The U.S. Environmental Protection Agency has just finalized a plan to clean up the Gowanus Canal in Brooklyn, N.Y., which is considered one of the most polluted bodies of water in the country.
Gowanus Canal, Brooklyn, N.Y. Photo courtesy of the U.S. Environmental Protection Agency.Completed in 1869, the canal has been one of the nation’s busiest commercial waterways, serving industries including: gas works (manufactured gas plants), coal yards, cement makers, soap makers, tanneries, paint and ink factories, machine shops, chemical plants, and oil refineries.
In recent decades, the canal has been used as a repository for untreated industrial wastes, raw sewage, and runoff.
Today, the EPA says that although much of the industrial activity along the canal has ceased, high levels of contamination remain in its groundwater and sediment. Contamination stills flows into the canal from overflows of sewer systems that carry sanitary waste from homes, as well as from rainwater coming from storm drains and industrial pollutants.
The EPA’s remedial investigation of the site found that it has been polluted with high levels of over a dozen contaminants, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and heavy metals, including mercury, lead, and cooper.
PAHs and heavy metals were also found in the canal water. PAHs are a group of chemicals that are formed during the incomplete burning of coal, oil, gas, wood, garbage, or other organic substances.
PCBs were used as coolants and lubricants in transformers, capacitors, and other electrical equipment, and their manufacture was banned in 1979.
The EPA says that, “PCBs and PAHs are suspected of being cancer-causing, and PCBs can have neurological effects as well,” also expressing concern that, “To this day, people can still be found fishing in the Gowanus despite advisories about eating fish from the canal.”
In 2010, the Gowanus Canal was added to the federal Superfund list of the nation’s most contaminated hazardous waste sites. The EPA explains that the “Superfund program operates on the principal that those legally responsible for the pollution should perform or pay for investigations and cleanups, rather than passing the costs to the taxpayers.”
The EPA says that it has identified a number of “parties potentially responsible for the contamination, including National Grid, the city of New York, and other private and federal government entities (most recently adding Chemtura Corp. to the list).
The EPA also says that it’s “continuing its efforts to identify additional potentially responsible parties.” The cost of the cleanup plan is currently estimated to be at $506 million.
The EPA has divided the Gowanus cleanup into three segments that correspond to the upper, middle, and lower portions of the canal.
The first segment (which runs from the top of the canal to the 3rd Street Bridge) and the second segment (which runs from the 3rd Street Bridge to just south of the Hamilton Avenue Bridge) contain the most heavily contaminated sediment. The third segment (which runs from the Hamilton Avenue Bridge to the mouth of the canal) is the least contamination portion of the canal.
For the cleanup, the EPA plan will require the first and second portion of the canal to be dredged of about 307,000 cubic yards of highly contaminated sediment. In addition, the areas contaminated with liquid coal tar in deep sediment will be stabilized by mixing them with cement or similar binding materials.
The EPA says that the stabilized areas will then be covered with multiple layers of clean material, including an ‘active layer’ designed with an unspecified absorbent material to remove PAH contamination that could possibly rise from below.
The cleanup will also include an ‘isolation layer’ of sand and gravel to ensure the contaminants won’t be exposed, and an ‘armor layer’ of heavier gravel and stone to prevent erosion of the underlying layers from boat traffic and currents. Finally, clean sand will be placed on top of the armor layer to restore the canal bottom as a habitat.
For the third segment of the canal, the EPA will require the dredging of about 280,000 cubic yards of contaminated sediment and capping of the area with all four layers – the active, isolation, armor, and habitat restoring sand layer.
The overall cleanup plan will also require the removal of decades old contaminated materials placed in the 1st Street turning basin of the canal and restoring about 475 feet of the former basin.
In addition, the EPA will require the excavation and restoration of the portion of the 5th Street turning basin beginning underneath the 3rd Street Bride and extending about 25 feet to the east of the bridge.
The final plan is also expected to include various methods for managing the contaminated sediment after dredging, depending on the levels of contamination.
This plan will include the transporting of dredged sediment highly impacted by liquid coal tar away from the area to a facility where it can be thermally treated for the removal of organic contaminants and then, according to the EPA, be “put to beneficial reuse such as a landfill cover, if possible.”
The EPA added that for less contaminated sediment, treatment might involve stabilizing the sediment at a facility out of the area, followed by a “beneficial reuse.”
In addition, the final plan will require controls to significantly reduce the flow into the upper canal of contaminated sewage from sewer overflows.
The EPA says, “These overflows are not being addressed by the current New York City upgrades to the sewer system. Without these controls, contaminated sewage solid discharges would recontaminate the canal after its cleanup.”
The EPA plans to require that two major portions of the upper canal be outfitted with retention tanks to reduce the volume of contaminated sewage discharge. The agency estimates that “a reduction of 58 percent to 78 percent of these discharges will be needed to maintain the effectiveness of the cleanup.”
The EPA added that in coordination with the New York State Department of Environmental Conservation, it has also begun addressing “contaminated land sites along the canal, including three former manufacturing gas plants.”
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