The Difference Between Drainage Fields & Soakaways

18 Feb 2021


The difference between drainage fields and soakaways

We often get asked about options for wastewater disposal via the ground. Many builders, architects, ground workers and consumers understand they need to use a septic tank or treatment plant to clean the wastewater from their house. However, many don’t have a firm grip on the legislation surrounding discharging that cleaned water to the environment, especially when it comes to discharging it to ground.

We have regular conversations with people who were going to install a soakaway after a septic tank rather than a drainage field. We also speak to many people that don’t understand the differences between a soakaway and drainage field, and understandably so, it is not well documented.

In this article, I will aim to help you understand the differences between a drainage field and a soak away, and why it is important to use them correctly.

What is a drainage field?

A drainage field is a loop of solid slotted pipes in the ground, surrounded in, and on a bed of gravel. The aim of the drainage field is to allow wastewater to trickle down through the gravel so that bacteria will form on the gravel. This helps to remove contaminants from the water prior to it entering the ground.

What is a soakaway?

A soakaway is used for allowing rainwater to percolate through the ground. It is normally constructed by installing “soakaway crates” in the ground, these crates allow a large volume of water to enter and slowly drain away. A soakaway should only be used for rain and surface water.

What is the difference between a drainage field and a soakaway?

To summarise the difference between the two, a drainage field is designed to add additional treatment to the water. Whereas a soakaway is designed to store a large volume of water allowing time for it to release into the ground (i. e. in a heavy downpour).

It is common for people to think that a soakaway can be used for wastewater (even if it has been treated by a sewage treatment plant first. However, this is incorrect. British Water have recently produced a new guide for discharging wastewater to the ground. The guide is intended for use by specialists, architects, builders, ground workers and anyone planning on discharging water to the environment. It provides best practice for discharging wastewater

The guide can be downloaded here.

Another useful resource for anyone planning to discharge treated water to the ground is Building Regs Part H. It details exactly how to size a drainage field, and can be downloaded here.

At Owls Hall Environmental we pride ourselves in offering the most accurate advice possible.  You can view our sewage treatment range here.  If you have any questions around which sewage treatment product to install, our team is always happy to advise you. Call us today.

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