A project to replace two badly corroded sewer pipes underneath Salem Harbor in Massachusetts was recognized by the American Public Works Association (APWA) as its environmental Public Works Projects of the Year for 2016 for projects of $5 million to $25 million.
WSP provided condition assessment, preliminary and final design, permitting and construction administration/resident inspection for the Marblehead Pipeline Replacement Project.
“It was an honor for WSP and a well-deserved recognition of our client’s actions to proactively address a potentially disastrous pipeline failure in a way that produced a ‘triple bottom line’ benefit – economic, social and environmental,” said Christopher Barnett, principal-in-charge for WSP.
The award promotes excellence in the management and administration of public works projects by recognizing the alliance between the managing agency, the consultant/architect/engineer and the contractor. It was presented on Aug. 29 during the APWA’s Public Works Expo in Minneapolis, Minnesota.
The project began with a curious observation made in February 2013 by a recreational lobsterman.
“Salem Harbor is still covered with ice at that time of year, but a lobsterman noticed an unusual patch where the ice has melted away, with seagulls dive-bombing the opening,” Barnett said. “He contacted the Town of Marblehead, and South Essex Sewerage officials soon determined that the melting was caused by a leak of a sewer pipe underneath the harbor.”
Fortunately, the leaking pipe was shut down before any serious environmental damage had occurred, and flow was transferred to the parallel existing pipe to maintain uninterrupted service between Marblehead and the South Essex Sewerage District (SESD) waste water treatment facility, located on the other side of the harbor in Salem.
In cooperation with federal, state and local agencies, SESD performed emergency repairs to the pipe. SESD retained WSP in April 2013 to conduct a condition assessment of the damage to the 6,000-foot-long twin pipes. Divers dug through several feet of sediment at the bottom of the harbor to inspect and test the ductile iron pipes at several locations along the length of the pipelines, which revealed the extensive corrosion damage that had taken place.
“It was surprising that the pipes lasted as long as they did,” said Scott Williamson, project engineer. “Ductile iron was a new and popular material to use in the construction of pipelines when these pipes were installed in the mid-1970s. Unfortunately, the material did not live up to people’s expectations for this marine application.”
The pipes survived 40 years with routine maintenance, but the pipe leak raised a red flag about their long-term durability.
“We conducted non-destructive ultrasonic testing to test the wall thickness of the pipes,” said Rachel Burckardt, project manager. “They are very critical pieces of infrastructure that handle sewage from Marblehead, so we needed to determine if corrosion was affecting the whole pipe.”
The assessment found several areas of advanced corrosion, and WSP recommended replacement to avoid potentially devastating environmental consequences and service disruption. “The existing pipes were in fragile condition and it was simply too risky to attempt to repair the pipes,” Burckardt said. “Replacement was the only viable option.”
Once the assessment was complete, WSP shifted gears and began the design work.
“The design team was able to move forward as soon as assessment results had been reviewed by SESD and accepted,” Barnett said.
The project team overcame numerous challenges: zero tolerance for service interruptions, a sensitive marine environment, historically harsh weather conditions and working underwater in a popular boating location.
“The pipeline crosses one of the busiest recreational harbors in the U.S., which required careful scheduling to minimize conflicts with moorings, recreational boating and commercial shipping,” Barnett said.
“It’s a real honest-to-goodness recreational harbor,” Williamson added. “Once spring arrives, there are boats out there by the thousands, and they are an important part of the local economy. We wanted to impact that as little as possible.”
The project marked the first major subsea sewer in New England installed by the “float and sink” method. The method requires 500- to 1,000-foot-long pipes to be strung out and floated on the water surface. Environmental protections, such as floating booms and silt curtains, were also employed on the harbor surface throughout construction. Innovative design measures and ongoing coordination with harbormasters and boaters ensured the public safety at all times, as this was a paramount concern. Avoiding conflict was key.
It was also the first major marine pressure main in Massachusetts constructed out of high-density polyethylene (HDPE) plastic.
“Use of HDPE provides longer service life than alternative pipe materials, and avoided the need for marine pile driving associated with conventional ductile iron or concrete pipelines,” Barnett said.
The project also included successful environmental mitigation and monitoring during construction, such as the protection of sensitive eel grass beds close to the pipeline alignment.
“This was also one of the first marine archeology programs, which focused on examining paleolithic soil materials for signs that could indicate human habitation of the harbor area during the period following the last ice age,” Barnett said.
“Exploration of the sea bottom for artifacts is not something that comes up too often on a project,” Burckardt added. “Fortunately, our firm’s marine and coastal experience on other projects has given us a relationship with specialty firms who were able to help us meet that requirement.”
The project was bid in January 2015 with Caldwell Marine International selected as the contractor. Despite a very snowy winter, the project advanced through the winter and spring, with a temporary bypass pipe placed into service in May 2015, ahead of the peak boating season.
By August 2015, both pipes were installed and functional, with full completion of the project in May 2016. The new pipes provide improve capacity and redundancy, and are expected to provide service for well over 50 years.
Burckardt said it was rewarding to create something that will serve the community for decades to come.
“We physically got to oversee every part of the project,” she said. “Even if it’s something the public will never see, it was very satisfying to have that sense of ownership from inception through completion – to see the original concept reach its fruition.”
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