A radon mitigation system is a system installed in a building to reduce the amount of radon inside the building.  The EPA recommends that a home be mitigated if the radon levels are 4.0 pCi/L or higher.  A successfully installed mitigation system will lower the radon level in the home below 4.0 pCi/L.   Most mitigation systems can be installed at a reasonable price by a professional mitigation company.  When you hire someone to install a radon mitigation system ask what kind of guarantee they offer.  Many installers will guarantee that the system will lower the radon levels below a 4.0 pCi/L, but some installers make no guarantees.  After a mitigation system is installed another radon test should be conducted to be certain that  the radon level was brought down below 4.0 pCi/L.  The post mitigation test should be performed by someone other than the mitigation system installer to avoid a conflict of interest and ensure reliable results.  If the radon levels were not brought down below 4.0 pCi/L contact your installer to make some ajustments to the system.  If the installer had a guarantee he will usually make these adjustments at no additional charge to you.