St. Paul Regional Water Services Finds Efficiency with its Pipe Bursting Program 

Much can be said about the evolution of trenchless technology and the level of accessibility it has achieved. That’s credit to an industry that has pushed, promoted and supported the development and refinement of trenchless equipment, methods and applications. 

Does that mean that someday we might see a directional drill or tunnel boring machine parked in every suburban driveway? Not exactly. But in-house trenchless programs being initiated at utilities around the country are becoming much more common.

St. Paul Regional Water Services is the water utility for the city of St. Paul, Minnesota, and several surrounding suburbs. The utility maintains several construction crews that perform water distribution work for both water services and water main maintenance, including installation and replacement. But, until recently, the utility has sub-contracted out water main replacement via pipe bursting. 

“A few years ago we became quite interested in developing a self-performing the pipe bursting program,” said distribution division manager Todd Blomstrom. “We had field construction crews available and felt that by developing that type of program would achieve a higher level of efficiency with our water main replacement. We had a good pipe bursting contractor but wanted to be more in control of the process because of the amount of coordination it takes for projects like this,’ he said.

St. Paul Regional Water Services worked with trenchless equipment manufacturer TT Technologies, Aurora, Illinois, to develop a pipe bursting plan, as well as prepare and train crews in the trenchless pipe bursting method.

“Todd [Blomstrom] and the St. Paul Regional Water Services crew have really developed a strong in-house program. In many cases they’re achieving high production with their static bursting equipment that are comparable to any contractor,” said TT Technologies product specialist Mark Dorn.

Keeping it In-house

St. Paul Regional Water Services facilitates a robust in-house construction program. However, until 2022, pipe bursting work was contracted out to third-party providers. Utility crews would excavate launch and exit pips, set the trench boxes, and cut open the main. Then the contractor would fuse the HDPE pipe and perform the pipe bursting. St. Paul Regional crews would then reassemble the main, test it, reconnect the services and put it back in service. 

And while the utility had a positive working relationship with a pipe bursting contractor, it was determined that performing the work in-house could be more efficient when considering coordination and prep time and contractor availability. So, in 2022, St. Paul Regional Water Services launched its in-house pipe bursting program. Initial projects consisted of existing 6- and 8-in. cast iron replaced it with 6- and 8-in. HDPE. 

The Pipe Bursting Plan of Attack

With approximately 1,200 miles of water main in its system, spanning seven cities, developing a plan to address failing lines is a key component to the water utility’s in-house program. Much of its system is made up of cast iron pipe with some of the oldest pipes dating back to the late 1800s. To help prioritize projects, St. Paul Regional Water Services has a model of its system that shows main break history, as well as the consequence of main breaks. 

“The model does not put equal emphasis on each break, as higher risk facilities, such as area hospitals, medical facilities, schools, daycares, rank higher in importance within the model,” Blomstrom said. “It then identifies a risk score for a specific location. The main break count is also an element of that score and replacement projects are prioritized based on those results. It’s a great tool for helping map out our program.”

According to Blomstrom, once the pipe segments are identified, further evaluation takes place to determine whether the project will be an open cut excavation, pipe bursting project or a clean inline project. One factor that is taken into consideration is the density of service connections. 

“Pipe bursting is most efficient with a manageable number of service connections. Smaller residential lots with a high density of service connections are often best served through an open cut application,” Blomstrom said. “The other consideration is host pipe material, as the utility has not attempted pipe bursting on ductile iron pipe.” 

St. Paul Pipe Bursting

Pipe bursting runs average between 350 and 500 ft for residential applications. The presence of ductile iron repair sleeves can impact the length of bursting runs. Host pipe diameters range between 6 and 8 in. for the cast iron mains. Several 12-in. segments are scheduled and represent the largest diameter pipe assigned to the pipe bursting program. 

“The St. Paul crews have really taken to pipe bursting. Existing mains have been successfully upsized from 6 to 8 in. where capacity is a consideration,” Dorn said. “High Density Polyethylene Pipe (HDPE) is being used to replace the existing cast iron mains. Water mains are generally 8 ft deep with 10-ft trench boxes providing a secure workspace. They’re really working on efficiency and doing a great job.”

Traffic control and access are also significant parts of the utility’s pipe bursting efforts. Projects are planned and laid out to provide for optimum traffic flow. Hard and soft road closures are situational. Often, a street will be shut down with a soft closure allowing residents to access their properties while diverting through traffic to alternative route options. Crews will provide temporary service as needed per the specific project. 

Staging pipe is done in the most effective way to reduce the amount of disruption. Care is taken to ensure the new HDPE stays as clean as possible while being transported to the job site, during fusion and when it is staged. Upon successful application of the pipe bursting process, the new pipe goes through a chlorination process, as well as pressure testing.

Pipe Bursting on Target

According to Blomstrom, focusing on performance measures, benchmarking has been a large part of the utility’s success in development of its pipe bursting program. 

“By creating dashboards for data has allowed us to evaluate of the process and see where we’re succeeding and where we need to improve,” he said. “We’ve been able to determine that the program has been cost effective in terms of lower cost per foot, replacing mains with less disruption, reduced street restoration and traffic closures. That also is a reflection of our pre-project evaluation process and its effectiveness. If the criteria and conditions are correct, pipe bursting will work effectively in those situations.” 

Blomstrom says that investing the time to develop a five-year plan, and understanding what the highest priorities are, has also been part of the success of St. Paul Regional Water Services in-house program. 

“Once priorities are defined, it is possible to zero in on identifying the most efficient method for sections within the system,” he said. “That knowledge has helped us refine the pipe bursting program. Since starting the program, our crews have completed an average of 5,000 feet of main pipe bursting a year.” 

Jim Schill is a technical writer in Mankato, Minnesota.