# Ground-Water Availability in Fractured-Rock Aquifers of the Newark Basin \-- New York, New Jersey, and Pennsylvania

## Background

The Early Mesozoic rift basins, extending from Connecticut to South
Carolina, represent a principal sedimentary bedrock aquifer of the
eastern United States (fig. 1) characterized by fractured clastic
sedimentary rocks, dipping 10-20 degrees toward border faults. Ground
water moves through a complex network of interconnected openings along
joints, bedding-plane partings, and faults, within sedimentary units
that are intruded with diabase and bounded by Precambrian crystalline
rocks. The most important of the exposed Mesozoic rift basins in terms
of size, ground-water use, and proximity to major population centers is
the Newark Basin, which covers about 3,000 square miles in New York, New
Jersey, and Pennsylvania (fig. 2). The fractured-bedrock aquifers in the
Newark Basin provide about 300 Mgal/day of ground water for public
supply and industrial use in areas near Philadelphia, Newark, and New
York City.

Sustainability of ground-water resources in the Newark Basin is a
concern for water managers. Extensive suburban development has increased
water-supply demands, added impervious surfaces that may reduce
ground-water recharge, and caused transfers of water between basins
through water-distribution and sewer systems. Recent droughts have
underscored the interdependence of surface-water and ground-water
resources and their vulnerability to severe climatic conditions.
Locally, ground-water withdrawals exceed recharge rates and deplete
streamflow. In addition, ground-water contamination at more than 100
Superfund sites in the Newark Basin requires that water-quality concerns
be considered as part of the ground-water sustainability equation.

## Problem

Regional- and local-scale models are needed by Local, State, and Federal
agencies to manage ground-water resources in the Newark Basin. The
models must be able to simulate the effects of land-use change and
incorporate critical features such as headwater streams and small-scale
heterogeneity of dipping stratigraphic units. To be practical for
managing sustainable ground-water development, models need an interface
to facilitate their use by decision makers.

## Objectives

The objective of this proposed study is to develop an approach to assess
regional ground-water availability that is useful for active management
of Early Mesozoic aquifers in the eastern United States. Because the
Early Mesozoic basins have many geologic features in common, it is
expected the approach developed for the Newark Basin will have wide
transfer value. Specific objectives of the study are:

-   Develop modeling techniques to adequately characterize the structure
    of fractured-rock aquifer system (dipping layers, variable strike)

-   Couple regional and local-scale models to permit assessment of the
    relationships between ground-water withdrawals and base flow in
    stream reaches, and the effects of new or increased ground-water
    withdrawals;

-   Provide a tool to help estimate the impacts of the overall trends in
    development and population growth on the water resources, including
    a decision-support mechanism for allocation of water resources that
    is based on a realistic, technical model.

## Approach

In order to address the issues related to water-supply availability, a
region-wide view is necessary, but adequate characterization of
important features (especially stratigraphy) requires very local-scale
knowledge. The proposed solution is the use of separate regional- and
local-scale models that can be easily coupled. Because the
regional-scale water availability issues focus on land-use changes and
major water-budget components, we propose that a PRMS watershed model be
employed for that purpose. To address questions regarding water-level
declines, contributing areas to wells, and contaminant movement we
propose to illustrate how site-specific ground-water models developed
with MODFLOW can be linked to the regional PRMS model**.** Without a
user interface, any model is of limited value to water managers. Thus,
as part of this project, a decision-support GUI will be developed.

[Regional-Scale Modeling]{.underline}: The regional scale modeling
activity will entail the application of the PRMS watershed model
(Leavesley and others, 1983) that includes ground-water withdrawals from
the Newark Basin. This model will be calibrated using precipitation,
water use, and streamflow information. Based on growth scenarios from
management agencies, simulations of future consumptive water use and
land-use change will be used to identify areas where significant
streamflow depletion and other deleterious hydrologic effects are
likely.

[Local-Scale Modeling]{.underline}: Local-scale models will be developed
with MODFLOW coupled to PRMS in two areas where future development is
likely to cause the most hydrologic effects. These simulations will
provide the basis for water availability and sustainability decisions at
the local scale level.

In each local-scale area, two or more approaches of simulating dipping
water-bearing zones will be demonstrated and compared -- (1)
boundary-matching approach (Hoaglund and Pollard, 2003) and (2)
grid-overlay approach with general anisotropy. The boundary matching
approach involves orienting the model grid to parallel the dipping
stratigraphy, and has been successfully used in the Newark Basin by
Brown and others (2005), Brown and Rice (2002), Brown and dePaul (2000)
and Goode and Senior (2000) using MODFLOW. The grid-overlay approach
uses a conventional uniform finite-difference model grid that does not
correspond to the dipping stratigraphy, so a general anisotropy package
will be developed for MODFLOW to allow hydraulic conductivity direction
and ratio to vary from cell to cell.

## Methods Development

Two new methods will be developed in this study -- (1) a new package for
simulation of general x/y/z anisotropy in MODFLOW and (2) a
decision-support graphical-user interface (GUI).

