Guide To Small Sewage Treatment Plants

A very brief guide to a technical subject and if working on a Sewage Treatment System up to date Regulation and Guidance should be consulted.

1. From the 1^st January 2015 new rules were introduced for sewage treatment plants. This advice relates to England.
2. Most domestic properties in England are connected to the mains sewer system operated by the local water companies. If a new property is built within 30 meters of a public sewer then it should, if possible, connect into the public sewer and not have its own private system.
3. Sewage treatment plants do not require an Environmental Permit from the Environment Agency if they comply with the relevant regulations and guidance.

Houses which cannot connect to the public sewer system will have to use a   sewage treatment plant. There are three types:

(a) Cesspit.

(b) Septic Tank.

(c) Small Domestic Sewage Treatment Plant.

3.1       Cesspit

A cesspit is a completely enclosed system from which nothing escapes and which requires regular emptying. The owner’s duty is to ensure that it does not leak and is emptied sufficiently often.

3.2       Septic Tank

(a)        A septic tank is a series of chambers into which the foul sewage flows and by natural processes is treated and relatively clean water flows out of it.

(b)       There are no moving parts and septic tanks must be emptied of sludge from time to time.

(c)        A septic tank is permitted to discharge up to 2 cubic meters of waste water a day which is the equivalent of approximately 9 people living in a property         without the need to obtain an Environmental Permit.

(d)       The water flowing out of a septic tank must flow into a Drainage Field which is a series of pipes with holes in them laid in trenches so that the water can percolate away.

(e)        Since the 1^st January 2015 water from a septic tank MUST NOT be allowed to enter a water course.   If an old septic tank does discharge into a water course then it must be upgraded so that it either discharges to a Drainage Field or is replaced by a Small Domestic Sewage Treatment Plant.

(f)        Care must be taken when a septic tank serves more than one property to ensure that the discharge is not more than 2 cubic meters of waste water a day. If it does exceed 2 cubic meters a day then an Environmental Permit will be required.

(g)       There are certain areas where there are greater controls over the use of septic tanks.  In particular zones where ground water is specially protected.

(h)       In some places the ground is not suitable for a Drainage Field because it is not sufficiently porous for the water to percolate away.  In these circumstances a Small Domestic Sewage Treatment Plant has to be used.

3.3       Small Domestic Sewage Treatment Plants

(a)        A Small Domestic Sewage Treatment Plant is a mechanical treatment plant powered by electricity that actually treats the foul sewage and discharges clean water which is to a much higher standard than from a septic tank.

(b)       Small Domestic Sewage Treatment Plants can discharge to a drainage field but it can also discharge to a water course providing there is a constant flow of water through the water course (but this is still allowed if the water course dries up in exceptionally dry weather).

They are permitted to discharge up to 5 cubic meters a day which is the equivalent of 31 persons living at the property or properties served by the plant.  Any discharge greater than that will require an Environmental Permit.

4. General

4.1       Any new installation of Small Domestic Sewage Treatment Plant must comply with Building Regulations and may require planning consent.  However, before 1983 there were no Building Standards in place so providing the system complies with current  Regulations nothing further is required.

4.2       Apart from the protection of ground water there are other areas where greater controls  are imposed and Environmental Permits are required such as:

(a)        Special Areas of Conservation.

(b)       Biological sites of Special Scientific Interest, freshwater pearl and mussel population.

(c)        Designated bathing water.

(d)       Protected shellfish water

(e)        Within 200 meters of an aquatic local nature reserve.

(f)        Within 500 meters of a chalk river or aquatic local wildlife site.

(g)       Other special areas.

It is the owner of the Sewage Treatment Plants responsibility to make sure it is in  good working order and therefore there has to be regular inspections for:

(a)        Leaks.

(b)       Cracks in the tank walls or pipes.

(c)        Blocked pipes.

(d)       Signs of effluent not draining properly.

(e)        Sewage smells etc.

If any of these items are found they must be remedied or the treatment system repaired or replaced.

4.3       If you sell your property the new owner is likely to need to give details of the Sewage Treatment Plant which should include:-

(a)        Its description of the system.

(b)       Location of the main parts of the treatment plant.

(c)        Details of the changes made to the treatment plant.

(d)       Details of how the treatment plant should be maintained and the maintenance manual if there is one.

(e)        Maintenance records if you have them.

Anyone carrying out maintenance of Small Domestic Sewage Treatment Plants must be competent.  Competent people include those on British Waters List of Credited Service Engineers.

4.4       When purchasing a house which has a sewage treatment plant with the aid of a mortgage the lender must be notified that the property is served by it (Para 6.8 of UK Finance Mortgage Lenders Handbook).

4.5       If a sewage treatment plant is defective it could cause contamination problems and could be:

(a)        A criminal offence.

(b)       Trigger a requirement to carry out remediation work on the contaminated land    and the system.

(c)        Be a nuisance to neighbours.

5. For more detailed information see:

(a)        Building Regulations 2010 – Drainage and Waste Disposal https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/442889/BR_PDF_AD_H_2015.pdf

(b)       General Binding Rules: Small Sewage Discharge to Surface Water

(c)        General Binding Rules: Small Sewage Discharge to the Ground

https://www.gov.uk/guidance/general-binding-rules-small-sewage-discharge-to-the-ground