Sewerage

Sewerage (the sewer system), is the underground networks of pipes that carries sewage (waste water and excrement), waste water and surface water run-off, from buildings to treatment facilities or disposal points.

A sewer is; 'A pipe or channel taking domestic foul and/or surface water from buildings and associated paths and hardstandings from two or more curtilages and having proper outfall' Ref The SuDS Manual (C753), published by CIRIA in 2015.

Types of sewer include:

• Sanitary sewer: Used solely for carrying sewage.
• Surface water sewer: Used to drain groundwater and excess water from impervious surfaces.
• Combined sewer: Used to carry both sewage and surface water. This type of sewer can lead to water pollution problems when overflow conditions are experienced.
• Effluent sewer (sometimes referred to as Septic Tank Effluent Drainage (STED) or Solids-Free Sewers (SFS)) : These collect remaining sewage from septic tanks and carry it to a treatment plant.
• Separate sewer: For surface water or foul sewage, but not a combination of both.

There are a number of ways of moving the contents of sewers:

• Gravity sewers use differing elevations to facilitate movement.
• Force mains use pumps where sewers are at a lower elevation than the destination.
• Vacuum sewers use differential atmospheric pressure.

A sewerage undertaker is: 'A collective term relating to the statutory undertaking of water companies that are responsible for sewerage and sewage disposal, including surface water from roofs and yards of premises.' Ref The SuDS Manual.

In September 2010, the government announced that most private sewers that connected to the public sewer network would be transferred to the ownership of the regulated sewerage companies in England and Wales. Private sewers that were connected to the public sewer network before 1 July 2011 were transferred on 1 October 2011.

NB

• A drain is a pipe that serves only one building, conveying water and waste water to a sewer. A lateral drain is a section of drain positioned outside the boundary of a building, connecting with the drains from other buildings to become a sewer.
• Combined Sewer Overflow (CSO) is: ‘A structure on a combined or partially separate sewer system that allows the discharge of flow in excess of that which the sewer is designed to carry, usually to a receiving surface water body.’ Ref The SuDS Manual.

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