Water supply report for coastal zone management program (Task 8.5, Long Island subarea)

[From the U.S. Government Printing Office, www.gpo.gov]

Coastal Zone
information
Center

INTERIM REPORT

on
Water Supply for
Coastal Zone Management
(Task 8.5, Long Island Subarea)

April 1976

GB
705
N7
W-38
1976 NEW YORK STATE
DEPARTMENT OF ENVIRONMENTAL CONSERVATION

Water Stipply Report
for
Coastal Zone Management Program
(Task 8.5, Long Island Subarea)

Prepared by
New York State Department of Environmental Conservation
Office of Program Development, Planning and Research
50 Wolf Road
Albany, New York 12233

W li3-77

pro r) r. t 17 C r ar Y

Z\@

U S DEPARTMENT OF COMMERCE NOAA
COASTAL SERVICES CENTER
SOUTH HOE-SON AVENUE
CHARLESTON , SC 29405-2413

The preparation of this report plus accompanying maps was
financially aided through a Federal Grant from the Office
of Coastal Zone Management, National Oceanic and Atmospher-
ic Administration, under the Coastal Zone Management Act
of 1972.

This report plus accompanying maps was prepared under the
Co'astal Zone Management Act of 1972 for the Division of
State Planning, Department of State

May 12, 1976

Grant Number: 04-5-158-50002

Intro(luction

The Coastal Zone Management Program has to unravel many environmentally intert-

wined elements to create a program that will ensure the optimum use of the

coastal zone resources.

For purposes of the public water supply element of the coastal zone management

study the New York State coastal zone area was divided into five subareas. The

Long Island subarea is one of these divisions and consists of Nassau and Suffolk

Counties. As consistent with the other subareas, water supply is examined on a

county by county basis with emphasis placed on water supply systems serving com-

munities adjacent to the coast.

The North and South shores of Long Island contrast sharply in physical features.

The North shore tends to be rapid high rise cliffs like shore lines while the

South shore is a glacial outwash plain which includes off shore barrier beaches.

The narrow North and South "forks" on the easterly end of Suffolk County main-

tain these respective characteristics as they taper to land points in the At-

lantic Oce an.

Due to these geographical features the Long Island subarea is broken down into

separate north and south shore zones. Both forks due to their narrowness and by

being virtually surrounded by salt*water are treated as complete coastal units.

S MIARY

The Long Island.coastal zone area does not appear to be in a precarious state at

the present time due to current water supply practices.

The New York State Department of Environmental Conservation's responsibilities rc---
garding decisions on water supply applications for expansion, increased pumpages,
new locations etc., have aided greatly in protecting the underground reservoir.

Restrictions on pumping in shore areas and requiring new wells to be located in-

land are perhaps the most important actions-that have kept the Long Island shore

area secur.e from salt water intrusion.

While the study area does not reveal any major conflict with coastal zone resources

and present water supply needs. It is known however, that significant population

increases especially in the eastern forks of Suffolk, can jeopardize the fresh

water-salt water and ecological balances. Quality deterioration of the under-

ground reservoir must also be considered with population expansion.

The predictibility of changes in the coastal zone area under various proposed

water management alternatives should be greatly enhanced under the on going

PL 92-500 Section 208 waste water management'study. The 208 study being conduct-

ed under the Nassau-Suffolk Regional Planning Board includes a computerized model

study for the Long Island ground water system. Any water management determinations

should await the 208 study results.

COASTAL Z(1E MANAGEMENT
PUBLIC WATER SUPPLY
NASSAU COUNTY

Area Boundaries

For public water supply investigation in Nassau County's Coastal Zone the follow-

ing boundaries were arbitrarily selected.for purposes of this report only.

The Coastal Zone boundary for the South Shore of Nassau County will not be con-

.tiguous with the area of influence exerted on the coastal zone by water supply

considerations. For this reason the coastal area of concern for this report de-

signated on the attached map (See Figure 1) is bounded on the west by the Queens-

Nassau line and on the south by the southermost boundaries of the barrier beaches.

