Septic tank soakaway - Digging a new one and ...

[Devon]

I have a private sewage system that has worked (despite being close to sea level, on a flood plain and on clay) for the last 25 years. We have Tank 1 which takes the solids and has an outlet to Tank 2 which takes liquid overflow from Tank 1, Tank 2 has an outlet to the soakaway. We have had a problem with the soakaway of water coming back in to my 2nd tank. After much money spent on investigations, rodding, jetting and emptying my tanks every two weeks, we have been advised to put in a new soakaway. We are digging a trench that is 6' deep and have found the existing outlet soakaway pipe which is clay. All the companies I have had in to look at the job have said that they will use perforated pipes. Other people have said to use clay to the soakaway and then perforated in the land drains we are putting in either side of it. The land drains will feed in to a dry rhine another 10 mtrs away. So what pipe do we use, the trench from the 2nd tank to the soakaway is some 45 mtrs long and will be filled (as high as I can afford) nearly to the top with stone. We are having to do the job ourselves because of the costs involved so if anyone advise please, perforated from the tank to the soakaway or clay, we would be eternally grateful?

By the way, the trench runs through my paddock lawn and my car park so it is important we don't cause a flood here or indeed in the house.

[flowjoe]

I can not be site specific but;

Why did the original soak-away fail Devon ?, if you were getting water back through the outlet this would suggest that it was saturated or you were draining the flood plain. Are you sure that a new soakaway will not fill and surcharge the tank again.

Solid pipes will carry water from A to B, a perforated pipe will leak water into the subsoil over a distance (soak-away, leachfield). If you are confident that the new soak-aways will work then install a solid pipe (clay/plastic) up to them. I assume the dry rhine is an open ditch ( and not a bottle of plonk) bare in mind that whatever you put in the final discharge will have to be fairly clean.

If the problems due to the ground water level (tide/flood plane) your money would be better spent installing a pump chamber on the outlet of the tank, this way the waste leaves the tank but water can not surcharge back in.

Finally no need to fill your trenches with stone, waste of money if your on level ground, the water will be back in the tank before it ever reaches the top of the stone trench, you just need a good surround to support the pipe 100/150mm will do

[GB_Groundworks]

are you creating a soak away or a leach field?

a leach field is a large shallow network of perforated drains to allow the liquids to drain away slowly and into a larger area.

a soak away is a void created to allow the liquid to soak away into the sub soil directly.

see main site :

soak away http://www.pavingexpert.com/drain08.html

leach fields http://www.pavingexpert.com/drain03.htm

joe beat me to it while i was copying links



Edited By GB_Groundworks on 1265750455

[digerjones]

hi, i dont think you say why you are putting in a pipe between tank and soakaway. if the pipe has worked now for 25 years it should still be ok. problems i have found with soakaways not working is fat desposits. when you dig down to the soakaway theres a crust all around it, sealing it up. perhaps you can get away with just doing the soakaway.
cheers

[Devon]

You will all have to bear with me here, I have had not had any experience of soak aways or septic tank systems before and so I have had to ask lots of questions of the professionals that I have had looking at what we have here. Every pipe from the house to the tanks and the existing soakaway have been rodded and jetted so there are no blockages but we still had water running back in to our Tank 2 from the soak away outlet. Hence, we have been advised to replace the soak away because it is likely that it has come to the end of its days. We are on a flood plain and the water table does fluctuate but we have had no rain for 2 weeks now and the water is still running back in.

So we have dug down to the outlet from tank 2 and from there a trench which will lead to a new soakaway. The main reason for the soak away is to stop the issue we have with water coming back in to the septic tanks but land drainage on our garden would prove useful too. As the outlet pipe is clay I was questioning the drainage company saying they would use perforated pipe and not clay in the trench. If we use perforated pipe the water will filter out in the trench on its way to the soakaway, is this good or bad. Could the trench then work as both a soak away and land drains or am I being totally stupid!

The rhine is a dry one that the main drainage rhines feed in to when full, (we are in a valley/estuary) and the drainage board have said that the water will be clean enough by the time is has gone through the soakaway so I am not too bothered about that.

I have to be honest, I have no guarantee this will work but it has worked up till the last 6 months and we have to give it a try and in the cheapest way possible. When you say pumping chamber where is the water pumped to?

I am a female so I do apologise for coming across as being a touch thick!!! I'm just trying to understand the way these things work.

[flowjoe]

Hi Devon

You may not have had much rain but the ground everywhere is saturated after the big thaw last month, if you still have water running back into the tank after two weeks it does sound as though its a ground water issue.

Theres nothing wrong with running a perforated pipe from the outlet and letting the water disperse into th sub-soil. this is how many tanks work, but if that water doesn`t soa-away it comes back into the tank.

When we install tanks/treatment plants in water logged ground or running sand we make the tank and the pumping chamber on the outlet one sealed unit, so that the water can not get back into the tank, you could do this and run it to your existing soak-aways ?, the water should find its own level and take the easist path into the sub-soil ?

You need to find a competent contractor to determine you exact problem and come up with a site specific scheme, it doesnt sound like a DIY job to me but you need to know what you are doing will work before you spend big bucks on it

[Devon]

Yes, I think you are right, get one more in and stick with what they say.

Many thanks for all your advice so far ...