Seven borings, up to 140m (460-ft) deep, were advanced by a specialty contractor to install geothermal probes for heating of the town hall. This was planned to be a prestigious project for the municipality utilizing renewable energy. However, shortly after finishing the drilling, cracks appeared in the recently renovated town hall. First the cracks were attributed to drying of the plaster after renovation, but cracks increased and neighbors started complaining about the same observations in the surrounding buildings (some of them up to 600 years old).
A geotechnical expert was hired to investigate the problem. At this point, it is assumed that the drilling operations may have triggered the settlement. In approximately 32m (105-ft) depth, the drilling company encountered an artesian aquifer. The investigator indicated that even though the boreholes were cased, water may still migrate upwards, which may change stresses in the ground. It is planned to advance another 60m (195-ft) deep boring to obtain a subsurface profile and to perform additional investigations into soil permeability and stress distributions.
(Source of pictures: http://www.badische-zeitung.de/staufen-erdsenkungen-in-der-altstadt.103227)
Thanks Wolfgang. I appreciate you keeping us up to date on interesting geonews from your old stomping grounds.
Fascinating problem. You don’t really hear too much negative about geothermal, usually its pretty benign. But this is definitely a unique case. Anyone else ever heard of any problems related to geothermal wells? — Randy (rockman)
Just to clarify — because there seems to be a lot of confusion in the media about this, particularly by the hysterical “reportage” of the Daily Telegraph — this is not a geothermal power generation project. This is a geoexchange project, where the steady temperature of the earth at relatively shallow depths is used to heat and cool buildings.
In properly drilled wells that are cased and correctly cemented, leakage from an artesian aquifer could have been mananaged — if, indeed, that is what happened. The official report has yet to be reported.