Nassau-Suffolk Aquifer System
Nassau-Suffolk Aquifer System
Nassau and Suffolk Counties
- I. Introduction
- II. Hydrogeology
- A. Geologic Framework
- B. Geologic Setting
- C. Ground Water Hydrology
- D. Water Supplies
- E. Ground Water Quality
- F. Designated Areas
- III. Susceptibility to Contamination
- IV. Summary
- V. Selected References
- VI. Figures
- Figure 1. Nassau-Suffolk Aquifer System Designated Area
- Figure 2. Major Hydrogeologic Units of the Ground Water Reservoir of Long Island, New York
- Figure 3. Ground Water Movement and Discharge on Long Island, New York, Under Natural Conditions
- Figure 4. Approximate Time for Water to Move from the Water Table to Points within the Regional Ground Water System of Long Island, New York
The Safe Drinking Water Act (SDWA), Public Law 93-523, of December 16, 1974 contains a provision in Section 1424(e), which states that:
If the Administrator determines, on his own initiative or upon petition, that an area has an aquifer which is the sole or principal drinking water source for the area and which, if contaminated, would create significant hazard to public health, he shall publish notice of that determination in the Federal Register. After the publication of any such notice, no commitment for Federal financial assistance (through a grant, contract, loan guarantee, or otherwise) may be entered into for any project which the Administrator determines may contaminate such aquifer through a recharge zone so as to create a significant hazard to public health, but a commitment for Federal financial assistance may, if authorized under another provision of law, be entered into to plan or design the project to assure that it will not so contaminate the aquifer.
This section allows for the specific designation of areas which are dependent upon ground water supplies. Following designation, the review process will ensure that federal agencies will not commit funds toward projects which may contaminate these ground water supplies.
On January 21, 1975, the Environmental Defense Fund petitioned the U.S. Environmental Protection Agency (EPA) Administrator to designate the aquifers underlying Nassau and Suffolk Counties, Long Island, New York, as a sole source aquifer under the provision of the Act. A notice of receipt this petition, together with a request for comments, was published the Federal Register, Thursday, June 12, 1975.
Although the Long Island aquifer system underlies all of Nassau, Suffolk, Kings and Queens Counties, the Administrator has limited consideration of designation to Nassau and Suffolk Counties because the petition is limited to the ground water underlying Nassau and Suffolk Counties, because New York City is supplied almost completely with potable water from upstate New York, and because ground water movement is primarily north-south so that ground water underlying New York City does not impact upon the ground water underlying and Suffolk Counties except for that area of Queens County western border of Nassau County.
Long Island's present configuration is primarily the result of the glaciation which occurred during the Pleistocene Era, predominantly that of the last ice age, the Wisconsin which ended about ten thousand (10,000) years ago.
The geologic structure of Long Island is relatively uniform. The island is underlain by bedrock of the Precambrian system or Proterozoic Era, composed of crystalline metamorphic and igneous rock with a southeast slope of approximately sixty-five feet per mile (65 ft/mi) or slightly less than one degree (1ø). Lying over bedrock is a wedge-shaped mass of unconsolidated material. The wedge of unconsolidated sediments ranges in thickness from zero where the bedrock surfaces near the East River to one thousand one-hundred feet (1,100') in the southeast part of Queens to two-thousand feet (2.000') in southcentral Suffolk County.
Two advances of the Wisconsin ice sheet during the Upper Pleistocene of the Quaternary Period caused the island to be blanketed with till, ice-contact stratified drift, outwash deposits and deposits composed of clay, silt, sand, gravel and boulders. The terminal moraines and the north shore are composed primarily of stratified drift with some till. The areas between the moraines and south of them are mostly the outwash deposits. Central and south Long Island are of glaciofluvial origin .
There are four distinct formations on Long Island: The Upper Glacial, the Jameco, the Magothy and the Lloyd aquifers. They all occur in the unconsolidated materials overlying the bedrock (Figure 2).
