A drainage field is used to dispose of dirty water from a septic tank type sewage treatment plant. It consists of a series of interconnecting underground pipes that are perforated to allow the dirty water to trickle out. They are laid in trenches at a suitable depth and buried in shingle. It is good practice to line the sides and the top of the shingle with a geo-textile membrane to help prevent plant roots gaining access to the pipes and therefore blocking them. The Environment agency will grant ‘Consent to Discharge’ and work should not commence before this permission has been granted. The size / capacity of the drainage field will be dependent on the size and number of properties using its’ facility and significantly the results of a porosity test which indicate the speed at which water drains (or not!) through the soil.
A soak-away essentially does the same job as a drainage field, however, this time it is dealing with clean water. The size of a soak-away is calculated by factoring in the results of a soil porosity test and the quantity of storm / treated water it is expected to deal with. The idea is to create an underground void, large enough into which a stated period of rainfall can drain therefore filling the void. When rainfall stops the water in the chamber slowly reduces as it percolates out into the surrounding soil. Traditionally large pits in the ground were excavated, filled with hardcore and covered with soil. The modern alternative uses a series of heavy duty plastic crates which provide 97% void (compared to 35%) as well as being structurally strong enough to be sited under roads and driveways.
Grosvenor Buildings and Landscapes are conversant with all elements relating to the design and construction of drainage fields and soak-aways as well as the applicable legislation to be conformed to. We are happy to engage with projects from conception via EA consent, construction to Building Control approval where appropriate.