‘We need rain’: Drought threatens the very foundations of some Boston buildings

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Now, as a prolonged climate-fueled drought afflicts the region, groundwater levels have dropped to alarming levels, in some cases to record lows, raising fears that buildings across large swaths of the city are endangered as the piles are exposed to the air and begin to decay. There are nearly 10,000 townhouses and other buildings in nearly a dozen neighborhoods that rely on wooden stakes for support, from the North End to Back Bay and Fenway. Some of the city’s most historic landmarks, including Trinity Church, Custom House Tower, and Old South Church, are supported by pilings, which typically extend 15 to 20 feet below the surface.

Experts said the rot stops when groundwater levels rise, but will resume each time the piles are re-exposed, a prospect made increasingly possible by the likelihood of more frequent and long-lasting droughts.

“The longer the droughts, the more frequent we have them, the more sustained they are, the greater the risk to buildings that sit on stilts,” said Christian Simonelli, executive director of the Boston Groundwater Trust, an organization established by the Boston City Council to monitor groundwater levels in threatened parts of the city and make recommendations.

This summer, as Boston’s drought went from mild to severe to critical, the trust saw declines in many of its 813 monitoring wells across the city, including 31 at their lowest on record, a said Simonelli.

“I will be very clear: we need rain. We can’t last another three or four months like that.

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This is a potentially costly problem. In a Analysis 2021Garrett Dash Nelson, President of Norman B. Leventhal Map & Education Boston Public Library Center, found that more than $36 billion of property appraised in Boston sits on ancient mudflats filled with sand and gravel. Almost all the buildings in these old mudflats built in the early 20th century and earlier are supported by wooden stilts. “And there are a number of ways that estimate is really a floor,” Nelson told a recent Groundwater Trust meeting, noting that his estimate excludes properties not listed in the tax assessor’s database.

Giuliana Zelada-Tumialan, structural engineer at Simpson Gumpertz & Heger, said that taking into account today’s high costs in the construction industry, underpinning a typical Boston townhouse – in which steel supports and concrete replace the exposed tops of the rotting wood piles – runs about $400,000.

A short period of pile decay is not necessarily an immediate threat to a building, according to experts. But significant problems can begin to emerge in as little as three years. Rotting pilings can cause a building to settle and crack, making it hard or impossible to open windows and doors and leaving jagged scars on the facade – or, in the worst case, making it unsafe to occupy.

Worries about groundwater have dogged Boston for a century, having nothing to do with the climate. Historically, the biggest threat has been underground infrastructure such as subway tunnels, sewers and basements, which can crack and allow water to siphon out quickly. Before regular monitoring began in 1999, such leaks were sometimes only discovered when a building’s foundation cracked.

This summer, as Boston’s drought went from mild to severe to critical, the Groundwater Trust saw declines in many of its 813 monitoring wells across the city, including 31 at their lowest level on record.Jessica Rinaldi/Globe Staff

In 1929, for example, cracks began to appear in the walls of the Boston Public Library’s main building in Copley Square, caused by piles of rotting wood under the floor. More than 50 years later, in 1984, wood piles under nearly 20 townhouses on Brimmer Street in Beacon Hill were found to be rotting, rekindling concerns about Boston’s groundwater levels.

The Groundwater Trust was established in 1986 and in the years since has dug narrow wells in vulnerable neighborhoods to closely monitor changes. Constant monitoring, along with prompt repairs of underground leaks by the city, has led to a sharp decrease in groundwater problems. But now, with climate change, there is a new worry.

As global temperatures rise due to the burning of fossil fuels, global weather patterns have been increasingly disrupted. As part of this disturbing trend, Massachusetts is expected to experience an increase in extreme rainfall and drought, according to a recent report from UMass Boston. Both are problems for the city’s groundwater.

“We are going to have more precipitation, but when we do, it will be big storms with large amounts,” said Jayne Knott, a groundwater hydrologist who contributed to the UMass report. “It’s generally bad for groundwater, especially in a city where there are a lot of impervious surfaces, because when the water comes fast, it tends to run off.”

Since its inception in 1986, the Boston Groundwater Trust has dug narrow wells in vulnerable areas of the city to monitor changes in groundwater levels. Jessica Rinaldi/Globe Staff

Now the Groundwater Trust is partnering with city and state to focus on how best to prepare. The group will address the issue during a an event this month at the Boston Public Library.

Over the past few decades, the city has made significant changes to help capture more precipitation and redirect it into the ground. A special zoning district, established in 2006, requires any new building be made to capture rainwater to direct it into the ground rather than into storm drains. And a network of groundwater recharge systems has been built across the city, helping to pump more water in the soil.

New efforts in green infrastructure offer another solution, said Michelle Laboy, assistant professor of architecture at Northeastern University. “You can build a swale that almost looks like a vegetated ditch, and once it fills up, it can hold water for a little while and then slowly let it seep out,” she said. “The floor can be a sponge, but you have to give it time.”

As a result of that work, Simonelli said, groundwater test wells had fewer record lows during this drought than during the 2016 drought — the worst in state history — when 200 wells of test recorded the lowest level ever recorded.

But in a future where the extreme drought can happen more frequently, technology that catches rain can only help a lot, Simonelli said. “What do we do if it doesn’t rain? »


Sabrina Shankman can be reached at [email protected] Follow her on Twitter @shankman. Daniel Kool can be contacted at [email protected] Follow him on Twitter @dekool01.



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