The Upper Glacial aquifer, which underlies all of Nassau and Suffolk Counties, has a probable maximum thickness of about seven hundred feet (700'). It contains large quantities of ground water in both the outwash plain and the morainal deposits. The deposits underlying the outwash plain are composed largely of stratified, brown, fine to coarse sand and gravel.
The Jameco aquifer, a lower glacial deposit which exists locally along the northern and southern parts of Nassau County, ranges in thickness from zero to two-hundred feet (0-200') and is situated from about one-hundred to five-hundred fifty feet (100-550') below land surface. It contains dark gray and brown, fine to coarse sand and gravel with thin silt and clay layers. This aquifer is locally contaminated by saltwater intrusion.
The Magothy aquifer, which underlies both of Nassau and Suffolk Counties, ranges from zero to one thousand one-hundred feet (0 - 1,100') thick and is zero to six-hundred feet (0 - 600') below the land surface. Fine to medium sand is inter-bedded with clay and sandy clay of moderate permeability and silt and clay of low to very low permeability. The basal fifty to two-hundred feet (50 - 200') may commonly contain coarse sand and gravel.
The Lloyd aquifer, which lies immediately above solid bedrock, is approximately zero to five-hundred fifty feet (0 - 550') thick and is two-hundred to one thousand eight-hundred feet (200 - 1,800') below the surface. It contains fine to coarse sand and gravel with a clayey matrix with some layers of silty or solid clay.
The Long Island aquifer system is located in Long Island, New York, and lies within the Atlantic Coastal Plain physiographic province of the United States. Long Island is bounded on the north by Long Island Sound, on the east and south by the Atlantic Ocean and on the west by New York Bay and the East River (Figure 1). The island is one hundred twenty (120) miles wide. Including the barrier beach and other outlying islands, its area is approximately one thousand four hundred (1,400) square miles. There are four major physiographic features, the terminal moraines, the glacial plain, eroded headlands, and barrier beaches.
Two terminal moraines are located in the north and central parts of the island. The northern, the Harbor Hill moraine, continues eastward into the North Fork of the island, while the southern, the Ronkonkoma moraine, continues eastward into the South Fork. The western reaches of the two moraines converge. On the northern flanks of the moraines are their respective ground moraines. The Harbor Hill moraine has a maximum altitude (height above sea level) of three-hundred feet (300'). The Ronkonkoma moraine has a maximum altitude of four-hundred feet (400'). The inter-morainal area is from one- to two-hundred feet (100-200').
South of the Ronkonkoma terminal moraine is a moderately flat glacial outwash plain that extends to the south shore bays. It ranges in altitude from one hundred to one hundred-fifty feet (100-150') just south of the moraine to zero at the coast, with a twenty foot per mile (20 ft/mi) slope seaward. At the coast it merges with recent (Holocene) lagoon deposits.
Eroded headlands along the north shore are the result of various glacial and postglacial depositional and erosional processes. The relatively wide deep harbors of the western half of the north shore of the island were probably occupied by the last iceblock remnants of the stagnating Pleistocene ice sheet. In places, bluffs steepened by wave erosion are about one hundred feet (100') high.
Along the south shore, separated by shallow bays from the main part of the island, are barrier beaches or offshore bars created by wave and ocean currents. They are constantly eroded by a predominantly westdirectional longshore current. The shallow bays are gradually filling naturally with sand, silt and organic matter.
The entire ground water reservoir except for that underlying the two eastern forks may be regarded as a single hydraulic system in which the more permeable zones, which yield useable amounts of water to wells, aretermed aquifers, and the less permeable, which retard the movement of ground water, are termed confining beds.
On Long Island the fresh ground water is bounded laterally and underlain locally by salty ground water hydraulically connected to the sea. The salt water interface is known accurately only in the southwest Nassau and southeast Queens Counties.
Figure 3 depicts the general direction of ground water movement. The predominant flow pattern is northward and southward from the water table divide. (Figure 4). The approximate time for water near the Nassau-Suffolk County border to move from the water table hear the divide to points within the regional ground water system is also shown in Figure 4.
