What must a system do if results show nitrate levels at or above 5 mg/l?

When a water system detects nitrate levels at or above 5 mg/l, it is required to conduct quarterly monitoring to ensure that the situation is effectively managed and to track any changes in nitrate concentrations. This frequency is crucial for maintaining public health safety and provides timely data that can be used to make informed decisions about the water supply.

Quarterly monitoring allows the water operator to assess trends in nitrate levels over time and determine if corrective actions or treatments are necessary. This proactive approach helps in identifying potential sources of contamination and in implementing strategies to mitigate risks to public health.

While other actions like switching to different water sources, stopping operations, or notifying the public might be considered under specific circumstances, they are not mandatory or immediate requirements in all cases. The primary obligation in response to elevated nitrate levels is to enhance monitoring efforts to understand the situation better.