Ghent (Belgium) - Flux measurements for Brownfield redevelopment
Highlights
- Evaluate plume stability through flux measurements
- Adjust remediation design
- Follow up and modify remediation measures proactively
Situation
CVOCs , Chloroethenes and -ethanes
Source: industry - textile factory
Location: Ghent, Belgium
The site is a 10-hectare site. As a result of industrial activities, the soil and groundwater is contaminated with CVOCs. There are 3 source zones marked on the site. These were largely excavated in the period 2017-2018. After excavation, residual contamination remained in the soil and groundwater. Groundwater was extracted at the site in the past. The extracted water was used in the production process and discharged after treatment. The extraction affected the spread of contamination at the time. Other contamination with CVOC is known in the vicinity. The presence of these contaminants should be taken into account during remediation. The soil consists alternately of permeable and less permeable layers. After the core remediation, iFLUX measurements were carried out to ascertain the secondary delivery of residual contamination from the source zones and the strength of the contamination downstream in the plume. The measurements further allow to characterize the preferential flow paths along which the contamination spreads through the groundwater and to more accurately quantify the load moving downstream (or mass discharge).
Sampling
A total of 6 iFLUX samplers were installed, near the core at three depths, between 7 and 17 m b.g.l., further downstream at 2 depths between 15 and 19 m b.g.l. and then near the canal at about 19 m b.g.l..
Groundwater and CVOC flux were measured simultaneously using iFLUX samplers. The measurements were carried out for 28 days.
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Figure 1: Location with designation of industrial heritage (i.e. the buildings to be preserved)
"Thanks to the iFLUX campaign, a better understanding of the contaminant spreading was obtained and the cost of remediation could be significantly reduced" - Jan van Schaeren, Revive
Challenges
Redevelopment of brownfield site
- Are there preferential pathways?
- How does contamination behave in heterogeneous soils and under the influence of groundwater extraction and surface water?
- To what extent is there subsequent delivery from the source zones to the plume?
- Can plume stability be proven?
Solutions
Flux measurements for risk assessment and remediation design
- Flux measurements at different depths to characterize high and low flux zones.
- Simultaneous determination of groundwater and mass flux at different distances from the core allow the strength of the residual contamination to be determined at these distances and provide insight into the source, dilution and degradation of the contamination.
- By monitoring the flux even after remediation, the evolution of the contamination can be mapped more quickly and proactive action can be taken.
- Based on the flux measurements, the downstream contaminant migration at various distances can be determined.
Results
The iFLUX monitoring campaign aimed to further refine the conceptual site model. Flux measurements were used to better visualize the groundwater flow at the site and, in addition, it became clear through which pathways and to what extent the contamination load disperses.
The very low mass fluxes measured at the source level support previous theoretical expectations that no effective diffusion is occurring from the contamination.
"iFLUX measurements are considered complementary to classical groundwater sampling. Since iFLUX measurements are measured over a longer period, the flux and average concentration derived from it is less subject to fluctuations and a better measure of exposure. iFLUX measurements make the dataset more robust." - Aecom
Next
Aecom prepared the soil remediation project and provides iFLUX measurements to monitor the effect of the source remediation. At the level of the plume, monitoring is performed with iFLUX sampler in order to be able to decide faster whether an active remediation has to be started.
The remediation of the contamination is handled by Greensoil.