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What Does a Significant or High Hazard Potential Rating Mean?

The National Inventory of Dams Hazard Potential Classification is a system that categorizes dams according to the potential degree of adverse consequences of a failure or mis-operation of a dam. The classification does not reflect in any way the structural condition of the dam, nor does it reflect on what is contained behind the dam. For hazard potential classification purposes under this rating system, there is no distinction made between a coal ash impoundment and a drinking water reservoir.

The Hazard Potential Classification system considers the immediate physical damage that would result from the sudden release of the large volume of liquid and solid material held back by the dam or impoundment and categorizes dams based on the probable loss of human life and the impacts on economic, environmental and lifeline interests (critical infrastructure, highways, bridges, utilities).

There are three classification levels in the National Inventory of Dams classification system – Low, Significant and High – listed in order of increasing adverse consequences:

LOW HAZARD POTENTIAL - Failure or misoperation results in no probable loss of human life and low economic and/or environmental losses, principally limited to the owner’s property.

SIGNIFICANT HAZARD POTENTIAL - Failure or misoperation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or can impact other concerns.

HIGH HAZARD POTENTIAL - Failure or misoperation will probably cause loss of human life.

The EPA contractor inspectors have rated almost all of Duke’s Energy’s ash ponds for potential hazard, in accordance with the National Inventory of Dams rating criteria, as “Significant Hazard Potential.” The only ash ponds rated as “High Hazard Potential” are the two located at the Asheville Plant in North Carolina. These ponds are rated this way due to their location in the mountains, adjacent to Interstate 40 and the French Broad River.