Issue Date: February 23, 2009
The Foul Side Of 'Clean Coal'
THREE DAYS BEFORE Christmas last year, a sea of coal-ash sludge broke through a dam at the Tennessee Valley Authority (TVA) Kingston coal-fired power plant in eastern Tennessee. The reservoir covered 84 acres and was one of the plant's three holding ponds for the ash produced by burning coal. It released more than half its waste—some 5.4 million cubic yards of ash—which flowed through farmland and into the Emory and Tennessee Rivers. No one was killed, but once spread, the ash covered roads and an area of more than 275 acres in a 6-foot-deep mass of sludge containing arsenic and a mix of other elements with toxic properties.
The accident is symptomatic of a little-recognized problem caused by intensifying efforts to reduce air pollution from coal-fired power plants: "Clean coal" still comes with pollution that must be managed, and although good for the air, the tougher air pollution controls become, the higher the ash piles grow.
Over the past 30-plus years, air pollution has slowly come down to Earth. Coal-fired plants have cut smokestack emissions of soot, particulates, and sulfur dioxide by capturing and putting them and other waste ash into huge piles, reservoirs, and impoundments located near the plant sites. And now recent studies by Environmental Protection Agency scientists are finding that carcinogens and other contaminants in this ash can leach into water supplies at concentrations exceeding drinking water standards.
The tests have examined coal ash under a wider range of more realistic conditions than had been done in the past, and the results are likely to raise concerns over where coal ash can be placed to ensure it is isolated from water and human contact.
Each year, 131 million tons of ash is generated by the nation's 460 coal-fired power plants, made up of some 1,100 single-boiler furnaces. If loaded onto railcars, this ash would fill a train stretching from New York City to Los Angeles three-and-one-half times over. Some of the ash is used in products, but most is not. Even some beneficial uses may have significant problems.
Coal naturally contains arsenic, barium, beryllium, boron, cadmium, chromium, thallium, selenium, molybdenum, mercury, and other elements in small concentrations. When coal is burned, however, the metals become concentrated in ash residue at levels four or more times that in natural coal. Most of the metals are held in the ash and sulfur dioxide wastes captured by air pollution control equipment.
Of the 131 million tons of coal ash, 71 million tons is fly ash particulates, which are light, fine materials captured from exhaust gases, according to figures from the American Coal Ash Association (ACAA), an industry-funded organization that advocates beneficial use of coal ash. About 20 million tons is bottom ash and slag, which are heavy, coarse residues left after coal is burned in a furnace. About 33 million tons is calcium sulfate and calcium sulfide, created when sulfur is captured in calcium-based "flue gas desulfurization" air-scrubbing systems. A relatively small amount, 7 million tons, is ash generated through a combustion process that embeds limestone with the ash, the residues of which wind up in coal mines.
A VOLUNTARY INDUSTRY survey indicates that 43% of this waste material is reused in a beneficial way, David Goss, ACAA executive director, tells C&EN. About 20% of all ash is used in products—14% (19 million tons) of fly ash is bound in concrete and cement, and another 6% (8.2 million tons) of SO2 waste is used to make gypsum wallboard for home and office construction. Another 23% of ash is also used beneficially, according to Goss, and is placed on land as structural fill and road base. Some is spread on farmland to "amend" soil or is used to fill in depleted mines. But he admits that no one is sure where the other 56% (75 million tons) goes.
Despite the amount of ash and the potential for problems, no federal regulations control the fate of ash from coal-fired power plants. Instead, a hodgepodge of state regulations and power-plant economics determines whether the ash and other combustion wastes are stored in a wet or dry state or whether they wind up in a landfill, mine, wetland, quarry, as construction fill, spread on farmland, or in a product.
"This is outrageous," says Jeffrey Stant, with the Washington, D.C.-based Environmental Integrity Project (EIP). Stant supports ash use in cement, concrete, and wallboard but takes issue with other uses. "Dumping ash in holes in the ground and calling it a structural fill or dumping it in a mine just creates more dangers," he says. Putting ash in impoundments, reservoirs, and ponds is a "nightmare scenario," he adds, explaining that once the ash is exposed to water, people may wind up drinking low levels of contaminants.
