Old fashioned septic tank

[dunny]

I have an old style septic tank in my garden that looks like it is made out of cast concrete. I understand the basics of how the tank works but I cant find the outlet I was expecting.

I can see into the smaller chamber of the tank (which appears to contain mostly water) and I can see what appears to be an incoming pipe and a separate pipe that looks like it goes back into the other chamber.

Could this second pipe be the outlet?

D

 

[Hugh Jaleak]

Tank should have minimum of 2 sections, primary and secondary. Flow from house will enter primary, solids will settle off as sludge, and liquor should pass through to secondary section, where further settlement will take place. Possible outlet is either under water level, or wall is porous to allow permutation into surrounding subsoil. Assume tank isn't overflowing and is working as expected?

In case you weren't aware, keep detergents and any cleaning chemical usage to a minimum, to allow the bacteria in the tank to do their job. Desludge as required to prevent secondary section and/or soakaway sludging up.

 

[dunny]

Tank should have minimum of 2 sections, primary and secondary. Flow from house will enter primary, solids will settle off as sludge, and liquor should pass through to secondary section, where further settlement will take place. Possible outlet is either under water level, or wall is porous to allow permutation into surrounding subsoil. Assume tank isn't overflowing and is working as expected?

In case you weren't aware, keep detergents and any cleaning chemical usage to a minimum, to allow the bacteria in the tank to do their job. Desludge as required to prevent secondary section and/or soakaway sludging up.

Thanks Hugh.

Tank is fine and has been for the 4 years we have been here; we get it emptied once a year. It isn't porous (it is 1 foot thick concrete) so I am assuming there must be an outflow. I need to find the outflow as I am planning to dump a load of stone into the soakaway and I dont want to obstruct any outlet. The top of the tank is covered with concrete fence panels and this must let lots of rainwater into the tank - is this OK?

D

 

[Diver Fred]

Outlets are either at the top or the very base. I agree with Hugh that the second chamber should be liquor only but if not emptied regularly can get some solids into it. I suggest you should get the second chamber emptied and the bottom cleaned. What I expect you to find is that bottom is porus - i.e. has a number of holes in it, infact the whole base of the second chamber could be a checkerboard of holes. In which case the second chamber is the soakaway.

 

[Ian H]

If the outlet was a normal pipe it would normally be slightly lower than the inlet and be a T-piece. If your second chamber let's stuff soak through or is some kind of filter bed then the outlet could be lower.

How do you mean you are planning to dump a load of stone in the soakaway?

 

[dunny]

Thanks @wgt52, that would explain it as I cant see any outlet either level with or above the water level.

@Ian H - downhill from the tank is a hollow in the ground where a separate land drain outfalls. I am assuming that the septic tank also drains out into this hollow. The ground here is absolutely saturated so whilst this is the 'soakaway' it isn't doing a very good job. My plan therefore is to fill this area with a load of stone which will raise the ground level and provide a much more effective soakaway area. Once the ground is raised here (by maybe 3 feet) I will then backfill over the top with soil.

D

 

[Ian H]

Ah!! A dye test of the tank would confirm that. If you could get some green into the second tank then run a hose for a while you should see it in the hollow.

 

[dunny]

So a bit of an update after further exploration today. The tank has been covered in ivy and so today I uncovered it all so I could get a better look. The top is covered in 1 foot wide concrete slabs and a few of them were broken. I removed them all today and exposed the whole tank so it is much more obvious what is going on. In doing so I found the outflow chamber so I now know where the run off goes.

The tank is basically in 4 chambers; the slurry / water chamber which is the inlet from the house. The solids go to the bottom of this chamber and the water leaches through the blockwork into a tank full of stone / soil. This chamber has 4 outlets at the bottom into the third chamber which then discharges into the 4th chamber where it meets a huge land drain run off.

Other than the tank cover the tank itself is in good shape and I now have the added benefit of locating a major land drain outlet that I plan to reuse!!

Thanks for the tips.

D

 

[Hugh Jaleak]

Advise you cover it again though, (if you haven't already). Otherwise its a death trap for children or animals. Secondly, you are aware of the dangers of Hydrogen Sulphide? Never, under any circumstances, enter the tank unless gas tested and you have appropriate support and means of rescue.

 

[dunny]

Hi Hugh,

I have covered it again with the original panels but I am not happy with the state they are in as they are cracked in multiple places. I will be replacing the cover most likely with a series of manholes. It will be a while though before doing so.

I wasn't aware specifically of the dangers of Hydrogen Sulphide but knew that there were danges associated with gasses in general. There appears to be no need to enter any of the chambers now so this shouldn't be an issue. The only thing (in addition to sorting out the cover) that I will need to do is to break into the outflow chamber to connect to the land drain.

D

 

[Hugh Jaleak]

H2S is nasty stuff, doesn't take much to do you some damage. Advise you research before entering any pit, chamber or excavation where it could accumulate.