January 2009 Vol. 64 No. 1
Features
Huntsville Undertakes Nation’s Largest Root Control Project
The city of Huntsville, AL recently completed one of the largest sanitary sewer chemical root control projects in the country.
Over a one year period, 1.6 million linear feet of sewer pipes ranging in size from 6 to 24 inches in diameter were treated with Category E non carcinogenic herbicide. Huntsville’s sewer system is operated by the city’s Water Pollution Control Department (WPC). Duke’s Root Control Inc. performed the work.
Huntsville, AL, is one of the nation’s fastest growing cities and is an interesting combination of high tech industry and old South charm. With a population of more than 170,000 and growing, Huntsville residents find the city’s size is “just right” – big enough to attract diverse businesses and be the home of NASA’s Marshall Space Flight Center and Redstone Arsenal, but without the urban sprawl and traffic of large metropolitan areas.
Huntsville’s wastewater collection system is composed of more than 1,300 miles of underground pipes ranging from six to 78 inches in diameter, 33,000 manholes and 57 pumping stations. Wastewater is treated in six treatment plants. Keeping the collection system running smoothly is a full time, year round job.
Huntsville is a beautiful city and those who live there are proud of its progressive attitude along with its rich history which is carefully preserved. Stately trees line the streets of the Twickenham historic district which contains Alabama’s largest collection of homes constructed before the Civil War. Huntsville takes great effort to protect trees throughout the city, and each year is designated a Tree City USA Community by the National Arbor Day Foundation.
However, the roots of those trees have posed a continuing problem to Huntsville’s sanitary sewer system, a situation often shared by other cities.
Lots of trees, lots of roots
Roots enter sewer pipes as tiny, hair like structures which grow quickly. Roots thrive inside sewer pipes because the pipes provide a perfect environment for growth: a well ventilated area with a steady supply of water containing high levels of nutrients, continually replenished by fertilizer in temperatures that remain relatively constant.
Roots not only restrict flow, but separate and crack pipe joints. Often sewer system owners are not aware of root problems until a major blockage occurs, and when roots are removed, inspection reveals major damage to pipes.
The U.S. Environmental Protection Agency (EPA) identifies root intrusion as the single most destructive problem of maintaining wastewater piping systems.
“We’ve been fighting roots for years,” says Mark Huber, collection system manager of the Huntsville Water Pollution Control Department. “In the past we’ve used conventional methods to cut roots out of pipes.”
However, the process is time consuming, labor intensive and the cutting process actually encourages faster, thicker regrowth. Mechanical cutting tools cannot reach roots that are penetrating through joints, and the cutting process itself can cause damage to pipes.
Searching for a better, longer lasting solution to dealing with roots, Huber said chemical control methods were considered for the first time. Before committing to a full scale program, a test was performed in 2002 on 7,000 feet of pipe with a history of root problems and which had required field crews to clean or cut roots two times or more per year.
Test case
A Duke’s crew applied chemicals to the test section, and it was monitored over a four year period. There was not a single root problem during that time, says Huber.
In the drought years of 2005 and 2006, Huntsville’s root problems intensified.
“Our sewer lines became the only source of water for the roots, so inside the pipes is where they went,” says Huber.
With the documented success of the chemical test program, it became clear that large scale chemical treatment for roots could free field crews to focus on more preventative methods and that such a program also would prolong the life of the pipes in the collection system.
“To target segments of lines to be treated,” says Huber, “we reviewed the previous 20 years of line cleaning and repair data and put those with a history of root problems into the chemical treatment program. The lines needing attention were located throughout the city.”
Inspections revealed that the majority of the lines to be treated were structurally sound and with chemical maintenance should not soon need to be rehabilitated or replaced.
The contract for the 1.6 million feet of pipe was awarded to Duke’s and work began in April 2007.
“A two man crew treated sections of main lines between manholes,” says Stuart Tillery, Duke’s southeast sales manager. “We use specially equipped trucks with mixing supply tanks, hoses and a closed mixing system. The totally liquid formulation permits a completely closed mixing and application system.”
Process
Foam with a shaving cream consistency is pumped through a discharge hose filling the pipe and compressing against all pipe surfaces, into cracks and joints, into connecting pipes and into laterals. Roots die on contact, but trees are not harmed. “Dead roots,” says Tillery, “decay and slough off. The time it takes for roots to slough off varies with the type of tree, septic conditions and flow rates in the pipe. The process usually is complete within two to four months after treatment. In most cases, it is not necessary to mechanically cut roots either before or after treatment.”
The primary chemical used by Duke’s has liquid diquat dibromide as its active ingredient. Tillery says the product has excellent root control efficacy, is environmentally friendly, non carcinogenic, nonvolatile and is approved by the EPA for aquatic uses.
The Duke’s crew proceeded methodically with one to three two man crews on the job. Crews worked 10 days on, four days off and averaged 33,000 feet per week over the course of the project. Lines treated did not have to be taken out of service during application.
Expected benefits of the program included elimination of overflows in the areas treated, a reduction in homeowner’s calls about roots in laterals and that after treatment, pipes would be much easier to inspect and maintain without the presence of roots. In addition, by reducing the number of times crews had to perform redundant root control work, field crews would have time to focus on other priority needs.
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