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Power station waste safely sealed

A needle-punched geosynthetic clay liner seals ash and slag at Romanian power plant.

THIS SUMMER a new sealing system was installed to contain hazardous waste from Romania's Turceni Power Station.

The Valea Ceplea landfill was built as the main repository for slag and fly ash generated by the coal burning power station. Slag and ash are transported hydraulically to the landfill, in a valley about 3km away.

Its chemically active and hazardous leachate meant there was an urgent need for a cellular sealed disposal system for the ash and slag waste.

The new sealing system consists of a geosynthetic clay liner (GCL) covered with 500mm of soil, ash and slag. The soil, ash and slag material have an internal friction angle of about 30degrees. Loading on the sealing system immediately after installation is about 10kPa, with a hydraulic head of 1m. The final confining stress resulting from a full cell is estimated at 80kPa, with a hydraulic head of 20m. Target hydraulic conductivity is 1x 10 m/s.

Hydraulic conductivity for a number ofGCL products was measured under site specific conditions, because there were many unknowns that could influence the performance of the seal, such as the chemical composition of the leachate.

The site operators identified German-made Naue Fasertechnik GCL Bentofix as the most suitable product, mainly because it is a needlepunched GCL. This gives good stability of the bentonite layer between the geotextile outer layers. The product is also robust, which reduces the risk of damage during installation and allows the material to adapt itself to differential settlements while retaining its low hydraulic conductivity. This was measured by an independent German laboratory, while in contact with the site leachate from Ceplea Valley, at about 1x10 m/s, ten times better than required.

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