Assessment highlights

The Groundwater indicator status is assessed as Good based on chloride and nitrate concentration data from monitoring wells. The 10-year trend is Undetermined due to insufficient spatial coverage of monitoring wells that have enough long-term data to perform a trend analysis. Elevated concentrations of nitrate in groundwater typically result from improper fertilizer and livestock waste management, and/ or domestic wastewater (e.g., septic systems, leaky sewers) inputs. Elevated chloride concentrations are commonly observed in developed areas due to the application of deicing (road) salt, but also fertilizer use, domestic wastewater, and landfills. The assessment is based on data from 5,765 wells less than 40 meters deep, situated within the Great Lakes basin. These data were used to determine the status of groundwater quality at the tertiary watershed level. These tertiary watershed-level evaluations informed the assessment for each lake and the Great Lakes overall.