Centralized impoundments are wastewater-holding facilities that are:

• A natural topographic depression, manmade excavation or diked area formed primarily of earthen materials.

• Designed to hold fluids or semifluids associated with oil and gas activities, including wastewater, flowback and mine influenced water, the escape of which may result in air, water or land pollution or endanger persons or property.

• Constructed solely for the purpose of servicing multiple well sites.

Centralized impoundments are frequently used by drilling operators to hold vast quantities of hazardous fracking flowback and produced water generated by unconventional shale wells. Centralized impoundments differ from other types of impoundments by being associated solely with hazardous waste, as compared to freshwater dams, and by serving to hold waste from multiple wells and/or well pads in the area surrounding them.