Volume of Maine’s storm and sewage overflows more than doubled in 2023 (2024)

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Heavy rains coming in back-to-back storms, sometimes when the ground was frozen, contributed to high levels of untreated storm and sewer water being washed in Maine's rivers and bays last year, resulting in shellfish bed and beach closures.


Volume of Maine’s storm and sewage overflows more than doubled in 2023 (1)
Penelope OvertonPress Herald

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Volume of Maine’s storm and sewage overflows more than doubled in 2023 (3)

A swollen Kennebec River floods buildings on the back side of Water Street in Augusta after a severe rainstorm in December. Waters rose to more than 30 feet and reached a flow of 144,000 cubic feet per second in parts of the river between Augusta and Waterville, according to the National Oceanic and Atmospheric Administration. Photo courtesy of Dave Dostie

Last year’s extreme rainstorms flushed over 745 million gallons of raw storm and sewer water into Maine rivers and bays – more than twice as much as what overflowed the systems in 2022 and more than any other year since 2015.

According to a new Maine Department of Environmental Protection report, last year’s untreated stormwater-sewer overflow was 244% more than the 305.3 million gallons recorded in 2022. Maine’s biggest city, Portland, accounted for almost half of the state’s total overflow, or 368.7 million gallons.

It wasn’t just the amount of rain that caused overflows in the 31 Maine communities yet to separate their stormwater and sewage treatment systems, but when and how it fell – in big, high-intensity bursts, often one right after the other or when the ground was frozen.

That much overflow is almost enough to fill up 745 swimming pools – if they were as big as footfall fields.

“Make no mistake, 2023 was a challenging year,” said Mike Riley, the abatement coordinator at Maine Department of Environmental Protection. “Just when we were feeling bullish on the progress that has been made reducing discharge, along comes a year like 2023 to temper our optimism.”

A random combination of the worst runoff conditions turned 2023 into a terrible year, he said. Maine recorded more than 57 inches of rain, much of which came in large, high-intensity storms in maximum runoff conditions, such as when the ground was frozen or already soaked by another storm.


For example, Lewiston’s storm-sewer overflows in 2023 were all about timing. A July storm caused a minor overflow, while a December storm with only slightly more rain overwhelmed the system. Why? The frozen ground in December turned the rain into runoff, flooding the city’s sewer system.

“Last year was a good example of why we don’t judge progress on (combined sewer overflow) abatement based on one year’s results,” Riley said in DEP’s 2023 overflow report. “It’s the trendline that remains the most important indicator of overall progress, and in that regard, Maine communities continue to make progress.”

In 1987, Maine communities discharged 6.2 billion gallons of sewage-tainted water into Maine’s scenic waterways – an 88% difference that shows how far Maine has come but also how hard it can be to fix underground infrastructure built generations before environmental laws were created.

No one can say exactly what is in the floating streams of what’s called “brown tea” that jut out into the bay after big storms because nobody monitors the contents of overflows. But it gets its color from sediment, sewage and naturally occurring tannins that can leach out of plant debris from riverbeds.

But Friends of Casco Bay, a nonprofit founded in 1989 to protect the bay’s health, is pretty sure it’s not good. Runoff and wastewater already contain high amounts of phosphorous, nitrogen, soot, pesticides and heat – not to mention sewage – that can harm water quality, aquatic life and the local economy.

Earlier this year, after the January storms caused another round of overflows not included in the DEP report totals, Baykeeper Ivy Frignoca, the chief advocate of Friends of Casco Bay, talked about how the extreme weather patterns were complicating statewide protection efforts.


“It’s really hard to talk about the weather this winter and not have an emotional response to the storms and the impact they are having on our state, on the people of the state, and on the water resources we all love and want to protect,” Frignoca said.

In addition to street overflows and backed-up basem*nts, overflows can cause potential public health problems, including the closure of beaches and shellfishing areas due to bacterial contamination, and contamination of drinking water supplies.

It can be difficult to say an overflow is the only cause of a beach or shellfish closure because conditions that cause the combined sewer systems to overflow can often cause other public health threats, such as rainwaters carrying overwhelmed domestic systems or animal waste into the water.

In the DEP’s opinion, however, last year’s overflows caused at least one beach closure – East End Beach in Portland – and potentially degraded 12 other beaches, including one in Bar Harbor, five in Biddeford, three in Cape Elizabeth, one in South Portland, and one in Calais.

Three communities with combined systems – Calais, Machias and Portland – reported overflows in 2023 resulting in shellfishing area closures, including 11 in Machias. Machias is scheduled to complete a pump station and improve a river crossing this year, which should reduce its overflow risk.

Portland Water District maximizes how much water it can treat at its plants during wet weather. At East End, for example, the treated flow increases from about 15 million on a typical day to 80 million gallons on a rainy day. Without those maximization efforts, Portland’s overflow would double.


“With the observed increase in rainfall volume and intensity, the amount of water that must be managed continues to increase, making the issue more challenging and costly to address,” said Scott Firmin, the district’s wastewater services director.

Environmental groups such as the Natural Resources Council of Maine and Maine Rivers have applauded the federal government for investing in the long overdue upgrades to Maine’s wastewater systems and the state for making great progress in reducing wastewater pollution in its waters.

The storms have overwhelmed more than just the stormwater and sewer systems of communities that line Maine waterways, said Maine Rivers Executive Director Landis Hudson. Everybody knows we will face more unmanageable storm events, and most communities have already started planning for them.

“If we hadn’t made the progress that we’ve made over the past 35 years through the upgrades that have been made, it would have been much, much worse,” said Pete Didisheim, the NRCM advocacy director. “Which is why we need to keep working down the backlog of projects that DEP keeps track of.”

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