Protocol for the Collection, Transfer and ANSI/AARST MW-RN 2020 Measurement of Radon in Water 19 Note—While decisions to mitigate at any time are not prohibited, comprehensive testing provides confidence that decisions are not being made based on inconclusive or inconsistent collections or measurements. 7.3 Mitigation methods Best available technologies shall be used for mitigation of radon in water. A radon mitigation system shall be properly labeled and dated. Informative advisory —The best currently available technologies for mitigation of radon in water are: - Aeration Note—Aeration systems are often considered the best method for removing radon from water. An aeration system commonly consists of a reservoir of water that has air injected into it. Radon will readily come out of the aerated water and the air is exhausted from the tank through piping routed outside above the roof line. Radon removal rates near 99% are achievable. - Filtration with granular activated charcoal (GAC) Note—A mitigation system containing GAC for filtering radon from water should only be utilized when the radon level in the water is below 4,000 pCi/L (150 Bq/L). A single charcoal system can remove about 75% of the radon in water while a double charcoal system can remove about 90%. Note—New evolving technologies that are performance based and demonstrated as an acceptable mitigation method may be developed over time. Home water softeners and other water treatments are not radon mitigation systems and may become an additional source of radon. A water softener should not be backwashed into a septic tank without consent from state or local officials. 7.4 Post-mitigation testing 7.4.1 Initial testing to confirm effectiveness of mitigation efforts Evaluation for the effectiveness of applied remediation of radon in a water supply is best achieved through measurement of both untreated and treated samples. When a water supply is to be mitigated to reduce the radon level: a) Duplicate untreated samples shall be collected in conjunction with, or within 96 hours prior to, installation of any mitigation procedure where initial testing indicated less than 40,000 pCi/L (1500 Bq/L) of radon in a water test that was conducted within the previous year; and b) Duplicate post-mitigated water samples shall be collected no earlier than having flushed holding tanks and water lines in accordance with Section 4 and no later than 30 days after the full operation of the system commences. 7.4.2 Post-mitigation test locations The post-mitigation test locations and procedures shall meet all the requirements of Sections 4 with the post-mitigated water samples collected at a location that is prior to other water treatment equipment. The exact location of the spigot(s), date and time, collection method, and other pertinent information shall be recorded. 7.5 Mitigation maintenance and monitoring 7.5.1 Maintenance Informative advisory —It is critical that mitigation systems be properly maintained to protect occupants from hazards that can include radon, biological contaminants and other radiological concerns. Contaminants, such as bacterial contaminants, can also adversely influence effectiveness and life expectancy of the mitigation system.