January 4, 2019The No. 1 job for wastewater workers is to keep the sewage in the pipes. This statement is pretty straightforward, yet simplistic in message. That is the goal of everyone whose job it is to maintain underground utilities.
The City of Fresno, California, takes this goal to heart, especially in its work to clear its underground sewer lines of dreaded and damaging roots that infiltrate through cracks and joints. Cities around the world fight this good fight every day, with the City of Fresno turning to the use of chemical root control to keep its sewer lines free of root blockage and damage.
“I had a boss many years ago tell me that my No. 1 job is to keep the sewage in the lines,” says Art Alvarez, wastewater manager for the City of Fresno. “There are a lot of things that go along with that [advice], such as dealing with roots, which cause blockages, which cause sewage to come out of the pipes. Roots also cause other damage such as separation and regrowth. Roots restrict flow.”
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Fresno — with a population of more than 500,000 — is situated in central California, about three hours south of San Francisco and four hours north Los Angeles. The City’s sanitary sewer system is comprised of more than 1,600 miles, with roughly 24,189 sewer access structures, 55 junction structures and 15 lift stations; its service area covers approximately 225 sq miles.
A portion of the City’s sanitary sewer lines goes back to the late 1890s, with a majority of the entire system made up of vitrified clay pipe (VCP); the rest of the pipe is a combination of concrete, cast/ductile iron and PVC. Approximately 81 percent of the system was installed after 1950 with 23 percent installed during the 1970s.
Alvarez describes the overall condition of Fresno’s sewer pipes as “fairly good,” considering their age and pipe makeup. “When you have a large portion that is [vitrified clay pipe], there’s always going to be cracks and issues,” he says. “But the overall health of the system is really good. The City has been proactive about rehabilitation, especially with the large trunk lines. Now, we are starting to reach into more of the residential areas. When we are doing root control, it’s pipe preservation.”
For years, the City of Fresno, like many cities, used mechanical root cutting as part of its preventative maintenance program; however, using that method alone will not stop root intrusion and can make the problem worse. Fresno began in earnest to assess the condition of sewer lines in 2007 when it added three Aries CCTV cameras and trucks to replace the one camera and truck it already had, with a fourth camera and truck added in 2016. The purpose was to evaluate and take a hard look at what was going on underground.
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“When you get into older areas, where it’s predominately VCP, you start to see how the soil affects the pipe as far as sags and offsets,” Alvarez says. “Then you see the roots and the effect the roots have and how it grabs debris, along with any grease you get in the system: a combination for blockages and restricted flow.”
The revelation that came out of the CCTV assessment, Alvarez says, was that the City wasn’t doing enough to combat the root problem. The root masses only got worse. “Any time you cut a root back, it grows back stronger,” he says. “So anytime we would go in [to cut] on a frequency basis, we were actually causing the problem to come back a lot quicker. If you are just cutting [the roots] back, you are inciting the growth.”
Alvarez explains that prior to using chemical root treatments, the City was doing frequency-based cleaning — a solution that really wasn’t a solution at all. “Basically, we said we were going to get into these areas once a year and clean every line within the City,” he says. “Areas where we’ve had more issues, we’re going to clean them every six months. What you start to find is that the six months turns into every five months, then four months because they were coming back stronger than before.”
A few years back, the City decided to check out the use of chemical root control and invited a few vendors in to conduct demos on areas with root issues. In the end, Fresno went with Vaporooter products to treat its root intrusion issues.
Fresno wastewater operations supervisor Tolbert Campbell oversees the City’s root control program. He says besides having a great result with the product, the City likes the flexibility the product offers by allowing its workers to apply the treatment themselves. “We tried having an outside vendor come in and do it,” Campbell says. “It worked but for us, the biggest drawback is that you lose some of the control when you do that. You have to fit into their schedule as much as they have to fit into yours. By being able to do it on our own, we take ownership of it and gives us more flexibility.”
Alvarez says the City has been using chemical root control in combination with mechanically cutting roots for the last four years; however, the last two years the program has been much more intensive. “The first year was a learning curve [with the program]. We are building up our cycles,” he says. “We are actively going into our second year of a full-on cycle.”
Currently, the City cleans out the lines prior sending its Aries cameras for inspection and assessment and then chemical treatment. After the initial treatment on a pipe, crews return the following year for another dose and then two years after that and three years after that treatment. “The end result is that you want each pipe on a three-year treatment cycle,” Alvarez says. “We are trying to space it out so we have an even number of cycles each year.”
Beyond the Aries and Vaporooter equipment and product, Fresno also uses CUES TruVue system during the root removal process, giving the operator real-time video to maximize the use of equipment while at the same time protecting the video equipment.
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The City is more than pleased with the initial results of the program. “We have an area where we’ve done just regular cleaning and [mechanical cutting] over a period of time vs. another area where the chemical foam was used and there is a huge difference,” Alvarez says.
He says the crews are pretty comfortable with the program and the process. “The biggest thing is the results,” Alvarez says. “You go back and look at the videos and you see that there’s definitely changes in what’s in there. The documentation and data you collect keeps you motivated to do more. You know you are doing the right thing.”