Remediation of mercury-contaminated sediments

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Summary:

Pauliström (Svartjöarna) - Sweden

TenCate Geosynthetics

Geotextile tubes produced from a special designed fabric were used due to high water permeability and a small opening size providing a fast dewatering with a high solid retention. After the dewatering operation the units served as containment facility for the dewatered sludge.

Svartsjöarna in Sweden is located near Pauliström. Through the lake, a small river runs into the river Emån. This Emån river is 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. Svartsjöarna have for a long time served as sedimentation basin for pulp fibres coming from the Pauliström 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 was estimated that the total fibre discharge from the mill amounts to between 15 and 20.000 tons.

The remediation works in Svartsjöarna involved dredging of approx. 260.000 m3 of mercury contaminated fibre sediments. These sediments were pumped to the landfill nearby, specially prepared for this project where it is treated with polymers (flocculants) and pumped into TenCate Geotube®.
It was the first time that this new technology was used in Sweden.

TenCate Geotube® is a structure, made from special designed filtration fabric from TenCate, with small pores, resulting in effective dewatering of sediments. The dimensions of TenCate Geotube® for the project were approx. 50 meters long with a circumference of 18,3 meters. In order to reduce the landfill surface, TenCate Geotube® were stacked up to three layers high.

Dewatering of the sediments was done in a dewatering basin. After several times of filling and dewatering of TenCate Geotube® the consolidation of the sediments reached its final stage. The wastewater coming from the dewatering process was treated and controlled before it flowed back into the lake. After the final consolidation of the three layers, the landfill was covered with soils and closed in 2007 after final inspection.

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