A detailed 3D model was developed near Rønne to assess groundwater vulnerability. DualEM and PACES was conducted to support the modelling.
Robbedale formation is an important aquifer for the water supply of Rønne, Denmark. Therefore, it is essential for the municipality to map out where the aquifer is the most vulnerable to pollution.
In order map out the aquifer vulnerability, a detailed digital 3D model was made for the area. The model includes mapping the surface extent of the aquifer, the confining units, and the and groundwater level in the aquifer. Data used in the modelling included primarily borehole lithology and groundwater measurements. However, two geophysical studies were conducted, providing resistivity data to supplement the borehole data.
PACES was conducted in the open fields, providing resistivity data to a depth of approximately 30 m. DualEM was collected in the tighter areas between buildings where PACES was not possible, providing resistivity down to a depth of 10 m.
Combining the resistivity data from DualEM and PACES with the well lithology, it was possible to accurately map out the extent of the Robbedale aquifer, the confining shales above and below the aquifer as well as the precise location of a fault across the study area. The end product was an accurate 3D digital geological model. In addition, the resistivity data clearly showed the depth to the water table. Combining this information with water level measurements from the wells, it was possible to develop a detailed conceptual model of the groundwater flow from the surface to the groundwater abstraction wells.
The project provided a very detailed model of the area, allowing the municipality to determine where groundwater protection efforts should be focused.