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Research for New Regulation: UCMR2
Massachusetts Water Resources Authority

The US Environmental Protection Agency (EPA) periodically requires water systems across the country to conduct monitoring for substances that may be present in drinking water to help understand their national occurrence as part of the process of deciding whether to regulate them.  Under the Safe Drinking Water Act Amendments, EPA established the Unregulated Contaminant Monitoring Rule and is required once every five years to develop a list of up to 30 new contaminants that must be monitored during a three year period by public water systems that meet the criteria for sampling.  This monitoring is used by EPA to understand the frequency and level of occurrence of unregulated contaminants in the nation’s public water systems (PWSs).

EPA will collect and analyze data for all three years and from systems all across the country to develop an understanding of the occurrence, level and distribution of these substances in drinking water. That data, along with information on potential halth effects and water treatment effectiveness will be used by EPA to determine if any new regulations are needed.

Return to UCMR Main Page

UCMR 2 (2008-2010)

The Second Unregulated Contaminant Monitoring Rule (UCMR2) required larger water systems, and and sample of smaller water systems to sample for 25 potential contaminants in finished drinking water over a 1 year period during 2008-2010.

List 1 includes two insecticides, five flame retardants, and three explosives. List 2 includes three parent acetanilides, six acetanilide degradates, and six nitrosamines.

Here is a list of the UCMR 2 contaminants:

List 1 (10)
Terbufos sulfone
2,2',4,4'-tetrabromodiphenyl ether (BDE-47)
2,2',4,4',5-pentabromodiphenyl ether (BDE-99)
2,2',4,4',5,5'-hexabromobiphenyl (HBB)
2,2',4,4',5,5'-hexabromodiphenyl ether (BDE-153)
2,2',4,4',6-pentabromodiphenyl ether (BDE-100)
2,4,6-trinitrotoluene (TNT)
Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)


List 2 (15)
Acetochlor ethane sulfonic acid (ESA)
Acetochlor oxanilic acid (OA)
Alachlor ethane sulfonic acid (ESA)
Alachlor oxanilic acid (OA)
Metolachlor ethane sulfonic acid (ESA)
Metolachlor oxanilic acid (OA)
N-nitroso-diethylamine (NDEA)
N-nitroso-dimethylamine (NDMA)
N-nitroso-di-n-butylamine (NDBA)
N-nitroso-di-n-propylamine (NDPA)
N-nitroso-methylethylamine (NMEA)
N-nitroso-pyrrolidine (NPYR)


Only one of the 25 sampled contaminants, NDMA, was detected in MWRA water. All others were non detectable.

Substance Measurement Units Average Range
N-nitroso-dimethylamine  parts per trillion (ppt)   1.1 ND – 4.2

N-nitroso-dimethylamine (NDMA) can come from industrial pollution, or can be a disinfection byproduct of chloramination, and can also be a byproduct in filtration plants of certain coagulants and disinfectants. NDMA can for in small quantities in air, water and soil as a result of biological, chemical and photochemical processes. However, the largest source of human exposure is the reaction of stomach acids with nitrates in food. It is classified by EPA as a probable human carcinogen from long-term exposures.

The World Health Organization (WHO) has a guideline value for NDMA of 100 parts per trillion (ppt); Health Canada has a maximum allowable concentration of 40 ppt; and California has an enforceable response level of 500 ppt and a notification level of 10 ppt. MassDEP has an non-enforceable Office of Research and Standards Guidelinevalue for NDMA of 10 ppt.

Most of MWRA's samples had non-detectable levels. Sample sites at the extreme ends of the distribution system that have the longest travel time for the treatment plant had levels of 2 to 4 ppt. One non-UCMR sample from additional investigatory sampling had a result of 5.4 ppt. All results were well below any regulatory of health guidance values.

More information on these substances and UCMR2 can be found on the US EPA web site here.

Updated May 5, 2022

Historic Withdrawls Reservoir Levels