The Dutch have a special relationship with land and water. ‘Netherlands’ literally means ‘Low Countries,’ and for good reason. Of the roughly 41,500 square kilometers of Dutch land, about half is more than one meter above sea level, and a significant portion of the rest is man made, reclaimed from the sea. The Netherlands also boasts a population density of 407 humans per square kilometer, the 4th highest density worldwide. It’s easy to see why the Dutch don’t feel they have much to leave to waste; that’s where IJsseloog comes into play. IJsseloog is a truly innovative environmental containment facility.
The IJsseloog is a toxic sludge repository located in the middle of the Ketelmeer, a 3,500 hectare lake reclaimed from the Zuiderzee, and fed by the IJssel and Rijn rivers. The lake was built in the ’60s and ’70s, when the surrounding land masses, called the Polders, were constructed. The problem IJsseloog was designed to address is the decades long deposit of toxic sediments, generated by hundreds of sites upstream. Tens of millions of cubic meters of highly contaminated sludge covered the bottom of the lake to an average depth of 50 centimeters. In such a densely populated country, the loss of wildlife habitat and the use of the lake for human recreation was deemed unacceptable. IJsseloog is the solution.
The IJsseloog is an artificial island with an isolated holding facility for contaminated sediments in the middle of it. The containment pit is 1 km in diameter and 45 meters deep, with a total capacity of 23 million cubic meters.
The primary challenges addressed by the IJsseloog project were twofold; first, a facility for handling the toxic sediment had to be built close enough to the source, and secondly, the removal process had to be highly selective.
The natural solution to the first challenge was the construction of an artificial island on the waters of the lake itself. Royal Boskalis, a Dutch company with extensive experience in dredging and land reclaimation, took the lead position in the project. Construction of IJsseloog, (meaning ‘eye of IJssel’), took three years and was completed in 1999. Since decontaminating the sludge has been deemed unfeasible, the facility was construction with long term isolation of the toxic material in mind. A 10 meter high embankment surrounds the pit; that embankment and the sides of the pit are foil lined, and the floor is sealed with clay. Water levels within the pit are held well below lake level. When the facility is filled, it will be capped off and the surface reclaimed as a recreational site.
To address the second challenge, Boskalis engineered a proprietary dredging system designed to allow extremely thin yet high capacity dredging passes, with minimal water content and turbidity. The resulting system produced dredging rates upward of 500 cubic meters per hour and dredge concentrations of roughly 60% solids. These are significant performance statistics, in light of the volume of dredging needed to not only remove contaminated sludge, but improve the primary shipping channel through the Ketelmeer as well.
The lake and island have displayed remarkable recovery from its formerly highly contaminated state. The contractors who operate the IJsseloog site report “a rich collection of flora and fauna, such as swans, geese, spoonbills, shelducks and grebes, and some 55 species of trees and plants are growing there.” With the IJsseloog project, the Dutch have proven once again that innovation and long term perspective can achieve excellent results toward mitigating human-caused environmental damage.