For over a half-century, the U.S. Department of Energy nuclear weapons laboratory in Livermore, California has worked with plutonium in the course of its mission to research and develop nuclear weapons. Plutonium releases via the Laboratory's sewer system resulted in the contamination of sewage sludge that was distributed and used widely as soil conditioner in parks, landscaping around public buildings, and in home lawns and gardens. The amount of sludge distributed and the concentration of the radioactivity in the sludge are uncertain.