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The Pits - Porosity testing for drainage


Before you can instal a septic tank you need to establish firstly if the natural land drainage is suitable to support the drainage and if so you then need to calculate the amount of soakaway required to enable the septic tank to work effectively. To do this you need to conduct what are called Porosity tests.

To carry out the porosity tests you firstly need to dig a number of pits accross the land, all precisely the same diameter and depth, each 1 metre square and deep with a further smaller square pit in the centre at the bottom. This all has to be dug by hand and once you get down to a meter deep you find that as you leaning into the pit to dig further down falling headlong into your freshly dug pit becomes a regular hazard. 

Once all of the pits are dug, you can start the tests. Over a set number of days a specific amount of water is poured into each pit and recordings are taken to measure the time the water takes to fall between various levels in each pit. In addition other factors such as weather conditions and temperature are also recorded and factored in and t
he measurements which are sent to the Surveyor who uses them to calculate the size and layout of soak away drainage trenched required to support a septic tank.



 Tom, Dick and Harry our three Porosity test pits.

Note the branches poking out of the pits to enable shrews and other unfortunate creatures that have fallen into the pits to crawl back out again.

Baords are placed over each pit to cover and protect them from added rain spoiling our tests and to try and stop animals falling in.   In this instance it looks like a Iestyn has actually managed to crawl out of one of the pits and is making a break for freedom