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The objective of this study was to examine the spatial and seasonal evolution of THMs in twolarge size utilities based on a high-frequency data collection program. The two utilities are locatedin the Quebec City region (Canada). Because the collection of data related to chlorination byproducts (CBPs) in water utilitiesin the province of Quebec was not mandatory before June 2001, there is currently very littleinformation concerning variations in these compounds between the plant and the distributionsystem. 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 asimultaneous study of both THMs and haloacetic acids (HAAs) carried out between September 2000 and September2001. Phase 1 was designed to compare THM levels, on a seasonal basis, between the entrancepoint of the distribution system (following post-chlorination) and the system extremities. Phase 2was designed as a study of the spatial evolution of THMs and HAAs based on sampling at severallocations within the distribution system. The criteria for selecting sampling points within thedistribution 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 todownstream; at least one point had to represent the extremity of the distribution system; allpoints had to be supplied directly by the treatment plant, so there was no influence of rechlorinationfacilities or water storage within the distribution system; and, all points had to beaccessible 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 surfacewater temperature are greater) samples were collected weekly or twice per month in order toassess the variations on water quality in detail. From October 1999 to April 2000, the period when soiland surface water are covered by snow and ice, variations in water temperature are far less notableand samples were collected monthly. The collected samples were analyzed for different waterquality and operational parameters: pH (pH-meter); temperature (portable thermometer); freeresidual chlorine (DPD titrimetric method, Standard method 4500-Cl); total organic carbon- TOC(total carbon analyzer using unfiltered samples); UV-254 absorbance (UV/visiblespectrophotometry); 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 atUniversit¿ Laval. The procedures used for the conservation of the samples between their collectionand analysis were those recommended by Standard Methods (APHA, AWWA, WEF, 1996). Includes 13 references, tables, figures.

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Edition: Vol. - No. Published: 06/16/2002 Number of Pages: 10File Size: 1 file , 360 KB