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Frequently Asked Questions - Coal Ash

Wisconsin Public Service actively recycles its coal ash. At one time, most of this ash would have been landfilled. Now it is almost 100 percent recycled.

If your question is not answered here, or if you'd like further information, please contact us.

What is Ash?
Ash is a by-product of coal combustion. Two types of ash are produced by burning coal at Wisconsin Public Service's power plants: fly ash and bottom ash. Both ashes are also known as Coal Combustion Products (CCPs).

  • Fly ash - a very fine powder material that is carried with the stack gases and is collected by electrostatic precipitators or a baghouse prior to exiting the stack. It exhibits cementitious and/or pozzolanic properties, which makes it useful in concrete and geotechnical construction applications. When used in this way it actually makes the concrete stronger than if fly ash were not added to the mix. And since it reduces the amount of Portland cement that must be used, it saves energy that would have been expended making Portland cement and reduces associated greenhouse gas emissions.
  • Bottom ash - much coarser than fly ash. It is an almost sand-like material that is sluiced from the bottom of the boilers.

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How Much Ash Does Wisconsin Public Service Produce?
Wisconsin Public Service purchases coal from the Powder River Basin (PRB) in Wyoming. PRB coal inherently has about 5% ash.

  • The Pulliam Power Plant burns 1.5 million tons of coal annually, which produce 60,000-70,000 tons of fly ash and 10,000 tons of bottom ash annually.
  • The Weston Power Plant burns 2.1 million tons of coal annually, which produce 80,000-90,000 tons of fly ash and 30,000 tons of bottom ash annually.

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Are There Beneficial Reuses for Ash?
The biggest reuse is a replacement for Portland cement in concrete applications.

The next biggest use for WPSC's ash is in structural fill projects such as highway embankments. Bottom ash and fly ash that cannot be used for cement replacement are used in these types of projects.

Structural fill projects use ash in place of general fill, which reduces the amount of material that must be excavated elsewhere and trucked to the project. Structural fill projects incorporate special features to ensure environmental protection. Depending on the material and type of project, these features range from sloping and covering with clay and asphalt to fully lined projects with leachate collection systems.

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What Regulations Address Beneficial Reuses?
In Wisconsin, coal combustion by-products are regulated as a solid waste by the Wisconsin Department of Natural Resources (WDNR) under the NR 538 rule. In the past, each beneficial reuse project required its own special approval by the WDNR, but the adoption of NR 538 in 1997 streamlined the process. Under this rule, ash producers periodically sample and analyze their ash, known as ash characterization, so that the appropriate category of reuses and disposal methods are determined.

The Brown County Highway S embankment project, which was completed in 1999, was the first highway project that Wisconsin Public Service participated in that was regulated under NR 538 rather than the specific approval process. Overall, the NR 538 provisions are better for everyone. Because specific project approvals were eliminated, NR 538 saves time for both regulators and by-product generators. The public also benefits under NR 538 because of the public notice requirements that were lacking under the specific approval process.

NR 538 has also simplified the reporting requirements for ash used as cement replacement. In the past, annual reports by the ash producers that included a comprehensive chemical analysis of the ash were required. However, this use has proven to be so safe and effective over the years that the annual chemical analysis requirement has been eliminated under NR 538. WPSC now beneficially reuses nearly all of its annual production of 150,000 tons ash under NR 538.

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What Beneficial Reuses Has Wisconsin Public Service Pursued?
Both the Pulliam and Weston power plants produce and sell a high quality fly ash that is used to replace up to 30% or more of Portland cement in ready-mix applications. Additional beneficial reuse applications we have used or are considering are:

  • Structural Fill (highway embankments)
  • Subbase Fill (under paved highways)
  • Roller Compacted concrete
  • Permeable Base for paving projects
  • Stabilizer for in-place asphalt recycling
  • Soil cement compacted for an interior floor surface
  • Bottom ash may be used as daily cover in public and private landfills

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How Does Wisconsin Public Service Develop Beneficial Reuses?
To accomplish these beneficial reuses, Wisconsin Public Service has developed relationships with organizations that can use the material. Our premium ash sales to the construction industry are coordinated through Lafarge North America, the #1 worldwide leader in cementitious materials.

We've partnered with Wisconsin Department of Transportation District 3 since 1986 to place ash in highway embankments. The first Project was Highway 41 and County F in 1986; 55,000 tons were placed. Since then, projects have included local projects on Highways 441, 45, and 76. By the end of 2002, over 1.1 million tons of ash were placed in such projects.

More recently, we've placed ash in the central Wisconsin area with WDOT District 4's Hwy 29 and are planning to work together on future projects as well where ash is a good structural fit.

Also in central Wisconsin we have partnered with the Central Wisconsin Airport (CWA) to extend their east-west safetyway, placing over 310,000 tons since 1991. The project has sufficient capacity for many more years of beneficial ash placement.

Not only do we beneficially reuse our own ash production, we help several local paper mills to reuse their ash. At both the Pulliam and Weston power plants, coal ash from less efficient fluidized bed boilers operated by Wausau Paper is reburned in WPSC's boilers, thereby reducing the mills' volume of solid waste for disposal or beneficial reuses.

Of course, we're also pleased to support the University of Wisconsin - Milwaukee Center for By-Products Utilization (CBU) on several research and development projects as well as on an ongoing basis. Several projects were:

  • placing roller compacted concrete using fly ash as a paved surface around a portion of the Pulliam Plant, and
  • paving at the Green Bay Holmgren Way warehouse, but instead of a surface application, it was permeable base course construction with an asphalt top surface. It incorporated fly ash produced at Pulliam.

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Why Does Wisconsin Public Service Continue to Look for New Uses?
Although we have used Wisconsin Public Service ash in traditional beneficial reuses, we continue to look for new uses because:

  • Coal-fired power plants will always produce ash.
  • Beneficial reuse contributes to good environmental stewardship, because ash that is not beneficially reused would be a waste product destined for a landfill.
  • Beneficial reuse encourages new markets to develop, such as emerging markets for roller compacted concrete and permeable base course construction.
  • Beneficial reuse is cost effective in comparison to landfill tipping fees.

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Who do I contact for more information on coal ash?
For more information on coal ash, please contact:

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