Recently, a sharp eyed Riverkeeper watchdog reported a heavy discharge of unknown origin from a pipe at the foot of the Alexander Hamilton Bridge, on the Manhattan side of the Harlem River. The report was made after the individual photographed water pouring from the pipe during several trips past the site on Metro North, which runs along the opposite shore. Such a dry-weather discharge could normally indicate a serious problem such as a dry-weather combined sewer overflow (CSO).

With the Fletcher still on land prior to this year’s launch, we set out from Ossining with an 18’ outboard skiff, to observe the outfall firsthand.

The discharge water velocity and volume were both high. The discharge color had a bluish tint, not the blue/grey as we usually see with sewage. There was some of the characteristic effluent smell but not nearly as strong as at a typical CSO (and note that there is often a background sewage smell in parts of NY Harbor anyway). The discharge also produced a large amount of foam.

A green SPDES sign above the outfall is was in poor condition but included information which we passed along to the NYC DEP.

They confirmed the source of the water is a test release of fresh water from the Croton Reservoir system and the city’s new Croton Water Filtration Plant in the Bronx.

DEP notified the public last fall that, for a period of six months, the city would be releasing the drinking water into the Harlem River as part of the startup and testing of the plant. Before the treated water is allowed to enter the city’s drinking water system, it is being tested to ensure it meets standards for drinking water. During this process, the water is diverted to the Harlem river rather than entering the water supply.

As for the foaming that is observed around the pipe, it may be a result of the salinity in the Harlem/East Rivers. Because waters in this area are roughly 2/3 the salinity of ocean water, it’s possible that the foam could be similar to the foam created by wave action at an ocean beach, or observed in the wake created by vessels at sea.