ON LONG ISLAND, NEW YORK
Olin C. Braids, Ph.D.
ARCADIS Geraghty & Miller, Inc.
Long Island is a product of the last glacial age consisting of unconsolidated
materials of Pleistocene and Cretaceous ages. The northern quarter to one-third of the
island and extending along the northern border of the north fork is formed from morainal
deposits. The southern portion of the main body of the island and the south fork were
formed as an outwash plain. The main body of the island averages about 20 to 25 miles
wide north to south. The distance from the East River bounding Manhattan to Montauk
Point at the eastern extremity of the south fork is 128 miles.
Long Island is surrounded by seawater. The west boundary is the East River.
There are four major aquifers and two major confining units. The upper glacial aquifer,
the most permeable, consists chiefly of sand and gravel and is unconfined The Magothy
formation contains the Magothy aquifer beneath the upper glacial aquifer. It consists of
beds and lenses of fine to medium sand, clay, silt, and gravel and contains confined water.
In most of the area these aquifers are hydraulically closely connected. However, near the
south shore the Gardiners Clay retards movement between the aquifers.
The Raritan clay is a major confining layer between the Magothy and Lloyd
aquifers. This occurs on the southern portion of the island and extends southward beneath
South Bay and beneath the ocean. Because Magothy water is influence by seawater and is
brackish beneath the barrier beach, the Lloyd aquifer is reserved for public water supply in
that area. Wells tapping the aquifer are in excess of 1,000 feet deep. The artesian
hydraulic head is above land surface in some places.
All fresh groundwater is derived from local precipitation which averages 45 inches
per year. About half of this, 180 million gallons per day, goes to groundwater recharge in
Nassau County. Total groundwater pumpage for Long Island is over 400 million gallons
per day, predominantly from the Magothy. Combined fresh water storage is over 60
trillion gallons. Over 2,000 stormwater recharge basins have been constructed to enhance
groundwater recharge. Deep confined aquifers are recharged from the overlying
formations. It has been calculated that flow from the land surface to the Lloyd formation
at the barrier beach takes about 2,000 years.
ot~f~t~to ft I i"
18.3 (from Perlmutter and Geraghty, 1963)
DIRECTION OF GROUND WATER FLOW N180 I WATER LEVEL, IN FEET ALL WELLS ARE PROJECTED PERPINDICULAR
ESSENTIALLY IN PLANE OF SECTION WELL NUMBER CASING ABOVE MEAN SEA LEVEL TO THE LINE OF SECTION
Hydraulic profile showing probable flow of water in Magothy aquifer in southeastern Nassau County, New York,
liFLin;ii;r;-- ----;;-n-;--;;m-i-- -------:-l;r~l--;;i;=--;-;r--- ;-;i^-*;;anr-----;r~.-;;E~ir--i~~umr;i~
LINE OF EQUAL NET DECLINE IN
GROUND WATER LEVELS
0 5 10 15 20
AREAS SERVED BY SEWERS AND NOT
INCLUDED IN THIS ANALYSIS
(from Cohen, 1969)
Net decline in ground water levels in the water table aquifer due to drought conditions, 1961-66
~j;-;:L;::;;;;;;;=~i~----- --------------------- ----;- ----iii-i-;-?;?*-;i~-;?*~-rrc=rrili~~-
long island sound
Location of selected extensive subsurface clays
EXTENT OF GARDENERS CLAY
EXTENT OF PLEISTOCENE CLAY,
INCLUDING "20 FOOT" CLAY
i EXTENT OF MAGOTHY AQUIFER
-.. _. __. ~ __~,_ D- -~
LONG ISLAND UND
0 10 2 MILES
Location of recharge basins used for storm runoff on Long Island in 1969
IMPACTS ON THE GROUNDWATER RESOURCE
Groundwater is the only fresh water source for over 3 million people living on
Long Island. Some of Brooklyn is served by the upstate Croton Reservoir system because
local pumping began to induce seawater intrusion in the 1930's. In the 1970's, the
Magothy was one of the first aquifers to be designated as a sole source aquifer by the U.S.
Environmental Protection Agency. This designation enabled more stringent controls to be
placed on water use and quality. It also directed assessments of water management and
planning including one taken under Section 208 in the late 1970's.
Seawater intrusion is a threat along the whole waterfront of the island as
groundwater is pumped heavily lowering the water table and, in turn, reducing the
hydraulic head holding seawater away from the land. The north shore has several necks
protruding into Long Island Sound. Local pumping on the necks has to be carefully
controlled to prevent salt water intrusion. Several years of studies were performed in East
Rockaway on the south shore by the U.S. Geological Survey and Nassau County with
injecting fresh water to produce a barrier to seawater intrusion. Tertiary treated effluent
from a wastewater treatment plant was the fresh water source. Various schemes of
injection were used to test the practicality of utilizing a string of such wells to protect
inland aquifer quality. Groundwater is soft on Long Island because thereare virtually no
carbonates in the geologic formations. Iron pyrite is a common mineral in the Magothy
formation that dissolved when water was injected leading to a high dissolved iron content.
