USING HEAT AS A TRACER TO DETERMINE THE INFLUENCE OF PUMPING WELLS ON STREAM DISCHARGE AND SALT CONTAMINATION OF GROUNDWATER IN WATERVILLE, NEW YORK

Municipal wells in Waterville, New York started showing abnormally high levels of sodium and chloride sometime after the completion of the wells twenty years ago. Based on earlier studies, we believe that an uncovered road salt storage area located two km upgradient from the wells is the source of the salt. A stream that flows between the salt source and the wells should act as a hydraulic barrier to salt transport in shallow groundwater. However, some reaches of the stream dry up during especially dry summer months. Increased pumping of the municipal wells during these periods may exacerbate the problem by inducing infiltration from the stream. During these times, the stream may no longer act as a barrier to groundwater flow, and salty groundwater flows to the wells.

We are currently measuring vertical streambed temperature profiles to quantify flux through the streambed and to evaluate temporal changes in flux due to pumping. This will help us evaluate how changes from gaining to losing in critical reaches affect salt distribution and movement in the aquifer. Results from earlier studies using vertical head gradients from minipiezometers show that reaches of the stream near the wells appear to be losing. But these data were snapshots and cannot be correlated with pumping history. Preliminary results from the temperature profile measurements show that when the municipal wells are pumped, there is a greater downward flux under the stream. In addition, conductivity values in monitoring wells appear to increase after pumping periods. When combined with the results of the earlier studies, the results of this work will help us determine when and where the salt travels beneath the stream to reach the municipal wells.