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“There’s a lot of legacy pollution in the Bay Area from military use from the technological explosions in Silicon Valley—leaving a lot of bad stuff out,” says Kris May, a coastal engineer and climate scientist who founded the Pathways Climate Institute. “And most of the time, we relocate low-income homes to these areas after they have been corrected. But they still leave a certain amount of pollution in the soil, and these adjustments were based on the absence of rising groundwater levels.”

Now the groundwater level is rising. And as it does, it saturates the soil by unlocking pollutants like benzene. These chemicals are highly volatile and can easily find their way into homes as gases through sewer lines.

This is the effect of groundwater rise on a single system – sewage. But it can affect much more. Embedded power lines that are not properly sealed will short-circuit; the foundations will begin to erode. Some even fear that seismic faults may be suppressed.

How does water find a way?

To protect themselves against rising seas, cities turn to the tools they have used for centuries: embankments and seawalls. Boston proposed a 175-mile seawall called the Sea Gates Project. Miami has a $6 billion proposal for a 20-foot-tall seawall. New York has proposed its own $119 billion, six-mile-long project called the New York Harbor Storm-Surge Barrier. From Florida to California, homeowners are building barriers to keep the ocean out. But the basic problem with all these interventions is the same: a sea wall holding up the sea, not groundwater.

In some areas, if the underlying ground is relatively impermeable, it is possible to build a seawall or embankments that slow the rise of groundwater. But then you’re left with other problems. Remember that water moves towards the ocean. A barrier that prevents groundwater from rising with sea level will also prevent rainwater from, for example, recent rains from flowing into the sea.

“If you don’t let the water flow into the ocean, you basically have to pump it over the wall. “This is what the Netherlands has been doing for centuries,” says Rozell of Stony Brook. But that can also be problematic, because many of the places these seawalls have worked hard to save – most of Lower Manhattan, large parts of San Francisco and Boston – are built on wetlands, landfills, or both. “If they pump, the ground will sink,” Hill says.

And even if cities are willing to follow such a path, not everywhere can. “There are so many conditions that you can pump all day long and the water level won’t drop,” says Fletcher of the University of Hawaii.

Recall that groundwater is water that enters voids or pores in sediment. In some places, like Miami, “the pores are so large you’re pulling water from the ocean from the estuary,” Fletcher says. “You can pump as much as you want and it will continue to come from an endless body of water” – the sea.