As you saw in the previous section, radon atoms are fairly short-lived. Over the course of several days a radon atom becomes a lead atom. While it is a radon atom, however, it is a gas. Because radon is a gas, it can seep from the ground into the air in a house. The primary way that radon enters a house is through the foundation (crawl space, basement) by a variety of paths:
- cracks in basement floors
- sump pumps
- exposed soil
- construction joints (mortar, floor-wall)
- loose fitting pipes
Radon may also enter the air of a house from well water, but this is a minor source compared to that coming in through the foundation. Some parts of the United States have higher risks of radon than others. The U.S. Environmental Protection Agency has a map that shows which counties and states have higher average radon levels. You can see the map here.