For 18 years, five TD-4100 monitors have monitored the Danube River in Vienna for hydrocarbons. The dam was the last built in Austria, and is in the centre of the capital.
A lot of environmental monitoring is needed to make sure that the dam does not cause contamination of the groundwater. The monitors are in stations that have a lot of other instruments. On the left of the photo, you can see the top of the station, which is located underground.