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Septic System Vertical Section

It is important that people who use septic systems, understand the rudiments of how they work. It is really very simple and relies upon the scientific fact that human sewage takes from 18 - 21 days to degrade anaerobically [without air].


Vertical Section

A ‘sewage works’ usually enjoys the input of energy [electrical power] to spin the aerators that are necessary to mix in the atmospheric oxygen to catalyse the break-down of complex organic products – that modern man uses in his diet.


A septic system is anaerobic, [works without mixed-in air: - oxygen], and is a simple bio-digestor which is intended to convert raw sewage from solids to water and gas by the latent microbes, within the sewage and during the course of this process they degrade the solids to evermore molecular simpler products, and ultimately to  natural gasses and water.  The gasses escape up the sewer pipe to be dispersed harmlessly in the breeze via the vent above the roof, and the solids become water; ‘digested’ by the microbes [bacteria]. Water flows into the 2nd chamber by displacement, and ends up in the soakaway [either a pit or, better, a trench – as shown in the above sketch], where the partially treated water slowly filters through the bacterial slimes coating the ‘media’, crushed stone, bricks or old car tyres, and ultimately soaks away to the surrounding soil – the leach field.


Between the septic tank and the soakaway, there should be a lest one inspection chamber to facilitate rodding in the event of a blockage [normally roots or a collapsed sewer pipe – caused by accidental weight over the pipe - which should be below the surface by +- 100mm] . Between the house and the septic tank, every junction should be via an inspection chamber; especially the grease trap.


Always keep the inspection chambers into the tank cut back, clear of weeds & grass: clean; to avoid fouling the air-seal. It is a good idea to measure  obscured; [buried] inspection chambers from two corners of the house [they don’t move]. Keep the measurements in your electricity  metre box Then, when you need to find them; where the tapes cross, there is the inspection cover – it’s an old military trick, - [for recovering land mines], called: ‘resection’


In the drg [above] NGL indicates Natural Ground Level, and for practical purposes, the tops of the inspection covers of septic tank, and the lid of the soakaway should be at this level for ease of access: [you can build-up.the inspection chambers – limit to 3 courses of brickwork – a good idea as this gives 325mm thickness of soil to plant grass or herbs].


A trench soakaway is on ‘contour’ and has a considerably larger ‘seepage’ area than a pit- Think about it. Also folk dig them too deep. The permeable soil is the top layers, and compost plays it’s part.                                                                
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