You must use a septic tank or small sewage treatment plant to treat the sewage and then discharge the effluent (treated liquid) to ground via a drainage field.
A septic tank is an underground tank where the solids sink to the bottom, forming a sludge, and the liquid flows out to a drainage field.
A small sewage treatment plant, also known as a package treatment plant, works in a similar way to a septic tank but uses mechanical parts to treat the liquid to a higher standard before it goes to a drainage field.
A drainage field, also known as an infiltration system, is a series of pipes with holes placed in trenches and arranged so that the effluent can trickle through the ground for further treatment.
You cannot use a soakaway (designed for draining rainwater), well or borehole for discharging effluent to ground. Instead you must either upgrade to a drainage field or apply for a permit so that the Environment Agency can assess the risk of using this sort of system in your location.
Your treatment system must meet the right standards
Your treatment system must meet the relevant British Standard in force at the time of installation. The standards currently in force for new systems are:
BS EN 12566 for septic tanks and small sewage treatment plants
BS 6297:2007 for drainage fields
Your septic tank or treatment plant met the British Standard in place at the time of installation if:
You can also ask the company that installed your equipment to confirm that it complies with the British Standard that was in place at the time the equipment was installed.
If there were no British Standards in place when your treatment system was installed (that is before 1983) you do not need to do anything else to meet this requirement.
Your treatment system must be installed correctly and have enough capacity
Your treatment system must be large enough to handle the maximum amount of sewage it will need to treat. If you install a new septic tank, small sewage treatment plant or drainage field you must check with the installer that it meets the sizing requirements in British Water’s Flows and Loads 4 guidance.
If the amount of sewage the system needs to treat increases (eg because you’ve extended your property or connected an additional property) you must make sure the treatment system is still big enough. You must also recalculate the maximum daily volume of your discharge and apply for a permit if it is more than 2 cubic metres (2,000 litres) a day.
Your treatment system must be installed in line with the manufacturer’s specification (the instruction manual or technical set of requirements that comes with the equipment).
Have your treatment system regularly emptied and maintained
You must get the sludge that builds up in your septic tank or small sewage treatment plant removed (desludged) before it exceeds the maximum capacity. As a minimum, you should have your treatment system desludged once a year or in line with the manufacturer’s instructions.
The company you use to dispose of your waste sludge must be a registered waste carrier. Ask the company to confirm this when you arrange to have your tank emptied or ask the tanker driver for a copy of the company’s waste carrier certificate.
You should have your treatment system regularly maintained in line with the manufacturer’s instructions. If these aren’t available, ask your local maintenance company for advice.
You must have your treatment system repaired or replaced if it isn’t in good working order, for example if it has:
cracks in tank walls or pipes
signs that the effluent isn’t draining properly, pools of water around the drainage point
any area within 50 metres of a private water supply for human consumption - ask your neighbours if they have one and if so how far their spring, well or borehole is from your drainage field
You must apply for a permit if you have an existing discharge or are planning to start a new discharge to the ground in a SPZ1. The permit costs £125. A permit will include additional conditions to the general binding rules.
The Environment Agency will grant the permit if there’s:
no evidence of pollution
the risk of pollution is acceptable
If there is evidence of pollution or the risk of pollution is unacceptable the Environment Agency will ask you to make changes to your system and may issue a permit with improvement conditions.
The Environment Agency regularly checks:
surface and groundwater quality
If they find your system may be causing pollution to surface or groundwater they will contact you to discuss the issues. This may result in your permit being reviewed or revoked. See the guidance on how to comply with your permit.