THE EFFECTS OF ROAD SALT ON GROUNDWATER AND DRINKING WATER IN NORWELL, MA

Sodium and chloride concentrations in natural waters from winter de-icing activities are widely observed to cause a degradation of water quality, to adversely affect plants and fish in surface waters, and to raise the risk to human health. In the Town of Norwell, SE MA, which is the focus of this study, public water supply is pumped from an area located a short distance from two state highways, a large shopping center, and a salt storage shed. Over the past decade, sodium levels in groundwater have been steadily increasing and are now close to five times the state recommended levels of 20 mg/L. To better understand road salt pathways between the source areas and the public water supply wells, three sensors were installed near a producing well at different aquifer depths on March 4th 2011 and an additional one in the nearby stream in August 2011. The sensors form an independent telemetric network accessible over the internet and a cell phone network. All four sensors are recording specific conductance, water depth and temperature on regular 15 min schedule. Nine months of continually acquired data clearly show a vertical stratification within the “Old Pond Meadows” aquifer and a strong seasonal impact within the upper part of the aquifer. The specific conductance, and therefore chloride concentration, is greatest in the shallow and medium depths, which increased from March to August, and is currently decreasing toward March levels. The deepest shows a steady increase since March. My results suggest that continued application of road salt during winter leads to increasing concentrations of sodium and chloride in the local groundwater, inhomogeneity of road salt distribution within the aquifer, and strong seasonal variations with peak concentrations during the summer months. Thus, Norwell can distribute the highest quality water by pumping at the exact depth of the least concentrated salt content.