NEWBURYPORT — It seemed like they had mostly disappeared from our local shores, perhaps swallowed up by the vast sea or picked up by beachcombers.
But in the past few weeks, those little white discs that two years ago escaped by the millions from a New Hampshire sewage treatment plant have been showing up again, in large quantities. They are scattered all along Plum Island beach, they are caught in the reeds and detritus along the banks of the Merrimack River, and they’re peeking out from the storm surge debris found in waterfront places like Newburyport’s Cashman Park.
According to officials, this sudden appearance isn’t the result of a new disc spill upriver. This is a lingering phenomenon that will likely visit local waters and the coast whenever there are ocean storm surges or high water events in the river, for months to come if not longer.
In early March 2011, an estimated 4.3 million sewage treatment discs -- about the size and thickness of a silver dollar, with a screen pattern running across them -- flowed into the river when a downpour overwhelmed the Hooksett, N.H. sewage treatment plant. The plant is located on the bank of the Merrimack River near Manchester, and the discs came down the river like a plastic tidal wave.
About 4 million were picked up, according to Geoffrey Brown of Enpro, the Newburyport firm that was hired to clean up the mess. Enpro was employed at the task from March through November 2011, and a number of local environmental groups and volunteers have also conducted cleanups.
But this winter’s storms have dislodged perhaps many thousands of discs that were stuck along the riverbank. The storms tossed ashore others that were floating on the seas.
“We anticipated that this would happen, especially with big storms. I’m not surprised that people are finding them on the beach,” said James Martin, a spokesman for the New Hampshire Division of Environmental Services.