soakaways
You can get one of the manufacturers to do all the sums for you, Dave, on a project of that scale. The basic calculation is pretty much the same as that I give on the Soakaways page, but, because you'll end up with a sizable chamber, the manaufacturers of segmental soakways will help you design what is required and present all the relevant calculations to your BCO or development team.
Try Polypipe (for uPVC) or Marshalls (for concrete) - they are usually very helpful in this sort of thing. The contact details for both are given on the Drainage Links page
Try Polypipe (for uPVC) or Marshalls (for concrete) - they are usually very helpful in this sort of thing. The contact details for both are given on the Drainage Links page