Septic Tanks Discharging to Surface Water.

Original Article
August 10th, 2019


If a septic tank discharges effluent directly to surface water, it will need to be upgraded or replaced by 1 January 2020 or when the owners of the septic tank sell the property, whichever is sooner. This is the result of legal requirements that were issued by the Environment Agency in 2015, under the general binding rules. In this article we summarise how septic tanks work and focus on the rule relating to septic tanks discharging directly to surface water and consider what surveyors should be aware of.

How do septic tanks work?
As defined in Part H of the Building Regulations, a septic tank ‘provides suitable conditions for the settlement, storage and partial decomposition of solids which need to be removed at regular intervals.’

Septic tanks are made up of underground chambers with air vents and a system of pipes. Some septic tanks have one chamber and can be shaped like an onion, others have two chambers. For the purposes of this description, we will describe how a two-chamber system operates.

The first chamber collects new effluent – heavy solids sink to the bottom and lighter waste such as grease floats to the surface. The surface waste is in contact with the air which results in aerobic bacterial breakdown resulting in a crust forming at the top. The air vent allows sewer gases to dissipate to the outside air and lets air in (the more air in, the better).

The pipes within the chamber work by ensuring the ‘crust’ or surface layer is undisturbed. As the contents are not in contact with the air, anaerobic bacteria break down the waste resulting in a dense sludge forming at the bottom. In the past, it was common for an animal carcass to be added to provide extra bacteria.

Another set of pipes connecting the first chamber to the second chamber allow any excess to flow into the second chamber. It is here where the finer solids are broken down further by anaerobic bacteria, resulting in a partially treated liquid outflow.

Up to this point, the waste has only received a basic level of treatment and, as per the new rules, further treatment is needed before the waste can be discharged either to the ground or to surface water such as a stream, river or ditch.
For the purposes of this article, we will only be referring to discharges to surface water.

Figure 1 – diagram of a two-chamber septic tank

Sewage treatment plants
A small sewage treatment plant or ‘package treatment plant’ treats the waste so it is clean enough to be discharged to surface water (or to ground). The treatment process collects waste in a similar way to septic tanks but is more advanced and often uses electricity to run internal mechanical parts (unlike a septic tank) although bio rock systems can provide secondary treatment without using electricity or mechanical parts.

With a mechanically operated plant, the solids and liquids separate in the primary chamber. The liquid then passes into the biozone and it can be biologically treated using a filter bed, rotating disc media or air injection, for example. By introducing air, aerobic bacteria break down the waste. This is more effective than septic tanks alone and creates a cleaner liquid, allowing it to be discharged into a water course (or to ground).

Figure 2 – diagram of a sewage treatment plant

What are ‘general binding rules’?
General binding rules (GBRs) are legally binding requirements in regulations that set the minimum standards or conditions which apply. The general binding rules for small sewage discharges set out the conditions that need to meet in order to be used without an environmental permit and they have been specified by the Environment Agency. The full set of rules for septic tanks or small sewage treatment plants discharging to surface water can be found here:

What’s the correct treatment system?
The GBRs state that discharging effluent directly from a septic tank to surface water is not allowed. The reason for this is to reduce the amount of pollution entering surface water throughout the UK, and ultimately to reduce the pollution entering our bathing beaches.

 “You must use a small sewage treatment plant to treat the sewage if you’re discharging to a surface water such as a river or stream. A small sewage treatment plant (also known as a package treatment plant) uses mechanical parts to treat the liquid so it’s clean enough to go into a river or stream.

Discharges from septic tanks directly to a surface water are not allowed under the general binding rules.”

If a septic tank does discharge directly to surface water, the responsible person will need to replace or upgrade the system by 1 January 2020 or earlier if the Environment Agency establish the septic tank is causing pollution.

The rules also explain: “Where properties with septic tanks that discharge directly to surface water are sold before 1 January 2020, responsibility for the replacement or upgrade of the existing treatment system should be addressed between the buyer and seller as a condition of sale.”

If the discharge is directly to surface water, there are several possible solutions: 

  • Replace or upgrade the system with a sewage treatment plant 
  • Connect to a mains sewer if possible  
  • Install a drainage field/infiltration system and then the discharge will be to ground (and therefore the general binding rules relating to discharges to ground will apply) 

The homeowner can also apply for a permit if they do not meet the general binding rules; however, permits are only granted in exceptional circumstances. The Environment Agency can provide further information. If upgrading the system by installing a septic tank conversion unit, homeowners should contact the Environment Agency to ensure it meets the required standard and a permit will still be necessary.  

