EVALUATING GROUNDWATER CONTAMINATION RISK UNDER CHANGING WATERSHED CONDITIONS

Groundwater quality is commonly impacted in rural regions due to practices associated with agricultural activity. In order to ensure the protection of groundwater resources and sustainable use for future generations, it is important to understand the inherent vulnerability of an aquifer system as well as the contamination risk associated with pollutant loading (e.g. nutrient leaching). Index-overlay methods are a popular approach for assessing groundwater contamination risk given their relatively simple data and analysis requirements. However, these methods are typically implemented in a static manner, thereby ignoring the potential for changing contamination risk attributed to dynamic land use and climate. This research proposes a methodology for assessing changes in groundwater contamination risk due to variability in future watershed conditions that is based on a modified DRASTIC-LU approach. The Upper Parkhill watershed, an agricultural headwater catchment in southwestern Ontario, Canada, serves as a case study for method application. Watershed intrinsic properties and land use have been combined to qualitatively assess the spatial variability of groundwater contamination risk and the sensitivity of input factors, including consideration of tile drainage and cropping patterns. A baseline evaluation was expanded upon to predict changes in the spatial variability of groundwater contamination risk as a function of dynamic land use, water table depth, and recharge. This approach represents a valuable screening tool to inform future groundwater and land management strategies.