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Simulated Effects of Pumping and 

Drought on Ground-Water Levels and the 

Freshwater-Saltwater Interface on the 

North Fork, Long Island, New York

By Paul E. Misut, Christopher E. Schubert, Richard G. Bova, and 

Steven R. Colabufo

In cooperation with

SUFFOLK COUNTY WATER AUTHORITY

Water-Resources Investigations Report 03-4184

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For additional information about this report write to:

U.S. Geological Survey

2045 Route 112, Bldg. 4

Coram, NY 11727

Email: askny@usgs.gov

World Wide Web: http://ny.usgs.gov/

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.
iii

Contents

Abstract .......................................................................................................................................................... 1

Introduction ................................................................................................................................................... 1

Approach ............................................................................................................................................... 2

Purpose and Scope ............................................................................................................................. 3

Previous Investigations ...................................................................................................................... 3

Acknowledgments ............................................................................................................................... 3

North Fork Study Area ................................................................................................................................. 3

Land Use and Population ................................................................................................................... 3

Water Use ............................................................................................................................................. 3

Hydrogeology ....................................................................................................................................... 5

Hydrogeologic Framework ........................................................................................................ 5

Pleistocene Hydrogeologic Units .................................................................................... 5

Cretaceous Hydrogeologic Units .................................................................................... 7

Hydraulic Properties .................................................................................................................. 7

Hydrologic System .................................................................................................................... 17

Hydrologic Boundaries ................................................................................................... 17

Freshwater-Saltwater Interface .................................................................................... 18

Ground-Water Levels ...................................................................................................... 18

Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater 

Interface ........................................................................................................................................ 18

Development of Flow Model ........................................................................................................... 19

Model Grid ................................................................................................................................. 20

Boundary Conditions ................................................................................................................ 22

Model Calibration ..................................................................................................................... 24

Sensitivity Analysis ................................................................................................................... 28

1994 Steady-State Simulation Results ............................................................................................ 28

Simulation of Historical Record ....................................................................................................... 34

Analysis of Projected Future Conditions ........................................................................................ 34

Limitations of Analysis ............................................................................................................. 38

Results of Average-Recharge Simulations ........................................................................... 38

Average-Recharge Scenario 1 ...................................................................................... 38

Average-Recharge Scenario 2 ...................................................................................... 38

Average-Recharge Scenario 3 ...................................................................................... 38

Average-Recharge Scenario 4 ...................................................................................... 38

Results of Drought Simulations .............................................................................................. 38

Drought Scenario 1 .......................................................................................................... 39

Drought Scenario 2 .......................................................................................................... 39

Drought Scenario 3 .......................................................................................................... 41

Drought Scenario 4 .......................................................................................................... 41

Summary and Conclusions ........................................................................................................................ 41

References Cited ........................................................................................................................................ 42

Appendix ...................................................................................................................................................... 44
iv

Figures

1. Location of study area on North Fork, Suffolk County, N.Y. and selected features in the 

study area. .............................................................................................................................................. 2

2. Past and projected public water-supply areas on North Fork, Suffolk County, N.Y.: 

A. Village of Greenport and North Fork water supply districts in 1957. B. Riverhead and 

Suffolk County Water Authority supply districts in 1994. C. Riverhead and Suffolk County 

Water Authority supply districts in 1998. D. Projected Riverhead and Suffolk County 

Water Authority supply districts in 2010. E. Projected Riverhead and Suffolk County 

Water Authority supply districts in 2020. ........................................................................................... 4

 3. Past and projected public-supply wellfields on North Fork, Suffolk County, N.Y.: A. Publicsupply wellfield locations in 1957. B. Public-supply wellfield locations in 1994. C. Publicsupply wellfield locations in 1998. D. Projected public-supply wellfield locations in 2010. 

E. Projected public-supply wellfield locations in 2020. ................................................................... 6

4. Sewage-treatment district of the Village of Greenport on the North Fork, Suffolk 

County, N.Y. ............................................................................................................................................ 7

5. Sections A-A/ and B-B/ showing hydrogeologic units in the North Fork study area ................ 10

6. Surficial distribution of moraine, outwash, and drift on the North Fork, Suffolk 

County, N.Y. .......................................................................................................................................... 11

7. Lower surface altitude and thickness of the upper glacial aquifer zone A on North Fork, 

Suffolk County, N.Y.: A. Lower surface altitude. B. Thickness ..................................................... 11

8. Lower surface altitude and thickness of the upper confining unit on North Fork, Suffolk 

County, N.Y.: A. Lower surface altitude. B. Thickness .................................................................. 12

9. Lower surface altitude and thickness of the upper glacial aquifer zone B on North Fork, 

Suffolk County, N.Y.: A. Lower surface altitude. B. Thickness ..................................................... 12

10. Lower surface altitude and thickness of the lower confining unit on North Fork, Suffolk 

County, N.Y.: A. Lower surface altitude. B. Thickness .................................................................. 13

11. Lower surface altitude and thickness of the upper glacial aquifer zone C on North Fork, 

Suffolk County, N.Y.: A. Lower surface elevation. B. Thickness .................................................. 14

12. Upper and lower surface altitude and thickness of the Magothy aquifer on North Fork, 

Suffolk County, N.Y.: A. Upper surface elevation. B. Lower surface elevation. 

C. Thickness ......................................................................................................................................... 15

13. Vertical leakance values for the Pleistocene upper and lower confining units on the 

North Fork, Suffolk County, N.Y.: A. Upper confining unit. B. Lower confining unit ................. 16

14. Location of local freshwater flow systems on North Fork, Suffolk County, N.Y. ....................... 17

15. Water-table altitude in March-April 1994 on North Fork, Suffolk County, N.Y. ......................... 19

16. Schematic representation of the freshwater-saltwater interface along model row i, 

layer k, columns j-1, j and j+1 ............................................................................................................ 20

17. North Fork model grid, Suffolk County, N.Y. ..................................................................................... 21

18. Sea floor bathymetry near North Fork, Suffolk County, N.Y. ........................................................ 21

19. Conceptual diagram showing boundary conditions of the North Fork Model, Suffolk 

County, N.Y. ........................................................................................................................................... 22

20. Locations of recharge zones, public water-supply districts, freshwater bodies, and 

recharge rates used for 1994 steady-state simulations in North Fork model, Suffolk 

County, N.Y.: A. Recharge zones and locations of freshwater bodies. B. Public watersupply districts. C. Ground-water-recharge rates ......................................................................... 23
v

21. Locations of public-supply and commercial-supply wells in 1994 in North Fork model, 

Suffolk County, N.Y.: A. Public- and commercial-supply wells screened less than 45 feet 

below sea level. B. Public- and commercial-supply wells screened 45 feet or more 

below sea level. C. Agricultural parcels and irrigation wells ...................................................... 25

22. Locations of observation wells used in calibration of North Fork model, Suffolk County, 

N.Y.: A. Wells used for water-level measurement. B. Wells used for freshwatersaltwater interface measurement. C. Secondary wells near western extent of grid ............. 26

 23. Measured and simulated ground-water level and freshwater-saltwater interface 

depths: A. Measured and simulated water levels at well S16764. B. Simulated head and 

interface depth at well S4091 ............................................................................................................ 29

24. Sensitivity of simulated hydraulic head to variations in the values of selected 

parameters in the North Fork model: A. Mean residual. B. Root mean square error .............. 30

25. Simulated water-level and freshwater-saltwater interface position for the upper glacial 

aquifer zone A, 1994 average annual conditions on the North Fork, Suffolk County, N.Y.:

A. Simulated 1994 water levels in freshwater-flow system. B. Simulated 1994 freshwatersaltwater interface position .............................................................................................................. 31

26. Simulated water-level and position of freshwater-saltwater interface position for the 

upper glacial aquifer zone B, 1994 average annual conditions on North Fork, Suffolk 

County, N.Y.: A. Simulated 1994 water levels in freshwater-flow system. B. Simulated 

1994 freshwater-saltwater interface position. C. Simulated 1994 vertical gradient 

between upper glacial aquifer zones A and B ............................................................................... 33

27. Simulated water level and freshwater-saltwater interface for the upper glacial aquifer 

zone C,1994 average annual conditions on North Fork, Suffolk County, N.Y.: A. Simulated 

1994 water levels in freshwater-flow system. B. Simulated 1994 freshwater-saltwater 

interface position. C. Simulated 1994 vertical gradient between upper glacial aquifer 

zones B and C ...................................................................................................................................... 34

28. Simulated water level and position of freshwater-saltwater interface for the Magothy 

aquifer, 1994 average annual conditions on North Fork, Suffolk County, N.Y.: A. Simulated 

1994 water levels in freshwater-flow system. B. Simulated 1994 freshwater-saltwater 

interface position. C. Simulated 1994 vertical gradient between upper glacial aquifer 

zone C and Magothy layer ................................................................................................................. 35

29. Vertical sections showing simulated position of freshwater-saltwater interface under 

1994 average annual conditions in North Fork model, Suffolk County, N.Y. ............................. 36

30. Vertical sections showing model-generated heads and freshwater-saltwater interface 

positions at selected wells in scenarios 1 through 4 under simulated average-recharge 

conditions in North Fork model, Suffolk County, N.Y.: A. Scenario 1: Well S105669 

(redeveloped as S108347). B. Scenario 2: Well S15795 ................................................................ 38

Tables

1. Geologic and hydrogeologic units in the North Fork study area of eastern Long 

Island, N.Y. ............................................................................................................................................. 9

 2. Hydraulic conductivity of Pleistocene and uppermost Cretaceous hydrogeologic units 

for North Fork model ........................................................................................................................... 17

3. Discharge of Moores Drain at Route 25 in Greenport, Suffolk County, N.Y., on four 

sampling dates in 1998-99 .................................................................................................................. 19
vi

4. Simulated 1994 ground-water-recharge rates for North Fork model, Suffolk County, N.Y ..... 24

5. Measured (March-April 1994) and simulated water levels and hydraulic gradients at six 

well pairs in North Fork study area, Suffolk County, N.Y. ............................................................. 27

6. Calibration statistics on ground-water levels and saltwater interface for hydrogeologic 

units in North Fork model ................................................................................................................... 28

 7. Parameter values used in North Fork model .................................................................................. 28

8. Model-generated fresh-ground-water budget for 1994 average annual conditions .............. 31

9. Monthly distribution of recharge and discharge in North Fork model ....................................... 37

10. Data used for the five stress periods of the 65-year (1941-2005) simulation in North 

Fork model ............................................................................................................................................ 37

11. Summary of water-supply scenarios for years 2006-20 in North Fork model ........................... 37

CONVERSION FACTORS, ABBREVIATIONS , AND VERTICAL DATUM

Multiply By To Obtain

feet (ft) 0.3048 meter

feet per day (ft/d) 0.3048 meter per day

gallon per minute (gal/min) 0.002228 cubic feet per second

square mile (mi2) 2.590 square kilometer

acres 43 560 square feet 

inches per year (in/yr) 2.54 centimeters per year

million gallons per day (Mgal/d) 0.04381 cubic meter per second

gallon (gal) 3.785 liter

cubic feet per second (ft3/s) 448.83 gallons per minute

pound per cubic feet (lb/ft3) 16.018 kilograms per cubic meter

pound per second per foot(lb/s/ft) 14.88195 kilogram per second per meter

Other abbreviations used in this report:

milligrams per liter (mg/L)

microsiemens per centimeter at 25 ̊Celsius (μS/cm)

 In this report, the term “sea level” is used to refer to the local coastal mean sea-level datum 

and is not used as a substitute for the National Geodetic Vertical Datum of 1929 or the North 

American Vertical Datum of 1988.
Simulated Effects of Pumping and Drought on GroundWater Levels and the Freshwater-Saltwater Interface 

on the North Fork of Long Island, New York

By Paul E. Misut1, Christopher E. Schubert1 , Richard G. Bova2 , and Steven R. Colabufo2

Abstract

Ground water is the sole source of freshwater on the 

North Fork of Long Island. Future demands for the limited 

freshwater supply during a prolonged drought could cause 

drawdowns that induce saltwater intrusion and render the 

supply unusable. The freshwater system on the North Fork 

contains several localized, hydraulically isolated aquifers 

bounded by salty water. The need for information on the 

ability of these aquifers to meet future demands prompted a 4-

year study to develop a ground-water flow model to simulate 

several proposed pumping scenarios under long-term average 

conditions and during a hypothetical drought, and to delineate 

the resulting ground-water levels and movement of the 

freshwater-saltwater interface. The model code selected was 

SHARP, a quasi-three-dimensional finite-difference method of 

simulating freshwater and saltwater flow simultaneously.

Two sets of four proposed pumping scenarios were 

evaluated. The first represented average recharge from 

precipitation during 2006-20; the second represented the 

same period and conditions except for a 5-year period of 

drought conditions. The average-recharge simulations used the 

long-term (1959-99) rate of recharge; the drought simulations 

applied a 20-percent reduction in recharge rate and a 

20-percent increase in the 1999 rate of agricultural pumpage 

during 2011-15. 

