CITY OF NEWBURGH – An emergency bypass for a section of Newburgh’s sewer system is being built in response to the discovery of leaking from a retaining wall along the west side of Water Street that is raising fears of damage to a sewer line carrying waste water for as much as two-thirds of the city.

The wall rises from the bottom of a hill below the Granite Factory. Running underneath it is a sewer main for the North Interceptor, a trunk line that captures waste from smaller lines and carries it to the city’s waterfront treatment plant.

Once the bypass is built, the city will use a remote camera to search for damage. A collapse of the Interceptor could leave as much as 3 million gallons a day of untreated sewage flowing down Renwick and Water streets to the Hudson River, Engineer Jason Morris said.

“During a wet-weather event, the flows could be upwards of 10 million gallons per day of untreated combined sewage,” Morris said.

Tests of the seepage so far have proved inconclusive, but Morris said it looks “very suspect” and algae are growing along and underneath the wall.

The wall is along a non-residential stretch of Water Street that has no walkways, so the public should not come in contact with sewage, Morris said.

On Wednesday morning contractors deployed at the intersection of Colden and Washington streets were digging underground and heavy equipment was being staged nearby. A detour was set up on Renwick Street, just west of the intersection with Water Street.

Newburgh reported the leak to the state Department of Environmental Conservation on Tuesday evening, triggering an environmental alert, a system set up to notify the public when partially treated or untreated sewage is discharged.

“My concern is if the wall fails, we’ll have a huge disaster,” Morris said.

Both the North and South Interceptors were installed in the early 1970s to divert untreated stormwater and sewage away from the Hudson River and to the treatment plant.

Part of a $9.4 million loan and $3.1 million grant Newburgh received last year for sewer projects will be used for the design of improvements to the North Interceptor.

In 2012 a breach in a major trunk line led to the spillage of an estimated 3 million gallons of sewage into the Quassaick Creek. The damage also led to at least $800,000 in emergency repairs, including the construction of a temporary bypass system.

lsparks@th-record.com