AWWA ACE56287

The objective of this study was to examine the spatial and seasonal evolution of THMs in two large size utilities based on a high-frequency data collection program. The two utilities are located in the Quebec City region (Canada). Because the collection of data related to chlorination byproducts (CBPs) in water utilities in the province of Quebec was not mandatory before June 2001, there is currently very little information concerning variations in these compounds between the plant and the distribution system. The paper lists the general characteristics of the utilities under study. The data for this analysis were generated in two different phases. Phase 1 represents a study of trihalomethanes (THM) variations carried out between May 1999 and September 2000, and Phase 2 represents a simultaneous study of both THMs and haloacetic acids (HAAs) carried out between September 2000 and September 2001. Phase 1 was designed to compare THM levels, on a seasonal basis, between the entrance point of the distribution system (following post-chlorination) and the system extremities. Phase 2 was designed as a study of the spatial evolution of THMs and HAAs based on sampling at several locations within the distribution system. The criteria for selecting sampling points within the distribution systems were numerous: the points had to be located at variable distances from the plant, to favor variable residence times of water; they had to be located on-line from upstream to downstream; at least one point had to represent the extremity of the distribution system; all points had to be supplied directly by the treatment plant, so there was no influence of rechlorination facilities or water storage within the distribution system; and, all points had to be accessible for sampling the same day, every week over a year. For both Phase 1 and Phase 2 from May to September (a period at which the variations of surface water temperature are greater) samples were collected weekly or twice per month in order to assess the variations on water quality in detail. From October 1999 to April 2000, the period when soil and surface water are covered by snow and ice, variations in water temperature are far less notable and samples were collected monthly. The collected samples were analyzed for different water quality and operational parameters: pH (pH-meter); temperature (portable thermometer); free residual chlorine (DPD titrimetric method, Standard method 4500-Cl); total organic carbon- TOC (total carbon analyzer using unfiltered samples); UV-254 absorbance (UV/visible spectrophotometry); and, THMs and HAA5 (E-capture chromatography, EPA 551,2 and 552,2 methods, respectively). The first three parameters were measured in the field, the others in the laboratory at Universit¿ Laval. The procedures used for the conservation of the samples between their collection and analysis were those recommended by Standard Methods (APHA, AWWA, WEF, 1996). Includes 13 references, tables, figures.