SEWER: Gaining Ground

Chemical foam root treatments and a repair-and-replace program for vitrified clay pipe help a Pennsylvania city protect its sewer infrastructure and its budget

The city of Mt. Lebanon, Pa., has a verdant landscape of tree-lined streets. But lush growth on top means deep root growth below the soil, and older clay sewer lines are coming under attack.

A consistent and assertive program of annual chemical foam root-control treatments over the past decade has helped the city tame its root problem to manageable proportions, as the worst lines are repaired and replaced. As a smaller community (population 33,000), the city finds that farming out the service to specialized contractors helps keep it affordable and on budget.

Attacking the culprit

In 1850, the Rev. Joseph Clokey imported two Cedar of Lebanon trees from Palestine and planted them in front of his house, giving the town of Mt. Lebanon its name. More than 150 years later, the municipality still values its trees, although the city, less than 10 miles south of Pittsburgh, continues to battle invasive roots.

“Although we use a lot of CCTV inspection in the system, you often don’t need to see the video to know you have a root problem,” says Rudy Sukal, Mt. Lebanon public works superintendent. “We’re part of the Tree City U.S.A. program run by the Arbor Day Foundation. Our own forestry crews maintain about 10,000 municipal trees lining our streets between the sewer and the sidewalk, in very close proximity to the sewers. Probably the biggest problem tree is the silver maple.”

While some of the city’s sewer lines are made of PVC, about 95 percent are made of vitrified clay with a joint every 3 feet. That’s the type of environment tree roots are quick to exploit.

More than 10 years ago, the city used a regular program of root cutting with its own high-pressure water jetter, manufactured by Aquatech (a part of Hi-Vac Corp.). “The roots were starting to become a chronic problem,” says Sukal. “We were clearing roots from some trouble spots up to twice a year.

“The more we did to cut and control the roots, the more they seemed to grow back thicker and stronger. The roots were starting to degrade the sewer lines, and the high-powered hydraulic jetters were further damaging the weakened clay pipe. We were starting to wonder if our own root-control program was going to cause the pipes to collapse structurally.”

Putting out a contract

Sukal and his staff found they were devoting excessive staff resources to root control. “With a three- or four-person crew on root control, one of our biggest concerns was trying to find a way to reduce or eliminate the manpower we were expending on dealing with roots and putting those people to work elsewhere,” he says.

“We didn’t want to invest a lot of capital in equipment like tanks and foam generators that we couldn’t make a lot of use of. It simply wouldn’t have been a wise investment for a department our size. We would also need to get a state license to apply pesticide, and while our crews are capable, we would need to get pesticide training for our staff for just one application per year. From the beginning, we decided to contract out our chemical root control.”

The Public Works Department devised a pilot program in 2000-2001, identifying several particularly troublesome sewer segments. “These were areas with shallow pipes close to trees,” says Sukal. “Our television contractor had also noted these lines were a problem, and we had them identified as part of what we called our ‘periodic checklist.’”

The city chose Duke’s Root Control Inc. of Syracuse, N.Y., to apply the herbicide diquat dibromide under the trade name Razorooter II, a U.S. EPA-registered product applied manhole-to-manhole in root-infested lines.

The product is registered for aquatic use and as an algaecide in ponds, so it adds no extra burden to wastewater treatment. It is applied as a foam created in a foam-generating tank that temporarily fills the sewer line. The foam affects only the roots that are exposed to the product, destroying up to a foot of the root length outside the line.

Tree remains healthy

“The rest of the tree remains healthy,” says Sukal. “We haven’t lost a tree yet. The product kills the root pretty much on contact, but it takes awhile to see results — sometimes a couple of weeks or months.

“We inspected the pipe with CCTV to see what the results were, and we could see the roots softening and sloughing off. Roots that were once white and crispy stop growing and turn black and slimy. We also wanted to make sure the mushy root material didn’t give the wastewater treatment system any trouble. With good results, we went ahead with a more ambitious plan to treat all of the root-infested areas in the sewer lines.”

Mt. Lebanon opens the job up for bidding each year, targeting 10,000 to 35,000 linear feet of pipe annually, where crews have identified the worst root incursion. Duke’s Root Control won the contract eight of the last nine years. The application works best in warmer weather. The 2009 contract, which spans March and April, involves 30,000 linear feet of treatment at a total cost of around $40,000.

Crews use foam applicators inserted at the manhole, while a public works inspector accompanies them to observe the process. “They typically treat about 4,000 linear feet a day, with an eight-hour day,” says Sukal.

Repeated application

Roots will eventually return if ignored, so the city repeats the treatments in the same problem areas every two to three years. Sukal says the product’s warranty structure encourages continued use. Each application is guaranteed for two years, so if roots return during that time, they are treated at no added cost.

Concurrent with the root-treatment program, the city is repairing and replacing the worst of its sewer lines. Some lines are being replaced by polyvinyl chloride (PVC) pipe or repaired, manhole-to-manhole, using structural cured-in-place pipe (CIPP) liners.

That process was accelerated by a consent order issued by the Allegheny County Health Department in 2003 to bring 61 county communities into compliance with the Clean Water Act. The order required the communities to inspect and map their systems by 2007. Mt. Lebanon must televise its sewer system by May 2010, and major repairs must be completed by November 2010. The inspection phase is already underway.

“We’re required to repair any major defects we find within six months of detecting them,” says Sukal. “Wherever we’ve placed PVC or inserted CIPP liners, the root problem is over. As we complete the mandated CCTV inspection, we’re keeping careful track of any problems related to roots. The evidence shows we’re definitely gaining on them.”



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