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A summary of the occurrence of N-nitrosodimethylamine (NDMA) in Metropolitan's treatedwaters and within its distribution system from February 2006 to November 2008 is presented.Based on quarterly data, NDMA concentrations ranged from not detected (ND, 2.0 ng/L) to8.3 ng/L in the effluents from Metropolitan's five treatment plants, with median values for eachplant ranging from ND to 2.5 ng/L. Within Metropolitan's distribution system, NDMAconcentrations ranged from ND to 10 ng/L. At some sampling sites within Metropolitan'streated water distribution system, NDMA levels did not appear to change significantly fromthose measured at the treatment plant effluent. This may have been due to the destruction ofNDMA precursors during pre-oxidation at the treatment plants and/or short detention timeswithin the distribution system (where NDMA is slow to form). At other sites, significantlygreater NDMA levels have been measured, which has been of concern. Higher NDMAconcentrations may be associated with longer detention times and/or the practice of supplementalchlorine addition at finished-water reservoirs within Metropolitan's distribution system. Includes 11 references, figures, table.

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Edition: Vol. - No. Published: 11/01/2009 Number of Pages: 30File Size: 1 file , 2.3 MB