Don’t get me wrong, I like sand in my run. It’s worked for me.I want to know this too! I sprinkled 2 bags of sand in and figured I'd need at least 10 more to make a difference.
Twice a year I take out a few wheelbarrows full of the dirt/sand mixture and dump it around my shrubs and in my flower gardens to improve drainage. But a 50 lb bag of sand only gives me about 4-6 square feet of reasonable coverage.