AWWA WQTC65773

In order to comply with impending Stage 1 Disinfection/Disinfection Byproduct Rule, Tampa Bay Water implemented chloramination in its regional system in May 2002. In September 2002 and March 2003, two newly treated surface water sources were brought on line to meet growing demand and regulatory decreases in permitted groundwater use. Historically, the Tampa Bay region relied solely on treated groundwater. Pinellas County also instituted a unidirectional flushing program in April 2002 (roughly). Following these major operational changes, Pinellas County Utilities (PCU) observed a significant increases in the number of positive Total Coliform samples for both their routine compliance sampling and special auxiliary monitoring. County staff related the increase to the change in disinfectant and/or the introduction of the new sources. The apparent temporal correlation between these events and the sudden increase in positive total coliform samples led to the hypothesis that some or all of these changes led to the increased positive samples. In order to evaluate possible causal relationships between the new water sources or new treatment and the bacteriological issues, PCU and Tampa Bay Water initiated an intensive, year long monitoring program at eight locations in the regional transmission system and at connection points between the wholesale and retail systems. Preliminary monitoring by PCU suggested that larger volume samples were more likely to detect total coliform positive results when total coliform bacteria were present (Pryor et al, 2005). Preliminary statistical monitoring using bootstrap analyses supported that larger sample sizes were more effective at detecting total coliform bacteria when they were present. Since the objective of the sampling was to identify sources of total coliform, the participants agreed that larger sample volumes would be appropriate. Due to method limitations and to help the entire industry address the effectiveness of the larger sample volumes, the larger volume samples were taken as multiple 250 ml samples. In order for these results to be comparable with historical total coliform samples a 100 ml samples was also taken at the same time so that the results of 100 ml samples could be compared with progressively increasing volumes ranging from 250 mls up to two liters. Includes reference.