Solid waste managers take in the world's undesirables every day, but in doing so, a potential bomb chromated copper arsenate (CCA)-treated wood is waiting to drop on the industry. In approximately 15 years, the amount of CCA-treated wood headed for disposal is expected to peak. And like an unwelcome mother-in-law, over time, the effects of arsenic leaching from the wood could wind up being a nagging problem.
CCA-treated wood recently has received much attention over soil and water contamination from structures made from this common building material; the possible effects on those working with the wood; and the potential danger to children who play on treated wood structures. These issues continue to unfold.
However, for the past five years, a team of researchers led by Helena Solo-Gabriele of the University of Miami, Fla., and Timothy G. Townsend of the University of Florida, Gainesville, with funding from the Florida Center for Solid and Hazardous Waste Management, a statewide research center located at the University of Florida, have been studying the implications of the material's disposal.
“The research has been good and quite strong, and there is a bona fide concern,” says Bill Hinkley, chief of the bureau of solid and hazardous waste for the Florida Department of Environmental Protection (FDEP), Tallahassee. “The bottom line is that there's no arguing that arsenic leaches out of CCA-treated wood, and there's no doubt that the burden is going to fall on the waste industry to sort out. The dispute centers on what we are going to do about it.”
While all aspects of CCA-treated wood use currently are facing scrutiny in the state, Florida research primarily has focused on the effects of discarded CCA-treated wood. In fact, it was a waste management issue that began the interest in this subject, Townsend says [See “More than Child's Play].Basic Facts
Preserved or treated wood is a common component of the solid waste stream. A 1998 U.S. Environmental Protection Agency (EPA) study estimated that 136 million tons of building-related construction and demolition (C&D) debris were generated in 1996, with wood representing the largest component. According to the report, approximately 500 wood processing facilities in the United States derive wood from C&D.
Because preserved wood products are treated by applying pesticide to the wood to prevent fungal or microbial decay, questions often arise as to how to best manage discarded treated wood, from both from a regulatory and an environmental perspective.
Common U.S. wood preservatives include creosote and pentachlorophenol. But the predominant preservative used today is CCA, which introduces concentrations of copper, chromium and arsenic to the wood.
As part of the CCA wood treatment process, wood first is dried in a kiln. The dried wood then is placed in a vessel where a vacuum is applied to the wood's pore space. CCA solution is introduced into the vessel, which then is placed under pressure. This causes the CCA solution to enter the wood's pore space. A vacuum extracts the excess solution. And after the wood is removed from the vessel, it dries over a drip pad.
CCA solutions vary among wood treaters, but there are three typical formulations, as defined by the American Wood Preservers Institute (AWPI), Fairfax, Va., based on the solution composition by percent mass of the metal compounds used [See “CCA-Treated Wood Types and Requirements]. Of types A, B and C, C is most commonly used. The concentration of CCA remaining in the wood after treatment is rated in pounds of CCA per cubic foot of wood, defined as the standard retention value.
|Composition||Type A||Type B||Type C|
|Hexavalent Chromium, calculated as CrO3||65.5%||35.3%||47.5%|
|Bivalent copper, calculated as CuO||18.1%||19.6%||18.5%|
|Pentavalent Arsenic, calculated as As2O5||16.4%||45.1%||34.0%|
|Source: American Wood Preservers Institute|
Typical CCA-treated wood applications include telephone poles, fence posts, decks, and components of home construction [See “Standard Retention in Various CCA-treated Wood Products].
At low retention values, CCA-treated wood maintains a natural look and can easily be painted. CCA also produces no smell or vapor.
|Attributes||Standard Retention (PCF)|
|Above ground use (deck boards and fence boards)||0.25|
|Ground or fresh water contact (deck posts and fence posts)||0.40|
|Salt water splash (decking for docks and marinas)||0.60|
|Wood foundations and heavy structural use (foundations and poles)||0.60|
|Foundation piles (a key part of high rise foundation construction)||0.60|
|Salt water immersion (docks and marinas)||2.50|
|Source: American Wood Preservers Institute|
|PCF=pounds per cubic foot|
The AWPI estimates that CCA increases the life of wood products exposed to the environment approximately seven to 12 times to 20 to 50 years, preserving millions of trees annually. But for many wood product applications, appearance more than performance dictates the material's actual life-span.Discarded CCA Wood
Solid waste managers should note that CCA treated wood was not widely used until the early 1970s, at which time it represented less than 15 percent of the treated wood market. Today CCA-treated wood represents nearly 80 percent of the market, with more than 450 million cubic feet currently being sold in the United States, according to Florida research. Approximately 6.5 billion board feet are treated each year, says Scott Ramminger, AWPI president.
