Recommendations for Sewer System Operators on Managing Stormwater
Drainage systems remove water from the soil. In buildings, drainage systems are primarily used to protect the underground structure from moisture damage—often without determining where the water collected by the drainage system should be discharged. From a wastewater regulation perspective, handling this drainage water is very straightforward: since drainage water cannot be classified as wastewater, discharging it into the sewer system is not permitted. Furthermore, the Model Drainage Ordinance explicitly prohibits the discharge of groundwater and spring water.
Nevertheless, a large number of drainage systems are connected to the sewer system. Dealing with these existing drainage systems connected to the sewer system—as well as preventing the installation of new ones—is often not a trivial matter in practice. The function of drainage systems—to safely divert water away from structures to prevent moisture damage—cannot generally be disabled in existing buildings. If there are no alternative discharge options for the drainage water, it may be necessary to connect the drainage water to the existing sewer system or to maintain the existing connection.
Project Number: 78e197
Client: Bavarian State Office for the Environment
Project Period: 2018–2021
Project team at Augsburg University of Applied Sciences:
- Prof. Dr.-Ing. R. Hilliges
- M.Sc. J. Mühlegg
- M.Eng. S. Leonhard
- Dipl.-Ing. (FH) M. Brand
Alternatives for connecting drainage water to the sewer system can vary and should be thoroughly evaluated to reduce the amount of extraneous water entering the sewer system. Because of the limits on the permissible amount of extraneous water in the sewer network, municipalities and network operators often need to take action in this regard. This applies in particular to new construction. In some cases, it may make sense to construct a separate drainage channel. This also raises the question of how and by whom the costs of the measure(s) are to be borne.
If connection to the sewer system is unavoidable, the question arises as to how to allocate the costs associated with the additional load on the sewer network, the wastewater treatment plant, and the drainage systems.
To support affected municipalities and network operators in Bavaria, a practical guide is to be developed that comprehensively addresses the issues described. To this end, materials such as sample presentations, informational flyers, and data collection forms for network operators will also be created.
In addition to developing the guide, it will be applied to pilot municipalities to facilitate its refinement. Another objective of the project is to identify insights regarding the possibility of pragmatically estimating drainage water volumes using practical models.
Drainage systems are increasingly being identified during inspections of property drainage systems and are coming under greater scrutiny as sources of extraneous water. For this reason, recommendations on how to handle drainage systems connected to the sewer network are becoming increasingly important. Consequently, in addition to the current research project at Augsburg University of Applied Sciences, there is also a working group on this topic within the German Association for Water, Wastewater, and Waste (DWA).