§ Mr. Barry Field
To ask the Secretary of State for the Environment what size of served population gives rise to a requirement for additional sewerage treatment before the discharge into the sea; and over what period such population figures are calculated. 
§ Mr. Clappison
Under the urban waste water treatment directive, sewage discharges with a population equivalent greater than 10,000 normally receive secondary treatment before discharge to coastal waters, but if the discharge is into a high natural dispersion area and it can be demonstrated that the environment will not be adversely affected, primary treatment may be sufficient.
Population equivalent is a measure of organic biodegradable load. The size of discharge is calculated on the basis of the maximum average weekly load entering treatment plants during a year and excludes the effect of unusual weather conditions.