Environmental guidance for your business in Northern Ireland & Scotland

Using septic tanks and package treatment plants

Septic tanks and package treatment plants

If your business is in an area where no mains sewers are available, you may need to treat your effluent on site before discharging it to surface waters or groundwater. You may need to use a wastewater treatment system such as a package treatment plant, septic tank or cesspool. (Note that you are not allowed to use cesspools in Scotland)

What you must do

Septic tanks and package treatment plants

Septic tanks provide basic sewage treatment. You should make sure the effluent from your septic tank is further treated - eg by a soakaway or (in Scotland) using a filter or reed bed - before you dispose of it to a watercourse.

You should make sure that your soakaway, also known as a drainage field, conforms to the British Standard:

BS 6297 Code of practice for the design and installation of drainage fields for use in wastewater treatment

Septic tanks must be installed following the standards set out in the building regulations.

In Northern Ireland:

The Building Regulations (Northern Ireland) 1990 Technical Booklet N

Also available from The Stationary Office, Belfast on 02890 238 451

In Scotland:

Scottish Government: Technical Handbook – Domestic - section 3.9

Package treatment plants

Package treatment plants are available in different sizes, suitable for dealing with different volumes of effluent.

Correctly operated and well-maintained package treatment plants produce a higher quality effluent which you may be able to discharge to surface water or groundwater.

You will need to carry out a percolation test if you want to use a soakaway or drainage field to dispose of the effluent from your septic tank or package treatment plant. This will confirm whether the area is suitable for a soakaway and will determine the size of the drainage area you need.

GPP 4 Treatment and disposal of sewage where no foul sewer is available (Adobe PDF – 244KB)

If you plan to install a new system or alter your existing system of sewage disposal, you should contact your environmental regulator at an early stage to discuss your plans.

Using a soakaway

You may be able to dispose of the septic tank effluent by soaking it away to ground, for example by using a herringbone drainage field, if you have sufficient land and the drainage conditions are favourable. Permission to do this will depend on the distance of your septic tank from local groundwater sources and other protected areas. You should read our more detailed guidance on septic tanks, or contact your environmental regulator for advice.

Septic tanks

Contact your environmental regulator

Get authorisation for your septic tank or package treatment plant

Before you discharge any sewage, effluent or contaminated run-off to land, surface waters or groundwater you must have:

  • In Northern Ireland: a discharge consent, groundwater authorisation or pollution prevention and control (PPC) permit from the NIEA
  • In Scotland: an authorisation under the Controlled Activities Regulations (CAR). CAR requirements are also meet within authorisations under pollution prevention and control (PPC) permit, Waste Management Licence (WML) or the Radioactive Substances Act from the Scottish Environment Protection Agency (SEPA).

You will not normally get an authorisation to discharge if it is reasonable for you to connect to the public sewer.

You may need a waste management licence from the NIEA or SEPA if you treat effluent from another business' site.

In Scotland, if you need to construct a new outfall structure for your discharge your discharge authorisation will cover the construction.

In Northern Ireland, the construction of a new outfall structure is not covered by the discharge consent. This consent only regulates the discharge itself. Consent under Schedule 6 of the Drainage (Northern Ireland) Order 1973 will be needed from the Rivers Agency for any works likely to affect any watercourse, which may included the construction of an outfall pipe.


A cesspool is a watertight tank with no outlet. You are not allowed to use a cesspool in Scotland.

You will need to empty your cesspool regularly to prevent it overflowing. Fit an alarm that will go off when your cesspool is nearly full. This is an emergency back-up and you should check the tank regularly.

Maintain your wastewater treatment system

Follow the manufacturer's operating and maintenance instructions to make sure that your wastewater treatment system operates effectively.

You must use a registered waste carrier to remove sludge from your septic tank or treatment plant.

NIEA Registration of Carriers for information

SEPA: Who is registered?

You should make sure that clean surface water run-off, eg from roofs and parking areas, does not enter your treatment system. The extra water will reduce the effective capacity of the system and may flush solids out.

Read the next section on avoiding spills and unauthorised discharges.

Startup information for packaged wastewater treatment plants after the shut down period

Following the actions that the UK government established in March 2020 to help to reduce the transmission of coronavirus in our communities, certain businesses and venues have been required by law to stay closed to the public for a prolonged period.

For businesses who use off-mains wastewater treatment, such as package treatment plants, there are a number of recommended actions that should be taken in order to:

  • protect your equipment,
  • enable a smooth start-up, and
  • minimise the risk of pollution when restarting your plant

A list of these actions can be found in the British Water guidance document - Startup information for packaged wastewater treatment plants after shut down period.(Adobe PDF - 177KB).

This guidance may also be useful for businesses who are re-starting package treatment plants or septic tanks after a long shutdown, eg after the winter on holiday sites.

Further information

NetRegs: Septic tanks

GPP 4 Treatment and disposal of sewage where no foul sewer is available (Adobe PDF – 244KB)

Preventing water pollution

British Water: Guide for Users of Packaged Wastewater Treatment Plants (Adobe PDF - 686KB)

In this Guideline

How to deal with Trade Effluent

Disposal top a public sewer

Dealing with effluent that cannot go to foul sewer

Disposal to land where no public sewer is available

Disposal to water where no public sewer is available

Using septic tanks and package treatment plants

Reducing and treating your trade effluent

Avoiding spills and unauthorised effluent discharges

Trade effluent environmental legislation

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