The use of soakaway crates for the dispersal of sewage effluent is talked about a lot on the internet and youtube. This article aims to clear up any miss information, providing you the facts around the use of soakaway crates.
Soakaway crates, sometimes called stormwater crates, are plastic “crates” that are installed in the ground and designed to create a “void” in the ground, allowing water to enter the crates and then slowly percolate into the ground.
A soakaway tunnel is essentially the same as a soakaway crate, and therefore for the purpose of this article, when I refer to crates, I also mean tunnels.
An infiltration system is a generic term used for allowing water to enter the ground. Both soakaway crates, and a drainage field are technically infiltration systems
A soakaway is used for rainwater or stormwater, a drainage field is used for wastewater (cleaned sewage, or effluent. A drainage field provides biological treatment of the water, treating it prior to entering the ground. A soakaway does not provide biological treatment.
The construction of a drainage field is very different to the construction of a soakaway
To adhere to general binding rules, you must design any infiltration system to British standards. The British standard for sewage drainage is BS6297:2007+A1:2008 – essentially, percolation tests must be carried out and a drainage field constructed.
I've often seen this done by contractors, with the argument that the treatment plant is producing water that can be discharged to a ditch, and therefore should be ok to go into a soakaway. Whilst this is an argument we can have until the cows come home; we must look to the regulations.
Firstly, General binding rules state that the “system” (which is the treatment plant and infiltration system), must beet British standards at the time of installation, and British standards for wastewater dicharges into ground do not say that a soakaway is acceptable. Therefore the use of a soakaway would be against general binding rules.
Anything that does not adhere to general binding rules must be permitted by the Environment Agency (you will need a permit).
The reason for it requiring a permit is so that the EA can make a decision as to the possible impact on groundwater. Their groundwater team will look at the application and most certainly ask for evidence that proper percolation tests have been carried out and ask for justification as to why you are not designing as per British standards.
It is highly unlikely the Environment agency will allow this as there is little to no biological treatment happening within the overall sewage system. (by system, I am referring to the septic tank & infiltration system).
You might use crates over a drainage field in the event that there was very limited room for a drainage field. However, as I have already alluded to, you will require a permit from the environment agency to do so.