New York Water Science Center
Problem - The Village of Dryden, rural homeowners, farms, and businesses in the Virgil Creek Valley tap several confined sand and gravel aquifers in the Virgil Creek valley in the town of Dryden . The valley contains a large moraine with complex stratigraphy consisting of continuous and discontinuous layers of till, lake deposits, and glaciofluvial sand and gravel. Sand and gravel units form the aquifers in the valley-fill deposits. There are at least three extensive confined aquifer units at various depths. However, little is known about (1) the location of recharge and discharge areas, (2) direction of groundwater flow, (3) extent of hydraulic connection between aquifer units, and (4) extent of surface- and ground-water interaction. The Town of Dryden and Tompkins County need a better understanding of the geohydrologic system in the Virgil Creek valley to manage and protect this water resource. Interest in the interaction between ground water and surface water has increased in recent years because of widespread concerns related to water supply; contamination of ground water, lakes, and streams by toxic substances; loss of wetlands due to development; and other changes in aquatic environments. The need to better understand how the development of one water resource affects another will increase as development in Tompkins County intensifies.
Objectives - The objectives are to characterize the hydrogeologic framework, groundwater flow system, and groundwater quality of the aquifer system; and to simulate the groundwater flow in the system through construction of a numerical groundwater flow model. This information would impart local government, water-managers, businesses, and homeowners with water information to ensure that there will be (1) safe drinking water for the public, (2) an assessment of the water available for economic development, and (3) information to help provide healthy aquatic environments in the town.
Approach - Phase I- for general hydrogeologic assessment 1) collect and compile well logs, 2) conduct seismic-refraction surveys to determine the thickness of the valley-fill deposits and configuration of the bedrock floor that underlies the valley, 3) install test wells where subsurface data is lacking, and 4) construct geohydrologic sections showing the stratigraphy of the unconsolidated valley-fill deposits. In addition, measure groundwater levels in wells that will be used to construct a potentiometric surface map that will indicate direction of groundwater flow and monitor water levels in wells in the surrounding area near the Village of Dryden municipal well field to determine the hydraulic connections between geohydrologic units.
A general assessment of water quality will be made by collecting samples from selected wells and analyzing the water for common ions and nutrients. Dating groundwater will be done by determining the concentration environmental tracers, such as chlorofluorocarbons (CFCs) and tritium.
A numerical, steady-state groundwater flow model (MODFLOW) will be constructed to (1) simulate the groundwater flow in the valley-fill aquifer system, (2) estimate general direction of groundwater flow throughout the valley, and (3) calculate a water budget for the aquifer system. Groundwater flowpaths and areas potentially contributing recharge to municipal wells will be estimated for average-recharge conditions with a particle-tracking routine MODPATH.