Very scanty information indicates that the Lloyd aquifer and the deep Magothy aquifer contain salty ground water beneath the forks at the eastern end of Long Island. The fresh ground water occurs in a lens ranging in thickness from a few meters to greater than a hundred meters.
Under natural conditions the ultimate source of the ground water recharge is infiltration of precipitation into the zone of aeration and subsequent downward percolation through the zone of aeration to the water table. Estimates of annual recharge range from about ten to thirty-five inches (10 - 35") inches of water, with an estimated average of twenty-two to twenty-three inches (22-23") of water or about onehalf of the average annual precipitation. This corresponds to about one million gallons per day per square mile (1 mgd/sq mi). It is probably less in the northern part of the island and higher in the outwash plains.
The ground water reservoir, exclusive of the eastern forks, may be regarded as a single hydraulic system. The freshwater reservoir is bounded by the saltwater interfaces in the various aquifers to the north, south, east and west, the water table above, and the bedrock below. It is estimated that about ten to twenty-trillion gallons of water could be obtained if the aquifers were drained. (This excludes the North and South Forks).
In the past two decades, most new housing developments have been required to include construction of one or more drainage basins. Most of the highway drainage is also collected in this way. These basins probably compensate for some of the lost permeable area.
Since 1933 New York State has been empowered to regulate all wells on Long Island that withdraw more than 100,000 gpd from the ground water reservoir. In 1954 the law was modified to include all wells having capacities of more than forty-five gallons per minute (45 gpd) or 65,000 gpd. The State policy has been that the drilling of new industrial wells for air conditioning or cooling water purposes with capacities in excess of 100,000 gpd be prohibited unless the water pumped is returned in a chemically uncontaminated condition into the ground through diffusion wells or other approved structures. There are more than one-thousand such wells in Long Island, including King and Queens Counties. Most of the water has been used for air conditioning and then been recharged at higher temperatures. The wells vary in depth from three to six (3 -6) meters especially in the older wells, to a hundred meters or more. Water used for other purposes need not be returned but can be discharged with State and Federal approval. In addition, under the State Pollutant Discharge Elimination System a permit is required for any ground water discharge in excess of one-thousand gallons per day (1,000 gpd).
The main elements of natural discharge from the aquifers are evapo-transpiration, seepage to streams and springs, and subsurface outflow.
Losses from the zone of saturation through evaporation and transpiration vary seasonally and depend in large degree on the position of the water table with respect to the land surface.
It appears that stream flow is not appreciably derived from direct runoff under natural conditions. Less than five percent (5%) of total measured stream flow is direct runoff, about one percent (1%) of the precipitation. The remaining ninety-five percent (95%) is supplied by ground water.
In Nassau County the community water supply is provided by thirty-seven (37) municipally or publicly owned systems, five (5) privately owned systems and three (3) institutional systems. The water for these systems comes from four hundred seventy-four (474) operating wells. Out of a total population of 1,530,629, about 3,000 relied on individual sources, and 1,419,789 people relied on the community water supplies. This last figure includes a transient school population of 16,000. It does not include 123,840 people served by the Jamaica Water Company of New York City.
In Suffolk County, the community water is provided by the Suffolk County Water Authority, nineteen (19) municipal water districts, village owned water systems and fifty-six (56) individually owned water corporations. In mid1969 there were five hundred twenty-three (523) operating community supply wells and pumping stations. Large areas are still without a community water supply. In 1965, a total estimated population of 893,000, more than 260,000 people still had to reply on individual sources.
The natural water quality of the aquifers is generally good, except for iron. The dissolved solids concentration is very low, about 40 to 50 mg/l, varying with aquifer. Locally the iron content of the waters of the Magothy and Lloyd aquifers is about two to five times higher than the 0.3 mg/l recommended for public water supply.
