So, what are my sewage treatment options?

If you’re close enough to a main sewer then we’d always recommend that you try to join it and let United Utilities take care of your wastewater. In fact, the Government, through Defra and the Environment Agency, insist that if you’re within a certain distance – starting at 30m per house – that you join the main sewer unless there are very good reasons you can’t. We’ve a lot of experience with crude sewage package pump stations, and can organise the necessary design and documentation to apply to United Utilities to join their sewer network, and then install and maintain that solution. If you can’t reach a main sewer to go on-mains then you can either have a septic tank discharging to a drainage field or a package sewage treatment plant discharging to a drainage field or to a water course.

Unfortunately there’s no sewer anywhere near me so I’m going to have to be off-mains: remind me
of the differences between a septic tank and a package sewage treatment plant?

A septic tank is a watertight underground vessel that allows the separation of solids from liquids, and then stores the separated solids until they can be removed every so often by a tanker. The treatment process is almost completely physical, rather than biological: heavy solids sink, light solids float, and the liquid part (sewage is 99% water, albeit very dirty) leaves the septic tank for further treatment and disposal in the drainage field.

Hang on – a septic tank doesn’t really do very much then? I was told it “digested” the sewage.

A septic tank is just one part of a two part sewage treatment system and makes an important contribution to the effectiveness and long life of that system but as for “digesting” sewage, not really. There’s no oxygen in the contents of a septic tank, so any processes of digestion are anaerobic. Anaerobic breakdown processes are so slow in septic tanks in the UK because of our cool temperatures that they’re to all intents and purposes non-existent. But the septic tank’s job of retaining separated solids is essential.

How so?

The second part of the two part system is the drainage field downstream of the septic tank. A drainage field is a series of underground pipes that distribute the liquid from the septic tank over a wide enough area for it to soak into the ground at a slow enough rate for the naturally occurring physical, chemical and biological processes in the ground to completely clean the septic tank liquid. The drainage field is the expensive part of the system to replace and its life is finite so you want it to last as long as possible. Keeping solids out of it extends its life a lot.

Ah, you mean a herring-bone soakaway?

Drainage fields did used to be set out in a “herring-bone” pattern, or just as a long trench, but not any longer because they’ve been shown to work better as a continuous loop rather than having dead ends. As for “soakaway”, provided that you remember the purpose of the drainage field is both to treat the septic tank liquid as well as to get rid of it, and not just to get rid of it as quickly as possible, then yes, soakaway is ok.

My neighbour’s soakaway was put in by a friendly farmer; it’s a big hole filled with bricks. He said
that’d be fine. Is it?

Pit-type soakaways for sewage treatment fell out of favour in the 1950s because even then it was realised they didn’t do anything to treat the sewage. The still-contaminated wastewater pollutes the groundwater from which drinking water is often abstracted. Not disposing properly of sewage makes the price of drinking water higher because it has to be treated more thoroughly. Your neighbours won’t be able to see the pollution they’re causing but they’re definitely causing some. What’s more, the friendly farmer won’t have gone through Building Regulations so, if and when they come to sell their house they will have to upgrade the soakaway to the current standards, so they’ll have paid twice. If they’d done it properly in the first place they’d have paid less and would have had a clear conscience. The only winner is the “friendly” farmer.

And the package sewage treatment plant?

Broadly speaking a septic tank removes 20-40% of contaminants if it’s emptied often enough. That leaves the drainage field to remove the remaining 60-80%. A good package sewage treatment plant removes 90-95% of contaminants, so it replaces the functions of both the septic tank and the drainage field. It’s because of this very effective treatment that package sewage treatment plants can discharge the treated wastewater direct to a water course, such as a beck or a river. You said earlier that a package sewage treatment plant can discharge to a drainage field? That’s correct, and they can – not everyone has a stream nearby to which they can discharge. Using a package sewage treatment plant to discharge to a drainage field is an expensive option because you have the additional costs associated with the (usually) powered treatment plant over a passive septic tank plus the cost of the drainage field. But where land availability is limited it can make sense to use a treatment plant in order to fit in a smaller drainage field and/or to make that drainage field last as long as possible.

What would you recommend?

There’s no one-size-fits-all solution. It depends on if you’re building a new house with a new sewage treatment system, adding new bedrooms to an existing house and system, converting a barn to make a shared system, wanting to leave a shared system, replacing an existing failed septic tank and failed drainage field, how much land you own or have access to, how well it drains, how close a water course is, how big your project is… And then there are the regulations.

Regulations? That sounds ominous! What are they?

They’re not at all ominous if you know what you’re doing and why. They’re intended to make sure that what you and we do is correct and sustainable. First off, there are the “General Binding Rules” for small sewage discharges. This a list of 21
 conditions that need to be met if you are to discharge treated sewage (it all has to be treated in some way, obviously – no-one is allowed to discharge untreated sewage willy-nilly) into the environment.

