EVALUATION OF ENVIRONMENTAL IMPACTS OF DEICING CHEMICALS ON GROUNDWATER

Common deicing chemicals used on state and municipal highways, roads, and streets in Massachusetts are usually mixtures of crystalline sodium chloride and concentrated solutions of calcium chloride. Applications of calcium chloride solutions are usually carried out ahead of an impending storm, thus anti-icing to prevent formation of ice layers on road surfaces by melting snow at its first contact with the road surface. Other deicing chemicals used on residential as well as commercial open lots and driveways are magnesium chloride or mixtures of calcium, magnesium, and sodium chlorides. In this presentation we will report on data and observations of pathways of these chemicals in the environment and their impact on groundwater quality in fresh water aquifers.

Recent advances in instrumental techniques and remote field monitoring instrumentation in combination with more frequent water sampling for laboratory chemical analysis allow not only for a fast water quality assessment but provide unique insights into the patterns of deicer migrations within the environment. Approximately only a half of the total of applied deicers is removed from the area within the season of dispensation by direct runoffs or delayed runoffs by subsequent precipitation events. The other half becomes incorporated into the aquifer systems creating density and concentration gradients in both horizontal and vertical directions. Multivariate statistical analyses of chemical data coupled with long term continuous water quality measurements and frequent sampling of water provide substantial evidence for existence of two forms of deicer pathways: overland runoff and ground water discharge as base flow. Chloride transport by overland flow can often lead to intermittent high chloride levels in the nearby streams exceeding 230 (382, 425) mg/L chloride (chronic aquatic life toxic exposure). Base flow chloride levels are season independent near 100 mg/L of Cl in many streams and near 200 mg/L Cl in several stressed streams. The time to reach steady state conditions (seasonal rates of removal = seasonal rates of deicer application) will likely require additional decades of current deicer application rates with projected chloride levels above the regulatory limits for both drinking water and aquatic life standards.