Unregulated Contaminant Monitoring Rule (UCMR4)

WSSC Water participated in the U.S. Environmental Protection Agency’s (EPA) fourth round of the Unregulated Contaminant Monitoring Rule (UCMR4) and completed sampling at the end of 2018.Approximately 6,000 utilities nationwide will monitor unregulated contaminants for a year to help the EPA determine the occurrence of these contaminants in drinking water and whether or not they need to be regulated for protection of public health. More information on UCMR4 is available here.

As part of the UCMR4 program, WSSC Water collected two sets of samples quarterly throughout 2018. Samples were collected from our source and finished water from both of our water treatment plants as well as sixteen distribution system sites representing the WSSC Water distribution system. In addition to quarterly samples, cyanotoxin samples were collected twice a month beginning in July 2018 and ending in October 2018.

In accordance to the requirements of Public Utilities Article 28-301(b)(2), WSSC Water will continue to monitor unregulated contaminants under UCMR4 at the same frequency until the next cycle of federal UCMR monitoring begins. The detected contaminants of the UCMR4 sampling are listed in this table.

We are committed to protecting public health and will continue to monitor and support EPA’s research on these contaminant

*Parts Per Billion (ppb) = Half of a teaspoon of water in an Olympic-sized swimming pool would be about one part per billion. Also, the equivalent of one minute in 2,000 years, or one penny in $10 million.


MCL – Maximum Contaminant Level –  “The maximum permissible level of a contaminant in water which is delivered to any user of a public water system."(EPA)
MCLG – Maximum Contaminant Level Goal – “The level of a contaminant in drinking water below which there is no known or expected risk to health.” (EPA)

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