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A Brief History of NDMA Findings in Drinking Water

Last Update: January 4, 2011

1998—In February-March, samples from a drinking water well in eastern Sacramento County confirmed the presence of N-nitrosodimethyamine (NDMA) at ~0.15 microgram per liter (µg/L).  This well was taken out of service by the utility.  Sampling was in response to concern about the presence of NDMA contamination at an aerospace facility.

1998—In April, CDHS (the California Department of Health Services, now CPDH) established an action level for NDMA of 0.002 µg/L, based on a de minimis cancer risk level.  However, analytical capabilities did not enable detection at that concentration, so any detectable quantity of NDMA was over the AL. The action level was derived from regulatory risk level of 0.04 µg/day for purposes of Proposition 65 implementation (Title 22 of the California Code of Regulations, Section 12705), which corresponds to a 10-5 lifetime cancer risk.  Dividing 0.04 µg/day by 2 liters of drinking water/day gives 0.02 µg/L, and dividing by 10 yields 0.002 µg/L, a de minimis, or 10-6, cancer risk level.  This is the level CDHS generally uses for notification levels for carcinogenic chemicals.

1998—In May, NDMA was detected in three drinking water wells in the San Gabriel Basin. Two wells with NDMA at concentrations of 0.07 µg/L were removed from service. The third well, already out of service because of trichloroethylene and perchlorate contamination, contained NDMA at 3 µg/L. 

1999—Limited sampling indicated that NDMA appeared to be present at very low levels (<0.01 µg/L) in treated drinking water. Preliminary analyses suggested that NDMA's presence in drinking water was related to disinfection processes, but very limited data were available, and often they appeared to be inconclusive.  Coincidental with more sensitive analytical methods becoming available, DHS initiated studies with drinking water utilities to investigate the occurrence of NDMA in raw, treated and distributed water, the role water quality and treatment processes may play in the production of NDMA, and the possible extent of NDMA production at various steps in the water treatment process. 

1999—As interest in NDMA monitoring increased in the water treatment community, DHS was informed of NDMA findings in treated waste water. From the standpoint of protecting drinking water consumers and sources, DHS considered this finding to be important in the evaluation of proposed recycled water projects involving waste water discharges and ground water recharge.

1999—In November, CDHS revised the action level to 0.02 µg/L to accommodate studies on NDMA's production in drinking water treatment

2000—In May, two wells in Orange County had NDMA at concentrations of approximately 0.03 to 0.04 µg/L, and were taken out of service.  A nearby groundwater recharge operation involving injection of treated wastewater contained NDMA in its injected water. DHS informed the wastewater treatment plant that its activities were impairing groundwater, and directed them to reduce the levels of NDMA accordingly.

2000—Also in May, a system in Los Angeles County found NDMA in its groundwater sources at 0.032 to 0.076 µg/L, apparently associated with the past production of chemicals used in the aerospace industry. 

2000—In June, a system in Los Angeles County found NDMA at about 0.03 µg/L, apparently related to resins used in water treatment for nitrate removal.  

2000—Also in June, in Los Angeles County, NDMA at 0.049 and 0.074 µg/L (duplicates) and 0.091 µg/L was found in treated wastewater that was blended for use as groundwater recharge.

2002—In March, CDHS requested a public health goal (PHG) for NDMA from the Office of Environmental Health Hazard Assessment (OEHHA).  A PHG is an early step in the regulatory process involved in developing a drinking water standard.

2002—Also in March, CDHS posted on its website results of studies on NDMA's production in drinking water treatment, as well as a revised notification level, to 0.01 µg/L.  

2004—In July, OEHHA initiated a risk assessment for NDMA that will lead to a PHG.

2004—In September, CDHS added a 0.01-µg/L notification level for another nitrosamine, N-nitrosodiethyamine (NDEA).

2005—In May, CDHS added a 0.01-µg/L notification level for N-nitroso-n-propylamine (NDPA).  NDPA and NDMA were found in some disposable resins being evaluated for drinking water treatment.

2006—In February, OEHHA released a 0.003-µg/L draft PHG for NDMA.

2006—In December, OEHHA established the PHG for NDMA at 0.003 µg/L.  CDHS' notification level remains at 0.01 µg/L.

2007—In July, the Drinking Water Program became part of the new CDPH. 

Current—NDMA and other nitrosamines are considered "emerging contaminants."  More information about emerging contaminants is here.

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Last modified on: 12/29/2013 11:41 AM