A state with primary enforcement responsibility under the U.S. Safe Drinking Water Act may relieve a public water system from a requirement respecting an MCL, treatment technique, or both, by granting an exemption if certain conditions exist. These are: 1. The system cannot comply with an MCL or treatment technique due to compelling factors which may include economic factors; 2. The system was in operation on the effective date of the MCL or treatment technique requirement; 3. The exemption will not result in an unreasonable public health risk.