SEGH Articles

# Flux Based Management of a Groundwater Pollution: from Mass Flux Measurements to Regulatory Decisions

01 August 2011
Goedele Verrydt won the Springer / Hemphill Prize for Student Oral Presentation at SEGH 2011 in Ormskirk, UK.

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.

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### Abstract

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### Abstract

The presence of phosphorus (P) and heavy metals (HMs) in surface sediments originating from lakes Volvi, Kerkini, and Doirani (N. Greece), as well as their fractionation patterns, were investigated. No statistically significant differences in total P content were observed among the studied lakes, but notable differences were observed among sampling periods. HM contents in all lakes presented a consistent trend, i.e., Mn > Cr > Zn > Pb > Ni > Cu > Cd, while the highest concentrations were recorded in Lake Kerkini. Most of the HMs exceeded probable effect level value indicating a probable biological effect, while Ni in many cases even exceeded threshold effects level, suggesting severe toxic effects. P was dominantly bound to metal oxides, while a significant shift toward the labile fractions was observed during the spring period. The sum of potentially bioavailable HM fractions followed a downward trend of Mn > Cr > Pb > Zn > Cu > Ni > Cd for most lakes. The geoaccumulation index Igeo values of Cr, Cu, Mn, Ni, and Zn in all lakes characterized the sediments as “unpolluted,” while many sediments in lakes Volvi and Kerkini were characterized as “moderately to heavily polluted” with regard to Cd. The descending order of potential ecological risk $$E_{\text{r}}^{i}$$ was Cd > Pb > Cu > Ni > Cr > Zn > Mn for all the studied lakes. Ni and Cr presented the highest toxic risk index values in all lake sediments. Finally, the role of mineralogical divergences among lake sediments on the contamination degree was signified.