Abstract
Abstract. A direct current (DC) resistivity and time domain induced polarization (TDIP) survey was undertaken at a decommissioned landfill site situated in Hørløkke, Denmark, for the purpose of mapping the waste deposits and to discriminate important geological units that control the hydrology of the surrounding area. It is known that both waste deposits and clay have clear signatures in TDIP data, making it possible to enhance the resolution of geological structures compared to DC surveys alone. Four DC/TDIP profiles were carried out crossing the landfill, and another seven profiles in the surroundings provide a sufficiently dense coverage of the entire area. The whole dataset was inverted using a 1-D laterally constrained inversion scheme, recently implemented for TDIP data, in order to use the entire decay curves for reconstructing the electrical parameters of the soil in terms of the Cole-Cole polarization model. Results show that it is possible to resolve both the geometry of the buried waste body and key geological structures. In particular, it was possible to find a silt/clay lens at depth that correlates with the flow direction of the pollution plume spreading out from the landfill and to map a shallow sandy layer rich in clay that likely has a strong influence on the hydrology of the site. This interpretation of the geophysical findings was constrained by borehole data, in terms of geology and gamma ray logging. The results of this study are important for the impact of the resolved geological units on the hydrology of the area, making it possible to construct more realistic scenarios of the variation of the pollution plume as a function of the climate change.
Highlights
Due to the expected climate changes, there is an increasing need to develop hydrogeological models for predicting water flows in sensitive areas, such as former landfills
The time domain induced polarization (TDIP) method measures the voltage decay induced by the turn-off of an exciting current pulse and uses the characteristics of the decay to study the induced polarization of the soil, known as chargeability
The equipment used in the field is the same as used for direct current (DC) measurements, and the set-up consists of potential and current electrodes distributed along a profile
Summary
Due to the expected climate changes, there is an increasing need to develop hydrogeological models for predicting water flows in sensitive areas, such as former landfills. It is believed that groundwater fluctuations will become more extreme in the years to come. As a consequence, it would affect the time pattern and the intensity of precipitation, yielding dry summers and more rainfall in the winter season in northern Europe (see some examples of scenarios in UK in Jackson et al, 2011 and Hulme et al, 2002). In Denmark, many landfills operational between 1950 and 1980 were designed without any kind of capture system underneath. In case of percolation through the waste, the predicted changes in winter rainfall will probably
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