It’s an essential part of the city’s infrastructure that residents never want to see.

Millions of linear feet of sewer pipes lie buried underground across Aurora, and while the network remains invisible to its users, it is still subject to the same kind of wear and decay that’s hit the city’s roads and bridges during the past five decades.

“The need is there. These things are just so out of sight, out of mind. But if we have sewer failures … the cost is a lot more to clean those up after they break,” said Aurora Capital Projects Manager Larry Catalano in article in the Aurora Sentinel.

More than 2.5 million linear feet of sewer pipes across the city have been designated as poor and in need of repair by the city. Tree roots have pushed their way in through cracks, and extraneous water is also making its way into the pipes. These 50- to 60-year-old clay pipes lie deep underground, but city maintenance officials want to repair the lines without turning up even a shovelful of earth.

Using a technology called cured-in-place-pipe repair, Aurora Water officials have started planning a multimillion dollar overhaul to these aged parts of the city’s underground infrastructure during the next three years, a reconstruction they say will have very little impact on traffic patterns and residential sewer systems.

“The (CIPP) process is not very invasive at all. There would be very little disruption to traffic and very little disruption to people in their homes,” Catalano said. “We don’t anticipate having to dig up anything.”

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Catalano said the technology would help reduce excess water flows into the system and lessen the chances for sanitary sewer overflows and stoppages.

The approach is aimed specifically at more than 2.5 million linear feet of vitrified clay pipes in Aurora, a standard type of pipe used in construction during the 1950s, 1960s and 1970s, but that has since been replaced with polyvinyl chloride pipes, which are more lightweight and have fewer joints.

“The VCP pipes can be up to 60 years old. That used to be the standard for sewer pipes,” said Greg Baker, spokesman for Aurora Water. “A lot of homeowners and cities started with these clay pipes.”

The city’s Water Policy Committee has given initial approval to a plan that would expend no more than $5 million per year during the next three years to replace sewer lines in specific sections of Aurora. The bid process is scheduled to start next week, with approval from the Aurora City Council expected in May.

The CIPP repair would begin in June or July.

“The area that we’re looking at right now to rehabilitate is 26th Avenue on the north side, south to East Colfax Avenue,” Catalano said. “Then we’re looking at Yosemite Street on the west to Peoria Street on the east.”

The CIPP process, which implements resin-saturated felt tubes, steam heat and robotic cutting tools, is nothing new. First developed in 1971 by Eric Wood, the technology uses the existing pipeline as a conduit to create an inner replacement.

“It’s basically a felt tube that’s been impregnated with resin. That tube is pulled into a pipe,” said Aura Joyce, spokesman for Missouri-based Insituform Technologies, Inc., a company that has regional offices in Littleton. Insituform’s founding followed Wood’s patent of the CIPP process in the early 1970s. “Once it’s in place, we cure it with hot water or steam. That forms a new pipe within that existing pipe … We go in through the manholes.”

While the CIPP process has existed for more than 35 years and has been implemented in other parts of the state, Aurora officials said its implementation in the city will stand as a first. It represents a departure from their previous approach to the problem, which relied on a priority system that ultimately proved ineffective.

“What we’ve done in the past is that we’ve budgeting rehabilitation dollars and not getting it spent,” Catalano said. “We thought we were taking care of the high priorities first … The approach was trying to take care of the critical needs, but it wasn’t very cost effective.”

In the 2008 adopted budget, Catalano said the city spent about $4,000 for every mile of sewer pipe in the city, a sum that went largely toward seeking out roots that had made their way into the system.

“It was cleaning out root intrusions — when the roots grown in the sanitary sewers,” Catalano said, adding that the phenomenon is especially pronounced during a drought. “All the trees want to search for water — they’re really sending out their roots now. They essentially go down the pipe until they find water. What happens is those roots cause backups. They can back up into people’s basements or the worst-case scenario, cause a creek or street overflow.”

The CIPP replacements will help improve the capacity of the sewer system, Catalano said, and reduce annual cleaning costs associated with routine root removal.

But even as the city plans to replace hundreds of thousands of feet of clay pipes throughout the city during the next three years, the sheer scope of the existing network means the overall replacement effort may last much longer.

“The city has 2.5 million feet of vitrified clay pipe. They were even installing this pipe in the late ‘70s and early ‘80s. There’s a lot of it in our system,” Catalano said. “A lot of these have just exceeded their useful life, so it’s time to rehabilitate the system. We’re probably looking at between 10 and 20 years to do it all.”

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