Radon is a colorless, odorless, radioactive gas that forms naturally in soil. Radon can easily seep into homes through the foundation and become part of the air we breathe. Long term exposure to radon can increase the risk of lung cancer. In fact, radon is the second-leading cause of lung cancer in the United States. Almost 47% of radon tests done in Broomfield between 2005 and 2011 had elevated levels of radon.