For 46 Years, Pilgrim Nuclear Plant Has Used Water From Cape Cod Bay. How Has It Impacted The Ecosystem?07:24

The discharge canal at Pilgrim, where water used for cooling at the plant is released back into Cape Cod Bay. (Robin Lubbock/WBUR)
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The Pilgrim Nuclear Power Station in Plymouth pumps about a half-billion gallons of water from Cape Cod Bay into the plant every day. The water cycles continuously, passing through the plant's condenser, and returning to the bay about 10 minutes later — and 30 degrees warmer.

Ever since Pilgrim began producing power in 1972, local environmentalists have argued the cooling system harms Cape Cod Bay in two ways: First, by killing or injuring millions of marine organisms like fish and plankton. And second, by discharging huge quantities of hot water that scour the ocean floor and exacerbate climate change-induced ocean warming.

“Cape Cod Bay is a unique and magnificent habitat and [Pilgrim] has been a very damaging influence,” says Pine duBois, executive director of the nonprofit Jones River Watershed Association. Her organization monitors protected fish like alewife and blueback herring that travel between the Jones River and Cape Cod Bay — fish she says Pilgrim has harmed over the last 46 years.

Entergy Nuclear Operations, which owns the plant, doesn’t dispute that its cooling system discharges hot water and kills fish, but it does dispute the scale of the problem.

Pat O’Brien, an Entergy spokesman, writes in an email that many claims environmentalists make about Pilgrim’s ecological impacts “are both over-exaggerated and not consistent with the decades of scientific monitoring that has been performed by various federal, state and local agencies.”

The Pilgrim Nuclear Power Station on Rocky Point, Plymouth, Mass. (Robin Lubbock/WBUR)

Cape Cod Bay's ecosystem is complex and affected by multiple — often compounding — trends like ocean warming, ocean acidification and pollution. And because there have been no independent and comprehensive studies looking at Pilgrim’s ecological impact on the bay, the best source of information comes from the Nuclear Regulatory Commission (NRC). The commission has repeatedly said the plant hasn't had a significant impact on the bay and its greater ecosystem.

“I don’t think the impact on the surrounding environment has been given the weight that it should have been given over the years,” says Andrew Gottlieb, executive director of the nonprofit Association to Preserve Cape Cod (APCC). "I think the notion that the ocean is vast and can therefore have a limitless ability to assume and assimilate all of the insults that we impose on it has been proven to be incorrect.”

As Pilgrim prepares to close at the end of May, here are answers to some questions about the plant's water use and how it impacts the bay.

Why Does Pilgrim Use So Much Water?

A nuclear power plant harnesses energy (heat) from splitting atoms. The heat boils water into steam, which turns a turbine to generate electricity. After steam goes through the turbine, machinery condenses it back into water so it can be used again.

To cool the steam back into water, power plants pump cold water around metal "condenser pipes" to absorb excess heat. (About 33 percent of the heat generated by a nuclear plant is used to power the grid; the rest is considered waste.) This cooling water, in Pilgrim's case, comes from Cape Cod Bay.

Pilgrim uses what’s called a “once-through” cooling system. A steady stream of ocean water is pumped in and out of the condenser to absorb excess heat, creating "thermal pollution" in the bay.

Despite local opposition throughout the '70s, the Environmental Protection Agency (EPA) ruled in 1978 that Boston Edison, the former owner of the plant, could continue using a once-through cooling system.

How Does Water Get In And Out Of Pilgrim?

The EPA allows Pilgrim to pump up to 510 million gallons of water a day from Cape Cod Bay, or about 300,000 gallons per minute. As water is sucked through the intake structure, it passes through a series of screens to keep out debris like seaweed, trash and fish. Live fish are returned to the ocean through a sluiceway. (That's an artificial channel that flushes water back out into the bay.)

The plant treats the water with small amounts of chlorine and anti-corrosive chemicals and sends it to the condenser. By the time it leaves the plant it’s about 30 degrees warmer.

Legally, Pilgrim is not allowed to discharge water more than 32 degrees above the ambient temperature of the bay, or over 102 degrees. Most days, this isn’t a problem, but there have been a few times — most recently, last August — when the bay got too warm and the plant had to power down.

Marine life can build up inside the condenser tubes and intake structure, so the plant must occasionally reverse the flow of the water and “backwash” the system. In these situations, the plant is allowed to discharge water hotter than the 102 degrees. Thermal backwashes occur four to six times a year at Pilgrim. The NRC says while backwashes create a thin thermal plume near the intake structure, it dissipates within a few hours and has little impact on the surrounding environment.

What Happens To Marine Life Near The Discharge Canal?

Warm water usually leaves the plant via a 900-foot-long discharge canal. On cool days, you can see steam rising from the surface of the water.

“Years and years and years of half a billion gallons a day being continuously discharged has an effect on the ocean floor,” Gottlieb says. “It’s basically denuded those areas of life."

According to the Association to Preserve Cape Cod, the flow of warm water has created a 15,000-square-foot dead zone around the end of the discharge canal. Essentially, nothing can live there. Surrounding that is an even larger area of stunted marine life.

Entergy says the discharge system is designed to mix the warm water with the cooler bay water as efficiently as possible, though the thermal plume varies in size and depth depending on the tide and temperature of the bay. During high tides, when the plume is at its largest, it ranges from 3 to 8 feet deep and can cover an area up to 216 acres.

