HYDROGEOLOGICAL AND ANTHROPOGENIC CONTROLS ON SPATIAL AND TEMPORAL VARIATIONS IN GROUNDWATER CHEMISTRY IN A GLACIAL-AQUIFER SYSTEM IN CORTLAND, NEW YORK

A highly productive glacial-aquifer system located in Cortland, New York is the sole source of potable water for about 20,000 residents of the City of Cortland and surrounding communities. This makes it important to understand the groundwater system and the water quality for future management practices under a changing climate. The objective of this study was to analyze the spatial and temporal variations among six groundwater wells in the winter, spring and fall of 2017. The study area is within the Otter Creek watershed, which is a tributary to the Tioughnioga River and later drains into Chesapeake Bay. The six groundwater wells used in this study are located within the City of Cortland Municipal Water Works where 2.5 million gallons of water are pumped every day. Sixty-three samples were collected from January to November of 2017 and in-situ parameters including pH and specific conductivity, were measured using a YSI meter. Two conductivity data loggers were installed for continuous measurement in the fall of 2017. The concentrations of chloride, sulfate, nitrate, sodium, magnesium, calcium, and potassium were analyzed in the lab via Ion Chromatography. Results show that pH remained fairly constant throughout the study period. The variations of specific conductivity are likely due to dilution from rainfall and snowmelt events. Elevated concentrations of sodium (Na⁺) and chloride (Cl^-) in groundwater are likely the result of the application of de-icing salts to roads in the winter months which will be impacted from climate change and future salting practices. Concentrations of Na⁺ and Cl^- were higher in the shallow wells compared to the deep wells, suggesting the vulnerability of shallow groundwater to potential pollution. Higher molar concentrations of chloride than sodium may be attributed to the presence of magnesium chloride (MgCl₂) and calcium chloride (CaCl₂) in the applied salt. Our work shows that shallow drinking water aquifers are vulnerable to contamination, and that controls on the transport of contaminants to shallow aquifers may be climate driven. This information is vital for assuring the quality of drinking water resources and providing predictions for future water quality changes given a changing climate.