from consulting with the city water department to helping lead it.

“When I was on the consulting side, I worked on several water main replacement projects,” he says. “That piqued my interest, and I made the move to the city.” The pipe replacement work continues to be a “pet project” of Borns, but his interests range way beyond laying new line. “My team is doing a really good job of looking for new technology and being creative in ways that we can better our utility.”

There is plenty of evidence to support that assertion.

Local sources

Sioux Falls is the largest city in the state and it continues to grow. In 2010, the census showed a population of 154,000 but since then the population has swelled by more than 50,000 and the growth is expected to continue. Some financial and health institutions have a large presence in the economy, augmenting a traditional manufacturing base.

Several college and technical school campuses are situated around the city. The arts culture is burgeoning, with a blues festival, Native American arts market, an arts and science pavilion, and the mayor’s office handing out annual literary and music awards. Plus free public concerts and programs showcase music and art on the banks of the Big Sioux River.

For all of these reasons, the city needs a dependable water supply and distribution system. The water department and city leaders are in step with that mission. “It is no secret to the mayor and city council that our infrastructure needs are extremely important because of the growth we are experiencing,” Borns says.

Forty-five wells pull water for the city from a pair of aquifers underlying the region, one of which is the delightfully named Skunk Creek Aquifer. The wells account for about 40% of water distributed across the system, with the river directly contributing just 3%. The river is key to recharging the aquifers, however, so it is an overall critical component.

Obviously, both ground and surface water are dependent upon precipitation, and Sioux Falls on average receives some 45 inches of snow and 27 inches of rain annually. About half of South Dakota, however, is currently experiencing severe or extreme drought conditions, according to a national drought tracking agency. That tends to focus the minds of those responsible for water supplies.

Under such conditions, Sioux Falls is in good shape only because it connected a decade ago to the Lewis & Clark Regional Water System, a 20-member organization that supplies water to communities in South Dakota, Iowa and Minnesota. More than half of the city’s water supply flows in from two connections to the regional supplier. “We are fortunate we have the local water sources and also the Lewis & Clark Water System,” says Borns, perhaps understating the matter.

Data acquisition

When Borns, a South Dakota native, began work in the city, he quickly understood that the existing system of tracking water flow was not reliable. The engineer was loath to rely on existing data to determine where new distribution lines would be installed, especially since the city was about to undertake an expansive master plan.

So, his team launched a six-month water model calibration in search of accurate data. It entailed a hundred hydrant flow tests, pressure monitors and analysis of the water leaving the water plant. “We found some areas in which tests didn’t follow the modeling. We found closed valves that we didn’t realize were closed,” Borns says of the investigation.

The completed calibration gave the city hard information upon which decisions could be made about proper sizing of infrastructure, how to most effectively troubleshoot future flow problems and other management issues. “It was a long project, but a very critical one to appropriately master plan.”

Analysis of water sourcing also was extensive — that is, gauging the depths of city-serving aquifers, and determining how quickly water travels in the underground pools from one area to another area. “The aquifer research, field testing and modeling were critical to obtaining reliable source water data. Completing those tasks allowed us to jump into the city’s master plan.”

After 16 months, that master planning process is nearing an end. The document will incorporate future water use projections, conservation measures, construction issues (pressure zones, capital priorities, etc.), water rights and on and on. “It has been exciting times for us in water as we gathered critical water planning information,” Borns says.

Pipe protection

All of that was groundwork for some big projects. One of the more significant projects is the replacement of the city’s Minnesota Avenue transmission main, a 2-mile-long 36-inch prestressed concrete line laid in 1967 that connects with three of the city’s four reservoirs. Reconstructing the street and replacing the line is a four-year project. The second phase of construction is scheduled for 2024.

The concrete main — which used to be a primary artery for the system before the Lewis & Clark source was tapped — is being upgraded to a 42-inch ductile iron line. Because he was concerned about the main being out of service for extended periods, Borns engineered a 20-inch transmission interconnection. The interconnector ties together four transmission mains, which allows water to back-feed and reduces dependence on each of the mains.

Because Minnesota Avenue is a gateway to downtown Sioux Falls and connects the city to the airport, the underground work is being undertaken at the same time the corridor’s streetscape is being revitalized with new paving, landscaping, lighting, safety medians, parking and sidewalks.

The city is maximizing efforts to mitigate corrosion of the new water main. It is zinc-coated and V-Bio poly-wrapped, and fittings are epoxy-coated. In addition, the waterline is being cathodically protected, a technology Borns and his team embraced in 2021 on a retrofit pilot project on 26th Street.

“We’ve learned that our ductile iron pipe is not agreeing with the soils here. We have some areas of highly corrosive soils. Those ductile iron mains — installed from the early 1970s to the late 1990s — are the ones we’re targeting for protection,” Borns says. “The life in those pipes is worth extending. We should be able to do so for 20 or 30 years, at which point we can replace them in conjunction with street reconstruction work.”

About 40% of water mains in Sioux Falls are ductile iron — twice as much as the cast iron component of the system — and accounts for roughly the same number of pipe failures as the cast iron pipe. The difference is the age of the pipe: the cast iron pipe is 70 years old on average, the ductile iron less than half that. (PVC pipe constitutes the rest of the system.)

Consequently, when the older cast iron experiences failure, it usually is just replaced. It’s reached the end of its service life. However, the newer generation ductile iron should be able to function for many more years — if it is protected from further corrosion. That’s what Borns is attempting to do.

“Typically for us, the first indication we have of corrosion is we see some water valves leaking. Then we see breaks in nearby 6- and 8-inch distribution lines and, finally, breaks on the main transmission pipe.” The engineer tries to time his corrosion-prevention work on a pipe when the street above it is scheduled for an overlay of pavement. Hence, one street due to be repaired this summer will have the pipe running under it cathodically protected.

In the 26th Street pilot project, Borns retrofitted 20-inch-diameter pipe with corrosion-fighting anodes. Specifically, 307 18-inch-in-diameter cores were drilled through asphalt or concrete pavement at 20-foot spacings. Through the pavement cuts, a shaft was hydrovacuumed through the soil to within 6 inches of the water main.

Into this shaft, a cotton bag was dropped. It contained either a magnesium or zinc rod — metals to which surrounding corrosive soils aggressively react. This “sacrificial” material in the bag is connected to the pipe by a lead wire that is Cadweld-ed in place. In this way, the bagged metal becomes a satellite of the pipe and attracts corrosive forces in the soil, sparing the pipe the destruction.

Healthy system

The cathodic-protection project mostly was bid out, as is the bulk of major maintenance for the water system. The in-house crew has its hands full with preventive maintenance and emergency repairs, leaving significant overhauls to area contractors.

“Overall, the condition of our system is healthy,” says Borns. He adds that the city’s water plant, which periodically has been added to and updated, is in the same condition. “Our city leaders have done a nice job of staying ahead of repair needs.”

Besides the major undertakings heretofore described, more typical repair projects occur as needed. “We adjusted the water main replacement volume this year to accommodate planned capital projects,” Borns says. “As all cities can relate to, cost escalations have required us to evaluate budget priorities.”

Still, some things just can’t be put off, such as cathodic-protection projects. Corrosion waits for no one.


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