AWWA CSC91050

The key tool that the Nassau County Water Authority (New York) is using to guide water resources management planning is a three- dimensional regional groundwater model. The model assembles all of the interrelated natural and manmade factors that affect the quantity and quality of groundwater, and synthesizes them into a comprehensive description of the groundwater system. The modeling process organizes and enhances the existing database and helps to highlight areas where additional data would be useful. This paper describes the model development, calibration, and application. The model comprises seven layers, based on research done by the US Geological Survey. The model was extended into neighboring counties to the natural hydraulic boundaries, such as surface water bodies, groundwater divides, and impermeable formations that hydraulically isolate groundwater flow systems. The model has been used for a two-phase model that can simulate the movement of the saltwater interfaces along the north and south shores, and for subregional models to study local south shore streams. The model's interactive grid-editing capability facilitates the development of more detailed grids, which are required to investigate local problems.