THE HYDROGEOLOGIC SETTING OF THE ABANDONED MINER RESERVOIR, ALTONA-FLAT ROCK, NEW YORK

The Altona-Flat Rocks in Clinton County New York is the site of the abandoned Miner Dam in the Little Chazy River watershed. A ridge of Potsdam Sandstone and Cobblestone Hill confine the reservoir behind the dam. Cobblestone Hill is deposit of cobblestone on top of the Potsdam Sandstone. As part of an REU project sponsored by NSF, the W.H. Miner Agricultural Research Institute and SUNY Plattsburgh we investigated the hydrogeologic setting of the reservoir. Our objective was to estimate net ground-water flux to the reservoir during May and June 2000. We compared our results to groundwater flux estimates using a hydrologic budget.

We installed 7 10-cm diameter uncased ground-water wells ranging between 12 and 40 meters depth. In addition we used nine wells that were drilled in 1992. All wells were leveled to a local datum using a rotating laser level. Even though these wells are open, the hydraulic head in the wells is dominated by fractures in the bedrock, thus the wells behave hydrologically more similar to piezometers than water table wells. Hydraulic conductivity and transmissivity were measured using a variety of in situ single and multi-well pump tests as well as slug tests. From hydraulic head observations we constructed several flow nets showing equipontial lines along various transects. From the flow nets we used the Dupuit Assumptions to calculate groundwater flux to the reservoir. The calculated groundwater flux to the reservoir is about 800 cubic meters per day. The net flux was more difficult to estimate because we had less hydraulic head information at Cobblestone Hill. However, our estimates on the basis of reasonable assumptions about the hydraulic conductivity of Cobblestone Hill suggest that the net groundwater flux during the study period was very small. Seasonally the net groundwater flux can vary considerably due to the development or lack of development of a groundwater mound under Cobblestone Hill and the Potsdam Sandstone.