After tree roots infiltrate a prominent Eagle River Water & Sanitation District pipe, repair uses specialized technology to solve the problem

In June, Eagle River Water and Sanitation District staff learned of a problem: The sewer interceptor pipe running through EagleVail had an irregular flow pattern. While there were only minor impacts to service at the time  — one customer’s wastewater was not draining properly — an investigation of the pipe revealed a greater issue.

Tree roots in several places infiltrated the vitrified clay pipe that made up the sewer interceptor. An interceptor, also called a trunk line, is a larger type of pipe that absorbs the flow from smaller pipes as it moves down the system. This particular trunk line is essential because it carries wastewater between Vail and Avon. The pipe was partially filled with roots in some places, leaving significantly less space for wastewater to flow.

While the issue was non-emergent — many days, wastewater only fills a third of the pipe — it remained top of mind for district staff. The monthlong repair, which cleared out the roots and installed a cured-in-place pipe to keep them from returning, wrapped up last month.

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What was the project?

From Oct. 22 through Nov. 20, district staff supervised a specialized contractor-led repair using a cured-in-place pipe liner, essentially a custom-made sleeve that hardens in place once it is inserted into the pipe, creating one long pipe surface and reinforcing the existing pipe’s walls.

Brad Zachman, the district’s director of operations, Niko Nemcanin, the district’s field operations manager, and Micah Schuette, the project manager, presented the construction progress to the district board on Dec. 5.

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When Eagle County’s upper valley was starting to fill out in the 1960s and 1970s, the district installed a sewer system to serve its new residents. That system was primarily made out of clay pipe. 

As clay pipe ages, water sometimes escapes from the joints where individual pipes are connected, and tree roots will trace their way to the source. Over time, roots can create significant impediments within the pipe as they grow, fed by the nutrients flowing through the pipe. 

“When you have the trees planted on top of our pipes and our easements, it can lead to this type of intrusion,” Schuette said.

It is in the district’s rules and regulations that trees — along with any other landscaping or structures — should not be planted or built within district easements.

The sewer interceptor in EagleVail runs from West Vail to Avon, carrying wastewater between the district’s Vail Wastewater Treatment Facility to the Avon Wastewater Treatment Facility. The pipe operates all day, every day, and is the main transporter of that area’s wastewater.

The four sections that needed to be repaired totaled 1,260 linear feet long, making it the biggest pipe-lining project the district had ever taken on, Nemcanin said.

The process of fixing the pipe required multiple steps. First, the pipe had to be bypassed, moving its contents into an alternative pipe without disrupting service. The sewer interceptor then had to be cleaned of tree roots and rocks with specialized tools. Finally, the liner was installed.

Residents of EagleVail and Avon may be familiar with the bypass, a 3,000-foot-long pipe that ran aboveground on the south shoulder of U.S. Highway 6 from east of the Post Boulevard roundabout to Stonebridge Drive.

The liner, which is 9 millimeters thick, was custom-made to fit the pipe. The pipe was measured several times before the liner was made.

“One of the risks of the CIPP is if you haven’t thoroughly characterized the inside of the pipe and they show up with this impregnated folded liner and it’s the wrong size, or you run into a situation where the pipe is damaged … you eat the cost of that liner because it can’t be used” in another pipe, Zachman said.

The liner arrived looking like a heavy, deflated bag, Schuette said. The liner was inserted into the pipe and was then molded to the pipe with heat. During transit, the liner was kept cold with ice. “As soon as it heats up, then it starts to cure,” Schuette said.

To mold the pipe in place, steam was passed through the pipe. A small wire running through the bottom of the pipe measured the temperature, as the liner had to reach 150 degrees for around an hour to properly harden in place.

While there are no joints in the cured-in-place pipe, an “important disadvantage” of the liner is that when sections of the liner need to be cut out where the sewer interceptor connects to other pipes or manholes, those can become “a pathway for roots,” Zachman said. To combat this, special inserts will be added to block out the roots in those places.

Will there be more repairs in other areas?

In the end, the pilot project cost $516,000. Schuette called this “a pretty good price” compared to an open trench repair, which would have required excavating and potentially replacing the whole pipe and the roadway above it, a much longer, more disruptive and costlier project.

While the EagleVail repair was a big undertaking, the four sections made up only a quarter mile of the roughly 18 miles of clay pipe in the district’s system. Any section of pipe that is made of clay will need to be investigated for similar root infiltration. Though not all 18 miles of pipe are interceptor, most pipe installed between Vail and Avon is likely clay. 

If the pipe were to be installed today, district staff would use a new PVC technology that is flexible, will not crack lengthwise, and, most importantly, has gaskets that prevent trees from gaining access to the interior, Nemcanin said.

The district is already beginning talks with contractors about the next phase of the project.

In addition to the repairs in EagleVail, the contractors investigated three segments of pipe upstream and downstream of the repaired sections and did not find major intrusions, Nemcanin said. Notably, these un-infiltrated sections did not have large trees on or around them.

The section of pipe from Avon to Edwards is made of PVC pipe and thus less susceptible to the root infiltration issue, so the investigation for other damaged sections of pipe will head east from EagleVail. The presence of trees on the aerial map of the area will help identify priority areas for investigation.

As other infiltrated sections of pipe are identified, the results of the contractor’s inspection will determine whether a full replacement is needed, or a cured-in-place liner will suffice.