If an MCL is exceeded, what must a Non-Transient Non-Community Water System (NTNCWS) do?

When a Maximum Contaminant Level (MCL) is exceeded in a Non-Transient Non-Community Water System (NTNCWS), the system is required to inform the public about the violation in a way that ensures the information is widely disseminated. Continuous posting in a conspicuous location serves as an effective method for communication, ensuring that all users of the water system are made aware of the issue in a timely manner. This requirement is part of the regulatory framework aimed at protecting public health and ensuring that individuals have access to important information regarding the safety of their drinking water.

Notifying the state authorities is also necessary but does not replace the requirement to inform the public directly. Just shutting down the water supply may not be practical or required unless immediate health risks necessitate such an action. Waiting for public feedback before taking action is not a recognized step in this scenario; instead, prompt communication to the public is prioritized to ensure safety and awareness.