With the product's recent increase in use and long service life, most of the material is presumed to still be in service [See “Projection of CCA-Treated Wood Entering Florida's Waste Stream” on page 42]. Solo-Gabriele and Townsend estimate that, assuming the current use stays constant, the amount of CCA-treated wood entering the waste stream will not peak until 2015.
“I wouldn't be able to speculate when the amount of wood being disposed of will peak. It's possible that it already has peaked, frankly,” Ramminger says, “but we're interested in what the [Florida] researchers come up with and are cooperating with them.”
Regardless of when the wood reaches its maximum disposal point, the issue, at least in Florida, is causing concern. Particularly, CCA's status under U.S. federal hazardous waste regulations, current disposal practices, and future management and product options are being questioned.Hazwaste Characterization
Current U.S. hazardous waste regulations require certain solid wastes to be managed more stringently because of potential human health and environmental risks. These hazwastes must comply with more controlled regulations regarding storage, transport, treatment and disposal. Both elevated levels of arsenic and chromium can result in a solid waste being classified as a toxicity characteristic hazardous waste.
Toxicity characteristic leaching procedure (TCLP) results of newly CCA-treated wood at the lowest retention levels show that arsenic leaches at concentrations greater than the toxicity characteristic limit (5 milligrams per liter (mg/l)), more than half the time, Florida research says. However, data on older, weathered wood appears to be less available. Research currently is being conducted on weathered wood, but data is not yet available, Townsend says.
However, discarded CCA-treated wood, among other materials, is exempt from the regulations. Part 261.4 of the Code of Federal regulations exempts:
Solid waste which consists of discarded arsenical-treated wood or wood products which fails the test for the Toxicity Characteristic for Hazardous Waste Codes D004 through D017 and which is not a hazardous waste for any other reason if the waste is generated by persons who utilize the arsenical-treated wood and wood product for these materials' intended end use.”Current Disposal Practices
As a result, most states handle CCA-treated wood similarly to other discarded wood products. However, one state, Minnesota, has not adopted this exemption in its state hazardous waste program [See “Minnesota at the Margin” on page 42].
CCA-treated wood in Florida primarily is managed at unlined C&D waste landfills or at C&D recycling facilities, with smaller amounts managed as municipal solid waste (MSW) in lined landfills or at waste-to-energy (WTE) facilities.
Herein lies the potential problem.
“We try to make two statements about CCA-treated wood that relate to disposal,” AWPI's Ramminger says. “One, you should not burn the wood, and two, [the wood] should not be recycled into mulch.”
But because of the hazwaste exemption, CCA-treated wood in Florida, and possibly in other states, is going into unlined C&D landfills; being burned at WTE facilities, which increases the ash's metal concentration; and is inadvertently being recycled into mulch.
“Are we properly disposing of this wood?” questions FDEP's Hinkley. “For the most part, according to the exemption, we are. And the CCA fraction right now isn't that much. But CCA-treated wood reaching disposal is projected to rise to 35 percent of the wood waste stream, and then all of a sudden this venerable wood is going into disposal and fast. In 20 years, we'll have created a concentrated pile of CCA-treated wood that leaches arsenic.”
“The issue becomes a matter of how much [arsenic] is in the CCA-treated wood,” says Ed Repa, environmental programs director for the National Solid Wastes Management Association of the Environmental Industry Associations, Washington, D.C. “If you pressure-treat wood, how much [of the pesticide] really penetrates the wood? How much will leach out of the wood at the landfill after it has been sitting above ground for years? I'm not sure there has been enough testing to determine this.”
This is true. No discernible pattern of CCA contaminating groundwater or soil, or increased leachate toxicity in a landfill has been established. “But the question becomes, do we wait until it becomes a problem that we're forced to clean up, we're forced into some kind of compliance, or something else?” Hinkley asks.
From a waste manager's point of view, in all three areas landfills, recycling and WTE there are some very real concerns and decisions that should be made.Landfills
Disposal is the primary issue Florida is wrestling with, Hinkley says. Whether you bury the wood in a C&D, MSW or hazardous waste landfill, arsenic-leaching potential should be considered.
Because of the federal hazwaste exemption, much of the CCA-treated wood is being disposed of in C&D waste landfills, which in Florida do not require liner systems. This raises concerns about arsenic from the wood possibly leaching into the groundwater.