The simulated movement of the freshwater-saltwater 

interface in future withdrawal and recharge scenarios indicates 

that the interface may rise beneath pumped wells at Inlet 

Drive, Brecknock Hall, Main Bayview Road, Islands End, 

North Road, and Alvah’s Lane. Either (1) movement of the 

interface to within 50 feet of the well screen, (2) a large 

percent change in the distance between the interface and the 

well screen, or (3) movement of the interface through a clay 

layer is a cause for concern. Wellfields in which saltwater 

intrusion does not appear to be a cause for concern were those 

at Ackerly Pond, Kenney’s Road, Middle Road, Rocky Point 

Road, and hypothetical sites where future wellfields have 

been proposed.

Introduction

Ground water is the sole source of drinking water and 

irrigation supply on the North Fork of eastern Long Island 

(fig. 1), where the freshwater system consists of a sequence of 

sand and gravel aquifers that are mostly bounded by saltwater. 

Nearly all drinking water and irrigation water is withdrawn 

from the surficial (Pleistocene) aquifers; the deeper aquifers 

contain mostly saline water and are not used for water supply 

or irrigation.

Previous studies by the U.S. Geological Survey (USGS) 

and other agencies have documented the susceptibility of 

the North Fork aquifers to saltwater intrusion and upconing 

at water-supply wells in response to heavy pumping. Early 

water-resources investigations (Hoffman, 1961; Crandell, 

1963) reported steady increases in ground-water pumping 

starting about 1950, followed by saltwater intrusion during 

subsequent years. In addition, a growing body of evidence 

indicates extensive pesticide contamination of monitoring 

wells and private water-supply wells near agricultural areas 

throughout eastern Long Island (Baier and Moran, 1981; Baier 

and Robbins, 1982a and 1982b; Soren and Steltz, 1984; BohnBuxton and others, 1996); this contamination further limits the 

finite freshwater supply.

Concerns have been raised recently over the ability of 

public water-supply systems on the North Fork to meet current 

and future demands for drinking water and irrigation water 

in summer, when the population doubles. This increased 

summer demand in a prolonged drought could result in 

drawdowns that induce saltwater intrusion and potential 

abandonment of affected wells. These concerns, in addition 

to reported contamination of supply wells by domestic 

wastewater (E.J. Rosavitch, Suffolk County Water Authority, 

oral commun., 1997) and the potential for migration of 

contaminants from a local landfill, have prompted efforts to 

plan for the maintenance, upgrading, and expansion of present 

public water-supply systems and to protect the remaining 1

 U.S. Geological Survey, Coram, N.Y.

2 Suffolk County Water Authority, Great River, N.Y. 
potable ground-water supplies. Such planning will require 

the development of water-supply strategies that account for 

the effects of present and future withdrawals and drought 

on ground-water levels and the position of the freshwatersaltwater interface.

Approach

The need for information on aquifer capacity to meet 

projected demands prompted the USGS, in cooperation with 

the Suffolk County Water Authority (SCWA), to begin a 

4-year study in 1996 to analyze the effects of pumping and 

drought on ground-water levels and the position of freshwatersaltwater interface. This effort entailed (1) development of 

a model of freshwater and saltwater flow to simulate a wide 

range of hypothetical pumping scenarios through the year 

2020, and (2) evaluation of the model-generated water levels 

and interface response within the individual aquifers. Two sets 

of four scenarios were evaluated: the first set represented a 

wide range of public-supply, agricultural, and miscellaneous 

pumping rates under normal (average long-term) rates of 

recharge from precipitation; the second set represented the 

same conditions with the addition of a 5-year drought during 

the years 2011-2015, represented by a 20-percent decrease in 

LONG ISLAND SOUND

HASHAMOMUCK

POND

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

.

CONNECTICUT NEW

YORK

NEW

JERSEY

LONG ISLAND SUFFOLK CO.

NASSAU CO.

QUEENS

CO. KINGS

CO.

SOUTH FORK

NORTH FORK

BLOCK

ISLAND

SOUND

ATLANTIC OCEAN

LONG ISLAND SOUND

Port Jefferson

Riverhead

Greenport

ThreeMile

Harbor

0 10 20 MILES

0 10 20 KILOMETERS

A. Location of study area

South Jamesport

41o

40o

30'

74o 73o 30' 73o 72o 30' 72o

Approximate extent of

Peconic Estuary

Tidal benchmark

Precipitation-measurement station

MATTITUCK

INLET

GOLDSMITH INLET

EXPLANATION

Town boundary

A A' Trace of section

shown in figure 5

Greenport

Great Hog 

Neck

GREAT

PECONIC

BAY

Cutchogue

Riverhead

Southold

40o

56'

41o 72o 30' 41o 06' 72o 24'

B'

A'

B

A

Bridgehampton

Little

Hog

Neck

B. Selected features in the study area

STUDY AREA

EXPLANATION

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

Figure 1. Location of study area on North Fork, Suffolk County, N.Y. and selected features in the study area.

2 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
recharge rate and a corresponding increase in the agricultural 

irrigation requirement to offset the diminished precipitation. 

The resulting simulated changes in ground-water levels and 

interface altitude were tabulated and evaluated.

Purpose and Scope

This report (1) describes the geologic framework and the 

hydrologic boundaries of the aquifer system, (2) describes 

the development and calibration of transient-state and steadystate three-dimensional ground-water-flow simulations, (3) 

depicts in maps and vertical sections the present and predicted 

future ground-water levels, freshwater-saltwater interface 

position, and directions of ground-water flow, and (4) depicts 

the effects of simulated pumping rates under normal-recharge 

and drought conditions on water levels and the interface, 

as indicated by the two sets of water-use scenarios. Tables 

of precipitation, recharge, and pumpage data are given in 

appendixes at the end of the report. 

Previous Investigations

The first islandwide descriptions of the geology and 

ground-water conditions of Long Island were given by Fuller 

(1914) and Veatch and others (1906), respectively. A more 

recent comprehensive account of Long Island hydrology is 

given by Cohen and others (1968). The history of groundwater development on Long Island is summarized in 

Nemickas and others (1989). The first digital ground-water 

models of the North Fork were developed and described by 

Bohn-Buxton and others (1996). Ground-water contributingarea boundaries on the North Fork were delineated by 

Schubert (1998), who also defined ground-water flow paths 

and traveltimes (Schubert, 1999). A model of the freshwatersaltwater interface in the Brooklyn-Queens aquifer system was 

constructed by Kontis (1999), and models of the freshwatersaltwater interface on Cape Cod, Martha’s Vineyard, and 

Nantucket, Mass., were constructed by Masterson and Barlow 

(1997). The freshwater-saltwater interface in the Coastal Plain 

aquifer system of New Jersey was evaluated by Spitz (1998) 

and Pope and Gordon (1999). The interface in the coastal 

aquifer system of Virginia was studied by Richardson (1994). 

A bibliography on the occurrence of saltwater intrusion in 

aquifers along the Atlantic Coast is given by Barlow and 

Wild (2002).

Acknowledgments

Thanks are extended to Edward Rosavitch and Joseph 

Pokorny, former and current Chief Engineers of the SCWA, 

respectively, for their technical support and cooperation 

during the investigation. Appreciation also is expressed to 

Jeff Altorfer and Tyrand Fuller of the SCWA Engineering 

Department for providing information and assisting with 

data collection.

North Fork Study Area

The North Fork is bordered by Long Island Sound on 

the north and by embayments of the Peconic Estuary on the 

south (fig. 1). Local tidal benchmarks are at Port Jefferson, 

Threemile Harbor, and South Jamesport; precipitation stations 

are at Riverhead, Greenport, and Bridgehampton (fig. 1). The 

modeled study area encompasses about 100 mi2 in the Town of 

Southold and the eastern part of the Town of Riverhead (fig. 

1). The highest elevation is about 160 ft above sea level, west 

of Mattituck Inlet (fig. 1); the lowest bathymetric elevation is 

about 100 ft below sea level, north of Greenport (fig. 1).

Land Use and Population 

About 50 percent of the study area is used for agricultural 

purposes that include truck farming, sod farming, and 

viniculture (Suffolk County Department of Planning 

Department, 2001). About 25 percent has residences, although 

some of the residences are unoccupied during the winter. 

Proposed development of the vacant residential land could 

result in the creation of about 9,230 new dwelling units. In 

1990, the Town of Southold contained 12,979 dwelling units; 

thus, maximum development could result in a total of about 

22,200 dwelling units. This represents a 71-percent increase 

from the 1990 level. About 3 percent of the land available for 

development is zoned commercial and (or) industrial. 

The combined year-round and seasonal population of the 

Town of Southold in 1990 was about 36,000 and is expected 

to increase by about 72 percent at maximum development 

around the year 2020 (Suffolk County Department of 

Planning, 2001). The year-round population in 1990 was 

about 56 percent of the total and is expected to increase only 

slightly--to 57 percent of the total--by 2020, which is about a 

75-percent increase in the year-round population. The vacation 

season runs from about Memorial Day (the end of May) to 

Labor Day (the beginning of September). 

Water Use

Communities on the North Fork were served in 2002 by 

the SCWA and Riverhead Water District. Past and projected 

service areas (1957, 1994, 1998, 2010, and 2020) are depicted 

in figures 2A-E. The service-area locations for the Riverhead 

Water District are based on geographic information system 

(GIS) coverages (Dennis Jackson, Suffolk County Department 

of Health Services, written commun., 1995). The locations 

of public-supply wells operated prior to 1958 were digitized 

and used to estimate the service-area location for the former 

North Fork Study Area 3
Figure 2. Past and 

projected public 

water-supply areas 

on North Fork, Suffolk 

County, N.Y.: A. Village 

of Greenport and North 

Fork water supply 

districts in 1957. B. 

Riverhead and Suffolk 

County Water Authority 

supply districts in 

1994. C. Riverhead 

and Suffolk County 

Water Authority supply 

districts in 1998. D. 

Projected Riverhead 

and Suffolk County 

Water Authority supply 

districts in 2010. E. 

Projected Riverhead 

and Suffolk County 

Water Authority supply 

districts in 2020. 

(Location is shown in 

fig. 1)

LONG ISLAND SOUND

EXPLANATION

SCWA-Southold district

Riverhead district

GREAT

PECONIC

BAY

40o

56'

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

E. Projected Riverhead and Suffolk County Water Authority supply districts in 2020

LONG ISLAND SOUND

EXPLANATION

SCWA-Southold district

Riverhead district

Southold

Mattituck

SCWA-Mattituck district 40o

56'

GREAT

PECONIC

BAY

D. Projected Riverhead and Suffolk County Water Authority supply districts in 2010

LONG ISLAND SOUND

EXPLANATION

SCWA-Southold district

Riverhead district

Mattituck 

Southold

 SCWA-Mattituck district

GREAT

PECONIC

BAY

40o

56'

C. Riverhead and Suffolk County Water Authority supply districts in 1998

LONG ISLAND SOUND

EXPLANATION

SCWA-Greenport district

Other SCWA districts

Riverhead district

Laurel

Mattituck 

Southold 40o

56'

GREAT

PECONIC

BAY

B. Riverhead and Suffolk County Water Authority supply districts in 1994

41o 72o 30' 41o 06' 72o 24'

LONG ISLAND SOUND

EXPLANATION

Village of Greenport district

North Fork Supply Co. district 40o

56'

GREAT

PECONIC

BAY 0

0 2 4 KILOMETERS

1 2 3 MILES

A. V 1 3 illage of Greenport and North Fork water-supply districts in 1957

4 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
North Fork Water Company and Village of Greenport Water 

Supply; the service-area locations for the former Greenport 

Water District were digitized by Schubert (1998) from a 1992 

map of current and proposed facilities (Roy F. Weston, Inc., 

1992). The service-area locations for the SCWA in 1994 

were digitized by Schubert (1998) from the SCWA’s 1995 

distribution-system maps (Jeff Altorfer, Suffolk County Water 

Authority, written commun., 1996); the remaining service-area 

locations were assembled by the SCWA (Jeff Altorfer, written 

commun., 1999).

Locations of public-supply wellfields in 1957, 1994, and 

1998, and of projected future public-supply systems in 2010 

and 2020, are shown in figures 3A-E. The wellfield locations 

for the former Greenport Water District were digitized by 

Schubert (1998) from a 1992 map of current and proposed 

facilities (Roy F. Weston, Inc., 1992). Wellfield locations for 

the SCWA in 1994 were digitized by Schubert (1998) from 

the SCWA’s 1995 distribution-system maps (Jeff Altorfer, 

written commun., 1996); the wellfield locations in 1998 were 

assembled by the SCWA (Jeff Altorfer, written commun., 

1999). 

Annual public-supply pumpage for 1957, 1994, and 

1998 are summarized in appendixes 1, 2, and 3, respectively; 

miscellaneous pumpage for 1993-95 is summarized in 

appendix 4. Estimated past and projected (2020) pumpage 

values are as follows: 

Category

Pumpage, in million gallons per day

1957 1994 1998 2020

Public supply 0.5 1.1 1.1 2.0 - 4.0

Miscellaneous pumpage 0.1 0.2 0.2 0.2

Monthly 1994 pumpage for each wellfield associated 

with the Greenport and Riverhead Water Districts and SCWA 

was compiled by Schubert (1998) from data provided by T.A. 