Rather than list them one by one you can download them from our website as a pdf or find them on the gov.uk website


The “General Binding Rules are split into two sections: conditions 1-14 apply to all small sewage discharges regardless of how long they’ve been going on; conditions 15-21 apply to small sewage discharges that started on or after 1 January 2015. At the same time they’re split into two further sections: discharges made through a drainage field into the ground and therefore to groundwater, and discharges made directly through a pipe that drops into surface water like a beck, river, tarn or lake.

More Government guidance on discharges through a drainage field into the ground can be found


More Government guidance on discharges direct to surface water can be found here:


Most small sewage discharges are low-risk and will therefore meet the conditions of the General Binding Rules. Where there is a higher public health risk or a higher risk of damage to an environmentally sensitive or delicate area a permit may be needed. They’re not expensive for a domestic house or group of houses. We can arrange the preparation, submission and management of Environment Agency permit applications for you: like any technical/legal documentation, they’re are straightforward when you’re familiar with them.

Beyond environmental regulations there are Building Regulations and Planning, two separate and distinct areas. Building Regulations deal with the technical and quality aspects of the work, to ensure it function, durability and safety, whereas Planning answers the “How does this affect people living nearby?” question.

Whether or not Planning Permission is required can be a grey area and is most easily clarified by a call to the Local Authority Planning Department’s Duty Planner to discuss the proposed works. We can have that discussion on your behalf if you want us to. If Planning Permission is needed we can then put you in touch with an architect if you don’t know one already.

We’d always advise that Building Regulations approval is applied for because it provides independent documentary evidence that the work has been carried out to the required standards. If you don’t have a completion certificate for work carried out while you’ve owned the property it’s very likely that anyone buying you house in the future will ask you to prove that the work was carried out to the required standards. Given that everything is underground, that will undoubtedly cost far more than the original Building Regulations approval submission and certification would have cost. If you think that’s a risk worth taking, ask yourself if you’d buy a house from someone who couldn’t prove that the work they’d had done on your future home was carried out to the required standards of function, durability and safety? You might, but not without asking for a substantial price reduction to assume that risk, which is what your prospective purchaser will ask of you.

OK, you’ve convinced me that shortcuts lead to problems and that we need to do this properly. But you didn’t really answer my question on whether you’d recommend a septic tank and drainage field or a package sewage treatment plant. Come on, stop sitting on the fence!

If I was building a new house and I had enough of my own land and it drained well, I’d go for a septic tank and drainage field: the septic tank doesn’t need any power and a well-designed and properly constructed drainage field in good ground will be both effective and last a long time. The same would apply if I had a failing septic tank and failing drainage field.

If I didn’t have enough land or the land was marshy and drained poorly, a drainage field isn’t an option because it won’t work – how can even treated sewage effluent from a package sewage treatment plant soak away in already wet ground? The answer is it can’t, and it will eventually break the ground surface, smell and, worse still, present a health hazard, much in the same way as a failed drainage field. A package sewage treatment plant discharging to a water course is the answer here.

What about a septic tank discharging to a stream?

That’s a definite no. The Government, through DEFRA and DEFRA through the Environment Agency, made that illegal from 1 January 2020. If you have a septic tank that discharges to a stream, beck, river, lake, pond or any type of surface water, you need either to upgrade it to a package sewage treatment plant or route the discharge to a properly designed, well-constructed drainage field. You could try applying for a permit but the Environment Agency would only issue one in exceptional circumstances – and we haven’t come across any exceptional enough in the past 5 years since this rule was introduced.

Does that apply retrospectively to all discharges?

It does, so if you septic tank was installed in 1890 or 1990 and its outlet is piped to a water course you must upgrade it.

My other neighbour’s septic tank discharges to a soakaway with a high-level overflow to a stream –
the friendly farmer put it in when the soakaway failed years ago. Is that ok?

No. If there’s a pipe connecting the septic tank to surface water that discharge must either stopped or upgraded.

How would anyone find out?

It’s now common practice for solicitors to ask lots of questions about off-mains sewage treatment systems when houses are put on the market. You can either upgrade the system yourself and make it easier to sell your house, or accept a price reduction to cover the cost and inconvenience of the new owners having the work done. The latter usually costs more, and we’ve known house sales fall through because of problems with the drainage.

What if I’m not selling my house?

Then it depends on your conscience and how much you value your environment. What would you think of your neighbours upstream of you discharging untreated sewage into the stream that runs through your garden, or into the river near the footpath where you walk and your children splash around, or into the lake where you all swim?

Yuk, that’s a fair point and something I hadn’t thought of. It sounds like you know your stuff. What
next, then?

It’s our job to give you the fullest, best and technically correct advice for your situation. Get in touch with us for a friendly initial chat or to arrange a free-of-charge, no obligation site visit and quote.



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