This condition imposed severe limitations on the injection life of the well and degraded
groundwater quality as a result of injection.
The experience with the experimental injection well indicated that it would be
impractical to install a line of injection wells to prevent seawater intrusion. More
conventional water management techniques that reduce near-shore pumpage have since
proven to be effective.
In the late 1970's, a little less than half of Nassau County and less than 20 percent
of Suffolk County were sewered. About 1.7 million persons lived in unsewered areas and
were served with 400,000+ septic tanks and seepage pits. It was estimated that 120
million gallons per day of septic effluent were discharged into the subsurface. The septic
effluent carried a nutrient loading of nitrogen, phosphorus, and potassium along with
numerous synthetic organic compounds. These consisted of pesticides, solvents, cleaning
agents, and other household and industrial chemicals that were flushed through the
long island sound
NOTE: POSITIVE HEAD DIFFERENCE MEANS THE WATER TABLE
ELEVATION IS HIGHER THAN THE ELEVATION OF THE BASAL
MAGOTHY POTENTIOMETRIC SURFACE AT A GIVEN POINT.
LOCATION OF HYDROLOGIC PROF I
SEE FIGURES 25.26. 27 AND
Areas of generally positive or negative head differences between wells screened in the water table and lower Magothy
aquifers, based on USGS maps for 1966, 1972, 1974 and 1975
long island sound
S GREATER THAN 40 LBS OF NITROGEN/ACRE/YE
FROM CESSPOOLS AND SEPTIC TANKS
Areas of major concentrations of on-site domestic waste disposal systems
A practice that was particularly damaging was the use of commercially available
liquid septic tank cleaning solvents. One brand name, Drainz, contained trichloroethene,
1,1,1-trichloroethane, and mineral spirits. One or more gallons of such solvents would be
used for a single "treatment." This practice, combined with industrial use and mishandling
of the same solvents, led to widespread contamination of the upper glacial and Magothy
aquifers. In 1982, 54 public supply wells in Nassau and Suffolk Counties were closed
because of organic chemical contamination. Some of the wells were screened as deep as
550 feet. About 200 monitoring wells functioning as early warning wells for the public
supply wells were contaminated at least once in the 1977 to 1982 period. The Nassau
County Department of Health filed a lawsuit to prevent the sale of Drainz and other
products containing volatile organic compounds for use as septic tank degreasers in 1979.
This was the first banning of such substances that was quickly followed by similar bans in
New Jersey and Rhode Island.
The threat to water quality by the septic systems spurred the desire to expand
public sewer systems. Counteracting that was the concern that exporting water to the sea
that had been effectively recycled into the aquifer from the septic systems would lower the
water table and dry up gaining streams and lakes on the south shore. A public relations
campaign was launched to gain public support for building a large sewer system in
southwestern Suffolk County. Some calculated that circa 1977 the project would cost
$44,000 per household served. This was more than the average price of a house in the
area served at the time. Nassau County at that time was over 50percent sewered, and it is
now over 75 percent sewered.
Protection of groundwater quality won out over the issue of water balance. The
sewer system was installed in southwestern Suffolk County and the treatment plant was
constructed on the south shore with an effluent outfall piped under Great South Bay,
crossing under the barrier beach at Jones Beach, and leading two miles out to sea. The
normal flow was by gravity, while several 15,000 gallon per minute pumps were present
should pressure be needed in the event of a storm surge.
In the twenty years since the sewering was begun, there has been some lowering of
the water table. This is attributable to increased pumping for a larger population and
increased export of water to the sea. Streams and lakes have been dredged to deepen
them thus intercepting the lowered water table and maintaining the surface water bodies in
a condition observationally unchanged.
In 1980, there were 40 active and abandoned unlined landfills on Long Island. I
performed a detailed study of the effects ofleachate on groundwater quality at two
landfills in Babylon and Islip. Leachate plumes were mapped that extended over two miles
downgradient at the Babylon landfill. The sandy texture of soil and the upper glacial
aquifer provided little potential for attenuation of chemicals or retardation of flow. At that
SPresently sewered areas
long island sound
S DOMESTIC WASTE TREATMENT PLANT
Domestic waste treatment plants discharging to ground water
time, there were about three million tons per year of solid wastes being generated. This
figure has certainly grown, while the facilities for disposal have been reduced.
