The Tennessee Valley Authority (TVA) has vowed to clean up the 5.4 million cubic yards of wet coal ash—enough to flood more than 3,000 acres one foot deep—that spilled last week when the earthen retaining wall of an ash pond at the Kingston Fossil Plant, about 40 miles west of Knoxville, failed.

That reservoir, one of three containment areas at the 1,700-MW Kingston plant in Harriman, Tenn., was 40 acres wide and said to hold 2.2 million pounds of fly ash and bottom ash—decades worth of the coal-fired power plant’s by-product, according to The New York Times. The broken dike is said to have left 4 or 5 feet of water and mud over 250 to 400 acres of rural land. Authorities said no one was seriously injured or hospitalized.

Fly ash (lightweight ash) and bottom ash (heavier coarse residue) are both pumped to ash ponds. Once the ash settles in the ash pond, the ash is pumped to “dredge cells”—engineered and permitted facilities that are surrounded by dikes constructed using compacted ash, and which incorporate engineered drain systems, water runoff controls, and monitoring systems. The water flows into a settling pond.

On Dec. 22—the day the spill occurred—ash in the Kingston dredge cell storage areas reached heights up to 55 feet above water level in the ash pond prior to failure, but it was well within permit limits. A TVA spokesman suggested that heavy rains and freezing temperatures could have been to blame for the failure. Overnight temperatures for the region had dropped to 14F, and Harriman had already received 4.9 inches of rainfall—compared to the 2.8 inches of rainfall typical for the month of December.

The TVA said that it conducted comprehensive inspections of its ash containment areas, including daily visual inspections, quarterly solid waste and dike inspections, and annual detailed inspections of the ash-handling and storage dikes.

The most recent annual inspection was concluded in October 2008. Although this inspection’s formal report is not complete, a preliminary report shows that a “wet spot” was found, indicating a minor leaking issue. In a prior inspection (PDF), which concluded on Dec. 4, 2007, an inspector had recommended that the TVA should “repair any dikes showing signs of erosion on the pond side.” It is unclear whether the utility made those repairs.

The TVA said no significant problems otherwise suggested that the dikes were unstable and on the brink of failure.

The TVA said in a recent advisory that seven of the nine units at Kingston had been shut down, along with several other TVA fossil units, due to reduced demand for electricity as mild weather remains in the Tennessee Valley.

The Kingston Fossil Plant, located at the confluence of the Emory and Clinch Rivers near Kingston, Tenn., is one of TVA’s larger fossil plants. The plant’s construction began in 1951 and was completed in 1955.

In 2003 and 2006, the TVA reported that the dike at Kingston experienced smaller, localized seepage that released some ash from one of the dredge cells. After each incident, TVA made changes and repairs to improve the condition of the dike. The utility also noted that these problems were in an area of the dike southwest of the suspected location of the current failure.

Experts are calling the coal ash spill the largest environmental disaster of its kind in the U.S. owing to the toxic nature of fly ash. A 2007 inventory filed with the Environmental Protection Agency (EPA) and uncovered by The New York Times suggested that in one year, the plant’s by-products included 45,000 pounds of arsenic, 49,000 pounds of lead, 1.4 million pounds of barium, 91,000 pounds of chromium, and 140,000 pounds of manganese.

But in a recent statement, the TVA said that preliminary environmental data of the ash release showed no indication of acute health effects resulting from contact with the coal ash material—though it discouraged direct contact with it.

The TVA also said that while sampling in the vicinity of the Kingston water plant and of the water being served by Kingston showed no violations of drinking water standards, samples taken closer to the ash release did “slightly” exceed drinking water standards for several heavy metals, including arsenic.

Fly ash is the ash captured in the stack of a power plant and is a very fine, powdery material. As wet fly ash sediments dried out, the TVA was concerned that dust would become an issue for area residents. Response officials are currently evaluating the potential for health effects associated with the dust, and both the EPA and TVA have begun monitoring for levels of fly ash in the air.

"In the meantime, it is suggested that people avoid activities that generate dust. The dust may be irritating to the skin and nasal passages, especially to those who have conditions affecting their breathing, such as asthma or other respiratory illnesses,” the utility said.

Sources: TVA, EPA, The New York Times