The NRC notes in its 2007 Environmental Review that during low tide, the water flow out of the canal “is strong enough to scour the [ocean] bottom in the area near the discharge" and likely to affect fish and plants. But during high tide, "the heated discharge water does not displace the denser, colder, ambient water that remains near the bottom,” and therefore does not affect marine life.

The NRC says the additional heat is — almost literally — a drop in the ocean with “relatively insignificant” impact.

Warmer water also attracts some marine life. So the area around the discharge canal was once a popular fishing spot for locals. But after 9/11, the plant restricted public access for security purposes.

When fish attracted to the warm flowing water enter Pilgrim's system, the trip can be fatal. Pilgrim caused its first major fish kill in 1973, shortly after it opened. About 43,000 Atlantic menhaden swam up the discharge canal — perhaps mistaking it for the river where they spawn — and died.

Three years later, another 5,000 menhaden died in the canal. Boston Edison, the plant's owner at the time, put up a net to block out fish near the end of the canal. The EPA let the plant remove the net in 1994; since then, there have been no documented fish kills in the discharge canal, a spokesman for Entergy confirms.

Gottlieb, of the APCC, isn't convinced the impact of the warm water flow adds up to being "relatively insignificant," as the NRC says.

An ecosystem like Cape Cod Bay is “very complex and subject to numerous number of influences that compound or offset one another, so it’s hard to single out one [factor],” he says. But "you’re taking systems that are already under an enormous amount of stress due to global climate change, and then you’re tacking 30 degrees on top of that? You can’t be doing that system any good.”

Does Pilgrim Impact Cape Cod Bay Fisheries?

It depends on whom you ask.

Gottlieb and duBois, the head of Jones River Watershed Association, are certain the answer is yes because every year, thousands of fish and shellfish get trapped against the Pilgrim’s intake screens, or "impinged." And millions of fish eggs and plankton are "entrained," or sucked through the screens, where they die from heat or chlorine. (Again, some of the trapped marine life are returned to the bay through a sluiceway.)

“There’s a significant impact on recreational fisheries, larvae and small juveniles as a result of the intake structure,” Gottlieb says, “and that’s causing some significant loss in populations.”

But whether Pilgrim has had a noticeable effect on the overall population is disputed and unclear.

In 2007, Entergy concluded the plant’s “operations have not had a significant effect on local and regional populations of fish and shellfish” and that “trends in abundance of groundfish, pelagic fish, and shellfish (lobsters in particular) in western Cape Cod Bay mirror population trends in the larger Gulf of Maine and the western North Atlantic.”

The NRC, meanwhile, said there's potential for the plant to have a moderate impact on local populations of winter flounder and rainbow smelt, but that "the cumulative impacts ... on other marine aquatic resources is expected to be small to moderate."

Since the plant opened, it has impinged at least 80 species of fish and marine life and returned many of them to the bay. Whether any of these fish are injured, or even die shortly afterward from stress or exhaustion, remains unknown.

There have been at least 21 “significant impingement events” — when more than 1,000 fish die within a few days — since the plant opened. That doesn't include the two menhaden fish kills in the discharge canal.

Pine duBois stands by the Jones River. (Miriam Wasser/WBUR)

“If the Gulf of Maine is one of the richest fisheries in the world, [Cape Cod Bay] is its nursery,” duBois says. “And when you kill a large segment of a population, it takes time to regenerate, to come back.”

In 2011, an environmental consulting group, Normandeau Associates, analyzed Pilgrim’s impingement data from 1980 to 2010. They found that on average, 46,000 fish are trapped in the plant’s screens annually. But there’s a lot of variability from year to year: About 4,000 fish were impinged in 1980 while 302,000 — the highest recorded number available — were impinged in 2005.

Didn't One Of Pilgrim’s Clean Water Act Permits Expire? How Does That Fit In?

Pilgrim, like any industrial facility, needs a special permit to release anything — even hot water — into the environment.

The National Pollutant Discharge Elimination System (NPDES — pronounced “nip-dees”) permit is supposed to be reviewed every five years to reflect advances in science and make sure a plant is using the best available technology.

Pilgrim’s NPDES permit expired in 1996 and has been “administratively extended” ever since. Gottlieb, of the APCC, says it’s not uncommon for five-year reviews to run late, but he calls a 23-year lapse “excessive.” And he worries that by letting the permit lapse, the EPA and Massachusetts Department of Environmental Protection might unwittingly be allowing Pilgrim to damage the environment.

The EPA released a draft permit in 2014 and took public comments. In an email this month, EPA spokeswoman Emily Bender says the agency hopes to issue an updated permit in the next six to nine months.

Though Pilgrim shuts down at the end of May, the plant will continue to use water from Cape Cod Bay for a few years during decommissioning. The updated permit is expected to spell out what the plant can and cannot discharge during this period.

So What Is Pilgrim’s Legacy In Cape Cod Bay?

Do thousands of dead fish — and a dead zone around the plant's discharge canal — have more than a localized impact? It’s hard to say.

DuBois says local fisheries have been harmed. But it's difficult to disentangle the plant's impact from the impact of climate change, pollution and over-fishing.

Gottlieb says you probably can’t. But, he adds, that doesn’t vindicate Pilgrim.

“The whole warming trend is putting the entire system under stress,” he says. “And everything we know about warming would indicate that additional heat load is a bad thing."

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This segment aired on April 19, 2019.


Miriam Wasser Twitter Reporter, EarthWhile
Miriam Wasser is a reporter for WBUR's environmental vertical.