Surfside Collapse Exposes An Overlooked Threat: Salt Water Rising From Underground

Shortly after a condo tower in Surfside, Florida collapsed last June, Randall Parkinson had what he calls an epiphany.

Parkinson, a coastal geologist who studies the impact of climate change at Florida International University in Miami, wondered if rising sea levels had driven salt water into the ground beneath the tower, corroding its concrete foundations. Others were asking similar questions, but he couldn’t find anyone who had studied the effect of saltwater intrusion on residential buildings.

“So I decided to dig a little deeper,” Parkinson said.

More than seven months after the June 24 collapse, which left 98 people dead, there is no definitive answer as to what caused the 40-year-old condo Champlain Towers South to fall. Parkinson is one of many scientists who believe the tower may have been damaged by salt water seeping into its underground foundations.

He and others had already discovered that rising sea levels were squeezing underground salt water closer to the foundations of coastal buildings. They also note that photos showed corroded columns and flooding in the Champlain Towers South underground garage and that staff members reported pumping water out of the garage.

In a December report, a Miami-Dade County grand jury investigating the collapse also speculated that the saltwater intrusion likely damaged the building’s foundation.

Parkinson and other experts stress that they are not saying such damage caused the 12-story building to collapse; the cause of the collapse, on a barrier island that includes Miami Beach, is under investigation by federal authorities. Champlain Towers South suffered from construction defects and extensive surface corrosion. Locals complained that its foundation shook during the construction of a tower next to it. An environmental scientist documented that the building slowly sank in the 1990s.

But even if saltwater intrusion was not a cause of the collapse, experts say they want to raise awareness of an unseen and overlooked threat that could render many more residential towers on the coast of Florida vulnerable to decay.

“I really feel like it was completely missed,” Parkinson said. “You can see the coastal erosion. You can see if you are losing your shoreline or if your property is flooded. But what you don’t see, and what people hadn’t really started to think about, is everything that’s going on hidden underground. It’s out of sight, out of mind.

Still, Parkinson and other scientists may struggle to persuade Floridians to take action in response to the threat of rising groundwater, not only because research remains thin, but also because resolving the damage to buildings would likely be expensive and could hamper a condo industry that helps boost the state’s economy.

Many building foundations are made of reinforced concrete. If not properly protected, the concrete can absorb salt water, causing the supporting steel inside to corrode. This leads to “scaling”, in which the steel rebar expands, crumbling the concrete around it.

In its December report examining the safety of condos after the collapse, the Miami-Dade County grand jury noted the “open and obvious” chipping of Champlain Towers South and concluded it was “virtually certain that there was invisible corrosion and weakening of the concrete in the foundation”. and underground pillars.

The grand jury also warned that saltwater intrusion could pose a significant hazard beyond Champlain Towers South, saying it “could create hazardous conditions that will negatively impact concrete pillars and foundations. that support building structures, especially those in coastal communities”.

The panel foreman declined to comment on the findings, as did a spokesperson for the Miami-Dade State’s Attorney’s Office, citing confidentiality rules. The grand jury was tasked with exploring the public safety implications of the collapse, not recommending criminal charges. This work will be taken over by local prosecutors after federal authorities determine the cause.

In November, Parkinson published the first peer-reviewed study on the issue of sea-level rise underground attack on residential buildings, which was later reported by The Palm Beach Post. Using data from nearby monitoring wells, Parkinson showed that with sea level rise, the number of times groundwater rose above ground level in the garage des tours Champlain Sud went from an average of 244 times per year from 1994 to 2006 to 636 times per year from 1994 to 2006. 2007 to 2020.

Although Parkinson was unable to obtain water salinity data, he hypothesized that during the natural tidal cycle, particularly during extremely high “king tides”, the underground seawater and the layer of fresh water above – called the “lens” – probably mixed. The frequency of mixing will increase as sea levels continue to rise, Parkinson said.

