New Jersey Water Science Center
Recovery of Ground-Water Levels From 1988 to 2003 and Analysis of Potential Water-Supply Management Options in Critical Area 1, East-Central New JerseyPrepared in cooperation with the New Jersey Department of Environmental ProtectionBy Frederick J. Spitz, Martha K. Watt, and Vincent T. dePaulScientific Investigations Report 2007-5193 |
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Water levels in four confined aquifers in the New Jersey Coastal Plain within Water Supply Critical Area 1 have recovered as a result of reductions in ground-water withdrawals initiated by the State in the late 1980s. The aquifers are the Wenonah-Mount Laurel, the Upper and Middle Potomac-Raritan-Magothy, and Englishtown aquifer system. Because of increased water demand due to increased development in Monmouth, Ocean, and Middlesex Counties, five base and nine alternate management models were designed for the four aquifers to evaluate the effects resulting from potential reallocation of part of the Critical Area 1 reductions in withdrawals. The change in withdrawals and associated water-level changes in the aquifers for 1988-2003 are discussed. Generally, withdrawals decreased 25 to 30 Mgal/d (million gallons per day), and water levels increased 0 to 80 ft (feet).
The Regional Aquifer-System Analysis (RASA) ground-water-flow model of the New Jersey Coastal Plain developed by the U.S. Geological Survey was used to simulate ground-water flow and optimize withdrawals using the Ground-Water Management Process (GWM) for MODFLOW. Results of the model were used to evaluate the effects of several possible water-supply management options in order to provide the information to water managers. The optimization method, which provides a means to set constraints that support mandated hydrologic conditions, then determine the maximum withdrawals that meet the constraints, is a more cost-effective approach than simulating a range of withdrawals to determine the effects on the aquifer system. The optimization method is particularly beneficial for a regional-scale study of this kind because of the large number of wells to be evaluated. Before the model was run, a buffer analysis was done to define an area with no additional withdrawals that minimizes changes in simulated streamflow in aquifer outcrop areas and simulated movement of ground water toward the wells from areas of possible high chloride concentrations in the northern and southern parts of the Critical Area.
Five base water-supply management models were developed. Each management model has an objective function, decision variables, and constraints. Two of the five management models were test cases: clean slate option and reallocation from the Wenonah-Mount Laurel aquifer and Englishtown aquifer system to small volume wells for potable water use. Nine other models also were developed as part of a trade-off analysis between withdrawal amounts and constraint values. The 14 management models included current (2003) or regularly spaced well locations with variations on the constraints of ground-water head, drawdown, velocity at the 250-mg/L (milligram per liter) isochlor, and withdrawal rate.
Results of each management model were evaluated in terms of withdrawals, heads, saltwater intrusion, and source of water by aquifer. Each trade-off curve was defined by using six to nine separate management model runs. Results of the management models designed in this study indicate that a withdrawal reallocation of 5 to 20 Mgal/d within Critical Area 1 would increase the area of heads below -30 ft and the velocity at the 250-mg/L isochlor by up to 4 times that of the simulated 2003 results; the range of values are 0 to 521 square miles and 1 to 20 feet per year, respectively. The increase in area of heads below -30 ft was larger in the Middle Potomac-Raritan-Magothy aquifer than in other aquifers because that area was negligible in 2003. The range of modeled withdrawals is closely tied to management-model design. Interpretation of management model results is provided as well as a discussion of limitations.
Abstract
Introduction
Purpose and Scope
Description of Study Area
Hydrogeology
Previous Investigations
Recovery Of Ground-Water Levels
Ground-Water-Flow System
Changes in Withdrawals and Water Levels from 1988 to 2003
Evaluation Of Water-Supply Management Options
Ground-Water-Flow Model
Buffer Analysis
Water-Supply Management Models
Ground-Water Management Process
Formulation
Input
Output
Base Applications
Current (2003) Well Locations (Management Models MM01 and MM02)
Regularly Spaced Well Locations (Management Model MM03)
Clean Slate (Management Model MM04)
Reallocation to Small Volume Wenonah-Mount Laurel Aquifer and Englishtown Aquifer System Potable Users (Management Model MM05)
Trade-Off Analysis
Maximum Allowable Drawdown in the Wenonah-Mount Laurel aquifer and Englishtown aquifer system (Management Models MM06 and MM07)
Minimum Allowable Head in the Wenonah-Mount Laurel aquifer and Englishtown aquifer system (Management Model MM08)
Maximum Allowable Drawdown at the 250-mg/L Isochlor in the Upper Potomac-Raritan-Magothy and Middle Potomac-Raritan-Magothy Aquifers (Management Models MM09 and MM10)
Maximum Allowable Velocity at the 250-mg/L Isochlor in the Upper Potomac-Raritan-Magothy and Middle Potomac-Raritan-Magothy Aquifers (Management Models MM11 and MM12)
Maximum Allowable Withdrawal Rates at Wells (Management Models MM13 and MM14)
Comparison of Water-Supply Management Models
Limitations of the Analysis
Summary and Conclusions
References Cited
Glossary
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