Interception drainage & helophyte filter in Zwolle (NL)

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The groundwater below the city centre of Zwolle is contaminated with chlorinated solvents. This pollution, especially vinyl chloride, is  flowing into the nearby located drinking water aquifer. This is an undesirable situation.


To stop the migration of contaminated groundwater towards the drinking water wells, HMVT installed, operates, monitors and maintains a hydraulic barrier and purifies the polluted groundwater by a Constructed Wetland. The energy from the extracted groundwater is also used to pre-heat and cool a nearby homeless shelter in both winter and summer times. The treated groundwater is re-infiltrated into the aquifer.

In collaboration with Antea Group, HMVT has realized the following treatment systems:

  • An extraction well, screening 10-89 m bgl. Extraction of ca. 8 m³/hr.
  • Piping via the homeless shelter to the Constructed Wetland.
  • A Constructed Wetland consisting of an aeration & sedimentation basin to remove iron, the plant basin and an infiltration ditch.

The system is monitored 24/7 by a PLC system incl. automated alarms. Operating data like flow, temperatures and oxygen levels are monitored on a continuous basis.


The construction of the Geohydrological Barrier and Wetland started in 2010. Since then the project has run without any major downtime. In 2019 the Constructed Wetland was cleaned: removal of iron sludge as well as removal of surplus of plants.