Simulated effects of projected 2010 withdrawals on ground-water flow and water levels in the New Jersey coastal plain – A task of the New Jersey Water Supply Plan, 2006 revision

Alison D. Gordon

doi:10.3133/sir20075134

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Simulated effects of projected 2010 withdrawals on ground-water flow and water levels in the New Jersey coastal plain – A task of the New Jersey Water Supply Plan, 2006 revision

Alison D. Gordon

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Abstract

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 aquif

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Alison D. Gordon. 2007. Simulated effects of projected 2010 withdrawals on ground-water flow and water levels in the New Jersey coastal plain – A task of the New Jersey Water Supply Plan, 2006 revision. https://doi.org/10.3133/sir20075134

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