When a building (or house) is found to have an elevated level of radon gas (defined by the U.S. Environmental Protection Agency as a radon result of 4.0 pCi/l or higher,) methods of reducing the levels can be applied to cure the problem. The most common method of Radon mitigation (also known as remediation or abatement) is Active Soil Depressurization (ASD.) This method utilizes PVC piping attached to an electric suction fan. The piping typically begins below the lowest floor of the structure's foundation (penetrating the slab of the basement or the plastic membrane of the crawl space) and extends upward to an exit point above ground level. The inline suction fan is mounted in an inconspicuous location on the exterior or within an attic above the home. In cases where the radon fan is installed in the attic, the discharge pipe extends out through the roof so the gas can be released outdoors.
Active (fan assisted) radon mitigation systems can reduce the radon gas entry by as much as 99%. A qualified radon contractor (also known as a radon mitigator or radon remediation specialist) can typically install a mitigation system in a home in less than a day. After the system is installed, the radon levels begin to drop almost immediately. Passive radon reduction techniques (such as sealing cracks or installing pipes without an inline fan) are rarely effective at reducing radon levels. The reason that these "passive" techniques are ineffective is because radon gas is under pressure and must escape from the ground. It is a very inert, un-reactive gas that can be drawn up through the pours of concrete, around drains, utility penetrations, or expansion joints. Attempting to "seal out" radon is similar to trying to keep water out of a basement by painting the walls and floor with waterproofing paint. It may work temporarily if the problem is minor, but it wouldn't keep standing water out. The only way to fix a water problem is to redirect the water somewhere else before it enters the home. The same principles apply to radon correction. Sealing cracks and openings is part of the radon mitigation process; however this is to prevent the downward draw of conditioned air from the home and to improve the pressure field extension of the system below the slab.