In 1980 fear for a chemical time bomb still prevailed. It would only be a matter of time before the toxic waste from the heavily polluted Volgermeer was going to spread uncontrollably into the environment. Today the situation looks a lot more promising. Under the name of Adviescombinatie Volgermeer (ACV), consulting engineers Tauw and Witteveen+Bos joined forces and during the remediation activities they developed the ‘natural cap’ concept. ‘Natural cap’ is a sustainable solution with great potential for dump site remediation, both at home and abroad.
History
The Volgermeer is an area of approximately 105 hectares, which in the twentieth century was used as a dump site for large quantities of chemical waste. The waste included 30,000 barrels of pesticide residues, making the Volgermeer the most heavily contaminated area in Western Europe. In the eighties of the last century local authorities took the initiative towards remediation.
ACV accepted the remediation tender in 2001. In addition to the remediation of the polder and adjacent areas, the tender also included the construction of 59 ‘sawas’ (ponds) with the purpose to create wetlands. The structural design of the landscape was drawn up by Vista Landscape and Urban design b.v.
Natural cap
To prevent contact and risks of waste spread, a standard cover was initially opted for in the remediation. This cover consists of a top layer construction of soil from excavation works in the area, containing a layer of HDPE liner.
HDPE liner, however, has a limited life span. To avoid having to replace the liner eventually, ACV developed a surprisingly simple and effective concept: the ‘natural cap’. This concept consists of a gradual, functional replacement of the synthetic top layer construction by a natural layer of living, organic material.
The organic cover provides a natural and durable isolation. Consequently, the HDPE liner does not need to be replaced anymore. Not only considerable costs will be avoided, but also disruption of newly developed nature.
Attractive and durable landscape
The ‘natural cap’ is not only simple but also cheap to implement. Peat grows naturally and has added value for the development of nature. The peat landscape that will arise over the years is very attractive from a landscape point of view and freely accessible for recreation.
The ‘natural cap’ is currently applied in the Volgermeer over an area of about 60 hectares in 59 sawas. The first bench terrace was grafted with peat on 17 November 2008, generating a lot of media coverage. In cooperation with the Centre for Wetland Ecology and the municipality of Amsterdam ACV is conducting further research to continue the development of the ‘natural cap’ concept, and further optimize the design for the Volgermeer.
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