Environmental Health - Toxic Substances Hydrology Program
N-nitrosodimethylamine (NDMA) is an unintended, highly toxic byproduct of the chlorination of wastewater at many wastewater treatment plants. Water-resource managers in California became concerned about the potential for NDMA to reach ground water after NDMA was detected in two drinking-water supply wells located near a water reclamation facility where treated wastewater was injected directly into the subsurface to recharge ground water (see text box below). USGS scientists collaborated with Sanitation Districts of Los Angeles County, California, to study the potential for NDMA to biodegrade in the soils of the Rio Hondo spreading grounds. Treated wastewater is applied to the spreading grounds and allowed to soak into the subsurface to recharge a drinking-water aquifer. The objective of the study was to determine if microorganisms present in the spreading ground soil could degrade NDMA before it reaches the underlying drinking-water aquifer. The scientists documented significant biodegradation of NDMA to harmless end products in soils at the facility. Their results showed that biodegradation of NDMA under both oxic and anoxic conditions (with oxygen and without oxygen) is an important component of the natural attenuation of NDMA in soils at ground-water recharge facilities. These results indicate that water-resource managers can use this approach to remove NDMA from wastewater at ground-water recharge facilities with appropriate conditions. In addition, water-resource managers can use the field and laboratory methods employed by the USGS scientists during this study to assess the potential for natural attenuation of NDMA in soil. This is useful information to have when assessing the safety of ground-water recharge facilities that recycle treated wastewater.
Concern About NDMA in California
Two drinking-water supply wells in Orange County, California, were removed from service in 2000 following the detection of NDMA at concentrations of 30-40 ng/L (nanograms per liter), which were above the California Department of Health Services' drinking-water action level of 10 ng/L for NDMA. NDMA contamination in the aquifer that the wells were withdrawing from was attributed to the recharge activities at a nearby water reclamation facility. The facility was directly injecting treated wastewater into an aquifer to recharge ground water supplies.
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