The Environment Agency has issued detailed new guidance to water companies on environmental permits for storm overflows and emergency overflows – on issues ranging from drainage strategy, screens, telemetry systems, pumping systems and connections for new developments.

Key issues included in the guidance include:

• Use of urban pollution management (UPM) and a partnership approach
• Design standards for storm overflows
• Water quality standards for freshwaters, bathing waters, shellfish waters, estuaries and coastal waters
• Solutions for unsatisfactory overflows
• Permits for new emergency overflows
• Reporting
• Notification of failures

The Environment Agency regulates intermittent discharges from sewer overflows and waste water treatment works (WWTW) through environmental permits.

Water companies are required to design, construct and maintain sewerage systems according to best technical knowledge not entailing excessive cost (BTKNEEC), together with limiting pollution from storm overflows.

Storm overflows must be classified as part of the utility’s drainage strategy according to three main categories:

• unsatisfactory
• substandard
• satisfactory

The Environment Agency classes storm overflows as unsatisfactory when they:

• operate in dry weather conditions
• operate in breach of permit conditions
• cause significant visual or aesthetic impact due to solids or sewage fungus
• cause or significantly contribute to a deterioration in the biological or chemical status of the receiving water
• cause or significantly contribute to failures in water quality standards
• cause groundwater pollution

The guidance recommends the water companies to use urban pollution management (UPM) and a partnership approach, suggesting they should read the UPM manual published by the Foundation for Water Research.

The companies must also carry out modelling work according to modelling codes of practice published by the Chartered Institute of Water and Environmental Management (CIWEM) Urban Drainage Group (UDG) ( formerly known as the Wastewater Planning Users Group) and the WaPUG guide to quality modelling of sewer systems and other related guides.

Solutions for unsatisfactory overflows

The guidance points out that the water companies must design, construct and maintain solution schemes, and the drainage system as a whole, according to BTKNEEC.

It also says that sewer flooding and pollution from storm overflows are expected to increase as a result of:

• population growth
• climate change
• urban creep

Suggested methods to assess the impact of urban creep include an UKWIR report on approaches to predict the impact of urban creep on sewerage systems and approaches to account for climate change in the CIWEM urban drainage group’s Rainfall Modelling Guide 2015.

The Agency says that the water companies’ long-term drainage strategies should manage the flood risks posed by population growth, urban creep and climate change and that “new or increased discharges from storm overflows are not an acceptable solution to inadequate planning, design or maintenance of the sewer network.”

Solution schemes should consider the potential for surface water separation and SUDS

The guidance also says that sustainable drainage systems (SUDS) reduce the pressure on the sewerage network and can support wider environmental objectives such as local amenity and biodiversity. Solution schemes should consider the potential for surface water separation and SUDS to meet the scheme’s objectives. Where feasible, the water companies are recommended to retrofit SUDS solutions to address flood risk problems and CSO drivers in existing catchments.

Where there is evidence that the overflow is currently unsatisfactory, the water companies are allowed up to three years to improve it to meet water quality, aesthetic and design standards.

The need for new storm overflows must be kept to an absolute minimum, the guidance says, while permits for emergency overflows at sewage pumping stations permit will only be granted if the reduced risk of a discharge outweighs the risk of legitimising a potentially polluting discharge.

On new developments, the guidance says these should be drained by separate foul and surface water systems constructed to standards set out in Sewers for Adoption 7th edition. The developer must also provide sufficient storage and telemetry warning systems to allow time for a tanker to attend in an emergency.

Commenting on reporting, the guidance says that the Environment Agency must be notified as soon as reasonably practicable, if a pumping station failure is detected that is likely to cause significant pollution.

Water companies in England and Wales to produce Drainage and Wastewater Management Plans by 2022

The guidance also recommends the water companies to read Ofwat’s own guide to preparing a drainage strategy published in 2013. 

A Drainage Strategy should help customers and other stakeholders understand how a water and sewerage company intends to deliver its functions over the long term within a particular area, the Ofwat guide says. A Drainage Strategy should also explain how a water and sewerage company will do this in conjunction with other organisations (e.g. The Environment Agency, Natural Resources Wales, local authorities, highways authorities, housing developers) and how the company, in turn, will support these organisations in delivering their own responsibilities as well.

The water companies have an ongoing focus on drainage and wastewater management plans via a new framework published yesterday for the long term planning of drainage and wastewater services under the aegis of the 21st Century Drainage Programme.

The Drainage and Wastewater Management Plan framework provides the basis for more collaborative and integrated long term planning by companies, working with other organisations that have responsibilities relating to drainage, flooding and protection of the environment.

The water and wastewater companies in England and Wales will produce Drainage and Wastewater Management Plans using the framework by the end of 2022, to support their business plans for the 2024 Price Review.

Click here to access the Environment Agency guidance

Click here to download the Drainage and Wastewater Management Plan framework