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TitleDetermination of the origin of groundwater nitrate at an air weapons range using the dual isotope approach
AuthorBordeleau, G; Savard, M M; Martel, R; Ampleman, G; Thiboutot, S
SourceJournal of Contaminant Hydrology vol. 98, 2008 p. 97-105,
Alt SeriesEarth Sciences Sector, Contribution Series 20070018
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
ProvinceAlberta; Saskatchewan
NTS73K/13; 73L/16
AreaCold Lake; Primrose Lake; Jimmy Lake
Lat/Long WENS-110.5000 -109.5000 55.0000 54.7500
Subjectshydrogeology; environmental geology; geochemistry; groundwater; groundwater geochemistry; groundwater regimes; groundwater pollution; nitrate; environmental studies; environmental analysis; isotopes; isotope ratios
Illustrationslocation maps; graphs; tables
ProgramGroundwater Mapping Program
AbstractNitrate is one of the most common contaminants in shallow groundwater, and many sources may contribute to the nitrate load within an aquifer. Groundwater nitrate plumes have been detected at several ammunition production sites. However, the presence of multiple potential sources and the lack of existing isotopic data concerning explosive degradation-induced nitrate constitute a limitation when it comes to linking both types of contaminants. On military training ranges, high nitrate concentrations in groundwater were reported for the first time as part of the hydrogeological characterization of the Cold Lake Air Weapons Range (CLAWR), Alberta, Canada. Explosives degradation is thought to be the main source of nitrate contamination at CLAWR, as no other major source is present. Isotopic analyses of N and O in nitrate were performed on groundwater samples from the unconfined and confined aquifers; the dual isotopic analysis approach was used in order to increase the chances of identifying the source of nitrate. The isotopic ratios for the groundwater samples with low nitrate concentration suggested a natural origin with a strong contribution of anthropogenic atmospheric NOx. For the samples with nitrate concentration above the expected background level the isotopic ratios did not correspond to any source documented in the literature. Dissolved RDX samples were degraded in the laboratory and results showed that all reproduced degradation processes released nitrate with a strong fractionation. Laboratory isotopic values for RDX-derived NO3- produced a trend of high delta18O-low delta15N to low delta18O-high delta15N, and groundwater samples with nitrate concentrations above the expected background level appeared along this trend. Our results thus point toward a characteristic field of isotopic ratios for nitrate being derived from the degradation of RDX.