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What are my off-main drainage options?

1. Packaged sewage treatment plant

A packaged sewage treatment system is recommended where possible, as these provide secondary biological treatment to produce a high-quality effluent suitable for discharge directly to a watercourse, or drainage field if a suitable watercourse is not available.

All Klargester and Conder systems are BSEN12566/3 certified, are suitable for most applications and are readily accepted by Building Control and the Environment Agency.

Information on siting your sewage treatment system is available in Building Regulation Approved Document H.

2. Septic tank

A septic tank provides minimal treatment of effluent – the septic tank settles out the solids, and the settled effluent relies upon further treatment in a well-constructed drainage field. Septic tanks should not discharge directly or indirectly to watercourses – the effluent needs to be further treated through aerated layers of soil and percolated into surrounding soil.

Septic tanks can only be installed if ground conditions are suitable, which means conducting a soil porosity (percolation) test.

When siting a septic tank, there are clear regulations to follow regarding proximity to buildings which are outlined in Building Regulations Approved Document H

3. Cesspool

A cesspool is simply a storage tank with an inlet and no outlet – when the tank is full, the raw sewage must be tankered off-site to a sewage treatment works. In Scotland, Building Regulations do not permit the use of cesspools. In the UK, depending on the size of the cesspool, Building Regulations request a minimum of 18000l for two people + 6800l for each additional person. Due to there being no treatment of effluent and consequently no outlet drainage, the cesspool may require frequent emptying which can be prohibitively expensive.

Useful Documents

Building Regulations Approved Document H

Environment Agency Pollution Prevention Guidelines 4 – treatment and disposal of sewage where no foul sewer is available