Off- Mains Sewage Disposal

The Law changed on 1 January 2020 concerning the use of what are often collectively known as private drainage systems. Here we provide further insight to this:-

Cesspool This is sometimes referred to as a cesspit, it is the same thing. It comprises a sealed holding tank, usually located underground. It has an inlet for the effluent from the house, a removable cover for emptying and a fresh air inlet to ventilate the tank and allow the escape of gases. It must have no other outlet and must not leak. The purpose of the cesspool is simply to hold the effluent and it has to be emptied on a regular basis. The frequency depends on the number of people using it and is typically every 6 – 10 weeks for a medium sized residence. Emptying must be by a certified waste carrier. This can be expensive.

If no public sewer is close enough for a property to be connected it is necessary to provide some sort of self-contained system. There are four main types of system in existence: a cesspool, a septic tank, a small (or packaged) sewage disposal plant or some alternative type such as a reed bed.

Septic tank This is very similar to a cesspool but compartmentalised to allow the separation of solid and liquid waste. Solids are retained in the tank and liquid is discharged to a drainage field or infiltration system to be cleaned by percolation through soil. Solids are emptied from the tank in the same way as a cesspool but typically this will only be done once or twice each year. Such a system relies on the subsoil being capable of receiving the final discharge without backing up and preventing the unit from working. This is determined by a percolation test. The drainage field must be carefully designed to enable it to work efficiently and, even then, it may have a limited life as eventually it may become clogged and refurbishment or renewal becomes necessary. In the event that the ground is unsuitable then it is usual to employ a sewage treatment plant. Septic tanks are a common solution for off-mains properties. Capital cost is low, running cost is low and it is a well understood system.

Small or packaged sewage treatment plant This is a package which is partly mechanical and treats the water so that it is clean enough to be discharged into a stream or watercourse or, if necessary, into a drainage field as described above. These usually constitute the best option for off-mains sewage disposal. They still have to be de-sludged (emptied of solids) once every year or so and mechanical parts serviced annually but are otherwise generally trouble free. If de-sludging is not carried out the solids build up, become very hard, prevent the proper operation of the system and are very hard to remove without causing damage. That also applies to a septic tank.

Reed bed Reed beds are not usually a complete sewage treatment system on their own but are generally used with a septic tank or treatment plant. They allow microorganisms to digest the sewage and clean the water. There are two basic types of reed bed – vertical flow and horizontal flow – and the best system often results from combining the two. Reed beds are the ecological solution. They do largely the same job as a treatment plant but produce cleaner water and need a septic tank as well. They’re prettier to look at and provide a rich habitat but are difficult to justify on any other grounds. Specialist advice is needed if you propose such a system.

The Regulations The operation of off-mains sewage disposal systems are covered by The General Binding Rules which we shall attempt to summarise briefly below.

If you have a cesspool you do not have to comply with the General Binding Rules or apply for a permit, but you must maintain it and make sure that it is regularly emptied by a registered waste carrier and that it does not leak or overflow. The Environment Agency or your local council can make you repair or replace your cesspool if it is in poor condition. If you install a new cesspool you must get building regulation approval, possibly also planning permission, and make sure that it has a minimum capacity of 18,000 litres for up to 2 regular users plus another 6,800 litres for each extra user.

If you have a septic tank or a small sewage treatment plant you must follow the General Binding Rules:

• The sewage must be domestic i.e from a lavatory, bathroom, shower or kitchen in a house, flat or business such as a pub, hotel or office. • It must not cause pollution.

There are other rules depending on whether you are releasing to the ground, for example in your back garden; or to a surface water such as a river or stream.

1). If you are releasing to the ground you must use a septic tank or a small treatment plant and a drainage field. You must apply for a permit if you discharge:

• To a well, borehole or other deep structure

• More than 2 cubic metres (2,000 litres) per day. You can download the ‘Daily discharge calculator for domestic properties (ODS, 5KB)’ from the internet but, as a rough guide, a 4 bedroomed house probably discharges around 1,000 litres per day.

• In a groundwater source protection zone (SPZ1). This may be an area around a commercial water supply or any area within 50 metres of a private water supply for human consumption – ask your neighbours if they have a spring, well or borehole and how far it is from your drainage field.

2). If you are releasing to a surface water, you must use a small sewage treatment plant and you must apply for a permit if you are discharging more that 5 cubic metres (5,000 litres) per day. There are further rules for discharging sewage to a surface water which should be read, and different rules apply to commercial properties including holiday lets. If in doubt contact the Environment Agency.

It is important to stress that all of the above applies to existing systems as well as to new or proposed systems. If you propose to install a new system you must get building regulation approval and you may need planning permission also.

If you are buying or selling a property with a septic tank that discharges directly to a watercourse, you should agree with the buyer or seller who will be responsible for the replacement or upgrade of the existing treatment system if that is necessary. You should agree this as a condition of sale.

The above notes are an attempt to outline the somewhat complicated matter of the legality of off-mains sewage disposal but any further questions should be addressed to the Environment Agency .