As Duke Energy spends heavily to control the coal ash stored at its power plants, millions of tons of the potentially toxic byproduct lie unchecked across the Charlotte region.

Duke plans to spend $140 million in the Carolinas - $365 million company-wide - by 2013 on protective caps and liners at its ash landfills, according to Securities and Exchange Commission filings. The liners are intended to keep ash that is laden with arsenic, mercury and other metals from contaminating groundwater.

But 2.7 million tons of Duke's ash, used to fill gullies, level roadbeds and prepare building foundations, was deposited between 1992 and 2003 without the protective measures now required at landfills.

Experts say large ash deposits near drinking-water wells bear watching. Duke had to shut down an old ash landfill at its Belews Creek plant in Stokes County last year after groundwater samples repeatedly broke state safety standards. Duke has also recently detected tainted groundwater near its power plant basins that hold a slurry of ash and water.

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