Currently, ash is stored in some 1,300 U.S. locations, according to interviews and federal data. About 620 sites are active ash landfills, ponds, or surface impoundments located near power plants, according to Jim Roewer, executive director of the Utility Solid Waste Activities Group, an organization of electrical utilities. The rest are old dump sites, Stant says, citing federal data.
About 45% of the operating ash sites are wet impoundments, ponds, or reservoirs of some sort, Roewer estimates. Like Goss, Roewer bases his figures primarily on voluntary industry-supplied information. Stant says there are many more wet dump sites.
Last year's Kingston spill is not an isolated incident. A few weeks later, another TVA ash pond leaked. This one contained scrubber waste from air pollution controls intended to remove sulfur dioxide emissions from TVA's Widows Creek Plant in Alabama. The leak was smaller than that at Kingston—some 10,000 gal—and wound up in Widows Creek, which also flows into the Tennessee River.
ALSO LAST DECEMBER, a local Maryland judge signed off on a $54 million settlement between Constellation Energy and residents of Gambrills, Md., in which the utility was penalized for dumping coal ash in a wet sand and gravel quarry, ostensibly as part of a "reclamation" effort. The ash waste contaminated private wells near the quarry with aluminum, arsenic, beryllium, cadmium, lead, manganese, and thallium above accepted drinking water levels.
No comprehensive authoritative records are kept of such accidents. However, in a 2007 report, EPA evaluated community and environmental groups' complaints of water contamination from leaking coal ash ponds and landfills and found proof of contamination from 24 of 85 sites identified in complaints. Another 43 cases were potentially damaging, EPA said, but the agency dropped the investigations because it could not determine whether the damage was due exclusively to coal ash.
Coal is incredibly important to the U.S. economy, however, notes Thomas J. Feeley III, technology manager at the Department of Energy's National Energy Technology Laboratory, pointing out that the U.S. gets half its electricity from coal.
But because of coal's problems—air pollution, destructive mining practices, greenhouse gas emissions of carbon dioxide, and ash generation—coal-fired power generation is becoming a tempting target to replace with cleaner sources of renewable electricity. Many coal-fired power plants are being planned, but few are being built today.
Still, the amount of ash is going to grow, Feeley says. "Probably the first federal Clean Air Act regulation, which goes back to 1970, went after black soot emitted by coal plants," he notes. As a result, he says, nearly every power plant today has some systems to capture fly ash particulates. And as air pollution requirements grew, utilities captured more particulates, as well as sulfur dioxide, nitrogen oxides, and mercury in more exotic pollution control equipment.
Feeley estimates that about 30% of emissions from electricity generation by coal-fired power plants is now "scrubbed" to remove SO2. This waste is often mixed with ash for disposal.
The amount of SO2 waste, Feeley says, will double in the next few years as more and more plants comply with new Clean Air Act requirements. Also utilities must now specifically capture mercury emissions, which will wind up either in the fly ash or in SO2 scrubber waste. Although both the mercury emissions and Clean Air Act regulations are in flux right now, the handwriting is on the wall: The new Congress and Administration are going to cut air emissions.
Several members of Congress have already shown support for new ash-handling requirements and an inventory of waste sites. The Department of Justice and federal judges also have begun taking more actions against coal plants. For example, just last month a federal judge ordered four TVA plants to install better pollution controls, including the two with leaking ash impoundments.
ALL THESE ACTIONS will create more ash and solid waste, and Feeley predicts that nationally at least 30 million more tons of ash and waste will be generated in the years ahead, primarily captured along with sulfur dioxide, as well as some 50 tons of mercury in fly ash and SO2 wastes.
Although there are no federal ash regulations on the books, EPA has been studying ash since the 1980s. In 1993, the agency determined that coal ash should be regulated as a nonhazardous "solid waste." The distinction is important because solid waste is left to the states to regulate; a classification of hazardous waste would call for a federal regulatory scheme that would include monitoring and greater isolation of the material, as well as liners and systems to collect water leaching from the ash.