In rainwater leaching tests using the U.S. EPA's synthetic precipitation leaching procedure (SPLP) CCA-treated wood leaches arsenic many times above the U.S. primary drinking water standard of 50 parts per billion (ppb). New CCA-treated wood exposed to rainwater leaches approximately the same amount of arsenic as that leached using the TCLP.
Additionally, C&D waste landfills simulated in the laboratory and field that contain CCA-treated wood have been found to leach arsenic. Arsenic concentrations in some leachates were greater than the arsenic drinking water standard, which serves as Florida's Class I groundwater standard.
While some degree of dilution is permitted in the mixing zone underneath the landfill, the eventual lowering of the arsenic drinking water standard, currently a topic of national debate [See “Up in Arms over Arsenic” on page 45], increases the chance that C&D waste landfills disposing of CCA-treated wood will have groundwater exceedances.
There is no concrete data on what impact CCA-treated wood in C&D landfills will have on groundwater. Current Florida research is focusing on large field simulations of new treated wood and old, weathered treated wood mixed with MSW and C&D debris to determine whether old, weathered wood poses a problem if it goes into an MSW landfill. However, the data won't be available for a few years, Townsend says. Groundwater monitoring only recently has been required in Florida, so the state needs more time to closely examine groundwater quality data.
“A good bit of newly treated scrap wood fails TCLP for arsenic, but I haven't seen any data on weathered wood and whether it fails TCLP,” says Greg Helms, environmental protection specialist with the U.S. EPA Office of Solid Waste, Crystal City, Va. “So we don't know what the residual levels of arsenic are in the wood that's coming out of service. And we don't know how much is going into landfills.”
Nevertheless, “in Florida, most of the peninsula is sand, and there's very little clay in the soil, so arsenic has the potential to go right into the groundwater,” Hinkley says. “We don't have evidence of this, but there clearly is cause to protect groundwater. We have high rainfall, high groundwater tables and shallow wells. Add to this Florida's problem that all of its landfills are high-rise, with some C&D landfills 60 to 70 feet off-grade, and we believe there is a potential threat.”
But make no mistake, the problem won't be solved by getting rid of the hazwaste exemption and sending CCA wood to a MSW or hazwaste facility. And the solution isn't as simple as requiring C&D landfills to install liners.
“The liner is just the beginning,” Hinkley says. “If you require a liner on the bottom of the landfill, you have to put a liner on the top, too, to prevent the bowl effect. And if you put in a liner, you'll create leachate and gas. So then you'll have to put in a [leachate and gas] collection system, and you'll have to pipe the leachate to a wastewater treatment plant. And suddenly you've gone from a bowel pit where construction guys are dumping in C&D and turned it into a full waste management site.”
A few years ago, Florida required C&D sites to install groundwater monitoring systems. When this happened, nearly half of the state's C&D disposal sites closed, Hinkley says. The FDEP fears that if it changes its C&D regulations and requires liners, another half of the sites could close.
“The people who operate C&D sites often did not start off in the waste management business, many were in the construction business,” Hinkley explains. “If we put in a new set of regulations, many may decide to get out of the waste business, and I fear we'll end up with a huge upsurge in illegal dumping, especially in rural areas where the one C&D site in the area could close.”
If CCA-treated wood is banned from C&D facilities, it most likely will go to municipal solid waste Subtitle D landfills or hazardous waste Subtitle C facilities. But this could potentially increase the metal concentration in those facilities' leachate.
“A landfill operating under Subtitle D with normal leachate treatment systems will detect any release long before it becomes a serious environmental problem,” says John Skinner, executive director and CEO of the Solid Waste Association of North America (SWANA), Silver Spring, Md. “But you may have additional requirements to treat the leachate and hazardous leachate if arsenic does leach once it's in a landfill.”
If a wastewater treatment facility land-applies its sludge but can't dilute the leachate enough to meet the allowable levels of arsenic, it might not accept a facility's leachate, Hinkley says. Then, the landfill is going to have to pay to truck the leachate elsewhere, or install a pretreatment system.Recycling Facilities
Recycling presents its own set of challenges. Florida is home to a large number of C&D waste recycling facilities that accept mixed loads of C&D debris, then separate the components for reuse. Wood, the largest component by volume, is recovered for biomass fuel and landscape mulch.
Red mulch is very popular in Florida, Hinkley says. To create the mulch, producers chop a 1-inch chip from a mixed wood stream, which includes C&D wood waste, untreated lumber, oriented strand board (OSB) and particle board, then dye it for decorative or commercial landscaping use. “The red mulch is taking the place of cypress mulch, which is great as a recycling issue because recovered wood is serving as a replacement for indigenous trees.” However, CCA-treated wood sometimes is found in this mix.
