Impoundment Closures


Ames Construction is engaged in a multi-year effort to close the north and south coal combustion residuals (CCR) surface impoundments at a power plant in Iowa. Crews are excavating the CCR to native sand, which will then be backfilled with clean sand material to achieve the designed elevation above possible flood levels. After placing the clean sand over the native material, the CCR will be redistributed and capped with a liner.

Ames is using an innovative conveyor system in place of haul trucks to import borrow material. The 5.5-mile-long conveyor has three overhead crossings—two over roadways and one over a railroad—along with two underground crossings beneath high-traffic roadways. The system eliminates 409,000 truck trips and nearly 4,500,000 round-trip miles, saving 11,000 metric tons of carbon dioxide from entering the atmosphere. That’s equivalent to the greenhouse gas emissions from 2,370 gasoline-powered passenger vehicles driven for one year.

To mitigate high groundwater levels caused by the adjacent Missouri River, Ames developed a comprehensive dewatering plan to serve both the on-site excavation and the off-site borrow source. To allow excavation below the groundwater table, crews used floating pumps, wells and wellpoints to lower the groundwater, and when needed incorporated Portland cement into the excavated CCR material to accelerate drying.

Following the staged installation of the protective liner over the CCR material, the project is on track for completion in January 2024.