Nanos of the Suffolk County Department of Health Services 

(written commun., 1995, 1996) and by Paul Kuzman of the 

Suffolk County Water Authority (written commun., 1995). 

SCWA pumpage in 1998 by each wellfield was also was 

compiled by Paul Kuzman (written commun., 1999). 

Most public-supply water is returned to the water table, 

mainly through septic systems but also, to a lesser extent, 

as leakage from the water-distribution system; the rest is 

not returned and is lost from the ground-water system. The 

amount of public-supply water that reaches the water table 

in unsewered areas of other parts of Long Island has been 

estimated to be about 85 percent of total public-supply 

pumpage (Franke and McClymonds, 1972). Communities 

on the North Fork and elsewhere in eastern Suffolk County 

that obtain drinking water from local water-supply systems 

or private wells generally return most of this water to the 

ground-water system at nearly the same location from which 

it is withdrawn (Schubert, 1998); therefore, the withdrawal 

and return flow of local- or private-supply water was not 

considered in this investigation. All water pumped for public 

supply and distributed in the sewage-treatment district of 

the Village of Greenport (fig. 4), which discharges treated 

wastewater to Long Island Sound, is considered to be removed 

from the ground-water system. 

Irrigation water in the study area is pumped from shallow 

wells. A method for estimating the total agricultural irrigation 

requirement, in inches per year, was described and applied 

to 1994 conditions by Schubert (1998). Estimated past and 

projected irrigation requirements calculated by this method are 

as follows: 1941-61 and 1967-70: 7.0 in/yr; 1962-66 drought: 

10.4 in/yr; and 1971-2020 (1999 conditions): 3 in/yr. The 

irrigation requirement during a future projected drought is 

estimated to total 5.3 in/yr.

Hydrogeology

The hydrogeology of the North Fork was evaluated from 

published information and from exploratory drilling of five 

deep (about 400 ft) wells during this study. The hydraulic 

properties of hydrogeologic units were compiled from 

previous investigations of unconsolidated deposits on Long 

Island and in similar settings in the Atlantic Coastal Plain 

of New Jersey and on western Cape Cod, Massachusetts. 

Detailed information on the hydrogeologic framework of 

the North Fork is given in a companion report (Schubert and 

others, 2003).

Hydrogeologic Framework

The framework of the North Fork consists of a series of 

Pleistocene and Cretaceous aquifers and confining units that 

overlie southeastward-sloping Paleozoic and Precambrian 

bedrock (Schubert and others, 2003). Descriptions of the 

geologic and hydrogeologic units are given in table 1. The 

generalized hydrogeologic framework along southwestnortheast (A-A/

) and northwest-southeast (B-B/) sections is 

depicted in figure 5 (location of section traces shown in fig. 1). 

The focus of this investigation was the fresh ground-water 

flow system in the Pleistocene and uppermost Cretaceous 

units. The deeper Cretaceous units contain saline water.

Pleistocene Hydrogeologic Units

On Long Island, saturated coarse-grained deposits of 

Pleistocene age commonly are referred to as the upper glacial 

aquifer. In this report, following the work of Schubert and 

others (2003), the upper glacial aquifer has been divided into 

three zones (table 1). In general, zone A is the upper glacial 

aquifer above the upper confining unit; zone B is the upper 

glacial aquifer between the upper and lower confining units; 

and zone C is the upper glacial aquifer below the lower 

confining unit. 

Upper glacial aquifer zone A, which is unconfined, 

is further divided based on the surficial distribution of the 

Roanoke Point outwash and moraine and Ronkonkoma drift 

North Fork Study Area 5
Figure 3. Past and 

projected publicsupply wellfields 

on North Fork, 

Suffolk County, 

N.Y.: A. Publicsupply wellfield 

locations in 1957. 

B. Public-supply 

wellfield locations 

in 1994. C. Publicsupply wellfield 

locations in 1998. 

D. Projected 

public-supply 

wellfield locations 

in 2010. E. 

Projected publicsupply wellfield 

locations in 2020. 

(Location is shown 

in fig. 1)

LONG ISLAND SOUND

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

SOUTH HARBOR

ROAD

THE

LONG MOORES WAY LANE ISLANDS

END

INLET DRIVE

SUNSET DRIVE

 MAIN BAYVIEW ROAD 

MIDDLE

ROAD

BRECKNOCK HALL

KENNEYS

ROAD

NORTH ROAD

MILL LANE (PECONIC)

LAUREL LAKE

NORTH ROAD

PARCEL 1 PARCEL 7

PARCEL 10

PARCEL 15

PARCEL 16

ALVAHS

LANE NORTH ROAD (PECONIC) ACKERLY POND LANE

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

E. Projected public-supply wellfield locations in 2020

LONG ISLAND SOUND

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

INLET DRIVE

SUNSET DRIVE

MAIN BAYVIEW ROAD 

MIDDLE

ROAD

BRECKNOCK

HALL

KENNEYS

ROAD

NORTH ROAD

MILL LANE

(PECONIC)

LAUREL LAKE

ACKERLY POND LANE

D. Projected public-supply wellfield locations in 2010

LONG ISLAND SOUND

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

MIDDLE

ROAD

BRECKNOCK

HALL

KENNEYS

ROAD

NORTH ROAD

C. Public-supply wellfield locations in 1998

INLET DRIVE

SUNSET DRIVE

MAIN BAYVIEW ROAD 

MILL LANE ACKERLY POND LANE (PECONIC)

LAUREL LAKE

LONG ISLAND SOUND

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

PLANT 12 PLANT 3

PLANT 9

PLANT 4

B. Public-supply wellfield locations in 1994

PLANT 15

PLANT 6

PLANT 7

INLET DRIVE

SUNSET DRIVE

 MAIN BAYVIEW ROAD 

PLANT 8

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

PLANT 5

PLANT 3

PLANT 1 PLANT 4

A. Public-supply wellfield locations in 1957

PLANT 5 Wellfield location

and name

EXPLANATION

6 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
(fig. 6). In the northernmost part of the study area, zone A 

consists of moraine deposits, and in the central part it consists 

of outwash. In the south where the drift is at the surface, 

zone A consists of the upper part of the drift. The outwash 

deposits are moderately to well-sorted sand, gravel, and silt; 

the moraine deposits are poorly to moderately sorted silt, sand, 

and gravel; and the drift deposits are poorly to well-sorted 

sand, gravel, and silt. The upper confining unit is glacial-lake 

clay with silt and fine sand. The lower-surface altitude and 

thickness of the upper glacial aquifer zone A are depicted in 

figures 7A-B. The lower-surface altitude and thickness of the 

upper confining unit are depicted in figures 8A-B.

Upper glacial aquifer zone B includes the Ronkonkoma 

drift where it is confined below the upper glacial-lake clay. 

Unconfined parts of zone B include the drift present below 

the outwash and moraine where the glacial-lake clay is absent, 

and the lower part of the drift where it is at the surface in the 

southern part of the study area. Below zone B is the lower 

confining unit, which is marine and nonmarine clay with 

lenses of sand and gravel in the southern part of the study area, 

and, elsewhere, glacial-lake clay and silt. The lower-surface 

altitude and thickness of the upper glacial aquifer zone B 

are depicted in figures 9A-B. The lower-surface altitude and 

thickness of the upper confining unit are depicted in figures 

10A-B.

Upper glacial aquifer zone C includes poorly to wellsorted sand and gravel associated with the Montauk till, 

and post-Cretaceous (?) deposits confined below marine, 

nonmarine, and (or) glacial-lake clay. Below zone C is the 

Magothy aquifer of Cretaceous age. The lower-surface altitude 

and thickness of the upper glacial aquifer zone C are depicted 

in figures 11A-B. 

Cretaceous Hydrogeologic Units

The Cretaceous hydrogeologic units in descending order 

include the Magothy aquifer, Raritan confining unit, and 

Lloyd aquifer. The Magothy aquifer includes the deposits of 

the Magothy Formation-Matawan Group, undifferentiated, 

which consist of sand with silt, clay, and lignite and, in the 

basal 100-200 ft, gravel (Jensen and Soren, 1974). The lowerand upper-surface altitudes and thickness of the Magothy 

aquifer are depicted in figures 12A-B. Below the Magothy 

aquifer is the Raritan confining unit, which consists of clay 

and silt deposits of the unnamed clay member of the Raritan 

Formation. The deepest Cretaceous unit is the Lloyd aquifer, 

which consists of sand and gravel of the Lloyd Sand Member 

of the Raritan Formation. 

Hydraulic Properties

Horizontal and vertical hydraulic conductivity values of 

aquifers and confining units were compiled from previous 

studies on Long Island and Cape Cod and are summarized in 

table 2. The depositional environment and lithology of western 

Cape Cod are comparable to those of glacial deposits on the 

North Fork (Schubert, 1999). The moraine deposits above the 

upper confining layer are probably the least homogeneous and, 

therefore, the least accurately represented by a bulk hydraulic 

value. Vertical leakance values for the two confined aquifers 

are shown in figures 13A-B. Vertical leakance between two 

aquifers separated by a confining unit is calculated as follows 

(Essaid, oral commun., 2000):

where: 

Leakance (x,y) = leakance [1/time] between two aquifers 

separated by a confining unit

b(x,y)

lower, b(x,y)lower, b(x,y)conf = thickness [length] 

of lower unit, upper unit, and confining unit, 

respectively. These are functions of horizontal location x,y.

Figure 4. Sewage-treatment district of the Village of Greenport on the North Fork, Suffolk County, N.Y. (Location is shown in fig. 1)

LONG ISLAND SOUND

SEWAGE -TREATMENT

DISTRICT

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

North Fork Study Area 7
Table 1. Geologic and hydrogeologic units in the North Fork study area of eastern Long Island, N.Y. 

[From Schubert and others, 2003. Descriptions of selected Pleistocene deposits adapted from Soren, 1978; Nemickas and Koszalka, 1982; Soren and Stelz, 1984; Prince, 

1986; and Schubert, 1999. Descriptions of Cretaceous deposits and bedrock modified from Jensen and Soren, 1974.]

Age Geologic unit Hydrogeologic unit Description 

Roanoke Point outwash and moraine Upper glacial aquifer 

zone A

Outwash deposits consist of tan, moderately to well-sorted 

fine to coarse sand and gravel, locally with light-brown, fine 

sand and silt in basal 10-20 feet. Moraine deposits consist of 

brown, poorly to moderately sorted, medium to coarse sand 

and gravel with some fine sand and silt, and discontinuous, 

poorly to unsorted lenses of gray and brown, fine to medium 

sand and silt with some clay, coarse sand, and gravel. 

Upper glacial-lake clay Upper confining unit Tan, gray, and brown fine sand, silt, and clay, commonly with 

abundant mica, interbedded with brown clay and silt, locally 

with some fine to coarse sand and gravel.

Ronkonkoma drift Upper glacial aquifer 

zone Ba

Tan, gray, and brown, poorly to moderately sorted deposits of 

medium to fine sand, silt, and some coarse sand and gravel, 

with discontinuous lenses of moderately to well-sorted fine to 

coarse sand, gravel, and some silt.

Lower glacial-lake clay Lower confining unit Gray silt, clay, silty clay, and sandy clay, commonly with 

abundant mica, interbedded with brown clay and silt, and 

locally with lenses of gray and brown silty sand and fine sand.

Montauk Till and associated 

glaciofluvial deposits

Upper glacial aquifer 

zone C

Montauk Till consists of unsorted deposits of gravel, sand, silt, 

and clay. Glaciofluvial deposits consist of fine to coarse and 

gravel with thin lenses of silt and clay.

Marine clay Lower confining unitb Grayish-green, dark-gray, and brown clay, silty clay, and 

sandy clay, locally with marine fossils and some thin lenses of 

sand and gravel.

Nonmarine clay Mainly brown and reddish-brown clay, locally with thin beds 

of silt and fine sand.

? Post-Cretaceous(?) deposits Upper glacial aquifer 

zone C

Tan, gray, and brown poorly to well sorted deposits of fine to 

coarse sand and gravel, with some silt and clay.

Matawan Group and Magothy 

Formation, undifferentiated Magothy aquifer

Gray to white, fine to coarse sand with interstitial clay, silt, 

lignite, interbedded with layers of gray clay, silt, and clayey 

and silty sand, and lenses of lignite and pyrite. Coarse sand 

and gravel generally present in basal 100-200 feet.

Raritan 

Formation

Unnamed clay 

member Raritan confining unit

Multicolored clay, silty clay, and clayey and silty fine sand, 

commonly with beds and lenses of lignite, pyrite, and sand, 

and locally with thin beds of gravel.

Lloyd Sand 

Member

Lloyd aquifer White and gray, fine to coarse sand and gravel, with 

intercalated beds and lenses of gray clay, silt, clayey and silty 

sand, and some lignite and pyrite.

