Unregulated Contaminant Monitoring Rule (UCMR) data is collected to assist the EPA in determining the upcoming regulatory standard for Cr 6 and other pending standards. The maximum contaminant level (MCL) that the EPA has always established is 100 ppb of total chromium. The World Health Organization standard has always been 50 ppb for total chromium. The results we gathered for total chromium and our historical data on total chromium showed that we are very far below these MCLs. We continue to run total chromium on an annual basis requirements for monitoring. The total number includes the CR 6, CR 3, etc.
The 0.02 ppb is the California Public Health Goal (PHG) for Chromium 6 not the MCL. Their MCL is 10 ppb. EPA is in the process of determining their Cr 6 MCL. California’s establishes their PHG’s based on the risk of an adverse health effect caused from drinking 1 liter of water for 70 years in one person out of one million. EPA also establishes what they call MCL goals (MCLG) for contaminants. The goals are typically determined first and then further risk assessment and study determine the MCL. If you look at MAWC’s Annual Water Quality Report you will see these MCLGs noted with the MCLs. For instance, the MCL for Total Trihalomethanes is 80 ppb but the MCLG is 0.0 ppb. All the results from our UCMR3 testing for Cr 6 were well below the only established MCL, California’s. Therefore MAWC concluded the testing. Once the EPA establishes an MCL for Cr 6 (if they do)and a testing cycle MAWC will monitor for Cr 6. Until then MAWC will use the Total Chromium results since California’s MCL for Cr 6 is higher the minimum reporting level of Total Cr. So if we get a Total Cr above 5 ppb we can start to sample for CR 6. We have not seen Total Cr above 1 ppb historically.