If Hollywood made horror movies about sediment control, the
fly ash spill in Tennessee two weeks ago would provide a great scenario. On
December 22, near Knoxville, an earthen dam holding back the contents of a
retention pond collapsed. The resulting torrent destroyed three houses,
reportedly derailed a train, and covered hundreds of acres.
And it kept growing: estimates of the amount of fly ash
released ranged from an initial 1.7 million cubic yards to more than 5 million
cubic yards. Officials still don’t know exactly how much water was released when
the pond broke, although it was said to hold more than 40 million gallons. Fly
ash, a very fine powder, is a by-product of coal-fired plants and is sometimes
sold to be used in cement.
There are two main concerns surrounding the spill. One is the
sheer amount of material that was released and how to clean it up. Work is
ongoing to remove the sludge from roads and to rebuild damaged rail lines. As
the sludge dries, airborne dust is a potential problem, and much of the area is
being covered either by liquid dust suppressant or with straw, seed, and
fertilizer applied by helicopter.
The other concern, potentially affecting many more people
than just those in the direct line of the spill, is the potential water-quality
hazards posed by the fly ash. Municipal water supplies and water from private
wells are being sampled and have been declared safe, and a weir has been
constructed in the nearby Emory River to help contain the ash. Fly ash contains
some toxic metals, and soil sampling shows that the levels of most of them in
the area of the spill are no higher than typical background levels of these
metals found in the area’s soils. The levels of arsenic are slightly higher than
background levels, but not high enough to be classified as hazardous.
In the aftermath of the spill, Tennessee’s governor, Phil
Bredesen, has called for more state inspections of Tennessee Valley Authority
facilities. TVA, a federal agency, operates several coal plants in the state.
What implications will this incident have for the way similar
large retention ponds are managed and inspected? Have you faced a similar
large-scale disaster in your area, such as sediment released from a broken dam
or flooding from a large storm? What do you think of the way the situation in
Tennessee is being handled?