There are two types
of ash produced at the Rawhide Energy Station--fly ash and bottom ash.
Fly ash is a non-hazardous powdery
material and the main byproduct of coal combustion. It is transported
from the boiler by the flue gas and trapped within Teflon®-coated
fiberglass bag filters contained in Rawhide's baghouses. Bottom
ash is coarser material that settles to the bottom of the boiler.
Most of the
fly ash and bottom ash produced at Rawhide is disposed of in a State
of Colorado-approved monofill located on the 4,400 acre plant
site. The monofill is underlain by naturally occurring highly impermeable
clay and shale strata.
The monofill is
inspected regularly by the Colorado Department of Public Health and
Environment and the Larimer County
Department of
Health and
Environment. Inspection results have been consistently excellent.
Fly ash is taken from a special silo located adjacent to Rawhide’s
baghouses and transferred to the monofill in large trucks.
Bottom
ash is removed from the boiler and sluiced through pipes to one of
two
temporary storage transfer ponds. The transfer ponds were constructed
by excavating below existing grade and lined with 18 inches of impervious
clay to prevent seepage. When one pond is two-thirds to three-quarters
full, the water in the pond is allowed to evaporate while the other
pond receives bottom ash. When the bottom ash in the first pond is
dry, it
is dredged and trucked to the monofill.
At the monofill, fly ash and bottom ash are compacted, contoured to match
the surrounding topography, covered with two feet of soil and seeded
with native plants.
There has never
been a release of ash from Rawhide's
monofill or bottom ash transfer ponds. Also, a number of monitoring
wells are
used
at the monofill and the bottom ash transfer ponds. There has been no
evidence that anything contained in the ash has leached into ground
or surface water.
With goals of avoiding disposal costs and saving natural resources,
Platte River works to find beneficial uses
for Rawhide fly ash.
