I have used Kingsford charcoal for a patio hibachi, going through maybe 10 - 15 x 18 lb bags a summer. I just rinse this out, and the water flows off the concrete patio and onto the grass, and it has made no difference what so ever after 10 years of doing so.
This fall, I bought a couple 18 lb bags of Kingsford "mesquite" charcoal to roast chili. The ash from that stuff turned the grass yellow. It has since recovered, but still.