Radon mitigation
Radon mitigation is any process used to reduce radon gas concentrations in the breathing zones of occupied buildings or radon from water supplies. Mitigation of radon in the air is accomplished through ventilation, either collected below a concrete floor slab or membrane on the ground, or by increasing the air changes per hour in the building. Treatment systems using aeration or activated charcoal are available to remove radon from domestic water supplies.
The first step in mitigation is testing to see if the indoor-air and/or domestic water radon concentrations should be reduced. No level of radiation is considered completely safe but it cannot be totally eliminated so governments around the world have set various action levels to provide guidance on when radon concentrations should be reduced while recognizing that radon cannot be eliminated. The World Health Organization's International Radon Project has recommended an action level of 2.7 pCi/l for radon in the air. Radon in the air is considered to be a larger health threat than radon in domestic water so the US Environmental Protection Agency recommendation is to not test for radon in water unless a radon in air test is above the action level. However, some US states, such as Maine where radon levels are higher than the national average, recommend all well water should be tested for radon. The US government has not set an action level for radon in water.
Air-radon levels fluctuate naturally on a daily and seasonal basis. A short term test (90 days or less) might not be an accurate assessment of a home's average radon level, but are recommended for initial testing to quickly determine unhealthy conditions. Transient weather such as wind and changes in barometric pressure can affect short-term concentrations as well as ventilation such as open windows and the operation of exhaust fans.
Testing for radon in the air is accomplished using passive or active devices placed in the building. Some devices are promptly sent to a laboratory for analysis, others calculate the results on-site. Radon-in-water testing requires a water sample being sent to a laboratory.
Retesting is recommended in several situations such as to double check test results before spending money on the installation of a mitigation system. Test results which exceed accuracy tolerances also require re-testing. When a mitigation system installation is warranted, a retest after the system is functional is advised to be sure the system is effectively reducing the radon concentration below the action level, and after any mitigation system repairs such as replacing a fan unit. Retesting is also recommended every ten years.
ASTM E-2121 is a US standard for reducing air-born radon in homes as far as practicable below the action level of 4 picocuries per liter (pCi/L) (148 Bq/m3). Some states recommend achieving 2.0 pCi/L or less.
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