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October 1, 2003
Kim A. O'Connell
TREATING LUMBER WITH chromated copper arsenate (CCA) has largely freed the construction industry from such creepy-crawlies as microbes, termites and other wood-boring insects. Yet in treating wood, we may have traded one danger for another. Research continues to uncover the potential hazards of arsenic and chromium leaching from discarded CCA-treated wood. Before a partial industry phase-out of the wood was announced, between 100 million and 400 million cubic feet of CCA-treated wood was expected to be disposed of in landfills each year through 2016. Although the phase-out should gradually limit the amount of CCA in the waste stream, some states still are taking preventive action now — instead of waiting to find out whether the resulting leachate will contaminate their groundwater.
CCA is a chemical preservative used to pressure-treat lumber employed in construction projects such as playground structures, decks and other landscape features. Because CCA-treated wood increasingly is entering the waste stream, controversy over its disposal recently has intensified. [See www.poisonwood.wasteage.com for full coverage.] Researchers proved years ago that arsenic leaches from preserved wood, but tests continue to examine the extent to which this could contaminate soil and groundwater. In the meantime, discarded CCA-treated wood is exempt from the federal definition of hazardous waste, which would require that it be disposed of in special facilities. So, for example, Florida laws currently allow CCA-treated wood to be disposed of in unlined landfills.
With about 12.7 million tons of wood waste generated in 2000, according to the U.S. Environmental Protection Agency (EPA), Washington, D.C., and with disposal of CCA wood expected to peak in about 20 years, the potential dangers will continue to be a thorn in the industry's side. Already, several states, such as California and Florida, are taking steps to protect soil and groundwater from possible threats. Should the waste industry as a whole be following suit?
Current research on CCA is dominated by a team of scientists funded by the Florida Center for Solid and Hazardous Waste Management at the University of Florida. Led by Helena Solo-Gabriele at the University of Miami and Timothy Townsend at the University of Florida-Gainesville, the team is focused on evaluating the toxicity of CCA-treated wood disposal.
Recently, the researchers published “Arsenic and Chromium Speciation of Leachates from CCA-Treated Wood,” which tested leachate from old wood, as well as tested groundwater near landfills. The study indicated that more arsenic leaches from weathered wood than unweathered wood. Furthermore, the results suggested that the arsenic leaching from untreated wood is less toxic than the types of arsenic leaching from CCA-treated wood.
Researchers also collected groundwater samples taken near 21 unlined construction and demolition (C&D) debris landfills, to determine whether arsenic concentrations were higher than normal. Of the 48 samples collected, 21 contained arsenic greater than the 5 micrograms per liter (ug/L) detection limit. Six samples taken from three separate landfills had arsenic concentrations greater than 20 ug/L — double the EPA's new 10 ug/L standard for arsenic in drinking water.
Townsend says it is too early to tell whether CCA-treated wood is a major threat to groundwater, although he suggests the research may be pointing in that direction. “CCA-treated wood doesn't meet the definition of C&D debris, [which dictates] that the waste won't leach chemicals,” Townsend says. “There is certainly rationale for why it should go to a lined landfill. But there is not a huge amount of compelling evidence that it's leaching into the groundwater. Out of 21 landfill sites, only three had notable arsenic concentrations above drinking water standards.”
Although the evidence is not conclusive, it raises a bigger question, Townsend adds. “If you're not seeing it in the groundwater, does that mean it's not a problem?” he asks. “It could also very well be that groundwater takes a while to travel. It could be a problem we encountered in the future. The quandary is whether we wait or act upon the evidence that we have right now.”
The wood treatment industry currently is phasing-out CCA-treated wood use in residential applications, which Townsend says will remove about 75 percent of CCA wood from the market. By this fall, CCA wood may all but disappear from home improvement chains such as Home Depot and Lowe's. But with the wood representing about 90 percent of the waterborne wood preservative market, and about 6.5 billion board feet being treated each year, the remaining 25 percent still could pose a problem.
How the treated wood will be used also is a continuing issue. For instance, entities such as the Consumer Product Safety Commission, Washington, D.C., are concerned about the use of mulch and playground equipment made from CCA wood. Townsend's team now is testing the toxicity levels of mulch sold at common home improvement stores.
In Florida, the issues are amplified. The state is the largest user of CCA wood, representing 10 percent of the national market. The state also presents a challenging environment for preserving wood, with its high rainfall, ample insect populations and widespread presence of wood-rotting molds and fungi.
Even with the industry phase-out, Florida has about 440 million cubic feet of CCA-treated wood in service, according to Solo-Gabriele. Studies of three C&D waste piles in 1999 showed that CCA-treated wood comprised between 9 and 30 percent. In 2001, a test at a single C&D facility showed that 22 percent of its wood was CCA-treated, Solo-Gabriele says.
Bill Hinkley, chief of Florida Department of Environmental Protection's (DEP) Bureau of Solid Waste in Tallahassee, believes enough evidence exists to warrant amending state regulations governing CCA waste disposal. This past July, the department hosted a workshop to address CCA wood management in Florida, among other technical changes.
“We have the authority to regulate CCA, and we were basically waiting on research that has just been completed in the last year that gave us strong enough evidence to write good regulations,” Hinkley says. “We're trying to deal with the mulching of CCA wood, [which is] improper but nevertheless going on, [and] which has the potential to leach into groundwater. We're also dealing with combustion, looking at primarily open burning and air-curtain incinerators (ACIs), ensuring that CCA is not burned in those ACIs.”
