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Foul Drainage Assessment

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Foul Drainage Assessment

Any type of development that connects to a non-mains system will need a drainage assessment or statement to confirm the proposed arrangement. This includes householder applications for additional bedrooms / bathrooms.

Any proposal (except householder or listed building consent) to connect to the main sewer will need written permission from South West Water (SWW) to confirm acceptance of the additional flows and check capacity.

Mains Sewage Assessment

If the proposed development is within 90m of a public sewer, then the development must connect to it (If the development provides more than 3 dwellings then the distance is the No. of units x 30m). For sites that are below the sewer invert, a pumping station will be required and this must have a 24h emergency storage capacity. Full details and calculation must be included in the assessment. Full details of the existing system must be shown on the application drawing(s) and be within the location plan red line.

Non-Mains Sewage Assessment

A Foul Drainage Assessment (FDA1) form will be required for all residential or commercial development where the applicant does not intend to connect to the mains foul sewer system.

The FDA must be completed in full and must be submitted with  justification for why connection to the mains sewerage system is not feasible, plus:

  • Full details of the proposed flows
  • A plan showing the location of the proposed treatment plant and appropriately sized soakaway field/discharge point (within the red line application site)

Percolation test results to demonstrate the viability of soakaways (if proposed). 

A foul drainage assessment should include a full assessment of the site, its location and the arrangements for storing, transporting and treating sewage, and for properly disposing of cleaned water.  Reasoning and justification for not connecting to the public sewer, including a map showing the location of the nearest public sewer, must also be included. 

The Environment Agency provides guidance on the hierarchy to be considered in selecting alternatives to non-mains drainage.  For reasons of public health protection, small reception tanks, cess pits or earth closets will not be acceptable.  In exceptional circumstances any provision of this type must be justified and sited in a separate building away from living accommodation

If the proposal is a major development involving a non-mains system, pre-application advice can be obtained from the Environment Agency via their cost-recovered planning advice service: Email SPDC

For other developments, pre-application advice should be sought from the Environmental Health Team.


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