Challenge
In the east of the Dutch province of Friesland, a site is contaminated with volatile aromatics (BTEX) and mineral oils. Both the soil and groundwater are contaminated. By now, the contamination has penetrated to a depth of 38 metres. What’s more, there is an NAPL layer present. In view of the activities at the contaminated site and the complex infrastructure above and below ground, it is not possible to excavate everywhere.
Solution
HMVT has set up a three-step plan to remove this mobile contamination from the soil. The first step is a soil remediation whereby the contamination is excavated as much as possible. The remaining contamination is then tackled using in-situ techniques. These techniques consist of a Multi-Phase Extraction (MPE) and groundwater extraction. The water and air that are extracted are purified on site. The third step is aftercare and monitoring.
In this way, the source of the contamination is removed, any further spread is stopped and a manageable situation is created.
Results
Phase 1: Soil remediation
Due to the large amount of contamination in the soil, this soil had to be excavated under special conditions. The soil was transported to a certified processor. In total, some 250 tonnes were excavated. The client’s operations continued throughout the excavations, which complicated our work.
Phase 2: Installation of extraction and purification systems
A total of 2000 metres of piping were laid with 35 TFE filters at a depth of 2 to 3 metres. In addition, 4 deep wells were placed at depths varying from 6 to 40 metres below ground level. The water and air purification installation has a capacity of 20 m3 water and 2000 m3 air per hour. The installation consists of:
- Control container
- Extraction container
- Oil-water separator
- 2 stripping towers placed in series
- Air-side activated carbon filter
- Automatic backwash sand filter
- Water-side activated carbon filter
- Clean-water buffer
- Wastewater buffer
All these components are located at a liquid-proof set-up location in order to prevent the spread of contaminants to the surroundings in the event of an accident.
Phase 3: Execution phase
The project has now been running for 10 weeks and the influent and effluent rates are meeting expectations. The load removal is running according to the prearranged plan.