THE IMPACT OF ROAD SALT ON DOMESTIC WELLS IN THE VICINITY OF THE BARNES AQUIFER IN WESTERN MASSACHUSETTS

The Barnes Aquifer is an unconsolidated stratified drift aquifer located in the Connecticut River Valley of western Massachusetts. Eleven municipal wells tapping this aquifer supply 5 million gallons of water per day to 60,000 residents of 4 cities and towns in the area. In addition, numerous domestic wells supply individual residences at the margins of the aquifer. Many of these wells are screened in the underlying Mesozoic sedimentary rocks. Water quality concerns prompted the Barnes Aquifer Advisory Committee to sponsor a study of the impact of road salt on these domestic wells.

Between 2004 and 2008 four sampling campaigns collected samples from up to 60 wells within the City of Westfield and the Town of Southampton. Water samples were analyzed for all major cations and anions together with pH, alkalinity and a suite of trace metals including arsenic. Wells were considered salt-impacted if the concentration of chloride exceeded 30.8 mg/L, the amount that results from dissolving just enough salt to create a 20 mg/L concentration of sodium. By this measure 42 percent of the wells were found to be salt impacted with 10 percent having chloride concentrations in excess of 250 mg/L. The high chloride wells all occurred adjacent to the most heavily traveled roads. Water from these wells had molar concentrations of chloride much higher than sodium. The sodium deficiency was balanced by high calcium concentrations not associated with alkalinity, suggesting exchange reactions with soil calcium. This has caused these wells to yield water with very high hardness.

A cluster of wells was found that yielded waters with high sodium not balanced by chloride. These samples also had anomalously high concentrations of lithium, fluoride and arsenic that perhaps represent the presence of fresh water evaporites in the underlying Mesozoic sedimentary rocks.

While the shallow wells in stratified drift were not as affected by road salt as the bedrock wells, they did show a significant increase in chloride concentrations through time suggesting that continued use of road salt could impact municipal groundwater supplies in the future.