Experts have a good understanding of Harpswell’s potable water sources and extraction methods, but data limitations make it impossible to predict how many more residents the town’s groundwater can support.

That was one of the key messages a state hydrogeologist conveyed during a presentation on Wednesday, Sept. 11, at Harpswell Community School. She issued a call to action for residents to start participating in the data-gathering process so the state can make better predictions.

Hosted by Harpswell’s Conservation Commission, the lecture was the first installment in a series titled “Fractured Bedrock: Understanding Harpswell’s Water Supply.”

Its presenter, Jessica Meeks, of the Maine Geological Survey, said gathering more data on local wells and water quality also would help experts predict future impacts of climate change on Harpswell’s potable water supply.

“We don’t have enough data to adequately advise communities on carrying capacity,” Meeks told an audience of about 100 residents, with dozens more watching online. “That’s the challenge right now.”

Where is the water?

Geologists have determined Harpswell’s underground aquifers collect much more fresh water than residents use each year, but that’s merely an aggregate figure, Meeks said.

She explained that Harpswell has no “significant aquifer,” a designation for saturated deposits of sand and gravel from which a well can pump water continuously at a rate of 10 gallons per minute or more.

Instead, the town sits mostly on outcrops of metamorphic bedrock, originally sedimentary rock that was altered by heat, pressure and chemical processes deep within the Earth’s crust. That bedrock has formed many fissures within which fresh water collects.

Harpswell’s geology makes well drilling unpredictable, Meeks said. Property owners run the risk of missing a fissure entirely, or tapping into one with low water yield because it isn’t well connected to the surrounding aquifer.

“While there is a trend in the fractures’ orientation over a region, it is impossible to know exactly the depth, distribution and interconnection of fractures and the resulting water yield at a site until you put in a well,” she said.

There’s also the risk of seawater infiltrating the fissures. Meeks said residents should dig their wells as far away from the shore as possible to prevent seawater contamination, noting that the “zones of dispersion” where fresh and salty water mix can shift over time.

State geologists estimate annual freshwater infiltration of roughly 15 billion gallons per year in Harpswell. Infiltration occurs when water seeps through the surface and permeates unsaturated ground until it reaches the saturated zone, where it becomes part of the aquifer system.

Meanwhile, town residents only use an estimated 101 million gallons of fresh water each year, Meeks said. That figure is based on the town’s population of roughly 5,000 multiplied by the average per capita daily water use of 55 gallons.

Still, Meeks noted that water use is more concentrated in some areas, and that localized shortages could occur. In general, the “freshwater lens” is narrower in thinner parts of the peninsulas and islands, meaning that less drinking water is available.

“But again, I don’t have solid data,” she said. “What we really need is data over time, to see how things are changing.”

Good and bad news

While climate change is already impacting Harpswell in the form of more intense storms and increased coastal erosion, Meeks said not all the news is bad.

In the coming decades, Harpswell could see significant sea-level rise, which may submerge low-lying areas, inundate wetlands and threaten freshwater resources with saltwater intrusion, particularly in coastal wells​.

Meeks referred attendees to the “Coastal Risk Explorer,” an interactive online map created by The Nature Conservancy that shows how different increases in sea level could affect various properties. It shows which homes and roads will become inundated or inaccessible at different sea-level increases.

Fortunately, she said, Maine’s coastal aquifers have been filling up over time because of increased precipitation, another climate change impact.

“We actually have more water falling on us now,” Meeks said. “We have more (fresh water) than we used to.”

Overuse of drinkable water is a serious concern along the coast, according to Meeks, as it can actually shrink the “zone of transition” where fresh water floats atop heavier, saline water.

“If you keep drawing on that well and go hog wild with it, you’re going to suck the transition zone up into your well stream, and then you’ll start having briny or sandy water,” she said.

Help wanted

The Conservation Commission has said it decided to host a lecture series on groundwater in response to concerns about the town’s water supply that arose during public meetings about updating Harpswell’s comprehensive plan.

A draft of the plan acknowledges that maintaining Harpswell’s potable water supply will be vital to building a sustainable future for all residents. It includes four goals related to understanding and protecting the town’s groundwater resources.

Meeks said there are a number of ways residents can participate in the Maine Geological Survey’s data-gathering efforts. The state agency is responsible for mapping, studying and providing information on geological resources, including groundwater.

But its Maine Water Well Database, the state’s leading data repository, is incomplete, she said, with only about one-third of all wells having been registered by their owners.

Although registration is required by law, many older wells are grandfathered, and Meeks said there is no enforcement mechanism for registering new wells. So, simply making sure your well is registered would help, she said.

The state is also asking local groups to participate in data collection projects involving private property owners, according to Meeks. She added that all property-specific data is kept confidential.

Common approaches include occasional water quality sampling and/or installing usage meters or devices that gather information about groundwater levels, as well as recharge and infiltration rates.

Meeks said the next installment in the groundwater lecture series will go into greater detail about how residents can get involved. It is scheduled for 6 p.m. on Wednesday, Oct. 30, and will focus on water conservation methods. The venue had yet to be determined as of mid-September.

For more information, visit the Conservation Commission’s webpage at harpswell.maine.gov.