Bedrock Bedrock Mainly gneiss and schist capped by a weathered zone of 

greenish-white residual clay.

a Upper part of the Ronkonkoma drift is included in the upper glacial aquifer zone A where it is at the surface in the southern part of the study area.

b The lower glacial-lake clay, marine clay, and nonmarine clay are considered as one hydrogeologic unit in this study and are referred to as the lower confining unit. 

(See discussion in text.) Upper Cretaceous Paleozoic and Precambrian Pleistocene

8 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Pleistocene confining layer

Aquifer

EXPLANATION

Raritan Clay (not modeled)

Well and well number, flag is

estimated altitude of freshwatersaltwater interface. Datum is NGVD

of 1929.

Upper glacial zone A

Upper glacial

Upper zone B

glacial 

zone C

Magothy aquifer

Southwest Northeast

A A'

0

0 2 4 KILOMETERS

1 2 3 MILES

VERTICAL SCALE GREATLY EXAGGERATED

Raritan clay

Hashamomuck

Pond

Mattituck

Inlet

Upper glacial 

zone B

Magothy aquifer 

Upper glacial 

zone A

Upper 

glacial 

zone C

Northwest Southeast

B B'

Peconic

Bay

Raritan clay 

71576

91815

106415

71170, B-B'

68831

114868

490

95446

95443

490

1 3

0

-100

-200

-300

-400

-500

-600

-700

-800

100

FEET

0

-100

-200

-300

-400

-500

-600

-700

100

FEET

71044

71170, A-A'

102249

71279

112562

3123

Figure 5. Sections A-A’ and B-B’ showing hydrogeologic 

units in the North Fork study area. (Traces of sections are 

shown in fig. 1)

North Fork Study Area 9
Figure 6. Surficial distribution of moraine, outwash, and drift on the North Fork, Suffolk County, N.Y. (Location is shown in fig. 1)

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Moraine

Outwash

Undifferentiated drift

Lake

EXPLANATION

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

Figure 7. Lower surface altitude and thickness of the upper glacial aquifer zone A on North Fork, Suffolk County, N.Y.: A. Lower surface 

altitude. B. Thickness. (Location is shown in fig. 1)

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

1

2 to 20

21 to 40

41 to 60

Thickness, in feet

EXPLANATION

A. Lower surface altitude

61 to 80

81 to 130

No data (not part 

of study area)

-125 to -110

-109 to -87

-86 to -62

-61 to -11

Altitude, in feet.

Datum is NGVD of 1929.

EXPLANATION

-10

-9 to 0

No data (not part 

of study area)

B. Thickness

10 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Figure 8. Lower surface altitude and thickness of the upper confining unit on North Fork, Suffolk County, N.Y.: A. Lower surface altitude. 

B. Thickness. (Location is shown in fig. 1)

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

1 to 5

6 to 10

11 to 15

Thickness, in feet

EXPLANATION

A. Lower surface altitude

16 to 20

21 to 59

No data (not part 

of study area)

-125 to -110

-109 to -88

-87 to -63

-62 to -38

Altitude, in feet.

Datum is NGVD of 1929

EXPLANATION

-37 to -19

-18 to 0

No data (not part 

of study area)

B. Thickness

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

North Fork Study Area 11
LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0 to 1

2 to 20

21 to 40

41 to 60

Thickness, in feet

EXPLANATION

A. Lower surface altitude

61 to 80

81 to 115

No data (not part 

of study area)

-150 to -126

-125 to -116

-115 to -101

-100

Altitude, in feet.

Datum is NGVD of 1929

EXPLANATION

-99 to -75

-74 to -50

No data (not part 

of study area)

B. Thickness

Figure 9. Lower surface altitude and thickness of the upper glacial aquifer zone B on North Fork, Suffolk County N.Y.: A. Lower surface 

altitude. B. Thickness. (Location is shown in fig. 1)

12 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Figure 10. Lower surface altitude and thickness of the lower confining unit on North Fork, Suffolk County, N.Y.: A. Lower surface 

altitude. B. Thickness. (Location is shown in fig. 1)

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0 to 1

2 to 30

31 to 60

61 to 102

Thickness, in feet

EXPLANATION

A. Lower surface altitude

103 to 161

162 to 303

No data (not part 

of study area)

-441 to -352

-351 to -278

-277 to -215

-214 to -159

Altitude, in feet.

Datum is NGVD of 1929.

EXPLANATION

-158 to -116

-115 to -50

No data (not part 

of study area)

B. Thickness

North Fork Study Area 13
Figure 11. Lower surface altitude and thickness of the upper glacial aquifer zone C on North Fork, Suffolk County, N.Y.: A. Lower surface 

elevation. B. Thickness. (Location is shown in fig. 1)

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0 to 1

2 to 38

39 to 67

68 to 88

Thickness, in feet

EXPLANATION

A. Lower surface altitude

89 to 122

123 to 500

No data (not part 

of study area)

-699 to -577

-576 to -457

-456 to -374

-373 to -309

Altitude, in feet.

Datum is NGVD of 1929.

EXPLANATION

-308 to -241

-240 to -150

No data (not part 

of study area)

B. Thickness

14 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Figure 12. Upper and lower surface altitude and thickness of the Magothy aquifer on North Fork, Suffolk County, N.Y.: A. Upper surface 

elevation. B. Lower surface elevation. C.Thickness. (Location is shown in fig. 1)

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0 to 8

9 to 295

296 to 400

401 to 461

Thickness, in feet

EXPLANATION

A. Upper surface altitude

462 to 520

521 to 674

No data (not part 

of study area)

Altitude, in feet.

Datum is NGVD of 1929.

EXPLANATION

C. Thickness

-699 to -577

-576 to -457

-456 to -374

-373 to -309

Altitude, in feet.

Datum is NGVD of 1929.

EXPLANATION

-308 to -241

-240 to -150

No data (not part 

of study area)

B. Lower surface altitude

-699 to -577

-576 to -457

-456 to -374

-373 to -309

-308 to -241

-240 to -150

No data (not part 

of study area)

North Fork Study Area 15
Figure 13. Vertical leakance values for the Pleistocene upper and lower confining units on the North Fork, Suffolk County, N.Y.: 

A. Upper confining unit. B. Lower confining unit. (Location is shown in fig. 1) 

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0 to 0.004

0.004 to 0.09

0.09 to 0.123

0.123 to 0.196

Leakance, in 1/second

EXPLANATION

A. Upper confining unit

0.196 to 1.0

No data (not part 

of study area)

0 to 0.004

0.004 to 0.09

0.09 to 0.123

0.123 to 0.196

Leakance, in 1/second

EXPLANATION

0.196 to 1.0

No data (not part 

of study area)

B. Lower confining unit

Table 2. Hydraulic conductivity of Pleistocene and uppermost Cretaceous hydrogeologic units for North Fork mode

[From Schubert and others, 2003. Dashes indicate no value was estimated.]

Hydrogeologic unit

Hydraulic conductivity

Ratio of 

horizontal to vertical Horizontal (feet per day) Vertical (feet per day)

Upper glacial aquifer zone A Outwash 200 20 10:1

Upper glacial aquifer zone A Moraine 80 8 10:1

Upper glacial aquifer zone A Drift 200 20 10:1

Upper confining unit -- 0.4 --

Upper glacial aquifer zone B 200 20 10:1

Lower confining unit -- 0.1 --

Upper glacial aquifer zone C 300 30 10:1

Magothy aquifer 50 0.5 100:1

16 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Figure 14. Location of local freshwater flow systems on North Fork, Suffolk County, N.Y. (Location is shown in fig. 1)

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

Boundary between flow systems

EXPLANATION

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

MAIN LONG ISLAND

SYSTEM

MATTITUCK

INLET

JAMES CREEK

CUTCHOGUE SYSTEM

LITTLE

HOG

NECK

GREAT

HOG

NECK

HASHAMOMUCK

POND

DAM

POND

GREENPORT SYSTEM

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Kv(x,y) lower, Kv(x,y) upper, Kv(x,y) conf = vertical hydraulic 

conductivity [length/time] of lower unit, upper unit, and 

confining unit, respectively. These are functions of horizontal 

location x,y.

Porosity of all aquifers has been assumed to average 30 

percent (Franke and Cohen, 1972). Porosity of the glacial 

aquifer of western Cape Cod has been estimated by Masterson 

and others (1997) to average about 35 percent.

Hydrologic System

The fresh ground-water flow system on the North Fork 

consists of a series of five hydraulically isolated lenses that 

are bounded below (and laterally in areas near the shore) by 

saltwater (fig. 14). The westernmost system, in the area west 

of Mattituck Inlet and James Creek (fig. 14), is part of the 

flow system of the main body of Long Island. The area to the 

northeast of these creeks and southwest of Hashamomuck 

Pond contains the Cutchogue flow system. Great Hog Neck 

and Little Hog Neck, along the southern shore of the North 

Fork, represent two isolated flow systems. The area east of 

Hashamomuck Pond and west of Dam Pond contains the 

Greenport flow system. 

The movement of fresh ground water within each 

freshwater system on the North Fork is controlled by the 

hydraulic characteristics of the stratigraphic units and the 

distribution of hydrologic boundaries. Ground water generally 

flows seaward and downward from water-table mounds in 

the center of the peninsula, although the downward flow 

component may be diverted laterally by local confining layers. 

The lateral (seaward) flow curves upward near the shore, 

which is a discharge boundary. 

Hydrologic Boundaries

The hydrologic boundaries of each freshwater system 

on the North Fork control the rate at which water enters and 

exits the system. The upper boundary on land is the water 

table; in offshore areas it is the sea floor. The lateral and lower 

boundaries are freshwater-saltwater interfaces. Freshwater 

recharge occurs where precipitation infiltrates the soil and 

reaches the water table; it also occurs in unsewered areas 

as return flow of used public-supply water through septic 

systems. Natural discharge occurs in offshore areas either 

as upward seepage through the sea floor into saline surface 

waters or as seepage through confining layers into sediments 

bearing saline ground water. Discharge also occurs where the 

land surface intersects the water table (such as in streams, 

ponds, and wetlands); here freshwater exits the system as 

seepage (base flow) to streams and through evapotranspiration. 

The lower boundary of each freshwater flow system is a 

zone of diffusion that separates freshwater from the denser 

saltwater. This lower boundary moves gradually in response to 

changes in the balance between recharge and discharge within 

the system, including in response to pumping.

Precipitation and Recharge.-- The main source of recharge 

on the North Fork is precipitation. Not all precipitation that 

falls on land surface becomes recharge, however, because 

some is lost through evapotranspiration or as surface runoff 

to streams. Precipitation rates are fairly uniform throughout 

the year (Peterson, 1987), but most recharge occurs during the 

fall, winter, and early spring because nearly all precipitation 

during the summer growing season is lost through 

evapotranspiration. The seasonal differences in recharge 

rate generally are greater than any annual or longer term 

fluctuations. Long-term precipitation records from stations in 

Bridgehampton, Riverhead, and Greenport (fig. 1) were the 

sources of precipitation data used in this study; the seasonal 

and annual precipitation values, and the values of recharge 

from land surface and lakes calculated from data from these 

stations, are given in appendix 5. Long-term (1959-99) mean 

annual precipitation totals for Bridgehampton, Greenport, and 

Riverhead are 46.08 in., 44.91 in., and 45.33 in., respectively. 

Most of the long-term mean precipitation that falls from 

North Fork Study Area 17
October 15 through May 15 (82 percent is used for the 

calculation) becomes ground-water recharge; no significant 

amount of precipitation becomes ground-water recharge 

during the remainder of the year (Steenhius and others, 1985).

Ground-Water Discharge.-- Most natural fresh groundwater discharge in the study area occurs as shoreline or subsea 

underflow; the rest occurs as stream base flow and through 

pond and wetland evapotranspiration. Periodic streamflow 

measurements are available for sites along Meetinghouse 

Creek and Moores Drain (fig. 1). The historical mean base 

flow of Meetinghouse Creek, calculated from 17 measurements 

made during 1949-58, a period of average precipitation, is 

about 1.42 ft3/s (Schubert, 1999). Streamflow measurements 

made in 1998-99 at Moores Drain (table 3) indicate its base 

flow to be generally less than 0.1 ft3/s, although it may be 1.48 

ft3/s or more for a few days after storms. 

Freshwater-Saltwater Interface

The freshwater-saltwater interface is a transition zone 

that results from the mixing of waters through diffusion 

and mechanical dispersion (Essaid, 1990). In this study, the 

interface is conceptualized as a moving, impermeable, sharp 

boundary resulting from the density difference between 

completely fresh water and salty water. This conceptualization 

is a simplification that does not allow for mixing and is more 

accurate at regional scales than at localized scales, such as that 

of an individual well undergoing saltwater intrusion. A sharp 

boundary moves landward or seaward in response to changes 

in head. The position of the freshwater-saltwater interface, 

conceptualized as a sharp boundary, has been delineated 

by Schubert and others (2003) from data from filter-press 

core samples, water samples collected through a screened 

auger, and borehole geophysical logs in accordance with 

the approach described by Schubert (1999). The freshwatersaltwater interface location was specified as the point where 

chloride concentration was about 250 mg/L (from filter-press 

core samples) or where specific conductance was estimated to 

be 500 μS/cm.

