Water Balance and Efficiency of Landfill Covers Composed of Layers of Dredged Material : Results from Long-term Measurements in Northern Germany(Symposium 3.5.2 Risk Assessment and Risk Based Remediation,<Special Issue>International Symposium: Soil Degrad

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Since 1995/1996, the water balance and long-term performance of a 4-m thick landfill cover system with layers composed of processed dredged material have been measured in situ in large-scale lysimeters (test fields) on the dredged material Francop landfill in Hamburg, Germany. A 1.5-m thick barrier layer of landfill cover was constructed of processed fine-textured dredged material and was covered by a 1.0-m thick lateral drainage layer composed of medium sand separated from the dredged material. The lysimeters were integrated in the landfill cover and were constructed using an identical technique to ensure representative measurement results. For a period of greater than 12 years until the end of data evaluation in November 2007, the cover system performed well. The average discharge below the barrier layer was 16mm/yr and was nearly constant throughout the year with only slight seasonal variations. The main reasons for the good performance were the large thickness of the barrier layer, the large overload on the barrier, the 'slow' lateral drainage layer, and the presence of a root barrier that smoothed inflow into the drainage layer. Due to the material used and the slow biological, mechanical, and hydrological processes, the water balance and discharge measurements for monitoring of the cover system will be continued.