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19th November 2019

Domestic Septic Tanks – more time to comply

Whilst new domestic septic tanks (installed since 1 January 2015) cannot discharge to surface water, older tanks have enjoyed an exemption as long as they didn’t cause pollution.
This exemption from the Environmental Agency (EA) was set to end on 1 January 2020. However, with the deadline fast approaching, the EA revised their guidance in October 2019, effectively extending the exemption to at least October 2020.

The EA now advises that septic tanks discharging to a watercourse must be upgraded “as soon as possible” and that owners must have “plans in place to carry out this work within a reasonable timescale, typically 12 months”. It is ambiguous whether the EA expects the actual works or just the plan for the work to be completed within a year, and it is not clear when this timescale starts running. In any case, the owners of existing septic tanks can now, to a certain extent, relax and take some time formulating a plan to deal with their liquid effluent.

Plans to upgrade septic tanks that discharge to surface water should consider the following options:

  • Connecting the residence to the mains sewer, which is a tenable option only if a public sewer is in the general vicinity. However, if more than one property needs a sewerage upgrade there may be a legal duty on the sewerage undertaker to build and pay for the connection.
  • Install an infiltration system (drainage field). Discharges to the ground remain exempt. However, if there is a public sewer within 30 metres of the dwelling or treatment system the discharge to ground will not be allowed.
  • Replace the septic tank with a small sewage treatment plant. The discharge from these plants is safer to discharge to a watercourse. However, if the discharge to surface water is more than 5 cubic metres (5,000 litres) per day a permit will be required.
Discharge exemptions hinge on where the effluent from your septic tank will discharge to. Discharges to ground are exempt, whilst discharges to water are not. This however can cause some confusion. Discharges to the sea, lakes, and waterways are obviously to water. But an existing discharge to an otherwise dry open ditch would also be considered a release to surface water. New discharges to ditches and waterways that that do not have flowing water all year round are not allowed.

To be exempt, discharges to ground must be within the ground, allowing the effluent to infiltrate and trickle through the soil and subsoil layers, providing additional treatment. Consequentially, an underground discharge that bypasses the infiltration process is not exempt. The use of rainwater soakaways, wells or boreholes for effluent disposal is not a suitable discharge to ground and an upgrade or permit would be required.

In addition, whilst a small septic tank or sewage treatment plant that has a drainage field is an exempt discharge to ground, a permit will still be required if the system discharges more than 2 cubic metres (2,000 litres) per day or is in a groundwater source protection zone.

Furthermore, a new or upgraded septic tank/sewage treatment plant will require building regulations approval and potentially planning permission.


For more information or assistance with the legal requirements of domestic sewage discharges, please contact Karen Luxton-Walsh on 01223 532733 or click here to email Karen.
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