Imagine the construction of a large building, and the complexity of activities involved: a smart design, budgets, detailed engineering, permits, contractors and sub-contractors, logistics of material transports, deadlines, etc.. Considering the complexity of this job, an unexpected event which stops the construction process is a nightmare. Below is the story how a groundwater contamination disturbed the construction works in Utrecht, NL, and how the problems were solved jointly with Norit Activated Carbon.

Preparations to the construction works
The Van der Hoeven (VDH) clinic in Utrecht (NL) – a closed resort for mentally ill persons – houses over 300 patients. Due to expansion of the activities, the construction of a new building was required, starting February 2007. In the past, Utrecht – like many other cities – used to house industrial activities in the old city center; close to the VDH clinic the groundwater has been polluted by VOC (trichloroethylene, vinyl chloride) inherited from a former metal plating industry. Before starting construction activities, the groundwater flows and contaminations were carefully reviewed and a groundwater management plan was developed based on sophisticated modeling techniques. However, once construction work was started, the reality showed to be different. “Against expectations based on model predictions, we found vinyl chloride in our wells at concentration levels up to 30 µg/l,” reports Sven Brink, technical manager of the VDH clinic.

Contaminated groundwater
Following its discovery, the VOC polluted groundwater forced the VDH clinic to stop the construction activities immediately. “Obviously, with major implications on planning and costs,” Henri Wiertsema, managing director, comments. “We were extremely keen on a sound and quick solution”, A special challenge was to remove the contaminants anaerobically (i.e. under the exclusion of any oxygen/air), and then return the treated water into the aquifer. The anaerobic VOC polluted groundwater contained high concentrations of dissolved iron, which would precipitate in the presence of oxygen, and generate clogging problems.

The flexible solution
Following a review of various options, treatment by Norit granular activated carbon (GAC) in mobile filter units was selected. A total flow appr. 500 m3/h was successfully treated by the GAC filters for a period of 6 months until the project was finished. At intervals of two months the exhausted GAC was regenerated at the closest Norit Activated Carbon reactivation plantin Zaandam, NL. During thermal reactivation, the contaminants are destroyed at high temperature, the GAC regaining its original adsorption properties. Norit Activated Carbon’s facility in Zaandam is a state-of-the-art reactivation plant, qualified under ISO 9001 (Quality Assurance) and 14000 (Environmental Care).

Indeed, a sustainable solution as a result of professionals – represented by the VDH clinic, the engineering consultants and Norit Activated Carbon – teaming up!

For more information:
dikkenberg.janvanden.nl@norit.com
www.norit-ac.com