As sea levels rise, many coastal communities are talking about building higher to avoid potential floodwaters. But in Portland, engineers have gone underground on a massive scale to improve the health of Casco Bay and strengthen the city's resiliency against increasingly severe storms.
The most visible aspects of that decades-long project can be seen today by drivers along Interstate 295 near Portland’s Back Cove in the Bayside neighborhood. That’s where construction crews are installing four massive, underground tanks that hold millions of gallons of a combination of stormwater and untreated sewage that otherwise would have dumped straight into Back Cove.
“So welcome to tank Number 1,” Bradley Roland, senior project engineer with Portland’s public works department, said recently after he and a group descended several stories below ground. Tank Number 1 is a cavernous concrete bunker about 1.5 times longer than an Olympic pool and three times as deep with a capacity of nearly 800,000 gallons.
This story is part of our series "Climate Driven: A deep dive into Maine's response, one county at a time."
“Normally, 90% of the city’s storms are less than one inch of rain. And that has begun to change and so they are becoming a little bit more intensified,” Roland said. “This whole system here is 3.5 million gallons and is designed to collect that one-inch rain event from a CSO standpoint.”
CSOs are combined sewer overflows, which are a big problem for a lot of older East Coast cities, including Portland. They are a legacy of decisions made decades ago to consolidate stormwater and sewage infrastructure. That system still works well most of the time. But when the rain falls too hard and fast for Portland's treatment plants to keep up, that unhealthy soup of stormwater and untreated sewage has to go somewhere. So it gushes from more than a dozen CSO outfalls directly into Back Cove, Portland Harbor or several local streams in violation of the city's federal permits.
Roland said the system had 164 million gallons of CSO discharges last year.
“In Back Cove, we had 92 million [gallons] and these three combined sewer overflows were 70 million of it,” he said while pointing to the huge, circular holes in the wall that will eventually carry the mix of sewage and stormwater into the tank until it can be treated by Portland Water District’s plants. When combined with 2.25 million additional gallons of storage nearing completion across Back Cove, the new system is expected to cut Portland's CSO totals in half.
“So that’s going to be huge. And it’s taken a long time to get here,” Roland said.
Portland’s decades-long project to separate those CSOs began in the 1980s to bring the city into compliance with federal water quality permits rather than to address the implications of a changing climate. But rising sea levels, more powerful precipitation events and larger storm surges add urgency to the project.
The price tag several years ago was expected to be around $250 million, much the cost of which is born by Portland Water District ratepayers.
It's an example of the complex — and costly — infrastructure decisions facing many of Maine's coastal towns as the climate shifts.
“I think communities are definitely starting to have these conversations,” said Gayle Bowness, who works with coastal and island communities as part of the Gulf of Maine Research Institute’s municipal climate action program.
“We’re planning for a future we’ve never experienced. So that’s a very difficult thing to envision,” Bowness said. “And it’s a difficult thing to bring your community members on board with as well.”
Bowness and her team connect communities with highly detailed maps showing various sea level rise projections, oftentimes down to the property level. They enlist local citizens to gather on-the-ground data to better understand localized flooding. And GMRI works with the Island Institute and other groups to facilitate community conversations about how to prioritize limited resources.
“We are going to have to invest in adapting to climate change because change is coming, it’s really inevitable,” she said. “So how do we make sure that those dollars that we are investing are also not just supporting climate adaptation but are reflective of a what community values and needs and wants.”
Portland and South Portland may have set the benchmark in Maine for climate planning.
The two cities spent years developing a 300-page report, called One Climate Future, that lays out a vision for buildings, roads and waterfront areas as well as strategies for reducing greenhouse gas emissions. The report also discusses potential policy changes, including stricter building regulations in areas likely to be flooded more often as sea levels rise.
Bill Needelman, Portland's waterfront coordinator, said many of the city's private pier, boatyard and building owners along Commercial Street are already taking steps.
"Because we've already experienced nearly a foot of sea level rise over the last hundred years and many of our piers are well over 100 years old,” Needelman said.
Part of the city's historic working waterfront already flood more frequently during storms and higher annual tides. And last December's pre-Christmas storm demonstrated the dangerous potential when storm surges and astronomically high tides coincide.
"Dumpsters were floating across pier decks — it was dramatic,” Needelman said.
City-owned infrastructure like the Portland Fish Pier and the Ocean Gateway terminal as well as Commercial Street itself are more elevated than those older piers. But Needelman said the city can't get complacent. And he adds that private waterfront property owners will have to gauge their own vulnerabilities and potential for adaptation.
"Open yard construction is much easier to elevate than infrastructure with buildings,” Needelman said. “Buildings with very tall first floors can adjust the height of that first floor and that may be an option for some property owners. Some buildings are going to be much more difficult to adapt than others."
While the climate crisis undoubtedly brings major challenges, Needelman said it could also present opportunities. Portland’s working waterfront is already a major port for sustainable commercial fishing and aquaculture, which some view as parts of a much-needed global shift away from more carbon-intensive land-based animal agriculture. Portland’s deep harbor and existing infrastructure can also support other industries like those needed to support offshore wind, he said.
Back across Portland peninsula, city engineer Bradley Roland and crew have re-emerged from the depths of tank Number 1 into the sunlight and construction zone along Back Cove.
Roland said this site should be complete by the end of the year while the 2.25 million gallon CSO storage complex across Back Cove could be operational this month. Once the Back Cove South project is complete, crews will re-sod the grass and re-create the heavily used soccer fields only with improvements.
"And as far as climate resiliency, when we started down here we recognized that the playing field flooded a number of times every year,” Roland said. “And talking with the parks department, it was decided that we would raise the whole thing. So when we're all done, the playing field will be about three feet higher than it was before."
The adjacent section of Back Cove’s walking and biking path was also elevated during the project, all of which should translate into drier and cleaner sneakers — not to mention cleaner and healthier waters in Back Cove and Casco Bay.