During recent years groundwater quality has deteriorated. The majors are nitrate and detergents. Also, local problems of saltwater intrusion and thermal and industrial waste pollution have contributed to the deterioration. Because of the use of septic tanks, organics present in detergents have entered the aquifers, especially the Upper Glacial aquifer. Although perhaps not a health problem, detergent residues do cause effects which are not aesthetically pleasing, such as foaming. Suffolk County banned the sale of detergents for several years. Test wells show decreasing amounts of detergents but not to a level where Suffolk County would consider removing the ban.
Perhaps the greatest problem of groundwater contamination in Long Island is by nitrate. The increased nitrate content of ground water and streams, mainly due to infiltration of sewage and leachate from chemicalfertilizers, is a major water quality problem in Nassau County. Approximately thirty-five percent (35%) of the four hundred twenty-six (426) water supply wells located throughout Nassau County have shown the trend of increasing nitrate concentrations. In 1973, twenty-five (25) wells exceeded the state standard for drinking water of 10 mg/l nitrate as N. Since 1967, thirty (30) wells have been closed because of the same water quality problem.
The Suffolk County Water Authority has indicated that nitrate concentrations have been increasing in some Suffolk County public supply wells, but that at present none have been abandoned because of nitrate levels exceeding the public health standard. Although the problem is less severe in this more sparsely populated county, parallel trends of development indicate that nitrate contamination will approach that of Nassau County in the future. Potential serious water supply problems exist on the North and South Forks of Long Island. At these locations, available supply is extracted only from shallow wells which tap fresh water underlain by salt water. No deep Magothy source exists at these locations.
While ocean discharge of wastewater reduces direct contamination of the aquifer, it increases the consumptive use and may result in saltwater intrusion. Saltwater intrusion so far is largely a local problem in a small area on the southern Queens-Nassau County. The North Fork also has experienced intrusion due to its highly consumptive use, mainly because of agricultural use.
The area that has been designated as the Sole Source Aquifer is defined as the stratified drift and glacial outwash within the valleys. This area is coincident with that identified as a Primary Water Supply Aquifer by New York State Department of Health (1981) and New York State Department of Environmental Conservation (1987). The aquifer service area is the same as the aquifer area. Figure 1 shows the location and boundaries of the designated area.
The NassauSuffolk Aquifer System is highly vulnerable to contamination. Ground water management is being addressed locally through area wide waste management planning. The Nassau Suffolk Regional Planning Board (NSRPB) is the agency designated to develop an Area wide Waste Treatment Management Plan for Nassau and Suffolk Counties. Although the NSRPB is the designated agency, the Clean Water Act, Section 208 program represents a joint effort of the NSRPB and various operating agencies in Nassau and Suffolk Counties. The Suffolk County Water Authority, Health Department and Department of Environmental Control as well as the Nassau County Department of Planning Health and Public Works are voting members of the Technical Advisory Committee. The New York State Department of Environmental Conservation and the EPA are also represented.
Preliminary results from the 208 planning are that all population projections indicate an expanding population in Nassau and Suffolk Counties with increased ground water use and increased wastewater discharges.
Major surface and ground water pollution problems have been identified on Long Island. One of the goals of the 208 planning process in the bicounty region is to develop and implement a plan for water management which satisfies both surface and ground water quality objectives in a cost effective manner while distributing current and future costs and benefits on an equitable basis. Alternative water supplies such as water from upstate New York or desalinization will be examined.
Based upon the information presented, the Nassau-Suffolk Aquifer System meets the technical requirements for SSA designation. More than fifty percent (50%) of the drinking water for the aquifer service area is supplied by the Nassau-Suffolk Aquifer System. It is therefore recommended that the Nassau-Suffolk Aquifer System be designated a SSA. Designation will provide an additional review of those projects for which Federal financial assistance is requested, and will ensure ground water protection measures, incorporating state and local measures whenever possible, are built into the projects.
