It’s the case of the mysterious water, and now the city is eyeing the Mohawk River as the culprit.
For years, city workers have tried to reduce the amount of stormwater flowing into the sewage system during heavy storms. The influx has sometimes forced untreated sewage to overflow into the river, and that’s where the state Department of Environmental Conservation stepped in.
The DEC wants the city to stop putting untreated waste in the river. Yet all of the city’s efforts to cut off connections between stormwater pipes and sewer pipes haven’t worked.
At first, city officials thought they’d succeeded. When Irene and Lee hit, not a single drop of untreated sewage was released into the river. But this year, amid less-than-hurricane-strength storms, the city has released raw sewage on several occasions.
Finally, workers began to notice every release happened when the river was above a certain depth.
“If the river is below a certain level, no matter how much rain we get, we don’t have to” release sewage, Mayor Gary McCarthy said. “What it seems to indicate is our system has the capacity to handle it.”
But when the rain falls and the river is high, the system overflows. Workers now suspect the river is somehow affecting the system.
“Is there some old pipe that’s allowing the river to back into the system?” McCarthy said. “We’ve had people going along the river, the shoreline, looking for an old pipe, a manhole. They haven’t been able to find it.”
The city also sent its pipe camera into the system, looking for clues. So far, that hasn’t turned up anything either.
So the city is hiring CDM Smith, a Latham consulting firm, to solve the case.
“There’s something out there that we don’t know,” McCarthy said.
He said engineers are also looking into whether the depth of the river could cause hydrostatic pressure on the system, putting the sewage under so much pressure that it blows manhole covers on Front Street, which is near the river. When those covers blow, the city releases raw sewage to resolve the problem.
The theory until now has been the manhole covers blow when the system is overflowing with sewage. Now they’re counting on the investigators to figure it out.
“Hopefully it won’t be a too-expensive fix,” McCarthy said.
The city is signing a consent order with DEC on the issue. The order says the city must stop releasing sewage into the river.
“They don’t want the untreated sewage to go into the river. We don’t want that,” McCarthy said. “So this whole review will identify what the problem is and stop it.”