NRG POWERTON ASH BYPASS BASIN RETROFIT

The Ash Bypass Basin at the Powerton Generating Station is a legacy coal combustion residual (CCR) surface impoundment previously used as a settling pond for bottom ash, transport water, and other plant process wastewater. The Bypass Basin had been inactive since October 2020, when cleanout operations began. Because it was built under older design standards that no longer met current environmental requirements, the basin required retrofit and upgrades to comply with Illinois EPA CCR regulations.

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In response, NRG Energy and the State of Illinois partnered to deliver the first project completed under the Illinois Pollution Control Board’s new Coal Combustion Residuals (CCR) rules. The existing bypass basin was fully cleaned of CCR materials, and the geomembrane liner and supporting structures were decontaminated and tested. A new composite liner and leachate collection system were then installed on top of the newly installed basin liner system to meet regulatory and environmental standards.

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Bluff City Construction, LLC served as the General Contractor, performing all associated earthwork and liner installation operations while maintaining strict environmental controls and protection of the existing liner system.

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The scope of work included:

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• Adding a 1-ft compacted clay and sand structural fill layer over the existing geomembrane liner system at precise grades

• Utilizing GPS controlled equipment to meet strict ground pressure requirements for work within and on top of the existing basin liner system

• Installing the sand layer to create a new leachate collection system trench that ran the length of the basin

• Installing a new 12-inch HDPE pipe side slope leachate collection riser system

• Excavating a new perimeter anchor trench system

• Installing a new geomembrane liner system over the entire basin

• Installing a sand protective layer and aggregate placement over the new liner system

• Decommissioning existing basin outlet structures and piping systems

• Installation of new inlet structures to the basin

• Installing a 36-inch pipe with associated manholes and headwalls for plant process water