Oklahoma City is reaping the rewards of proactively implementing a chemical root control program, setting up a five-year plan to rid its sewer pipes of the unwanted and tangled mess of roots that have caused backups, blockages and overflows.
The city completed its first project in summer 2008 in a northern subdivision, netting the results city public works officials were looking for — elimination of those backups, blockages and overflows.
The city’s utility department is responsible for approximately 2,552 miles of sewer pipe, ranging in diameter from 4 to 96 in. The average age of the pipe is nearly 34 years old, although there are some sections of the city where it is common to see 100-plus year-old concrete and clay tile pipe. As many cities struggle with the overall deterioration of its underground pipes, Oklahoma City’s situation is a little different.
“I would describe the condition of our system as being a bit above average. A lot of cities on the East Coast are considerably older than we are. As a state, we are just over 100 years old,” said Allen McDonald, line maintenance manager for the Oklahoma City utilities department. “We do have areas in town where we have some older pipe that causes quite a few problems and we work to keep those clean or we replace them. We have done a lot of work over the last 10 to 15 years.”
Oklahoma City covers 621 sq miles, 607 of which covers land and the remaining 14 sq miles covering water. The Oklahoma City Utility Trust, which oversees the utilities department, handles the sewer and water needs of 500,498 city residents, as well as the flow and treatment of several surrounding communities.
As in most American cities, the Oklahoma City landscape is a sight to see when everything is in full bloom, including the trees. But while those beautiful trees dot the landscape aboveground, the damage they cause below it keeps public works officials busy trying to get rid of the roots that have invaded their sewer lines, creating pipe blockages and possible structural damage to the pipe itself.
Oklahoma City is no different than any other city in the United States when it comes to dealing with root intrusion. With almost 50 percent of the city’s pipe made of clay tile, roots are the primary reason the city experiences a high number of sewer backups and overflows.
“Our soils in Oklahoma City move considerably and the clay tile pipe is very brittle, causing bends and breaks,” McDonald said. “We get cracks in the line and root intrusion through those cracks. We also have a lot of hammer tap applications and we get a lot of root intrusion through the service connections.
“In a normal municipality, grease problems outweigh your root problems,” he said. “It’s just the opposite here. Our root problems are generally 40-plus percent of all of our issues.”
Up until a few years ago, McDonald said that root problems were dealt with using mechanical means — using a hydraulic root saw attached to a jetter to cut away the roots. But that was a short-term fix and it only exacerbated the problem as the roots would grow back twice the size and thicker, further expanding into cracks in the pipe.
McDonald said his department began looking into a chemical root control program two years ago — by seeing what was available and talking to other municipalities that have implemented a program. With the support of the Oklahoma City Utility Trust and City Council, McDonald was able to move forward with a chemical root control program.
“They know what our issues are,” he said. “The last two to three years, we have had heavy, record rainfall and that has definitely showed us the weakness of our collection system.”
The city’s first root control project took place in summer 2008, covering 136,818 ft of pipe 8 to 21 in. in diameter. The pipe was located in a subdivision in the northern section of the city. Familiar with work done by Duke’s Root Control in neighboring municipalities, McDonald contracted with the company to handle this project. Cost of the project was $200,000.
“We were going into that subdivision twice a week for backup calls and overflows,” McDonald said. “In our initial video inspection of the pipe, we found huge root masses and 75 percent blockages. We were not surprised. We knew they were bad and we knew we needed to do something about them.”
The project was done over a 37-day period between June and August 2008, with Duke’s using two- and three-person crews to apply its thick herbicidal foam to the targeted sewer pipe through the manholes. Once the foam is released into the pipe, it compresses against the pipe surfaces, penetrating cracks, joints and connecting sewers, killing the roots on contact.
McDonald said follow-up inspections were done six months later and the results have been exactly what the city was looking for. The sewer pipes were also flushed to clear them of the dead roots. “Our follow-up inspection showed that they did a tremendous job and the chemicals did exactly what they were supposed to do,” he said. “Our post-inspection showed the pipe was completely cleared.”
Duke’s applications prevent root re-growth for three to five years; however, McDonald noted that Duke’s gave the city a two-year guarantee on this project.
The project was so successful that a five-year chemical root control program was created, each worth $200,000 a year. “We’ve had great success so far. That 136,000 ft — we really don’t have to do much there right now except for the usual maintenance,” McDonald said. “We’ve got areas identified for the next five years that we want to treat and have prioritized them based on the data in those areas.”
Sharon M. Bueno is managing editor of Trenchless Technology.