N-nitrosodimethylamine (NDMA) was first detected in 1990 as a problem pollutant in drinking water wells at levels as high as 3,000 ppt in Elmira, Ontario, Canada. The waste from a large chemical plant over many years had led to the contamination of the drinking water wells for the community. After extensive evaluation and testing, it was determined that UV photolysis was the most effective treatment method which led to the installation of a Calgon 270 kW Rayox® UV system in 1991. The system has been continuously treating water to this day. At about the same time, NDMA was found in the drinking water on an Indian reserve in Ontario, and a similar UV system was installed to remove NDMA from that water. Since then NDMA has been detected as a pollutant in ground waters, surface waters, industrial effluents and wastewaters in many jurisdictions. Many sources have been identified, including chemical plants that manufacture pesticides and herbicides, rubber manufacturing plants, rocket fuel manufacturing plants and wastewater treatment plants.
Recently there has been considerable concern in California about the detection of NDMA in drinking water feed wells at levels as high as 900 ppt. NDMA was found to be a carcinogen in animals and assessed as a Class 1 carcinogen by the USEPA. It is currently listed as a priority pollutant on the US EPA National Priorities List. California has set an 'action level' of 20 ppt for NDMA and treatment systems are required to treat to the detection limit of 2 ppt.