Cat. No.: H46-2/96-206E
This study examined disinfection by-product (DBP) concentrations in drinking water as a function of treatment practice, season and location in the distribution system for each of three water treatment plants that applied different treatment processes (chlorine-chloramine, chlorine-chlorine, ozone-chlorine). On a monthly basis, over a 13 month period, DBP concentrations were measured in raw water samples and in treated water samples collected at four locations in the distribution system for each treatment plant. The major DBPs observed were chloroform (TCM), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA). The concentrations of other DBPs (chloral hydrate, haloacetonitriles, halopropanones, chloropicrin) were usually an order of magnitude lower. The overall picture that emerged was that no single sampling event captured the complete image of the behaviour of DBPs in the distribution system. DBP concentrations were observed to fluctuate as a function of water treatment practice (and variations therein), age of the water and temperature of the water. DBP concentrations were usually higher in the summer than in the winter for all treatment processes. With chlorinechloramine treatment DBP concentrations did not, in general, increase significantly with distance (time) in the distribution system. With chlorine-chlorine treatment THM concentrations increased with distance (time) in the distribution system and maximum values were found at the sampling point furthest from the treatment plant. The behaviour of the other DBPs was more complex. Their concentrations showed an increase in the first part of the distribution system but depending on the season and age of the water the DBP concentrations could either increase or decrease at greater distances (time) in the distribution system. Of particular importance from a regulatory viewpoint was that no single site or time of year could be selected to provide simultaneous maximum values for the three major DBPs (TCM, DCAA and TCAA). The development of a sound sampling strategy to assess consumer exposure to DBPs will require more in depth studies to provide a greater understanding of the DBP behaviour within distribution systems.