The former industrial activities on a galvanising plant in The Netherlands resulted in a significant impact of soil and groundwater. Source areas with cVOC and hexavalent chromium were identified, as well as a more heterogeneous contamination with heavy metals. The contaminated area is within an urban area and a significant part of the contamination is located under a monumental building, which limits the possibilities to tackle the contamination.
In the past, remediation works were carried out that consisted of a partial excavation, multi-phase extraction and isolation of the residual contamination in combination with extensive monitoring of the natural degradation. The monitoring results, however, showed that the set objectives were not achieved, and additional remediation measures were required.
GreenSoil was appointed to carry out additional remediation measures to tackle the risks arising from the contamination with heavy metals in the soil and the cVOC contamination in the groundwater.
The remediation was carried out in steps:
The contaminated soil was replaced with clean soil and underground infrastructure were repaired.
in the groundwater by means of approx. 70 direct injections with organic substrate (Dehalo GSTM) and a cultivated bacterial culture.
To deal with the contamination in the solid matrix, the possibility of flushing the contaminated (unsaturated)soil was investigated.
In the saturated zone, the focus was on the chemical reduction of Cr (VI) to Cr (III) via biological processes.
Following the promising feasibility study, the contamination in the unsaturated zone was leached out. The leachate was extracted and disposed of to an offsite treatment facility as this water was severely contaminated. Subsequently, injections of the electron donor Dehalo-GS were carried out with the aim of creating anaerobic conditions to achieve a reduction of the toxic Cr (VI) to the immobile Cr (III) inside the building
The predefined objectives for cVOC and Cr (VI) were achieved within less than a year. Thus, the infrastructure was restored by GreenSoil, and the monumental building can now be put to its next meaningful use.
Figure right shows the monitoring results (expressed in ug/l) before and after biological remediation was stimulated. A decreasing trend of the concentration levels over time can be clearly observed.
During the implementation of phase 4, the strong yellow colour of the dissolved Cr (VI) in the leaching water was striking as it is possible to see.
Concentrations of Cr (VI) as high as 4,000 µg/l were reduced to values of about 7.8 µg/l. By implementing biological processes, the required geochemical environment was created. The results show a successful- reduction of the toxic Cr (VI) contamination to Cr (III) and a reduction of the mobile fraction > 99%
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