The northern boundary, Sunrise Highway, approximates the 20' contour. This water

supply sector has an area of about 40 square miles, with an additional 6 square

miles of low tidal lands in the bay area.

The Coastal Zone boundary for the North Shore of Nassau County will encompass a

relatively small area immediately adjacent to the bays, harbors and the Long Is-

land Sound. For purpose of this water supply report a relatively larger area has

to be considered due to its implication on causes and effects relating to the

coastal zone. The arbitrary southern boundary that has been selected is the east-,

west surface water divide which is north of but approximates the Long Island Ex-

pressway (See Figure 1). The area included is approximately 70 square miles

(about 26% of the total county areas) and contains about 15% of the county popula-

tion.

General Description

Nassau County, an area of about 300 square miles located on Long Island, is border-

ed on the west by Queens County (N.Y.C.) and on the east by the Suffolk County

boundary. The north and south boundaries are Long Island Sound and the Atlantic

Ocean respectively. The barrier beach area on the Atlantic is separated from the

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mainland by a bay area which contains dozens of marsh and wetland islands which

are an important part of the local ecology.

The North Shore coastal area is broken into five distinct bays and harbors.
(Little Neck Bay, Manhasset Bay, Hempstead Harbor, Oyster Bay and Cold Spring

Harbor) between the New York City and Suffolk boundaries. The shoreline is

characterized by steep slopes or bluffs, many of them wooded, with narrow sandy

or rocky beaches. In some instances the land elevation is over 100 feet above

sea level less than 1,000 feet from the shoreline. Such feature's have limited

access and shoreline development, but there are lowlands and previously filled

wetlands particularly at the heads of harbors which have major residential and

commercial development.

Population and Land Use

Nassau County has rapidly transformed from a semi-rural surburb of New York City
with a population of 400,000 in 1940 to a present dynamic urban center of approxi-

mately 1.5-million residents, with the largest concentrations in the South Shore

area. Extensive development in this area has stabilized the population to some

extent with medium to intermediate population densities and with average and high

population densities in the City of Long Beach and in local sectors of several

other communities. Present (1975) LILCO population estimates indicate 204,000

people now located in the mainland study area and 47,000 within the Long Beach,

Island Park areas; averaging over 12 persons per acre.

With less than 5% vacant land remaining in the South Shore study area, and with

the Nassau-Suffolk Comprehensive Development Plan indicating the subject area may

expand to complete medium to high population densities, apartment and high-rise

type*dwellings will be part of future development. The Development Plan indicates

that within the townships of Hempstead and Oyster Bay, of which the study area is

part, that by 1985, 54,500 apartment units should be built and 13,300 publicly

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assisted housing units should be provided. Relatively little of the housing ex-
pansion is expected south of Sunrise Higliway with the possible exception of Long

Beach.

The Nassau Suffolk Regional Planning Board Comprehensive Development Plan indi-
cates that future North Shore population densities may reach intermediate to
medium density figures with significant area earmarked for park and conservation

purposes.

PUBLIC WATER SUPPLY

All water supply is from groundwater sources and all groundwater originates from

precipitation that falls on the county. Half of the average precipitation of 45
inches infiltrates-into the groundwater reservoir and the remainder is lost by

evapotranspiration and direct runoff into tidal water.

Sandy unconsolidated deposits which underlie the county make up the three major
aquifers used for water supply. The Glacial aquifer is the uppermost and is

readily accessible for water supply. The Magothy aquifer is directly below and

is the largest, accounting for 80% of the public pumpage. The Lloyd formation is
the deepest aquifer and lies above bedrock and under a Raritan clay layer.

The groundwater flows away from the groundwater divide near the central portion
of the county towards Long Island Sound and the Atlantic Ocean at about I foot per
day. Near the groundwater divide a downward component of flow serves to recharge
the deeper formations. As the groundwater moves toward the shoreline an upward
flow component exists. Thus recharge water in the inner portion of the county

eventually will be a part of and interact with the shallow coastline subsurface

flows into Long Island Sound and the Atlantic Ocean. (See Figure 2)

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LONG ISLAND AILANTIC
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SALT WATER

CROSS SECTION NASSAU COUNTY-GROUND WATER FLOW

FIG 2

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South Shore @4ater Supply Area

The study area's public water supply needs are served by five municipal and two

private suppliers. All water is obtained from ground water wells and rainfall is

the sole source of recharge.

