Field evidence of biodegradation of N-Nitrosodimethylamine (NDMA) in groundwater with incidental and active recycled water recharge |
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Authors: | Quanlin Zhou Sally McCraven Monica Gasca William E Motzer |
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Affiliation: | a Earth Sciences Division, Lawrence Berkeley National Laboratory, University of California, One Cyclotron Road, MS90-1116, Berkeley, CA 94720, United States b Todd Engineers, 2490 Mariner Square Loop, Suite 215, Alameda, CA 94501, United States c Calpine-The Geysers, 10350 Socrates Mine Road, Middletown, CA 94561, United States d County Sanitation Districts of Los Angeles County, 1955 Workman Mill Road, Whittier, CA 90601, United States e Water Replenishment District of Southern California, 4040 Paramount Blvd., Lakewood, CA 90712, United States |
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Abstract: | Biodegradation of N-Nitrosodimethylamine (NDMA) has been found through laboratory incubation in unsaturated and saturated soil samples under both aerobic and anaerobic conditions. However, direct field evidence of in situ biodegradation in groundwater is very limited. This research aimed to evaluate biodegradation of NDMA in a large-scale groundwater system receiving recycled water as incidental and active recharge. NDMA concentrations in 32 monitoring and production wells with different screen intervals were monitored over a period of seven years. Groundwater monitoring was used to characterize changes in the magnitude and extent of NDMA in groundwater in response to seasonal hydrogeologic conditions and, more importantly, to significant concentration variations in effluent from water reclamation plants (associated with treatment-process changes). Extensive monitoring of NDMA concentrations and flow rates at effluent discharge locations and surface-water stations was also conducted to reasonably estimate mass loading through unlined river reaches to underlying groundwater. Monitoring results indicate that significant biodegradation of NDMA occurred in groundwater, accounting for an estimated 90% mass reduction over the seven-year monitoring period. In addition, a discrete effluent-discharge and groundwater-extraction event was extensively monitored in a well-characterized, localized groundwater subsystem for 626 days. Analysis of the associated NDMA fate and transport in the subsystem indicated that an estimated 80% of the recharged mass was biodegraded. The observed field evidence of NDMA biodegradation is supported by groundwater transport modeling accounting for various dilution mechanisms and first-order decay for biodegradation, and by a previous laboratory study on soil samples collected from the study site Bradley, P.M., Carr, S.A., Baird, R.B., Chapelle, F.H., 2005. Biodegradation of N-Nitrosodimethylamine in soil from a water reclamation facility. Bioremediat. J. 9 (2), 115-120.]. |
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Keywords: | N-Nitrosodimethylamine (NDMA) Biodegradation Photolysis Artificial recharge Groundwater Surface water |
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