An outflow pipe from an overboard discharge system is visible among rockweed at low tide in Cundy’s Harbor on Dec. 13, 2024. Sam Lemonick photo

With no municipal sewer system, almost all of Harpswell’s homes and businesses rely on septic systems to handle their wastewater. But a few dozen properties that are too small or too rocky for conventional septic systems still use what are called overboard discharge systems, even as the state and town governments work to replace them.

Overboard discharges, or OBDs, release treated wastewater to surface water such as a river or the ocean, whereas in a conventional septic system, the cleaned wastewater trickles down into groundwater.

The Maine Department of Environmental Protection tests each OBD’s outflow annually to ensure it is clean. But because an overboard discharge that isn’t working correctly could introduce bacteria and other pathogens directly into bodies of water, Maine has a goal of eventually eliminating all overboard discharges. The Maine Department of Marine Resources prohibits shellfish harvesting in areas near OBD outflows as a precaution.

Overboard discharge systems replaced so-called straight-pipe systems, which discharge raw wastewater, when those were banned in the 1970s. New OBDs have not been allowed since around 1990, according to Irene Saumur, who handles overboard discharge licensing at the Department of Environmental Protection. Of the roughly 2,000 overboard discharges existing then, Saumur said about 600 remain. Harpswell has 44 of those, the fifth most among Maine towns. Only Boothbay, Bristol, Georgetown and Southport have more.

Saumur said a certain number of overboard discharges — maybe 300 or 350 statewide — may never be replaced. Those are on lots that are too small or too rocky for even the most compact modern septic systems.

Impacts on clam harvesting

Overboard discharges often draw attention because they force closures of clam flats. Harpswell Harbor Master Paul Plummer said that topic comes up occasionally at the town’s Marine Resources Committee and among town staff.

The committee has discussed working with the town and the Department of Environmental Protection to identify OBDs that could be replaced, after which the Department of Marine Resources could consider reopening the area for shellfish harvesting. But Plummer said those discussions have not advanced.

Saumur cautioned that removing an overboard discharge does not mean an area will be reopened. On the contrary, she said, when the Department of Marine Resources begins its multiyear process of evaluating an area, their testing often finds unrelated sources of pollution that keep the area closed. Those sources might include an aging septic system.

She pointed to Bristol Consolidated School, about an hour northeast of Harpswell, as one example. In 2012, voters approved spending $86,000 — about half of which the DEP reimbursed — to replace the school’s overboard discharge, with the health of the nearby Pemaquid River and its shellfish mentioned in news articles. More than a decade later, however, the area is closed to harvesting from May through October because of pollution.

Alternatives available, but expensive

The state keeps track of overboard discharges through licenses, which require a $450 annual fee. Owners must apply to renew their license every five years or when the property changes hands.

Renewal involves a site evaluation from a licensed septic system designer, who can assess whether the overboard discharge can be replaced by another system. Those evaluations cost a few hundred dollars.

Like a traditional septic system, overboard discharge systems start with a septic tank, where different components of wastewater settle and microbes begin to break the waste down. But instead of a leach field, where water seeps through soil and rock to finish the cleaning process, an overboard discharge has one or more additional tanks to filter the wastewater or mix it up to promote microbe growth. The last step disinfects the water with chlorine or ultraviolet light before it’s discharged.

Around 2010, Maine regulators approved newer septic system products that use much smaller leach fields — “the size of the rug in your living room,” Saumur said. These can replace many OBDs, though not all.

Saumur said that not all property owners or site evaluators are familiar with these more modern systems. There are likely OBDs that these compact septic systems could replace but haven’t yet.

These newer septic designs are also expensive. One example, the Fuji Clean system, costs between $40,000 and $50,000 to install, said Robert Carter, septic manager at R.A. Webber & Sons Inc., of Cundy’s Harbor. For comparison, he said a conventional system runs about $25,000–$30,000.

Maine has a grant program to help property owners pay for overboard discharge replacement, but Saumur said there is a long waitlist for the limited funds available.

Challenges, approaches vary

Owners’ experiences of OBDs vary. Bill Briscoe, who owns several neighboring homes in Cundy’s Harbor, replaced the properties’ shared overboard discharge in the fall of 2024. He estimated that he was spending about $10,000 each year on the OBD, including the cost of electricity.

Briscoe said that because he swims in the waters where the system discharged, and he knows that the town encourages replacement, he was happy to install a compact septic system. He said the new system had cost about $60,000.

A little farther south, at the house he rents next to Watson’s General Store, T.J. Watson said he is generally satisfied with his OBD. He adds chlorine tablets when needed, and he said the crabs and other animals along his shoreline show him that it’s not impacting sea life.

But Watson said the paperwork required to maintain an OBD license has gotten more onerous over the last 10–15 years. And because the property is all ledge, there aren’t any alternatives.

The Sundrenched restaurant, just south of the Cribstone Bridge on Bailey Island, also has an overboard discharge. Zac Leeman, who leases the property and runs the restaurant with his wife, Khristine, described it as an older system. He said the most recent site evaluator suggested replacing it with more modern, computerized equipment when the license was last renewed.

Leeman said he prefers the older system because he can do a lot of the repairs and maintenance himself. But he also said it’s getting difficult to find contractors who can service or supply the older equipment in his system. He expects to spend $3,000–$4,000 this winter replacing some of the OBD’s seven pumps to get it running before Sundrenched reopens for the 2025 season.

Sam Lemonick is a freelance reporter. He lives in Cundy’s Harbor.