Imagine 22,000 lbs of ground-up tires with all the steel and other crap removed, ground to @ 1/8" pebbles. This is the material in the backstop of a shootingrange. There is a conservative estimate of 10,000 lbs of lead and copper to a much lesser degree in the rubber. This isn't the first clean-out/rebuild, the last one was five years ago. The idea is to remove all the material, separate it and reuse the rubber. One of the ideas we've had is to float the rubber in water and skim it off. But, 1/2 of a sample amount floats, 1/3 sinks and 1/6 stays suspended. In a 1/3 cup of the material, there was 64 grams of lead! I doubt that there is much lead in the material above the target line. The sample was taken at the very bottom, about 5' below the target line. They don't really want the range down for more than a week to do the clean-out and replace the front which is 4' wide x 3/4" thick conveyor belt lengths suspended from the ceiling and anchored to the floor and overlap by 8" and screwed together. The conveyor belting is bulging out close to a foot in the center of each of the ten lanes. It seems that this type of backstop is excellent for stopping bullets and keeping the dust to a minimum.