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Water Seeps and Toe Drains at
North Carolina Coal Ash Basins
What are seeps and toe drains?
A seep is a wet area or generally small flow that occurs when water moves from a coal ash basin through the earthen dam.
Seeps can also occur naturally as groundwater reaches the surface.
Some amount of seepage is common and a result of the earthen-type dam design. Toe drains are engineered in earthen dams to
allow water to be safely removed from the earthen dam.
In some cases, toe drain systems are engineered into the
dam using small piping to effectively channel the water.
In other cases, seeps surface naturally from the ground and
may have an orange-like color, which is often caused by iron
bacteria, a naturally occurring and non-harmful bacteria that
occurs commonly in North Carolina’s iron-rich soil.
Seeps at ash basins generally occur at low flows and contain low levels of the constituents that are found in coal ash, so the
nearby lake or river continues to be well protected and not influenced by these types of discharges.
Managing seeps and toe drains
The best way to reduce or eliminate seeps altogether is to dewater ash basins that are no longer needed and move swiftly to
close them. We have committed to do both.
In addition to closing basins, we are addressing seeps with state regulators through a more robust reporting process in the new
Coal Ash Management Act (CAMA).
Although regulators have been generally aware of seeps at basins, CAMA creates a more robust process to identify, test and
monitor them. We have shared detailed data with the state regulators so they can make informed permitting decisions.
www.duke-energy.com
Feb. 2015