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How rising groundwater caused by climate change could devastate coastal communities

Higher sea levels will push the water table up with them, causing flooding, contamination, and all manner of unseen chaos.

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Jon Han

Fae Saulenas does not want your sympathy. 

Saulenas, along with her 46-year-old daughter Lauren, spent last winter—their covid winter—in Saugus, Massachusetts, in a house without a working furnace. Saulenas is in her 70s. Lauren, because of brain injuries she experienced in the womb, is quadriplegic, blind, and affected by a seizure disorder, among other disabilities. In winter, it’s not unusual for overnight temperatures in Saugus to dip into the teens. The two could not long survive without heat, so absent a furnace, they relied on a space heater. But the cost of electricity to power it was $750 in February alone, and it warmed only a single bedroom.

Saulenas doesn’t tell this story to engender sympathy but, rather, as a warning. The water table, she says, is rising—seeping into gas lines and corroding furnaces from the inside out. That’s what happened to hers. And she wants you to know that if you live anywhere near a coast—even one, two, three miles away—that water might be coming for you too.

For something you’ve probably never heard about, rising groundwater presents a real, and potentially catastrophic, threat to our infrastructure. Roadways will be eroded from below; septic systems won’t drain; seawalls will keep the ocean out but trap the water seeping up, leading to more flooding. Home foundations will crack; sewers will backflow and potentially leak toxic gases into people’s homes. 

Saugus is a small town roughly 10 miles northeast of Boston. On maps, water is one of its defining features, with the Saugus River and its tributaries meandering through the town and heading through marshland to the Atlantic Ocean. Among those salt marshes, blocked from the Atlantic by the peninsula of Revere Beach, is where Saulenas bought her house in 1975. 

Given the proximity to the ocean, the source of her recent woes would seem obvious: sea-level rise. Since 1950, sea level in the region has risen by eight inches, and that change has not been linear. The sea is rising faster now than it did a generation ago—about an inch every eight years. But the water that left Saulenas out in the cold did not come from the sea, at least not directly.

Her problems began in 2018, when she lost gas—and thus heat—because of water entering an underground main. It was a problem that would persist, intermittently, for several years. Water would enter the gas main, and her utility, National Grid, would be forced to shut off the gas. National Grid would then try to find where the water was coming from, patch the leak, and pump the water out. 

Officially, National Grid has not named the source of the problem. But Saulenas thinks the culprit is groundwater.

Even under normal circumstances, the cast iron pipes that make up roughly a third of National Grid’s infrastructure in Massachusetts are prone to rust and corrosion. She thinks these pipes, which once sat comfortably above the water table, are finding themselves intermittently swamped during seasonal high tides that essentially push up the groundwater. And it’s that elevated groundwater that she thinks seeped into the gas main, flooded out her gas meter, and eventually corroded her furnace. 

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“The problem is huge. We’ve way underestimated the flooding problem.” 

Kristina Hill, an associate professor at the University of California, Berkeley, whom Saulenas reached out to in pursuit of answers, agrees. “She was asking me, is this something that comes from sea-level rise? And obviously, the answer is yes,” says Hill. 

Hill is one of a number of researchers trying to get the public and policymakers to take the risks of rising groundwater seriously. Unlike rising seas, where the dangers are obvious, groundwater rise has remained under the radar. Hydrologists are aware of the problem and it’s all over the scholarly research, but it has yet to surface in a significant way outside of those bubbles. Groundwater rise is only briefly mentioned in the most recent edition of the National Climate Assessment, released in 2018; it’s absent from many state and regional climate adaptation plans, and even from flood maps.

A 2021 study in the journal Cities found that when coastal cities conduct a climate vulnerability assessment, they rarely factor in groundwater rise. “They talk mostly about sea-level rise, storm surges,” says Daniel Rozell, an engineer and scientist affiliated with Stony Brook University, who wrote the 2021 paper. “But there haven’t been a lot of questions about what’s going to happen to the groundwater.”

Impacts on existing infrastructure and planned climate adaptations could be catastrophic. Remediation efforts that haven’t planned for groundwater rise will be rendered useless. Billions of dollars in infrastructure will need to be upgraded. And it will likely affect an area much larger than what’s captured on most flood maps. A 2012 study by researchers at the University of Hawaii that factored groundwater into flood risks found that nationwide, the area threatened was more than twice the area at risk from sea-level rise alone.

Any coastal area where “the land is really flat, and the geology is [the kind of] loose material that water moves through really easily,” says Hill, is “where this is really going to be a problem.” This includes places like Miami, but also Oakland, California, and Brooklyn, New York. Silicon Valley communities like Mountain View are susceptible to groundwater rise, as is Washington, DC. Worldwide, the area at risk includes portions of northwestern Europe and coastal areas of the United Kingdom, Africa, South America, and Southeast Asia. 

“The problem is huge,” says Hill. “We’ve way underestimated the flooding problem.”

And because of how groundwater moves, people who are at risk may not know it until it’s too late. “One of the most important things about the groundwater is that the rising groundwater level precedes any inundation of the surface,” says Rozell. Put another way, we will experience groundwater flooding long before the ocean comes lapping at our front door. 

