The goal was to remove the sludge accumulated on the bottom and thus increase the water volume of the lagoon. This was found a necessary measure to keep water in the lagoon for a longer time so the toxicity of water discharged into the sea would decrease as much as possible. This way, the maximum emissions allowed for in the environmental permit would not be surpassed even temporarily.
First, the consistency of matter accumulating on the bottom and that of the surrounding grounds were examined. The consistency of the bottom area, 22,000 square meters in all, was found to vary greatly. Next, a suitable polymer was chosen to be mixed in with the sludge directed into the Geotubes®.
In the beginning of 2015, Neste Oyj signed a project management contract with Sito Rakennuttajat. Besides the implementation of the project, also monitoring subcontractors and writing the final report were included in the contract. Vesirakennus Ojanen Oy was chosen as the subcontractor, thanks to its vast experience in the Geotube® method.
On-site work began in April 2015. The Geotubes® were installed in three layers on top of a tight-seam geomembrane welded onto the exhaust piping. The workings of the polymer treatment was monitored closely every few hours from samples of the dredged sludge. All in all 87,000 cubic meters of sludge-water mixture was dredged. The project proceeded fast and was completed already in June. Costs remained low also because less polymer was needed than expected.
The sludge directed into the Geotubes® will be drying until 2016, after which the Geotube® field will be dismantled. Thus the sludge treatment area will be available for other use at the Naantali refinery for the overhaul break of 2017.
SITO was the project supervisor responsible for both planning and implementation of the work at the site.