65% of fly ash produced from coal power stations is disposed of in landfills and ash ponds. Ash that is stored or deposited outdoors can eventually leach toxic compounds into underground water aquifers. For this reason, much of the current debate around fly ash disposal revolves around creating specially lined landfills that prevent the chemical compounds from being leached into the ground water and local ecosystems. Since coal was the dominant energy source in the United States for many decades, power companies often located their coal plants near metropolitan areas. Compounding the environmental issues, the coal plants need significant amounts of water to operate their boilers, leading coal plants (and later their fly ash storage basins) to be located near metropolitan areas and near rivers and lakes which are often used as drinking supplies by nearby cities. Many of those fly ash basins were unlined and also at great risk of spilling and flooding from nearby rivers and lakes. For example, Duke Energy in North Carolina has been involved in several major lawsuits related to its coal ash storage and spills into the leakage of ash into the water basin. The recycling of fly ash has become an increasing concern in recent years due to increasing landfill costs and current interest in sustainable development. , coal-fired power plants in the US reported producing of fly ash, of which were reused in various applications. Environmental benefits to recycling fly ash includes reducing the demand for virgin materials that would need quarrying and cheap substitution for materials such as Portland cement. Reuse There is no US governmental registration or labelling of fly ash utilization in the different sectors of the economy – industry, infrastructures and agriculture. Fly ash utilization survey data, acknowledged as incomplete, are published annually by the American Coal Ash Association. Coal ash uses include (approximately in order of decreasing importance): Concrete production, as a substitute material for Portland cement, sand. Corrosion control in RC structures Fly-ash pellets which can replace normal aggregate in concrete mixture. Embankments and other structural fills (usually for road construction) Grout and Flowable fill production Waste stabilization and solidification Cement clinker production (as a substitute material for clay) Mine reclamation Stabilization of soft soils Road subbase construction As aggregate substitute material (e.g. for brick production) Mineral filler in asphaltic concrete Agricultural uses: soil amendment, fertilizer, cattle feeders, soil stabilization in stock feed yards, and agricultural