Remediation of the mercury-contaminated sediments in Svartsjoarna with Geotube

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Courtesy of TenCate Geosynthetics Netherlands bv

The Challenge

Svartsjoarna in Sweden are located near Paulistrom. Through the lake, a small river runs into the river Eman. This Eman river is considered to be one of the most valuable water courses in Sweden. The river has a very high diversity of fish species and animal like otter. Some parts of the river have very well developed meander systems. For these reasons, a remediation had to be carried out very carefully.

Industrial sites have been located along the river since the 1700's, affecting the water quality. Svartsjoarna have for a long time served as sedimentation basin for pulp fibres coming from the Paulistrom paper mill, 3 km upstream of the lake. In the mid-60's, a mercury based product was used for protecting the pulp from bacteria. The contaminated sediments consist of cellulose fibres polluted with mercury. It is estimated that the total fibre discharge from the mill amounts to between 15 and 20.000 tons.

The Solution

A joint venture of DEME Environmental Contractors (DEC) and Dredging International was rewarded this design and construct contract DEC-DI is a Belgian consortium with long standing international experience from similar environmental projects. The remediation works in Svartsjoarna involves dredging of approx 260.000 m1 of mercury contaminated fibre sediments. These sediments are pumped to the landfill nearby, specially prepared for this project where it is treated with polymers (flocculants) and pumped into Geotube

It is the first time that this new technology is used in Sweden and the largest project in Europe with Geotube till now (sept 2006). Geotube is a structure, made from filterweave from TenCate, with small pores, resulting in effective dewatering of sediments. The dimensions of Geotube for the project are approx 50 meters long with a circumference of 18,3 meters. In order to reduce the landfill surface, Geotube will be stacked up to three layers high. Dewatering of the sediments takes place in the basin. After several times of filling and dewatering of Geotube the consolidation of the sediments reaches its final stage. The wastewater coming from the dewatering process is treated and controlled before it flows back into the lake. After the final consolidation of the three layers, the landfill will be covered with soils and closed in 2007 after final inspection.

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