In a town of bedrock surrounded by salt water, groundwater is a precious — and vulnerable — resource

Harpswell’s dramatic rocky shores are a big part of what makes the town such an attractive place to live. They also make it a precarious place to call home.

The great majority of the residences here depend on drilled wells for their water. Ample supplies of clean water are essential to health and happiness — not to mention property values. But the town’s bedrock geology and proximity to the sea make those wells unusually vulnerable.

Some wells may not provide enough water to sustain a household comfortably. They may contain high levels of naturally occurring minerals than can corrode pipes and appliances, or even pose health risks. And if that’s not worry enough, the water can turn brackish from saltwater intrusion.

All of this is because of the bedrock under our feet and the salt water surrounding our islands and peninsulas. In simplest terms, there is not enough sand, gravel and soil covering the bedrock. And many of the cracks in the rock connect to nearby bays and coves.

‘A rocky place’

“Harpswell doesn’t have any deposits of sand and gravel,” explained Ryan P. Gordon, a hydrogeologist with the Maine Geological Survey. “That means people are entirely dependent on the bedrock.”

The source of our well water is rain that seeps into the soil, then descends through fractures in the rock.

When drillers are looking for water, they bore a hole through the ground, passing through any looser material — what geologists call overburden —before entering the bedrock. As the drill bit passes through the hard rock, it intersects with cracks through which water can flow. If the well is a successful one, the drill will have intersected enough water-bearing cracks to produce a pool of water at the base of the hole.

Until that happens, no one can predict how much water will be found or what the quality of that water will be. Even when close to each other, wells can vary widely in productivity and water quality.

“A well isn’t tapping a large lake or reservoir underground,” Gordon said. “The cracks are small.”

The overburden can play a crucial role in the productivity of a well. Rain falling on bare rock will mostly be lost to runoff. The overburden, however, can serve as a kind of reservoir. Rainwater that seeps into the ground can be stored in the tiny spaces between particles of soil, sand, gravel and other porous material.

“Sand and gravel on top of bedrock make excellent aquifers,” Gordon said.

The deeper the overburden, the greater its storage capacity and the more water is available to recharge the fractures.

Along much of the Maine coast, few formations of sand and gravel were left behind when the last glaciers disappeared 13,000 years ago.

“That means it’s rocky, lots of exposed bedrock,” Gordon said. “There’s very little soil atop the bedrock. That’s especially true in Harpswell. It’s a rocky place.”

All of this affects Harpswell’s capacity for growth. A water and septic study done for the town in 2008 by Ransom Environmental Consultants Inc., of Portland, and CES Inc., of Brewer, observed, “Areas in Harpswell with limited soil thickness can often represent future development limitations.”

But that does not mean all of Harpswell is lacking in productive wells. As a general rule, a residential well that produces less than a gallon of water per minute is considered marginal.  The 2008 study identified more than 400 wells that produced 10 to 50 gallons per minute. Thus, while groundwater supplies are modest in much of the town, significant numbers of wells are producing ample amounts.

How salt infiltrates wells

Even if a well is supplying sufficient water, the town’s geology and geography can combine to create another problem: saltwater intrusion.

If the fractures feeding a well connect to a bay, saltwater can flow into them and turn the well water into brine.

As gravity pulls the fresh water down the fractures, it pressurizes the cracks. When a crack meets salt water, that pressure normally prevents the saltwater from moving up the fracture.

Now imagine a house party with many guests using large amounts of water. The pump works hard, pulling water up from the well. That upward pull reduces the pressure exerted by the fresh water where it interfaces with the saltwater. The salt water starts rising in the crack. Fresh water does float on salt water. But eventually, as the fresh water rises in the crack, the level of the salt water may reach the bottom of the well.

“When you take water out of an aquifer, you are changing the aquifer,” Gordon said. “When you are drawing water, you can draw (salt) water in.”

Or imagine your neighbors, in a dry year, keep watering their large lawn.

“The density of wells is an issue,” Gordon said. “If they are close together, they can interact with each other.”

The cracks in the bedrock are often connected. “You’re really blind to the network. You really don’t know what the fracture network is going to be,” Gordon said.

So in a dry season, the water going to the neighbor’s lawn can lower the pressure of the water in the interconnecting cracks and salt water can infiltrate your well.

“Being really close to the ocean is a hazard,” Gordon said. “There may be fresh water beneath your feet, but it may not be enough.”

Vulnerability to saltwater intrusion is, to some extent, a matter of luck. In any given area, fractures tend to run in similar directions. In Harpswell, where the landforms generally run from north to south, a fracture network that runs east to west is problematic. More of those cracks are likely to interface with the nearby salt water, as opposed to a north-south network in which the fractures run parallel to saltwater bodies rather than toward them.

And don’t forget about minerals

Then there’s the issue of high levels of naturally occurring minerals that can make water unsuitable for use. This too is a consequence of geology.

Harpswell’s rock is mostly metamorphic, which simply means that one form of rock has changed into another, generally as result of high heat and/or pressure. Harpswell’s bedrock, Gordon said, was “pushed together by tectonic forces over hundreds of millions of years.”

While the rock may be of the same general type, at the same time the town’s geology is “really complicated,” he added. “You get rocks really close to each other that have different geologic histories.”

One of the consequences of this complicated geology is a wide range of minerals that can create problems in the well water. Iron can turn water rusty. Sulfites can make it acidic. Arsenic can make it poisonous.

