In 2019, about 100 homes in a Newmarket, New Hampshire neighborhood switched their water supply from private wells to public water, after a modeling study showed that the amount of saltwater in those wells would only increase over time, eventually becoming unsafe to drink.
That’s a scenario that could play out in more Seacoast neighborhoods and communities in the next few decades. In the last century, sea level has risen eight inches along New Hampshire’s coast, and scientists anticipate the increase will only accelerate as the climate changes.
While some risks, like flooding, might be more obvious, local scientists, engineers and planners want to get a clearer picture on a less obvious vulnerability that’s becoming more prominent: sea-level induced groundwater rise and its effects on coastal water sources.
How groundwater rise affects water sources
Groundwater rise has the potential to bring more disruptions to infrastructure than surface flooding in coastal areas, said Jayne Knott, environmental engineer who has worked on modeling projects for some Seacoast communities.
The closer to the coast a drinking water well or aquifer is, the more likely it is for saltwater to enter from below, known as saltwater intrusion. Wells that are drilled deep into bedrock are also increasingly vulnerable to saltwater intrusion.
“Saltwater is more dense than freshwater, allowing it to move further inland in the deeper geologic materials,” said Knott.
Septic systems can also fail if they become submerged in water, said Jennifer Jacobs, engineering professor at the University of New Hampshire.
“In order to work, septic systems need to have some distance between the system and the groundwater below it, where it provides treatment to the waste,” said Jacobs.
If wastewater isn’t treated properly, it can increase the risk of pathogens and bacteria contaminating nearby water supplies.
Saltwater intrusion can be exacerbated by over pumping freshwater sources. Knott said the way to reduce the likelihood of this is through conserving the water in the aquifers.
Limited freshwater resources
Brandon Kernen, administrator for the drinking water division of the Department of Environmental Services, said coastal areas don’t have access to many freshwater bodies, which has caused problems to arise in the past for communities such as Hampton and Seabrook.
“There isn't a Lake Winnipesaukee or a Merrimack River there,” said Kernen. “They have to develop a large number of smaller water supply sources and diversify so that if any one of those smaller ones are impacted, they have other options.”
Kyle Pimental, assistant director of the Strafford County Planning Commission, said one thing his group is weighing is how population growth may affect demand on water supplies. County planners expect more people to move to the Seacoast, because of access to employment centers and major cities, like Boston and Portland.
“So with that, communities are going to have to continue to think about how they not only sustain their drinking water supplies, but also be prepared for exploring new sources,” Pimental said.
How can drinking water infrastructure weather these changes?
Several Seacoast towns have already undertaken some studies to assess their drinking water source vulnerabilities, including Newmarket and Durham.
Taking inventory of what data a town has on water assets was one of the most frequent recommendations that came from these studies. Records such as the age of structures and the depth of a structure in the ground can inform necessary planning.
The studies also predict how much sea level rise will change in the next 25 and 75 years, which can signal how frequently structures need to be maintained in order to weather these changes.
“When we put infrastructure in place, we're not thinking about what's happening in the next five years or even the next ten years. We tend to think much longer, much longer in the future,” said Jacobs.
What’s some emerging work related to this issue?
Knott and Jacobs are working with the state’s environmental agency to do an updated coastal risk assessment for coastal communities in the state, which they said should conclude in September of next year.
That assessment will include more inland communities, such as Dover, Madbury, Rollinsford, Exeter and Newcastle to evaluate how they might experience groundwater rise, in addition to other vulnerabilities associated with coastal proximity, Knott said.
Knott and Jacobs are also working on a detailed modeling study for Portsmouth to look at their infrastructure.
Knott said following the conclusion of this vulnerability assessment, they are planning on installing 10 wells near the coast in Portsmouth to monitor how groundwater rises with sea level rise. They’ll also be measuring for increases in salinity over time.
In addition to the coastal risk assessment, Kernen, with the state’s environmental agency, said the region has been taking steps toward drinking water resiliency through water system interconnections. The Seacoast Commission on Long Term Goals and Requirements for Drinking Water is studying how existing connections can be improved.
If any emergency situation occurs, such as water contamination or equipment malfunction, an interconnection can be used to send water from one public water supply to another.
“We're also going to look at supply and demand holistically for the Seacoast, both what it is now and what the projections are 20 years from now to see if there's any deficit issues and if so, what can be done to address it by regionally cooperating and managing the water resources,” said Kernen.
Portsmouth and Dover have been working on securing funding for an emergency water interconnection between their towns, which can also be used for ten additional Seacoast communities.
John Storer, director of community services in Dover, told NHPR earlier this month that Seacoast communities are trying to ensure they can make it through any emergencies that can affect anyone’s access to water.
“All communities are still trying to keep an eye towards the future of where we might be able to get more water. And if we can't find more water supplies, the question is ‘How can we rely on one another in a potential time of crisis?’”
This story is a production of the New England News Collaborative. It was originally published by New Hampshire Public Radio.