Fourth Unregulated Contaminant Monitoring Rule (UCMR 4)
UCMR 4 Overview
Every five years, the U.S. Environmental Protection Agency (EPA) implements the Unregulated Contaminant Monitoring Rule (UCMR). The purpose of UCMR is to collect data from across the country on contaminants that may be present in drinking water. EPA uses this data to decide if the contaminants occur at frequencies and concentrations high enough to be regulated in the future.
The fourth round of UCMR, UCMR 4, requires monitoring for 30 contaminants between 2018 and 2020. The contaminants include 2 metals, 9 pesticides, 3 alcohols, 3 semi-volatiles, 3 brominated haloacetic-acid groups, 2 disinfection by-product indicators, and, for surface water systems, 10 cyanotoxins. These contaminants are not regulated under the Safe Drinking Water Act.
More information is available at EPA’s Fourth Unregulated Contaminant Monitoring Rule.
Human Health-Based Comparison Values for the UCMR 4 Contaminants
The UCMR 4 contaminants are being studied at very low levels. The levels are based on how low we can detect them in a lab. They are not based on a level established as “significant” or “harmful.” The levels at which we can detect the UCMR 4 contaminants are often below current human health-based guidance values, such as EPA health advisories (HAs) and MDH Health Based Values (HBVs) - to the extent these values have been established.
The detection of a UCMR 4 contaminant does not represent cause for concern, in and of itself. The meaning of a detection should be determined considering current health effects information. This information is often still under development or being refined for unregulated contaminants.
The intent of the following table is to identify human health-based UCMR comparison values, where possible. These comparison values provide context around the detection of a particular UCMR contaminant. A person drinking water with a contaminant at or below the comparison value would be at little or no risk for harmful health effects. The comparison value does not represent an “action level.” Because these contaminants are unregulated, EPA and MDH require no particular action based on detection of a UCMR 4 contaminant.
Table of Comparison Values
|Contaminant||Comparison Value (μg/L)||Value Type|
|2-Methoxyethanol||Not available||Not available|
|2-Propen-1-ol||35||EPA CCL4 HRL|
|Alpha-Hexachlorocyclohexane||0.02||MDH Rapid Assessment|
|Butylated hydroxyl anisole||Not available||Not available|
|Germanium||Not available||Not available|
|HAA6BR||Not available||Not available|
|HAA9||Not available||Not available|
|Microsystin - Total||0.3||EPA HA|
|Nodularin-R||Not available||Not available|
|o-Toluidine||Not available||Not available|
|Tebuconazole||30||MDH Rapid Assessment|
|Permethrins - Total||10||MDH Rapid Assessment|
*Note: HAA5 is regulated under EPA's Disinfectants and Disinfection Byproducts Rule. Under this rule, HAA5 has a maximum contaminant level (MCL) of 60 μg/L.
- EPA: U.S. Environmental Protection Agency
- EPA CCL4 HRL: U.S. Environmental Protection Agency Contaminant Candidate List 4 Health Reference Level
- EPA HA: U.S. Environmental Protection Agency Health Advisory
- EPA HHBP: U.S. Environmental Protection Agency Human Health Benchmarks for Pesticides (PDF)
- HAA: Haloacetic acids
- μg/L (micrograms per liter): One μg/L is the same as one part per billion (ppb), which is like one drop in one billion drops of water.
- MDH HBV: Minnesota Department of Health Health-Based Value
- MDH HRL: Minnesota Department of Health Health Risk Limit
- MDH RAA: Minnesota Department of Health Risk Assessment Advice
- MDH Rapid Assessment
- Not available: No MDH or EPA comparison value available