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Environmental and Geotechnical Construction Services


Wet Ash Impoundment Closure - Midwest

  • Closure of a 140-acre wet fly ash impoundment
  • Excavation of approximately 1.2M CY
  • Placement of approximately 1M CY of fill
  • Excavation and placement of approx. 700K CY of CCR
  • Phased dewatering program

    ENTACT is currently implementing closure of a 140-acre wet fly ash impoundment project for a Midwest Utility. The current elevation of fly ash in the impoundment varies from approximately 624 to 695 FT MSL containing approximately 8,200 acre-ft. (13.4 million CY) of coal combustion residual (CCR). The overall scope of work for the project includes a sequentially phased closure of the impoundment, which includes the lowering of the main dam and removal of the saddle dam and construction of a new spillway for the main dam and saddle dam. Closure construction includes the draining of surface water via pumping and/or temporary drainage channels in the deposited ash to direct water to an area immediately behind the main dam. Concurrent with management of surface water, exposed fly ash will be regraded. The regrading process, with addition of borrow material as needed, will establish the subgrade that sets the final elevations needed to direct storm water flow across the closed impoundment. A cap system will be installed (e.g. geomembrane, geosynthetic materials, and protective cover soil layer) and seeded to establish a vegetative cover following completion of the subgrade in each phase. Work is progressing from the highest to lowest elevations across the impoundment in phases to manage storm water during construction. The dam will be partially lowered and a new spillway constructed to allow storm water from the balance of the closed site to flow through a newly constructed spillway to the Creek.