Translating scientific findings into actions: Modeling the effects of salt application reduction on reservoir water quality using CE-QUAL-W2

Road salt applications are essential for winter traffic safety but can degrade water quality in nearby drinking water reservoirs. This study assesses impacts of various salt application reduction scenarios on reservoir water quality across the Wachusett watershed in the Northeastern USA. Specifically, this study investigates the impacts for subbasins with high inflow (high discharge) versus those with high salt concentrations as measured by conductivity using the CE-QUAL-W2 reservoir water quality model. The Wachusett Reservoir, a major drinking-water supply for metropolitan Boston, receives inflow from three main sources: minor tributaries, the Quinapoxet and Stillwater rivers, and the Quabbin Aqueduct transfer. Across the 10 main tributaries included in the model, annual average flows range from 0.056 to 2.12 m³/s and mean specific conductivity varies from approximately 100–800 µS/cm. This study investigates (1) multi-scenario, multi-subbasin salt reduction planning for Wachusett, and (2) explicit comparison of high-flow vs. high-concentration subbasins, which has not been systematically tested before. Results show that a 40% reduction of salt application (indicated as a feasible target) across the entire watershed during the winter salt application season (November-March) would result in average maximum reduction of less than 20% in peak conductivity levels at Cosgrove Intake and Basin North locations. A 20% reduction in the subbasins with the highest flows produced reductions in peak reservoir conductivity comparable to those from a 40% reduction in the subbasins with the highest salt concentrations. Scenarios that simulate only salt reduction in the subbasins with high concentrations, but low flows do not have a significant impact on reservoir water quality. Thus, this study concluded that efforts to reduce salt application should target the subbasins with the highest flows to the reservoir. The use of computational tools and scenario exploration can assist managers in providing safe roads and clean water and this study provides a quantitative basis for prioritizing subbasins in salt-reduction plans.