Help - Septic tank backing up again after only 4 weeks from emptying? Whats the problem?

[maggiso]

We have bought a new house but are not yet living there, although builders are there in the day. Under 4 weeks ago the sinks/loos backed up so at great expense (and not knowing if the previous owners - 'emptied it last year' was accurate) we had it pumped out. We were advised to have it inspected in the new year. Less than 4 weeks later the same thing has happened! It has been raining rather a lot - so the garden and ground field is quite soggy- almost a pool in one corner. The septic tank and ground field was put in 35 years ago. According to the plans it has 4 soak away gravel and perforated pipe ditch soak away things ( cannot remember the name). We have organised someone to come and inspect the system(organised before it backed up again!) - but it will be a while. It also has to be pumped out yet again before that can be done (and the builders can uh - go).
We are new to septic tanks, but the builders know to avoid harsh chemicals. What has gone wrong? Is this normal for septic tanks and heavy rain?

if it is filling with, er, what they fill with then there's a blockage somewhere, or you have a LOT of builders.

never mind 'harsh chemicals' - septic tanks mean no bleach and nothing down the toilet except body waste and a normal amount of toilet paper. Do the builders know that? Nothing down the sinks either except water and washing up liquid.

rainwater should not go into septic tanks, but does it? Idiot builders or DIYers may do it.

Presumably builders are not having many baths, running washer, etc, so why is it filling?

Sounds like the tank is discharged via finger drains, it's possible they have collapsed (especially if heavy vehicles have driven over the ground). Ask someone to look at the t-pieces from the tank outlet, they can be broken off by tanker hose. If they have been then they will be lying in the bottom of the tank. Do you know if it is made of GRP construction or brick built? If it is GRP and you live in an area with a high water table then it's possible the tank has been pushed up by the pressure and caused a crack in the base. If it's brick built then they bricks and morter can crumble away over time again letting ground water in.

Harsh chemicals will do nothing to the tank itself, it will just affect the biological process meaning that you will be discharging effluent at a poor quality than deemed in your consent (unless you are running under an exemption which is probable if it only serves one house).

I am a sewage geek

Only 2 builders and as they are putting in new bathrooms there is only a functioning cloakroom - no shower or bath as yet. Only coffee mugs to wash out. So even the cleanest thirstiest builders cannot have filled a 1000lt tank with washing and the rest in under 4 weeks (less since not there over Christmas/new year)! Sounds like something is wrong. What stops rain or ground water from draining back into the septic tank in very wet conditions? ( I know rain water does not get fed into the tank)

SmokingGun

Is it your bread and butter?

We had exactly the same problem - it was caused by a collapsed soakaway, unfortunately they do fail. You need to locate where the soakaway is and find out if the waste pipe is blocked which may be causing the problem (easily remedied)

Soakaways are either basic gravel filled pits or sophisticated herringbone type wide area dispersal systems which are used when land drainage is a problem.

Major and complex issue for us last year. I had sleepless nights worrying about it.

Rainwater shouldn't get in and if you're not living there you shouldn't be producing that much waste water, so it suggests that land run off is somehow entering the system.

I'd get a reputable specialist in. It's not cheap I'm afraid - I now get ours serviced every 6 months. Good luck - hope is not to bad.

I suspect the water table is very high, especially if you say that the surrounding field is waterlogged.
We had a septic tank in our first home (old cottage) and it was a nightmare because of poor drainage - nothing was wrong with the tank, purely surrounded by very wet clay and field was a big in all but the driest weather.

Unlikely it is from the builders using it. More likely there are problems with the septic field and outdoor drainage. You will need a proper review including the perimeter tiles around the house.

PigletJohn - it is indeed! Couldn't be in the industry without having love for it 😂

Are you sure it's only 1000l tank OP? That's tiny. It's probably more like 1000g but even still shouldn't have filled up.

First things first, nip to b&q and buy some drain dye, preferably 2 different colours. Use one colour for the foul drains and check that comes through into the tank. The use the different due for storm. The storm drains shouldn't be routed into the tank but cross connections happen an awful lot. If no dye from the storm drain comes through then it suggests you have a pretty big ground water leak (either through the tank walls or base or a crack in the drain run itself) or the soak away is blinded (blocked up) or collapsed.

