Foul water drain field design/parts

[islandboy]

Hi all,

 

To cut a long story short our septic tank soakaway has packed in, again! My thinking for this happening again only 4 or 5 years after replacing the last soakaway is that in the winter the water table is high causing the effluent to remain static in the soakaway and turning into sludge meaning long term damage to the soakaway leading to thermal failure.

What I am planning on doing is replacing the septic tank with a sewage treatment plant and pumping the effluent to a raised soakaway. Ive got a good idea of how to construct the raised soakawy but Im struggling to find anywhere that actually sell the necessary parts to construct the field drain. I was intending to use 110mm perforated twin wall pipe. The pipe is easy enough to source but I cant find the parts, should I just use normal 100mm soil pipe parts?

Any thoughts would be much appreciated.

 

[ProDave]

I did a lot of research into filter mound soakaways and made a long thread about it on ebuild but that is gone. (should be able to find it on the way back machine)

 

You basically build a raised mound out of graded filter sand, and put the soakaway on that, then cover with earth.  The sand is not cheap, it would have cost roughly £1000

 

There is a BRE document that describes the design of the mound. It is fiendishly expensive for a little 20 page publication, so I borrowed it from our local library on an inter library loan.

 

I have to go out now, I will be back later with more details.

[ToughButterCup]

1 hour ago, islandboy said:

[...]

. I was intending to use 110mm perforated twin wall pipe. The pipe is easy enough to source but I cant find the parts, should I just use normal 100mm soil pipe parts?

[...]

 

Here's chapter and verse; Approved Document H

You also need to follow the General Binding Rules.  - and all for free (That'll please @ProDave )

 

Normal soil pipe parts are widely available. (Just imagine if they weren't!)

[Jeremy Harris]

Septic tank leach fields/soakaways always fail within about ten years, but it's rare for that failure to be noticeable unless the water table is high.  To work properly, a septic tank absolutely must have an aerobic tertiary treatment system that does 99% of the effluent treatment.  Traditionally with was done by using aerobic soil bacteria around the leach field.  The snag is that over a period of 5 to 10 years these aerobic bacteria tend to build up bacterial ,films that prevent atmospheric oxygen from permeating the surrounding soil.  What then happens is that the effectiveness of the tertiary treatment drops and the leach field becomes septic, with predominately anaerobic bacteria feeding from the effluent.  This isn't good news, as it means that the effluent that drains away has a very high biological oxygen demand (BOD), which makes it exceptionally harmful if it enters a watercourse, plus it allows the proliferation of anaerobic pathogens, which are generally significantly more harmful to both humans and wildlife.

 

There are lots of ways around the problem, but the best fix is to convert the anaerobic septic tank (the clue is in it's name as to the type of bacteria in contains) to an aerobic treatment plant.  The effluent from an aerobic treatment plant has a very low BOD, so can be far more safely discharged and tends not to have the same biofilm problem, simply because the BOD of the effluent is too low to support the growth of the bacteria that tend to form biofilms that clog things up.

[Gone West]

1 hour ago, islandboy said:

Any thoughts would be much appreciated.

 

It is possible to convert septic tanks to treatment plants. Don't know how effective they are but if they meet the requirements I guess they're okay. Other makes are available.

https://www.wte-ltd.co.uk/septictankconversion.html