The Cover-method

A new remediation method to cap contaminated sediment

In Sweden, as well as in the rest of the world, there are many locations where sediment has been contaminated by heavy metals or organic pollutants. These pollutants are being passed through the ecosystem and causing environmental problems.

These pollutants are transported from the sediment to biota in two major ways. The first is via resuspension of particulate matter and the second through bioturbation. Traditionally, dredging the polluted sediment and disposing of it in landfill sites has provided a solution to these problems.

The Cover-method was invented and developed by Vattenresurs. This method is based on the production of a layer of artificial sediment that caps the contaminated surface, preventing the effects of resuspension and bioturbation. The artificial sediment is created from chemical precipitation and is produced, together with structuring and ballasting materials, in the mixing process in the nozzles of the spray unit approximately 2m above the polluted sediment.
 A new bottom, several centimetres thick, is built layer-by-layer creating a physical barrier between contaminated sediment and the water above. The fauna which live on the bottom will find a new life in this artificial sediment. As time goes by new sediment will cover the bottom and secure future water quality.

The Cover-method is much cheaper than alternatives like dredging.

The method was developed and laboratory tests were begun in 1993. Further testing of erosion durability was performed in large scale laboratory tests. Later, a field test was carried out in Lake Turingen, ordered by the Lake Turingen Remediation Project. In 1998, the field test showed that the method could be used in full scale. Year 2000-2003 the remediation of Lake Turingen (100 ha) is successfully completed at a cost of 26 mill.SEK.

About chemistry and impact - please read Phosphorus Precipitation of Lakes

The vessel is navigated with a high level of precision             home


The vessel spreads the capping material from about 2 m above the bottom. The material is deposited layer by layer, creating a sediment ‘carpet’, and forms a 4-6 cm cap.






Below - Capped sediment