New or existing?
The GBRs explain that if the system was installed and discharging on or after 1 January 2015, the discharge is ‘new’. Any system installed before this date is ‘existing’. However, a change in discharge from surface to ground or vice versa would be considered a new discharge. In addition, if a new drainage pipe is installed which discharges more than 10 metres away from the existing one or which goes to a different surface water, it would also be considered a new discharge.
If the system was installed on or after 1 January 2015, then planning permission and building regulation approval is required. If permission and approval was not granted, the responsible person must apply retrospectively for both.

You should note there are additional rules for new treatment systems installed and in use on or after 1 January 2015. 

Building Regulations
The Building Regulations 2010, Drainage and Waste Disposal, Approved Document H includes practical guidance with respect to the requirements of Schedule 1 and Regulation 7 of the Building Regulations 2010 (SI 2010/2214) for England and Wales. Section H2 includes guidance on treatment systems including septic tanks, infiltration systems and packaged treatment works. Whilst they have not been changed following the general binding rules published in 2015, new discharges must comply with building regulations as well as the general binding rules.

The surveyor’s role
Chartered Surveyor, Mike Ridgell MSc MRICS, advises how he reports on private drainage:

“If you come across a private drainage system at an inspection, you should conduct a simple risk assessment to try and establish what system is in place and to establish if there is a treatment plant present or not.

If it is a septic tank, you should consider whether it is old or new, the type of system you’re looking at, and if it is shared and the components are within the property boundaries and whether there is access to empty it.   

Check the chamber cover of what is, in effect, a deep pit and establish if there is a screwed down or safe cover to stop a person falling in.

Inspect the area to establish if discharge is to either water or ground. Is there a stream or ditch nearby? It’s not as common for septic tanks to be connected to water in my area, but they can be. 

You should explain in the report the likely component parts and ask that the legal adviser confirm the legal position. You should also reiterate that the survey is non-invasive and you can only conduct a visual inspection. As you are unable to inspect a buried drainage system, it is likely that you will recommend further investigation which, for a Home Condition Survey, justifies a Condition Rating 3.

You can enquire about the drainage system with the current vendor, although you should not rely solely on this information when informing your client.”

Case Study
Last year, Sava handled a complaint about a Home Condition Survey on behalf of one of our members. The complaint was made because a septic tank was found to be draining directly to a stream at the bottom of the garden. The clients were only made aware of this when they requested a quote from a contractor to extend the drainage system to allow an extra toilet to be installed.

The surveyor did report in the Home Condition Survey about the discharge by explaining that they could not definitively confirm the function of a pipe near the stream. The surveyor confirmed the toilets were flushed and observations were made and there was no indication that any discharge was entering the stream via the pipe or elsewhere. The surveyor also obtained an old Exemption Certificate for the address from a government sponsored website which stated: “Existing discharge to ground of two cubic metres or less”, further suggesting that there was a discharge to ground and not to surface water. The vendor also confirmed to the surveyor that the pipe near the stream was not connected to the septic tank. Whilst this would not be relied upon alone, this statement, along with the description on the certificate and the lack of water discharging from the pipe when the toilet was flushed several times, did not give any cause for concern. Nonetheless, the surveyor did confirm that a definitive answer could not be given.

When the complaint was escalated to Sava, we responded to the complainant with our findings, concluding that whilst we sympathise with the situation, the surveyor had not been negligent and reported on the findings within the remit of a non-invasive survey. We also pointed out the requirements of the homeowner as described in the general binding rules which explain that from June 2015, if a homeowner is selling their property, they must tell the new operator (the owner or person responsible for the septic tank or small sewage treatment plant) in writing that a sewage discharge is in place. They should include:

•             a description of the treatment plant and drainage system

•             the location of the main parts of the treatment plant, drainage system and discharge point

•             details of any changes made to the treatment plant and drainage system

•             details of how the treatment plant should be maintained, and the maintenance manual if available

•             maintenance records if they have them

The complainant responded to say they would discuss the matter further with their solicitors and we did not hear any more. This case shows that, even when a surveyor is diligent, complaints can still arise, so it is important to ensure you have inspected and reported appropriately in order to defend yourself if a problem arises for the client. However, as described above, the seller has a legal obligation to confirm to the buyer the details regarding the drainage system and the conveyancer acting for the client also has a duty of care to raise sufficient enquiries to the seller regarding the private drainage.

Other information
Our factsheet on private drainage includes more detail on how private drainage systems work and the maintenance required, which you can download here.