Toxic sludge cakes the bottom

of the Gowanus Canal. Snaking through Brooklyn, New York, the canal is a newly EPA-designated Superfund site. To clean the 300,000 cubic yards of mud mixed with industrial metals, coal, tar and sewage, the EPA will most likely have to dredge the waterway over the next decade. The question that remains is what to do with the muck once they dig it up. One option that the agency is considering is melting the ooze into something both non-toxic and surprisingly attractive: washing machine-sized glass cubes. Using a process called vitrification, the agency could put the sludge in metal molds and heat them up to very high temperatures. If there is enough sand in the material, the result will be transparent blocks that can be used in building construction or sculptures.

Vitrification is, in fact, a proven cleanup method that has been successful at other contaminated sites and is also used to treat nuclear waste. The high temperatures, which can reach upwards of 2000 F, kill the organic matter in hazardous waste. The silica, or sand, binds with the heavy metals, locking them into place and yielding a product that is harmless and resistant to corrosion. The process also significantly reduces the sludge's volume.

If the EPA does decide to remove this black mayonnaise, as some refer to the gunk, a contractor will first remove water from the material. The resulting product will then be poured into a mold and exposed to extreme heat until it turns to glass. A filter is used to catch emissions. (The method is also applied to underground contaminants, in which case the earth is heated with electrified rods.)

The biggest possible barrier for this technique, says Christos Tsiamis, the Superfund's project manager, is whether it makes financial sense. The EPA plans to conduct a feasibility and economic viability study before they decide to pursue this option, which has been employed at nuclear waste sites and hazardous waste sites in the United States and abroad. If turning sludge into glass turns out to be too expensive, other options include dredging the canal and shipping the material to a landfill, where it will be treated as hazardous waste, or laying a heavy clay over sections of the waterway, encasing the contaminants.

"Could [vitrification] be applicable to the Gowanus?" says Eric Stern, regional contaminated-sediment program manager for the EPA. "The short answer is yes," Stern says. "The long answer is that it's part of an integrated approach to sediment management. It's not like, 'Give me sediment decontamination or give me death.' There are a lot of things to consider."

Last year, Stern and his colleagues conducted a demonstration project with dredged sludge from the Passaic River, part of the Diamond Alkali Superfund site. They showed that the contaminated sediments could be treated in a process similar to vitrification and added to a concrete mixture that they then used to pour Montclair University sidewalks.

Sometimes even seemingly elegant solutions die on a study's spreadsheets, Tsiamis says. Yet as environmental regulations become more stringent, and landfill space decreases, vitrification may turn out to be a more desirable alternative to remediating Superfund sites in the future.

Officials should know by the end of next year, after they finish their study of how to deal with the material, if they can make a thing of beauty from the Gowanus Canal's beastly gunk.

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