AWWA WQTC58849

Many authors have documented the positive effects of flushing on water quality. Oberoi (1994), in a study on the Edmonton water network, found that chlorine residuals and turbidity levels were improved by flushing and the benefits remained for up to two years. Two other authors (Kuehn et al., 2001; Cossins et al., 1999) found lower turbidity levels in the network following UDF. Coliform positive episodes were also found to be reduced after UDF in Fort Belvoir, according to Antoun et al. (1997). Another study conducted by the same authors in Virginia and North Carolina came to the same conclusions (Antoun et al., 1999). Although the benefits of UDF have been often described, there has not been extensive analysis of the potential adverse short term effects of flushing, due to the incomplete removal of loose deposits at the end of the procedure. The objective of this study was to identify the short term (1 day to 1 week) effects of flushing on water quality. To address this issue, three unidirectional flushing campaigns were performed in Jonquiere (Quebec, Canada) from May 2001 to May 2002. UDF conditions were characterized by velocities of 1 to 2 m/s and a closure criterion of 5 NTU turbidity. Water quality samples were collected before, shortly after (24 hours) and one week after flushing and analyzed for parameters that included: turbidity, chlorine residual, total iron, total coliforms, total viable counts, total direct counts and heterotrophic plate counts. Seven sampling locations in total were selected for this analysis: two at the plants (as a control for influent); and five in the selected sites. A total of 20 analyses were performed for each parameter. Water quality data from the flushing sites were compared to samples from the plants in order to disregard variations attributable to distributed water quality. Includes 7 references, tables, figure.