New Jersey Water Science Center
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A ground-water flow model previously developed as part of a Regional Aquifer System Analysis (RASA) of the New Jersey Coastal Plain was used to simulate ground-water flow in eight major confined aquifers to help evaluate ground-water resources in support of the New Jersey Department of Environmental Protection’s revision of the New Jersey State Water Supply Plan. This model was calibrated to 1998 steady-state and transient conditions. Withdrawals at wells in operation in 1998 were varied in three scenarios to evaluate their effects on flow directions, water levels, and water budgets in the confined aquifers. The scenarios used to predict changes in pumpage from 1998 to 2010 were based on (1) a continuation of 1990-99 trends in water use, (2) public-supply withdrawals estimated from county population projections, and (3) restricted withdrawals in Water-Supply Critical Areas. Total withdrawals in these three scenarios were approximately 366, 362, and 355 million gallons per day, respectively. The results of these simulations are used by New Jersey water-management officials to help address water-supply concerns for the State.
In the revision of the New Jersey State Water Supply Plan, the eight major confined aquifers of the New Jersey Coastal Plain and their outcrop areas are divided into 41 hydrologic budget areas (HBAs). Simulation results were used to assess the effects of changing ground-water withdrawals on water levels and the flow budgets in each budget area. Simulation results for each scenario were compared with 1998 (baseline) simulated water levels and flow budgets.
The 41 hydrologic budget areas are in areas of large ground-water withdrawals, water-level declines, and (or) saltwater-intrusion potential. Their boundaries are based on various hydrologic, geohydrologic, and withdrawal conditions, such as aquifer extent, location of the 250-milligram-per-liter isochlor, aquifer outcrop area, and ground-water divides. The budget areas include primarily the onshore, freshwater portions of the aquifers. A budget analysis was done for each of the hydrologic budget areas for each scenario. Ground-water withdrawals, leakage to streams, net leakage to overlying and underlying aquifers, lateral flow to adjacent budget areas, and the flow direction at the 250-milligram-per-liter isochlor were evaluated.
Although three different methods were applied to predict future pumping rates, the simulated water levels for scenarios 1 and 2 were generally within 2 feet of each other in most areas in the confined aquifers, but differences of more than 2 feet occurred locally. Differences in values of flow-budget components between scenarios 1 and 2 as a percentage change from 1998 values were generally within 2 percent in most hydrologic budget areas, but values of some budget components in some hydrologic budget areas differed by more than 2 percent. Simulated water levels recovered as much as 4 feet more in northeastern Camden and northwestern Burlington Counties in the Lower Potomac-Raritan-Magothy aquifer, and as much as 3 feet more in the same area in the Upper and Middle Potomac-Raritan-Magothy aquifers when pumpage restrictions were imposed in Critical Area 2 (scenario 3).
In the Wenonah-Mount-Laurel aquifer, water levels declined continually in Monmouth County (HBA 8) downdip from the outcrop (in Critical Area 1) from 1988 to 2010 in all three scenarios, although most of the water levels farther downdip from this area in Critical Area 1 are still recovering because of mandated reductions in pumpage in the 1990s. In the Englishtown aquifer system, water levels declined continually in small areas in HBA 13—in central Monmouth County (in Critical Area 1) and in western Monmouth County downdip from the outcrop from 1988 to 2010 in all three scenarios, although most of the water levels farther downdip from this area are still recovering because of the mandated reductions in pumpage.
In the Upper Potomac-Raritan-Magothy aquifer in Critical Area 1 in Monmouth County (HBA 15), water levels were recovering in 1998, but declined again by 2010 in all three scenarios when pumpage was increased, but the area of decline was smaller in scenario 3. In Critical Area 2 in central Camden and in Gloucester and western Burlington Counties (HBA 16), water levels were recovering in 1998 in scenarios 1 and 2, but had declined again by 2010 when pumpage was increased. In scenario 3, water levels in this area were still recovering in 2010.
In the Middle Potomac-Raritan-Magothy aquifer, water levels were recovering in 1998, but then declined by 2010 both inside and outside Critical Area 1 downdip from the outcrop in Middlesex, Monmouth, and southeastern Mercer Counties (HBA 18) in scenarios 1 and 2; however, the area of decline in Monmouth County was smaller in scenario 3. In scenario 1, water levels in Critical Area 2 downdip from the outcrop in Camden and Gloucester Counties (HBA 19) were recovering in 1998, but then declined by 2010; however, the area of decline was much smaller in scenario 2 and limited to Gloucester County, and no decline was observed in this area in scenario 3.
In scenario 1, water levels in the Lower Potomac-Raritan-Magothy aquifer in Critical Area 2 in Camden and Gloucester Counties (HBA 22) were recovering in 1998, but then declined by 2010 when pumpage was increased. The area of decline was less extensive in scenario 2, and in scenario 3 water levels were recovering. In scenarios 1 and 2, water levels in a small part of the updip area of Gloucester County declined continually from 1988 to 2010, but the area of decline was smaller in scenario 2. The water levels in the same area were recovering after 1998 in scenario 3.