When chipped into mulch, the arsenic leaching potential of CCA-treated wood increases dramatically because the material is spread around and the surface area-to-mass ratio increases, the research states. This widens the possibility of soil or groundwater contamination.
“I hasten to add that making mulch from treated or painted wood is not legal,” Hinkley says. “It should not be occurring under the law.” But when wood goes to a recycler, in some cases, identifying the wood is difficult.
“Facilities do try to pull out [CCA-treated wood]. And in some cases, CCA-treated wood may be distinguished from the rest of the wood waste,” Hinkley says. “But when CCA-treated wood oxidizes and turns gray, it can be difficult to separate from untreated wood.”
Samples collected from Florida C&D waste recycling facilities in 1997 found an average 6 percent CCA wood content in chipped wood piles. More recent field sorts of wood piles have found treated wood concentrations ranging from 9 percent to 30 percent.
Thus, CCA-treated wood presents recycling difficulties. Research indicates that the presence of 5 to 6 percent CCA wood in wood fuel can cause the ash to be a hazardous waste. An even smaller amount of CCA wood causes arsenic to leach from wood mulch at levels higher than allowable in landfills. And if the fraction of CCA is greater than 1 percent by weight in mulch, it will leach arsenic in concentrations that exceed the 50 parts per billion allowable under the safe water drinking act, Townsend says.
Additionally, The Connecticut Agricultural Experiment Station, New Haven, has researched CCA uptake by edible plants and found that romaine lettuce and the plant family that includes vegetables such as mustard and collard greens accumulate arsenic in their leafy parts.
“The concern is that some people are using these decorative mulches in gardens,” which could potentially affect human health, Hinkley says.WTE
Some people suggest burning the wood at waste-to-energy facilities as a CCA-treated wood disposal option. “This may be our best solution,” Hinkley says, considering that Florida houses 13 WTE facilities more than any other state. “But there are some questions that have to be evaluated here, too.”
During combustion, the metals in CCA-treated wood are not destroyed, but are emitted in the flue gas or concentrated in the ash. Arsenic is known to be volatile at higher temperatures, so WTE facilities' air pollution control equipment would need to be adequately designed to remove it.
“All you need is 6 percent CCA wood in the mixture and you could fail TCLP,” Hinkley says. “People want to be able to land-apply their WTE ash, but CCA could make this unfeasible. The ash could have thousands of parts per million of arsenic.”
Already, Florida researchers have conducted a simulation to determine the effects of combusting CCA-treated wood in Florida's WTE facilities [See “Simulation of WTE Ash Mass and Arsenic Concentration from 1995 to 2016,” on right].
Assuming all discarded CCA-treated wood was disposed in Florida's WTE facilities starting in 2000, the simulation shows that the total mass of ash does not increase significantly, but the concentration of arsenic does. In 2000, the concentration increases five times from 35 milligrams of arsenic per kilogram of ash (mg/kg) to 177 mg/kg. The arsenic concentration in the ash then increases yearly. This pattern follows the same trend as the amount of CCA-treated wood being discarded. By 2016, the arsenic concentration in the WTE ash in the simulation reaches 940 mg/kg, an increase of 25 times.Possible Future Practices
“We're in a conundrum,” Hinkley says. There are options to choose from WTE, disposal, recycling or waste minimization but each has its limitations.
Burning the wood concentrates the metals. Disposing of the wood in landfills where it could leach arsenic potentially contaminates groundwater or increases leachate management costs.
Reuse is the most obvious recycling option. For example, a utility that uses CCA wood telephone poles could give the material to a farmer to build a barn or fence. However, utilities are beginning to become aware of the potential liability of giving these materials away, so fewer businesses want to do so, Hinkley says.
Additionally, there are limits to reuse because people frequently get rid of CCA-treated wood because it doesn't look good anymore. If the wood is not aesthetically pleasing, other people may not want to reuse it, Hinkley adds.
As another recycling option, the wood could be chipped then pressed into engineered wood products, such as OSB. But according to Townsend and Solo-Gabriele, no one currently is producing treated engineered wood products. The AWPI is sponsoring research at Louisiana State, Baton Rouge, to test the feasibility of recycling CCA wood into strand board. But businesses that create untreated engineered products have expressed reluctance to mix in CCA-treated wood because it has other properties than their typical wood mixture and presents a liability, Townsend says.
