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New Jersey Water Science Center
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Summary of Annual Hydrologic Conditions - 2000
Volume 2: Groundwater
More than one-half of New Jersey's drinking water comes from ground water. The New Jersey Statewide Water Supply Plan reported in 1990 that the majority of New Jersey's water supplies are now developed, and although supplies are sufficient for the foreseeable future in most regions, some regions (mostly those relying heavily on ground water) are presently in deficit. Others are expected to face a deficit before the year 2040. If New Jersey is to meet its future water-supply needs, strategic water management will be required. Long-term water-level records are needed to evaluate the effects of climate changes on ground-water systems, to develop a data base that can be used to measure the effects of development, to facilitate the prediction of future ground-water supplies, and to provide data for ground-water-resource management. These data document the general response of the ground-water system to climate changes and ground-water withdrawals. The U.S. Geological Survey (USGS) has operated a network of observation wells in New Jersey for the purpose of monitoring water-level changes throughout the State since 1923.
During the 2000 water year, ground-water levels were measured in 194 wells. Observation wells in which water levels exceeded their previous measured extremes (highest or lowest water levels), and for which more than 2 years of data are available, are listed in table 1. Previous record low water levels were exceeded in 15 of the 194 wells in the statewide observation-well network during the 2000 water year. Fourteen of the record low water levels were in wells located in the Coastal Plain, and one was in a well located in the northern part of the State. Previous record high water levels were exceeded in 17 network observation wells during the 2000 water year. Fifteen of these wells are located in the Coastal Plain, and 2 are located in the northern part of the State.
Water levels measured in confined aquifers in the Coastal Plain in water year 2000, together with those measured during previous years, show four general trends. (1) Water levels in observation wells that tap the Atlantic City 800-foot sand of the Kirkwood Formation, parts of the Wenonah-Mount Laurel aquifer, and the Piney Point Formation in the southern part of the Coastal Plain continued to undergo long-term net declines. (2) Water levels in the Englishtown aquifer system and the Wenonah-Mount Laurel aquifer in the northeastern part of the Coastal Plain (Monmouth and Ocean Counties) continued to rise. (3) A 4-year rise in water levels in most wells in the Potomac-Raritan-Magothy aquifer system in Burlington, Camden, Gloucester, and Salem Counties has reversed a trend of long-term water-level declines. (4) The use of a desalination plant, which pumps brackish water from the Atlantic City 800-foot sand in Cape May City, has affected two confined aquifers in the Cape May City area. Increased withdrawals from the Atlantic City 800-foot sand resulted in a decline in the water level in the Coast Guard 800 observation well (NJ-WRD well number 9-302). A reduction in withdrawals from the Cohansey sand resulted in record setting high water levels during spring 2000 in three observation wells (NJ-WRD well numbers 9-48, 9-49, and 9-150) in the Cape May City area.
The greatest long-term water-level decline in an observation well occurred in the New Brooklyn Park 3 observation well (NJ-WRD well number 07-478), screened in the Wenonah-Mount Laurel aquifer in Camden County. The water level in this well declined more than 71 feet since April 1983. In contrast, the greatest increase in water levels occurred in the PPWD 6 observation well (NJ-WRD well number 29-530), screened in the Englishtown aquifer system in Ocean County. The water level in this well rose more than 172 feet from August 1989 to April 2000.
In 1986, the New Jersey Department of Environmental Protection (NJDEP) designated two 'Critical Water-Supply Management Areas' in the New Jersey Coastal Plain. This legislation was initiated as a result of concerns about long-term declines in ground-water levels in these areas where ground water is the primary source of water supply. Ground-water withdrawals from specified aquifers in these areas were reduced, and new allocations may be limited. In Critical Area 1, which consists of Middlesex, Monmouth, and Ocean Counties, withdrawals from the Wenonah-Mount Laurel aquifer, Englishtown aquifer system, and Upper and Middle Potomac-Raritan-Magothy aquifers are restricted. Pumpage restrictions in this area began in 1989. In Critical Area 2, which consists of Camden, most of Burlington and Gloucester, and parts of Atlantic, Cumberland, Ocean, Monmouth, and Salem Counties, withdrawals from the Potomac-Raritan-Magothy aquifer system are restricted. Pumping restrictions here went into effect in 1996.
