MAPPING GROUNDWATER RESOURCES IN BURIED PALEO CHANNELS

CASE STORY

The supply of drinking water in Denmark is entirely based on groundwater resources, and the water only passes through a very simple filtration and aeration process before being distributed to the consumers. In order to maintain this low level of water treatment high quality standards must be maintained on the extracted groundwater.

The authorities as well as local producers of drinking are initiating investigations in order to find and protect the groundwater resources.

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ABEM WALKTEM

CHALLENGE

Groundwater quality in deeper aquifers in Denmark is generally good, but with no indication at the surface, deep aquifers can be hard to find. In search for geological structures holding groundwater resources, geophysical methods are widely used. The TEM (Transient ElectroMagnetic) method has proven extremely efficient in mapping deep paleo channels eroded in Paleogene clays and filled with quaternary sand and gravel sediments down to more than a hundred meter of depth.

The survey area is located near the village of Tinning in the central part of Denmark and is characterized by open farmland. The terrain is relatively flat and holds no indications of the deep geological structures that may represent a valuable groundwater resource.

Information from local boreholes within the survey area indicates a groundwater aquifer of significant thickness. However, the lateral extension of the aquifer nor the presence of geological barriers were not known.

SOLUTION

In this survey, the ABEM WalkTEM, an RC5 receiver antenna and a 40×40 m Tx loop was used by a crew of two. The crew managed to achieve a daily production of 16 soundings.

Low Moment data are measured at a transmitter current of 1 Amp and High Moment data at 8.5 Amps.

The data were processed and inverted in Aarhus SPIA TEM software from Aarhus Geosoftware and visualized in sections and horizontal sliced maps in Aarhus Workbench, also from Aarhus Geosoftware.

RESULTS

The geophysical result from the survey is visualized in the section below. The vertical bars indicate the TEM soundings along the section line.

Boreholes along the profile are also indicated in the section and show remarkable good compliance with the geophysical results.

Geophysical results

Based on a combination of the geophysical results and geological information from the boreholes, a geological interpretation of the geological layers in the section is produced:

Geological results

ACKNOWLEDGEMENT

Guideline Geo wishes to thank the staff from Aarhus Geosoftware for help in collecting the data for this example.