At the end of July 2023, 3.07 inches of rain fell on Boston in a single day. The city’s sewer systems were overwhelmed, leading to a discharge of sewage into Boston Harbor that resulted in a public health warning. The summer of 2023 would appear to be Boston’s second rainiest on record.
About two months later, 8.65 inches of rain fell on New York City—more than any September day since Hurricane Donna in 1960. The city’s low-lying areas were flooded, and half of its subway lines were suspended as water flooded underground stations.
East Coast cities are increasingly prone to flooding due to climate change. But changing weather patterns are only half the problem – the other is inadequate infrastructure. These recent flood events were particularly exacerbated by Boston and New York’s combined sewer systems, which carry both stormwater and sewage in the same pipes. When such a system reaches capacity during heavy rainfall or storms, it backs up and sends a mixture of stormwater and raw sewage into waterways (and sometimes also into streets and homes).
Many other cities across the country also have combined sewer systems, but as two of the oldest, densest major cities in America, Boston and New York face an uphill battle when it comes to climate proofing their sewer systems. And the cities chose two very different paths: Boston chose separate the combined portion from its sewer system so that sewage no longer mixes with storm water during floods, while New York bets on new, detached ones rain management infrastructure to ease the burden on its combined sewer when it rains.
The success of their respective solutions is not only a matter of reducing flood hazards for city dwellers and surrounding ecosystems – it is also required by law. That’s because flood-related backups that send sewage into waterways, known as combined system overflows, are a violation of the Clean Water Act. In response to combined system overflows, the U.S. Environmental Protection Agency entered into consent decrees with Boston and New York City’s municipal governments—legally binding agreements requiring the cities to prevent further overflows. John Sullivan, the chief engineer at the Boston Water and Sewer Commissionestimates that 90 percent of sewer systems in the country are under a consent decree.
A consent decree “describes how many years you have to fix this problem,” Sullivan said, “and they give you enough time, but you have to take steps to meet the things that you haven’t met.”
Boston is in dire need of better flood management infrastructure right now. Sea level rise is occurring disproportionately faster on America’s East Coast, due to factors including wind patterns and a changing Gulf Stream. Meanwhile, climate change is too increase the amount of moisture in the atmospheremaking heavy precipitation more likely. The double whammy of rising sea levels and increasing heavy rainfall exacerbates the impact of flooding during storms. In Boston specifically, high tide flooding is increasing more than three times faster than the national averageaccording to the National Oceanic and Atmospheric Administration. Such floods can swallow outfalls, the pipes that send excess sewage into waterways when the system is flooded, further reducing the rate at which water drains from cities.
Boston has actually been working to separate its sewer system since before climate-related flooding became a major threat. In response to a 1987 court order, the Massachusetts Water Resources Authority undertook nine sewage separation projects in the Boston area between 2000 and 2015, along with dozens of other sewer improvements intended to prevent combined system overflows. Today, only about 10 percent of the Boston Water and Sewer Commission’s 1,538 miles of sewer pipes are combined.
Currently, the commission is working on two additional sewage separation projects South and East Boston. The city prioritizes overflow prevention in areas where the risk of human contact with contaminated water is deemed highest, such as at public beaches.
These projects are expensive. According to the sewer commission’s calculations, the city’s sewer separation works cost an average of $340,000 per acre in 2021. About 88 acres of work was done that year — translating into a price tag of more than $30 million. From 2024 to 2029, the city plans to separate sewers 230 acres in East Boston and 400 acres in South Boston. These planned works account for approximately 3 percent of Boston’s sewer system, which consists of approximately 20,500 hectaresincluding portions that have always been separate.
Another problem is finding enough space for adding new pipes – a luxury in some areas of the city. Sullivan sent Grist a blueprint of plans for sewer separation works in South Boston. It contains a flurry of lines of varying thickness and color, some solid and others dotted, stacked on top of each other. Each represents a different underground pipe.
Courtesy of Boston Water and Sewer Commission
“You can see how messy they can be trying to fit these pipes under the gas pipes, under the electric, under the phone,” Sullivan said.
Sewer replacement – most of which takes place deep underground – also presents safety concerns for workers, such as low oxygen levels, inhalation of resin fiberglass fumes and the presence of foreign objects in sewage. The contractors overseeing the work install oxygen meters in tunnels that sound when oxygen levels drop to a dangerously low level.
