Provided in cooperation with New Jersey Department of Environmental Protection
Program to Maintain and Update Groundwater Models
Cape May--Shallow and Deep
Future water-supply scenarios, Cape May County, New Jersey, 2003-2050
By Pierre J. Lacombe, Glen B. Carleton, Daryll A. Pope, and Donald E. Rice
This project simulated flow in both the deep and shallow groundwater system. The shallow system flow was simulated by using a new model with the same model area as the Cape May-SHARP model. The deep system flow was simulated by using a modified version of the Cape May 800-ft Sand model. The Cape May 800-ft Sand model was revised from that described in WRIR 95-4280 by adding a layer to represent the Rio Grande water-bearing zone that overlies the Atlantic City 800-foot sand, updating withdrawal rates to 2003, and calibrating to 2003 measured water levels. Boundary flows for this model were calculated from simulation results from the NJCP SHARP model which was updated with 2003 withdrawals.
SHALLOW SYSTEM--SEAWAT, transient
DEEP SYSTEM--MODFLOW-2000, steady-state
AREA STUDIED: Cape May County, New Jersey
SHALLOW SYSTEM--Holly Beach, Estuarine Sand, and Cohansey aquifer
DEEP SYSTEM--Rio Grande, Atlantic 800-Foot Sand
MOST RECENT WITHDRAWALS SIMULATED:
SHALLOW SYSTEM--13 layers, 204 rows, 135 columns
DEEP SYSTEM--3 layers, 100 rows, 140 columns
MINIMUM GRID SPACING:
SHALLOW SYSTEM--1,000 feet X 1,000 feet
DEEP SYSTEM--1,320 feet X 1,320 feet
REPORT: USGS Scientific Investigations Report 2009-5187
Archived model files are available.
Stewards of the water supply in New Jersey are interested in developing a plan to supply potable and non-potable water to residents and businesses of Cape May County 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.
This report documents past and projected potable, non-potable, and ecological water-supply demands. Past and ongoing adverse effects to production and domestic wells caused by withdrawals include saltwater intrusion and water-level declines in the freshwater aquifers. Adverse effects on the ecological water supplies caused by groundwater withdrawals include premature drying of seasonal wetlands, delayed recovery of water levels in the water-table aquifer, and reduced streamflow. To predict the effects of future actions on the water supplies, three baseline and six future scenarios were created and simulated.
Baseline Scenarios 1, 2, and 3 represent withdrawals using existing wells projected until 2050. Baseline Scenario 1 represents average 1998-2003 withdrawals, and Scenario 2 represents New Jersey Department of Environmental Protection (NJDEP) full allocation withdrawals. These withdrawals do not meet projected future water demands. Baseline Scenario 3 represents the estimated full build-out water demands. Results of simulations of the three baseline scenarios indicate that saltwater would intrude into the Cohansey aquifer as much as 7,100 feet (ft) to adversely affect production wells used by Lower Township and the Wildwoods, as well as some other near-shore domestic wells; water-level altitudes in the Atlantic City 800-foot sand would decline to -156 ft; base flow in streams would be depleted by 0 to 26 percent; and water levels in the water-table aquifer would decline as much as 0.7 ft. [Specific water-level altitudes, land-surface altitudes, and present sea level when used in this report are referenced to the North American Vertical Datum of 1988 (NAVD 88).]
Future scenarios 4 to 9 represent withdrawals and the effects on the water supply while using estimated full build-out water demands. In most townships, existing wells would be used for withdrawals in the simulation. However, in Lower and Middle Townships, the Wildwoods, and the Cape Mays, withdrawals from some wells would be terminated, reduced, or increased. 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. Simulations indicate that future Scenarios 4 to 9 would reduce many of the adverse effects of Scenarios 1, 2, and 3. No future scenario will minimize all adverse impacts.
In Scenario 4, Lower Township would drill two production wells in the Cohansey aquifer farther from the Delaware shoreline than existing wells and reduce withdrawals from wells near the shoreline. Wildwood Water Utility (WWU)would reduce withdrawals from existing wells in the Cohansey aquifer and increase withdrawals from wells in the Rio Grande water-bearing zone. Results of the simulation indicate that saltwater intrusion and ecological-water supply problems would be reduced but not as much as in Scenarios 5, 7, 8, and 9.
In Scenario 5, the Wildwoods and Lower Township each would install a desalination plant and drill two wells to withdraw saltwater from the Atlantic City 800-foot sand. Saltwater intrusion problems would be reduced to the greatest extent with this scenario. Ecological water supplies remain constant or decline from 2003 baseline values. Water-level altitudes would decline to -193 ft in the Atlantic City 800-foot sand, the deepest potentiometric level for all scenarios.
In Scenario 6, Lower Township would build a tertiary treatment system and drill three wells open to the Cohansey aquifer, west of their existing production wells. Lower Township would inject reclaimed water into the Cohansey aquifer to create a freshwater barrier to prevent saltwater intrusion. Results of the simulation indicate that the barrier would work as designed near the injection wells, but elsewhere in the county, the adverse effects of withdrawals would be similar to those of the baseline scenarios.
In Scenario 7, Lower Township, the Wildwoods, and Middle Township would drill two wells into the Cohansey aquifer and four wells into the Atlantic City 800-foot sand along the spine of the peninsula. Results of the simulation indicate that this scenario reduces saltwater intrusion in the shallow aquifers and reduces the depletion of ecological water supplies. Water-level altitudes would decline to -177 ft within the Atlantic City 800-foot sand.
In Scenario 8, Lower Township and the Wildwoods would build a desalination plant at the airport and install four wells to withdraw salty water from Atlantic City 800-foot sand. Results of the simulation indicate that this scenario reduces saltwater intrusion and reduces depletion of the ecological-water supplies. Water-level altitudes would decline to -192 ft the Atlantic City 800-foot sand.
In Scenario 9, Lower Township, Cape May City, and Wildwood would expand the existing Cape May City desalination plant by increasing the number of reverse osmosis units and drilling four additional wells into the salty part of the Atlantic City 800-foot sand. Results indicate that this scenario would reduce saltwater intrusion in the Cohansey aquifer, cause the saltwater front in the Atlantic City 800-foot sand to move southward away from more northerly freshwater production wells, and reduce the effects on the ecological-water supply. In Scenario 9, the water-level altitude would decline to -156 ft within the Atlantic City 800-foot sand near Cape May City, the greatest decline in water levels in the Cape May City area.