Discharging to land via a soakaway
A soakaway is a sealed system of gravel filled trenches that allows the safe discharge of sewage effluent to the surrounding land. This is sometimes referred to as an infiltration system.
A soakaway also includes mound soakaways. This is a type of soakaway that is built above ground where percolation is slow or where digging trenches may be too difficult. For example, where bedrock is close to the surface.
If you plan to discharge to a soakaway, please read the guidance below.
Constructing a soakaway
Soakaways must be constructed following the Building Standards Technical Handbook. Their construction is regulated by local authority building control. Before constructing a soakaway, you will need to contact your local authority to apply for a building warrant.
Choosing a location for a soakaway
The highest seasonal water table (in winter) should be more than one metre below the base of your soakaway. This is to make sure that there is no direct discharge of sewage to groundwater.
Your soakaway shouldn't be close to a spring, well, or borehole that provides water for human consumption (i.e. drinking water). Contact your local authority Environmental Health department or speak to your neighbours to find the location of water supplies in your area.
You will need to check that there are no springs, wells, or boreholes used for water for human consumption within:
- 50 metres of your discharge if the discharge is from between one and three domestic properties or less than or equal to 15 population equivalent from non-domestic properties.
- 250 metres of your discharge if the discharge is from between four and 10 domestic properties or between 16 and 50 population equivalent from non-domestic properties.
If there are, you will need to re-locate your soakaway further from the water supply.
If you can't relocate your soakaway, you should find out what type of water supply it is - spring well or borehole - and if it is pumped or gravity fed, then contact us to discuss by emailing the Water Permitting Team.
Permeable drains and watercourses
You should locate your soakaway at least 10 metres from any permeable drain, watercourse, loch, or the sea. A permeable drain includes a field drain or land drain (a perforated underground pipe or titles used for draining land). You may be able to find out this information from your neighbours or local landowners.
You must carry out a soil percolation test to work out if your discharge will drain from a soakaway. This should be carried out by a specialist drainage contractor.
If the percolation value is more than 100 seconds per millimetre (s/mm), you should contact your local authority Building Control department. They may require you to use additional treatment or use a mound soakaway.
If the percolation value is 15 seconds per millimetre (s/mm) or less, you must install a secondary treatment system. This should be designed to meet a mean limit of no greater than five milligrams of ammoniacal nitrogen (as nitrogen) per litre (mg/l). You should consider a dosing system (e.g., by using a bell siphon or pump) to ensure effective distribution of effluent throughout the soakaway system.
The soakaway must also have a minimum area of:
- 15 square metres (m2) multiplied by the total number of domestic properties, or
- three square metres (m2) multiplied by the total population equivalent.
Example one:
For three domestic properties:
- minimum area = 15m2 x 3
- minimum area = 45m2
The required soakaway size is 45m2.
Example two:
For one domestic property and a small café of 30 population equivalent:
One domestic property = five population equivalent so total population equivalent = 30 + 5 = 35
- minimum area = 3m2 x 35
- minimum area = 105m2.
The required soakaway size 105m2.
If the percolation value is more than 15 seconds per millimetre (s/mm), you must install:
- a septic tank as a minimum if the discharge between one and three domestic properties or less than or equal to 15 population equivalent.
- a secondary treatment system if the discharge is from between four and 10 domestic properties or between 16 and 50 population equivalent.
Our online registration service will help you work out what type of treatment system you need.