John Harrison of Bilfinger Berger Environment describes the remediation via thermal desorption of a former tar works in the West Midlands.
Bilfinger Berger Environment Ltd (BBE) has recently completed the remediation of a former tar works site in the West Midlands, allowing the site to be redeveloped for community housing. The site had historically been used for the manufacture of tar products and the resulting contamination had made the site commercially un-developable.
BBE were appointed as specialist remediation contractors to undertake the remediation of the soil that was heavily impacted with tarry wastes. Thermal desorption had been identified as the only remediation technique that would be able to treat the levels of contamination to the required end use criteria.
Landfill had been considered but was not financially viable within the budget for the development and the post remediation land value. The soil on site also did not meet the Waste Acceptance Criteria for landfill.
BBE completed the project ahead of schedule and within budget. The treatment was viewed positively by the regulators and the project was completed with no impact on the local residents.
Thermal treatment
Thermal desorption uses heat energy to dislodge the organic contamination from the soil structure into gaseous phase which is then oxidised to destroy the organic species. The removal of the contamination of the soil is relatively easy but the treatment of the off-gas can be more problematic. BBE has one of the few plants that can successfully treat heavily contaminated soils whilst still meeting UK and EU emissions levels for discharges to air.
Clean soils are produced at a rate of up to 20 tonnes per hour, 24 hours a day and can be placed back into the excavation area thus removing the requirement for off-site disposal and importation of clean fill.
This method of remediation also comes with many benefits to the developer such as the reduction in heavy plant movements on site, the elimination of additional traffic on local roads and the certainty of attaining the required clean-up criteria.
Confidence
The work conducted by BBE has demonstrated the growing confidence in this technology and the financial benefits. The site which was quoted as being "on the fringe of what is deemed possible to remediate" has now been successfully re-developed allowing construction of 150 properties to commence.
The remedial works were completed in six months on site and a total of 34,000 tonnes of contaminated soil with TPH concentrations in excess of 45,000 mg/kg were treated to below the Site Specific Target Level (SSTL). After treatment TPH concentrations were typically reduced by up to 98%, much lower than SSTL of 5,000 mg/kg.
Benefits
Some of the major benefits demonstrated on this project were:
- The vastly reduced remediation time compared to traditional biological methods. Thermal Desorption is capable of remediating 40,000 t of contaminated soils in six months compared to bioremediation techniques which could take over two years to complete.
- The certainty to which the remedial target could be met as compared to bioremediation techniques.
- The sub division of the site into ‘clean' and ‘dirty' areas so the work of the developer is not disrupted by the remediation work.
- The reduced possibility of cross-contamination on site. No contaminated material was allowed to come in to contact with a clean area such as would be the case with conventional dig and dump.
- Environmental benefits of using Recycled Fuel Oil (RFO), which is rated as having zero carbon footprint.
- Recycling of all water and use of heat exchangers help reduce the carbon footprint of the process.
- Cost effective remediation solution when compared to landfilling options.
This project has confirmed that thermal desorption is a real alternative to landfill or lengthy bioremediation whist not incurring excessive costs. The technique opens up the possibility of remediating land that was previously not considered as being commercially viable.
John Harrison, Contracts Manager. Bilfinger Berger Environmental Ltd
