Non-mains drainage validation guidance

Where a planning application proposes new or altered non-mains drainage arrangements we will require a minimum amount of information about the new arrangements to be provided before we validate your planning application.

What is non-mains drainage?

Non-mains foul drainage means the different methods of sewage disposal which are used when mains sewerage is not available.  There are three main types:

  • Package treatment plants
  • Septic tanks
  • Cesspools

What information do I need to provide?

If your application proposes new or altered non-mains drainage you must provide the following information before we can register your planning application:

  • Scale plans showing the location of the proposed installation, including any drainage field or outfall
  • Details of the proposed installation, including scale plans and sections showing the proposed installation
  • Where outfall is to ground, percolation test results
  • Confirmation of whether:
    • an Environment Agency discharge permit is required; or
    • whether the installation meets the exemption requirements
  • Supporting statement detailing whether the non-mains drainage system will have adverse effects

You can use the questionnaire in Box 1 below to provide this information.

What type of sewerage system should I use?

Government guidance to Local Planning Authorities explains that when drawing up sewerage proposals for any development, the presumption must always be to discharge into a public sewer where connection is available and viable.  There is an absolute right in law for connection to the public sewer network, however you should discuss connection with United Utilities at an early stage to understand their requirements.

If connection to a public sewer is not possible, you must consider a package sewage treatment plant incorporating a combination of treatment processes.  The plant should offer full treatment with the final effluent discharge from it meeting the standard and conditions set by the Environment Agency.

Only if neither a mains or package treatment plant solution is feasible should a system incorporating septic tanks be considered. Applications for planning permission should be supported by a full assessment of the proposed use of septic tanks, to confirm that no adverse effects will arise from the installation. This assessment should focus on the likely effects on the environment, amenity and public health. In particular your assessment should include a thorough examination of the impact of disposal of the final effluent whether it is discharged to a watercourse or disposed of by soakage into the ground.

If the non-mains sewerage and/or sewage disposal proposed is likely to lead to a significant environmental, amenity or public health problem in any area, national guidance states that this would normally be sufficient to justify refusal of planning permission.

What is a percolation test?

A percolation test assesses whether the ground conditions of a site will allow a package treatment plant or septic tank to satisfactorily discharge by soakage into the ground without the need for additional secondary treatment. The Building Regulations 2000: Approved Document H (Drainage and Waste Disposal) provide further details of how to undertake a percolation test.

Non-mains drainage questionnaire