1. Philip Cohen and G.E. Kimmel, Status of Salt Water Encroachment in 1969 in Southern Nassau and Southeastern Queens Counties, Long Island, New York: U.S. Geological Survey Professional Paper 700-D. U.S. Geological Survey, 1970. pp. D281-286.
2. O.L. Franke and Philip Cohen, Regional Rates of Ground Water Movement on Long Island, New York: U.S. Geological Survey Proffessional Paper 800-C. U.S. Geological Survey, 1972. pp. C271-277.
3. O.L. Franke and N.E. McClymonds, Summary of the Hydrologic Situation on Long Island, New York, as a Guide to Water Management Alternatives: U.S. Geological Survey Professional Paper 627-F. U.S. Geological Survey, 1972. pp. 59.
4. Grant E. Kimmel, The Water Table on Long Island, New York, in March 1970: Long Island Water Resources Bulletin Number 2. U.S. Geological Survey. pp. 8.
5. Ellis Koch, Anthony A. Giaimo, and Dennis J. Sulam, Design and Operation of the Artificial-Recharge Plant at Bay Park, New York: U.S. Geological Survey Professional Paper 751-B. U.S. Geological Survey, 1973. pp 14.
6. Henry F.H. Ku, John Vecchioli, and Stephen E. Ragone, Changes in Concentration of Certain Constituents of the Treated Waste Water During Movement Through the Magothy Aquifer, Bay Park, New York: U.S. Geological Survey Journal Research, Vol. 3, No. 1, Jan-Feb 1975. U.S. Geological Survey. pp. 89-92.
7. N.E. McClymonds and O.L. Franke, Water Transmitting Properties of Aquifers on Long Island, New York; U.S. Geological Survey Professional Paper 627-E. U.S. Geological Survey, 1972. pp. 24.
8. J.F. Miller and R.H. Frederick, The Precipitation Regime of Long Island, New York: Hydrology and Some Effects on Urbanization on Long Island, New York, Geological Survey Professional Paper 627-A. U.S. Geological Survey, 1969. 21 pp.
9. N.M. Perlmutter, F.J. Pearson, and G.D. Bennett, Deep-Well Injection of Treated Waste Water--An Experiment in Re-Use of Ground Water in Western Long Island, New York: Repeat from New York State Geological Association Guidebook, 40th Annual Meeting, 1968. pp. 221-231.
10. Nathaniel M. Perlmutter, and Ellis Koch, Preliminary Hydrogeologic Appraisal of Nitrate in Ground Water and Streams, Southern Nassau County, Long Island, New York: U.S. Geological Survey Professional Paper 800-B, 1972. pp. B225-235.
11. Nathaniel M. Perlmutter and Theodore Arnow, Ground Water in Bronx, New York, Richmond Counties with Summary Data on Kings and Queens Counties, New York City, New York: Bulletin GW-32. Water Power and Control Commission, U.S. Geological Survey in Cooperation with New York State Department of Conservation, 1953. 86 pp.
12. G.E. Seaburn, Preliminary Results of Hydrologic Studies at Two Recharge Basins on Long Island, New York; U.S. Geological Survey Professional Paper 627-C. U.S. Geological Survey, 1970. pp. 17.
13. Joseph E. Upson, The Gardiners Clay of Eastern Long Island, New York--A Reexamination; U.S. Geological Survey Professional Paper 700-B. U.S. Geological Survey, 1970. pp. 157-160.
14. John Vecchioli and Henry F.H. Ku, Preliminary Results of Injecting Highly Treated Sewage-Plant Effluent Into a Deep Sand Aquifer at Bay Park, New York: U.S. Geological Survey Professional Paper 751-A. U.S. Geological Survey, 1972. pp. 14.
15. John Vecchioli and Anthony A. Giaimo, Corrosion of Well Casing and Screen Metals in Water From the Magothy Aquifer and in Injected Reclaimed Water, Bay Park, Long Island, New York: U.S. Geological Survey Professional Paper 800-B. U.S. Geological Survey, 1972. pp. B247-251.