Impoundment Closures

Ames Construction performed closure by consolidation for two coal combustion residual (CCR) surface impoundments at a power plant in Iowa.

Crews excavated the highly saturated CCR to native sand, which was then 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 was redistributed and capped with a liner.

Ames used an innovative conveyor system in lieu of haul trucks to import borrow material. The 5.5-mile-long conveyor had three overhead crossings—two over roadways and one over a railroad—and two underground crossings beneath high-traffic roadways. The system eliminated 700,000 truck trips, 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 for 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. Portland cement was incorporated into the excavated CCR material when needed to accelerate drying.