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in off mains drainage systems

A septic tank separates the contents and, after the dense matter has sunk to the bottom and the fat, oil and grease has floated to the top, the separated waste water left in the middle exits the septic tank into a drainage field. The drainage field is where the wastewater gets treated. In a sewage treatment plant all the treatment occurs inside the sewage treatment plant meaning the treated effluent that exits it just needs to be dispersed, it doesn’t need to be treated.

A septic tank can only discharge to a drainage field unless there is a specific permit from the environmental regulator stating it can disperse to an alternative location, but this is rare. A sewage treatment plant can discharge to a drainage field, a surface water (ditch, stream etc), a soakaway chamber, a bore hole soakaway or a drainage mound.

There are so many variables it’s impossible to give an accurate price without carrying out a site visit first. The price will be impacted by what the access is like, how deep the current drainage is, or will be, in the case of a new build property, and what the ground is like.

A cesspit is a perfectly legal drainage asset, but it’s a last resort. To have a cesspit sanctioned by the local building control officer, you will need to demonstrate that all options have been explored first. This is because if there was ever a breach in the cesspit walls or base, there will be a large volume of untreated waste and waste water going straight to ground. It could cause a pollution event. Cesspits are very big, they’re expensive to install and, as they require emptying every 6-8 weeks, they’re expensive to run.

The Small Sewage Discharge General Binding Rules, to give it the full title, is a regulatory reform introduced by DEFRA in England in January 2015 and policed by the Environment Agency. The General Binding Rules state what wastewater system can be used and where it can discharge. It’s an excellent safety net for anyone with an off mains drainage system to double check that the system is compliant, and if its not, what you need to do to make it compliant.

Firstly, the Solicitors will be exchanging questions and answers on this subject, but without fail, the best advice is to have your own survey carried out to ensure you know what the system is, where it is, is it performing, is it compliant, is it in a good condition and is any work required. The costs for any necessary works to make a system complaint should form part of the condition of sale. It is therefore imperative a survey is carried out and before exchange.

This is a specific test to establish if the ground is suitable to install a drainage field. For foul systems there is a specific document called the BS6297 which explains how the test should be carried out, how to calculate the results and how to design a drainage field. For surface/rain water soakaways there is a document called the BRE365 which explains the test procedure. It’s important to appreciate these tests are different and under no circumstance can a drainage field or a soakaway serve both a foul water and surface/rain water, they must be kept separate.

There is no electric and no moving parts in a septic tank so the annual cost should be no more than an empty from a local vacuum tanker company, and dependant where you live in the UK, this will vary from £150-350.