What must be reported to the state by the end of the day if an EC+ is found?

Reporting the EC+ sample result after analysis is essential because it signifies that coliform bacteria are present in the water supply, indicating a potential contamination issue that poses a risk to public health. This swift notification allows state authorities to investigate the source of contamination and take necessary actions to protect water consumers.

Timely reporting of such results is critical in water treatment operations to ensure that corrective measures can be enacted to rectify the issue and prevent waterborne illnesses. The requirement for immediate reporting aligns with regulatory standards aimed at maintaining water safety and public health.

The other options involve reporting samples or data that are not as urgent as the EC+ result. Monthly sample results or past TC- samples do not directly address immediate public health threats posed by the presence of coliform bacteria in the water.