Formatted Title
Biological Soil and Groundwater Remediation as Part of an Integrated Approach for Sustainable Redevelopment of Industrial Sites: Two Innovative Case Studies
Background/Objectives
How can soil and groundwater remediation be combined with sustainable redevelopment of industrial sites? For two projects in Belgium, biological remediation for soil and groundwater was implemented together with a sustainable and circular strategy for redevelopment of the sites.
One is a former triacetate production site that caused a heavy xylene contamination up to 27.850 mg/kg in soil and 89.000 µg/L in groundwater to a depth of 10 m-bgl resulting in a total mass of 90T of xylene. GreenSoil offered a lump sum contract that included a 100% on site and in situ biological remedial approach as a more sustainable and economical alternative to conventional (off-site) techniques.
The other is a former telecommunication site with soil and groundwater contaminated with cVOCs. At the site, two source zones contaminated with TCA (up to 200,000 µg/L) and PCE (100,000 µg/L) were present up to a depth of 21 m-bgl. A groundwater plume of over 400 m was formed. The implementation in the field was challenging due to the presence of multiple stakeholders on the site and plans for the construction of a windmill on top of one of the source areas.
Approach/Activities
Remediation of the site contaminated with xylenes consisted of excavation and 100% on-site landfarming for soil and biosparging for groundwater. The excavated soils were placed in biopiles, where dosing of nutrients and bioventing stimulated biodegradation of the contaminants. Contaminated air from the piles was treated with an innovative bioscrubber technique and active coal. To save costs and materials, after completion of the soil treatment, biopiles were redesigned to treat the soil vapors (500-2000 ppm of xylene) originating from new biopiles, as they still contained nutrients and active bacteria. After soil treatment, the site was levelled and an enhanced in situ biosparging system was installed below ground level to treat residual soil and groundwater contamination.
For the site contaminated with cVOCs, a remediation approach was proposed that integrated bioremediation with the redevelopment of the site with the construction of a windmill. Following the excavation of the two source zones, the wells for the groundwater recirculation system were installed as part of the foundation of the windmill. To treat the groundwater plume, various biobarriers were installed to remediate the plume and avoid off-site migration of groundwater contamination. The contaminated groundwater was, without treatment, circulated over these barriers with a high flowrate, the electron donor Dehalo-GS was added as well as bacteria. In this way, over a short timeframe conditions were optimized in the plume for anaerobic biodegradation. On a contractual/financial basis, GreenSoil took over the liability of the client on this project.
Results/Lessons Learned
At the xylene-contaminated site, all 20.500 m3 of heavily impacted soil were cleaned in biopiles to far below remedial target values (~400 mg/kg) in 1.5 year. Both innovative soil vapor cleaning techniques reached removal efficiencies between 60 and 90% and the impacted groundwater (up to 89,000 µg/L of xylene) was treated by in situ biosparging resulting in a 70-99% decrease of concentration levels within one year. 99% of the contamination was degraded biologically either in soil, groundwater or air. Due to the circular approach, 0 m3 of soil left the site and cleaned soil was reused as air treatment which also reduced active carbon consumption by 98%. Due to the successful remediation, the site will be ready for future redevelopment.
At the cVOC-contaminated site, the windmill was successfully built on top of the remediation system. The decrease in concentration levels for PCE and TCA was followed by the increasing concentrations of the degradation products. The active groundwater circulation system was operated for about 2 years, creating the right conditions for the anaerobic biological degradation in the entire remediation area and leading to the achievement of the objective limits. The project is in the final stage of the monitoring phase of the remediation.
The combination of innovative biological techniques, innovation driven by contractual agreements and smart collaboration with stakeholders led to an effective redevelopment of both industrial sites.