The water beneath our feet 

It might seem puzzling that rising seas could cause groundwater to rise. At first blush the two seem unrelated, but the connection is actually simple. That it has long been ignored reflects our bias toward addressing problems we can easily see.

To understand the link, it first helps to understand a bit about groundwater. The water nestled in sediments underground started as surface water, like rain or snow, and eventually seeped down. A layer of saturated soil rests below a layer of unsaturated soil; the boundary between the two is what’s known as the water table. And in many coastal areas this layer of saturated soil, which can be meters thick, rests atop salt water from the ocean. As sea levels rise, the groundwater gets pushed up because salt water is denser than fresh water. 

And this isn’t the only way that the ocean and groundwater are connected. 

“Groundwater normally flows out to the sea,” says Rozell. “All along the coast, there’s what they call submarine groundwater discharge. You might even notice it if you go to the beach at low tide. If you stand in the water, you might feel really cold water right at the edge, in the sand. And that’s groundwater just running out continuously into the ocean.” 

Thus, any protection designed to keep rising seas from encroaching onto land must also factor in how to let groundwater out.

“It has the capacity to affect millions, and nobody’s paying attention.” 

Arguably the first big study in a prominent scientific journal that looked at what sea-level rise might mean to groundwater levels was published in 2012 in the journal Nature by researchers Kolja Rotzoll and Chip Fletcher of the University of Hawaii. The study came on the heels of a report by the United States Geological Survey and Yale University researchers who looked at what would happen to groundwater in coastal New Haven, Connecticut, as sea levels rose. In both cases researchers found that the two would rise in concert. 

“We looked at well records and found that the water table in the coastal zone goes up and down with the tides,” says Fletcher. “And so we realized there’s a direct connection between the ocean and the water table. And as the ocean rises due to climate change, the water table is going to rise and eventually flood the land. So we’re gonna have all these wetlands in urbanized areas and around roads, where we don’t really want them. And it turns out this is a form of sea-level rise that in many areas is more damaging than what people classically think of as the ocean flowing over the shoreline and flooding.”

And we’re already seeing the effects. 

Danger to human health 

In talking with experts about groundwater rise, what often comes up is that it’s more complicated and harder to adapt to than sea-level rise. Any solution to one aspect of the problem can create a cascade of others. Take, for example, something as straightforward as sanitation. Ordinarily, in most parts of the United States, when you flush the toilet one of three things happens, depending on where you live: it goes out to a cesspool, a septic system, or a sewer line. But groundwater rise presents increasing challenges for all three. 

Cesspools are essentially concrete cylinders with an open bottom and perforated sides. Especially in coastal areas, the cesspools, which should be dry, instead find themselves constantly inundated, says Josh Stanbro, a senior policy director for Honolulu’s city council, who until last January was the city’s chief resilience officer. “They’re now sort of always wet,” he says. Microbes stay alive because they are wet, and because there’s so much more water around, they can leach out.

And Honolulu is not the only city with this issue. Miami-Dade County is facing similar problems with septic tanks, which in theory provide a layer of filtration that cesspools do not. But to do that filtration, the systems require a layer of soil two feet deep, and that layer shrinks as water tables rise. Already, 56% of the county’s systems are periodically compromised during storms. By 2040, estimates suggest, that number will rise to 64%. Failed septic systems can contaminate the local aquifers that a community depends on for drinking water. 

One workaround is to switch those households and businesses currently on septic or cesspool systems over to sewer lines. In Miami-Dade County, the estimated cost for that shift is $2.3 billion. 

Nor are sewer systems a panacea, cautions Berkeley’s Kristina Hill. “Most American sewer pipes, both sanitary and storm sewer pipes, are typically cracked, because we do such bad maintenance. We’re like an international joke,” she says. “People start conferences in civil engineering in Europe with slides of how bad American systems are, to loosen up the audience.” Those cracked sewer pipes let groundwater in. And in places like New York City and Boston, which have what are known as combined sewer systems, water from rain and water from raw sewage mingle, so there’s less space in the pipes. This is why as groundwater rises, places like New York City’s Jamaica Bay community end up with liquid bubbling up from storm drains during high tide. 

Newer cities tend to have systems where rainwater goes into one  pipe and sewage into another. But if the pipes are full of groundwater when it rains, there’s still nowhere for that rainwater to go. So in both cases, according to Hill, you’ll get more flooding. 

There’s another way, too, in which rising groundwater can turn our sanitation systems into killers. 

“In the Bay Area there’s so much legacy contamination under the ground from military use, from the Silicon Valley tech booms—it left a lot of nasty stuff,” says Kris May, a coastal engineer and climate scientist who founded Pathways Climate Institute. “And what often happens is we put low-income houses in those areas after they’re remediated. But they still leave a certain amount of contamination in the ground, and those regulations were based on no rising groundwater table.”

Now the groundwater table is rising. And as it does, it saturates the soil, unlocking contaminants such as benzene. These chemicals are highly volatile, and as gases they can easily find their ways through sewer lines and into homes. 