The freshwater-saltwater interface on the North Fork is 

near sea level at the shores and descends inland through the 

unconfined and shallow confined parts of the flow system in 

general conformance with the Ghyben-Herzberg principle, 

which states that the freshwater thickness extends 40 ft below 

sea level for 1 ft of freshwater head above sea level. The 

interface below the upper surface of the lower confining unit 

may extend seaward of its position directly above this unit, 

particularly near the western end of the North Fork as a result 

of impedance by the overlying clay. The interface descends 

westward within the Magothy aquifer and generally is deepest 

near the western end of the North Fork, where the water table 

is highest and where some freshwater enters the system from 

upgradient parts of Long Island’s main flow system. The 

interface ascends eastward where the North Fork narrows. 

The interface within the Cutchogue flow system, where the 

Magothy aquifer contains mostly salty water, generally is as 

high as the base of the upper glacial aquifer; in the other flow 

systems it is within the shallow confined parts of the upper 

glacial aquifer or extends only through the unconfined zone.

Ground-Water Levels

Ground-water levels were measured at 246 wells by the 

USGS and Suffolk County Department of Health Services 

during March-April 1994 and were used by Schubert (1998) to 

map the water-table altitude in the study area (fig. 15). Groundwater levels on the North Fork respond to seasonal and annual 

variations in recharge from precipitation and, to a lesser extent, 

to seasonal variations in water use. The water table generally 

declines from May through early October, when recharge 

is lowest and water use is greatest, and generally rises from 

the end of October through the end of April, when recharge 

is greatest and water use is lowest (Nemickas and Koszalka, 

1982). Seasonal variations in water levels within a given year 

generally exceed the annual and longer term fluctuations. The 

water-table altitude decreases to zero near the shore. 

Effects of Pumping and Drought 

on Ground-Water Levels and the 

Freshwater-Saltwater Interface 

The freshwater-saltwater interface on the North Fork 

moves downward and seaward in response to recharge, or 

upward and landward in response to withdrawals such as 

pumping or decreased recharge during drought. Consequently, 

overpumping creates a potential for saltwater intrusion into 

public-supply wells, especially during drought conditions. 

Concern over the effect of increased future pumping on the 

interface prompted the development of a model to simulate 

several pumping and drought scenarios. 

The effects of pumping and drought on the freshwatersaltwater interface were evaluated through two sets 

of pumping scenarios—four under average long-term 

precipitation (recharge) conditions, projected to the year 

2020, followed by the same four simulations under drought 

Table 3. Discharge of Moores Drain at Route 25 in Greenport, 

Suffolk County, N.Y., on four sampling dates in 1998-99

[Location is shown in fig. 20A.]

Date (mo/d/yr) Discharge (cubic feet per second)

5/28/98 0.02

7/1/98 1.48

8/24/98 0.04

5/12/99 0.09

Mean 0.41

Median 0.07

18 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
conditions. Total annual public-supply and miscellaneous 

pumpage for the four scenarios were as follows: 

Public-supply pumpage was varied over two 6-month 

seasons—from May through October (summer) and from 

November through April (winter), with winter pumpage 

applied at about 50 percent of the summer pumpage rate. 

Miscellaneous pumpage had a 3-month summer season 

(from June through August) and a 9-month winter season 

(from September through May), where winter miscellaneous 

pumpage was applied at 50 percent of the summer rate. The 

5-year drought (years 2011-15) in the second set of scenarios 

was represented by a 20-percent decrease in annual recharge 

with an offsetting equivalent increase in the agricultural 

irrigation requirement.

Development of Flow Model 

The freshwater-saltwater interface is not a sharp surface, 

but a zone of diffusion that is difficult to simulate; therefore, 

appropriate simplifying assumptions generally are made that 

provide a reasonable approximation of the relation between 

saline and fresh ground water (Reilly, 1993). The two most 

common methods of simulating this relation are the sharpinterface approach and the variable-density approach. In the 

sharp-interface approach, the system is assumed to consist of 

two immiscible fluids (Essaid, 1990); in the variable-density 

approach, it is assumed that one miscible fluid transports a 

solute, and the solute affects the density and viscosity of the 

fluid. The variable-density approach also includes the effects 

of dispersion and chemical reactions associated with advective 

movement. The sharp-interface approach is preferred if only 

general estimates of the location of the freshwater-saltwater 

interface are desired; the less tractable variable-density 

approach is used if estimates of local dissolved-chloride 

concentrations in water are desired. A comprehensive review 

of the hydrologic conditions near freshwater-saltwater 

environments, and the methods of flow analysis, are given in 

Reilly (1993). 

The aquifer system of the North Fork was simulated 

through use of the SHARP model code (Essaid, 1990). 

SHARP is a quasi-three-dimensional finite-difference code 

Figure 15. Water-table altitude in March-April 1994 on North Fork, Suffolk County, N.Y. (From Schubert, 1998, pl. 1.) 

(Location is shown in fig. 1)

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

Modified from Schubert, 1997, pl. 1

10

5

5

2

2

WATER-TABLE CONTOUR--Shows

altitude of water table, in feet, MarchApril 1994. Contour interval is

variable. Datum is NGVD of 1929.

EXPLANATION

0 2

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Summary of water-supply scenarios for years 2006-20 (four based on average-recharge conditions, and four based on average 

conditions except during 5-year drought (2011-15) in North Fork model, Suffolk County, N.Y.

[Percent increases are in relation to scenario 1 rates.] 

 Public-supply Public-supply Commercial Miscellaneous

Scenario pumpage return flow pumpage pumpage 

Scenarios based on average recharge from precipitation

1 1998 rates 1998 rates 1994 rates 1999 rates 

2 186-percent increase 47-percent increase no increase no increase

3 268-percent increase 68-percent increase no increase no increase

4 365-percent increase 92-percent increase 157-percent increase no increase

Scenarios based on drought conditions 

Drought was applied to the above scenarios as a 20-percent decrease from long-term rate of recharge from precipitation and a 

20-percent increase from 1999 agricultural pumpage during years 2011-15. 

Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface 19
that simulates freshwater and saltwater flow in layered coastal 

aquifers by coupling two mathematical equations representing 

the freshwater and saltwater flow. The equations are coupled 

because the fresh and saline fluids share a boundary at the 

interface. The parabolic partial-differential equations are 

solved simultaneously for freshwater and saltwater head. 

Once the heads are calculated, the interface elevation is 

calculated by an equation for continuity of fluid pressure at 

the interface according to the Ghyben-Herzberg relation. A 

given model cell is characterized as a freshwater cell if the 

calculated altitude of the interface is at the base of the cell 

or below it; as a saltwater cell if the interface is at or above 

the top of the cell, or as a mixed-water cell if the interface 

is within the cell. The intersection of the interface with the 

top or bottom of an aquifer cell is termed the tip or toe of the 

interface, respectively (fig. 16), and its location is determined 

by extrapolation of the calculated interface slope at the center 

of surrounding model cells. Applying a transient stress near 

an interface will cause the interface to move as a function 

of time. For example, an increase in pumping that causes a 

decrease in seaward freshwater flow will cause the interface 

to move landward and upward. Depending on the rate of 

interface movement over a given time interval, the interface 

may rise above the base of a freshwater cell and cause that cell 

to become a mixed-water cell or a saltwater cell. 

The SHARP method introduces inaccuracies concerning 

the potability limit with respect to chloride concentrations, 

and local upconing at well screens. In a SHARP model, the 

zone in which freshwater and saltwater mix is assumed to be 

abrupt even though it is probably hundreds to thousands of 

feet wide, as indicated by measured chloride concentrations. 

This characteristic of the real-world interface implies that the 

boundary between potable and impotable water is landward 

of the simulated SHARP interface. Spitz (1998) has noted 

that, because ground-water velocities within the mixing zone 

vary, simulated movement of a SHARP interface can be 

much smaller than the estimated movement of the “potability 

interface” (representing the approximate location of the 250-

mg/L chloride concentration). Ground-water velocities are 

affected locally by pumping, and the effects of local upconing 

at wells are thus underrepresented.

Model Grid

The model grid was constructed to represent quasithree-dimensional flow through the sequence of aquifers and 

confining units described by Schubert and others (2003) and 

summarized in the earlier section Hydrogeologic Framework. 

The method of representation is summarized in the following 

paragraphs as a sequence of logical conditions applied on a 

cell-by-cell basis. 

The model grid was oriented north-south (fig. 17) with 

182 rows, 168 columns, and 4 layers. Each grid cell represents 

a 500-ft x 500-ft square, and thickness varies from cell to 

cell. The complete grid contains 44,312 active cells and 3,960 

inactive cells. The study area is indicated by the smaller 

rotated rectangle in figure 17, and is used in most other 

illustrations throughout this report. The southeastern corner 

of the study-area rectangle extends beyond the model grid; 

this nondiscretized area is masked by map explanations in the 

other illustrations. 

The model layers generally represent the upper glacial 

aquifer zones A, B, and C and the Magothy aquifer. Modellayer thickness is assigned an integer value, in feet, with a 1-ft 

minimum. The upper boundary of the top layer represents the 

water table on land and the sea floor offshore. The onshoreoffshore boundary is a discretized coastline that is shown 

together with modeled sea-floor depth in figure 18. Onshore 

cells with three sides facing offshore were not permitted 

because of a limitation in the SHARP method used to 

calculate the interface elevation. The thickness of the onshore 

(partly saturated) zone of the unconfined aquifer depends on 

the water-table altitude, whose maximum was specified at 

20 ft above sea level. The model represents the upper glacial 

aquifer zone A as three distinct hydraulic zones in its top 

layer; these correspond to the moraine, outwash, and drift 

units depicted in figure 6. Where aquifer units pinch out in 

other model layers, a 1-ft layer thickness is assigned together 

with hydraulic-property values corresponding to those of an 

overlying or underlying aquifer unit.

Layer-bottom elevation is represented as an integer value 

and generally corresponds to the bottom of each of the four 

aquifer units. The bottom of the top layer corresponds to 

the top of the upper confining unit where present; however, 

the confining unit generally is absent along the south shore 

of the North Fork and in some areas along the north shore. 

The bottom of the top layer along the south shore is set at 

10 ft below sea level or 1 ft below the sea floor, whichever 

is deeper. In north-shore areas where the upper confining 

unit also is absent, an approximate contact between the 

moraine and underlying drift is extrapolated offshore and 

forms the bottom of the top layer. The confining units are 

Figure 16. Schematic representation of the freshwatersaltwater interface along model row i, layer k, columns j-1, 

j and j+1. (Modified from Essaid, 1990)

Tip of interface

Calculated interface altitude

within finite-difference cell

Freshwater Saltwater Sharp interface

i,j-1,k i,j,k i,j+1,k

Toe of interface

20 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
41o

41o

06'

72o 36' 72o 18'

0

0 2 3 KILOMETERS

1 2 MILES

1

INACTIVE 

INACTIVE 

ROW

COLUMN

1

1 10 100 168

100

EXPLANATION

Active cell

Inactive cell

10

182

NORTH FORK

STUDY AREA

(LOCATION

SHOWN IN FIG. 1)

Figure 17. North Fork model grid, Suffolk County, N.Y., Suffolk County, N.Y. (Location is shown in fig. 1)

Figure 18. Sea floor bathymetry near North Fork, Suffolk County, N.Y. (Location is shown in fig. 1)

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

-97 to -28

-27 to -18

-17 to -12

-11 to -5

Altitude, in feet.

Datum is NGVD of 1929.

EXPLANATION

-4 to -1

Onshore

No data (not part 

of study area)

Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface 21
not represented explicitly as model layers, but implicitly as 

restrictions in flow between the model layers, which represent 

only aquifers. The second layer represents upper glacial 

aquifer zone B; its bottom is the top of the lower confining 

unit. The third layer represents upper glacial aquifer zone 

C; its bottom is the top of the Magothy aquifer. The fourth 

and lowest model layer represents the Magothy aquifer. No 

confining unit is present between the third and fourth layers. 

The bottom of the fourth layer is the top of the Raritan Clay.

A geographic information system (GIS) was used to 

interpolate the hydrogeologic surfaces developed by Schubert 

(2003) onto the grid and to assign hydraulic properties, 

boundary conditions, and initial conditions. Some flattening 

or “shelving” of the framework unit surfaces results from the 

10-ft contour interval of the source data, as seen in the vertical 

section in figure 5, but the effect of this approximation on flow 

simulation is negligible.

Boundary Conditions

Model boundary conditions are depicted in a schematic 

section in figure 19. No-flow boundaries are specified at the 

lateral boundaries between active and inactive zones (fig. 17) 

and at the bottom of the model layer representing the Magothy 

aquifer (fig. 6A). The bottom of the Magothy aquifer is 

entirely salty and underlain in most places by a thick confining 

unit. The saline ground-water-flow system below the model’s 

bottom boundary (Raritan Formation) was omitted because its 

effect on the movement of the freshwater-saltwater interface in 

response to freshwater pumping is assumed to be negligible.

