Cape May 800-foot Sand

Science Center Objects

Evaluation of Saltwater Intrusion and Travel Time in the Atlantic City 800-Foot Sand

By Lois M. Voronin, Frederick J. Spitz, and Steven D. McAuley

 

MODEL VERSION/TYPE: MODFLOW-2000, steady state

AREA STUDIED: Cape May County, New Jersey

AQUIFERS SIMULATED: Atlantic City 800-foot sand

MOST RECENT WITHDRAWALS SIMULATED: Aug 83-88, updated to 1998

MODEL SIZE: 2 layers, 100 rows, 140 columns

MINIMUM GRID SPACING:1,320 feet x 1,320 feet

MODEL ARCHIVE is available by email request at gs-nj-model-request@usgs.gov

 

Regional and subregional groundwater-flow models were coupled, and the output was analyzed by a particle-tracking method. The results were then used to assess the effects of groundwater withdrawals on the flow of saltwater in the Atlantic City 800-foot sand in Cape May County, New Jersey, and to estimate the travel time from areas in which the chloride concentration of the groundwater exceeds 250 milligrams per liter to the county's nearest public-supply wells.

First, a quasi-three-dimensional finite-difference computer model of freshwater and saltwater flow that simulated regional groundwater flow through the unconsolidated materials underlying the New Jersey Coastal Plain was used to estimate flow at the boundaries of the subregional study area. The results of the regional simulation were used as input to a second quasi-three-dimensional finite-difference model that was used to simulate flow in the subregion, the Atlantic City 800-foot sand in Cape May County.

The results of the simulation of flow in the subregion were analyzed by a semianalytical particle-tracking method to estimate groundwater flow paths and travel time of groundwater from areas in which chloride concentrations exceed 250 milligrams per liter to public-supply wells located at Stone Harbor, New Jersey. Groundwater withdrawals from the Atlantic City 800-foot sand were assumed to be equal to those reported for 1991. Results of the analysis indicate that the time required for saltwater to reach the public-supply wells is on the order of hundreds of years. These results, however, are based on the assumption that the aquifer is homogeneous. The presence of zones of high permeability in the aquifer could reduce the predicted travel times of the saltwater from its present location to the supply wells. Travel times also could be reduced if groundwater withdrawals increase.