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Summary of Annual Hydrologic Conditions - 2001
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. As population and demand for water increase, strategic water management will be required if New Jersey is to meet its future water-supply needs. 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 2001 water year, ground-water levels were measured in 193 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 27 of the 193 wells in the statewide observation-well network during the 2001 water year. Twenty-five of the record low water levels were in wells located in the Coastal Plain, and two were in wells located in the northern part of the State. Previous record high water levels were exceeded in 16 network observation wells during the 2001 water year. Twelve of these wells are located in the Coastal Plain, and four are located in the northern part of the State.
Water levels measured in confined aquifers in the Coastal Plain in water year 2001, 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 rise in water levels in many observation wells in the Potomac-Raritan-Magothy aquifer system in Burlington, 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 has resulted in higher water levels over the past 3 years 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 72 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 173 feet from August 1989 to April 2001.
In 1986, the New Jersey Department of Environmental Protection (NJDEP) designated two "Critical Water-Supply Management Areas" in the New Jersey Coastal Plain. (See figure 1.) 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, 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, 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 2001, 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 25-486, 29-503, 29-530, and 29-534). 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, water levels rose from 1996 through 1999 in many 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 four observation wells screened in the Potomac-Raritan Magothy aquifer system in this Critical Area during the 2001 water year (table 1).
The shifting of water withdrawals to shallower confined and unconfined aquifers will likely result in reduced groundwater flow to streams and wetlands. In addition, the vulnerability of these aquifers to drought and to recharge from undesirable sources likely will increase. 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, 5-1387, 33-20). In the northern part of the State, a large part of ground-water withdrawals are from unconfined and fractured rock aquifers. Water levels in two observation wells open to stratified drift exceeded their previous record lows during 2001, and 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 1998 and March 2000, and remained near the lowest recorded levels since 1967.
During 2001, the U.S.Geological Survey, in cooperation with the New Jersey Department of Environmental Protection (NJDEP) established a Drought Monitoring Network. NJDEP divided New Jersey into six drought regions on the basis of watersheds and water-supply characteristics. Drought indicators (ground-water levels, precipitation, streamflow, and reservoir contents) are monitored continuously in each region. The ground-water-level network, which is one part of the Drought Monitoring Network, was created to provide data to indicate water-level trends in shallow ground-water systems. Satellite telemetry was added to seven wells with continuous recorders in order to make the data available in the shortest time possible. An additional seven wells, which previously were measured periodically, were equipped with continuous recorders, and the frequency of measurements was increased at four additional wells. Current data from these wells, and other shallow observation wells, are compared to monthly statistics of historical data to put the current water levels in context. These data, along with data on precipitation, streamflow, and reservoir contents provide the information needed to determine the hydrologic conditions in each drought region. The USGS Fact Sheet FS-011-02 "Real-Time Ground-Water Level Monitoring in New Jersey, 2001" (Jones and others, 2002) describes the ground-water level satellite telemetry segment of the Drought Monitoring Network in more detail. Real-time ground-water-level data can be accessed on the Internet web pages of the USGS at http://waterdata.usgs.gov/nj/nwis/current/?type=gw.
The effects of climate on daily mean water levels in six observation wells during water year 2001 can be seen in the hydrographs shown in figure 2. Monthly extreme and long-term average water levels are shown for comparison. The Taylor, Cranston Farms 15, and Readington School 11 Obs wells (NJ-WRD well numbers 37-202, 21-364, and 19-270) are open to fractured-rock aquifers; the Lebanon State Forest 23-D, Morrell 1, and Vocational School 2 Obs wells (NJ-WRD well numbers 5-689, 23-104 and 11-42) tap unconfined sand and gravel aquifers. These wells are all part of the new Drought Monitoring Network.
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 March 14, 2002, on the World Wide Web at URL http://climate.rutgers.edu/) ranged from 7.5 to 8.5 inches below normal in New Jersey between October 2000 and September 2001. (Normal is based on precipitation values from 1971 to 2000). Below-average cumulative precipitation, ranging from 4.7 inches below normal in the north to 3.9 inches below normal in the south, from October to February, caused water levels in many observation wells to decline. Above normal precipitation was recorded during the months of March and June and water levels in many observation wells rose. A prolonged dry spell in April and May, and rainfall that ranged from 2 inches (north) to 4 inches (south) below normal from July to September caused water levels in many observation wells that tap unconfined and fractured rock aquifers to decline to below average levels. (See figure 2.) Previous record low water levels were exceeded in seven observation wells, and record high water levels were exceeded in five observation wells open to unconfined or fractured-rock aquifers during the 2001 water year. (See table 1.)