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Having a correctly installed and functioning drainage field is an essential part of having a septic tank/ sewage treatment plant installed, this is just as vital as ensuring your tanks are appropriately maintained and emptied.

A major part of the design and construction of a drainage field is ensuring that sufficient aerobic contact is available between the effluent and the surrounding subsoils. If you have read one of our recent blogs about the important of oxygen (here), we noted that for a drainage field to work efficiently this should be no deeper than 1 metre below ground level.

We were recently contracted to look into a property which was experiencing issues with their existing drainage field and subsequently were looking at rectifying the problem by installing a new suitable drainage field.

The soakaway that had been installed on site to provide the secondary treatment of the domestic BioDisc was to a deep of 1.4 metre and was constructed using soakaway crates. This was causing a number of issues as a result of the necessary treatment not taking place.

Our proposal was to therefore install a new pump well inside the BioDisc to lift the effluent to a higher level within the proposed area. However, before any of this work could be undertaken the ground porosity on site needed to be checked.

Appropriate percolation tests were carried out in the installation area which confirmed the ground percolation value to be 24.4 which fell within the Building Control Part H guidelines of being between 12 and 100. Therefore, based on the unit already installed we proposed to install a drainage field to 40 metres long in 900mm wide trenches.

In order to allow the drainage field to be installed in line with BS EN 6297:2007 the effluent from the BioDisc needed to be lifted to an appropriate level to ensure that treatment was taking place within the subsoils. We therefore looked to install a submersible pump chamber within the BioDisc to lift the treated waste to the new drainage field.

Prior to the new drainage field an outlet sample point needed to be installed to slow the incoming flow allowing for dispersal into the drainage area to be at a controlled rate giving time for the water to soak away.

The new drainage field was installed comprising 110mm slotted pipework bedded and surrounded on a clean washed gravel and overlaid with a protective membrane, this was then backfilled and lightly compacted with excavated spoil.

If you want to ensure your system and drainage are installed to a compliant standard why not give us a call on 01388 537030