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Wastewater stabilization ponds (WSPs) are commonly used to reduce wastewater metal(loid) concentrations from drinking water treatment plants (DWTPs) through sedimentation. However, this results in increased sediment concentrations that can be released back into the overlying water. Thus, our goal was to evaluate the WSP metal(loid)s occurrence and leaching potential. Currently, a Saskatchewan based DWTP's WSP system was investigated given historically elevated effluent As and Fe concentrations. The WSP consists of five ponds that were sampled on six occasions in 2019 and 2020. In addition, sediments were used in laboratory-based experiments to determine their leaching potential. Overall, the sediments were found to contain elevated concentrations of As and Fe of 25 to 400 mg/kg and 10 000 to 45 000 mg/kg, respectively. Leaching experiments indicated that the pond sediments could potentially release As and Fe with log [K.sub.d] values ranging from 2.21 to 4.31 L/kg, whereas Fe ranged from 3.32 to 5.53 L/kg. Key words: arsenic, iron, wastewater stabilization ponds, drinking water treatment, sediment leaching. Les bassins de stabilisation des eaux usees (BSEU) sont couramment utilises pour reduire les concentrations de metaux (metalloides) provenant des usines de production d'eau potable (UEP) par sedimentation. Toutefois, cela entraine une augmentation des concentrations de sediments qui peuvent etre rejetes dans l'eau sus-jacente. Ainsi, l'objectif des auteurs etait d'evaluer la presence de metaux (metalloides) dans les BSEU et leur potentiel de lixiviation. A l'heure actuelle, un systeme de BSEU d'une UEP en Saskatchewan a fait l'objet d'une etude, compte tenu des concentrations historiquement elevees d'As et de Fe dans les effluents. Le BSEU comprend cinq bassins qui ont ete echantillonnes a six reprises en 2019 et 2020. De plus, les sediments ont ete utilises dans des experiences en laboratoire pour determiner leur potentiel de lixiviation. Dans l'ensemble, les sediments contenaient des concentrations elevees d'As et de Fe de 25 a 400 et de 10 000 a 45 000 mg/kg, respectivement. Les experiences de lixiviation ont indique que les sediments du bassin pourraient rejeter de l'As et du Fe avec des valeurs de log [K.sub.d] ([K.sub.d], rapport de distribution) allant de 2,21 a 4,31 L/kg pour l'As, tandis que Fe variait de 3,32 a 5,53 L/kg. Mots-cles : arsenic (As), fer (Fe), bassins de stabilisation des eaux usees (BSEU), production de l'eau potable, lixiviation des sediments., Introduction Raw water sources for drinking water treatment plants (DWTPs) include surface waters and groundwaters that may contain elevated concentrations of heavy metals and metalloids. Of most interest in the [...]

Drinking water treatment plants (DWTPs) produce wastewaters with elevated concentrations of heavy metals, metalloids, ammonia, and other contaminants. These wastewaters require treatment via processes including wastewater stabilization ponds (WSPs). This study assessed the arsenic (As), iron (Fe), and ammonia (N[H.sub.3]) concentrations in a Saskatchewan DWTP WSP system of five sequential ponds. Drone imaging combined with flow and depth data was used to estimate retention times which increased from 7-9 to 8-10 days after the DWTP upgrade. Concentration trends showed Fe decreased from Pond 1 to 3 and increased in Ponds 3 and 5, while As decreased from Pond 1 to 5. Average effluent As concentrations of 10.6 [micro]g/L were above the 5.0 [micro]g/L guideline, while concentration guidelines for both Fe and N[H.sub.3] were easily met postupgrade in 2020. Several actions are recommended to ensure adequate WSP operation including dredging, aeration, and installing macrophytes capable of As uptake. Key words: arsenic, iron, wastewater stabilization ponds, drinking water treatment, residual wastewaters. Les usines de production d'eau potable (UPEP) rejettent des eaux usees contenant des concentrations elevees de metaux lourds, de metalloides, d'ammoniac et d'autres contaminants. Ces eaux usees doivent etre traitees au moyen de procedes, y compris les bassins de stabilisation des eaux usees (BSEU). Cette etude a evalue les concentrations d'arsenic (As), de fer (Fe) et d'ammoniac (N[H.sub.3]) dans un systeme UPEP BSEU de cinq etangs sequentiels en Saskatchewan. L'imagerie de drones, jumelee aux donnees de debit et de profondeur, a ete utilisee pour estimer les temps de retention qui sont passes de 7-9 a 8-10 jours apres la mise a niveau de l'UPEP. Les tendances en matiere de concentration ont montre que Fe diminuait du bassin 1 a 3 et augmentait dans les bassins 3 et 5, tandis que l'As diminuait du bassin 1 a 5. Les concentrations moyennes d'As dans l'effluent de 10,6 [micro]g/L etaient superieures a la recommandation de 5,0 [micro]g/L , les concentrations de Fe et de N[H.sub.3] selon les recommandations ont ete facilement atteintes apres la mise a niveau en 2020. Plusieurs mesures sont recommandees pour assurer un fonctionnement adequat des BSEU, y compris le dragage, l'aeration et l'installation de macrophytes capables d'absorber l'As. [Traduit par la Redaction] Mots-cles : arsenic, fer, bassins de stabilisation des eaux usees (BSEU), production d'eau potable, eaux usees residuelles., 1. Introduction Drinking water treatment plants (DWTPs) use a suite of treatment processes to improve the quality of source surface waters or groundwaters to meet relevant drinking water standards. As [...]