When it comes to managing domestic wastewater, septic tanks often get a bad rap. Frequently portrayed as outdated or problematic, the reality is that septic tanks are a legal and viable alternative to sewage treatment plants. However, their installation and maintenance are governed by stringent regulations to ensure environmental safety and public health.
But before diving into the legal requirements and benefits, let’s get back to basics: What exactly is a septic tank, and how does it work? Understanding the fundamentals of septic tanks will provide a solid foundation for appreciating their role in effective wastewater management. Whether you’re a homeowner considering a septic system or simply curious about wastewater management options, we’ll break it all down for you.
1. What is a septic tank?
A septic tank is a settlement tank in which raw incoming sewage is retained long enough for suspended solids to settle out as sludges and for liquid organic matter to undergo anaerobic decomposition. All septic tanks must drain into an appropriate form of secondary treatment, most commonly a drainage field but other options include reedbeds.
2. How does it work?
As the sewage settles, a scum forms on top of the tank consisting of fats and soaps, and heavily organic matter settles at the bottom of the tank as sludge. The relatively clear liquid, called septic tank effluent, which lies in between the scum and sludge, leaves the tank and then undergoes secondary treatment in a drainage field.
It is therefore the drainage field which receives the septic effluent from the septic tank which does most of the treatment and it is the septic tank’s job to separate out the solids to stop the drainage field becoming blocked.
3. What type of septic tank do I have?
Over the decades septic tanks have evolved. The main types of septic tank are:
- Brick or block-built tank with 1-3 chambers. The tank may be rendered.
- Tank consisting of concrete rings with cast inlet and outlet dip pipes.
- Fiberglass ‘onion style’ tanks with various baffle arrangements.
- Plastic ‘submarine’ shaped tanks possibly fitted with an effluent filter.
4. What shouldn’t enter my septic tank?
It is easier to say what should enter a septic tank. If you live by the Three Ps – pee, paper and poo – you can’t go wrong. Items that should be avoided range from wet wipes, drain unblocker, dog poo, hair, sanitary items, tooth floss, ear buds, chemicals (weed killers, Jeyes Fluid, motor oil, antifreeze), medicines, paint, food waste, cooking oil, grease or fat ….
Products that should be limited and spread throughout the week include bleach and detergent.
Often a dead animal, special worms or enzymes may have been added to a septic tank to ‘improve’ the bacteria within the tank. These are unnecessary and unproven.
5. How often should I empty my septic tank?
An adequately sized septic tank will typically need to be emptied by a licenced waste carrier every 12 months, but timescales vary depending on use. For example, a large 6 bed house with only 2 people in residence may only need to be emptied every 3 years. Your WCI Service Engineer will be able to measure the sludge level annually and report when your system needs emptying.
It is important to empty your septic tank when required to ensure that solids within the septic tank don’t carry through into the drainage field or secondary treatment and cause a blockage risk which can cause the septic effluent to pool above ground or back up in the drains.
Unless you have a discharge pump, your septic tank won’t have any other servicing requirements other than a homeowner monthly inspection to ensure all is looking good!
6. What legislation governs the installation and use of septic tanks?
Environment Agency General Binding Rules
The new rules for small sewage discharges came into force on 1 January 2015. If you are the operator of a septic tank, you will not need a permit if you meet all the general binding rules that apply to your system. The rules can be a little complicated in particular when it comes to aged septic tanks and soakaways but please contact Naomi on 01984 623404 if you have any questions.
The rules are broken down into three categories:
- Existing discharges that started before 1 January 2015
- Existing discharges that started on or after 1 January 2015 but before 2 October 2023 or
- New discharges that started on or after 2 October 2023
More information can be found on the Government website at https://www.gov.uk/permits-you-need-for-septic-tanks and https://www.wci.co.uk/water-wastewater-engineers/permitting/ on the WCI website.
Building Regulations
Approved Document H (2015 edition) provides guidance on how to meet the Building Regulations in relation to drainage and waste disposal. Part H contains guidance on foul and surface water drainage, and therefore the placement, sizing and operation of septic tanks.
When installing a new or replacement septic tank the installation should be under a Building Control notice and be inspected and signed off by a Building Control Officer.
Planning permission
Whether planning permission is required for the installation or replacement of your septic tank and/ or drainage field often differs council to council. WCI often find that Planning is required within the National Parks but installation outside these areas when installation is simple and unobstructive often falls under permitted development rights. If in doubt, ask your Local Planning Authority.
Feeling overwhelmed and confused? WCI can help. WCI handles hundreds of Environmental Permit applications each year. we have an intimate understanding of the Environmental Permitting Regulations, General Binding Rules, Water and Groundwater Frameworks, Building Regulations and the National Planning Policy Framework.
7. Why has my septic tank been classed as illegal/ non-compliant?
You may be selling your property and had your septic tank inspected as part of a compliance survey. The survey may well have classed your tank as illegal (i.e. the system does not meet General binding Rules) for several reasons:
- The septic tank drains into a watercourse.
- The system discharges more than 2 m3/ day to ground via a secondary form of treatment and does not have an EA permit.
- The system is non-functional and causing pollution.
- The system is undersized for the application.
- There is an abstraction point for drinking water/ SPZ 1 within 50m of the dispersal field i.e. a borehole or well and the system does not have an EA permit.
Systems that do not meet the General Binding Rules will need work. Depending on the reason for their non-compliance this could be as easy as proving you have a wholesome water supply and applying for an EA permit, installing a drainage field, or replacing the septic tank with a mains connection or new sewage treatment plant.
8. Why would I upgrade my septic tank with a new package sewage treatment plant?
While there is some anaerobic decomposition that takes place in a septic tank, this bacterial action is not efficient enough to fully treat the sewage to a level which is safe to disperse into a watercourse. A septic tank alone will only reduce the strength of the incoming sewage by 30-50% under ideal conditions.
Package sewage treatment plants treat to a much higher standard and allow discharge into a watercourse or a smaller drainage field.
9. When would a septic tank be better suited to a site (rather than a package sewage treatment plant)?
If you have a low flow site that is seasonal, there may not be enough sewage produced on site to establish and maintain the bacterial population within a sewage treatment plant and treatment quality may be compromised. Equally where a site is off grid, and the land doesn’t have enough slope to install a non-electric sewage treatment plant – a septic tank may well be the best option.
The conclusion? While septic tanks remain a viable option and may be better suited to certain site conditions, it’s crucial that any installation adheres to current regulations to ensure legality and environmental safety. Still have questions? Give us a call on 01984 623404 or drop us an email enquiries@wci.co.uk and we’ll be happy to offer some guidance.
