Remediating lasting contamination using in-situ thermal and dual phase extraction technology, Sweden
The Challenge
This former industrial site in Nyköping, Sweden, was earmarked for development into a new transport centre.
However, the presence of extensive recalcitrant contamination, plus its position next to active railway lines, meant traditional remediation methods would not be possible.
The site had a long history of hydrocarbon storage, with widespread contamination including:
- Free-phase hydrocarbons (NAPL) running at 7mbgl
- Extensive metals in soils
- Aliphatic and aromatic hydrocarbons, PAHs and BTEX hydrocarbons in both soil and groundwater
The thickness of free-phase product varied across the site with a maximum of 1.7m in places, and the site’s geology was highly variable.
Our Solution
Analysis revealed in-situ thermal remediation to be the best treatment option, with McMillan-McGee Corp (Mc2) partnering with Geostream Group to deliver a programme of thermal remediation and dual-phase extraction.
Mc2 brought its patented Electro-Thermal Dynamic Stripping Process (ET-DSPTM) to the project, which is designed to be more effective than other forms of electro-thermal heating.
ET-DSPTM’s heat transfer mechanism volatilises contaminants, driving them to extraction wells via. a guided steam front. Application of convective heating, accomplished by injecting water at controlled rates into the ends of the electrodes where the electrical field has the highest density, makes ET-DSPTM more effective than rival technologies.
Application in the field
With the depth to bedrock varying across the site, the team carried out a pre-design investigation which tagged the depth at each electrode and extraction well location.
Mc2 used this data to design an electrode configuration unique to each borehole, providing effective heating at the soil interval and the top of the underlying bedrock below
On average, each electrode had an energy input of 6kW and – with multiple electrodes in each well across the site – total site energy was 978kW. To cool the electrodes, and allow a supply of water for steam production, a liquid injection rate of 22l/min was used on the site.
The system ran for 281 days and achieved 92% uptime (including planned maintenance).
Dual-phase extraction at high temperatures
Geostream created a dual-phase extraction system to remove contaminants from the gas flow at very high temperatures.
Once the gasses entering the treatment plant had been condensed to below 8oC, the liquid and remaining gasses were separated. Liquid phases were then further separated, with hydrocarbons removed before the water was sent to an air stripper. There, hydrocarbons were removed from water that had been passed to activated carbon filters, then on to a consented discharge.
Off-gasses from dual phase extraction and air stripping were passed to an electric catalytic oxidizer and activated carbon filters.
The Results
- 75% lower carbon footprint than the other viable remediation option, excavation, with zero onsite carbon emissions
- Cut programme time by approx. 35% (reducing associated energy use and cost) through bespoke application of one-of-kind ET-DSPTM technology
- Recovered a contaminant mass of 34,889kg – 20,000kg more than the mass estimate
- Enabled creation of a new travel centre for the local community
- A truly international collaboration, bringing in specialists from Canada, Italy, Sweden and Belgium
