A homeowner should hire a radon mitigation contractor after she has tested her home for radon a few times and found elevated levels of the element. Radon test kits are available at hardware stores, and some state agencies or universities offer discounted radon test kits.
The Environmental Protection Agency recommends radon mitigation if the levels are above 4 picocuries per liter, though this level can be lower if the area of the house is heavily trafficked. If high levels are found in the home, the homeowner can then contact her state radon contact. They can steer her to a professional who can perform radon testing and mitigation.