CIPP Proves Best Option Under Complex Site Conditions

North Andover, Mass., is a community of approximately 30,000 residents just north of Boston that had been experiencing chronic backups and sanitary sewer overflows (SSOs) during wet weather events for years. Rehabilitation, or even just investigating the issue, seemed next to impossible as the town’s interceptor is located next to a river prone to flooding, a very busy interstate highway, and an active commuter rail line.

The complicated logistics of upgrading this aging piece of infrastructure would prove to be just the beginning in terms of completing the project successfully, but using a holistic approach and trenchless methods minimized disruption to the surrounding community and significantly improved the health and stability of its sewer system.

The project entailed rehabilitating approximately 2,700 lf of a 24-in. reinforced concrete pipe (RCP) gravity sewer that was bordered by the Shawsheen River, Interstate 495, and a Massachusetts Bay Transportation Authority (MBTA) Commuter Railway, distinguishing it from other projects where a traditional open-cut replacement of the pipe would not pose much of an issue.

Before taking any other action, the town hired a pipeline assessment contractor to inspect the interceptor using closed circuit television (CCTV). The inspection, which revealed heavy root intrusion, grease buildup, groundwater infiltration, and deteriorated pipe conditions, confirmed two things: Rehabilitation was needed, and that the interceptor’s tricky location wasn’t the only obstacle they’d have to overcome.

RELATED: Lateral Lining: Comprehensive Approach to Sewers

Portions of the interceptor were more than 75 percent blocked due to roots and grease buildups that were so severe a CCTV inspection could not even be conducted on one 70-ft section. It became obvious that, to avoid potential sewerage surcharging into nearby residences, SSOs into the resource areas during high-groundwater conditions, or complete pipe collapse and failure, an expedited permitting, design, and completed solution would be necessary.

One of the main concerns when evaluating the alternatives — root removal and cleaning, digging up and replacing the pipe, and no-dig rehabilitation —was how the challenges faced during inspection would affect the outcome of rehabilitation efforts. Whichever alternative was chosen, innovation and progressive techniques were certainly necessary in order to address all the existing issues with minimal disruption to the surrounding area and before the next high-groundwater, wet weather event occurred. With this in mind, the project involved constructing a 1,500-lf access road through 30 years of overgrown vegetation; locating manholes; mechanical root removal; cured-in-place pipe (CIPP); monolithic manhole liners; bypass pumping; wetland protection and restoration; and environmental, MassHighway and railroad permitting.

CIPP Allows for Timely, Cost-effective Solution

CIPP was ultimately selected to repair the interceptor for a few reasons: ease of installation, a more limited project footprint, cost and the impact to the surrounding area. The engineer worked closely with the local conservation commission, the Massachusetts Bay Commuter Railroad, and Massachusetts Highway Division to expedite the permitting process, which was made possible due to the project’s minimized impact.

RELATED: Sherwood, Ark., Tackles Manhole I/I Issues Using Trenchless Methods

Work began as the easement was cleared to facilitate Vactor cleaning truck and camera truck access to select manhole structures, and CCTV cleaning crews and root treatment crews worked tirelessly on root removal. The crews discovered that the segment of inaccessible pipe was merely a 70-lf rootball impacting up to 75 percent of the cross sectional area, but aside from that, the pipe was mostly without structural defects. This was much needed good news, and after removing the roots with high-pressure water jetting and mechanical cutting, the pipe was ready for CIPP liner installation. From start to finish the CIPP process took two weeks and was completed with five, hot water cured shots ranging from 250 lf to 700 lf each. After the installation and post-CCTV inspection, a cementitious coating was used in manholes to seal up annular spaces between the pipe and the CIPP liner and provide additional infiltration protection.

Town Sees Multiple Benefits from Project Approach

The project accomplished the goal of providing a leak-free sewer interceptor that would no longer experience infiltration-related issues, and also reduced the overall capital cost significantly by selecting CIPP. Traditional, open-cut alternative could have cost nearly $1 million but by using CIPP, the cost was reduced by more than half to $425,000 due to factors like the length of the construction phase, limited wetland protection and restoration, and the negligible impact on the interstate highway and commuter railway.

Using CIPP had social benefits for the Town of North Andover too. The reduced overall project cost improves user affordability too — keeping out infiltration reduces the number of gallons that have to be treated, offsetting increases or even lowering water and sewer bills. Some estimate that CIPP technology can cut project timelines by a factor of four, which is crucial for a project like this one that was conducted in a high traffic area with the potential to impact thousands of commuters per day. Lastly, CIPP helped improve worker safety by allowing the pipe to be rehabilitated underneath the nearby railroad while commuter trains continued their regular schedule, rather than digging through the railroad and impacting commuters. This also translated to zero downtime or schedule changes for the commuter rail or interstate — a feat that would have been impossible had open-cut construction been used.



CIPP rehabilitation also had a significantly smaller impact on the environment than a traditional repair method would have. An open-cut approach might have required digging through wetlands, river banks, flood areas, and areas of endangered species, but with CIPP, none of that digging was required, thereby avoiding detrimental impacts to ecosystems or habitats and minimizing the restoration necessary at the end of the project. This greatly reduced environmental impact simplified the project’s permitting, saving the project team time that could be spent on directly addressing the issues at hand.

The challenges encountered during this project bring home how important holistic thinking is when determining pipe locations during sewer construction projects and shed light on how getting to the root of a problem prior to any investment in other infrastructure repairs can save a town from significant costs and prolonged ad-hoc repairs. One of these challenges was clearing the easement to gain access to manholes for both the design and construction efforts, as poorly maintained infrastructure easements pose significant obstacles to access when emergencies occur. In this case, if the easement had been cleared annually, the environmental permitting and access would have been simple; however, when dealing with 30 years’ worth of tree growth in a bald eagle habitat, the environmental permitting process requires substantial consideration. In the end, though, trenchless technology made overcoming all of the project’s challenges easier in comparison to an open-cut repair project.

RELATED: NASTT, NTA Join to Promote Trenchless Technology in the Northeast

In engineering, finding the right solution to a problem is always satisfying, particularly when the benefits of a successful project are so visible for the community. A solution that strikes the perfect balance on a project’s financial, environmental, and social bottom line is not always easy to come by, but through a careful examination of all the alternatives, it is certainly possible. In this case, CIPP proved to be the “right solution” as it was able to resolve the sewer backups and overflows issues while saving money, protecting the environment, and causing minimal disruption — achieving the goals outlined at the project’s outset while continuing to develop a strong partnership with the Town of North Andover.

Justin deMello, P.E., is a project manager at Woodard & Curran with over a decade of experience working on wastewater, water, and water resource projects for municipalities and private sector clients.