Soil near disused septic tanks

Leif

I'm digging the area at the end of my garden where there is an old septic tank, consisting of two concrete cubes, buried 1 foot below the surface. Oddly the soil seems to be a ~6" layer of so-so soil, a ~6" layer of orange clay, very sticky, with flints in, and some lumps of chalk, and then a deep layer of dark brown soil, that is dry, very crumbly and full of flints. It seems ideal for growing in. Could this dark layer be the result of the outflow from the tanks percolating into the surrounding soil? I would say yes, but the outlet from the tank is about 3 feet below the top of the tank, so 3 feet below the top of the dark brown soil layer. Could the outflow percolate up? Or is this more likely to be natural?

Davesnave

Outflows from septic tanks aren't coloured, but clear, unless there's something wrong with them.

Leif

Davesnave wrote: »

Outflows from septic tanks aren't coloured, but clear, unless there's something wrong with them.

My assumption is that the outflow is nutrient rich, which is confirmed by various online sources which are as far as I can tell kosher. These sources suggest that in heavy rain the nutrient rich water can rise close to the surface. I'm wondering if anyone else has come across what I describe i.e. seemingly richer soil below the top layer(s). I suspect it is worth digging this soil or at least making sure it is accessible to plants by breaking up the clay above.

Leif

Oh, and another question that occurred to me. I know that it is not good to grow veg above a septic tank and/or the drain field, while they are in use, due to the presence of bacteria and viruses in the outflow. Is there likely to be any problem if the tank has been out of use for ~20 years? My guess is that bacteria would be as per normal soil, but how about viruses, given that they are in a sense not alive, and hence might lie dormant?

Davesnave

I suppose tanks will vary, but the outflow field is often at quite a distance from the tank itself. In the three I have on my land, the run out travels between 10 - 30 metres before entering the percolation pipe.

There's no effect on the land close to the tanks, though that has areas of clay present, no doubt exhumed when the pits for the tanks were created.

Leif

Davesnave wrote: »

I suppose tanks will vary, but the outflow field is often at quite a distance from the tank itself. In the three I have on my land, the run out travels between 10 - 30 metres before entering the percolation pipe.

There's no effect on the land close to the tanks, though that has areas of clay present, no doubt exhumed when the pits for the tanks were created.

I have a smaller garden I guess. The garden is 17m wide, and I believe the drain field is along the rear boundary, the tanks being in one corner. I don't know why your drain field is so distant. My neighbour still uses his septic tank, and his drains in the area near the tanks. He had to dig a new soakaway for it, as he had overflow problems due to poor drainage.

Yes, one explanation is that the soil was turned over during excavation of the tank holes, which might be the reason for clay near the surface.

Davesnave

Leif wrote: »

. I don't know why your drain field is so distant.

Maybe because this property owns the fields and the original owner didn't want any drainage into the garden.

In the case of one tank, (not mine and not compliant with regs) the waste goes across a B class road into a tank, and from there the outflow is in a pipe across a ditch and then into my land, where it percolates into the soil.....:eek:

The present owners have no idea that this will all come to an end when they attempt to sell! :rotfl:

Leif

It all sounds a bit odd, the outflow from a septic tank is harmless as long as you do not plant crops above the drain field, as you do get pathogens travelling up to the surface and onto plants.

Davesnave wrote: »

The present owners have no idea that this will all come to an end when they attempt to sell! :rotfl:

I am not sure I understand the point you are making in the quote. Could you explain, I am curious? I thought you owned the property and fields?

Davesnave

Leif wrote: »

It all sounds a bit odd, the outflow from a septic tank is harmless as long as you do not plant crops above the drain field, as you do get pathogens travelling up to the surface and onto plants.
Sheep graze on what grows above ours, and before that it was horses. The grass is also cut for hay once a year.
I am not sure I understand the point you are making in the quote. Could you explain, I am curious? I thought you owned the property and fields?

The people who are using the field for their drainage have no legal agreement or permit to do this, so their house is unsaleable, but they're too naive to realise. The system was set up long ago in less 'enlightened' times. As they intend to move soon, it seems politic to wait for things to resolve themselves as a result of that, rather than drop them in it with the Environment Agency. They'll have to go for a more modern bio-disc system.

Leif

Davesnave wrote: »

The people who are using the field for their drainage have no legal agreement or permit to do this, so their house is unsaleable, but they're too naive to realise. The system was set up long ago in less 'enlightened' times. As they intend to move soon, it seems politic to wait for things to resolve themselves as a result of that, rather than drop them in it with the Environment Agency. They'll have to go for a more modern bio-disc system.

So they have a pleasant surprise awaiting them.

I am new to septic tanks, so to speak, and to be honest they do seem a good thing apart from there being limits on what you can dispose of in sinks, loos etc. My neighbour prefers his to mains sewage, as it is cheaper. His has not been pumped for 10 years, as it is very efficient. My house went onto main sewage about 20 years ago.