As sea levels rise and torrential rainfall inundates the land, an invisible threat upwells beneath our feet, say groundwater experts. They’re urging municipalities to heed the massive infrastructure and public health risks posed by overflowing water tables.
The climate crisis is usually associated with groundwater levels being depleted by extreme heat and drought. But “in some areas, this water is actually creeping higher, thanks to rising sea levels and more intense rainfall, bringing a surge of problems for which few communities are prepared,” writes Grist.
“Places in the United States where the water table is inching higher—along the coasts, yes, but also inland, in parts of the Midwest—are already beginning to experience problems with infrastructure,” the news story adds. Old, cracked pipes are being inundated, leaving plumbing unfit to carry stormwater and waste. “Pavement is degrading faster. Trees are drowning as the soil becomes soupier, starving their roots of oxygen.”
For poor and low-lying communities, a dangerous concern is that “rising groundwater will mobilize contaminants that have been lurking in the soil for years, left behind by industrial and military sites, and allow them to spread, unnoticed, beneath our feet.”
This threat is now a reality in West Oakland, in the San Francisco Bay area.
“A once-thriving Black community decimated by racist urban-planning practises,” West Oakland has found itself hosting all manner of toxin-producing industries over the years, from shipyards, to smelters, to a former army base.
In February, 2020, a local high school was forced to close for several weeks after the carcinogenic industrial solvent trichloroethylene (TCE) was discovered in groundwater beneath the campus. The source of the TCE was never pinpointed, but a local news organization reported at the time it could be “any or all of five polluting sites within a half-mile of the school, including a metal finishing shop and a former dry cleaner.”
Groundwater rise is compounding an already acute environmental injustice, said Kristina Hill, a professor at the University of California, Berkeley, who studies rising groundwater in urban coastal areas. “Now those areas have both polluted soil from military or industrial activities, [and] they also have rising groundwater,” Hill said.
On the other side of the country, in South Carolina’s low-lying Beaufort County, rising groundwater is threatening septic systems. Just like in West Oakland, sea level rise is pushing water not only up, but inland, “raising groundwater levels miles away from the coast,” says Grist. This phenomenon occurs near coastlines, where the saturated soil below the water table itself sits atop salt water from the ocean. “As sea levels rise, the groundwater gets pushed up because salt water is denser than fresh water,” explains MIT Technology Review.
And this isn’t the only way that oceans and groundwater are connected, notes Grist.
Daniel Rozell, an engineer affiliated with Stony Brook University whose 2021 study warned that coastal cities are ignoring the perils of rising groundwater, said policy-makers must realize that groundwater is meant to flow into the sea, in a continuous process called “submarine groundwater discharge.”
That means seawalls designed to keep out the rising oceans must also be able to let out groundwater, lest it back up behind the wall, creating the very problems the seawall was designed to prevent.
Septic system failure is a genuine threat in places like Beaufort County because the process depends on having an adequate distance between the septic tank and groundwater. Otherwise, there isn’t time and space for waste to be filtered by soil and eaten by bacteria, and raw sewage ends up being washed into local waterways.
Some 20% of households in the U.S. depend on septic systems, and even in areas far from coasts, groundwater will still rise after climate-driven torrential rainfalls.
In places along the Vermilion River in Illinois, groundwater “is seeping into unlined pits containing coal ash—a hazardous waste—and carrying heavy metals into drinking-water aquifers,” Grist reports.
Concentrated in the Midwest and South, coal ash pits are a serious environmental threat. By 2019, the Environmental Integrity Project and Earthjustice had found that more than 90% had contaminated nearby groundwater with heavy metals like arsenic, cadmium, and mercury.