Evaluation of Arsenic and Iron Transport from Sediments of a Potable Water Treatment Wastewater Pond System

High concentrations of metal(loid)s, such as arsenic (As) and iron (Fe), in wastewater streams are of environmental concern for drinking water treatment plants (DWTP), especially those which use groundwater as their source water. Metal(loid)s can be present in residual wastewaters, sludges, and sediments that make it necessary for them to be treated before release into receiving environments. The present study evaluated As and Fe sediment concentrations for wastewater treatment ponds of a municipal DWTP in Saskatchewan which used both surface and groundwater raw water sources until 2019. The residual wastewater stabilization pond (WSP) system consists of five ponds used for contaminant treatment and/or settling. The evaluation of metal(loid)s in these pond sediments is of importance due to the possibility of their leaching from sediments into groundwater and/or to be released back into the residual wastewater over time. In 2019, As and Fe, among other parameters, were monitored in sediments collected from each of the ponds on three occasions (July, August, and October). Results showed As and Fe in sediments ranged from 46.5 to 580 and 10,000 to 51,800 mg/kg, respectively. Both As and Fe concentrations varied among the ponds and over time. Further assessment of these ponds was completed in 2020 when a new DWTP was commissioned using the same pond system while including only groundwaters as a raw water source.