On 22/09/2019 11:38, Graeme wrote:

Near here (Aberdeenshire), a fairly rough 1930s bungalow sold a while
ago, and was promptly demolished, to be replaced by a new detached
house.Â* Not a rural site as such, although a rural location, but a road
of similar houses, mains drains and electricity.

Following completion of the house, a large hole was dug in the rear
garden, with a huge digger.Â* Somewhere between 2x3 to 3x4 meters (I'm
nosing through the fence).Â* The spoil was then sieved using the digger
bucket, the hole lined with plastic tarpaulins, and the stones from the
sieving put in the bottom.Â* I missed what happened next, but the huge
pile of sieved spoil has gone, as has the hole BUT there are two
corrugated pipes protruding from the ex hole, with manhole type lids.
There was a trench from the house to the hole.Â* I cannot think what
could be in the hole other than a septic tank, but why install a septic
tank with mains drainage outside, or what else could it be?Â* Not enough
time elapsed to build a nuclear bunker!

It's possible that the bungalow run-off went into the local sewer rather
than a storm drain.

The new building probably required a new soakaway to be built. Certainly
rules don't permit surface water to enter the sewer system unless the
soil is impervious or there is a high water table.

I thought septic tanks required a more distributed outflow? But given
you never saw a tank, or a hole being dug for one suggests this was done
to make a soakaway.