[General Anisotropy Package]{.underline} -- A general anisotropy package
will be developed for MODFLOW to allow hydraulic conductivity direction
and ratio to vary in x/y/z directions from cell to cell. This
development will be of general utility to all MODFLOW users.

[Decision-Support GUI]{.underline} \-- A "user-friendly"
decision-support GUI will be developed for the coupled PRMS/MODFLOW
model for use by water-resource managers. Through this interface, each
of the surface- and ground-water models would be accessible to simulate
limited user-specified scenarios of land-use change, ground-water
withdrawals, and drought. The GUI would be transferable to other
applications.

## Collaboration / Leveraging

The proposed Newark Basin study would involve collaboration among USGS
scientists:

New York -- Dick Yager, Paul Heisig, and John Williams

New Jersey -- Otto Zapecza, Daryll Pope, and Leon Kauffman

Pennsylvania -- Dan Goode, Lisa Senior, Dennis Risser, Ed Koerkle

NRP -- George Leavesley, Robert Regan, and Claire Tiedeman

Geologic Discipline -- Nick Ratcliffe and William Burton

**Leveraging of Ongoing Studies --** Current or planned studies that
would be leveraged with OGW funding to provide enhanced benefits:

-   Assessment and modeling of ground-water resources in Rockland Co. NY
    by Paul Heisig and Dick Yager may provide a small-scale ground-water
    model that could be coupled to PRMS.

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-   Local-scale ground-water modeling for EPA Superfund program
    (Montgomery Co., PA) by Dan Goode, Lisa Senior, and Dennis Risser
    provides a boundary-matching ground-water model that could be
    coupled to a PRMS watershed model.

-   Research and ground-water modeling at USGS Toxic-Hydrology site in
    Trenton, NJ could provide modeling support for anisotropy and
    parameter estimation by Claire Tiedeman.

-   Planned work by Ed Koerkle for the U.S. Forest Service Highlands
    Regional Study in FY05 will provide PRMS models for the Pennsylvania
    part of the Newark Basin.

-   Development of a GUI for the PRMS/MODFLOW model in Centre Co., PA by
    George Leavesley and Robert Regan will provide some of the work
    needed for a decision-support GUI for this project.

## Selected References

Brown, J.L. and Jacobsen, Eric, 1995, Hydrogeology and Ground-Water
Flow, Fractured Mesozoic Structural-Basin Rocks, Stony Brook, Beden
Brook, and Jacobs Creek Drainage Basins, West-Central New Jersey, U.S.
Geological Survey, Water Resources Investigation Report 94-4147, 83p.

Brown, J.L. and dePaul, V.T., 2000, Ground-Water Flow and distribution
of Volatile Organic Compounds, Rutgers University Busch Campus and
Vicinity, Piscataway Township, New Jersey, U.S.Geological Survey, Water
Resources Investigation Report 99-4256, 72p.

Brown, J.L. and Rice, D.E., 2002, Simulated Ground-Water Flow, Naval Air
Warfare Center, West Trenton, New Jersey, U.S. Geological Survey, Water
Resources Investigations Report 02-4019, 44p.

Brown, J,L., Rice, D.E., Rosman, Robert, and Smith, N.P., 2005,
Hydrogeologic Framework, Ground-Water Quality, and Simulation of
Ground-Water Flow at the Fair Lawn Well Field Superfund Site, Bergen
County, New Jersey, U.S. Geological Survey, Scientific Investigations
Report 2004-5280, 109p.

Carleton, G.B., Welty, Claire, and Buxton, H.T., 1999, Design and
Analysis of Tracer Tests to Determine Effective Porosity and
Dispersivity in Fractured Sedimentary Rocks, Newark Basin, New Jersey,
U.S.Geological Survey, Water Resources Investigation Report 98-4126A,
80p.

Goode, D.J., and Senior, L.A., 2000, Simulation of Aquifer Tests and
Ground-Water Flowpaths at the Local Scale in Fractured Shales and
Sandstones of the Brunswick Group and Locakatong Formation, Lansdale,
Montgomery County, Pennsylvania: U.S. Geological Survey Open-File Report
00-97, 46 p.

Hoaglund, J.R. and D. Pollard, 2003.  Dip and Anisotropy Effects on Flow
using a Vertically Skewed Model Grid. Ground Water, vol. 41, no. 6, p.
841-846.

Leavesley, G.H., Lichty, R.W., Troutman, B.M., and Saindon, L.G., 1983,
Precipitation-Runoff Modeling System: User\'s Manual: U.S. Geological
Survey Water-Resources Investigations 83-4238, 207 p.

Lyttle, P.T., and Epstein, J.B., 1987, Geologic map of the Newark 1^o^ x
2^o^ Quadrangle, New Jersey, Pennsylvania and New York: U.S. Geological
Survey Miscellaneous Investigations Map I-1715, scale 1:250,000.

Senior, L.A., and Goode, D.J., 1999, Ground-water system, estimation of
aquifer hydraulic properties, and effects of pumping on ground-water
flow in Triassic Sedimentary Rocks in and near Lansdale, Pennsylvania:
U.S. Geological Survey Water-Resources Investigations Report 99-4228,
112 p.

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