Unregulated Contaminant Monitoring Rule (UCMR3)

WSSC is participating in the U.S. Environmental Protection Agency’s (EPA) third round of the Unregulated Contaminant Monitoring Rule (UCMR3).  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 UCMR3 is available here.


The EPA currently has drinking water regulations for more than 90 contaminants.  The 1996 Safe Drinking Water Act (SDWA) amendments require that once every five years the EPA issue a new list of no more than 30 unregulated contaminants to be monitored by public water systems (PWSs). The first Unregulated Contaminant Monitoring Rule (UCMR1) was published on September 17, 1999, the second (UCMR2) was published on January 4, 2007 and the third (UCMR3) was published on May 2, 2012. Here’s a link to the latest list of chemicals that were monitored (look for Lists 1 and 2 in the middle of the page.)  This monitoring provides a basis for future regulatory actions to protect public health. While the EPA requires utilities to report results in their annual Water Quality Reports (also known as Consumer Confidence Reports), a new Maryland law (effective October 1, 2013) requires WSSC to report detected contaminants within 30 days of receiving test results.

What WSSC is Doing

As part of the UCMR3 program, WSSC collected and analyzed four sets of quarterly samples between July 2013 and April 2014.  Samples were collected from four locations for each set - finished water from both of our water treatment plants as well as two distribution system sites representing the WSSC system locations furthest from the plants.  Although not required, source water samples (water before treatment) were also collected and analyzed during the last three quarterly sampling events to attempt to identify if the detected contaminants were present in the source water. The detected contaminants of the UCMR3 sampling are listed in this table.  Only 5 of the 28 tested contaminants were detected, and all detections were at low levels (parts per billion range).*   Hormones, perfluorinated compounds, synthetic organic compounds, and volatile organic compounds analyzed in the UCMR3 monitoring were not detected in our treated drinking water. The source water sampling results suggest that the detected contaminants appear to be present in the source water. The EPA has not established maximum contaminant levels (MCL) for these unregulated contaminants, and the human health effects of these contaminants at the levels they were found is unclear.  In the absence of MCLs and health standards, published guidance or health reference levels from the EPA are listed in the table (attached as pdf) as a point of comparison. 

The EPA UCMR3 program ended in April 2014, and WSSC is no longer required by the EPA to conduct monitoring of these unregulated contaminants.  WSSC discontinued testing at the end of the EPA requirement but reinstituted quarterly testing again in April 2015 to meet the requirements of the State legislation.

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

*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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