SEWER: No Big Dig

A small New England community finds the solution to its inflow and infiltration issues through trenchless technology and a no-dig approach

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As a suburb of Boston, Mass., the Town of Dedham was all too familiar with the pitfalls, disruption and enormous costs of infrastructure projects involving a “big dig.”

Not wishing to experience that firsthand, Dedham turned to trenchless technologies, especially cured-in-place pipe lining (CIPP), when looking for solutions to address its inflow and infiltration issues. A program of planned inspection, pipe cleaning, and follow-up rehabilitation with CIPP lining has significantly reduced I&I and as a result will bring savings in operational and wastewater treatment costs in the years ahead.

Dedham is one of 43 member communities of the Massachusetts Water Resources Association (MWRA), which treats wastewater for its members and rates their I&I percentages based on flow-metering studies. In 2003, Dedham ranked second for highest levels of nonsanitary flow into the treatment facility. Some 75 percent of the town’s 4.04 mgd was attributed to I&I, and that heavily impacted the sewage rates its residents paid.

Escalating rates and an outcry from town residents led the community to create a separate Engineering Department in 2005 to focus strictly on the underground infrastructure and capital improvement projects to reduce I&I and improve the overall performance and health of the wastewater collection system.

Knowing the score

“One of the first things we had to do to address I&I was to learn the real status of the sewer system,” says David Field, P.E., director of engineering. “None of the information existed in-house — it was with a private consultant. We didn’t know what lines had been inspected or not inspected or what our situation truly was.”

Using the town’s ESRI ArcMap geographic information system, Field and his department set to work compiling 2,300 inspection records, scanning them, and linking the scanned documents to the map database pipe segments. This created a list of which lines had been inspected and when, and told them how much of the system still required attention.

The GIS database revealed that as of the end of 2006, about 72 miles of Dedham’s 90 miles of mainlines had been inspected, at an average rate of 4.8 miles per year. The system is gravity-based, and lines range from 6 to 24 inches. Most pipes are VCP, although cast iron was used for crossings under streams and railroads, and large-diameter interceptor lines were built from brick and mortar.

The past inspections had been conducted for different reasons: some for an overall survey of system performance, and others to investigate trouble spots. In 2007, Dedham contracted for inspection of 32 miles of pipe by year’s end. The aim was to provide a complete picture of the health of the sewers and manholes as the basis for an I&I remediation action plan. The inspection data was to be supplied in digital format utilizing the NASSCO PACP standard and would be integrated with the GIS database.

Repeat offenders

Among its findings, the inspection uncovered a blocked main barrel and a partially blocked emergency barrel in a siphon that had been the site of numerous sanitary sewer overflows. To address the issue, the town ordered the immediate heavy cleaning of the twin 10-inch siphon using a Vactor combination truck to clear both barrels. The remote location of the line required the contractor to use a small boat to access the downstream chamber. After two weeks of heavy cleaning, the problem was resolved.

Throughout the inspection project, crews had to clean and inspect cross-country sewers, some which had received no attention since their installation because of steep grades or closeness to wetlands. An example was the Wigwam Brook line, an interceptor running between two main thoroughfares and through private property, including Ursuline Academy.

To inspect the pipe, the town had to secure permission from the academy and seek approval from the Dedham Conservation Commission to create a temporary access road through an adjacent wetland area and across a small stream.

In the end, the contractor found that the line was subject to significant infiltration even during a drought in which most of the wetland was dry. “Although the design of our infiltration reduction plan was not complete, at that point we knew we probably would have to use CIPP for the majority of our I&I rehabilitation repairs,” says Field. “The inspection showed that the line was leaking like a sieve. The window of time allotted to us by Ursuline Academy was small, so to take advantage of the access roadway, we issued an emergency change order for the immediate CIPP lining of 1,997 linear feet of 12- and 15-inch vitrified clay pipe.”

Because of the pipe’s length, a sharp bend in one section, and limited access points, the town chose to install the lining in two 1,000-foot sections from a single access manhole in the middle. Within hours of the liner installation, the surrounding wetland water level rose by 1 to 2 feet, indicating the extent of the infiltration.

