Dwell Time of Seepage Water in the Non-Saturated Zone
Thank you, rain! It replenishes Berlin’s groundwater supply time and again. On its way through the ground, however, it can pick up pollutants deposited there. Whether or not this actually contaminates the groundwater in the end depends on various factors: how quickly does rain seep away? Which soils and layers of sediment does it need to traverse? How far does it need to travel to reach the groundwater?
Experts use this information to determine the vulnerability to pollution. It depends on the time precipitation needs to travel from the surface to the water table below ground. The area between the two is called the unsaturated zone as water does not linger there, i.e. it is not permanently saturated. The more time it takes for precipitation to pass through this zone, the lower the risk that pollutants actually reach the groundwater.
The vulnerability fluctuates greatly throughout Berlin. In the Spandauer Forst, it is deemed very high, as rainwater reaches the groundwater in less than a year. In Prenzlauer Berg, the same process takes 25, sometimes 50 years. This means that the vulnerability is lower in that area. This information does not consider whether any pollutants are present in the soil to begin with.