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Chromium-6 (hexavalent chromium or Cr-6)

Chromium-6 (Cr-6) is a naturally occurring contaminant and an industrial chemical that has been linked to cancer. Research is underway regarding how much, if any, Cr-6 might pose a health risk in drinking water. There is no regulation for it. The City of Milwaukee Health Department determined in 2011 there is no evidence of an imminent public health risk or threat of acute illness based on Milwaukee Water Works monitoring results.  The Milwaukee Water Works has been conducting quarterly monitoring and reporting for Cr-6 since 2011.   

Summary of monitoring 2011-2018 for Cr-6
Results are in micrograms per liter (µg/L) or parts per billion (ppb)


Lake Michigan Source Water

Treated Water Water in the Distribution System
Maximum 0.46 0.41 0.29
Minimum 0.10 0.14 0.12
Median 0.21 0.21 0.21

The EPA is reviewing a proposal to set a safe level, known as a Maximum Contaminant Level (MCL), for Cr-6, and is assessing health effects based on available data and data now being collected by utilities like Milwaukee. EPA has not yet provided any risk context for the sampling or any operational guidance if Cr-6 was detected. Cr-6 is included in the EPA Unregulated Contaminant Monitoring Rule-3 (UCMR-3) mandatory monitoring to collect data. This requires quarterly monitoring of source water, treated water and water in the distribution system from one site per each of our two treatment plants. (Total Chromium is regulated by the EPA via the Safe Drinking Water Act (SDWA) while Cr-6 is not regulated.)

Why we monitor Cr-6 in Milwaukee
MWW began monitoring for Cr-6 after a January 2011 EPA guidance that encouraged utilities to conduct Cr-6 sampling of source, treated water, and water in the distribution system on a quarterly basis. We are prepared to respond, as we did by immediately ordering tests for chromium-6, to protect public health and meet federal and state water quality standards.

The latest US results
During the three-year period from January 2013 - December 2015, all community and nontransient noncommunity systems serving more than 10,000 persons, and a statistical sample of small systems, were required to monitor for Cr-6 and 27 other unregulated contaminants for one year. This UCMR3 data is released on EPA’s website periodically over the monitoring period.

California set its own MCL
In July 2014, California became the first U.S. state to determine an MCL specifically for hexavalent chromium of 10 parts per billion. The state’s public health goal for hexavalent chromium is 0.02 parts per billion. The EPA data show 88 systems are above California’s existing MCL. The level of Cr-6 in Milwaukee water results are below California’s existing MCL but above California's public health goal.

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