The top model boundary in offshore areas is a constanthead boundary in a quasi-layer above the sea floor that 

represents shoreline underflow of freshwater to saline surface 

waters. The constant hydraulic-head value is specified to be 

the equivalent freshwater head hf of the column of saltwater 

overlying the sea floor, calculated as (Essaid, 1990): 

where:

hf = equivalent freshwater head [length]

z = elevation of the sea floor relative to sea level 

[length]

 ρs = density of saltwater [mass/length3]

 ρf = density of freshwater [mass/length3]

During model calibration, the rate of saltwater flow into 

or out of the seabed is controlled by adjusting the vertical 

leakance through the sea floor. Freshwater is simulated to flow 

out of the sea floor, but not into it. 

The top boundary of the model in onshore areas is a 

moveable, saturated/unsaturated boundary that represents the 

water table, to which a specified flux representing groundwater recharge is applied. Ground-water recharge is simulated 

by several zones representing recharge from precipitation and 

from public-supply return flow. The ground-water-recharge 

zones that were used to simulate 1994 steady-state recharge 

from precipitation are shown in figure 20A, which includes 

the locations of simulated streams, ponds, and lakes (discharge 

cells). Locations of 1994 public water-supply-district cells are 

shown in figure 20B; the recharge rates applied to each zone 

for 1994 steady-state conditions are summarized in figure 

20C and table 4. Temporal variations in the applied rates of 

recharge from precipitation, and in the rates and extent of 

public-supply return flow, are discussed further on.

Streams in the upper model layer are simulated as 

constant-flux boundaries that represent base flow. Headdependent boundaries were not used because the streams 

contributed only a small percentage of flow out of 

corresponding model cells, making accurate simulation of 

base flow difficult. Measured base-flow values (described 

Figure 19. Conceptual diagram showing boundary conditions of 

the North Fork Model, Suffolk County, N.Y.

EXPLANATION

Seawater 

Freshwater

Confining unit

Impermeable unit

Hydrostatic-pressure boundary

Specified-flux boundary

x x Moving no-flow (SHARP) boundary

Offshore Onshore Offshore

Unsaturated zone

Recharge Stream

Water table Sea floor

x x

x x x x

x x x x

x x

22 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

Mattituck

Riverhead

Laurel

Greenport

Southold

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

Hallocks Pond

Laurel Lake

Marratooka Pond

Great Pond Moores Drain Marion

Lake

6.04

10.69

19.89

20.41

1994 Recharge rate, in inches per year

EXPLANATION

A. Precipitation zones and locations of freshwater bodies

21.31

23.96

24.24

26.31

Riverhead precipitation zone

Greenport precipitation zone

Cell representing stream, pond,

or lake

EXPLANATION

C. Ground-water recharge rates

B. Public water-supply districts (unsewered areas)

Figure 20. Locations of recharge zones, public water-supply districts, freshwater bodies, and recharge rates used for 1994 steady-state 

simulations in North Fork model, Suffolk County, N.Y.: A. Recharge zones and locations of freshwater bodies. B. Public water-supply 

districts. C. Ground-water-recharge rates. (Location is shown in fig. 1)

Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface 23
previously) were distributed evenly among the model cells 

that contain the freshwater reach of each stream (fig. 20C) and 

were assumed to represent long-term conditions. Flow-through 

conditions at ponds and lakes were represented by increased 

hydraulic conductivity and storage values at corresponding 

model cells. 

The lateral boundary along the onshore part of the 

western model boundary (column 1 of the model grid, fig. 17) 

is simulated as a constant-head boundary that hydraulically 

connects all four model layers to the flow system of the main 

body of Long Island. Constant-head values specified along 

this western upgradient boundary were interpolated from the 

recent water-table map of Schubert (1998).

Ground-water discharge to public-supply and 

miscellaneous wells was simulated as a constant-flux 

boundary at the model cell containing the screen of each 

well; the discharge of wells for which the screen penetrated 

multiple cells was distributed among those cells according to 

their percentage of total screen length. Locations of shallow 

public-supply wells (screened less than 45 ft below sea level) 

are shown in figure 21A; locations of deep public-supply wells 

(screened 45 ft or more below sea level) are shown in figure 

21B. Discharge to wells pumped for irrigation was simulated 

as a specified-flux boundary at the water-table-aquifer cell 

at the centroid of each agricultural parcel; locations of 1994 

agricultural parcels and points of withdrawal, analogous to 

wells, are shown in figure 21C. A map depicting agriculturalparcel location and size in 1999 was also available and shows 

only small changes from 1994.

Model Calibration

The North Fork model was calibrated through a quasisteady-state simulation of 1994 average-annual conditions; 

the results were then statistically compared with measured 

water levels and freshwater-saltwater interface positions that 

were assumed to match long-term equilibrium conditions. 

The water-level measurements used in the comparison were 

made in March-April 1994, and the interface positions were 

estimated by Schubert and others (2003) from data collected 

between about World War II and 2000. Locations of most 

of the observation wells used for water-level measurement 

are shown in figure 22A (some observation wells used for 

water-level measurement are not shown in the mapped area); 

locations of those used for interface-depth measurement are 

shown in figure 22B. Several other deep wells in the Town of 

Riverhead were also evaluated (fig. 22C; this western area is 

of secondary importance, however, because the simulation is 

constrained by nearby specified-head boundary conditions. 

Values of horizontal hydraulic conductivity and vertical 

leakance between units were calibrated to minimize the 

difference between vertical hydraulic gradients measured at 

six paired observation wells and those simulated from 1994 

average annual conditions. Observed (March-April 1994) 

and simulated water levels and gradients at these wells are 

summarized in table 5. 

Horizontal hydraulic conductivity values and vertical 

leakance values were calibrated to approach a target value 

of the mean residual and minimum root mean square error 

(RMSE) of the differences between measured and simulated 

values of head and interface elevation. The target mean 

residual used for water levels was the mean difference 

between three local mean sea-level datums and the National 

Geodetic Vertical Datum (NGVD) of 1929 , because reported 

water levels are calculated with reference to NVGD of 1929. 

The local mean sea-level datums at three sites on the North 

Fork and the corresponding mean are as follows:

Port Jefferson 0.53 ft

Threemile Harbor 0.48 ft

South Jamesport 0.32 ft

Mean 0.45 ft

The target mean residual for interface positions was 

assigned a value of zero. The accuracy of these statistics is 

limited, however, by a discretization (offset) error between 

the location of each field measurement and the center of the 

corresponding model cell for which simulated results are 

evaluated.

Residual mean, M, is calculated as:

where:

Xm = measured value 

Xs = simulated value

n = number of comparisons

RMSE is calculated as: 

Table 4. Simulated 1994 ground-water-recharge rates for North 

Fork model, Suffolk County, N.Y

[Values are in inches. Locations are shown in fig. 20.]

Simulated zone

Recharge 

from 

precipitation

Publicsupply 

return 

flow 

Total 

groundwater 

recharge

Riverhead 21.31 0 21.31

Ponds 10.69 0 10.69

Riverhead/Laurel districts 21.31 2.93 24.24

Mattituck district 21.31 5.00 26.31

Greenport 19.89 0 19.89

Ponds 6.04 0 6.04

Greenport district 19.89 4.07 23.96

Great Hog district 19.89 0.52 20.41

24 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Figure 21. Locations of public-supply and commercial-supply wells in 1994 in North Fork model, Suffolk County, N.Y.: A. Public- and 

commercial-supply wells screened less than 45 feet below sea level. B. Public- and commercial-supply wells screened 45 feet or more 

below sea level. C. Agricultural parcels and irrigation wells. (Location is shown in fig. 1)

LONG ISLAND SOUND

GREAT

PECONIC

BAY

41o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

LONG ISLAND SOUND

GREAT

PECONIC

BAY

41o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

S94138,LAY3,SB-121.8

S101947,LAY4,SB-45

S52086,LAY3,SB-63

S97502,LAY4,SB-53

S97501,LAY4,SB-66

S24850,LAY4,SB-46

S93794,LAY4,SB-46

S33775,LAY4,SB-49 S33990,LAY4,SB-55

S36799,LAY4,SB-52

S84076,LAY3,SB-45

S31448,LAY3,SB-75

LONG ISLAND SOUND

41o 72 30' 41 06' 72 24' o o o

GREAT

PECONIC

BAY

41o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

S17835,LAY4,SB-41

S6513,LAY4,SB-41

S105669,LAY1,SB-42.7

S45810,LAY4,SB-26

S45811,LAY4,SB-26

S45809,LAY4,SB-26

S84076,LAY3,SB-45

S94491,LAY3,SB-40

S26049,LAY4,SB-36 S24851,LAY4,SB-35

S98991,LAY4,SB-37

S3698,LAY4,SB-37

S76772,LAY4,SB-36

S11362,LAY3,SB-31

S94274,LAY3,SB-36

WATER-SUPPLY DISTRICT--

Names are given in fig. 17

POINT OF WITHDRAWAL--

Size is proportional to 1994

annual pumpage.

LAY indicates model layer.

SB indicates altitude of screen 

bottom, in feet. Datum is NGVD

of 1929.

S52086

LAY3

SB-63

EXPLANATION

A. Public- and commercial-supply wells screened less than 45 feet below sea level

B. Public- and commercial-supply wells screened 45 feet or more below sea level

WATER-SUPPLY DISTRICT--

Names are given in fig. 17

POINT OF WITHDRAWAL--

Size is proportional to 1994

annual pumpage.

LAY indicates model layer.

SB indicates altitude of screen 

bottom, in feet. Datum is NGVD

of 1929

S6513

LAY4

SB-41

EXPLANATION

C. Agricultural parcels and irrigation wells.

Agricultural parcel

Hypothesized irrigation

well at parcel centroid

EXPLANATION

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface 25
MATTITUCK INLET HASHOMOMUCK 

POND

Great Hog Neck

Little Hog Neck

MEETINGHOUSE

FLANDERS

CREEK

WESTERN 

EXTENT OF GRID

Riverhead 

Southold 

FLANDERS 

BAY GREAT 

PECONIC 

BAY

41o 72o 30' 41o 06'

LONG ISLAND SOUND

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

40o

55

Town boundary

33073 Well and well number--

 denotes estimated position of interface 

 denotes head measurement

EXPLANATION

* *

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

LONG ISLAND SOUND

GREAT

PECONIC

BAY

40o

56'

Southold

Riverhead

95439

Town boundary

Well and well number

EXPLANATION

A. Wells used for water-level measurement

B. Wells used to estimate position of freshwater-saltwater interface

C. Secondary wells near western extent of grid

41o 72o 30' 41o 06' 72o 24'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Southold

Riverhead

53537

Town boundary

Well and well number

EXPLANATION

51587

33073

51589

*

* 111891

* 106205

82938

*

106201

71566

111900

**

*

96233

111601 109670

102249

113118

105935

112562

71279

71286

71044

114381

111899

101755

112415

83709

71576

58429

94138

113817

4091 33775

69447

61015

95435

95488

95446 95443

95727

95441

95425

109173

114382

95428

112309

111901

91815

112310

112313

5475

3123

95432

111902

111903

111904

114867

111132

112419

95421

95442

114868

95439 95419

95437

53537

47234

53328

6524

53335

53338

61015

47233

65606

53326

69761

32390

65605

53324

53327 53334

53325 53322

53336

39269

53332

6558 51581

83709

71576

91812

51582 53333

53539

16783

53323 72784 95424

95727

95423 53331 72782

53330

Figure 22. Locations of observation wells used in calibration of North Fork model, Suffolk County, N.Y.: A. Wells used for water-level 

measurement. B. Wells used for freshwater-saltwater-interface measurement. C. Secondary wells near western extent of grid. 

(Location is shown in fig. 1)

26 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Table 5. Measured (March-April 1994) and simulated water levels and hydraulic gradients at six well pairs in North Fork study area, 

Suffolk County, N.Y.

[Water levels are in feet above sea level. Well locations are shown in fig. 22. Well numbers are assigned by New York State Department of Environmental 

Conservation; prefix S denoting Suffolk County is omitted.]