Proposed changes to the solid waste rule include language stating that CCA-treated wood is not “non-hazardous in nature,” thus exempting it from the state's definition of C&D debris. If the language is approved, CCA wood could not be made into mulch, chips or any wood product used as groundcover, nor could it be disposed of through open burning or combustion in a waste incinerator.
Ash from the combustion of CCA-wood, as well as a mixture of untreated wood and CCA wood, fails toxicity characteristic leaching procedure (TCLP) tests, Hinkley says. When chipped into mulch, CCA-treated wood's leaching potential increases because the surface area-to-mass ratio increases.
Another part of the rule would force CCA wood to be separated and disposed in an “approved disposal facility,” and the wood could not be knowingly accepted at a C&D disposal facility.
Hinkley expects the rulemaking process to take about one year. “The CCA issue … requires attention, but we don't want to create a crisis with draconian regulations,” he explains. “If all we accomplish is causing a bunch of C&D sites to close, and illegal dumping, the process isn't working — especially because a lot of the CCA can be pulled out, identified and diverted from the C&D waste stream.”
The Construction Materials Recycling Association (CMRA), Lisle, Ill., among others, is closely watching the Florida rulemaking. “We have had discussions with the Florida DEP, and we understand their concerns,” says William Turley, the association's executive director. “I'm not surprised that regulators want it out of the waste stream, even if the problem has been sensationalized. The regulations will be set up to follow best management practices to watch what goes into the waste stream. Our people don't want this material to go into end-products.”
CMRA wants a proven technology to help C&D recycling centers separate out CCA-treated wood. “The industry welcomes [CCA regulations], especially if we can find ways to economically do this,” Turley says. “All the recyclers hate CCA-treated wood and don't want it in the waste stream. You can ban it from C&D recycling centers, but if they don't have a way to separate it, and there's not a proven technology to get it out of there, how are they going to do it?”
Another avenue toward dealing with CCA-treated wood may be through state legislation. For example, several bills to prohibit CCA wood use in playground construction or the use of CCA-based mulches in playgrounds have been introduced in Florida. So far, none have been approved, but similar legislation is expected to be reintroduced.
In September 2002, New York Gov. George Pataki, R, signed a law prohibiting the use of CCA wood for any new public or school playground, which took effect in March 2003.
In California, new legislation would reauthorize a waiver process in which the state could grant waivers for low-level hazardous waste, such as pressure-treated wood, to be disposed of in Class 3 lined landfills, rather than Class 1 hazardous waste facilities. The bill was amended, however, to limit the applicability of the waivers to household hazardous waste — meaning that industrial CCA wood would have to be disposed of in hazardous waste facilities. Only three Class 1 facilities exist in the state, according to Turley, and it costs about $300 per ton, on average, to dump at Class 1 sites, compared to $40 per ton at Class 3 facilities.
Yet perhaps not all CCA-treated wood needs to be disposed of after all. The Brooks Forest Products Laboratory at Virginia Tech, Blacksburg, Va., has been researching possible end-uses for recycled CCA-treated wood, including such products as railings, trash can containers, pallets and outdoor furniture. Yet this still would require the C&D industry to find an economically and logistically feasible way to identify and separate out CCA-treated wood.
Looking ahead, the Florida researchers will continue their emphasis on groundwater, mulch sampling and landfill simulations. The team also is working to help the waste industry deal with the wood in the short- and long-term.
Long-term solutions involve substituting CCA-treated wood with non-arsenic-based preservatives, but these pose potential problems. Alternate preservatives leach less arsenic than CCA wood, but more chromium, according to the researchers. Alternatives also cost between 10 and 30 percent more than CCA-treated wood.
In the short term, the researchers are seeking strategies to identify CCA wood for separation. Current methods being studied include chemical stains and x-ray and laser technology, but they all pose difficulties. Townsend says some chemical indicators give false responses if the wood is wet, dirty or painted. In other cases, replacement wood preservatives sometimes react the way CCA does, which throws off the results.
Elaborate devices involving x-rays and lasers are more effective but tend to be costly. Townsend's team is planning a field demonstration of these devices to substantiate their performance and cost-effectiveness.
“We're going to be getting some grants to put these projects into real plants,” Turley says. “The question is will they work at a C&D plant processing a thousand tons a day?”
Other questions regarding CCA wood have yet to be explored, such as how CCA-tainted leachate might affect landfill bioreactors, which depend on leachate recirculation. The Florida Center for Solid and Hazardous Waste Management also happens to be leading bioreactor research, in which both Hinkley and Townsend are participating.
When asked about arsenic-tainted leachate affecting bioreactors, Hinkley says, “I don't know, and I don't know if anyone knows … If we collect all this leachate from these sites, it's inevitably going to be high in arsenic, which will inevitably limit what we do with it.”
Although many unknowns remain — such as the widespread impact of Florida's rulemaking and other state legislation — for Turley, at least, the answer may lie in emerging identification technology. “One of these technologies is going to work,” he says, “and that will solve a lot of problems.”
Kim A. O'Connell is a contributing editor based in Arlington, Va.
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