I'm grading my yard and have found a deep layer of sand (at least 2 ft) extending out about 10ft. Perhaps the sub base for a patio? I understand I need an impermeable layer to ensure rain runs away from the house rather than draining downwards. I plan to use regular, fairly dense soil from elsewhere in the yard.
Considering that no soil is completely impermeable, how thick should I make my soil layer to be effective? Do I really need to test the permeability of my soil?? That seems like overkill...
