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Summary of Annual Hydrologic Conditions - 1999

Volume 2: Groundwater

Groundwater Levels

More than one-half of New Jersey's drinking water comes from ground water. Concerns about the long-term availability of the ground-water supply and the effects of development on ground-water systems are of major importance. 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 natural 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 1999 water year, ground-water levels were measured in 192 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 49 of the 192 wells in the statewide observation-well network during the 1999 water year. Thirty of the record low water levels were in wells located in the Coastal Plain, and 19 were in wells located in the northern part of the State. Previous record high water levels were exceeded in 11 network observation wells during the 1999 water year. All of these wells are located in the Coastal Plain.

Water levels measured in confined aquifers in the Coastal Plain in water year 1999, 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, 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 Potomac-Raritan-Magothy aquifer system, Englishtown aquifer system, and the Wenonah-Mount Laurel aquifer in the northern part of the Coastal Plain (Monmouth, eastern Middlesex, and Ocean Counties), which had been rising since 1990, appear to be leveling off. (3) A 3-year rise in water levels in the Potomac-Raritan-Magothy aquifer system in Burlington, Camden, and Gloucester 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 1999 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 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 70 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 169 feet from August 1989 to April 1999.

In 1986, the New Jersey Department of Environmental Protection (NJDEP) designated two "Critical Water-Supply Management Areas" in the New Jersey Coastal Plain. 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 in the Potomac Raritan Magothy aquifer system and Mount Laurel Wenonah aquifer seem to have leveled off during 1998 and 1999, but water levels in two observation wells located in Ocean County and screened in the Englishtown aquifer system have continued to rise (NJ-WRD well numbers 29-503, and 29-530). This rise in water levels is the result of a reduction in ground-water withdrawals and an increase in surface-water withdrawals for public water supply and a shift in withdrawals from deep, confined aquifers to shallower aquifers.

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. Since spring 1995, the water level in the Hutton Hill 1 observation well (NJ-WRD well number 07-117) has risen more than 26 feet. The shift in withdrawals during recent years to shallower aquifers has caused water levels in the Wenonah-Mount Laurel aquifer and the Englishtown aquifer system to decline in several observation wells (NJ-WRD well numbers 5-259, 5-1155, 5-1387, 5-1390, 7-118, 15-1126, 33-20).

The effects of climate on daily mean water levels in four observation wells during water year 1999 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.

According to the New Jersey State Climatologist, monthly precipitation, calculated from a spatially weighted average of stations throughout New Jersey, was well below normal during July to December 1998 (Office of the NJ State Climatologist, Rutgers University, New Jersey, unpub. data accessed March 1, 2000, on the World Wide Web at URL http://climate.rutgers.edu). Precipitation during this period was more than 11 inches below normal (normal is based on average precipitation values from 1961-1990). This rainfall deficit caused ground-water levels to decline to record lows in many observation wells open to unconfined and fractured-rock aquifers throughout the State. Above-average cumulative precipitation from January through March provided enough water to nearly fill the surface-water reservoirs, but did not fully recharge the aquifers. Rainfall was more than 7 inches below normal from April to July 1999, causing ground-water levels to again fall to record low levels. Previous record low water levels were exceeded in 28 observation wells open to unconfined or fractured-rock aquifers during the 1999 water year. (See Table 1.) Ten of the new record lows were recorded during October 1998 to February 1999; the remaining 18 were recorded during June to September 1999.


Groundwater Table

 


Rainfall from Tropical Storm Floyd on September 16 and 17 caused a significant rise in ground-water levels in the fractured rock aquifers of northern New Jersey. The greatest rise in water level occurred in the Taylor Obs well (NJ-WRD well number 37-202) (See Figure 1.) Both the lowest and highest water levels of the 1999 water year were measured in this well on September 16. The lowest water level of the year occurred at 8 am before the rainfall began. The water level in this well rose more than 10 feet during that day, reaching its highest level of the water year at 8 pm.

Figure 1. Ground-water levels
at key observation wells
in New Jersey during
water year 1999.
Figure 1

A Drought Warning was issued on August 2, followed by a Drought Emergency on August 5. Mandatory restrictions were imposed on outdoor and nonessential water uses. The USGS increased the frequency of ground-water-level monitoring at many observation wells. A high level of cooperation among New Jersey's residents, businesses, and water suppliers helped curb consumption. Above normal rainfall during August and rainfall from Tropical Storm Floyd that ranged from 5 to 14 inches increased streamflows and reservoir levels enough to ease the water restrictions. Governor Whitman ended the Drought Emergency on September 15 in southern New Jersey and on September 27 in the northern part of the State.

 

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