Simulation of Groundwater Response to Development, Passaic River Basin, New Jersey

Fatoumata Barry (1, 2), Duke Ophori (1), Jeffrey Hoffman (2) and Robert Canace (2)

(1)Department of Earth and Environmental Studies, Montclair State University, Montclair, New Jersey 07043

(2)New Jersey Department of Environmental Protection (NJDEP), P.O. Box 427, Trenton, New Jersey 08625

Groundwater movement is being analyzed in the Passaic River Basin, New Jersey, in order to evaluate the response of the system to groundwater development. Population growth, urban development, and increased withdrawal have led to increased demand for water, decreased recharge, and decline in water levels in the basin. An existing groundwater flow model is updated and improved upon, and used to analyze the groundwater flow pattern, and to delineate areas of discharge and recharge, as well as wet areas. Hydrogeological field data collected over the past decade are used with numerical simulation techniques. The existing and new models consist of three layers: unconfined sand and gravel, semi-confined sand and gravel, and bedrock. The USGS three-dimensional finite-difference code, MODFLOW, as included in the Groundwater Modeling System (GMS) Package, was used to simulate both steady state and transient flow. The steady-state head distributions of the existing and new models were in good agreement, and the heads in the top layer of the model compared well with the surface elevation. An analysis of the system’s response to groundwater pumping over the past decade showed simulated transient heads of both models to be in agreement, while observed and simulated heads compared favorably. Under initial steady-state conditions, wet areas occupied approximately one half of the study area. After a long period of groundwater development, the wet areas appear to have been reduced in size to about one-third of the study area. Discharge and recharge areas are almost equally distributed under both steady and transient conditions, but discharge rates are variable in space.