A manhole cover in a brook released up to 10,000 gallons of raw sewage directly into the water last week in Wilmington, town officials say.
“We believe it was a blockage caused by grease,” said John Lazelle, the chief operator of Wilmington’s wastewater system. The sewage flowed directly into Beaver Brook, which feeds the North Branch of the Deerfield River.
Lazelle said such releases are rare and the town has only had “a couple minor ones” of a few hundred gallons in recent years.
The blockage happened Thursday, June 11 in the afternoon, and operators noticed the volume of the flow at the sewage treatment plant slowed significantly.
“We had it fixed within 30 minutes of finding it,” Lazelle said.
He said the town of Wilmington has between seven and eight miles of underground sewer lines, and every line is cleaned every three years on a rotating cycle.
“The goal is to try to prevent something like this from happening,” Lazelle said.
The section of sewer line with the blockage is part of the town’s original 1960s sewer system, Lazelle said, and is cleaned annually.
“It’s in a spot where the flow really slows down,” Lazelle said. Grease in sewer lines is more likely to cause a stoppage in areas of slow flow, he says.
Lazelle said there were “no solids visible” in Beaver Brook during the overflow.
“It was really just gray water,” he said.
Lazelle said official reported estimates that the release consisted of 10,000 gallons that flowed out of the manhole over three and a half hours are a “worst case scenario” and there was likely less sewage released over a shorter time.
He also said there are no plans to replace the 50-year-old sewer line where the blockage occurred in order to make such incidents less likely in the future.
“There’s really not a whole lot that could be done,” Lazelle said.