Question to the Department for Environment, Food and Rural Affairs:

To ask the Secretary of State for Environment, Food and Rural Affairs, how Ofwat and the Environment Agency establish whether wastewater treatment works have sufficient temporary storm storage to prevent unnecessary discharges of raw sewage.

At some sewage treatment works, where the permitted treatment capacity may be exceeded due to rainfall, storm tanks form part of the treatment process to limit spills of storm sewage (mixture of sewage and rainfall) to the water environment. These discharges are permitted by the Environment Agency under the Environmental Permitting Regulations.

The permit conditions typically define the assets that control the storm tanks’ performance, for example:

• Storage volume
• Environment.
• Screening
• Monitoring for event duration (how often and how long the storm overflows operate)
• Reporting

Permits also include a management system condition that requires the water to have a written management system that identifies and minimises risk of pollution, so far as is reasonably practicable, along with reporting and notification conditions. The Environment Agency then undertakes compliance assessments for the permits and the conditions they include. These assessments can include the use of monitoring data, reports provided by the water companies and inspections of the sewage treatment works themselves.