Early in the 1991 water year, long-term declines in water levels reversed in several observation wells screened in the Potomac-Raritan-Magothy aquifer system, Englishtown aquifer system, and Wenonah-Mount Laurel aquifer in Critical Area 1. Water levels rose dramatically in these aquifers from 1991 to 1998. Water levels in the Potomac Raritan Magothy aquifer system have remained level from 1998 to 2000, but water levels in four observation wells located in Critical area 1 and screened in the Englishtown aquifer system and the Wenonah-Mount Laurel aquifer have continued to rise (NJ-WRD well numbers 25-429, 25-486, 29-503, and 29-530). This rise in water levels is the result of the reduction in ground-water withdrawals from deep, confined aquifers, an increase in withdrawals from shallower aquifers, and a shift in withdrawals from ground water to surface water for some public water supply.
In Critical Area 2, the shift in withdrawals away from the deeper, confined aquifers to surface water and ground water in shallower, confined and unconfined aquifers began in 1996. As a result, the long-term water-level declines have ceased in observation wells screened in the Potomac-Raritan-Magothy aquifer system in the Critical area (NJ-WRD well numbers 5-258, 5-261, 5-262, 5-440, 5-645, 7-117, 7-412, 7-413, 7-476, 7-477, 15-671, 15-741, and 15-742). Water levels in several of these wells have recovered to the levels measured during the 1970's. Previous record high water levels were exceeded in eight wells screened in the Potomac-Raritan Magothy aquifer system during the 2000 water year (table 1).
The shifting of withdrawals of water to shallower confined and unconfined aquifers will require an increase in monitoring and management. Stream flows and wetlands can be affected by the pumping of wells screened in the unconfined aquifers. These aquifers have an increased vulnerability to drought and to recharge from undesirable sources. The effects of the shift in withdrawals can be seen in water levels in the southern part of the State, where water levels in the Wenonah-Mount Laurel aquifer and the Englishtown aquifer system have declined in several observation wells (NJ-WRD well numbers 5-259, 5-1155, 5-1387, 5-1390, 7-118, 15-1126, 33-20). In the northern part of the State, a large part of ground-water withdrawals are from unconfined and fractured rock aquifers. The water level in the Briarwood school observation well (NJ-WRD well number 27-12) in Morris County dropped steadily (7.2 feet) between June 30, 1998, and March 17, 2000, exceeding its previous record low during the 2000 water year.
The effects of climate on daily mean water levels in four observation wells during water year 2000 can be seen in the hydrographs shown in figure 1. Monthly extreme and long-term average water levels are shown for comparison. The Taylor Obs well (NJ-WRD well number 37-202) and the Cranston Farms 15 Obs well (NJ-WRD well number 21-364) are open to fractured-rock aquifers; the Lebanon State Forest 23-D Obs well (NJ-WRD well number 5-689) and the WTMUA Monitoring 1 Obs well (NJ-WRD well number 15-1033) are screened in an unconfined sand and gravel aquifer. These wells are distant from pumping centers.
Water year 2000 began with a heightened state of ground-water-level monitoring because of the Drought Emergency which was in effect in August and September 1999. The USGS, in cooperation with the NJDEP, increased the frequency of ground-water-level monitoring at many observation wells between August and December 1999. Above normal precipitation during August and September 1999 increased stream flows and helped recharge New Jersey's aquifers. According to the New Jersey State Climatologist, monthly precipitation, calculated from a spatially weighted average of stations throughout New Jersey, (Office of the NJ State Climatologist, Rutgers University, New Jersey, unpub. data accessed February 21, 2001, on the World Wide Web at http://climate.rutgers.edu/) ranged from more than 8 inches above normal in the north to more than 6 inches above normal in the southern parts of New Jersey between August and September 1999. (Normal is based on average precipitation values from 1961 to 1990). This rainfall caused ground-water levels in most of the observation wells completed in the more local unconfined and fractured-rock aquifers in the northern half of the State to rise to above average levels. Below-average cumulative precipitation, ranging from 4.3 inches below normal in the north to 2.6 inches below normal in the south, from October to May, caused water levels in many observation wells to remain below their normal monthly mean. Water levels in many observation wells that tap unconfined aquifers in the southern part of the State remained below their normal monthly mean throughout most, if not all, of the 2000 water year. (See Figure 1). Rainfall ranged from 3 inches (north) to 4 inches (south) above normal from June to September 2000, causing ground-water levels to rise. Previous record low water levels were exceeded in three observation wells, and record high water levels were exceeded in two observation wells open to unconfined or fractured-rock aquifers during the 2000 water year. (See Table 1.)
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