Initial Sample Data from UCMR4 Now Available

The first data from monitoring under the Fourth Unregulated Contaminant Monitoring Rule (UCMR4) is now available on EPA’s UCMR Occurrence Data web page.  This initial batch of data covers monitoring conducted earlier this year.  Additional batches of data will come out roughly quarterly until all UCMR4 data has been reported, sometime after the end of the monitoring period in 2020.  Each release will include a data summary which is a quick way to review the data.   The data summary reviews the contaminants on the list and their Minimum Reporting Levels (MRLs), plus any reference concentrations that can be used to evaluate the potential health risks.  Most, but not all, of the contaminants have a reference level.  A final table of statistics indicates the number of samples collected and water systems sampled for each contaminant.  The summary also indicates the percentage of samples and water systems with detects that exceed the MRL or the reference concentration.

Since this is the first batch of data, the number of samples is small and there are few surprises so far.  Manganese, quinoline, total microcystins, and the regulated Haloacetic Acids are the only contaminants where more than 0.5% of the systems monitored had a result above the reference level.  There were a number of germanium results above the MRL but there is no reference level.  As more monitoring is conducted and the sample size grows, we will get more clarity on the occurrence of these contaminants.   Another round of data should be released after the first of the year.