The natural cap construction was built up layer by layer. The first layer consisted of soil from ground works in the region, which is then covered with HDPE (high density polyethylene) foil. On top of this HDPE foil a second soil layer was placed and sawa dikes were built. The sawas were not filled artificially, but were left to fill up with rainwater (see Figure).
The bottom and the banks of existing waterways were also covered with HDPE foil and a soil layer. On the 60 ha low-lying area a wetland is created via a system of 59 sawas surrounded by dikes on top of the soil/HDPE cover. In some sawas reed rhizomes and mown reed were added to speed up reed growth. The remaining 45 ha is considered a dry area. As part of the remediation a buffer zone is created around the site in which groundwater quality is intensively monitored.