Effects of uranium mining discharges on water quality in the Puerco River basin, Arizona and New Mexico

Abstract

From 1967From until 1986, uranium mine dewatering increased dissolved gross alpha, gross beta, uranium and radium activities and dissolved selenium and molybdenum concentrations in the Puerco River as indicated by time trends, areal patterns involving distance from the mines and stream discharge. Additionally, increased dissolved uranium concentrations were identified in groundwater under the Puerco River from where mine discharges entered the river to approximately the Arizona-New Mexico State line about 65 km downstream. Total mass of uranium and gross alpha activity released to the Puerco River by mine dewatering were estimated as 560 M g (560 X 10 6 g) and 260 Ci, respectively. In comparison, a uranium mill tailings pond spill on 16 July 1979, released an estimated 1.5 Mg of uranium and 46 Ci of gross alpha activity. Mass balance calculations for alluvial ground water indicate that most of the uranium released did not remain in solution. Sorption of uranium on sediments and uptake of uranium by plants probably removed the uranium from solution.Effets des rejets provenant de l'exploitation des mines d'uranium sur la qualité des eaux du bassin du fleuve Puereo, en Arizona et au Nouveau-Mexique Résumé De 1967 a 1986, les opérations d'essorage des mines d'uranium ont eu pour effet d'augmenter les radioactivités alpha (valeur approchée), beta (valeur approchée), uranium et radium en solution, ainsi que les concentrations en sélénium et molybdène dissous, dans le fleuve Puereo, comme l'ont mis en évidence les relations liant ces valeurs aux facteurs de temps, distance aux mine et débit. En outre, des concentrations accrues d'uranium dissous ont été identifiées dans le réseau de nappes aquifères sous le fleuve Puereo, dans un secteur s'étendant du point où les effluents miniers débouchent dans le fleuve jusqu'au voisinage approximatif de la ligne de démarcation entre l'Arizona et le Nouveau-Mexique, â une distance d'environ 65 km en aval. Au total, la masse d'uranium et l'activité alpha (valeur approchée) déversées dans le fleuve Puerco par le procédé d'essorage minier ont été estimées, respectivement, a 560 Mg (560 X 10 6 g) et 260 Ci. Par comparaison, le débordement du bassin à résidus de l'usine d'uranium, survenu le 16 juillet 1979, a rejeté dans le fleuve des quantités évaluées â 1.5 Mg d'uranium et 46 Ci d'activité alpha (valeur approchée). Les calculs d'équilibre des masses pour les eaux souterraines alluviales indiquent que la plus grande partie de l'uranium rejeté n'est pas restée en solution. L'absorption de l'uranium par les dépôts sédimentaire et par les végétaux ont probablement éliminé l'uranium de la solution.

Rapid Dissolution of Soluble Uranyl Phases in Arid, Mine-Impacted Catchments near Church Rock, NM

“…Linear combination fitting of EXAFS spectra reveals that one or more uranophane-group minerals were the dominant soluble components of A7-0, A7-20, and A7-90 (Table SI- 6). The second, less-soluble uranium-bearing mineral suggested by the dissolution data was more difficult to identify by linear combination fitting.…”

“…During this time of active mining and processing, flow in the Puerco was perennial from mining-related releases. Concentrations of uranium and other contaminants were up to five times above background levels in groundwater, surface water, and suspended sediments (5), which presumably were stored in floodplains (6,7).…”

Biogeochemical aspects of uranium mineralization, mining, milling, and remediation

“…Prior to the 1980s, water generated during mine dewatering activities was discharged to the surface and allowed to flow into natural watercourses without any treatment, providing a direct source of contamination of sediments, alluvial aquifers, and deeper aquifers in areas of faulting (Schoeppner, 2008). From 1967 to 1986, dewatering of the Church Rock U mine in New Mexico released a total of 560 Â 10 6 g of U into the Puerco River, estimated from historical water quality and discharge data (Van Metre and Gray, 1992). In some cases, releases were accidental.…”

“…In some cases, releases were accidental. The failure of the Church Rock UMT dam in 1979 resulted in the release of approximately 1.5 Â 10 6 g of U and 1.7 Â 10 12 Bq (46 Ci) into the Puerco River (Van Metre and Gray, 1992). Most of the gross alpha activity in the dewatering effluent was derived from the decay of U, whereas alpha emitters other than U left behind after the milling process were responsible for the alpha activity in the tailings (Van Metre and Gray, 1992).…”

“…Most of the gross alpha activity in the dewatering effluent was derived from the decay of U, whereas alpha emitters other than U left behind after the milling process were responsible for the alpha activity in the tailings (Van Metre and Gray, 1992). Mass-balance calculations on alluvial groundwater suggested that most of the U was sorbed onto sediments or taken up by plants (Van Metre and Gray, 1992 , 2006). Some trace metals have since migrated down into the alluvial aquifer as well as the Upper, Middle and Lower Chinle aquifers at the site.…”