Bailer (hydrogeology)

Once lowered, the bailer uses a simple ball check valve to seal at the bottom in order to pull up a sample of the groundwater table.

The main drawback of using bailers is aeration of the water as the sample is obtained, which could release volatile organic compounds that need to be tested.

Also, if there is a high amount of sediment or turbidity, this may interfere with the ball check valve seating correctly.

A disposable bailer is light and easy to carry in field conditions in comparison to a heavy solid slug.

On the other hand, bailers cannot be used to do falling head tests (i.e. where the slug is quickly dropped below the water table).