The model flow budgets for each scenario indicate that the confined aquifers of New Jersey are recharged by vertical and lateral flow caused by recharge from precipitation on the outcrop areas and by vertical flow from overlying or underlying aquifers through confining units of varying leakance. The sources of water to wells as flows to and from the HBAs can be complex and are interdependent. The flow budgets indicate that as pumpage from the confined aquifers increased, inflow from the overlying aquifer usually increased, although some of this inflow became outflow to the underlying aquifer because of pumpage increases in the underlying aquifers. In HBA 16 in the Upper Potomac-Raritan-Magothy aquifer, inflow from the overlying aquifer increased 13, 13, and 9 percent, respectively, in scenarios 1, 2, and 3 from the 1998 simulation, but outflow to the underlying aquifer increased 7, 7, and 6 percent, respectively. In HBA 19 in the Middle Potomac-Raritan-Magothy aquifer, inflow from the overlying aquifer increased 8, 7, and 6 percent, respectively, in scenarios 1, 2, and 3, but outflow to the underlying aquifer increased 5, 4, and 2 percent, respectively, in these scenarios. The flow budgets also indicate that as pumpage from the Atlantic City 800-foot sand in HBA 1 increased (14, 11, and 11 percent, respectively), lateral inflow from the updip unconfined aquifer increased (6, 5, and 5 percent, respectively).
Leakage to streams decreased from baseline conditions in some hydrologic budget areas in the outcrop of the Upper and Middle Potomac-Raritan-Magothy aquifers because of increased pumpage in the budget areas in which the streams are located, or in adjacent budget areas. Leakage to streams in the outcrop areas of these aquifers decreased less in scenario 3 than in scenarios 1 and 2. Simulated leakage to streams in HBA 40 in the outcrop of the Upper Potomac-Raritan-Magothy aquifer in Critical Area 1 decreased 3, 3, and 1 percent, respectively, in scenarios 1, 2, and 3 from the 1998 simulation. Simulated leakage to streams in HBA 44 in the outcrop of the Middle Potomac-Raritan-Magothy aquifer in Critical Area 1 decreased 3, 3, and 2 percent, respectively, in scenarios 1, 2 and 3 from the 1998 simulation. In HBA 42 in the outcrop of the Upper Potomac-Raritan-Magothy aquifer in Critical Area 2, however, induced leakage from the stream to the aquifer occurred in 1998 and in all three scenarios, although the amount of leakage decreased 1, 1, and 3 percent in scenarios 1, 2, and 3, respectively.
In HBA 2 in the Atlantic City 800-foot sand, lateral inflow from the aquifer offshore increased 5, 3, and 3 percent in scenarios 1, 2, and 3, respectively. The 250-milligram-per-liter isochlor is approximately 10 miles offshore to the east of HBA 2, and about 4 to 6 miles inland to the south of HBA 2, and could move farther landward if ground-water withdrawals increase. In HBA 18 in the Middle Potomac-Raritan-Magothy aquifer, simulated inflow updip from the location of the 250-milligram-per-liter isochlor in Ocean County increased 2 percent in all three scenarios.
Abstract
Introduction
Purpose and Scope
Hydrogeologic Setting
Simulation Of Projected 2010 Withdrawals
Description of Ground-Water Flow Model
Ground-Water-Withdrawal Data
Description of the Hydrologic Budget Areas
Flow-Budget Terms
Simulated Effects Of Projected 2010 Withdrawals
Description of Scenarios and Projected Withdrawals in 2010
Scenario 1—Continuation of 1990-99 Withdrawal Trends
Atlantic City 800-Foot Sand
Piney Point Aquifer
Vincentown Aquifer
Wenonah-Mount Laurel Aquifer
Englishtown Aquifer System
Upper Potomac-Raritan-Magothy Aquifer
Middle Potomac-Raritan-Magothy Aquifer
Lower Potomac-Raritan-Magothy Aquifer
Scenario 2—Withdrawals Based on Population Projections by County
Atlantic City 800-Foot Sand
Piney Point Aquifer
Vincentown Aquifer
Wenonah-Mount Laurel Aquifer
Englishtown Aquifer System
Upper Potomac-Raritan-Magothy Aquifer
Middle Potomac-Raritan-Magothy Aquifer
Lower Potomac-Raritan-Magothy Aquifer
Scenario 3—Restrictions on Withdrawals in Critical Areas
Wenonah-Mount Laurel Aquifer
Englishtown Aquifer System
Upper Potomac-Raritan-Magothy Aquifer
Middle Potomac-Raritan-Magothy Aquifer
Lower Potomac-Raritan-Magothy Aquifer
Comparison of Results for Scenarios 1, 2, and 3
Water-Level Decline and Recovery in the Hydrologic Budget Areas
Model Limitations
Steady-State Simulation
Summary and Conclusions
References Cited
Appendix 1—Water-Level Monitoring Wells (2005) and Chloride-Measurement Wells (1999–2005), New Jersey Coastal Plain
Download: PDF of SIR2007-5134 (16.6Mb)
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