CCA-treated wood could be chipped then mixed with other aggregates to create a lightweight wood cement composite, but no one is practicing this either.
Or, the treated wood could be ground up then put through a pyrolysis process. Using this method, pyrolysis heats the organic compound of the wood and volatilizes it so only metals and carbon remain. The metals then are separated from the carbon and recovered or sent to a hazwaste landfill. Currently, two facilities are using this process: one in Finland that operates as a copper smelter, the other in France, which uses what its founders call their Chartherm process.
With each recycling option, two major points also must considered: How do you separate and collect the CCA-treated wood from the rest of the C&D waste stream? And once separated, what do you do with it?Separation
Florida research argues that CCA-treated wood could be difficult to separate out at the disposal site. New CCA-treated wood takes on a greenish tint that increases in intensity the greater the retention level, making the wood easy to distinguish from new, untreated wood. But when exposed to sun and rain, the treated wood surface often turns a similar color as weathered, untreated wood. This is especially true for species such as Southern Yellow Pine. Once treated and untreated wood commingle, they can be very difficult to distinguish from one another, say Solo-Gabriele and Townsend.
“Yes it's true some wood is difficult to distinguish by color,” Hinkley says, “but there's another way to approach this.” C&D recyclers could pull out CCA-treated wood based on its use.
“If you look at the sales of Yellow Pine, roughly half is used for decks, fences, four-by-fours and very obvious construction,” Hinkley explains. “When I go to C&D sites and look at wood piles, I can spot sections of a fence or deck and guarantee it's CCA. So you could set up a system in a mulching situation to pull the wood out, and I think it's feasible to eliminate CCA in that product.”
Chris Campman, SWANA landfill division chairman and manager for solid waste for Gannett Fleming Inc., Valley Forge, Pa., agrees it's possible for mulchers to pull out the treated wood. “We have a client that makes its own mulch that pulls out [treated wood] and ships it to a landfill,” he says. As the facility receives materials, it is put on a sorting line so that unwanted items, including plastic and glass, can be pulled out then sent to the landfill.
But setting up a sorting system requires additional setup and labor costs for many facilities.
And while separation may be possible for mulchers, Hinkley says it may not be as easy at WTE facilities. “If a 100-yard truck goes by where you're grinding huge amounts of wood, good grief. But such a facility could say it will only take new, white wood so that you could visibly see whether or not the wood is treated.”
There are other options to help distinguish CCA-treated wood. Surface staining methods can be used, but time constraints limit their application to small volumes of wood, and they are best used to “spot-check” fuel quality at wood recycling and burning facilities, according to Florida research. Detection systems X-ray fluorescence (XRF) or laser may be incorporated into a conveyor system at a processing facility. However, these systems are not commercially available and are only now being studied by a few Florida counties.
Even given separation's feasibility, sorting CCA wood from other C&D debris relies on education and compliance.Waste Minimization
Fortunately, other products are available. There are arsenic- and chromium-free wood preservatives, such as alkaline copper quat (ACQ). One focus of the ongoing Florida research is what impact these other water-borne preservatives have. Obviously there are no benefits to switching if 30 years down the road the industry realizes that these chemicals pose a different problem, Townsend says.
An ever better choice, at least for the waste industry, is plastic lumber, which is comprised of recycled plastics such as drink bottles.
“The good news is that this is a fascinating issue and we're moving in a good direction in terms of replacing CCA-treated wood,” Hinkley says. “On the disposal side, the industry is beginning to recognize the big picture of concerns, and steps will have to be taken, for example, keeping it out of mulch. Ash will have to be tested and monitored and possibly taken to a lined landfill, and we'll have to look at the exemption to determine whether it should continue to go to an unlined C&D landfill.
“Unfortunately, this could cause considerable expense,” Hinkley continues. “But do we wait until it's too late or handle it now? If we wait until we get hit in groundwater detection wells, it'll be 20 years down the road, and we won't have any choices. We know enough from other contaminated sites that if you're forced into pump and treat remediation, cleanup is very costly. So we're looking at this as an ounce of prevention is a pound of cure.”
Patricia-Anne Tom is Waste Age's managing editor.
Full reports of the Florida research conducted by Helena Solo-Gabriele, associate professor at the University of Miami, and Timothy G. Townsend, associate professor at the University of Florida, Gainesville, that is referenced in this article are available at www.ccaresearch.org.
For additional resources of CCA-treated wood information and continuing coverage of this topic, visit WasteAge.Com's Special Report on CCA-Treated Wood.