Impact of road deicing salts on the Upper Passaic River Basin, New Jersey: a geochemical analysis of the major ions in groundwater

Road deicing salts, primarily sodium chloride, has been used widely to remove snow and ice from roadways in New Jersey and the northern United States since the 1950s. Currently, New Jersey stores up to 141 million kg of rock salt and 2401 m³ of liquid calcium chloride in the winter season for road deicing. Road deicing helps to reduce accident rates, road delays, and to improve road accessibility. While it is known that the use of road deicers is beneficial, road salts have also been shown to affect surface water and groundwater quality. In this study, an analysis of major ion concentration of groundwater collected by the United States Geological Survey (USGS) for the Upper Passaic River Basin (UPRB) was carried out. The UPRB has a large area of urban land use and a number of significant roads that are regularly deiced during the winter. The results of the study have shown that the contribution of Cl⁻ to the TDS of groundwater increased significantly by the 2000s. Decadal bivariate plots of Na⁺ vs Cl⁻ and Cl⁻ vs TDS showed a strong increase in the correlations between these ions from the 1960s to the 2000s. Bivariate plots of Na⁺ vs Cl⁻ and Ca²⁺ vs Mg²⁺ display a strong correlation, while those of Na⁺ vs Ca²⁺ and Cl⁻ vs Ca²⁺ display a poor correlation. These observations suggest a link between Na⁺, Cl⁻ and TDS, a link between Ca²⁺ and Mg²⁺, and no link between Ca²⁺ and Cl⁻, and between Ca²⁺ and Na⁺. Plots of Piper diagrams show that the groundwater facies have changed through time, starting as a single Ca(HCO₃)₂ species and shifting gradually towards a NaCl-dominated species. Plots of individual ion concentrations versus specific conductance show an increase in Na⁺ and Cl⁻ over time and point towards an external influx of these ions. In general, groundwater in the UPRB is fresh with total dissolved solids less than 500 mg/L. Against the natural groundwater evolutionary trend, chloride is found to dominate over other chemical species in this freshwater system. These results provide evidence of a link between groundwater chlorides and road deicing salts in the UPRB.