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EPA Releases Updated UCMR4 Data Summary

On May 10th, EPA posted the third set of analytical results and a Data Summary for the Fourth Unregulated Contaminant Rule (UCMR 4). Under the rule, all large public water systems (PWSs) and a representative subset of small PWSs are required to monitor for four quarters for up to 30 contaminants (metals, cyanotoxins, pesticides, brominated disinfection byproducts, alcohols, and semi-volatile organic chemicals) between 2018 and 2020. The national summary is for the data received as of 5/1/19. EPA will continue to update the information on UCMR’s occurrence webpage approximately quarterly. The data are subject to change until a final dataset is published in early 2022.

The results for manganese monitoring has probably been the biggest surprise in the UCMR4 monitoring. According to this latest summary, 39 systems in 22 states have had sample results greater than the reference concentration of 300 ug/L (a 10-day health advisory for infants). The resultant actions that water systems have been strongly recommended to take have been a little unexpected for some of the water systems, as the health advisory is being treated the same as an enforceable Maximum Contaminant Level (MCL). Pierre, the capitol of South Dakota, is a recent example of water system that had to issue a “Do Not Drink” order based on the results of the UCMR4 monitoring, which is separate from traditional MCL compliance monitoring.