USING AN ANALYTIC ELEMENT MODEL TO DETERMINE THE INFLUENCE OF SURFACE WATER ON MUNICIPAL WELL WATER

The municipal water system of Clinton, New York pumps water from a series of wells located in a shallow alluvial aquifer. The aquifer is unconfined and consists of sand and gravel with an average thickness of 12m. Water is pumped from six wells ranging in distance from 38m to 180m from present-day Oriskany Creek. A wellhead protection study, using an analytic element model (GFLOW), was completed in 2001. The model accurately reproduces the configuration of the water table, but to date does not accurately simulate groundwater discharge to the stream. The model indicates that the two-year and five-year zones of contribution intersect the stream, and that the pumping induces infiltration of surface water into the aquifer. The New York State Department of Health mandates that water from municipal wells under the direct influence of surface water be filtered before consumption. This has important economic implications for the village of Clinton and other small communities that use groundwater from aquifers connected to streams. We plan to calibrate the model by adjusting recharge, hydraulic conductivity, and stream flow routing to more accurately simulate stream discharge. We will then verify the induced infiltration by using naturally occurring tracers. Continuously recorded temperature, salinity, and electrical conductivity data from both the stream and the aquifer will be compared. Synchronous behavior may reveal whether the stream influences the aquifer.