Henry N. Berry IV, a geologist and colleague of Gordon’s at the Maine Geological Survey, warned that the mineral content of a given well is not necessarily constant. “Conditions can change,” he said, expressing particular concern about arsenic.

“The only way to know is to test it, especially in an area with that complexity,” he said. “If you are concerned about water quality, and you should be, you should have the water tested.”

‘More critical than we realized’

Kara Douglas, of Ash Point, can attest to the vulnerability of wells in Harpswell. She has lived in her house since 2008. It has two water sources: an old dug well in the basement and a drilled well that she believes dates to the 1960s. She never experienced any problems, until 2020.

That summer, both of the wells went dry.

The water in the dug well is not potable, but she uses it for such tasks as watering the garden or flushing toilets when the power goes out. The well gives her a sense of the state of the water table, since she can look down into the well and see the level of the water. That summer she looked down to see nothing but dirt.

The summer of 2021 passed without problems. Then, in 2022, the dug well went dry again. And the pump serving her drilled well began to make familiar noises.

“It was behaving the same way it did in 2020, so we stopped using it,” she said. “That meant we had to haul water.”

Once a week, they would load their pickup truck with four to six 10-gallon containers and drive to the Brunswick and Topsham Water District’s headquarters in Topsham to buy water. “We were really, really judicious in our water use,” Douglas said.

Both summers were unusually dry. And in both years, the wells ran dry in late July. In 2020, some rain in August helped recharge her wells. In 2022, the water in the wells did not return until September. That, of course, represented a considerable hardship for a household with two adults and two children, who are now ages 11 and 17.

As far as she knows, none of her neighbors had problems with their wells.

Douglas said that her area has seen a substantial amount of development in the last five years. She worries that the new houses and their wells may be contributing to water problems.

“I’m not suggesting that it (development) is exclusively the issue,” she said. But she thinks the town should be taking a closer look at the vulnerability of its groundwater resources. She believes the situation may be “a little more critical than we realized.”

Old method produces new wells

When a well runs dry, turns salty or becomes contaminated by minerals, a homeowner may consider drilling a new one. But not all wells are created equal, according to Eric Wilson, head of Water Doctors, a Brunswick company that helps its customers find solutions to their water problems.

One of Wilson’s tools for helping people with inadequate supply is a well driller named Doug Baldwin. He employs a drilling technique Wilson describes as “pounding.” Baldwin’s wells can be more productive than typical drilled wells, depending on rock conditions and proximity to salt water, Wilson said.

“We refer people (to Baldwin) when we’ve tried everything else,” Wilson said.

Baldwin’s rig essentially drills and fractures the rock at the same time. The fracturing produces voids that act as reservoirs, according to Wilson.

Baldwin achieves his results using old-fashioned technology. His drill rig sits atop an Army surplus troop transport that was new in 1986. After removing the section where the soldiers sat, he mounted a drilling rig that dates to the 1950s.

He too is a bit of an antique, an 80-year-old man who has drilled about 1,000 wells, by his count, in a career that began in 1961 and paused only for two years in the Army.

Driven by a diesel engine, his rig employs a cable that lifts and then drops a drill bit mounted beneath an 1,800-pound weight. The carborundum bit repeatedly rises and crashes down, splintering the rock below.

More modern drills are air-driven devices that work like a jackhammer.

An air-driven rig can drill a 1,000-foot well in about two days, according to Baldwin. He never drills wells that deep. If he did, “it would probably take me a month,” he said.

Baldwin has a somewhat different explanation for his success than Wilson. Baldwin believes the high-pressure air in conventional drills tends to plug water-bearing fractures with loose material churned up in the bore holes. When Baldwin’s bit hits a fracture, in the absence of air pressure, water flows freely out of the crack, helping to keep it open.

Baldwin estimates that he has drilled 15 to 20 wells in Harpswell over the last five years. Most were new wells, but about a third were replacements for problem wells, he said.

While far from definitive, those numbers do suggest how vulnerable wells in Harpswell can be. That view is reinforced by some of the findings of the 2008 study on drinking water and septic systems.

While the report acknowledged the vulnerabilities and limitations of the town’s groundwater supplies, it went on to say that those conditions were “not expected to represent a major constraint on development.”

“Drillers have had reasonable success developing a substantial number of moderate- to high-yield wells throughout the town,” the report said.

‘Conservation measures should start now’

The town’s current comprehensive plan, adopted in 2005, contains a section on groundwater, including goals to “Protect groundwater quality from potential threats from future growth and development,” and “Assure that future groundwater use does not exceed available supply.”

The town has created a Comprehensive Plan Task Force to update the plan. Mary Ann Nahf, who chairs the town’s Conservation Commission, also serves on the Comprehensive Plan Task Force. She expects groundwater issues to be addressed in the new plan.

“It’s always been a topic of conversation in Harpswell,” she said of the town’s groundwater. “What makes it seem like an emergency is the amount of development in the last few years.”

She and the Conservation Commission have focused on protecting groundwater by encouraging property owners to plant trees along the shoreline and spread natural materials, like leaves and duff, to slow runoff and increase the amount of water soaked up by the ground.

She fears a critical point for groundwater supplies may be coming soon, given the town’s growth and drought conditions over the last few years.

“Increased conservation measures should start now, while we study how to address a long-term solution,” she said.

She does not expect the Comprehensive Plan Task Force to come up with solutions to the town’s water issues, but she hopes the group will point the way.

John Gormley is a retired journalist who lives in Cundy’s Harbor. His interests include fishing, tennis and gardening.

This article is part of “Development and the Harpswell Environment,” a Harpswell Anchor special report.