According to Sullivan, the risks of sewer replacement are worth it in the face of increasing precipitation.
Although he says 90 percent of Boston’s storms do not exceed 1 inch of precipitation, and can be mitigated by existing flood infrastructure, they can sometimes dump up to 6 inches of rainwater on the city.
“You need the infrastructure to move that 5 inches of water out,” Sullivan said. “And it’s not done by any green infrastructure, it’s pipes.”
However, New York City is betting that green infrastructure will do the trick. Over 60 percent of the Big Apple’s 7,400 miles of sewer lines are combined, and the city estimated that the complete modernization of the system would costs about $100 billion and takes decades. The New York City Department of Environmental Protection’s alternative to separating significant portions of its combined sewers is the Cloud Break Plandeveloped in partnership with the city of Copenhagen, Denmark, starting in 2017. The plan uses newly built gray infrastructure such as underground storage tanks, and green infrastructure such as rain gardens, to divert stormwater during heavy downpours. A rendering of Cloud Break infrastructure on the Department of Environmental Protection’s website illustrates how porous concrete in parking lanes can capture stormwater runoff and tip it into underground tanks for temporary storage.
New York City Department of Environmental Protection
In early 2023, the city revealed plans for $84 million in Cloudburst infrastructure at eight public housing developmentsinclusive sunken basketball courts which can collect storm water in the event of heavy rain. It also announced additional, larger Cloudburst initiatives funded by $390 million in capital funds in four focal neighborhoods in the Bronx, Brooklyn and Queens. These areas were selected based on several factors: history of flooding, future flooding risk via modeled stormwater flood maps, and socio-economic vulnerability.
Alexx Caceres is a native of East New York, one of the four focal neighborhoods, and works as the farm manager of East New York Farms. Caceres says they welcome the planned infrastructure. During the storm last September, the front of Caceres’ farm was flooded. They hope the Volkbreuk infrastructure will help prevent subsequent sewer overflows and floods.
“They’re trying to create infrastructure that holds the water,” Caceres said, “giving the sewer system time.”
Other peripheral Cloudburst initiatives in Staten Island and the Bronx sought to restore natural drainage corridors that had been built over by urban developments.
While effective at creating more pathways for stormwater to flow out of the city, these projects may be less feasible in more densely populated boroughs like Manhattan, according to Daniel Zarrilli, the chief climate and sustainability officer at Columbia University.
The New York City Department of Environmental Protection declined to comment on its plans to manage flooding.
Across America, other cities face the same choices as Boston and New York — often with less money available to them. States and localities are responsible for more than 90 percent of America’s public water infrastructure spending every year. According to Joseph Kane, a fellow at the Brookings Institution, a think tank that specializes in economic and policy research, that means cities bear most of the financial burden to address aging sewer systems.
“I don’t think communities often want to get to the point of a consent decree,” Kane said, but “the systems are old, and in many cases the utilities themselves haven’t had the financial ability to stay proactive with these repairs .”
An EPA Grant Program originated in 2018, amendments to the Clean Water Act provide small grants to cities to work on their sewer systems. The bipartisan Infrastructure Act of 2021 brought about another infusion of federal resources, primarily in the form of the Clean Water State’s revolving fundwhich extended $11.7 billion in loans to states, which in turn distributed them to individual utilities. However, Kane said this legislation only slightly eases the economic burden on states and utilities, which ultimately must repay these loans.
“It still pales in comparison to the magnitude of the costs that states and territories themselves have to bear,” Kane said of existing federal resources for flood management.
Funding from the bipartisan infrastructure bill would also last through 2026.
“There are already questions in Washington and across the country that when this funding expires in a few more years, is there going to be additional support for these kinds of projects?” Kane said.
Several American cities have turned to imposing stormwater fees to raise funds for sewer system improvements. The fees are paid by individual property owners, shifting the cost of flood prevention to the community. Stormwater charges are calculated based on the impervious surface cover of the property – those with a larger area of impervious surfaces, such as roofs and car parks, are charged a higher amount.
In April, the Boston Water and Sewer Commission instituted a stormwater charge that applies to all properties with more than 400 square feet of impervious area. New York City has not yet instituted any stormwater charges.
“Stormwater fees create a connection for property owners to save something for their contribution to the stormwater runoff challenges,” Kane said, “but there is a lot of debate about exactly how high these stormwater fees should be, how they are calculated, who pays what.”
