Septic tank - Stone filter replacement

[tom107]

Hi, I have an old septic tank that has a 3rd chamber which is filled with small stones This is now blocked and needs replacing.

What is the correct size for the filter chamber? Am I better off with a mixture of stone sizes? And which is the best rock type? Would granite be better than limestone?

I had a quick search and one site suggested 75/45mm washed limestone.

 

[Hugh Jaleak]

Before you do much more, a couple of questions. How old is the system, and how many People is it now serving?

 

[tom107]

Hi, It's brick lined, 3 chambers. With concrete top and heavy metal lids. I think it's 1970s as that is when property was converted.

Household is 6 people

The first 2 chambers are each 1.2m x 1.25m x 1.8m.

Stone filled chamber appears to be 1.2m x 1.2m x 1.7m when looking at the distribution pipes inspection chamber

 

[Dereekoo]

Not sure why you would have a stone filled chamber in a septic tank????

 

[Stivino]

In what way is it blocked?

 

[tom107]

In what way is it blocked?

The water level is much higher than the inspection chamber to drainage field by 1.7m. In the first 2 chambers of septic tank the water level is too far to high, nearly covering the outlet pipe.

These photos are similar to my tank, mine has 50cm water covering the stone. The last 4 photos are the replacement stone gravel.

 

[Hugh Jaleak]

You may be asking a lot for the flow from 6 People to be handled by a Soakaway that appears to be past its best, if it's waterlogged I'd suspect it has failed, and the surrounding ground is waterlogged. Bear in mind for successful operation, virtually every drop going into a Septic Tank needs to come out again as clarified effluent, so it may be time to bit the bullet and look at replacing it.

Assuming the ground is suitable for a Soakaway, (permeable and no heavy clay soil), then I'd look at a Crate system to replace it.