Clogged leach field in a septic task system

[RustyFiesta]

My relatives live in a very rural area, and have a septic tank that they share with their neighbours, like this:

[3 houses]->[2 chamber septic tank]->[settling tank]->[leach field]

I don't know if I've used the correct words. Rainwater from the houses also runs directly in the "settling tank", which is just a concrete-block lined hole in the corner of their field. The houses are uphill of the "leach field", which helps.

The "leach field" appears to consist an unknown amount of perforated

100mm pipe running underneath their field. The perforated pipe seems to be totally clogged up with something - maybe silt, maybe roots of numerous trees planted since the leach field was installed.

To stop the settling tank from overflowing, my relatives have dug a

30cm x 30cm x 20m trench in their field, which handles all the run-off from the "settling tank". Is this a really bad idea from a public health point of view?

I'd quite like to hire a mini-digger for a few days, and install a new leach field - is that a DIY job?

[Owain]

Yes, but you might want to try shoving a jetter down the perf pipe to clear it out a bit.

If nothing else, it might turn a winter job into a summer job :-)

Owain

PS On the upside though it's probably a less smelly job done when it's cold

[Nick Odell]

I used to live in rural fenland where people used to construct systems like that - and got clobbered pretty heavily by the authorities if they ever found out. I never discovered whether this was because they weren't building the right kind of system or whether the authority simply vetoed anything like it. Our old house with an original brick-built cesspool was accepted even though liquids leached into the soil and even so, with the water table so high round there, we went through phases when our cesspool needed to be emptied several times a season but that was just part of living where we did. Any new installations had to be plastic septic tanks (and no punching holes in them when the inspectors weren't looking). Soakaways for the surface water of course. I'm only saying all this because while what you are planning may be perfectly reasonable where you are, if I were back in fenland, I'd want to check into the local requirements before I started anything.

Nick

[Peter Crosland]

Rainwater should not be disposed of via the septic tank. It should be fed into a separate soakaway. A new soakaway needs formal permission from the Environment Agency before work starts. They will not grant retrospective permission and there are potential heavy fines for not getting it. Once permission is granted by the EA an application for Building Regulations approval is needed. There is nothing fundamentally difficult in doing the work but you do need to know the rules in order to satisfy the EA that the ground is suitable and to use the correct materials and design the system.

Peter Crosland

[Peter Crosland]

Just for clarity EA and Building Regulations permissions are required for all of England and Wales. There are no exceptions.

Peter Crosland

[Moonraker]

This can be caused by not having the tank pumped out at intervals. The solids eventually fill the tank then clogs. I had a new system installed a few years back, the job of digging the drain tench was immense, after it was dug it was not possible to see the workers when in the trench, which had a lot of gravel placed in it before the "holy" pipes. If you re-do the trench then I would have thought that it came under repair, and as such permission not needed. Another thing is that there are chemicals available to flush into the system periodically which greatly help the digestions. Bleach is a definite no no, there are other products available that do the job and are septic tank friendly, readily available in the supermarkets

[Steve Firth]

From your description of the problem the system is undersized for the task. A septic tank should never back up. If there's too much effluent for the first tank it should spill over into the second which should be an anaerobic filter, not a settling tank. There should be no particulates to settle in the outflow from a two-chamber septic tank.

It sounds as if the system you describe is too small for three houses. The only thing going to the leach field should be water which will have too much ammonia to be "clean" but should have no particulates at all.

It sounds as if the system you describe is letting solid waste flow right through to the leach field. Any fix you do - such as rodding out the leach field- will be temporary.

Fix is to install a proper system sized for three houses and to separate rainwater drainage from foul water.

FWIW the most recent system that I installed is sized for 12 residents (4 bathrooms) per house even though each house at present only has two residents. Experience shows me it is better to oversize septic tanks, for example Christmas is nearly here and isotopes will be adding their contribution. Size for peak demand or face problems.

[Jules Richardson]

Yes, I think the pipes on ours are only about 2' down, but there's a

*lot* of gravel below that. It's a wonder it all works at all, I suppose, given that the frost line here is more like 7' down. I think the drainfield pipework is around 250' - I'm not sure of the holding tank size.

I've heard recommendations to pump them anything between 4 and 10 years (so divide that by 3 for 3 houses) - but that's if you're *not* also dumping rainwater into them. If the drainfield does clog, I think septic companies can try flushing the pipes out, which sometimes works...

cheers

Jules

[harryagain]

These old fashioned blockwork "septic tanks" let a lot of sediment etc through into the leech field. The newer ones produce a much clearer effluent so the drains don't clog up so quick.

I f you cand etermine the whereabouts of the leechfield pipes and they have access points, they can be power flushed but they may well clog up again quickly. They are supposed to be laid in gravel but the gravel may be clogged up as well. Also if you soil is clay. it also clogs the gravel. There might not BE any gravel. You will probably have to start again. You need to do soil tests to determine the permeability of the soil & then you can work out how much pipe, gravel etc you need. The gravel bed is wrapped in geo-textile these days to keep the soil from clogging it.

These old fashioned blockwork septic tanks aren't allowed now, you will need the big light bulb sort with all the baffles and traps inside. If you have a bit of common sense you can DIY it. The manufacturers blurb has all sorts of info, start from there. Plenty info on the net too and local library. Rainwater into the septic tank is a very bad idea. The crap needs to be left warm and undisurbed to brew away. Reduces down by around 95%. Also bad idea are waste disposal units.