DEVELOPMENT AND CALIBRATION OF A GROUNDWATER FLOW MODEL, PASSAIC RIVER BASIN, NEW JERSEY

A groundwater flow model has been developed and calibrated for the Passaic River Basin, New Jersey. In the Basin, population growth, urban development, and increased withdrawal have led to increased demand for water, decreased recharge, and decline in water levels. The major objectives of this study were to update and improve on the development and calibration of an existing model, analyze groundwater flow paths, and delineate regional discharge and recharge areas. The models consisted of three layers: unconfined sand and gravel, semi-confined sand and gravel, and bedrock. The USGS three-dimensional finite-difference code, MODFLOW, was used to simulate both steady state and transient flow. The steady-state head distribution 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. Simulated transient heads of both models were also in agreement, while observed and simulated heads compared favorably. Under initial steady-state conditions, wetareas occupied approximately one half of the study area. After a long period of groundwater development, the wetareas were 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 significantly different in places.