When must positive bacti resampling take place?

Positive bacteriological resampling is a crucial part of water quality monitoring, particularly when a sample tests positive for coliform bacteria. The correct answer indicates that resampling must occur at the original location of contamination, along with one upstream and one downstream. This practice serves multiple important purposes.

First, resampling at the original location helps to confirm whether the initial positive result was accurate or a one-time anomaly. It allows operators to assess the immediate area where contamination was detected.

By taking additional samples upstream, water operators can check whether the contamination is isolated to the original site or if it is present in the water further upstream, which could indicate a broader issue in the source water or cross-contamination. Sampling downstream is equally critical, as it helps to determine whether the contamination has traveled further and potentially impacted more areas. This comprehensive approach enables water operators to better understand the extent of the problem and take appropriate action to manage water safety effectively.

Conducting resampling in this manner also aligns with established public health guidelines and regulatory requirements, ensuring that operators can accurately assess and respond to water quality issues to protect public health.