GROUNDWATER RESPONSE TO PRECIPITATION WITHIN THE UPPER GLACIAL, MAGOTHY AND LLOYD AQUIFERS, LONG ISLAND, NEW YORK

The groundwater system that lies below Long Island serves as the sole source of freshwater for both Suffolk and Nassau counties of New York. Long Island’s groundwater system is composed of three main aquifers, the Upper Glacial, Magothy and the Lloyd. Increased demand for groundwater resources within this area has caused many studies to be conducted in an attempt to monitor the health and sustainability of the aquifers that supply Long Island with freshwater.

This study aims to further understand the effect precipitation has on groundwater levels within the Upper Glacial, Magothy and Lloyd aquifers as well as how these aquifers interact with one another. Water levels from 41 wells spread across Suffolk and Nassau counties were analyzed for the year of 2017. Average weekly water levels were then plotted alongside the sum of precipitation for each week during the same time period to compare the effect precipitation has on each of these aquifers.

All three aquifers in this system were shown to have a very quick response to precipitation events to varying degrees. Within the Upper Glacial aquifer large rainfall events correlated with spikes in groundwater level, and a dominant water level fluctuation pattern was found. Within the Magothy aquifer strong responses to rainfall events were also found, but there was less similarity in water level patterns over the course of the year than what was found in the Upper Glacial aquifer. Within the Lloyd aquifer large precipitation events correlated with spikes in groundwater level in a similar fashion to the other two aquifers, but shallower wells (300-500 feet) were found to show more fluctuation than the deep wells (1000+ feet) of the aquifer, which was not found in the other two aquifers.

The correlation of precipitation events with changes in groundwater level of all three aquifers indicates that the Upper Glacial, Magothy, and Lloyd aquifers connected hydraulically to some degree. Further research into groundwater flow between these aquifers could help gain a better understanding of how these aquifers behave and could help sustain these aquifers as a water source for future generations.