Waste Management

An important aspect of environmental stewardship is properly transporting and disposing of the by-products from our generation facilities. The primary by-product we manage is coal combustion residuals (CCR). The American Coal Ash Association estimates that the electric utility industry generated 110 million tons of CCR in 2017. CCR consists of the ash left over from burning coal along with any additive that may have been inserted into the flue gas for emissions control.

In 2019 we invested approximately $3.4 million to retrofit Coyote Station’s bottom ash handling system and permanently remove CCR from three areas. These upgrades will help to ensure Coyote Station is well-positioned to properly manage CCR in the future and to comply with Environmental Protection Agency regulations. Completion of the Coyote Station project was the last step in the transition to dry CCR handling systems at all of our facilities.

We look for opportunities to responsibly reuse our CCR in useful and appropriate applications. Beneficial reuse saves landfill space and conserves natural resources by substituting CCR for a material that would have to be mined and processed. The demand for CCR in beneficial use applications is largely market-driven, but we do what we can to identify opportunities. During the last five years we’ve beneficially used an average of 28% of our boiler slag, which is a type of CCR. In 2019 we beneficially used 34% of our boiler slag.

2019 Waste Disposal





Fly ash

On-site landfills


Bottom ash

On-site landfills


Other materials (pond dredging waste)

On-site landfills



Flue Gas Desulfurization (FGD) product

On-site landfills


Boiler slag

On-site landfills


Other materials

(pond waste)

On-site landfills


Volume beneficially used

Donated or sold


Other non-coal wastes




FGD product

On-site landfills


Boiler slag

On-site landfills


Other materials (boiler insulation)

On-site landfills


Volume beneficially used

Donated or sold


Ash from pond closures

On-site landfills


Management of PCB Materials

Electricity distribution systems require oil-containing transformers. Although we’ve taken steps to remove polychlorinated biphenyl (PCB) oil from our larger substation transformers and regulators, a small percentage of electrical equipment within our distribution system does contain PCBs. When old equipment is retired, we test for PCBs and dispose of them properly. In 2019 we disposed of 9,340 pounds of PCB material. Should a leak or release occur from a unit potentially containing PCBs, it’s our policy to test the released material for the presence of PCBs and promptly clean up and dispose of any contamination according to state and federal standards.

Spills, Fines, and Sanctions

Despite our commitment to sound environmental stewardship, rare mistakes and uncontrollable events occur. When they do, we correct them as quickly as possible. Our Environmental Services Department ensures compliance with our environmental permits and regulations. In the event of noncompliance, we work with regulators to mitigate the instance and adjust processes. We train our employees to be aware of our environmental permit requirements and the steps they need to take to stay in compliance.


Equipment failures and weather events cause minor oil spills. The most significant one involved approximately 114 gallons of non-polychlorinated biphenyl (non-PCB) transformer oil that spilled after a snow removal contractor hit a transformer serving a business in Bemidji, MN in February 2019. The spill impacted the snow pile and area around the transformer. We promptly reported the spill to the appropriate authorities and hired a contractor to restore the area to its original condition.

Fines and sanctions

In 2019 we were fined for one environmental permit violation that occurred in 2018. Big Stone Plant operates under the conditions of a Title V Air Permit, which regulates the rates at which the plant can emit certain pollutants into the air. In August 2018 the plant emitted a higher level of particulate matter than was allowed in our permit, resulting in a Notice of Violation being issued by the South Dakota Department of Environment and Natural Resources. To mitigate the violation, we paid a monetary penalty of approximately $5,000, replaced fabric filter bags used to control particulate matter emissions, and updated our Operation, Maintenance, and Monitoring Plan.