Evaluation of Groundwater Vulnerability

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The groundwater vulnerability evaluation system according to HÖLTING et al. (1995) is based on the idea that mechanical, physico-chemical and microbiological processes depend on the percolation time of pollutants throughout the vadose zone. This parametrical evaluation system considers 5 input factors: the amount of annual seepage water, the thickness of groundwater overburden, the soils available water capacity, the lithology of the deeper underground (soft and hard rocks) as well as artesian or perched groundwater conditions. As a result the risk of groundwater pollution is given, divided into 5 classes. The classification characterizes the expected dwell time of pollutants in the vadose zone. It ranges from several hours up to one year (“very high risk of pollution”) and exceeds 25 years (“very low risk”).
The disadvantage of the Hölting method is, that the conditioning of input parameters and data is not defined in a consistent way (WIMMER, LEPPIG, DIETZ 2002).
Actually the evaluation system in use neglects important parameters like other significant soil properties (e.g. organic matter content, pH value) or sorption processes. Until now potential pollutants are treated equal without consideration of different transport and degradation processes.

The goal of the actual research project is to develop a new method to evaluate the groundwater vulnerability considering different potential pollutants.

A major research aim at Department of Engineering Geology and Hydrogeology will be the investigation of transport and degradation processes of different groups of pollutants in the vadose zone, regarding types of soils and land use. Emphasis will be put on sorption and desorption processes, especially in the soil medium. This approach leads to a more profound consideration of soil parameters such as organic matter, pH value, clay mineralogy, CEC etc. in combination with land use aspects.
In order to this, actual research work is carried out on a 100km² sized pilot area on the Venlo Block in the Lower Rhine Basin.

As a result, an evaluation of groundwater vulnerability considering different pollutants will be achieved. By the linking of controlling parameters to soil type and land use a transfer of known qualities to the area is ensured. The regionalisation of the results will be achieved using the GIS techniques.