Science Center Objects

Hydrogeology of, and Groundwater Flow in, a Valley-Fill and Carbonate-Rock Aquifer System Near Long Valley in the New Jersey Highlands

by Robert S. Nicholson, Steven D. McAuley, Julia L. Barringer, and Alison D. Gordon

By Robert S. Nicholson, Steven D. McAuley, Julia L. Barringer, and Alison D. Gordon

 

MODEL VERSION/TYPE: MODFLOW-96, steady state; updated to MODFLOW - 2000.

AREA STUDIED: SW Morris and NE Hunterdon Counties

AQUIFERS SIMULATED: Glacial and carbonate-rock aquifers

MOST RECENT WITHDRAWALS SIMULATED: 1989, updated 2003

MODEL SIZE:3 layers, 44 rows, 256 columns

MINIMUM GRID SPACING:500 feet x 500 feet

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

 

The valley-fill and carbonate-rock aquifer system near Long Valley is an important source of groundwater in southwestern Morris and northeastern Hunterdon Counties, where demand for water is increasing. Through this study, the hydrogeology of the area was assessed, and numerical-modeling techniques were used to evaluate the groundwater-flow system and the factors that limit water-supply availability.

The effects of recent and anticipated withdrawals on stream base flows, water levels, and the overall water budget were estimated. Simulation results indicate that recent withdrawals have resulted in water-level declines of up to 35 feet near pumping centers. Under conditions of projected increases in groundwater withdrawals of 121 percent, average water levels in the carbonate-rock aquifer would decline up to 28 feet, but water levels in two public-supply wells in the affected area during pumping would not approach the depths of present pump intakes. The magnitude of predicted average base-flow depletion, when compared with historic low flows, indicates that projected increases in pumpage may substantially deplete seasonal low flow of Drakes Brook and the South Branch Raritan River. Average base flow of Drakes Brook at Bartley would decrease from 20.5 cubic feet per second by as much as 5.3 cubic feet per second, or 26 percent. Historically, low flows at this location have been less than 5.3 cubic feet per second.

Water-budget changes that would result from increased withdrawals from the carbonate-rock aquifer include (1) decreased discharge to rivers from the aquifer system, (2) increased downward flow from and decreased upward flow to the lower valley-fill aquifer, (3) increased lateral flow of groundwater into the South Branch Raritan River Basin from the Lamington River Basin, and (4) a slight increase in tributary-stream leakage to the aquifer system. These water-budget changes are indicative of the sources of water to additional supply wells.

Water-quality data indicate that human activities are affecting groundwater, particularly in the northern and central parts of the study area. With the exception of an elevated iron concentration in water from one well, concentrations of inorganic constituents in water from 75 wells sampled did not exceed New Jersey primary or secondary drinking-water regulations. Volatile organic compounds were detected in water from several wells; in two samples, concentrations of specific compounds exceeded drinking-water regulations. A data-collection program designed for early detection of potential adverse effects of water-supply development would include (1) continuous gaging of streamflow in the South Branch Raritan River near Naughright, (2) frequent measurement of water levels in nests of wells open to each aquifer, and (3) water-quality sampling in nests of wells open to each aquifer.