All of the suppliers franchised areas, with the exception of the City of Long Beach

and Lido-Point Lookout, extend beyond the study area boundaries. The total pumpage

for public water supply wells within the study area, however, averaged 12 mgd (1974).

The greatest withdrawals within the study area were from the'Lloyds aquifer (6.3

mgs) followed by the Jameco (4.0 mgd), Magothy (1.6 mgd), and Glacial aquifers (0;2 rngd).

The study area encompasses an area outside the hydrologically-defined water budget

area of Nassau County (Greeley-Hansen Study-1971) and thus all pumpages for the

study area exceed the permissive sustained yield allowances as defined by the G-H

Study. The county total permissive sustained yield for an average year is 151 mgd

w1iich is projected to be exceeded by 1985.

Since 1954, glacial pumpage has dropped in Nassau County from 15% of Phe total pumpage

to less than 5%. while the Magothy pumpages increased from 72 to 85% of the total Pump-

age. This is a result of shutdowns and reduced glacial pumpage due to wells having,

high nitrates, iron, detergent or ammonia concentrations.

Saltwater encroachment is another serious concern in the study area aquifer. The

U.S.G.$. has confirmed bodies of salty groundwater or wedges under southwestern

Nassau.in each of the four aquifers. The approximate landward limit of the four

wedges has been delineated by Lusczynski and Swarzenski, 1966-(See Figure 3).

Recognizing the sensitivity of the area to increased chlor ides with increased

groundwater withdrawals, the former New York State Water Resources Commission and

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APPROXIMATE LAr4Dw4Hu EXTENT OF
INTERMEDIATE WEDGE OF SALTY GROUND WATER

APPROXIMATE LANDWARD EXTENT OF
DEEP WEDGE OF SALlY GROUND WATER

A!REF. POSITION9 OF SALTY WEDGES AFTER
LUSCZYNSKI 8k SWARZENSKI (1966)

NASSAU C".

the Department of Environmental Conservat:ion have prohibited new well construction

south of the Sunrise Highway. Existing mainland wells which are now south of Sun-

rise Highway are usually within a few hundred feet of the highway boundary. The

barrier beach section which includes Atlantic Beach and City of Long Beach lacks

any tie-in to mainland water supply sources and has historically had quality pro-

blems with chlorides in the shallow aquifers. As a result, all barrier beach public

suppliers now have wells exclusively in the lower Lloyd formation. The Lloyd forma.-

tion. rests above the bedrock formation and is considered the last resort for water

supply in the Long Island aquifer system. The Department of Environmental Conser-

vation practice is to protect the Lloyds whenever alt!rnative sources are --vailable..

.This is in part due to the experience with the Brooklyn area, where high population

and geographic and hydraulic conditions similar in most respects to southern Nassau

suffered drastic water-level reductions and severe salt water intrusion due to over.-

pumping in the 1930's. This resulted in abandonment of all Brooklyn groundwater

wells as a source of public water supply to the problem areas.

The quality of Nassau groundwater has undergone deterioration with nitrates and

detergent problems which have been documented by several reports. (Greeley-Hansen,

1971)., Some local situations involving thermal and industrial-waste contamination

are potential threats to groundwater quality, but widespread abuses, if existing,

have not been highlighted. Recharge of treated STP effluents in the shore areas

has at various times been proposed to protect the underground freshwater from salt

water intrusion. However, distances to the water table are shallow throughout this

shore area. Prospects for recharge are poor as little soil medium would be avail-

able for filtration and any high-quantity recharge would ultimately affect the bay

water salt concentration and existing estuary limits from a dilution standpoint.

The quality and nature of the recharge, of course, would demand further consider-

ation of theJocal ecology. While recharge is technically feasible, detailed eco-

logical studies from the effects of recharge have not been conducted to date.

