The U.S. Environmental Protection Agency rates coal ash ponds according to a National Inventory of Dams criteria that categorizes the ponds by the damage that would occur if the pond collapses. Coal ash ponds are usually earthen structures holding back millions of tons of toxic coal ash and water.
The NID hazard potential ratings refer to the potential for loss of life or damage if there is a dam failure:
309high and significant Hazard Coal Ash Dams
High, High* Hazard Failure or mis-operation of dam will probably cause loss of human life. (* are based on state data. EPA considers the hazard potential to be significant.)
Significant Hazard Failure or mis-operation of dam results in no probable loss of human life, but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns.