CONTROLS ON THE MOVEMENT OF ROAD SALT TO MUNICIPAL WELLS IN A SHALLOW UNCONFINED AQUIFER, WATERVILLE, NEW YORK

Using major ion content, stream discharge measurements, and numerical modeling, we linked increasing concentrations of sodium and chloride in municipal well water in Waterville, New York to an uncovered road salt storage area located 1.6 km upgradient. The salt dissolves during precipitation events and is transported through a sand and gravel aquifer to two municipal wells. Water samples from a series of monitoring wells arranged around the production wells show spatial variability of Na and Cl. Concentrations are lower on the east side of the well field and are higher in wells on the west side, probably reflecting groundwater flow paths between the salt source and the wells. A stream bisects the area between the salt source and the wells. Analyses of stream water show low concentrations of Na and Cl upstream of the well field area and high concentrations near the well field, particularly during the summer. The stream is a gaining stream most of the year, but a reach near the well field often goes dry in the late summer. The dry stretch of the stream may be related to increased pumping in the summer that induces infiltration of stream water into the aquifer. During gaining periods, the stream is a groundwater discharge area and acts as a hydraulic barrier to groundwater flow. But when the water table drops below the stream, the barrier is not present and Na and Cl-charged groundwater flows readily toward the well field. We believe that it is during these times that most of the contaminated groundwater travels under the stream to the well field. The results of particle-tracking in a numerical model show similar groundwater movement. When the stream is present, it captures particles started at the salt source before they reach the municipal wells. When the stream is dry, the particles flow under the stream channel and are captured by the wells.