Radon is a naturally-occurring radioactive gas that emits ionizing radiation. National and international scientific organizations have concluded that radon causes lung cancer in humans. The Maximum Contaminant Level Goal (MCLG), for radon in drinking water is zero. This is a non-enforceable goal. The regulation provides two options for the maximum level of radon that is allowable in community water supplies. The proposed Maximum Contaminant Level (MCL) is 300 picoCuries per liter (pCi/L) and the Alternative Maximum Contaminant Level (AMCL) is 4,000 pCi/L. The regulatory expectation of CWSs serving 10,000 persons or less is that they meet the 4,000 pCi/L AMCL and be associated with an approved MMM program plan – either developed by the State or by the CWS. High-performance aeration is the proposed BAT for all systems. High Performance Aeration is defined as the group of aeration technologies that are capable of being designed for high radon removal efficiencies (up to 99.9% Removal), i.e., Packed Tower Aeration, Multi-Stage Bubble Aeration, etc.