All new landfills or landfill expansions have been required to be constructed with
liners. There are also at least two solid waste incineration facilities that have been
constructed in the last decade. In addition to air quality issues, disposal of incinerator ash
has been a problem. Locating incinerator ash disposal sites and engineering the sites to
contain leachate have posed difficulties and incurred costs.
An example of the stress put on the system by having limited access to new landfill
sites is what has happened in the Town of Oyster Bay. The town extends from Long
Island Sound to the ocean on the east side of Nassau County. For the past five or six
years, all of the solid waste generated in the town has been compacted and trucked to
Ohio for disposal. This has imposed a significant cost to the town's residents. One of the
town's landfills, Old Bethpage Landfill, became a Superfund site. Several other landfill
sites are either on the Superfund list or have required post-closure groundwater treatment.
Industrial Waste Disposal
Most of Long Island's industry is located along the spine of the island roughly
along the pathway of the Long Island Expressway. This is where most of the deep aquifer
recharge occurs, making groundwater most vulnerable. In the late 1970's, 2.5 million
gallons per day of liquid industrial waste were discharged into the ground. Treatment and
permitting had been required since 1967, but standards were not commensurate with
groundwater quality requirements. Metal processing, electronic component
manufacturing, cosmetic manufacturing, laundries, dry cleaners, and aircraft
manufacturing all contributed to the waste loading.
Detection of volatile organic compounds as regional groundwater contaminants in
the late 1970's led to investigations of industrial activities that were contributing to the
problem. In turn, this resulted in better waste management, treatment, and disposal.
Expanded sewering also gave a disposal mechanism for pre-treated liquid waste.
Fertilizers and Pesticides.
Twenty years ago there were approximately 50,000 acres utilized for agricultural
crops. Potatoes, cauliflower, and brussels sprouts were the major crops entering the
wholesale market. Over these two decades the total acreage has been reduced as a result
of suburban development, particularly of seasonal homes located in the rural eastern Long
Island region where agriculture was prominent. Crops have also changed. Viticulture has
become a major endeavor on both the north and south forks of the island. With increasing
land values and tax loads to carry, wine production brings more revenue per acre than the
long island sound
* LANDFILL SITE
Principal active and abandoned landfills
long island sound
* INDUSTRIAL SITE
Major industrial sites discharging to ground water
Iopg island sound
long island sound
ALL VALUES TAKEN FROM CHEMICAL CONSTITUENTS OF
WATER FROM STREAMS IN NASSAU AND SUFFOLK COUNTIES,
LONG ISLAND, NEW YORK: 1966 THROUGH 1975, USGS OPEN
FILE REPORT, JUNE 1976
ja MEDIAN NITRATE-NITROGEN 1972-75, IN MILLIGRAMS
SPER LITER MEDIAN SPECIFIC CONDUCTANCE
1972-75. IN JMHOS
Median nitrate-nitrogen and specific conductance concentrations in streams in Nassau and Suffolk Counties, 1972-75
former crops. The climate is quite temperate because of the surrounding water providing
hospitable conditions for grapes.
Nitrate at concentrations exceeding the 10 milligram per Liter nitrate-nitrogen
standard and pesticide chemical residues are present at numerous locations in
groundwater. Aldicarb/Temik, a nematocide, was used extensively on potatoes. In the
early 1980's, residues in concentrations causing public health concern were present
regionally in the agricultural district on eastern Long Island. The chemical was shown in
preliminary toxicology tests to decompose in a matter of weeks to months by hydrolysis.
It apparently failed to do so. The result was an outfitting of activated carbon treatment
systems to over 2500 homes by Union Carbide, the manufacturer. Twelve years later
some of these systems are still required.
More recently herbicides used on golf courses and utility rights of way, Dacthal
and Simazine, have shown up as residues in groundwater. Changes in agricultural
management and more careful use of fertilizers on lawns and golf courses have led to a
reduction in exceedances of the nitrate standard. Grapes have a lower nitrogen and water
requirement than the crops they replace which has helped to improve groundwater quality.
Public water supply is provided by private water companies and municipalities in
Nassau County. There is no county-wide coordinating authority. The Suffolk County
Water Authority is an organization providing such coordination and production
management in Suffolk County. The authority operates its own wells and oversees
production by other private and municipal vendors. The past decade has seen an increase
in pumpage, but pressure applied for increased efficiency in water use has offset the
demand. A net savings of 5 to 10 percent has been realized.
A unique feature of public water supply in some locations is the absence of
chlorination as a standard water treatment. The natural water is very soft with low
dissolved solids. If microbiological testing is performed frequently, it can be distributed
without being chlorinated. This provides water that tastes better than most bottled waters.
A water supply that lies under the feet of over 3 million consumers is under
constant threat in both quantity and quality. Public awareness of its importance and
vulnerability has been a constant subject of the media and the associated agencies. This
has resulted in measurable improvements in groundwater quality over the past two