vivienz Posted January 16, 2018 Share Posted January 16, 2018 Our site has no mains drainage and the existing bungalow has an old septic tank that will need to be dug out and removed. Are there any particular requirements around this? I have no idea how old it is or of what construction, other than it's possibly in the region of 40 years old and has no electrics or pumps involved. Link to comment Share on other sites More sharing options...
ProDave Posted January 16, 2018 Share Posted January 16, 2018 Unless you are needing to put a new treatment plant in exactly the same place, I would just get it pumped out (deslusged) and fill it in with something. 2 Link to comment Share on other sites More sharing options...
vivienz Posted January 16, 2018 Author Share Posted January 16, 2018 Great, thanks Dave. A neat solution. Link to comment Share on other sites More sharing options...
Barney12 Posted January 16, 2018 Share Posted January 16, 2018 43 minutes ago, ProDave said: Unless you are needing to put a new treatment plant in exactly the same place, I would just get it pumped out (deslusged) and fill it in with something. This is exactly what we did. Pumped it out and then just smashed in the sides and covered it over. Ours was not too full, must have been something to do with the numerous cracks in the side walls Link to comment Share on other sites More sharing options...
Onoff Posted January 17, 2018 Share Posted January 17, 2018 Out of interest how long does the ground around one of these take to "recover" once it's gone? We have one, still in use, all clay piping running to it. All I know is the top is a curved brick structure as was evident when I had the digger scrape some top soil off as a tentative investigation to find it / the manhole. Not even sure what area mine covers. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted January 17, 2018 Share Posted January 17, 2018 1 hour ago, Onoff said: Out of interest how long does the ground around one of these take to "recover" once it's gone? We have one, still in use, all clay piping running to it. All I know is the top is a curved brick structure as was evident when I had the digger scrape some top soil off as a tentative investigation to find it / the manhole. Not even sure what area mine covers. Quite a long time unless you get some fresh soil/rubble in the hole that re-establishes the natural balance of aerobic/anaerobic bacteria. The main problem with septic tanks is that they operate anaerobically, and their effluent has an extremely high biochemical oxygen demand. After around 10 to 15 years of use, the area around any effluent drains/leaks will become highly anaerobic, killing off all the aerobic bacteria that live in the upper few feet of soil. The give away sign is often that this soil looks black. Soil at depth is usually anaerobic anyway, hence the unusual smells you often get when digging deep trenches and releasing some of the gases that these anaerobic bacteria release. Backfilling old tanks with rubble and a layer of soil usually works pretty well, and I suspect the natural balance is restored within a few years. The main risk factor is that anaerobic bacteria are the most common form of bacteria that cause disease in humans. To put that into balance, our bodies host billions of the things, so generally the risk is low. However, almost all problems we have with antibiotic resistant bacteria come from anaerobes that have developed resistance, from farmed animal antibiotic use, from human antibiotic use or the use of antibacterial cleaning agents in the home. Clearly a septic tank is going to be a very good breeding ground for a wide range of anaerobic bacteria than may well already be resistant to antimicrobial treatments and some of which may be dangerous to humans; it's one reason we call them "septic" tanks. The sure fire way to disable or kill the majority of anaerobes is to subject them to oxidation, hence the reason that modern treatment plants run aerobically and oxygenate the effluent. To some extent, draining and filling an old tank with rubble and covering it with fresh soil that contains a lot of aerobic bacteria will help to reduce the population of harmful anaerobes around the area of the tank. Link to comment Share on other sites More sharing options...
vivienz Posted January 17, 2018 Author Share Posted January 17, 2018 Hmm. The site of the existing septic tank will be under the footprint of the new house. Aside from making things rather smelly for the MBC crew, is it still a good idea to just fill it in? If it gets completely dug out, does the spoil need to be disposed of in a particular way? Link to comment Share on other sites More sharing options...
ProDave Posted January 17, 2018 Share Posted January 17, 2018 I would run that past the structural engineer. Take the lid off and fill with concrete or just compacted hardccore in layers thus not disturbing any more ground than you have to? Link to comment Share on other sites More sharing options...
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