Statistic Well number

Upper well 91813 53331 71045 65605 95424 83792

Measured water level 10.0 4.0 7.1 7.8 3.6 1.8

Simulated water level 9.7 3.5 8.3 8.8 3.2 2.8

Lower well 71576 95423 69761 53324 95727 83709

Measured water level 9.5 4.1 6.9 7.7 2.4 4.7

Simulated water level 9.1 3.5 8.3 8.8 3.1 5.1

Relation between water levels in upper and lower wells

Difference between measured values 0.5 -0.1 0.2 0.1 1.2 -2.9

Difference between simulated values 0.6 0 0 0 0.1 -2.3

Measured gradient between upper and lower wells 0.00198 -0.00216 0.0022 0.0066 0.0176 -0.0209

Simulated gradient between upper and lower wells 0.00194 0 0.00110 0 -0.0001 -0.0049

Ratio of simulated to measured gradient 0.979 0 0.498 0 -0.005 0.238

Table 6. Calibration statistics on ground-water levels and 

saltwater interface for hydrogeologic units in North Fork model

[Values are in feet. M, residual mean; RMSE, root mean square error; n.a., 

not applicable] 

Model layer M RMSE

Population 

(n)

Ground-water levels

Upper glacial zone A Outwash 0.44 0.93 27

Upper glacial zone A Moraine 0.59 0.81 6

Upper glacial zone B 0.30 0.79 10

Upper glacial zone C 0.54 0.54 2

Magothy 0.64 0.89 3

Total 0.44 0.88 48

Interface elevation below sea level

Upper glacial zone A 18.44 31.23 16

Upper glacial zone B 27.10 36.16 23

Upper glacial zone C -22.39 80.46 23

Total 6.51 n.a. 62

Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface 27

�

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�����������

���������������������������������������������

���

���

��� ������ ������ ������

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�����

�����

�����

�����

�����

��������������

������������������

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where variables are as stated above. Populations of head 

values and interface values, and subsets thereof, were 

summed. Head-data subsets were separated by aquifer 

according to the model layer or water-table zone (table 6) in 

which observation wells were screened, and interface-data 

subsets were separated according to the presence or absence 

of a confining layer above the interface. Final modeled 

hydraulic conductivity values that obtained the best calibration 

statistics are summarized in table 2; these values are generally 

consistent with previously reported values (see Schubert and 

others, 2003). Horizontal conductivity of the Magothy aquifer 

required a slight decrease from the previously reported values 

to obtain the best calibration statistic. Horizontal hydraulic 

conductivity of top-layer cells that represent major freshwater 

surface-water bodies was increased to 50,000 ft/d to provide 

a flow-through condition, wherein water flowing through 

the surface-water body becomes part of the simulated mass 

balance of the model cell.

 Model storage parameters (table 7) were tested and 

adjusted throughout the study. The final value for unconfined 

freshwater specific storativity was 0.15 ft-1, and that for 

confined storativity was 0.00002 ft-1. Storativity of top-layer 

cells containing major freshwater surface-water bodies was 

increased, from 0.15 ft-1 to 1.0 ft-1 to represent the effect of 

the fully saturated water body. The small value for confined 

aquifers results from the lack of dewatering of the porous 

aquifer medium. None of the aquifers are fully confined and, 

therefore, deep cones of depression do not develop in response 

to pumping.

Additional model parameters that were tested and 

adjusted throughout the study are included in table 7. These 

values were optimized for computer efficiency in conjunction 

with the head and interface adjustments described above. 

 Results of the transient-state simulation of 1941-2005 

seasonal conditions also were compared with measured 

values. The model-generated and historical water levels at a 

typical observation well with an extensive record (S16764, 

redeveloped as S53324; fig. 22A) are plotted as a time series 

in figure 23A. The simulated freshwater-saltwater interface 

(fig. 23B) shows seasonal fluctuations and moves upward 

during 1961-66—first as a result of agricultural pumping, then 

in response to the 1962-66 drought. After the drought, it levels 

off and approaches a steady state until about 1995, when it 

moves upward about 5 ft in response to an increase in publicsupply pumpage. Figures 23A-B are representative of about 20 

other graphs that were generated for the wells in the area for 

which long-term records are available.

Sensitivity Analysis

A sensitivity analysis defines model uncertainty in 

aquifer properties, hydrologic stresses, boundary conditions, 

and any other factors that may affect model results by 

varying their values individually and observing the changes 

in model results. The sensitivity analysis in this study was 

used to test the effects of aquifer hydraulic conductivity, 

confining-unit leakance, and recharge and withdrawal rates 

on model heads and interface position. Several values for 

each of these parameters were tested; the values ranged 

from one-half to twice the calibrated value throughout the 

model. Figures 24A-B show the response of calibration 

statistics, as defined in a previous section, to changes in 

parameters based on multiplication factors (amount of 

parameter change). The model showed greater sensitivity 

to aquifer hydraulic conductivity than to confining-unit 

leakance. Increasing the total anisotropy (ratio of horizontal 

to vertical hydraulic conductivity) of the model, either by 

increasing the scalar conductivity values for a model layer or 

decreasing confining-layer leakance, produced a flattening 

effect whereby the maximum depth of freshwater rose, 

and the maximum offshore extent of freshwater increased. 

Boundary-condition placement was a moderating factor—an 

observation corroborated by Spitz (1998). Sensitivities to 

saltwater interface movement were also analyzed. Porosity 

strongly affected the rate of transient-state saltwater-interface 

movement. 

1994 Steady-State Simulation Results

A model-generated freshwater budget of each aquifer for 

1994 average annual conditions on the North Fork is given in 

table 8. The lack of absolute balance was caused by use of a 

moderately loose convergence criterion and also inaccuracy 

resulting from the SHARP mixing method (discussed in a 

previous section). About 90 percent of the freshwater that 

enters the flow system represents recharge from precipitation 

and public-supply return flow; the remaining 10 percent enters 

as ground-water flow from the main body of Long Island. 

About half of the total recharge remains in the modeled 

upper glacial aquifer zone A and exits the system as shoreline 

discharge; another 40 percent reaches the upper glacial aquifer 

zone B, and about 10 percent reaches the upper glacial aquifer 

zone C. Less than 1 percent of total recharge at the water table 

reaches the Magothy aquifer.

Table 7. Parameter values used in North Fork model

[ft, foot; lb/ft3 pounds per cubic foot; lb/(ft•s), pound per foot second ]

Parameter Value

Specific storativity (unconfined) 0.15 /ft

Specific storativity (confined) 1.0 x 10-6 /ft

Specific weight, freshwater 62.41 lb/ft3

Specific weight, saltwater 63.60 lb/ft3

Dynamic viscosity, freshwater 2.09 x 10-6 lb/(ft•s)

Dynamic viscosity, saltwater 2.09 x 10-6 b/(ft•s)

SHARP1 leakage method restricted

SHARP convergence (iteration) 0.02

1 Essaid, 1990

28 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Figure 23. Measured and simulated ground-water level and freshwater-saltwater interface depths: A. Measured and 

simulated water levels at well S16764. B. Simulated head and interface depth at well S4091. (Well location shown in 

figure 22A)

S16764 (S53324)

WATER LEVEL, IN FEET ABOVE NGVD 1929

11

10

9

8

7

6

5

4

3

2

MEASURED

SIMULATED

S4091 SIMULATED WATER LEVEL

SIMULATED INTERFACE ALTITUDE

WELL CONSTRUCTED IN 1946

INTERFACE ALTITUDE AND

WELL-SCREEN INTERVAL , 

IN FEET ABOVE NGVD 1929

-18

-15

0

-10

-5

3

-65

-55

-25

-5

15

1941 1946 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001

A. Measured and simulated water levels

B. Simulated head and freshwater-saltwater interface altitude 

WELL-SCREEN INTERVAL

Figure 24. Sensitivity of simulated hydraulic head to variations in the values of selected parameters in the North Fork model: A. Mean 

residual. B. Root mean square error.

MULTIPLICATION FACTOR

0.50 0.75 1.00 1.25 1.50 1.75 2.00

MEAN RESIDUAL, IN FEET

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

Horizontal hydraulic conductivity

Vertical leakance

Recharge 

Withdrawal 

2.5

3.0

Horizontal hydraulic conductivity

Vertical leakance

Recharge 

Withdrawal 

EET

A. Mean residual

B. Root mean square error

MULTIPLICATION FACTOR

0.50 0.75 1.00 1.25 1.50 1.75 2.00

MEAN RESIDUAL, IN FEET

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

Horizontal hydraulic conductivity

Vertical leakance

Recharge 

Withdrawal 

MULTIPLICATION FACTOR

0.50 0.75 1.00 1.25 1.50 1.75 2.00

0.5

1.0

1.5

2.0

2.5

3.0

Horizontal hydraulic conductivity

Vertical leakance

Recharge 

Withdrawal 

ROOT MEAN SQUARE ERROR, IN FEET

A. Mean residual

B. Root mean square error

Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface 29
 The simulated water-table altitude under 1994 average 

annual conditions on the North Fork is depicted in figure 

25A, and can be compared with figure 15, which depicts the 

measured altitudes. The simulated head values reach a peak 

altitude of 12 ft in the main Long Island flow system, 9 ft 

in the Cutchogue system, and 6 ft in the Greenport system. 

Small water-table mounds with altitudes of less than 3 ft are 

indicated on Little Hog Neck and Great Hog Neck.

The position of the freshwater-saltwater interface in 

the upper glacial aquifer zone A under 1994 average annual 

conditions is shown in figure 25B. The interfaces occur in the 

band of cells that contain both freshwater and saltwater. The 

width of the band of mixed-water cells is a function of layer 

thickness, boundary conditions, and pumpage; it is narrowest 

in areas where the coastline is even rather than convoluted.

The all-freshwater part of the model can be separated 

conceptually at mixed-water cells into distinct lenses, or 

channels, that convey freshwater through a continuous 

sequence of model cells containing water that is either 

completely or partly fresh. The main Long Island/Cutchogue 

lens is the largest and extends from the main Long Island edge 

of the model eastward to the Cutchogue flow system east of 

Mattituck Inlet. The Little Hog Neck and Great Hog Neck 

lenses are separated from the main Long Island/Cutchogue 

lens by local embayments, and the Greenport lens is separated 

from the main Long Island/Cutchogue lens by Hashamomuck 

Pond. All of these lenses extend downward through the 

upper confining layer and may divide into sublenses in the 

Ronkonkoma drift layer.

The simulated potentiometric surface in the upper glacial 

aquifer zone B under 1994 average annual conditions is shown 

in figure 26A. The head configuration in zone B is similar to 

that of the water table (fig. 24A) except where fully salty cells 

appear in an inland area near Mattituck Inlet. The simulated 

position of the freshwater-saltwater interface is shown in 

figure 26B.

Flow lenses that originate in the upper glacial aquifer zone 

A divide into sublenses below the upper confining unit. The 

main Long Island/Cutchogue lens (fig. 25B) divides into main 

Long Island and Cutchogue sublenses that are separated by 

saltwater underlying the Mattituck Inlet. The Greenport lens 

(fig. 25B) divides into Greenport and East Marion sublenses 

that are separated by saltwater underlying several small 

embayments with the city of Greenport. The Little Hog Neck 

and Great Hog Neck lenses do not divide, and terminate in 

the Ronkonkoma drift layer. The East Marion sublens also 

terminates in the Ronkonkoma drift layer. The main Long 

Island and Greenport sublenses extend downward through the 

lower confining layer but do not divide in the bottom glacial 

layer.

Table 8. Model-generated fresh-ground-water budget for 1994 average annual conditions 

Aquifer and budget 

component

Budget value 

(cubic feet per second) 

Aquifer and budget 

component

Budget value 

(cubic feet per second)

Upper glacial aquifer zone A Upper glacial aquifer zone C

INFLOW INFLOW

Recharge 75.23 Constant head 2.26

Constant head 0.56 Leakage through top 7.25

Leakage through bottom 17.61 Leakage through bottom 4.60

OUTFLOW OUTFLOW

Pumpage 3.14 Pumpage 0

Constant head 0.98 Constant head 1.54

Leakage through top 53.73 Leakage through top 12.60

Leakage through bottom 37.32 Leakage through bottom 0.35

Upper glacial aquifer zone B Magothy aquifer

INFLOW INFLOW

Constant head 0.52 Constant head 5.59

Leakage through top 34.65 Leakage through top 0.35

Leakage through bottom 5.90

OUTFLOW OUTFLOW

Pumpage 0.21 Pumpage 0

Constant head 0.73 Constant head 0

Leakage through top 34.07 Leakage through top 5.61

Leakage through bottom 7.97

30 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Figure 25. Simulated water-level and freshwater-saltwater interface position for the upper glacial aquifer zone A, 1994 average annual 

conditions on the North Fork, Suffolk County, N.Y.: A. Simulated 1994 water levels in freshwater-flow system. B. Simulated 1994 

freshwater-saltwater interface position. (Location is shown in fig. 1)

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

MAIN LONG ISLAND CUTCHOGUE

GREENPORT

LITTLE

HOG

NECK

GREAT

HOG

NECK

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

-183.8 to -117.5

-117.4 to -80.0

-79.9 to -48.5

Altitude, in feet.

Datum is NGVD of 1929

EXPLANATION

A. Simulated 1994 water levels in freshwater-flow system in upper glacial aquifer zone A

-48.4 to -19.7

-19.6 to 0

Interface not

present in layer

0.0 to 3.0

3.1 to 6.0

6.1 to 9.0

9.1 to 12

Water-level altitude, in feet.

Datum is NGVD of 1929.

