Evaluation of the Final UCMR2 Database: Nationwide Trends in NDMA

The complete database of results from the second Unregulated Contaminant Monitoring Rule (UCMR2) was analyzed in depth for N‐nitrosodimethylamine (NDMA) occurrence across the United States and analyzed for trends associated with factors reported. Disinfectant type, source waters, regional variability, population density, and seasonal variability were all examined for potential impacts on NDMA. Detectable levels of NDMA were found in 17% of samples and 25% of treatment plants. The other five listed nitrosamines were detected in less than 1% of samples. The strongest factor found positively associated with NDMA occurrence was chloramine use. Likewise, the use of surface waters was found to be linked to NDMA occurrence such that surface waters (even when decoupled from chloramine use) demonstrated elevated levels of NDMA over groundwater sources. No clear seasonal trends could be deciphered, but data supplied from utilities servicing fewer than 10,000 customers provide evidence that smaller utilities have some of the most extreme NDMA levels and subsequently may have a difficult time meeting any future NDMA regulation.