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

To ask the Secretary of State for Environment, Food and Rural Affairs, what the capacity is of temporary storm storage tanks at each sewage treatment works in England.

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 requirement for storm tanks is that they must settle out solids and have a minimum capacity of 68litres/head served or a storage equivalent of 2 hours at the maximum flow rate to the storm tanks.

There are over 2,000 storm tanks at sewage treatment works. The required capacity of the storm tank is included within the permit, along with other requirements such as monitoring and reporting.