Brooklyn's 2.5 million residents occupy one of the most densely populated areas in the United States. With space at a premium, New Yorkers prize their land. Naturally, they would want Brooklyn's Gowanus Canal cleaned up, especially since the canal has been designated as a Superfund site since 2010.
New York City Department of Environmental Protection (DEP) and the EPA are working together to transform the canal and in addition, develop four acres of new public waterfront open space. The $1.7 billion project is bringing out the best in the city's planners and construction workers to reimagine a bright future for this long-neglected waterway.
NYC DEP photo
Construction teams are building two enormous combined sewer overflow storage tanks to hold up to 12 million gal. of water per storm that strikes the area. By capturing the water, the tanks will prevent polluted water from the sewers from overflowing into the canal.
Chief Climate Officer and DEP Commissioner Rohit T. Aggarwala acknowledged that the work will be challenging, especially with a tight schedule and operating in such a congested area.
"We are thrilled to be aligned with the EPA on a vision for a cleaner Gowanus Canal, and we are committed to working on an accelerated schedule," he said. "I am thankful for the dedicated team at DEP's Bureau of Engineering, Design and Construction for their expertise and creativity that will make this possible."
In the 1860s, a tidal creek was converted into a nearly 2-mi.-long canal for industrial use. Oil refineries, chemical plants and manufactured gas plants (MGP) dumped their waste into the Gowanus Canal. Coal tar is one of the byproducts from the plants that remain where the former MGP plants operated. Sewer overflows added to the pollution.
Planners and the construction team are building the two tanks as an important step in the cleanup process. In addition to building the new tanks, workers will construct facilities on top of the tanks to house the mechanical and electrical equipment necessary for operation of the system.
NYC DEP photo
Kevin Clarke, who has managed multiple projects for DEP over the past 28 years, has been orchestrating the Gowanus Canal tank program. Work on the canal has been proceeding rapidly on the two sites: Owls Head and Red Hook. Workers have removed a gigantic amount of material to create the room for the Red Hook tank — approximately137,000 cu. yds. in all.
The contractor for the Red Hook Tank is Gowanus Canal Constructors (a JV of Yonkers Contracting and John P. Picone Construction) and the key subcontractor for installation of the support of excavation system is Keller North America. The contractors for the Owls Head Tank are Posillico and Nicholson. This team is installing the support of excavation system. Two big components in the support of excavation (SOE) construction are a traditional clamshell style excavator and a hydro mill trench cutter. Workers used a Liebherr 8130 or Bauer Mc-96 with a clamshell excavator attachment to dig out the upper 40 ft. or so of each SOE panel.
Much of this material is fill, so unknown pieces are sometimes unearthed at this stage, including rubble and other materials not completely removed before. Slurry is added to the open panel excavation to keep the panel open until the excavation is complete.
The star of the excavation at the Red Hook site was the Bauer hydro mill. Two hydro mills were attached to a Bauer MC-128 or MC-96 crawler crane. This huge machine uses massive cutting wheels to chew through rock and soil. A mud pump sucks out the slurry, which carries the excavated material to the surface where it is run through a separation plant to remove the excavated material from the slurry.
Once the excavation is complete, at approximately 160 ft. deep, the panel is filled with concrete in a tremie fashion from the bottom up. The slurry is displaced and removed as the tremie pour progresses. It also is important to note that the upper 75 of the SOE panels are reinforced with rebar cages — those cages were placed using a Liebherr 1200 crane. These individual panels eventually form a complete perimeter and serve as the support of excavation so the mass excavation can begin on the inside and build the subsurface tank.
NYC DEP photo
Each slurry panel was designed to be approximately 160 ft. deep. Construction teams are now building the concrete floor and wall slabs to form the tank structure at the Red Hook site. Work on the slurry wall at the Owls Head tank site was completed in October.
In addition to the hydro mills, the projects will be using large excavators and earthmovers, drilling equipment for installation of piles and rigid inclusion, and cranes for support work, including lowering and raising materials in and out of the tank.
Clarke and his team are coordinating a complicated site.
"During the SOE phase we had some 50-70 concrete trucks arriving per day and a peak of nearly 90 trucks during the excavation," he said. "This is an immense project in highly urbanized Brooklyn. In addition, we have a lot of development going on around us; some of it is in the ground, some is coming out of the ground and other work is in vertical construction. It has required us to stay in constant communication with contractors on other projects."
Once the subsurface tanks are completed, the final steps of the project call for construction teams to build four acres of public open space atop the tanks, two acres at each site, with waterfront esplanades and views of the remediated canal.
The monumental project will take nearly 10 years to complete.
"When it is finished, kids will probably be playing in the park and have no idea about all the work that is going on below them to make this park and the adjacent Canal such a delight," said Aggarwala. "This is an engineering marvel. It is like constructing a six-story building upside down. The construction team is doing an amazing job in a difficult, crowded environment." CEG
