In the midwestern United States, Omaha, Nebraska, has a lofty goal: rehabilitate 25 miles of water mains annually by 2025.
In 2019, Omaha’s Metropolitan Utilities District (MUD) began ramping up its water infrastructure replacement program. Omaha is the largest city in Nebraska, with a population of about 486,000 and a metropolitan area of about 1.5 million people. MUD serves approximately 600,000 people.
“We understood that we needed to replace at a higher rate than we had been doing,” said infrastructure integrity director Jared Svagera.
Part of that replacement program was determining which piping material to use when rehabilitating portions of the city’s 3,100 miles of water mains.
Omaha has cast iron mains dating back to the 1880s, but it was the post-Depression-era spun cast iron installed in the 1940s that was identified as most critical for replacement. Other cast iron mains installed in the 1950s and 1960s were also marked as high-failure areas due to corrosion.
Omaha crews have also recorded a number of corrosion hole failures linked to imperfections in poly-wrapped ductile iron pipe installed in the 1990s. At the time, Svagera said, the poly wrap process wasn’t as well understood as it is today, leading to some improperly installed or tapped poly-wrap pipes that are now prone to failure due to targeted corrosion.
As MUD weighed those challenges, officials realized it was time for a change.
“We knew we needed to shift toward plastic pipe that won’t corrode,” Svagera said. “We began a couple of direct replacement projects with HDPE, installed using directional drilling.”
But it was a partnership with Murphy Pipeline Contractors that really got the ball rolling.
“Things really took off last year when we partnered with Murphy to do some pipe-bursting work for us,” Svagera said. “We had been doing pipe bursting for a few years with C900 PVC, but seeing them install HDPE via pipe bursting was a big eye-opener for our crews and our engineers.”
During pipe bursting, an expansion head is pulled through an existing line, causing the line to break apart. As the expansion head is pulled through the existing line, it also pulls the new pipeline behind it, immediately filling the space left by the previous pipeline. HDPE is especially well-suited for pipe bursting, due to its durability and flexibility.
In contrast to traditional methods, pipe bursting does not require unearthing to reconnect water services and less excavating to install the new pipe. This lessens the overall cost of replacement projects, while also minimizing disruptions for residents and businesses around the jobsite.
Murphy’s projects this season consist of more than three miles of pipe, the first project of which services about 157 residential water customers. This first phase began the last week of April, with a Murphy crew on-site fusing 6,600 ft of 6-in. and 8-in. HDPE in the northwest portion of the city.
Fusions were made using a McElroy TracStar 412 Series 2. Designed to butt fuse pipe sizes from 4-in. IPS to 12-in. DIPS, the TracStar 412 Series 2 offers a self-contained, self-propelled vehicle that allows fusion technicians to drive the machine directly to the fusion site.
The site superintendent, Jose “Lupe” Quintero, said his crew was able to fuse between 800 and 900 ft of HDPE each day with a single McElroy fusion machine.
“It’s one of our favorite machines to work with,” Quintero said. “Plus, HDPE is flexible, so it makes it easier to install the pipe as well, and there’s no risk of corrosion like you see with cast iron.”
MUD is targeting its rehabilitation efforts toward the areas with the highest failure rates, rather than targeting by the age or material of the pipe. Right now, the utility’s water main makeup is roughly 37 percent cast iron and 58 percent ductile iron pipe, with a smattering of plastic, steel, concrete and transite (cement pipe mixed with asbestos fibers) making up the difference between the two.
Because the rehabilitation is being done based on risk assessment, the replacement work is happening in stages.
“The pipe material influences your labor and design plans,” Svagera said. “HDPE represents a lower installation cost, plus a lower material cost, and we want to do right by our ratepayers by installing what will give us the highest quality and longest lifespan, at the end of the day.”
In the summer 2022, MUD designed its replacement plan around using PVC. However, after seeing the success of Murphy’s initial HDPE pipe-bursting project, the utility coordinated one HDPE project to see how their crew felt about the installation process.
“They just loved it,” Svagera said.
In 2023, the utility swapped many of its internal water projects to HDPE.
In-house fusion work will be completed using a McElroy TracStar 618. Like the TracStar 412, the TracStar 618 is self-contained, self-propelled and track-mounted. TracStar machines minimize damage to concrete and asphalt surfaces, which is a plus on public and private properties. Additionally, because the equipment can be driven directly to the jobsite, there’s no need for a crane or large piece of equipment to maneuver the fusion machine to the site.
While there is some overlap between the two machines’ pipe ranges, the TracStar 618 is capable of fusing pipe from 6-in. IPS to 18-in. OD. Crews gleaned some fusion expertise from the work done by Murphy, Svagera said, but utility crews were already fusion certified because of their work with MDPE gas mains throughout the city.
“Most of our construction crews are operator-qualified to fuse gas pipe,” Svagera said. “That knowledge translated right over to the water side.”
In 2023, Svagera expects to see MUD replace 16 miles of the existing water mains. He wants to see another 17 miles of replacement completed in 2024.
“We’re ramping up a mile at a time,” he said.