Two Nebraska cities — one a well known metropolis and the other considered the fastest-growing city in the state — are using chemical root control as a means to ensuring longer life of their underground pipes.
The cities of Lincoln and LaVista have been longtime proponents of using herbicides as part of their preventative maintenance programs to control the roots that infiltrate their sewer systems. Each city started their programs in early 1990s, when chemical root control was not a commonplace practice for U.S. municipalities.
LaVista has cut its number of root intrusion-related SSOs to 0 in 2008, while Lincoln — a much larger and older city — had no more than eight such incidents in 2008. Officials in both cities credit the continued implementation of chemical root control as the reason for the results.
The City of LaVista was founded in 1960 and has a population of 20,000. The LaVista Public Works Department owns 80 miles of sanitary sewer lines that serve residential, retail and industrial customers. Seventy-five percent of the city’s sewer lines are made of clay, with the remaining 25 percent PVC. Because the city is relatively young, the oldest lines are approximately 50 years old and in fairly good condition.
“Our main problem in the older parts of town is root intrusion,” said Tim Rush, LaVista sewer maintenance director, who has worked for the city since 1980 and instrumental in bringing chemical root control into the fold here in 1993.
“In the older section of town, we knew we had a root problem because when we’d flush [the pipes], we’d bring back particles of roots and we had many SSOs in that part of town,” Rush said. “We had one main line — a 1,200-ft section of pipe — that ran through the older part of the city and [after televising it], we could see it had roots at every 5-ft section, massive roots. Something had to be done.”
Initially, the city was going to reline the pipe because Rush figured with all the roots in it, the pipe must be damaged. But after cutting away the roots and televising the pipe, the city realized the pipe wasn’t damaged. “The pipe’s in good shape, there’s no sense in lining it,” Rush said. “So we started researching other options.”
In his research, Rush found chemical root control and since then, it’s been a constant in his department’s preventative maintenance program. The department tries to treat about 14,000 ft of pipe each year, using every penny of its $7,000 chemical root control budget. The pipes are on a three-year rotation for re-foaming and are video inspected every other year.
“We do every-other-year inspections on our healthy lines just to make sure everything is looking good,” Rush said. “It’s through televising that we find our root problems and that’s where we decide which ones are in line to be treated. If there is root intrusion in over 75 percent of the line’s joints, then we start foaming that line.”
Rush said the program is pretty simple: the lines are televised, roots are mechanically cut away and then the line is treated with the chemical root control. He said the foaming is typically down in the fall, when the leaves are falling and roots are thriving. All the work in the is process is done in-house, using equipment from Vaporooter, CUES, Sewer Equipment Co. of America and Super Products.
2006 marked the first year that LaVista had 0 SSOs attributed to root intrusion, and prior to that the city was averaging about two a year.
City of Lincoln’s Road
Don’t misunderstand Roger Krull: he loves trees. But the assistant superintendent of wastewater collection for Lincoln’s Public Works and Utilities, does not like what the trees are doing to Lincoln’s underground sewer lines.
“Lincoln is a Tree City USA city, so we have trees everywhere,” Krull said. “[Arborists] love planting them between the curb and sidewalks and they are beautiful. That just happens to be the location of the sanitary mains. And with the enormously dry conditions we went through in the 1990s and early 2000s, the root intrusion almost doubled in what we were seeing in areas of town that we were normally maintaining every couple of years. Now we are maintaining them on a yearly basis just because of the root intrusion.”
Krull said Lincoln developed its chemical root control program in 1991 to combat the number of stoppages the roots were causing. Sixty-five percent the 1,028 miles of sanitary sewer lines are made of clay and are up to 100 years old in some areas.
“When we started chemically treating, we found we were able to minimize the amount of time and effort committed to actual root cutting,” Krull said. “That’s not to say we don’t continue to root cut. We physically cannot and economically cannot treat every line in the city as we would like to or as frequently as we would like.”
Chemical root control has been critical in minimizing the damage to the aging pipes caused by the roots and root cutters, he said. “On a scale of 1 to 10, what the roots were doing to the pipes was about a 7 or 8 damage-wise,” Krull said.
Krull said when the program was first implemented, the plan was to treat 35 miles of pipe a year and that held true in the 2000s. But budget constraints forced his department to scale back its program in 2002 and utilize other preventative methods to maintain the system.
“Today, we try to do between 15 to 20 miles a year,” he said. “[Chemical root control] is a permanent part of our budget. We allocate about $15,000 a year for it and we try to use up every little bit of it.”
Like the City of LaVista, Lincoln uses CCTV to regularly inspect the lines, as well as to determine where the chemical treatment will be used. The lines are chemically treated between May and October and the CCTV inspections take place all year long. A combination of inspection, mechanical cutting and chemical treatment has become the city’s winning formula to keep roots from causing irreparable damage to the sewer lines.
Krull points to one root story in particular when discussing the damage roots inflict. “We were doing routine cleaning on an 8-in main and couldn’t get through. The whole side of the main was caved in. It was right in the middle of an intersection,” he said. “We dug up the pipe and found a root almost the same size as the main. It was about 6 in. in diameter. The closest tree to that location was 120 ft away. The root followed along that clay pipe and grew to the point where it broke the pipe.”
“The number of stoppages we have today vs. 20 years ago that we attributed directly to roots has been reduced by half,” Krull said, noting that Lincoln had no more than eight root-related SSOs in 2008.
Sharon M. Bueno is managing editor of Trenchless Technology.