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For 86 years, Plum Island scientists have been cleaning the North Shore’s clams. Today, they’re keeping a New England tradition alive.

For locals who grew up eating native clams—steamers swirled in hot butter, fried bellies with tangy tartar, creamy chowder—it’s hard to imagine summer without our bivalve buddies. But in 1925, disease traced to New York clams closed flats across the Northeast. To rescue the industry, Newburyport officials experimented with depuration, purging clams of bacteria by immersing them in spring water. Almost a century later, Plum Island’s Newburyport Shellfish Purification Plant is still cleaning the region’s soft shells, preserving a culinary tradition and a way of life for local diggers.

“I wouldn’t be able to dig these clams at all if it wasn’t for them,” says Chris Krafton, a 49-year-old Amesbury resident who’s been harvesting clams from the Merrimack River estuary for 17 years. Krafton digs in the pre-dawn hours, launching his 14-foot aluminum boat into the flats just south of the Salisbury Reservation. As a licensed subordina
digger, he works year-round under Bob Stanley, a master digger and the owner of the Stanley Seafood Co., a shellfish wholesaler in Revere. “It’s an old-time trade,” says Stanley, who relies on native North Shore clams for his business. “My father did it before me, and his father before him. It’d be kind of hard to change.”

Stanley is one of 67 licensed diggers who use the Newburyport plant to turn otherwise inedible clams into some of the cleanest shellfish in the industry. How clean are they? While federal regulations set safe levels of contamination at 230 fecal coliform (bacteria) for every 100 grams of clam meat, the plant’s shellfish emerge with fewer than 50 fecal coliform, far below the market standard. “No illness has ever been traced to this facility, from the beginning,” says Jeff Kennedy, regional shellfish supervisor for the Massachusetts Division of Marine Fisheries, which has run the plant since 1960. Only a handful of depuration plants operate in the U.S., and the Plum Island facility claims to be the oldest in the world.

Depuration is a relatively simple process. Bivalves are filter feeders, pulling water through their bodies to eat and breathe. As a result, they accumulate contaminants even in water deemed safe for swimming. But immerse clams in a contaminant-free habitat, and they’ll filter themselves clean.

Each morning, master diggers from as far south as Quincy bring their harvests to the plant, a gray-shingled building at the northern tip of Plum Island. Plant coordinator Ralph Stevens stacks the bushels in nine 3,500-gallon concrete tanks and fills them with clean saltwater pumped from wells deep beneath the dunes. For three days, cold salt water cycles through the tanks and is treated with ultraviolet light to kill bacteria. The immersion tricks the bivalves into thinking it’s high tide around the clock (a clam’s utopia), thereby accelerating a depuration process that would normally take three weeks.

“We’re asking them to run a marathon, and we cheer them on and give them everything they need to do it themselves,” says bacteriologist Diane Regan, who runs the purification plant’s laboratory. Regan constantly tests the water and makes several batches of clam meat smoothie—not for drinking, but for monitoring E. coli, an indicator bacteria that tells her when the clams have met the plant’s strict standards. Her job is made easier by state biologists, who test the Commonwealth’s 1.7 million acres of clam beds before they can be harvested. Environmental officials police restricted areas, and master diggers follow strict guidelines for harvesting, tracking, and transporting their hauls to the plant. “There’s tagging and traceability from the flats to the plate,” says Kennedy. “As one of our clammers says, ‘These are the most tested clams in America.’”

Of course, the impetus for these exhaustive measures is wastewater pollution. Although sewage treatment has significantly improved since the 1920s, overdevelopment strains our treatment plants. After heavy rains, the state closes many clam beds for five days to allow overflow to flush out with the tides. “The shores are being impacted because we’re building close to the water,” says William Robinson, a shellfish contamination expert and professor of environmental toxicology at the University of Massachusetts Boston. “It’s hard to regulate so many septic systems, and it’s hard to pin it down to any one system. They’re all contributing to it.”

Water quality is one factor leading to steep declines in soft-shell clam harvests. On the North Shore, soft-shell landings have fallen more than 70 percent since 2007, when almost 4.5 million pounds were harvested. Experts point to pollution, but they also cite climate change, predation by green crabs, and disease. Boston Harbor’s flats are still recovering from a 2011 clam cancer outbreak. Still, soft-shell clams are big business on the North Shore. The plant processes 10,000 bushels each year, generating an estimated $4.6 million in revenue for local diggers, dealers, shucking houses, truck drivers, and packers. “It’s huge for the local economy,” says Paul Hogg, Newburyport’s harbormaster and head shellfish constable.

When state lawmakers targeted the facility for closure in 2011 and 2012, plant officials defended its impact on jobs and public health. Since then, the plant has cut staff and introduced new revenue streams, including de-sanding, a one-day process that renders grit-free clams. The operation is also venturing into new species. Stevens recently depurated the first bushels of razor clams, a popular West Coast species that is catching on at Massachusetts restaurants.

For diggers and the plant, the best hope lies in the very thing that could put the facility out of business: cleaner clam beds. In 2013, officials reopened the Joppa Flats in Newburyport, a 250-acre parcel that was closed for 80 years. The flats are conditionally restricted, meaning more business for clammers and the depuration plant. “The state is trying, but I wouldn’t recommend [becoming a clammer] until they open more beds,” says Stanley. “It’s a hard business.”

Four months ago, a cold March rain forced Stanley and his crew from the flats. Inside the plant, racks of razor clams were purging themselves of bacteria and sand, creating a brown film that was sucked into gray tubes and sterilized by pulses of UV light. The scene seemed a long way from the flats outside, and even farther from the pristine shoreline where Native Americans first taught English settlers to look for squirts of water beneath the muck. “When I started here 30 years ago,” says Kennedy, “I thought the need for this would go away. But between population expansion and development, we never seem to get ahead of that curve.”

Shellfish Purification Plant

84 82nd Street, Plum Island Point, Newburyport