Murray, You were possibly digging up the beach area. We've dug down 18 to 20 feet with no caprock encountered here in south florida. Miami-Dade area is a little closer, if not right at the top and is a real pain in the ass to excavate and de-water. I hear that when they set fuel tanks in the Keys they hire a local blaster, but we stay outta that area. The Conchs are pretty protective of their local construction industry and very adept at setting charges ;~)