In the event of a positive total coliform result at a distribution site, where should resampling occur?

When a positive total coliform result is obtained at a distribution site, resampling is essential to confirm the presence of coliform bacteria and to determine the extent of contamination. The correct approach is to resample at the same location where the initial sample was taken, as this helps to verify whether the positive result was an anomaly or indicative of a systemic problem. Additionally, sampling one site upstream and one site downstream from the original location provides valuable information about the potential spread of contamination through the distribution system.

Sampling upstream helps assess if the source of contamination is localized to a specific area or if it originates from a deeper issue further along the distribution line, while sampling downstream can help identify if the contamination has affected other areas. This strategy is critical in understanding the water quality throughout the distribution network and is part of a proactive response to ensure public health safety. The combination of these three locations (the original sample site and one site each above and below) allows for a comprehensive evaluation of the situation.