The transport behaviour of elemental mercury DNAPL in saturated porous media: Analysis of field observations and two-phase flow modelling

“Mercury is a contaminant of global concern. The use of elemental mercury in various (former)
industrial processes, such as chlorine production at chlor-alkali plants, is known to have resulted in
soil and groundwater contaminations worldwide. However, the subsurface transport behaviour of
elemental mercury as an immiscible dense non-aqueous phase liquid (DNAPL) in porous media
has received minimal attention to date. Even though, such insight would aid in the remediation
effort of mercury contaminated sites. Therefore, in this study a detailed field characterization of
elemental mercury DNAPL distribution with depth was performed together with two-phase flow
modelling, using STOMP. This is to evaluate the dynamics of mercury DNAPL migration and the
controls on its distribution in saturated porous media. Using a CPT-probe mounted with a digital
camera, in-situ mercury DNAPL depth distribution was obtained at a former chlor-alkali-plant,
down to 9 m below ground surface. Images revealing the presence of silvery mercury DNAPL
droplets were used to quantify its distribution, characteristics and saturation, using an image
analysis method. These field-observations with depth were compared with results from a
one-dimensional two-phase flow model simulation for the same transect. Considering the
limitations of this approach, simulations reasonably reflected the variability and range of the
mercury DNAPL distribution. To further explore the impact of mercury’s physical properties
in comparison with more common DNAPLs, the migration of mercury and PCE DNAPL in
several typical hydrological scenarios was simulated. Comparison of the simulations suggest
that mercury’s higher density is the overall controlling factor in controlling its penetration in
saturated porousmedia, despite its higher resistance to flow due to its higher viscosity. Based
on these results the hazard of spilled mercury DNAPL to cause deep contamination of
groundwater systems seems larger than for any other DNAPL.”
© 2014 Elsevier B.V. All rights reserved.
(Citaat: Sweijen, T., Hartog, N., et al. The transport behaviour of elemental mercury DNAPL in saturated porous media; analysis of field observations and two-phase flow modelling – Journal of Contaminant Hydrology 161(2014), p.24-34)