Septic Tanks vs Sewage Treatment: How to choose the best solution

By Dave Vincent, Kingspan Klargester’s operations director. Kingspan Klargester is one of the UK’s marketing-leading brand offering a full range of waste water solutions.

It’s estimated that around 10,000 people became self-builders last year – and numbers look set to grow swiftly over the next few years, following moves by the Government to make good its pledge within its election manifesto and double the number of self-build properties by 2020.

The majority of these new homes will be built off-mains, which means that services and waste water will need to be managed within the bounds of the property.

Dealing with waste (notably our own) of course is not always top of a self-builder’s agenda. As a nation, we are still hamstrung by embarrassment when it comes to discussions involving waste water, which is probably why the first solution is often, unfortunately, the only solution. And it’s a fairly safe bet that first solution suggested will be a septic tank.

Septic tanks are a typical private drainage solution and the most common off-mains solution typed into Google. For some homes, given the right ground conditions and the addition of a reed bed, they are indeed all that’s needed. But, despite their ubiquity across the UK, septic tanks are not always the best, or indeed legally the correct, solution for the property or its local environment.

Worryingly, reports of sewage pollution incidents are increasing, the vast majority of which are caused by inappropriate installations of septic tanks.

The legal responsibility for the waste lies with the property’s owner who, in the event of causing local pollution, is at risk of prosecution under The Public Health Act 1936, and facing the prospect of a heavy fine and a large clean-up bill.

Recent changes to off-mains legislation in England and Wales have made off-mains drainage installation a less cumbersome and bureaucratic process, but this should not be mistaken for permission to act irresponsibly, and personal liability remains unchanged.

Legal Requirements

As UK Building Regulations make clear, whenever possible houses must be connected to the main sewer, if necessary using a sewage pumping station. If a property cannot be connected to a mains sewer even with a pumping station, then waste water can be managed within the property’s boundaries typically using a septic tank or sewage treatment plant.

The first step, therefore, should be a site inspection by a suitably qualified expert. This would be arranged by either the architect or the home-owner.

Their advice is vital because choosing the wrong solution is a disaster waiting to happen – think over-flowing toilets and blocked drains.

But effective sewage treatment certainly need not be unpleasant. Top-end sewage treatment plants produce clear – and odourless – overflow that is environmentally acceptable. Owners can even discharge the resulting effluent directly into watercourses, without affecting the water quality or wildlife, dependent on appropriate location and outflow quantity and Regulator approval. What’s more, they don’t cost significantly more than septic tanks when you consider both installation and maintenance (see chart).

Septic tanks on the other hand do not treat waste, they simply produce soluble waste from solids which is then discharged and filtered through the ground, usually requiring a reed bed. In the wrong location they can contaminate groundwater – our drinking water essentially – as well as streams, ponds and rivers. If the ground conditions don’t allow efficient filtration, then sooner or later the owner will know about it.

As part of the initial site assessment the ground should be tested to check its potential suitability as a drainage field before a decision is made about which drainage option to go with. If the area has poorly draining soil or is subject to flooding, or if the water table is less than one metre below the septic tank outlet, then a treatment plant is the only feasible option.

EPP2 Explained

Once the decision has been taken to install private drainage the homeowner must apply for a permit to discharge into groundwater or surface water, under the Environmental Permitting (England and Wales) Regulations 2010 (known as EPP2), revised in January 2015 with the introduction of new binding rules.

Not everyone needs a discharge permit – under EPP2 owners of a small, domestic sewage tanks or plants may, under certain circumstances, be exempt. Instead they must comply with various conditions including:

• following the industry guidelines on the installation of septic tanks and sewage treatment plants
• incorporating manufacturers’ operational guidance, the British Standard BS6297 regarding soakaway design
• complying with British Water’s advice regarding de-sludging and servicing

Most importantly homeowners will only be exempt from requiring a discharge permit if they have also installed a product that has been performance-tested and certificated in line with European Standards (EN12566). If uncertified product is used, then they will have to apply for a permit.

While there is no longer any need to register a septic tank, keep records of maintenance or notify the Environment Agency if the discharge ceases, homeowners still need to make sure their system is working well and not causing pollution.

And if there is any doubt as to the suitability of the garden to filter waste water, then we recommend your clients take the prudent course, protecting themselves and their families by installing a sewage treatment plant.