Discharge to a public foul sewer
Our engineers will oppose any suggested connection of surface water to a foul sewerage system. The NSfS also offers clarity that even if surface water is already being discharged to a foul sewerage system, then it cannot be classified as a combined sewer.
We consult the Public Sewer records or the asset owner (if different) to determine the classification of the sewer.
Discharge to a surface water sewer, combined sewer or another piped surface water drainage system
If a designer proposes to dispose of runoff to an appropriate sewer or piped surface water drainage system, then it is expected that hydraulic capacity checks, and permission in principle from the asset owner for the connection are submitted with the application.
Where the proposed connection is not to a public sewer, a condition survey will also need to be undertaken. Any remediation should be identified and agreed with the asset owner and approving body to ensure that the system is fit for purpose in terms of structural integrity and function.
If the capacity of the receiving system is an issue, permission to connect is withheld, or remediation measures cannot be agreed, then this can further restrict the proposed discharge rate or require a new discharge location. This can affect the scale and layout of the development - to allow access to a different outfall, or an increase in storage volume (if the discharge rate needs to be lower than what may be agreed based on the greenfield runoff rate calculations). Similarly, if permission for the connection is withheld, then there may be few alternative means of draining the site. All the above considerations could increase flood risk if unresolved.