This is the impact of groundwater rise on just one system—sewage. But it could affect many more. Buried electrical lines that aren’t properly sealed will short out; foundations will start to heave from the pressure. Some fear that seismic faults could even be put under pressure. 

How water finds a way 

To protect themselves against rising seas, cities are turning to the same tools they have used for centuries: levees and seawalls. Boston has proposed a 175-mile seawall called the Sea Gates Project. Miami has a proposal for a $6 billion, 20-foot-high seawall. New York has proposed its own $119 billion, six-mile-long project called the New York Harbor Storm-Surge Barrier. Homeowners from Florida to California are erecting barriers to keep the ocean out. But the fundamental problem with all these interventions is the same: a seawall holds back the sea, not groundwater.

In some areas, if the underlying ground is relatively impermeable, it is possible to build a seawall or levees that slow groundwater rise. But then you’re left with other problems. Recall that water moves toward the ocean. A barrier that stops groundwater from rising with sea level will also keep stormwater from, say, recent rainfall from flowing to the sea. 

“If you don’t let the water run out to the ocean, then you have to basically pump it over the wall. And that’s essentially what the Netherlands has been doing for several centuries,” says Stony Brook’s Rozell. But this too can create problems, because so many of the places these seawalls are working so hard to save—much of Lower Manhattan, large parts of San Francisco and Boston—were built on wetlands, landfill, or both. “If they pump, the land is going to sink,” says Hill. 

And even if cities were willing to pursue such a path, not every place can. “There are lots of conditions where you can pump all day long and the water table won’t go down,” says the University of Hawaii’s Fletcher. 

Recall that groundwater is water that makes its way into the spaces, or pores, in sediment. In some places, like Miami, “the pores are so large that you’re just pulling in water from the estuary from the ocean,” says Fletcher. “You can pump as hard as you want and it just keeps coming in from an endless body of water”—the sea.

Planners are often oblivious to the problem. In 2009, the Maldives, a low-lying island nation, held the world’s first underwater cabinet meeting to draw attention to the harm big climate polluters, like the United States, were perpetuating through climate inaction. The message was clear: You’re drowning us. These days, already dealing with the consequences of rising seas, the country is consolidating its outer island communities onto a new island called Hulhumalé. It’s designed to withstand sea-level rise. But the project did not factor in rising water tables.

“They did not understand that the water table will rise with sea-level rise,” says Fletcher. If the sea rises only two more feet—which some estimates say will happen as soon as 2040—most of this brand-new island will be uninhabitable wetland.

When he explained this to the project’s lead designer, “he just stared at me—he was speechless. It’s like he couldn’t comprehend what I was saying,” Fletcher says. “All the billions of dollars they had spent on this thing, and they didn’t build it high enough.”

Eroding away history 

There is at least one place where you can see people reckoning with rising groundwater in close to real time. Strawbery Banke Museum is in Portsmouth, New Hampshire, near the banks of the Piscataqua River, just a few miles from the Atlantic Ocean. The buildings were preserved to let us see three centuries into the past, but they are also giving us a glimpse into the future. Some of the structures, including the city’s second-oldest house, are flooding from below. 

“We’re getting these super tides, king tides, that elevate the water over two feet higher than typical. And so we’re starting to see this water get into our basements,” said Rodney D. Rowland, Strawbery Banke’s director of facilities and environmental sustainability, on a tour of the museum in late September. When you crouch down in basements with their ceilings too low for most adults to stand, it’s easy to see the water marks from past groundwater incursions. 

The museum has taken a two-pronged approach. The first element is educating the public. “One of the exciting things that we’re gonna add is a kiosk that is attached to sensors that were placed in the ground around the museum,” said Rowland. “And they will track the movement of the groundwater, [plus] salinity, temperature, water height. And so visitors will see that there’s water under their feet.”

But the museum also needs to preserve the buildings. And that goal must now be balanced with the fight against rising water. In one of the houses, “we made the decision to take out what was called a summer kitchen,” said Rowland. “There was a hearth down there where they cooked in the summertime. We took it out, and we put in a granite block.” They had to do that because the old hearth was acting like a candle wick, drawing water from the basement into the rest of the structure.

“So now the rest of the chimneys are preserved,” he added. “The water can’t get through that. But we lost that piece of history. And this is going to be a constant battle with how much are we going to lose to save what we can.”   

In some ways Rowland is lucky. His state, New Hampshire, is at least aware of the risk of groundwater rise and is factoring it into plans. But New Hampshire is an exception. Many other states, with more extensive coastlines, are going to have to face the issue in the coming years as not only buildings but lives are threatened by this unseen risk. 

Less than 50 miles down the coast in Saugus, Fae Saulenas plans on leaving for higher ground— but not without making some noise. She’s written legislators, National Grid, and the press to try to draw attention to the issue. “Groundwater is really important to me. And it’s important to me not only because it has affected my life profoundly, but because I think it has the capacity to affect millions of people,” she says. “And nobody’s prepared, and nobody’s paying attention.”

Kendra Pierre-Louis is a senior climate reporter with the Gimlet/Spotify podcast “How to Save a Planet.”

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