NORTH ANDOVER — A lumpy, noxious sludge has been spilling from three massive tanks at the region’s sewage treatment plant for two weeks, splashing to the ground in loud plops and pushing past concrete barriers into adjoining wetlands and storm drains.
None of the foul mix of human and industrial waste has run off the property or reached the Merrimack River a few hundred yards to the west, said Richard Hogan, executive director of the Greater Lawrence Sanitary District. But much of the sludge is flowing through and sometimes even over the two-feet-high containment barriers surrounding the tanks and into the narrow band of protected wetlands that circle the property.
Hogan said the cause of the viscous, black waterfalls pouring from the tops of the 40-foot tanks is uncertain and said there is no known fix except to allow it to run its course.
He said other overflows have occurred before, most recently about two years ago, and are not unusual in treatment tanks with similar designs nationwide, which have unsealed caps that float on top of the gases inside.
“I have no expectations because from past experiences, we don’t know when these instances will stop,” Hogan said. “Our hope is that it may be quick, but we understand it may go on for a while longer.”
Hogan also could not estimate how much sewage has spilled from the tanks since the overflows began about July 1.
Engineers with the state Department of Environmental Protection have visited the plant at least twice since then, including on Friday, when cleanup crews said the engineers were directing their work and taking samples.
DEP spokesman Joseph Ferson declined to be interviewed or to answer questions about the cleanup, the scope of the spill and the health and environmental threat it may pose.