Remediation of groundwater contamination on factory grounds in Hedensted for the Central Denmark Region

One of Denmark’s most extensive instances of trichloroethylene contamination is being monitored and remediated by means of a permeable reactive barrier (PRB) around highly contaminated sites, as well as by a system for pumping up groundwater and then air-stripping it.

Description

The groundwater was contaminated with chlorinated solvents on the factory grounds and in a contamination plume 2 or 3 kilometres long beneath the town of Hedensted. The purpose of the remediation is to remove the groundwater contamination and to safeguard the indoor climate of dwellings in a large residential area located downstream from the factory grounds. 

A PRB is an in-situ technological solution for cleaning contaminated groundwater, where a PRB made up of a permeable treatment zone, which contains a reactive material, is set up at a right angle to the flow of groundwater. 

When the contaminated groundwater flows through the PRB zone, the contamination is either immobilised through sorption to the reactive material or transformed into less toxic or easily biodegradable substances. In so doing, the barrier obstructs the contamination but not the flow of groundwater.

To supplement the PRB, a remediation system in the contamination plume has been set up, comprising horizontal filters in the secondary groundwater aquifer, from where the groundwater is pumped up and treated.

Sweco monitors the groundwater contamination on an ongoing basis in the form of documented water sampling in roughly 30 monitoring wells, and level metering of the groundwater table in roughly 40 monitoring wells, as well the operation of data loggers in roughly 10 monitoring wells. Also pore air samples are taken underneath selected dwellings.

Sweco assesses the analysis results on an ongoing basis and reassesses the monitoring programme to follow up on the effectiveness of the PRB and the air-stripping system. Data in the Region’s database is verified and updated.

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