Recommendations

The Nassau-Suffolk Comprehensive Development Plan indicates that the subject area

ultimately may have medium to high population densities. The area will soon be

almost 100% sewered, allowing for industrial and domestic waste to be treated

rather than recharged directly to the groundwater reservoir. The concerns which

have to be dealt with are the consequences of overpumping as the population in-

creases, and suitable recharge of treated effluents to counteract saltwater

intrusion and depletion of.the groundwater supply. If quality deterioration

continues, alternative sources or importation of water would have to be consider-

ed. The Greeley-Hans en Study (GPWS-60-Nassau County) has offared alternative

management suggestions and recommendations some of which are summarized as

follows:

Greeley-Hansen

A. Inject tertiary-treated STP effluent into the groundwater supply near

the salt water edge to raise the water table and prevent salt water

intrusion.

B. Inject treated STP effluent into a system of shallow recharge basins

together with injection wells to substitute for natural subsurface out-

flow and raise fresh water yield.

C. If no action is taken on "A" above then permit salt water intrusion'to

create new equilibrium which will reduce the groundwater withdrawal area.

D. Import water from Suffolk County or the New York City System where per-

missive sustained yields are high.

North Shore Water Supply Area

Public water supply needs within the defined coastal zone are furnished by 13

municipal and 4 privately owned suppliers. In 1974 these suppliers pumped an

average of 38 million gallons per day from .105 wells with the greatest pumpage

from the Magothy aquifer.

Public water supply pumpage in the Great Neck and Manhasset area has induced

changes in the natural freshwater saltwater interface and at times drastically

lowered the groundwater table. The Glacial aquifer is limited for pumping water

as it is believed to exist only as valley fill of the Magothy. The Magothy struc-

ture tends to be quite clayed in these areas and some wells intended for public

water supply were abandoned due to poor yields. Saltwater intrusion occurred

in Lloyd wells due to overpumping in the 1950's when chloride content jumped

from a range of 5 to 15 parts per million to 65 parts per million. Wells in all

aquifers in the Port Washington Water District are affected by increased chloride

levels during increased summer pumpage.

In several cases among the various water suppliers located near the shoreline,

groundwater levels dropped below sea level during periods of peak pumpage. For

example,'the Citizens Water Supply Company has had-pumping levels as low as 68

feet below sea level on peak days.

The former New York State Water Resources Commission recognizing the consequences

of overpumping in the peninsula areas imposed conditions and restructions on exist-

ing wells and regulated capacities on wells constructed during recent expansion..

As a result observation wells are now used to monitor pumping and pumping cannot

continue on certain wells if drawdown levels in observation wells are lowered be-

yond designated elevations and/or chlorides increase to 50 parts per million.

Due to, these sensitivities the Department of Environmental Conservation disapproved

the Port Washington Water Districtis request to construct wells within their own

district, but approval was given to construct two wells inland where drawdown and

chlorides are not critical.

Inland wells in some instances have had quality problems with nitrates. The United

States Geological Survey conducted a study of nitrate between 1966 and 1970 and

nitrate content exceeded the drinking water standards of 10 mg/l in Glacial and

Magothy wells in substantial portions of the mid-Nassau area. Computations indi-

cate insufficient dilution under Nassau County to bring nitrate nitrogen concen-
trations below 10 mg/l in unsewered areas where the population density is in ex-

cess of 3 persons per acre. With the Glacial formations showing the most serious

deterioration, community supply wells have moved to deeper formations. This may

only be a temporary expedient as degradation indicated by increasing nitrate con-

tent extends downward into the Magothy formation with this movement encouraged in

part by pumping of deeper wells in addition to natural flow. In 1973 25 of 384 com-

munity supply wells in Nassau County exceeded nitrate nitrogen drinking water

standards with the heaviest concentration in the northern and central portion.

Some steps taken to cope with degradation of water qualityare blending water from

2 or more wells and deepening wells. Ion-exchange nitrate removal plants are

being investigated and one such plant is presently in operationand being tested.