“In the end, it’s all going to go to the salt,” Parkinson said. “The ocean will be so high and flood the area and there won’t be a freshwater lens. We’re only at the beginning and we don’t have enough to know what it looks like now, but we can speculate on the direction it takes.

Champlain Towers South was among several condo buildings on a barrier island north of Miami Beach.Chandan Khanna/AFP via Getty Images File

About an hour up the coast from Parkinson’s office, two Florida Atlantic University professors pursued a similar theory. After the collapse, Fred Bloetscher, a civil engineer who studies how sea level rise affects municipal water systems, called Anthony Abbate, an architect focused on protecting buildings from climate change. They had previously raised the possibility that steel-reinforced concrete in a building’s foundation could fail due to deterioration caused by rising salty groundwater levels.

“Do you think that might be a factor?” asked Bloetscher.

“I don’t know, but it sure looks like it,” Abbate replied.

In mid-December, Bloetscher, Abbate and Florida Atlantic University colleague Khaled Sobhan submitted a study titled “Can Sea Level Rise and Accompanying Saltwater Intrusion Contribute to Catastrophic Building Failures?” to technology | Architecture + Design, a peer-reviewed journal. Using a methodology similar to work on Parkinson’s disease, the study found that water level data indicated that the foundation of Champlain Towers South, including the piles, columns, walls and garage floor , “may have been exposed to periodic salt water, which is known to accelerate corrosion, in increasing amounts and with more frequency.

Abbate said he has been trying for years to get architects and builders interested in the issue. So far, he said, studies of saltwater corrosion risks have largely focused on parts of buildings that are above ground or on public infrastructure, such as bridges. , roads and water systems; in Fort Lauderdale, where Abbate is based, saltwater intrusion contributed to the bursting of a series of sewer lines. But the collapse of the South Champlain Towers has added a sense of urgency to a potential new threat.

“Surfside was a very tragic and unexpected result of processes that we thought were going on, but we never had a clear study or funded research to show it,” Abbate said.

Federal authorities are still investigating the causes of the collapse of the south Champlain towers.File Joe Raedle/Getty Images

More scientific studies could help change building codes, which Abbate says could require tests showing the depth and salinity of water beneath buildings. New codes may also require foundations to be designed to better protect against corrosion. Ideally, foundations would be equipped with sensors that allow building owners to collect data on a building’s “vital signs,” Abbate said.

He and Bloetscher want to conduct more studies of South Florida properties to better understand the potential risk. Since the collapse of Surfside, they have lectured on the subject to local construction and design professionals. Engineers, bankers and contractors seem interested, but representatives from the real estate and insurance industries are expressing less concern, Bloetscher said.

He added that Florida’s condo laws and condo board policy do not encourage further investigation of potential threats because they can be costly and hurt the real estate market.

“My biggest concern is if that was a factor at Champlain Towers South, which we suspect, then it exists in many places and it’s invisible,” Bloetscher said of the rising groundwater. “That’s my real concern, that this goes unseen and that there’s no reason it shouldn’t happen again.”

Harold Wanless, a University of Miami geologist who has warned of the effects of rising sea levels in Florida for decades – and who once taught Parkinson’s – said he was agreement that Parkinson had identified a blind spot in the study of saltwater intrusion. But he warned that it is unclear whether seawater actually seeped into the foundations of the South Champlain Towers. “Without the data, we would have to be careful saying the salt water ate the concrete,” Wanless said.

Michael Sukop, a hydrogeologist at Florida International University, said he, too, is interested in saltwater attack on the concrete foundations of buildings like Champlain Towers South. He is working on a project measuring how salt water intrusion might affect the concrete in the foundations of coastal buildings. It’s hard to figure this out in Surfside because there isn’t enough information about how much salt water is in the ground, he said.

“I would like to see more monitoring of freshwater/saltwater interfaces on barrier islands and on the mainland,” Sukop said. “Otherwise, we struggle to answer these questions.”

Bonny J. Streater