Science Center Objects

Hydrogeology and Simulation of Groundwater Flow, Picatinny Arsenal and Vicinity, Morris County, New Jersey

By Lois M. Voronin and Donald E. Rice

 

MODEL VERSION/TYPE: MODFLOW-96, steady state

AREA STUDIED: Rockaway Township, Morris County

AQUIFERS SIMULATED: Glacial sediments and carbonate bedrock

MOST RECENT WITHDRAWALS SIMULATED: 1993

MODEL SIZE: 6 layers, 36 rows, 95 columns

MINIMUM GRID SPACING:70 feet X 80 feet

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

 

Groundwater flow in glacial sediments and bedrock at Picatinny Arsenal, N.J., was simulated by use of a three-dimensional finite-difference groundwater-flow model. The modeled area includes a 4.3-square-mile area that extends from Picatinny Lake to the Rockaway River. Most of the study area is bounded by the natural hydrologic boundaries of the groundwater system.

Geophysical logs, lithologic logs, particle-size data, and core data from selected wells and surface geophysical data were analyzed to define the hydrogeologic framework. Hydrogeologic sections and thickness maps define six permeable and three low-permeability layers that are represented in the model as aquifers and confining units, respectively.

Hydrologic data incorporated in the model include a rate of recharge from precipitation of 22 inches per year, estimated from long-term precipitation records and estimates of evapotranspiration. Additional recharge from infiltration along valleys was estimated from measured discharge of springs along the adjacent valley walls and from estimates of runoff from upland drainage that flows to the valley floor. Horizontal and vertical hydraulic conductivities of permeable and low-permeability layers were estimated from examination of aquifer-test data, gamma-ray logs, borehole cuttings, and previously published data. Horizontal hydraulic conductivities in glacial sediments range from 10 to 380 feet per day. Vertical hydraulic conductivities of the low-permeability layers range from 0.01 to 0.7 feet per day.

The model was calibrated by simulating steady-state conditions during 1989-93 and by closely matching simulated and measured groundwater levels, vertical groundwater-head differences, and streamflow gain and loss. Simulated steady-state potentiometric-surface maps produced for the six permeable layers indicate that groundwater in the unconfined material within Picatinny Arsenal flows predominantly toward the center of the valley, where it discharges to Green Pond Brook. Beneath the upper confining unit, groundwater flows southwestward, down the valley. Between First Street and Farley Avenue, the upper confining unit pinches out near the valley walls, resulting in a major input of water to, and causing a local potentiometric high in, the underlying aquifer layers. Groundwater-flow directions southwest of the southern arsenal boundary are predominantly to the Rockaway River.