Discussion of coastal zone public water supply necessitates examination of the

inland and mid-island sources With what is presently known of the natural under-

ground flow the deeper mid-island water is the potential water which travels out-

ward to the shoreline sectors (Figure 2) Freshwater contained within the coastal

zone sector is contiguous to the inland supply. High public water supply withdrawals

in the coastal areas lead quickly to changes in the saltwater-freshwater balance

mechanism both from capturing the normal freshwater outflow and the accompanying

drawdown effects. However, groundwater flows between the thr ee main Long Island

aquifers and their inter-relationship with the non-static freshwater-salt-water

interface are thought of as separate units and vary individually in respective

water quality and boundary limits.

Recommendation

The ecological changes which may result from introduction of salty and brackish

water into previously freshwater environments from overpumpinghave received little

study at this time. With complex inter -relationships it is advisable to prohibit

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any further-public water supply well con,,truction in the 2eninsula area until a

firm ecological knowledge base is established. The ongoing PL 92-500 Section 208
wastewater management study for Nassau-Suffoik counties is scheduled to investigate

such concerns using computerized model studies and any further determination should

await the 208 study results.

References

Greeley & Hansen. Report on Water Supply. (Nassau County) New York, 1963.

Greeley & Hansen. CPWS-60 Comprehensive Public Water Su2ply Study. (Nassau

County) 1971.

Nassau-Suffolk Regional Planning Board. Utilities, Inventory and Analysis, 1969.

Nassau-Suffolk Regional Planning Board. Comprehensive Development, Plan, 1970.
U.S. Geological Survey. Udrogeology Along the Proposed Barrier.-Recharge-Well

Alignment in Southern Nassau County, 1975.

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COASTAL ZONE, MANAGEMENT
PUBLIC WATER SUPPLY
SUFFOLK COUNTY

Area Boundaries

For public water supply investigation in Suffolk County's Coastal Zone the
following boundaries were arbitrarily selected for purposes of this report

only.

The South Shore water supply report area is defined as having the Nassau

County border line on the west, the Atlantic Ocean on the south and Route

27 (Sunrise Highway) on the north from Nassau County east to Shinnecock
Inlet. The entire south fork from Shinnecock Inlet east., due to its proximity
to Peconic Bay will be considered wholly as a coastal zone area (See Figure 1)

The North Shore water supply report area will be arbitrarily defined here

as having Nassau County as. its western boundary, Long Island Sound as the

north boundary, and Route 27A from Nassau County east to Riverhead as the

southern boundary. From Riverhead east the entire North Fork, due to its

proximity to Peconic Bay will be considered wholly as a coastal zone area.

General Description

Suffolk County comprises the eastern two-thirds of Long Island and includes

a land area of about 922 square miles. Its western boundary is Nassau County
and the remaining three sides are bounded by water. Suffolk County is recog-
nized as:a major suburban area of New York City with extensive residential and

industrial development and a total population of 1,300,000 (est. LILCO -

Jan. 1975).

The source of all freshwater in Suffolk County is precipitation which is

transmitted to the main groundwater body as recharge. All public water supply

is from wells tapping the groundwater reservoir. The only exception is Fishers
Island located about 12 miles east of Suffolk in Long Island Sound. Fishers

Island, with a year round population of less than 500, has some runoff @ed
ponds which are used as the primary public water supply. Suffolk County is
virtually unsewered at present and except for a few local areas, all waste

water is disposed of thru septic tanks or cessIpools.

The Suffolk shorelines are bounded by Long Island Sound on the north; Peconic

Bay on the east with several bays and the Atlantic Ocean off the barrier

beaches to'the south. The shorelines total 784 miles, with the Long Island

Sound shoreline 191'miles, the south shore bays 239 miles, the Atlantic

Ocean 92 miles and Peconic Bay 262 miles.

Geology and Aquifers

Suffolk County is composed of unconsolidated sediments resting on a Pre-

Cambrian rock base which varies in depth from 400 to 1800 feet below sea-

level. The deepest aquifer is the Lloyd sand formation, 150 to 300 feet

thick, which lies above the bedrock. A Raritan clay member (100 to 300 feet

thick) overlies the Lloyd sands. Above the Raritan clay is the Magothy

formation ranging from 200 to 1000 feet thick making up the Magothy aquifer.

