I also am on clay and BCO said “where are going to put your soakaway” I replied “you mean pond, we are on clay and it will not soakaway”, I explained that any rain falling on the plot would eventually run to the ditch along the bottom of the plot , so I piped it there. I would get your BCO out and see what he suggests. ( no two BCO,s read the regs the same, I was lucky).