What is radium? Radium is a radioactive metal that occurs naturally in trace amounts in rocks, soils, and groundwater. As radium decays, it continually releases energy into the environment until a stable, nonradioactive substance is formed. This energy is part of the natural radiation to which all living creatures are exposed. Radium readily dissolves in groundwater where acid conditions (low pH levels) are found. The various forms of naturally occurring radium found in groundwater are radium 224, 226, and 228. Source: Maryland Department of the Environment