Glacial deposits form the uppermost Glacial aquifer which in places may be

as much as 700 feet thick in buried Magothy valleys, but averages 100 to 200

feet thick.

The interface between fresh ground water which underlies Suffolk County and

the salty ground water which surrounds it varies with the different geological

and hydrological characteristics of the various aquifers and the hydraulic

potential within the aquifers. If large withdrawals of fresh water were to

lower the hydraulic potential, the surrounding salty groundwater would move

landward into a portion of the aquifer previously occupied by fresh water.

24 With the exception of a very few loca.'ized areas, there has been no salt

water encroachment to date in Suffolk County and the position of the inter-
face is a result of natural equilibrium. The Lloyd aquifer is fresh beneath

south shore beaches, but it is salty beneath the two eastern forks and

possibly beneath some of the North Shore necks. The Magothy is fresh for

its entire depth beneath the south shore beaches, but on the south fork

only the upper Magothy is fresh and then only in the center of the Island.

On the North Fork the Magothy is salty east of Mattituck Creek. The Glacial

aquifer contains at least some fresh water beneath land surfaces all over

Long Island and in most places is entirely fresh water.

The salt water interface in the Magothy and Lloyd aquifer lies an unknown

distance south of Fire Island in western Suffolk. A Hele-Shaw analog model

of a cross section from Huntington Harbor to Robert Moses State Park indicated

that the toe of the wedge might be close to Fire Island. The interface in the

Magothy is probably closer to the shore on the north shore than on the south.
(See Figure 2)

The position of the salt water interface is a function of the amount of fresh

water outflow from the aquifer system. Any large scale reduction in the amount

of outflow because of consumptive use will result in a landward movement of

the salt water interface.

In eastern Suffolk County the knowledge of the position of the salt water -

fresh water interface has been expanded significantly through the findings of

the Suffolk County Test Well Program. Test borings for five deep test wells

on the South Fork penetrated the fresh water - salt water interface. Studies

of the South Fork indicate some areas where chloride levels

are suspect of being 250 ppm. or greater. For any well located in the low

24 lying coastal areas localized salt water intrusion can be expected to occur.

Suffolk County - South _.'hote Water Supply Area
The South Shore Coastal area as defined here is about 140 square miles and an
estimated population of 24-0,000 people with highest densities occuring in the

western end. There are twenty-four corporately owned well sites located on the

maialand between Nassau and Shinnecock which furnish.over half of the area's

public water supply.

There are also seventeen public supply well sites on the barrier beaches,
many of which however, contain only one well, mainly for seasonal water supply

to summer communities. A great many residents within the defined south shore

coastal area, exclusive of the South Fork, are supplied from inland public
supply wells located outside the co4stal zone boundaries. As many as 60,000

residents depend on private domestic wells and total withdrawal from the

designated.area is estimated to range from 17 to 30 million gallons per day.

With a safe yield of one million gallons per day per square mile accepted

for the inland area of Suffolk, the population in the coastal area west of

Shinnecock can be adequately served in the foreseeable future without

environmental consequences even with anticipated population increases. With

NYS Department of Environmental Conservation permits required for all public

water supply well construction and exercising current powers for spacing,

pumping, and monitoring of public supply withdrawals, the NYS DEC is alert

to ecology considerations of public water supply. It does not appear for

the co astal area west of Shinnecock, that any limitations are warranted due

to water supply considerations.

For the south fork, however., future population expansion may stress the

availability of fresh water due to salt water encroachment.

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Recommendations

Public water supply well construction should be maintained in the middle

portion of the south fork with population expansion. As permissive sustained

yields are reached, land.use regulation or alternate sources of fresh water

such as importation from western Suffolk will have to be considered to main-

tain adequate supply.

Suffolk County North Shore Water Supply Area,

The total county area within the defined north shore water supply zone is
over 150 square miles, with an estimated population of 120,000. The popu-

lation density varies from 1400 persons per square mile in the western area

to less than 400 in the eastern portion.

Generally, like Nassau County, the north shore of Suffolk County consists of

lightly wooded bluffs which ascend steeply to a height of 30 to 100 feet or