AWWA ACE56329

Findings from AwwaRF Project 2676 - Sample Collection Procedures and Locations for Bacterial Compliance Monitoring are summarized and presented in this paper. The surveys of U.S. regulatory agencies and utilities throughout the United States indicated that there was a general lack of specific guidance in regard to selecting sampling points within distribution systems, and significant variations exist in sample site selection, sample tap configurations, and sample collection procedures. The critical factors affecting microbial sampling results are disinfection residual, materials of construction, service lines and hydraulic conditions, and sample collection and analytical methods. Other significant variables include temperature, corrosion and sediment accumulation, and presence of nutrients. As part of the laboratory testing phase of this project, two parallel laboratory pipe loops were designed and constructed to evaluate bacterial counts in unlined cast-iron and PVC pipe materials. Specific sampling procedures were studied, including flushing, flaming, and disinfectant applications. Conclusions from the pipe loop study indicate that dedicated and non-threaded (soldered) sampling ports accurately reflect bulk water bacterial levels when compared to threaded and plastic sampling taps, and that hydraulic conditions in household copper service and in dead-end segments of the distribution system can have significant influences on heterotrophic bacteria levels. A field study conducted at four drinking water utilities throughout the United States focused on locational aspects of bacterial monitoring. Sampling sites were located within high and low demand areas of the distribution system, close to and away from reservoirs and storage tanks, before and after booster chlorination, in areas of predominately high and low chlorine residual, and in areas containing specific pipe materials (old cast-iron, PVC, and AC). Dedicated sampling stations were compared to residential and commercial customer taps. Both interior and exterior residential and commercial customer taps were also evaluated. The results of the laboratory pipe loop investigations and field studies are presented in this paper. Includes tables, figures.