Homeseptic’s guidance on the rules, regulations and planning laws for Septic Soakaways, Drainage Fields and Rainwater Soakaways. 

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Soakaway Regulations

Regulations relating to foul drainage state that a soakaway is no longer an acceptable method of discharge. Instead, a Drainage Field must be used. For Rainwater, a soakaway is still acceptable. It must be located over five meters from a building and two and a half meters from a boundary. It must not come into contact with the water table and have sufficient storage capacity.

Soakaway regulation, rules and the legal environment can seem really complicated. We have tried in this article to answer some of the common questions our customers have around the regulation. We have also tried to provide enough information on the detail to help any experienced self-builders undertake their project.  If you do not find what you are looking for please give us a call. Even if we do not know the answer straight away someone will get back to you.

This page will deal with Foul Soakaways and their modern equivalent Drainage Fields.  If you are interested in Rainwater Soakaways please follow this link 

What is the difference between a Soakaway and a Drainage Field?

Traditionally a Soakaway is an undefined hole in the ground filled with rubble or more recently rainwater crates. A Drainage field is a series of perforated pipes laid in trenches 300mm to 900mm wide and backfilled with 20mm gravel. These trenches are between a maximum of 700mm deep. 

For a soakaway, liquid either from a spetic tank or rainwater would enter the backfilled hole and drain away. The two main reasons a soakaway is no longer acceptable for foul drainage are as follows.

  • A Soakaway does not necessarily allow for the treatment of effluent. This creates harmful pollution.
  • There often is little science in the exact size, depth and construction of a soakaway. This often leads to them not being fit for purpose.

A Drainage Field is a series of perforated pipe fitted to trenches backfilled with gravel. The width of the trenches are prescribed. The pipes are laid no deeper than 700mm into the ground. This ensures aerobic digestion can take place which allows the effluent to be treated. The minimum area covered by a drainage field is also prescribed by building regulations and ensures adequate drainage capacity. For more details on the design and construction please see this article Drainage Field, size calculation and design

The new laws for soakaways

As of the 1st of January 2015 a new set of rules came into effect for all owners of off mains drainage solutions. This included Septic Tanks, Sewage Treatment Plants and Cesspits.  The rules allow for exemptions for old tanks but not for how they discharge. The Rules are known as the General Binding Rules for small sewage discharges. This moved the legal responsibility for adherence firmly to the individual house owner. If you have an off mains drainage system then need to understand your responsibilities.  You also need to keep detailed records on what your system is and how it is maintained and serviced. 

  • If you discharge into the ground then you have to do so via a drainage field. If you do not then you will need to install one or apply to the environment agency for a permit to discharge.
  • Systems that discharge to a watercourse or drainage ditch were given until the 1st of January to conform. For those discharging to ground, the rules came into effect immediately.
  • The discharge to the ground section was not advertised by the Environment Agency. To the best of our knowledge, they are not actively checking. The main issue is when you come to sell your property, it will need to comply with the rules at this point. 

For a more detailed review of the new rules please see the following article: New Soakaway and Drainage field regulations

Do I already have a drainage field?

If you are asking this question then the answer is probably not. Most historic systems discharge to a soakaway, which is basically just a hole in the ground filled with rubble. This does not allow for the proper treatment of effluent which is why it is now illegal. If you are unsure we can come out free of charge and have a quick look.

What is Drainage Field?

A Drainage Field is a system of infiltration pipes placed in trenches and arranged so that effluent can be discharged to the ground. The field must be constructed in a certain way that allows for the effluent to be treated in the soil through aerobic digestion. This means it must be constructed in the top 700-800mm of the soil to ensure aerobic contact.

The Field must be big enough to treat and disperse the maximum amount of discharge the system will discharge to it. This is calculated by a formula that we will examine below in this article. The two main variables needed to calculate this are first, Vp, a measure of soil porosity gained from a percolation test. Secondly, the population of the household or population rating of the tank present in the system.

If a company comes to quote for a system, with a discharge to ground and do not require to undertake a percolation test then we would strongly advise you to discount their advice and quote. Without a percolation test, you cannot design a system that adheres to the Building Regulations or the General Binding Rules. Further, the system is unlikely to work properly.

Do I need planning permission for a soakaway?

If you are installing a replacement Soakaway then you will generally not require planning permission. If you are installing a new foul Soakaway or drainage field you should at least inform your local planning office. For all types of Soakaway building control guidelines are required to be followed. These are covered in the Building regulations 2010 section H Drainage and Waste Disposal.

The permission needed depends on the type of soakaway you are intending to build. For a septic soakaway, drain field or Sewerage treatment plant soakaway you will need planning permission. Unless it is a direct replacement.

For a Rainwater Soakaway, you should consult your local planning agency. The rules that govern Rainwater soakaways depend on the water capture area in m2. For those serving an area of 25m2 or less than Part H of Schedule 1 to the Building Regulations 2010 apply.

The Building Regulations dictate an order of priority for the rainwater runoff from buildings these are:

  • an adequate soakaway or another adequate filtration system, or if not reasonably practicable,
  • a watercourse, or where not reasonably practicable,
  • an appropriate sewer

 The key elements of the Part H rules are that the soakaway must by 5 meters from a building or road. The soakaway must be 2.5 meters from the boundary. The soakaway must not be in an area of unstable ground or where the lowest point of the soakaway meets the water table at any point of the year. The soakaway must not be near any other soakaway or drainage field, as this would compromise the absorption of the ground.

What are the regulations/ planning rules concerning Septic Soakaway or drainage field installation?

The most important rule concerning drainage fields is the new 2020 legislation that comes into force soon. Please see our guide.

The detailed rules can be found here and explain all the permits and rules you will need to adhere to in relation to a septic tank drainage field. For the general binding rules please see here.

The sewage must:

  • be domestic in nature – contact the Environment Agency if you’re not sure
  • not cause pollution – find out how to check for pollution

Rules on checking for Pollution: Septic Tank

You must check the area where you release sewage once a month for signs of pollution.

If you release sewage into the ground, check for:

  • sewage smells
  • signs that your sewage isn’t draining properly (eg pools of water in the area where you release sewage)

If you release sewage into the water, check for:

  • sewage smells
  • overflowing sludge
  • signs of white scum or foam on the water around the area where you release sewage

Contact the Environment Agency incident line if you see signs of pollution 0800 80 70 60. You should document your monthly checks.

In addition, You will need to apply for a permit if any of the following are relevant to your discharge.

  • to a well, borehole or other deep structure
  • more than 2 cubic meters (2,000 litres) per day
  • in a groundwater source protection zone (SPZ1)

If you intend to release to surface water you will need to use a sewerage treatment plant.

How deep should a soakaway be?

The Perforated pipe should be laid at a minimum depth of 200mm and a maximum depth of 700mm. This enables aerobic contact between the effluent and the drainage stone and soil particles. This leads to aerobic digestion and effectively treats the effluent. Each drainage trench can be up to 30 meters in length. The trenches can be between 300mm and 900mm.

How long should a Soakaway last?

If installed correctly a drainage field for effluent should last for around 25years as a minimum. A rainwater soakaway should last for far longer as long as the gutters are regularly cleaned and filtered. 

Building and regulations for Cesspit soakaways.

A Cesspit is a sealed unit that does not discharge anything. Therefore it does not need a soakaway. If you were to try and create a DIY drainage field you would almost certainly be breaking the law. Please see our Cesspit guide

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