Radon can be a problem in schools and work places, too. Radium, which releases radon, is common in the earth's crust. Soils and rocks containing high levels of uranium, such as granite, phosphate, shale and pitchblende are natural sources of radon. High levels of radon in the soil are primarily responsible for radon problems. The radon gas percolates up through porous soils under the home or building and enters through gaps and cracks in the foundation or in the insulation and through pipes, sumps, drains, walls or other openings.
Water is another possible pathway for bringing radon into the home.
Water, when in contact with rock containing uranium, absorbs the radon gas. The radon is then carried into the home and released into the air in household dishwashers, faucets, showers, or washing machines. Water-related radon problems usually involve deep private wells rather than community water supplies. In some unusual situations, radon may be released from home construction materials such as stone used to build fireplaces or solar heating storage systems. Radon is not a problem outdoors because it is quickly diluted to low levels by outdoor air.