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 2-foot-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.
In a brief email on Thursday, Ferson commended the clean-up effort and said the “volume of the discharge has greatly diminished and GLSD staff have made extensive efforts to ensure that the discharge is contained to the project site so that the public health impacts are minimized. We have directed the plant to determine the cause of the issue and identify a remedy.”
Hogan said the overflows may be caused by a sudden spike in the amount of inorganic material such as industrial waste that arrived at the plant about the time the overflows began, upsetting the biological process that breaks down the waste in the treatment tanks. He said plant officials surveyed the larger manufacturers in the five municipalities served by the plant to try to track the source. No source was determined.
The waste inside each of the 1.4 million-gallon tanks is in an early stage of treatment and still contains coliform bacteria and other pathogens that can cause a range of diseases, including hepatitis A, typhoid and salmonellosis, a gastrointestinal illness that sickened 92 bathers — sending 16 to hospitals — at a Rhode Island lake on July 4. Health officials in that state believe the outbreak was caused by human feces in the water.
The sewage treatment tanks are called digesters because of the process going on inside, where naturally forming bacteria feed on the sludge in an oxygen-free environment. The bacteria reduce but do not eliminate the pathogens in the waste and also reduce the volume before the waste is sent on to centrifuges and heating tumblers that further reduce it to pellets, which at that point can be safely used for fertilizer and other purposes.
The sewage treatment complex on Charles Street in North Andover serves both Andovers, Lawrence, Methuen and Salem, N.H. The facility is surrounded by runways of the Lawrence Municipal Airport on the north, east and south, and by railroad tracks and the Merrimack River on the west.
The isolated and buffered location suggests there is little risk of direct exposure to the general public, but a local health official and an environmental advocate said the larger threat is to the Merrimack River and to swimmers, fishermen and boaters who may come in contact with the waterway if it is contaminated by the spills.
“Most certainly, people most directly exposed should use protective gloves and masks and wash properly afterward,” Joel Gorn, chairman of Lawrence’s Board of Health, said about workers involved in the cleanup. “By all means, there should be some testing downstream. People swim downriver. They jump off their boats.”
Christopher Burkhart, president of the Greater Lawrence Sanitary District Employees Association, which represents about 26 workers, did not return a message left for him at the plant.
“The bacterial contamination that would be in this is one of the biggest problems for this river,” said Caroly Shumway, executive director of the Merrimack River Watershed Council, an advocacy group that regularly tests the river’s water quality and sends results to the federal Environmental Protection Agency. “There has to be better enforcement.”
Hogan, the sanitary district’s $130,000-a-year executive director, said employees have walked the drainage channels that run from the site and reported that “the foam material peters out” before reaching the Merrimack River. Hogan has run the plant since 1994 and retires later this year.
In addition to the DEC, Hogan said, plant officials have informed the EPA and North Andover’s Board of Selectmen and Conservation Commission about the spills.
”Everybody’s on it, that’s about all I can say at this point,” Selectwoman Rosemary Smedile said Friday. “Mr. Hogan has been keeping us fully abreast. There’s always concern, but I think everything that can be done is being done.”
“Everyone’s aware of it,” said Dave Deegan, a spokesman for the EPA’s New England office in Boston. Beyond that, Deegan said, the EPA does not confirm or deny whether any spill is under review. He referred questions to the state DEP.
Steve Harwood, operations director at the treatment plant, notified the DEP about the overflows on July 2 in an email that now appears to have been overly optimistic.
“We have the foam contained with jersey barriers,” Harwood said in his email to Mohatny Nihar, a DEP engineer. “As of now the foam has subsided on 2 of the 3 digesters and slowing down on the 3rd.”
Things apparently worsened as the week went on.
Three days later, aerial photographs showed wide streams of the sludge running past the containment barriers, pooling on the service road that loops past the tanks and flowing into the adjoining wetlands and the two storm drains that serve the area. A warning posted in a sludge-saturated stretch of the wetlands warns, “Protected wetlands. Restricted access.”
On Tuesday, at least two of the three tanks were gushing sludge, streaking the concrete sides of the tanks with black slime and fouling the circular aluminum stairways that run up along the outside.
On Thursday, one tank was bubbling over. On Friday, two were.
On Thursday, nearly two weeks after the spills began, the chairman of the sewer district’s board of directors said he had not been to the site.
“From what I understand, sometime this week they put plywood between the barriers to try to prevent it from leaking through,” Chairman Thomas Connors said. “I know they’re pumping it back into the tanks. They have a (pumper) truck to pick up anything that seeps through. Beyond that, I don’t know what else we can possibly do.”
The wetlands that circle the treatment complex and separate it from the airport runways and the rail tracks and river are regulated at least in part by the North Andover Conservation Commission. Hogan said Jennifer Hughes, the town’s conservation administrator, visited the plant after the spills began.
She did not return phone calls.
On Friday evening, a cleanup crew of five was slogging through the smelly black slop a few feet from a cascade of sludge pouring from one of the tanks, armed with a Squeegee, a water hose and a 2,500-gallon pumper truck they called “the sucker.” Crew member William Ferrier said he has seen several similar overflows since he began working at the plant when it opened about 38 years ago. He said the overflows — referred to in the industry, benignly, as “foaming” — are common at treatment plants with floating tops. The Lawrence tanks were installed in 2002.
“There’s nothing we’re doing wrong,” Ferrier said as he used a Squeegee to push pools of putrid water away from the wetlands and back toward the treatment tank, a task he said was ordered by the DEC engineers who visited. “It’s not unusual for a (treatment) process like this. It’s the nature of the beast.”
“This is the time of year it happens,” said Dan Roberge, another plant employee assigned to the cleanup Friday, who blamed the overflow on the recent hot weather. “We’re doing a really good job. We’re shorthanded.”
The Greater Lawrence Sanitary District has had a handful of other problems in recent years.
In 2006, the district paid a $254,000 fine and made upgrades costing $18 million to settle allegations by the EPA and DEC that it was releasing millions of gallons of untreated sewage annually to the Merrimack River.
More recently, on Feb. 28, a man working for an Atkinson, N.H., contractor broke several bones when he fell while making repairs inside one of the treatment tanks. The federal Occupational Safety and Health Administration issued two citations for unsafe working conditions against the contractor, Advanced Design Construction, and fined it $4,800.
The sanitary district was not cited or fined in the incident.