Remediation of a site contaminated with chlorinated solvents

DEC's remediation prooject of a site contaminated with chlorinated solvents

Challenge

The activities of a metallurgic company that had operated in Brussels, had led to substantial site contamination due to storing and discharging chlorinated solvents.

Two main areas of contamination (mainly by trichloroethene, 1.2-cis-dichloroethene and vinyl chloride) were found in the soil and groundwater. Additional contaminations of PAHs, mineral oil and heavy metals were also found. The soil remediation project involved the excavation of both contaminated areas.

Near the site, the alluvial clay of the river Zenne is present at about 2 m to 4 m-mv. Given the poor geotechnical quality of this ground layer, complex stabilising and drainage works (sheet piling and drainage with deep wells) and a groundwater purification plant were specified in the contract in order to excavate to about 6 mbgl.

Our solution

In order to avoid complex stabilising and drainage works and the construction of a groundwater purification plant, DEC proposed the cased excavation and filling technique. This involves placing a steel cylinder and - by means of orange peel grabs - the soil in the cylinder is excavated. Gradually, the cylinder is excavated and pushed further into the ground until the desired depth is reached. The steel cylinder absorbs all strain from the surrounding subsoil to prevent subsidence.

 

Next, the cylinder is gradually filled with soil (or stabilised sand) and compacted by pressing with the orange peel grabs. As the filling progresses, the cylinder is pulled up again. The quality of the excavated soil can be carefully examined by the soil remediation expert.
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