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"Andrew May" wrote in message
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Muddymike wrote:

On further inspection of the images I think you are right, The top/left
chamber may connect to the centre one further down, if so its certainly a
three stage septic tank. Ten rows of bricks down sounds high for the
water table. Is it that high outside the brickwork? If not it may be that
the chambers are still retaining water. If the rubble inside is loose it
could be the remains of the old lid structure. These were sometimes
concrete slab and sometimes corbeled brickwork the beginnings of which
can be seen.

Keep digging you may find treasure.

No treasure yet :-) but a few more details emerge.

There would appear to be a solid base about 3'6" below ground level. At
least there is in the centre chamber so I assume there is in the other
two.

As far as I can see - and remember it has muddy water at the bottom -
there is no obvious pipe connecting the left hand and centre chamber.
However there is a patch of brickwork at the bottom of the dividing wall
with no vertical mortar and winder than expected gaps. Could this be to
let water through? I don't know how septic tanks are supposed to work.

The fact that there are gaps in the mortar at the bottom of the wall tells
me that the first two chambers are in fact one, because water levels in
those would be equal in the two 'sections'. Once the water level had reached
the outlet into the other chamber, the solids would still be dropping to the
bottom of the first chamber for the water to flow over into the second as
before.

Once this second chamber was full, any solids which had escaped to the
second chamber would have sunk and 'in theory' the outlet from this second
chamber would be 'fairly' clean water, certainly not drinkable and in hot
weather still somewhat smelly.

I had a huge single chamber septic tank at my last house and the outfall
gave problems in that the water gave problems until I dug drainage ditches.

My neighbour, whose bungalow was built on my land in the 60's had a double
chamber septic tank, as yours but much larger, and his only trouble arose
was about 20 years later, when the porous pipe outfall from the second tank
which went underground to the bottom of the garden, not only let the water
out, but let the tree roots in and blocked it!!

Hope that gives an insight into septic tanks and almost comfirms, now you
have dug deeper, that you had a two chamber septic tank!!

Mike

Finally, I dug out a bit of the lawn and there does not appear to be any
evidence that the construction ever extended beyond the front wall. I was
hoping I might find cut off bricks where the wall used to extend.

Any more ideas?

Andrew