Long-planned Gowanus Canal tank project shifts to tunnel

The city is backing away from a years-in-the-making plan that would have used two underground sewage tanks along the Gowanus Canal to divert raw waste from the waterway, in favor of a massive tunnel to collect the fetid runoff.

Officials with the city’s Department of Environmental Protection (DEP) unveiled details on the sudden proposal at Tuesday’s Gowanus Community Advisory Group meeting, touting the tunnel as a better alternative because of its increased capacity, decreased construction impact, and its potential to allow for more public space. But one aspect of the tunnel is clearly superior to the sewage tanks, according to DEP.

“This is the kicker right here: It’s the scalability,” said Kevin Clarke, a portfolio manager with the agency’s Bureau of Engineering Design & Construction. “Once you build those two tanks they’re basically a dead-end-asset. It’s going to be very tough to build any additional capacity beyond the eight and four million gallons, but with the tunnel you can add on to that.”

The city first announced plans to install those enormous sewage tanks adjacent to the canal in 2013 as part of the EPA-led federal Superfund cleanup.

Last April, the New York City Council gave DEP the green light to use eminent domain to commandeer 234 Butler Street and 242 Nevins Street as the home for the larger tank and a new water filtration facility known as the headhouse. Meanwhile, the second, smaller tank was slated for a city-owned lot on Second Avenue near the Fourth Street Turning Basin.

But now, DEP aims to scrap that scheme. City officials initially announced in October that they instead want to build a half-mile, soft ground tunnel up to 150 feet beneath the earth that will store 16 million gallons of sewage overflow—more than the tanks combined total.

“The benefits of the tunnel that we’re proposing—it increases the storage capacity,” Clarke said. “We’re proposing at a minimum a 16 million gallon storage so it’s approximately 4 million more than the combined capacity of [the tanks.]”

The shaft would run along the canal from the headhouse site to where the the smaller tank is currently proposed and operate just as the tanks would—gathering waste and storm runoff that would typically pour into the canal, after treatment at the headhouse. But because it can hold more fluid, the tunnel would prevent four additional weather events from dumping millions of gallons of filth into the canal through Combined Sewage Overflows (CSOs) per year, according to DEP.

The new plan also has the boon of “additional design flexibility” for the public space planned near the headhouse, since the larger tank would no longer interfere with the design. But a tunnel is expected to cost some $50 million more than the original plan’s whopping $1.2 billion price tag—which includes land acquisition, headhouse construction, the creation of public space, and the installation of both tanks. Operating costs are expected to remain the same, officials said.

If DEP were to move forward with the tunnel, a supplemental Environmental Impact Statement would be required along with “a significant geotechnical and environmental boring program” that would inform the project’s design and determine which type of boring equipment is used to make the shaft, said Clarke.

All in all, the extra work would pad the project timeline to the end of 2030; the complete installation for both tanks was slated for mid-2030.

“Although the tunnel is going to take a little bit longer, we believe that that additional time is outweighed by the additional benefits that the tunnel provides,” said Clarke.

To build the tunnel, DEP would first need to construct a pumping station and a mining shaft on the land beside the northernmost part of the canal. Next, a tunnel boring machine will be lowered into the shaft and advance toward the Fourth Street Basin site at a rate of 50 feet per day. As the machine removes sediment it will line the tunnel with precast concrete liners—essentially piecing the tunnel together as it drills into the sediment.

Now that Gowanus is poised for a rezoning, the neighborhood’s industrial grit could be swapped for denser, new residential buildings. And the option to extend the tunnel further south in the future—namely along the length of the canal or down Second Avenue—could help address the neighborhood’s anticipated population growth, Clarke said.

“There’s also a rezoning that is coming—I mean, everybody knows that the area is rife for development—so we believe that the tunnel would be a better project to help support that future development in population growth,” said Clarke.

But with a more than a $1.2 billion price tag for a half-mile tunnel, some Gowanus Community Advisory Group members questioned if the project was cost-effective and if it goes far enough to address storm resiliency in the neighborhood. Some parts of Gowanus were inundated with five feet of water during Hurricane Sandy in 2012.

“I realize $1.2 billion is a lot of money, but are we thinking too small?” David Briggs of community group Gowanus By Design said at Tuesday’s meeting. “You know, there’s economies of scale when you’re doing something like this, and it seems a little odd that we stop just because we met this mandate when we could really keep going and it would be more cost effective per unit and we’d have a better, sort of robust solution. Are we really thinking far enough down the road?”

The question stumped Clarke. “I don’t really have a response for that. I think that’s why we’re recommending going to this approach—at least you have that option,” he said.

DEP’s pivot to a tunnel hinges on EPA approval, and neither agency has released a deadline for the decision. In the meantime, DEP will continue with the original project—which the city has spent $30 million designing to date.

“DEP continues work on parallel tracks—already meeting every milestone towards construction of the tanks while we have initiated detailed planning for the tunnel,” said Edward Timbers, a DEP spokesman. “We hope EPA’s decision comes soon so we avoid duplicating resources.”

EPA project officials with the canal’s Superfund clean up were unable to attend the meeting due to the government shutdown. A spokesperson for the EPA was not available for comment due to the shutdown.