Modeling a rapid infiltration basin for wastewater treatment in the Arctic under various operating conditions

Modeling subsurface environments in arctic regions is challenging due to the complex hydrogeological dynamics and the logistical and financial obstacles to obtaining field data to develop and calibrate models. Many northern and remote communities rely on passive systems to treat wastewater, including soil-based solutions such as rapid infiltration basins (RIBs). However, these systems often operate under atypical conditions, leaving gaps in our understanding of the hydrology and treatment efficacy of such systems in cold regions. In this study, HYDRUS 2D was used to develop a variably saturated water flow and solute transport model using field data from an existing municipal wastewater infiltration system in the Canadian Arctic. Various operating scenarios were considered to evaluate groundwater mounding and nitrogen and pathogen treatment performance. Both atypical operating conditions reported or observed in northern applications and operating routines recommended by standard guidelines were evaluated. Model results indicate that the harsh operating conditions in the studied system (year-round high loading rates and small application area) are only feasible due to the deep vadose zone and high-permeability material underlying the trench. However, in scenarios with increased population or where the water table is shallower, an improved effluent distribution system would be required to avoid system failure from excessive mounding. When compared to conventional operations, intermittent truck discharges exhibited advantages from a hydraulic perspective (less mounding) but also decreased pollutant removal efficiency. This research provides important insights and helps address knowledge gaps related to the use of rapid infiltration basins in the Arctic.