Goedele Verreydt, M.Sc. in Environmental Engineering (2004), commenced her PhD in the Department of Biology at the University of Antwerp in January 2008. Her PhD research concerns the determination and calculation of groundwater contaminant mass fluxes in the frame of a groundwater management, which she performs in the research group Land and Water Management at the Flemish Institute for Technological Research (VITO), Mol, Belgium.
The management of contaminated groundwater is very challenging. Most decisions regarding groundwater pollutions are driven by contaminant concentrations. Since concentration estimates may be highly uncertain and do not include the fluctuations caused by spatially and temporally varying hydrologic conditions, these strategies can be improved by additionally considering contaminant mass fluxes (mass of contaminants passing per unit time per unit area) and contaminant mass discharges (sum of all mass flux measures across an entire plume). The contaminant mass that effectively reaches a downgradient receptor, determines the actual risks for the receptor and should therefore be monitored on site. The combined monitoring of contaminant mass fluxes and groundwater fluxes along a control plane is possible with Passive Flux Meters (PFMs), recently developed passive sampling devices that are installed in monitoring wells for a certain period of time.
The main objectives of this study are:
- to delineate a robust interpretation method for the measurement and calculation of groundwater contaminant fluxes, based on mass flux measurement with Passive Flux Meters (PFMs);
- to define a clear strategy that supports regulatory decisions in a flux and risk based groundwater management.
The PFM consists of a permeable sorbent infused with soluble tracers packed in a nylon mesh tube. The measurements of the captured contaminants and the remaining resident tracer on the sorbent are used to estimate respectively contaminant and groundwater fluxes.
To calibrate and validate the PFMs, lab as well as field experiments are performed. In addition, the measured water fluxes and contaminant mass fluxes are compared to the results obtained by traditional measurement techniques. The proposed management strategy is based on a source-path-receptor approach.
The PFM has proven to be a valuable instrument for the measurement of contaminant mass flux in groundwater. The extrapolation options of the PFM flux data are defined. Mass discharge can be estimated by integrating the PFM mass flux data throughout the control plane, which converts the individual flux values to a time-stamped cumulative flux (or discharge value). Further, a theoretical framework for a flux based management strategy is set by introducing the term CMDmax (maximum accepted contaminant mass discharge) at a predefined plane of compliance, i.e. a control plane orthogonal to the main flow direction and upgradient the receptor. The proposed strategy includes remedial action if the CMDmax is exceeded.
G. Verreydt1,2, I. Van keer1 and J. Bronders1
1VITO, Land and Water Management, Boeretang 200, 2400 Mol, Belgium
2Artesis University College of Antwerp, Paardenmarkt 92, 2000 Antwerpen
Figure shows Mrs. Verreydt retrieving a PFM during a field demonstration in Rijmenam, Belgium.
Annable, L.D., K. Hatfield, J. Cho, H. Klammler, B.L. Parker, J.A. Cherry and P.S.C. Rao. 2005. Field-Scale Evaluation of the Passive Flux Meter for Simultaneous Measurement of Groundwater and Contaminant Fluxes. Environmental Science & Technology 39(18): 7194-7201.
Verreydt, G., Bronders, J., Van Keer, I., Diels, L. & Vanderauwera, P. (2010) Passive samplers for monitoring VOCs in groundwater and the prospects related to mass flux measurements. Ground Water Monitoring and Remediation 30(2): 114-126.