Just so you are know, EA use the following assumptions when calculating usage:

3 bed house, 5 residents discharge roughly 750l per day

Missed you question about draining back in the tank in bad weather. Technically nothing to stop it, however for the EA have have allowed a soak away to be performed a porosity test of the ground should have been carried out. This calculates how deep the soak away needs to be to stop this happening (how porous the different sections of the ground are). Normally you wouldn't see a back up if the soak away is fully operational due to the leave of the outlet. You might find it is slower to drain away though.

We live in an area that gets wet and boggy. We had to have a waste water treatment plant installed as a soakaway wouldn't work.
Maybe you might have to go with this option?

Thank you every one. I suspect we will need to at least dig out the gravel drainage channels but I suspect we may need to replace the whole set up. Sigh! Smoking Gun thank you so much for your expertise, porosity tests were done 35 years ago, and the gravelled soak away channels specified ( we have the original correspondence and drawings) would a small ride on mower be heavy enough to damage the drainage bed?

No it shouldn't be, it would need something heavier and on a regular basis

Thanks Smoking Gun. I so love the mower!! (and phew its probably not mu fault!).
I'll report back once the inspection is done. Thank you again.

We spent 20 years with a septic system and on our first winter rain was draining into the tank, turned out whoever smoothed out the ground had made it too high on one side of the tank lids (one lid was under the dirt). So Dh went and dug a shallow trench across the land, uphill from the tank lids, to channel rain water away from the tanks and we never had that problem again. Another problem we had was fine dirt got into the lines that soaks away the water. He had to get a hose and power wash the water out and made sure to flush them once a year, and that fixed that problem.
There's a learning curve with each septic system and the way it's been placed and the lay of the land. Once you have it all figured out it'll be smooth sailing.

I thought I would report back, now the tank has been emptied inspected and scrubbed out. Water was pouring in through the drainage beds because the adjacent farmers field slopes our way. There is supposed to be a drainage ditch to collect rain runoff from the field but is clearly not there. So having bunged up the outlet for the moment, (to prevent this temporarily, and put in a ditch to collect rain water to pump to the lateral ditch away from the tank) the next job (once the weather allows) is to dig a drainage ditch on our boundary with the field ( there is a lateral ditch to connect it into). We also need an overflow for the septic tank, and may need to revise the outflow pipe and ground. Septic tank itself is in one piece. I am sure this is not a new problem! The previous owner said the farmer was not good at digging out his ditches and the garden had flooded the previous year. We had therefore cleared out the lateral ditch thinking this the culprit. Now I understand! The northern drainage was never there! She must have meant he was not good at digging ditches!
You were right smoking gun, the tank is in gallons not litres - its too old to be in litres (stupid me!)
What fun!

www.kingspanenviro.com/kingspan-klargester-new You need to update to a Klargester, it will make life easier.

I would be surprised if the environment agency have not asked for you to upgrade when you went for a permit.

www.gov.uk/permits-you-need-for-septic-tanks/overview

www.ukseptictanks.co.uk/septic-tank-regulations

Thanks quote unquote. The septic tank was put in by the previous owner in accordance with the environment agency back then. We probably will need to update the system, but will still need to improve the drainage.

Thank you Sprinklesrule, I missed your post! It sounds like you had to put drainage in uphill of your tank to protect it from excess ground water flow too. That is the plan for ours at the moment. It's good to hear that worked for you. The house is only on gently sloping land, and there are other houses below it, so the garden is not in a soggy dip. The county surveyer is due a visit, so we can ask his opinion.
I will read up on klargesters and what is best for the environment, as well as current regulations. When we bought the house obviously the Surveyor and solicitor looked at all the paperwork and installations and the septic system seemed to be in order. We have a lot else to do- it's a listed house in need of TLC, but obviously we cannot move in until the waste system is in good working order.
We also have a well on sight which is fed by a natural spring, but I do not know which direction that comes from.

If you are getting the digger out to dig in more drainage, probable worth costing out the upgrade at the same time as the land work is a significant part of the cost.

Yes that is sensible Quoteunquote. It sounds like a small domestic plant, although expensive initially might be a good idea.

The Klargester looks similar to the one we had, only we had massive cement tanks underground, but it was a little treatment plant practically. It worked well.