Building over a soak away

[chaserdavid]

Interested to know your recommendations on the following scenario:
I have planning permission to build an oak frame garage which will be built on a brick plinth which would go onto a strip foundations.
Garage dimensions: 7m x 5.5m ridge height: 4.3m

I’ve just been figuring out where existing pipes (sewer, roof water, clean water etc.) are going in around the area of the site.

I notice one of the pipes (about 800mm underground) coming from our house’s down pipes is going towards where we plan to put a foundation and I’m concerned it also goes to a soak away right where we plan to put the garage.
There’s been no major construction around the house since the 70s so if there is a soak away it’s at least that old.

Could I decommission the existing soak away by rerouting the feed to somewhere else (sewer or another soak away)?
Then would I be able to build over the old soak away or would additional steps be needed?

I read in another post that a raft could be an option.

Would like to hear your ideas?

 

[George_engineer]

It will need digging out and backfilling properly.

Drains can be rerouted to a new soakaway, located a minimum 5m from buildings and boundary.

In theory a raft would work but a few hours with a digger and some stone is cheaper building a raft.

 

[^woody^]

The ground is going to be saturated and possibly soft for a good distance around and below.

And there may be some gound consolidation afterwards.