Rising sea levels bring salt water to private wells

WESTPORT — Tom Gebhard has owned a summer home in Westport Harbor for four decades, and he says an unpleasant taste creeps into the local tap water every August. But it wasn’t until he retired to town seven years ago and became president of the nonprofit Westport Harbor Water Association, that he figured out what was happening with his neighborhood wells.

“We were noticing that the neighbors were really complaining about the quality of the water, and it was rotting their appliances,” he said.

After conducting some summer groundwater testing, Gebhard and a team of volunteers found the taste resulted from a spike in groundwater salt content, from the wells sucking in ocean water.

This phenomenon is called saltwater intrusion, and it’s an emerging climate challenge for communities on groundwater across coastal New England. The introduction of ocean salt water into tap water makes it taste unpleasant and — in severe cases — undrinkable. Salty tap water also poses health concerns for those with high blood pressure. It corrodes home water systems and appliances.

Densely populated rural communities with wells near the coast are most affected right now: Westport, parts of South Dartmouth, and eastern Rhode Island. The problem is worse in summer, with less rainfall and with vacationers driving up groundwater demand.

But the incursion is not posing a problem in New Bedford, Marion, Mattapoisett, Fairhaven, or the remainder of Dartmouth. These communities are served by public water systems with inland water sources. New Bedford gets its water from inland ponds such as Assawompset Pond. Other towns tap wells near the Mattapoisett River. Dartmouth also uses inland wells.

Still, Thomas Boving, chair of the geosciences department at the University of Rhode Island, says Westport’s problem is the “canary in the coal mine” for Massachusetts communities that depend on coastal groundwater. He noted that the problem will only spread as sea levels rise and growing populations drive increased groundwater pumping.

Gebhard said his nonprofit’s water — which goes to about 50 homes in Westport — is still “perfectly safe” to drink in August, and the salinity declines after the month is over. Yet at home, Gebhard has spent about $3,000 in the past five years on new water heaters and a dishwasher, replacing appliances ruined by salt corrosion. He worries that in the future, salt concentrations will not decline in the wells after August ends.

“We are running with our old wells, knowing that they are on borrowed time,” Gebhard said. “We are trying to find a new water source, and we do have the Town of Westport helping us, but it’s not easy.”

Saltwater intrusion occurs in coastal wells. Underneath the surface of coastal land, a layer of fresh groundwater floats atop a wedge-shaped layer of ocean salt water, which protrudes inland.

The layer of fresh water floats because it is less dense than the saltwater layer. It’s recharged through rainfall infiltrating into the ground.

When coastal wells pump groundwater, they pull water in from above and below the well’s bottom hole, like when someone sucks on a straw in a glass of water. When sea level rise pushes the underground saltwater-freshwater line up too high, or overpumping pulls the line upwards, salty water can get sucked into the well water system.

James Heiss, a UMass-Lowell professor of hydrogeology, said seawater intrusion is slow to develop, and seems isolated to summers in a few northeastern towns right now. Yet he said that it may intensify across the state as rainfall changes, sea levels rise, and coastal development expands.

Eventually, he said, this problem will result in the loss of drinkable water sources.

“This is a long-term threat that might not be a huge issue for coastal communities today, but it is going to get worse in the future,” Heiss said. “In New England, it is something that I think we should be paying attention to.”

Opinions differ on how much saltwater intrusion will hurt Massachusetts.

State Department of Environmental Protection officials say they have not heard of problems with saltwater intrusion from South Coast towns other than Westport in recent years. And recent scientific reports found “significant” saltwater intrusion is not projected to happen in the Plymouth area’s sole-source aquifer in the next century, nor in the two major groundwater aquifers in central Cape Cod.

But Boving, the geosciences professor, cautioned that we have not seen the worst of sea level rise yet, and that homeowners will often avoid reporting saltwater intrusion through government channels, since it can hurt property values.

Boving said he and his lab found preliminary evidence of saltwater intrusion in Little Compton, Rhode Island, in 2021, based on anecdotal reports. The professor said Westport may also be more vulnerable to the effects of saltwater intrusion right now than other Massachusetts towns, given its geologic profile, which is similar to Little Compton’s.

