Septic tank regulations - the whats, whys and wherefores.

Regulatory | By Sam Warren

I’ll admit it, I started this article on septic tank regulations reluctantly.

The prospect of trawling through pages upon pages of regulations and legislation relating to septic tanks and drainage fields was a little off putting. There’s one way to lose hours of my life that I’ll never get back, I thought.

But then I realised that if this all seems daunting to me, it may well seem the same to plenty of other people who need to try to understand it. So maybe trying to simplify it all into plain English might be helpful.

As part of my public service, therefore, I’ve read each of the documents in detail (you can buy me a drink later) so that you don’t have to. So, if you want to know the difference between your Building Regulations, your General Binding Rules and your PPG4, then read on.

Unfortunately it’s way beyond my creative writing abilities to make this an interesting read, so the aim will just have to be to make it informative instead.

What’s the worst that can happen?

No one wants to fall foul of legislation, least of all when it comes to septic tank regulations. If your drainage system causes pollution, you can get prosecuted with a hefty fine. If that doesn’t scare you into swotting up on the relevant legislation, did you know that you could even end up spending time at Her Majesty’s pleasure for failing to rectify a problem?

Now, serving time for a dodgy septic tank wouldn’t make much of a tale for the grandchildren, so let’s run through all the different legislation which might apply to avoid that happening in the first place.

  1. DEFRA General binding rules for small sewage discharges

These were produced by DEFRA (Department for Environment, Food and Rural Affairs) and became law effective from January 2015. It’s mainly focused on preventing pollution of the environment, and covers such things as where a system can be located, and how the waste can be discharged.

It affects both existing septic tanks and sewage treatment plants, as well as any new installations after January 2015. The full document can be found here. If you are having work done to an existing tank then you need to look at the chart on the first page. For new installations, it’s the chart on page 3.

The document has two columns to highlight the applicable law depending on how your tank discharges. It separates it out into 'Discharge to surface water' and 'Discharge to ground'. I don’t think these are particularly clear to the lay person, so to explain:

Discharge to surface water: this typically means a solid pipe running straight from your sewage treatment plant to a watercourse such as a stream or ditch (you can’t have a septic tank discharging straight to a watercourse, as it doesn’t provide enough treatment to the waste). This watercourse must be free flowing.

Discharge to ground: this means a drainage field (also known as a soakaway system) which runs from the septic tank. It is a perforated network of pipes which provides a secondary form of treatment to the waste, making it safe to percolate through the sub-soil without causing any pollution.

Not adhering to these guidelines really could land you in the contents of your septic tank, so make sure you are working with experts* in repairing or installing a septic tank or sewage treatment plant.

  1. Building Regulations 2010 – Drainage and waste disposal

This is an important document relating to the installation of septic tanks and other off mains drainage systems. Here is where you can find the full document – it’s the H2 section that is relevant here.

It sets out what you, as the owner, are legally responsible for ensuring – namely that the system doesn’t 'cause pollution, a health hazard or a nuisance'. Local Authorities have the powers to test any off mains system that they think is causing a problem, and they can take action if they find any issues.

Before we get into the detail, I need to make a quick point about the use of the phrase 'septic tank'. At UKDP, we often find property owners referring to their septic tank, when actually they have a cesspit or a sewage treatment plant.

There is a difference you see, so before we get started if you’d like to know more about what type of drainage system you might have, check out our video here to give you a guide:

Whilst septic tanks are indeed the most common type of tank, we’ll also cover off cesspits and sewage treatment plants just in case (we wouldn't want them to feel left out).

What’s it all about?

This Building regulations document, produced by the Government, outlines the requirements for septic tanks, drainage fields, cesspits (or cesspools – it’s the same thing) and sewage treatment plants. The main aim is to make sure that they are:

  • Located in the right place
  • Sufficient in size for the property (or properties) connected to them
  • Not going to pollute local water courses
  • Appropriate for the local ground conditions – this is particularly important for drainage fields (or soakaway systems)
  • Emptied and maintained regularly to ensure that they can function properly

If you are installing a new septic tank, sewage treatment plant or cesspool, you will need to contact your local Council to apply for Building Control approval. Similarly, undertaking works to your existing drainage system, particularly if you are looking to change the system somehow, also needs approval. This is because drainage is classed as a 'controlled service or function' which is why Building Control need to be involved.

Here is an outline of some of the key areas that the document outlines.