No-dig approach

At the end of the inspection contract, Field and his team, working with the local consulting firm of Weston & Sampson Engineers Inc., began developing a comprehensive program to eliminate an estimated 1.2 million gpd of infiltration.

The town needed a cost-effective method to address the many trouble spots the inspections found. “The town had been dealing with I&I primarily by open cut and replacement of sewer mains,” Field says. “They would do drainage lines, and they would repair sidewalks and perhaps construct a whole new street where they’d installed a new sewer main.

“That method is great when you have an unlimited budget,” he notes. “They had only been able to do a handful of those projects, because the cost was prohibitive, and there wasn’t much actual I&I benefit for the money. In my experience with inflow issues, trenchless technologies were much more cost-effective. The nature of our system lent itself well to CIPP, and using that method would allow us to get a lot of I&I work done for dollars invested.”

Case in point: the Washington Street Sewer Replacement Project, designed before the Engineering Department was created and before the inspection program. The project called for open-cut and replacement of a line as deep at 30 feet in an existing street. When Field came on board, he examined the project carefully and saw that the open cut/replacement was not feasible without significant utility conflicts and other remediation risks.

The Engineering Department halted the project to review alternatives. An investigation found that CIPP lining would solve the problem and save the town over $700,000. “The old mindset was that if a pipe was old, it had to be replaced,” says Field. “This project proved that trenchless technologies could save us money and limit disruption from weeks to days or hours.”

Bundling projects

As trenchless technologies proved to be the right solution, Field and the consulting engineers created a final project design that called for testing and sealing 48,356 linear feet of sewer main, testing and sealing 557 service connections, and installing 21,867 linear feet of CIPP liner. The work also included 1,146 linear feet of short liners and rehabilitation of 3,252 vertical feet of sewer manholes using QM-1s, spray-applied cementitious lining by Quadex Inc.

To help Dedham get the most from its budget, Weston & Sampson recommended bundling similar repairs, such as groups of manhole-to-manhole runs. This would help the contractors deploy crews cost-effectively and so generate lower bids. The installation of the manhole-to-manhole runs was awarded to Insituform Technologies Inc.

The same principle held true in deciding which lines to repair with short liners installed by National Water Main Cleaning Co., using an epoxy-based, impregnated polyurethane-coated felt tubing liner. “We look at their recommendations and tweak them to make sure we can address the most critical areas, especially some of our interceptors, which are the backbone of our system,” Field says.

As part of the program, Dedham also examines and tests every joint and service connection for air-tightness. If a gap is found, chemical grout is applied to help stop water infiltration until a more permanent CIPP repair can be performed.

Funding for the project came partly from the MWRA and the balance from sewerage fees. Field notes that community support has been strong because of the department’s outreach and communication. Before all CIPP installations, the contractor delivers notices describing the work and asks residents and businesses to limit water usage while the liners are installed. Crews notify property owners one week in advance, 24 hours in advance, and again when the lining process is complete. Disruption to the property owner is usually limited to one day or less.

Proof positive

To date, Dedham rehabilitated sources of most of the system’s 2.5 mgd of observed infiltration and has gone from second to ninth place on MWRA’s list of I&I contributors. The Engineering Department plans to re-inspect the entire system on an ongoing basis to continue to reduce and eliminate sources of I&I.

The program has also helped reduce day-to-day maintenance costs. As the inspection program has pinpointed root intrusions and grease that contribute to SSOs, the Public Works Department addresses those issues on a preventive basis. That reduces the number of emergency calls. All this work is documented electronically and linked to the GIS database.

“Our biggest challenge when we started was being faced with the unknown,” says Field. “Recreating the history of our system over the last 20 years was a big obstacle. Now that we’ve compiled all the data into one central GIS system, we know where we stand and can manage our system more effectively. It will now be a lot easier going forward, and we’ll be able to bring down those I&I levels even further.”


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