In southern New England, two types of groundwater aquifers prevail — those forming in sands and gravels from glacial deposits on bedrock, and those found in fractured bedrock itself.

Glacial deposit aquifers are generally porous, retaining rainfall well and forming a buffer against seawater intrusion. Examples include the Plymouth Carver aquifer and the Monomoy and Sagamore aquifers on Cape Cod.

Meanwhile, fractured rock aquifers form in solid bedrock. These aquifers do not retain water as well, and water drains down from them and into the ocean more easily. Some examples include those in Westport, Little Compton, and Long Island, Maine.

Boving said that when groundwater is over-pumped from a fractured bedrock aquifer near the coast, the groundwater flow can reverse and suck salt water in from the ocean. He said this geology is why saltwater intrusion may be appearing in Little Compton and Westport wells now.

Bob Daylor, vice-chair of the Westport Planning Board, added that saltwater intrusion is not a major problem for other South Coast communities, since they installed public water and sewer systems decades ago, with aquifers far from the coastline. Westport never did that.

New Bedford gets its water from several inland freshwater ponds, including Assawompset Pond and Little Quittacas Pond.

In South Dartmouth, saltwater intrusion may affect a few coastal private wells. Yet most of the town gets its public drinking water from inland glacial deposit wells on Chase and Old Westport Roads. Marion, Mattapoisett, and Fairhaven rely on wells in the Mattapoisett River Valley glacial deposit aquifers for their water systems. Wareham gets its water from Plymouth’s major aquifer.

Despite these local safeguards, scientists are concerned about potential future saltwater intrusion in coastal Massachusetts.

The UMass Amherst study on the Plymouth Carver aquifer showed projected increases in salinity for Duxbury and Bourne coastal wells by the year 2100, as well as wells in three coastal sections of Plymouth. And towns on the outer Cape, such as Provincetown and Truro, have documented concerns with saltwater intrusion in their aquifers dating back 40 years.

Heiss and Boutt said that the potential for saltwater intrusion from sea level rise is understudied in coastal Massachusetts, with no recent reports on the Boston metro area, much of the South Coast, the Islands, or the North Shore. Only a few communities are monitoring their water sources for the problem. More than 3 million people in Massachusetts get their drinking water from groundwater sources.

“People are starting to realize something is going on,” Boving said. “And now’s the time to do something about it. Because the longer you wait, the more difficult it gets.”

In Westport, Boving’s message rings clear. Engineering firm Weston and Sampson initially estimated that a new groundwater system for the three coastal Westport neighborhoods dealing with saltwater intrusion would run roughly $11 million to $20 million. It would tap wells far inland.

Yet Jim Whitin, chair of the Westport Planning Board, says the town and the firm have identified a more affordable long-term water source closer to the coast, which may cost $3 million to $5 million.

In the meantime, Gebhard said his utility will drill three wells off River Road, which will provide fresh groundwater to the three salt-afflicted neighborhoods for 20 years. He expects to see that $1 million project completed within two years, and fully funded by customers. But saltwater intrusion will eventually afflict those wells, too, as sea level rises.

Westport may struggle to achieve a longer-term solution. Whitin and Daylor said that the well-heeled town — with one of the lowest property tax rates in Massachusetts — does not have millions of dollars in its budget to pay for a bigger project. And finding the funds will be a challenge.

Daylor said Westport residents have resisted installing a public water system for decades. They tend to want to keep their taxes low; earlier this year, they struck down a tax override that would have prevented budget cuts to town services.

“There’s really been an attitude that low taxes benefit everybody, and people’s problems with their water supplies are individual problems that need individual solutions,” Daylor said.

Whitin said implementing a public water system for the whole town would be impractical because of Westport’s sheer acreage. The town’s Planning Board, he said, is looking into funding such as U.S. Department of Agriculture rural development loans and the State Revolving Fund to finance the new multimillion-dollar water source. But the bulk will be funded by a few hundred private water users in the three affected neighborhoods: Westport Harbor, Acoaxet, and Pond Meadow.

“I think we need to use this as a template for the coming years,” Whitin said. “We have a company that can fund this [interim solution] right now while we — the town — figure out what we’re going to do about these things.”

Adam Goldstein is a Report for America corps member. Email him at [email protected].

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