The Miner Dam located at Altona-Flat Rocks in Clinton County, New York was abandoned decades ago. The spatial extent of the reservoir behind the dam is confined by a ridge of the Potsdam Sandstone and Cobblestone Hill. An NSF/ REU investigation of the hydrology suggests seasonal fluctuations in net groundwater flow to the reservoir. Changes in the net groundwater flux to the reservoir are probably triggered by occurrence of groundwater mounds in the Potsdam Sandstone and Cobblestone Hill. We are using a groundwater flow model to model the hydrogeology around the reservoir and to test conditions necessary to sustain groundwater mounding in the Potsdam Sandstone and Cobblestone Hill.

We used MODFLOW to develop a two-dimensional, steady-state cross-sectional model along a 3000 foot transect extending from the Potsdam Sandstone north through the reservoir and terminating on Cobblestone Hill. Constant head boundaries were assigned on basis of water table elevation. Hydraulic conductivities were measure from in situ pump test by students working on the NSF/REU project. The model was calibrated using field observation of hydraulic head measurements (relative to local datum) from several wells. These wells range in depth between 12 and 40 meters. They are uncased, but the hydraulic head in each well is controlled by fractures in bedrock, thus the wells behave like piezometers. We used bore-hole geophysical data from the USGS to determine the depth of the source of hydraulic head in each well. The next modeling phase includes a transient model with recharge to test conditions necessary to sustain groundwater mounding.

Our preliminary modeling results agree with the conceptual models developed by the REU/NSF investigation. Modeled groundwater flow shows groundwater inflow to the reservoir. The equipotential lines from the model agree with field observation of hydraulic head measurements from wells along the transect. We will present the results of the transient model to show the conditions necessary to change the net groundwater flux to the reservoir.