In the waning months of the Clinton Administration, EPA re-examined its decision and found itself caught between environmental groups who wanted tougher regulations and coal-based energy providers who did not. Eventually, EPA Administrator Carol M. Browner went with industry and left it to the states to continue regulating coal ash as they saw fit and as a nonhazardous waste.
Since that determination, EPA has been looking into coal ash and its ability to leach into water, says Susan Thorneloe, a researcher at EPA's Research Triangle Park, N.C., laboratory, who is leading that study.
"What I was asked to do," she explains, "was to determine the fate of metals and mercury from new multipollutant controls at coal-fired power plants." Her research followed recommendations of the independent EPA Science Advisory Board and a panel of the National Research Council whose members had voiced concerns about coal ash toxicity and whether contaminants can leach from ash at levels that are a threat to humans or the environment.
"We know that leachate is sensitive to pH levels and the ratio of liquid to solids, or the amount of water infiltration," Thorneloe says. According to a series of reports going back to 2002, she and her team found that the current method to test leachability is like a snapshot with a single pH value and doesn't match what is actually going on in the field.
When scientists collected samples from a range of power plants and subjected them to conditions similar to those in the environment, they found significantly higher leachability of contaminants. They also found that pollution control equipment itself influenced the concentration of contaminants and their leachability.
Looking at leachate from SO2 wastes, they found boron levels 10 times higher than drinking water standards; cadmium at levels 10 times above safe levels; and selenium at levels 60 times higher than the drinking water standard.
In leachate from fly ash, EPA found arsenic, barium, beryllium, boron, cadmium, chromium, thallium, selenium, and molybdenum at levels above drinking water standards. In particular, the level of arsenic was 30 times above the standard.
"The good news was mercury," Thorneloe says, because the metal stays bound in the material with fairly low levels of leachability.
Thorneloe underscores that her research indicates only the ability of ash to leach out contaminants at levels high enough to merit concern. Exposure is another matter. If ash is leaching to a rapidly flowing river, arsenic or other contaminants may be diluted to safe levels; if they wind up in a public water system, the contaminated water can be treated.
But Thorneloe's work indicates that where ash is placed should be closely examined and that ash should not be stored or used in environments where it will come in contact with water.
For EIP's Stant, the message is that ash types should be kept separate from one another, stored dry, and placed in a lined landfill; such a protocol is done for less than half the ash today. Instead, to aid transportation, many power-plant operators mix ash with water and pump the mixture to reservoirs. "Nothing can be done with ash when it is mixed in a wet slurry," Stant notes.
Goss agrees, and he and Roewer say the trend today is for utilities to shift to dry landfill storage. But replacing wet reservoirs with dry landfills will be expensive, Roewer says. He estimates that the shift to dry landfills will cost utilities about $50 million per plant or more than $10 billion for the industry.
"The challenge for us is to find technologies that allow continuous beneficial use of the material," Goss says. He holds up Wisconsin as an example in which utilities are using nearly all of their ash in beneficial applications.
This may not be easy as ash piles grow.
TAKE THE CASE of gypsum (calcium sulfate dihydrate), which is made from SO2 waste and used for wallboards. The figures compiled by Goss show that only about 8 million of the 33 million tons of generated scrubber waste is used annually for wallboard. The majority of scrubber waste is treated in a manner making it unsuitable for wallboard.
But even if more scrubber waste can be made useable for wallboard, the market is already saturated, with about one-third of all wallboard production using gypsum from coal ash, Goss says. Home construction has collapsed, he notes, and power plants are usually not located near wallboard plants. Transportation costs kill reuse economics, he adds.
Still, Goss believes TVA's Kingston plant accident has become a wake-up call for the industry. "I think the Kingston situation is going to drive a lot of electric utilities to consider converting to dry handling," he says. "My guess is what TVA does may lead industry in that direction by virtue of their leadership. If they had known 20 years ago what was going to happen, they may have changed their practices."
But TVA is unlikely to move ahead without a push from regulators.
"TVA is in compliance with its ash-handling permit," TVA spokesman Gilbert Francis says. "When the regulations change, we will change, too."
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