New Jersey Water Science Center
Recovery of Ground-Water Levels from 1988 to 2003 and Analysis of Effects of 2003 and Full-Allocation Withdrawals in Critical Area 2, Southern New JerseyPrepared in cooperation with the New Jersey Department of Environmental ProtectionBy Frederick J. Spitz and Vincent T. dePaulScientific Investigations Report 2008–5142 |
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Water levels in the Potomac-Raritan-Magothy aquifer system within Water Supply Critical Area 2 in the southern New Jersey Coastal Plain have recovered as a result of reductions in ground-water withdrawals initiated in the early 1990s. The Critical Area consists of the depleted zone and the threatened margin. The Potomac-Raritan-Magothy aquifer system consists of the Upper, Middle, and Lower aquifers. Generally, ground-water withdrawals from these aquifers declined 5 to 10 Mgal/d (million gallons per day) and water levels recovered 0 to 40 ft (foot) from 1988 to 2003. In order to reevaluate water-allocation restrictions in Critical Area 2 in response to changes in the ground-water-flow system and demands for additional water supply due to increased development, the New Jersey Department of Environmental Protection (NJDEP) needs information about the effects of changes in those allocations. Therefore, the U.S. Geological Survey (USGS), in cooperation with the NJDEP, used an existing ground-water-flow model of the New Jersey Coastal Plain to evaluate the effects of withdrawal alternatives on hydraulic heads in the Potomac-Raritan-Magothy aquifer system in Critical Area 2.
The U.S. Geological Survey Regional Aquifer System Analysis model was used to simulate steady-state ground-water flow. Two withdrawal conditions were tested by using the model to evaluate hydraulic heads and differences in heads in these aquifers: 2003 withdrawals and full-allocation withdrawals (17.4 Mgal/d greater than 2003 withdrawals). Model results are presented using head maps and head-difference maps that compare 2003 to full-allocation withdrawals. Mandated hydrologic conditions for Critical Area protection are that the simulated -30-ft head contour not extend beyond the boundary of the depleted zone and (or) be at least 5 mi (miles) updip from the 250-mg/L (milligram per liter) isochlor in all three aquifers.
Simulation results indicate that, for 2003 withdrawals, the simulated -30-ft head contour in all three aquifers is generally within the boundary of the depleted zone, except in the Lower aquifer in northern Camden and northwestern Burlington Counties, and is generally 1 to 10 mi downdip from the 250-mg/L isochlor. (Corresponding observed data indicate that the -30-ft water-level contour extends beyond the southwest boundary of the depleted zone in the Upper and Middle aquifers, and is generally 5 to 20 mi downdip from the 250-mg/L isochlor in all three aquifers.) The area in which heads are below -30 ft ranges from 389 mi2 (square miles) in the Middle aquifer to 427 mi2 in the Lower aquifer. For full-allocation withdrawals, the simulated -30-ft head contour extends beyond the boundary of the depleted zone in all three aquifers in northern Camden and northwestern Burlington Counties and in the Upper aquifer in Gloucester and Salem Counties, and is generally 5 to 15 mi downdip from the 250-mg/L isochlor. The area in which heads are below -30 ft ranges from 616 mi2 in the Upper aquifer to 813 mi2 in the Lower aquifer. These results and observed data indicate that any increase in withdrawals from 2003 values would likely cause heads in the three aquifers to decline below the minimum values mandated by the NJDEP for the Critical Area.
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 Effects of 2003 and Full-Allocation Withdrawals
Ground-water-flow model
Model Runs
2003 Withdrawals
Full-Allocation Withdrawals
Comparison of Results
Comparison with Observed Data
Limitations of the Analysis
Summary and Conclusions
References Cited
1. Map showing location of Water Supply Critical Area 2, southern New Jersey.
2. Generalized hydrogeologic section through the New Jersey Coastal Plain.
3. Maps showing observed potentiometric surfaces and distribution of withdrawals in 2003 in the (a) Upper, (b) Middle, and (c) Lower Potomac-Raritan-Magothy aquifers in Critical Area 2, southern New Jersey.
4. (a) Section showing potentiometric surfaces along section B-B’, 1988–2003 (b) graph showing withdrawals in the depleted zone of Critical Area 2, 1980–2003; and (c) map showing water-level changes in Critical Area 2, 1988–2003, in the Upper Potomac-Raritan-Magothy aquifer, southern New Jersey.
5. (a) Section showing potentiometric surfaces along section B-B’, 1988–2003; (b) graph showing withdrawals in the depleted zone of Critical Area 2, 1980–2003; and (c) map showing water-level changes in Critical Area 2, 1988–2003, in the Middle Potomac-Raritan-Magothy aquifer, southern New Jersey.
6. (a) Section showing potentiometric surfaces along section B-B’, 1988–2003; (b) graph showing withdrawals in the depleted zone of Critical Area 2, 1980–2003; and (c) map showing water-level changes in Critical Area 2, 1988–2003, in the Lower Potomac-Raritan-Magothy aquifer, southern New Jersey.
7–9. Maps showing—
7. Simulated potentiometric surface for 2003 withdrawals in the (a) Upper, (b) Middle, and (c) Lower Potomac-Raritan-Magothy aquifers in Critical Area 2, southern New Jersey.
8. Simulated potentiometric surface for full-allocation withdrawals in the (a) Upper, (b) Middle, and (c) Lower Potomac-Raritan-Magothy aquifers in Critical Area 2, southern New Jersey.
9. Simulated head difference between 2003 and full-allocation withdrawals in the (a) Upper, (b) Middle, and (c) Lower Potomac-Raritan-Magothy aquifers in Critical Area 2, southern New Jersey.
1. Withdrawals from and model locations of production wells in the depleted zone of Critical Area 2, southern New Jersey.
2. Withdrawals from and model locations of production wells outside the depleted zone of Critical Area 2 in Salem and Gloucester Counties, New Jersey.
Download: PDF of SIR2008–5142 (1.9 MB)
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