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SEAWAT, MODFLOW-2000, and SHARP models used to simulate future water-supply scenarios, Cape May County, New Jersey

November 18, 2021

Three groundwater flow models, using MODFLOW-2000, SEAWAT, and SHARP model codes, were used to evaluate plans to supply potable and non-potable water to residents and businesses of Cape May County, New Jersey until at least 2050. The ideal plan would meet projected demands and minimize adverse effects on currently used sources of potable, non-potable, and ecological water supplies. The U.S. Geological Survey used two previously developed groundwater flow models, as well as a newly developed groundwater flow model to evaluate the shallow and deep aquifer systems in Cape May County. The groundwater flow in the shallow and deep aquifer systems of Cape May County were simulated separately. The lateral hydrologic boundaries of the shallow aquifer system generally coincide with the political boundary of Cape May County, whereas the boundaries for the deep aquifer system extend well beyond the county boundaries. Flow in the shallow aquifers was simulated with a newly developed small-cell-size numerical model extending to the hydrologic boundaries. The saltwater transport modeling code, SEAWAT, was used to model the shallow system because of the accurate treatment of variable-density groundwater (saltwater front) and surface-water boundary (ecological water supply) conditions. Flow in the deep aquifers was simulated using MODFLOW-2000 with a previously developed medium-cell-size numerical model encompassing Cape May County. This sub-regional groundwater-flow model (CMAC) was originally developed by Voronin (https://pubs.er.usgs.gov/publication/wri954280) to simulate advective flow in the Atlantic City 800-foot sand from the estimated 250-mg/L isochlor toward Stone Harbor. For this study, the CMAC model was revised to include the Rio Grande water-bearing zone and recalibrated with recent (2003) withdrawal data and water-level measurements. Boundary flows to the CMAC model were provided from the New Jersey Coastal Plain regional model (NJCP SHARP) . This coarse-cell-size Coastal Plain-wide model uses the SHARP model code and simulates saltwater movement by treating the transition from freshwater to saltwater as a sharp interface, and therefore, only predicts large-scale movements of the 10,000-mg/L isochlor (https://pubs.usgs.gov/wri/wri98-4216/). To predict the effects of future actions on the water supplies, three baseline and six future scenarios were created and simulated with these three models. Depending on the scenario, proposed production wells would be installed in locations far from the saltwater fronts, in deep freshwater aquifers, in deeper saltwater aquifers, or proposed injection wells would be installed to inject reused water to create a freshwater barrier to saltwater intrusion. Particle-tracking was used with the CMAC model to estimate groundwater-flow paths and travel time from the location of the 250-mg/L isochlor to production wells or hypothetical production wells. This USGS data release contains all the input and output files for the simulations described in the associated model documentation report (https://pubs.usgs.gov/sir/2009/5187/).