Application of salt (primarily NaCl) as a de-icing agent on roadways has led to widespread contamination in the environment. In eastern New York, USA we have tracked the spread of chloride through small streams, shallow groundwater and deeper aquifers to understand the pathways and time scales of movement. A combination of frequent surface water sampling, continuous monitoring of conductivity and data from private drinking water wells has documented widespread occurrence of chloride above natural background levels. Most data from surface waters are ~ monthly samples over years to decades which are useful for detecting trends but certainly miss peak, episodic concentrations. Aquifer data are much less frequent and can really only be used to describe spatial patterns. The varying concentrations of chloride over time and in the different pools can be used to infer lag times or retention of salt after application.
Results/Conclusions
Chloride concentrations in surface waters in eastern New York can exceed 100’s of mg/L which is at least an order of magnitude above natural background levels and may be linked to negative effects on sensitive life stages or indicative of other stressors. Post-winter storm concentrations may reach several hundred mg/L Cl but with baseline concentrations of 50-100 mg/L, 2-3 hours of chronic exposure is equivalent to peak exposure following salt application. Continuous measurement of conductivity (generally driven by NaCl) shows behavior indicative of both point and non-point sources suggesting both direct wash-in from salting events as well as more gradual inputs most likely from a more diffuse source such as shallow groundwater. These lines of evidence suggest there are significant lags between salt delivery to a watershed and export as run-off and there are consequences for potential ecological effects which may be most significant at times far removed from salt application. Moreover, evidence for the effectiveness of management actions intended to reduce concentrations will be slow to appear but should not be used to argue against efforts at salt reduction.