Following the disastrous spill of a billion gallons of coal ash waste from the Tennessee Valley Authority's Kingston plant in December 2008, poorly regulated coal ash impoundments like the one that failed have landed in the public spotlight.

But other methods of disposing of coal ash waste have gotten less attention -- even though they still present serious environmental hazards.

A new report from the N.C. Sierra Club illuminates one practice of coal ash waste disposal that until now has stayed largely in the regulatory shadows: the use of the material in structural fills for development projects such as roads and buildings.

"Unlined Landfills? The Story of Coal Ash Waste in our Backyard" [pdf] documents how a lack of federal controls combined with weak state regulations have created what it calls a "gaping loophole" allowing an unknown volume of coal ash to be disposed of in this way. Under current North Carolina law, such so-called "beneficial use" of coal ash requires no permits, no liners, no regular inspections and no groundwater monitoring.

"North Carolina's current practice of allowing coal ash to be placed on the ground as fill material for land development with minimal oversight has led to numerous problems," the report finds. "These problems include groundwater contamination, surface water contamination, sham landfills, environmental violations and failure to track locations of coal ash fills."

One of the sites documented in the Sierra Club report -- the Swift Creek structural fill site in Nash County, N.C. -- was also included in "Out of Control: Mounting Damages From Coal Ash Waste Sites," a report that was released earlier this year by the Environmental Integrity Project and Earthjustice. That report noted that arsenic oozing from the site contaminated groundwater in an off-site aquifer.

The Sierra Club investigation also documents groundwater contamination at another North Carolina structural fill site on Alamac Road in Robeson County, where elevated sulfate and arsenic levels were found in the groundwater below the site:

ReUse Technology, a Georgia-based company that handles coal ash produced by utilities, was operating the Robeson County site without authorization. ... After the state began enforcement actions in the 1990s, ReUse Technology removed the ash from the Robeson County site.

In addition, the Sierra Club reports that high levels of toxic arsenic, iron and selenium were discovered last year in wetlands near Arthurs Creek in Northampton County, N.C. at a 21-acre coal ash structural fill site near the community of Garysburg.

The report also revisits a controversy that arose in 2000, when displaced survivors of Hurricane Floyd were temporarily housed in trailers at an industrial park in Edgecombe County, N.C. that turned out to be built on coal ash fill. In response to concerns raised by residents about uncovered ash at the site, the state conducted tests but claimed the soil presented no significant risks to residents.

Also addressed in the Sierra Club report are instances where mass soil excavation occurred at structural fill sites prior to the placement of the coal ash, essentially creating deep unlined landfills that put groundwater at risk.

The report faults North Carolina law for being lax about the use of coal ash at such sites:

According to state and federal (Clean Water Act) regulations -- as with all development -- coal ash cannot be placed within 50 feet of wetlands unless the U.S. Army Corps of Engineers approves. Structural fill sites must be set back from streams at least 50 feet. They must be 100 feet from water wells.

But beyond that, the state's rules for beneficial use of coal ash -- and especially for structural fill -- are overly permissive, provide inadequate state oversight, and fail to require minimum, commonsense safeguards.

The Sierra Club calls on the administration of North Carolina Gov. Beverly Perdue (D) to stop allowing coal ash to be used for land development and instead require that it be disposed of in lined landfills. It also calls for requiring groundwater monitoring at active structural fill sites and at sites created in the last 30 years, mandating cleanup by developers if monitoring data reveals groundwater or surface water contamination, identifying a funding source to enable adequate oversight and enforcement, and requiring that coal ash structural fills be permanently recorded on the deed for the affected property.

North Carolina imposed some regulations on coal ash structural fills in 1994, including a deed recording requirement. However, a 2002 state analysis found that only 56% of closed structural fill sites that held 1,000 cubic yards or more of coal ash had complied with that requirement, according to the report.

The Sierra Club investigation comes as long-promised federal regulations for coal ash -- originally supposed to be released in December -- remain in limbo at the White House Office of Management and Budget. The Obama administration is being lobbied heavily against declaring coal ash hazardous waste, in part because of how such a designation would affect so-called "beneficial uses" of the waste, including structural fills.

Among the many forces that have been lobbying against strict federal regulation of coal ash? The administration of North Carolina Gov. Perdue.