Septic tanks

  • Septic tanks should only be used in conjunction with a secondary form of treatment such as a drainage field (you can’t allow your septic tank to discharge straight to a local watercourse or ditch)
  • They should be sited at least 7 metres from any habitable parts of buildings
  • Where the septic tank is to be emptied by a tanker, it should be located within 30 metres of a vehicle access point. This works on the basis that the septic tank is no more than 3 metres below the level of the vehicle access. If it is, it would need to be nearer than 30 metres to allow for it.
  • The document also states that there should be a clear route for the hose and that the contents should not be taken through a dwelling or place of work…..but I’m hoping most people wouldn’t need that one pointing out!
  • Septic tanks should have a capacity below the level of inlet of at least 2,700 litres for up to 4 users. This should be increased by 180 litres for each additional user.
  • Ventilation of the nasty niffs coming from the septic tank should be kept away from buildings

Drainage fields

In our experience, drainage fields are by far the most common type of secondary treatment to work in conjunction with a septic tank, although the document also outlines the regulations relating to drainage mounds and reed beds. To keep this as simple as possible, I’ll just look at the drainage field section – feel free to delve into the full document if you want to know more about the other two.

  • A drainage field should be located at least 10 metres from any watercourse (e.g. a stream or pond) or permeable drain and at least 50 metres from the point at which a water supply is taken
  • A drainage field should be at least 15 metres from any building and should also be far enough away from any other drainage field or soakaway so that they don’t affect the overall soakage capacity of the ground
  • No access roads, driveways or paved areas should be located with the area of the drainage field

The document goes into a lot of detail about what the ground conditions should be like, and how to test these through trial holes and percolation tests. I won’t even try to summarise this section for you, since it’s complicated and detailed for a reason – it’s not something you want to get wrong.

If you need a percolation test to be undertaken, or if you’d like to know more about how it works, call our team on 01628 788600.

Sewage treatment plants (or 'packaged treatment works' as they are referred to in the document)

This one is relatively straightforward (phew).

The discharge from the treatment plant should be at least 10 metres away from any watercourses or other buildings. If the plant needs electricity to operate, it should be able to function without power for up to 6 hours, or have an power supply that can’t be interrupted.

Cesspools (or cesspits)

Generally speaking, a cesspool (which is just a holding tank for the waste from your property, providing no treatment) is seen as a last resort as far as a drainage system for your property goes.

The basics from this document relating to cesspools are:

  • They should be located at least 7 metres from any habitable parts of buildings
  • They should be sited within 30 metres of a vehicle access point
  • The capacity below the level of the inlet should be at least 18,000 litres for 2 users. This should be increased by 6,800 litres for each additional user.
  • They should have no openings apart from the pipe coming in, access for emptying and ventilation

So that’s a summary of the Building Regulations document. That, and the General Binding Rules are the two main ones you need to be aware of, but don’t get your coat as we’re not done yet. There are a couple more documents which also relate to septic tanks and other off mains drainage systems.

3. Environment Agency PPG4 (Pollution Prevention Guidelines)

I won’t go into too much detail about this one, because as far as these types of documents go, this one is relatively easy to navigate. Take a look at the full document here. It has a nice flowchart and everything. These are generally best practice guidelines, and the General Binding Rules outlined above turned some of it into law, but as it is a relatively helpful document it's still worth a look.

In short, the PPG4 helps you to work out which type of drainage system is suitable for your property. There are lots of considerations as to what would work – and also what the Environment Agency (EA) will or will not allow. It also lets you know when you need to gain consent from the EA, as you often need to get permission before installing or changing an off mains drainage system.

The document goes into some detail about percolation tests and drainage field size. Percolation tests assess the porosity of the soil at your property, and it is this that tells you if a drainage field or soakaway is suitable, and if it is suitable it tells you what size it needs to be.

There is a very detailed and excruciatingly long British Standard document relating to exactly how percolation tests should be undertaken. Even the name of the document will put you off reading it – BS6297:2007+A1:2008. My advice? Unless you are very technically minded, leave percolation tests and all the calculations that come with them to the experts.

(Did I mention that at UKDP we’re experts in percolation tests? I didn’t?)

4. Flows and Loads

We’re nearly done, I promise. This is the last one.

This document outlines the size that any septic tank, sewage treatment plant or cesspit needs to be in order to adequately serve the property (or properties) that will connect to it.

Each type of tank comes in various different sizes, and the correct tank size is determined by the number of bedrooms the property has.

The link to the full document is here (it's the 6th link down), but the most useful page is number 4. If you’re installing a new tank and need some advice, just call our team on 01628 788600.

Ok, so it won’t win any literature awards, but hopefully this article has given you an outline of the legislation and regulations relating to septic tanks, sewage treatment plants and cesspools. Here at UKDP, our technical team spend every day working with these documents (the lucky devils), so call us today on 01628 788600 or contact us here if you need any help.

*when I say 'experts I mean UKDP of course. No need to call anyone else. We really do know what we’re on about and we can help with any septic tank repair or installation.

0800 028 9903