When coal is used to produce electricity, several byproducts are created. Two types of coal combustion residuals (CCR), commonly referred to as ash, are fly ash and bottom ash. Both are considered non-hazardous materials by the U.S. Environmental Protection Agency (EPA).


Fly ash

The main byproduct of coal combustion is fly ash, a powdery material that is transported from the boiler by the flue gas where it is captured within Teflon®-coated fiberglass bag filters contained in Unit 1's baghouse. The fly ash is transferred to a silo adjacent to the baghouse, then transferred by large trucks to a permanent storage facility or trucked off site for beneficial use.

Bottom ash

Coarser material that settles to the bottom of the boiler during the combustion process is known as bottom ash. This material is regularly removed from the boiler through an inclined conveyor system, then is transferred to an enclosed trucking station outside the boiler facility. The bottom ash is then trucked to the permanent storage facility.

Ash storage

Most of the fly ash and bottom ash produced at Rawhide is placed in a state-approved monofill located on site. This storage facility is underlain by naturally occurring, highly impermeable clay and shale strata.

When placed in the monofill, the fly ash and bottom ash are compacted and contoured to match the surrounding topography. It is then covered by two feet of soil and seeded with native plants to mirror the existing landscape. Several monitoring wells are used around the monofill to continually monitor water quality, and Platte River provides regular reports to regulators based on samples taken from these wells.


Regulation of disposal

Platte River environmental staff inspect the monofill weekly to confirm that approved operating procedures are being followed. The Colorado Department of Public Health and Environment and the Larimer County Department of Health and Environment also conduct periodic inspections. The EPA regulates the disposal of coal ash under the Coal Combustion Residuals Rule, published in April 2015. Information that Platte River is required to provide under the new rule can be found at CCR Rule Compliance Data and Information.

Beneficial uses for fly ash

Rawhide Unit 1 is one of the most reliable, efficient and low-cost baseload energy resources of its kind in the nation; and the EPA has determined that fly ash is a non-hazardous byproduct of coal combustion. To save natural resources and reduce disposal and storage costs, Platte River seeks to find beneficial uses for fly ash whenever possible including for use in construction and industrial processes.

Since 2006, Platte River has successfully supplied a portion of fly ash to manufacturers of architectural block and operators of liquid waste disposal facilities. Block makers can reduce their costs by substituting Rawhide’s fly ash for a portion of the cement used in the process. By using less cement, block makers also reduce the amount of CO2 released into the atmosphere during their production process (approximately one metric ton of CO2 is emitted with every ton of cement produced). Waste management and oil field services companies also use Rawhide’s fly ash to solidify liquid waste, allowing material to be disposed with minimal hazard to land and ground water by encapsulating the waste.

Platte River Monofill

Contact ash@prpa.org for more information about the availability of Rawhide fly ash for beneficial uses.

Platte River Ash Block