Civil Engineering NEWS

B.VIRO.MB.'IAL

••••••••••• US. EPA Proposes Plan for Cleaning Up Long-Polluted Canal In New York City

A PLAN RECENTI.Y released by the U.S. Environmental Protection

Agency (EPA) calls fur cleaning up the long-polluted Gowanus Canal, a Super­fund site in the New York City borough ofBrooklyn that is considered one of the most contaminated waterways in the

REMEDIATION TARGET AREAS

nation. The proposed plan would in­clude dredging and capping the entire length of the nearly 2 mi long canal, re­moving contamination from adjacent industrial properties, and reducing the volume of combined sewer overflows entering the waterway. All told, the EPA estimates that the project will cost be­tween $467 million and $504 million and require nine years to complete.

The 100ft wide, 1.8 mi long Gowa­nus Canal was once a tidal creek draining to Upper New York Bay. By the 1860s the creek had been lined with bulkheads and converted into a canal to facilitate barge traffic associated with the many industrial facilities that had taken up residence along its shores. Such indus­tries eventually included manufactured gas plants, chemical plants, tanneries, soapmaking enterprises, paint and ink producers, machine shops, and oil re-

[ 24 ] C i vi I En 9 in e e r in 9 MucH z o u

fineries. Significant quantities of waste from these operations fOund their way into the canal, which initially served as an open sewer. Meanwhile, combined sewer overflows from the local com­bined sewer system have long entered the Gowan us Canal after periods of wet weather, contributing to pollutant loads in the canal's sediments. Other sources of pollutants include nearby properties that continue to discharge contaminat­ed groundwater to the canal.

In recent decades, many industrial facilities along the canal have closed. Today the Gowanus Canal flows by a mix of industrial, commercial, and resi­dential development. Although some businesses continue to rely on the canal fur maritime commerce, the waterway is also used for such recreational pur­poses as canoeing, kayaking, and div­ing. Despite watnings, anglers try their

luck in the canal, particularly near its mouth. By removing or capping contaminated sediment, the EPA intends to "reduce the risk that the canal sediment poses both to hu­mans and the benthic population," says Christos Tsiamis, the EPA's project manager fur the cleanup.

In March 2010, pursuant to the Comprehensive Environmental Re­sponse, Compensation, and Liability Act of 1980, the EPA designated the Gowanus Canal a fedetal SuperlUnd site. In its examination of the canal, the EPA distinguishes between the soft sediments that have accumulat­ed in the canal and the native sedi­ments that originally underlay it. Depending on the location, the soft sediments range in depth from 1 to 20ft. Sampling of the soft sediments has fOund high levels of polycyclic aromatic hydrocarbons, polychlo­rinated biphenyls, non-aqueous­phase liquids (NAPLs), and such metals as mercury, cadmium, lead, and copper. High levels of polycyclic aromatic hydrocarbons and NAPI..s have also been fOund in the native sediment. The highest levels of con­tamination are fOund in the mid­dle section of the canal, while the upper section exhibits intermediate levels of contamination. The lower section has the lowest contamina­tion levels. For the purposes of its

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[26] Civil Engineering MARCH zou

Civil Engineering NEWS

plan, the EPA has designated the upper, middle, and lower sections of the canal as respectively remediation target areas (RTAs) 1, 2, and 3.

Released in late December, the EPA's proposed plan would entail dredging a total of nearly 590,000 cu yd of contaminated sediment from the canal, which has a maximum depth of15 ft in its main channel at low tide. Approximately 307,000 cu yd of sediment would be dredged from RTAs 1 and 2, while anoth­er 281,000 cu yd would be dredged from RTA 3. All dredged areas then would be capped with various layers of clean materi­al to confine any contamination remaining in the canal's native sediments and prevent that confined material from being dis­turbed by canal traffic or water currents. The cap would include a treatment layer of oleophilic clay designed to capture any con­tamination passing upward from underlying sediments. What is more, in situ stabilization of native sediments would be con­ducted within certain areas ofRTAs 1 and 2 in which NAPU are expected to remain. Before capping is conducted in these areas, the native sediment would be stabilized to depths of3 to4 ft by means of concrete or similar marerials. In this way, the stabilized material would be expected to impede the upward movement of the underlying NAPU.

Highly polluted material removed ftom RTAs 1 and 2 would be treated by means of thermal desorption at an off­site fucility to remove organic contaminants, and the treated material could then be used beneficially elsewhere. Mean­while, less contaminated material removed from RTAs 1 and 3 would probably be stabilized and reused off-site. Howev­er, the plan also includes an option for stabilizing sediments ftom RTA 3 on-site and placing them in a confined disposal fucility that would be constructed on-site.

To reduce the volume of combined sewer overflows enter­ing the canal, the EPA's plan calls for installing in-line stor­age tanks neat two outf.ills. The latger of the twO outfulls dis­charges approximately 130 million gal to the canal each yeat, while the other outf.ill discharges neatly half this volume, Tsiamis says. The tanks are expected to reduce the total vol­ume of discharges from the two outfulls by 58 to 7 4 percent on an ovetall annual basis. Meanwhile, the New York Stare Department of Environmental Conservation is overseeing efforts to address contamination entering the canal from for­mer manufuctured gas plants.

The EPA estimates that its proposed plan for cleansing the Gowanus Canal would have capital costs of$286 million and operations and maintenance costs of $2 million annually. The cost to treat and dispose of dredged material is expected to range from $179 million to $216 million.

The EPA has set an April 27 deadline for accepting writ­ten comments on its proposed plan. The agency expects to announce its final decision regarding a plan for the Gowanus Canal by the end of summer, Tsiamis says. Design work will begin shortly thereafter and will probably be completed in 2016. Construction is expected to last roughly six years.

- JAY LANDERS