EXPLANATION

Saltwater

No data (not part 

of study area)

B. Simulated 1994 freshwater-saltwater interface position in upper glacial aquifer zone A

Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface 31
Figure 26. Simulated water-level and position of freshwater-saltwater interface position for the upper glacial aquifer zone B, 1994 

average annual conditions on North Fork, Suffolk County, N.Y.: A. Simulated 1994 water levels in freshwater-flow system. B. Simulated 

1994 freshwater-saltwater interface position. C. Simulated 1994 vertical gradient between upper glacial aquifer zones A and B. (Location 

is shown in fig. 1)

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

MAIN LONG ISLAND CUTCHOGUE

GREENPORT

EAST MARION

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

Strong downflow – gradient

from 0.003 to 0.008

Moderate downflow – gradient 

from 0.001 to 0.002

Weak downflow – gradient

from 0.0002 to 0.0009

Stagnant – gradient

from -0.0001 to 0.0001

Upflow--gradient

less than -0.0001

Gradient

EXPLANATION

A. Simulated 1994 water levels in freshwater-flow system in upper glacial aquifer zone B

0.0 to 3.0

3.1 to 6.0

6.1 to 9.0

9.1 to 12

Water-level altitude, in feet.

Datum is NGVD of 1929.

EXPLANATION

Saltwater

No data (not part 

of study area)

C. Simulated 1994 freshwater vertical gradient between upper glacial aquifer zones A and B

-217.9 to -135.5

-135.4 to -92.7

-92.6 to -56.5

-56.4 to -22.6

Altitude, in feet.

Datum is NGVD of 1929.

EXPLANATION

-22.5 to 0

Interface not 

present in layer

B. Simulated 1994 freshwater-saltwater interface position in upper glacial aquifer zone B

32 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Figure 27. Simulated water level and freshwater-saltwater interface for the upper glacial aquifer zone C,1994 average annual conditions 

on North Fork, Suffolk County, N.Y.: A. Simulated 1994 water levels in freshwater-flow system. B. Simulated 1994 freshwater-saltwaterinterface position. C. Simulated 1994 vertical gradient between upper glacial aquifer zones B and C. (Location is shown in fig. 1)

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

MAIN LONG ISLAND

CUTCHOGUE

GREENPORT SOUTHOLD

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

GREAT

PECONIC

BAY

40o

56'

Gradient

EXPLANATION

A. Simulated 1994 water levels in freshwater-flow system in upper glacial aquifer zone C

0.0 to 3.0

3.1 to 6.0

6.1 to 9.0

9.1 to 12

Water-level altitude, in feet.

Datum is NGVD of 1929.

EXPLANATION

Saltwater

No data (not part 

of study area)

C. Simulated 1994 freshwater vertical gradient between upper glacial aquifer zones B and C

-262.2 to -215.6

-215.5 to -172.1

-172.0 to -133.5

-133.4 to -66.5

Altitude, in feet.

Datum is NGVD of 1929.

EXPLANATION

-66.5 to 0

Interface not 

present in layer

B. Simulated 1994 freshwater-saltwater interface position in upper glacial aquifer zone C

Strong downflow – gradient

from 0.0053 to 0.0200

Moderate downflow – gradient 

from 0.0021 to 0.0052

Weak downflow – gradient

from 0.0002 to 0.0020

Stagnant – gradient

from -0.0001 to 0.0001

Upflow--gradient

less than -0.0001

Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface 33
The direction and magnitude of simulated vertical 

hydraulic gradients between upper glacial aquifer zone A and 

B (fig. 26C) indicate downflow below the recharge-mound 

peaks and upflow at the shore. The gradient is generally 

proportional to the vertical conductance of the upper confining 

unit (fig. 13A). Localized gradient reversals from downward 

to upward also are indicated at Laurel Lake (location is shown 

in fig. 20A) and at several wellfields.

The simulated head configuration and interface position in 

the upper glacial aquifer zone C (beneath the lower confining 

unit) are depicted in figures 27A-B, respectively. Here the 

main Long Island sublens continues downward to the Magothy 

layer, and the Cutchogue sublens divides into Cutchogue 

and Southold sublenses, which are separated by saltwater 

underlying an embayment between Little Hog and Great Hog 

Necks. The Greenport and Southold sublenses terminate in 

zone C. The western Cutchogue sublens continues downward 

into the Magothy layer.

The direction and magnitude of vertical hydraulic 

gradients between upper glacial aquifer zones B and C (fig. 

27C) indicate regional downflow below the recharge mounds 

and upflow near freshwater-saltwater interfaces. A localized 

gradient reversal also is seen in an area of about 30 cells in the 

eastern part of the main Long Island sublens, where the lower 

confining unit is absent.

The simulated-head configuration and the position of 

the freshwater-saltwater interface in the Magothy aquifer 

are depicted in figures 28A-B. The main Long Island and 

Cutchogue sublenses terminate in mixed-water cells of the 

Magothy layer. Freshwater does not extend to the bottom of 

the layer.

The direction and magnitude of vertical hydraulic 

gradients (fig. 28C) show a characteristic downward 

component below recharge mounds and an upward component 

at interfaces; however, the Cutchogue sublens is not 

completely surrounded by upward flow; the configuration 

of layer structure allows downflow at the western side of the 

Cutchogue sublens. 

The simulated vertical section A-A/ (fig. 29) depicts 

the interface elevation in relation to hydrogeologic-unit and 

model-layer geometry. The deepest interface elevation is near 

the western edge of the section and extends through about 

10 percent of the Magothy layer thickness. The shallowest 

interface elevation is at the eastern edge of the section and 

extends to the floor of Long Island Sound. Two distinct 

interface mounds occur beneath the Mattituck Inlet and 

Hashomomuck Pond embayments. Local interface depressions 

occur where confining units are thin and recharge mounds 

are nearby; however, the presence of significant flow vectors 

orthogonal to this section makes this correlation more difficult 

to visualize in vertical section than plan view (figs. 25- 28).

Simulation of Historical Record

Ground-water flow and locations of freshwater-saltwater 

interfaces were simulated in an initial predevelopment phase 

under nonpumping conditions to provide the starting point 

for simulation of the historical record. The predevelopment 

simulation used the long-term (1959-99) mean rate of 

recharge from precipitation and the long-term average stream 

discharges. After simulation of 250 years, when a steady 

state was approached, the run was halted, and its results were 

used as the starting point for simulation of a 65-year phase 

representing 1941 to 2005. The pumping rates used for the 

simulated 65-year phase were seasonal and were apportioned 

among five periods, as listed in table 9; table 5 also provides 

(1) the simulated peak and off-peak rates of recharge from 

precipitation and public-supply return, and (2) the discharges 

from base flow, irrigation pumpage, and public-supply 

pumpage, for each of the five seasonal periods.

 The sources of recharge and discharge data for each of 

five stress periods of the 65-year simulation are summarized 

in table 10. Seasonal public-supply pumpage and return flow 

rates for 1957, 1994, and 1998 are tabulated by water-supply 

district in appendix 6. 

 Simulated heads and interface positions obtained at 

the end of the 65-year historical simulation were then used 

as initial conditions for the two sets of four scenarios: one 

representing years 2006-20 under average-recharge conditions 

for the entire 15-year period, and the other representing 

average conditions except for a 5-year (2011-15) drought. All 

scenarios used the projected water-use values, as follows:

Scenario 1 simulated long-term rates of recharge 

from precipitation and water usage that was essentially a 

continuation of that used during the fifth (1996-2005) stress 

period (table 6 and appendix 6). 

Scenarios 2 and 3 simulated most conditions used 

in scenario 1 except for increased rates of public-supply 

pumpage and return flow, summarized in table 6 and 

appendixes 7 and 8. Return flow of public-supply pumpage 

was applied to areas shown in figure 2E.

Scenario 4 simulated most conditions used in scenario 

3 except for additional increases in public-supply pumpage 

and return flow (table 6 and appendix 9) and miscellaneous 

pumpage (appendix 10). Return flow of public-supply 

pumpage was applied to areas shown in figure 2E.

The four drought scenarios used the same conditions as 

outlined above, except for a 20-percent reduction in recharge 

from precipitation and an offsetting increase in the agricultural 

irrigation requirement during the 5-year (2011-15) drought. 

Analysis of Projected Future Conditions

The effects of pumping and recharge on ground-water 

flow and the freshwater-saltwater interface position in the 

eight 15-year (2006-20) water-supply scenarios under averagerecharge conditions with and without a 5-year (2011-15) 

drought are summarized below. The percent increases in 

pumpage and return flow rates used in each simulation are 

summarized in table 11.

34 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Figure 28. Simulated water level and position of freshwater-saltwater interface for the Magothy aquifer, 1994 average annual 

conditions on North Fork, Suffolk County, N.Y.: A. Simulated 1994 water levels in freshwater-flow system. B. Simulated 1994 

freshwater-saltwater-interface position. C. Simulated 1994 vertical gradient between upper glacial aquifer zone C and Magothy layer. 

(Location is shown in fig. 1)

LONG ISLAND SOUND

GREAT

PECONIC

BAY

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

C. Simulated 1994 freshwater vertical gradient between the upper glacial aquifer zone C and the Magothy model layer

Base from U.S. Geological Survey digital data, 1:24,000,

Universal Transverse Mercator projection, NAD27, Zone 18

LONG ISLAND SOUND

B. Simulated 1994 freshwater-saltwater interface position in Magothy model layer

GREAT

PECONIC

BAY

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

LONG ISLAND SOUND

41o 72o 30' 41o 06' 72o 24'

A. Simulated 1994 water levels in freshwater-flow system in Magothy model layer

GREAT

PECONIC

BAY

40o

56'

0

0 2 4 KILOMETERS

1 2 3 MILES

1 3

41o 72o 30' 41o 06' 72o 24'

40o

56'

41o 72o 30' 41o 06' 72o 24'

40o

56'

0.0 to 3.0

3.1 to 6.0

6.1 to 9.0

9.1 to 12

Saltwater

No data (not part of study area)

Water level, in feet.

Datum is NGVD of 1929.

EXPLANATION

-382.2 to -304.9

-304.8 to -251.0

-250.9 to -198.7

-198.6 to -98.6

-98.5 to 0

Interface not present in layer

Altitude, in feet.

Datum is NGVD of 1929.

EXPLANATION

Gradient

EXPLANATION

Strong downflow – gradient

from 0.0043 to 0.0178

Moderate downflow – gradient 

from 0.0007 to 0.0043

Weak downflow – gradient

from 0.0002 to 0.0006

Stagnant – gradient

from -0.0001 to 0.0001

Upflow--gradient

less than -0.0001

Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface 35
3123

Pleistocene confining layer

Freshwater aquifer

EXPLANATION

Saltwater aquifer

Well and well number, flag is 

estimated altitude of freshwatersaltwater interface, in feet.

Datum is NGVD of 1929.

0

0 2 4 KILOMETERS

1 2 3 MILES

VERTICAL SCALE GREATLY EXAGGERATED

Upper glacial 

zone B

Upper glacial 

zone A

Upper 

glacial 

zone C

Northwest Southeast

B B'

Peconic

Bay

490

1 3

0

-100

-200

-300

-400

-500

-600

-700

100

FEET

71044

71170, A-A' 102249

71279

112562

Upper glacial zone A

Upper glacial

Upper zone B

glacial 

zone C

Magothy aquifer

Southwest Northeast

A A'

Raritan clay

Hashamomuck

Pond

Mattituck

Inlet

71576

91815

106415

71170, B-B'

68831

114868

490

95446

95443

0

-100

-200

-300

-400

-500

-600

-700

-800

100

FEET

Magothy aquifer 

Raritan clay 

Raritan clay (not modeled)

Simulated freshwater-saltwater 

interface

Figure 29. Vertical sections showing simulated position 

of freshwater-saltwater interface under 1994 average 

annual conditions in North Fork model, Suffolk County, 

N.Y. (Trace of section is shown in fig. 1)

36 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Table 9. Monthly distribution of recharge and discharge in North Fork model

Pumping 

period Month

Recharge Discharge

Precipitation

Public-supply 

return Base flow

Agricultural 

pumpage Public supply

1 January Peak Offpeak Annual None Offpeak

February Peak Offpeak Annual None Offpeak

March Peak Offpeak Annual None Offpeak

April Peak Offpeak Annual None Offpeak

2 May Offpeak Peak Annual None Offpeak

3 June Offpeak Peak Annual Total Peak

July Offpeak Peak Annual Total Peak

August Offpeak Peak Annual Total Peak

4 September Offpeak Peak Annual None Offpeak

October Offpeak Peak Annual None Offpeak

5 November Peak Offpeak Annual None Offpeak

December Peak Offpeak Annual None Offpeak

Table 10. Data used for the five stress periods of the 65-year (1941-2005) simulation in North Fork model

Stress period

Recharge Withdrawals

Recharge from 

precipitation

Public-supply 

return flow 

Agricultural 

withdrawal 

Public-supply 

pumpage 

Miscellaneous 

pumpage Mean base flows

1941-61 1957 1957 1957 1957 1957 1959-99

1962-66 (drought) 1962-66 1957 1962-66 1957 1957 1959-99

1967-70 1957 1957 1957 1957 1957 1959-99

1971-95 1992-94 1994 1994 1994 1994 1959-99

1996-2005 1996-98 1998 1999 1998 1994 1959-99

Table 11. Summary of water-supply scenarios for years 2006-20 in North Fork model

[Percent increases are in relation to scenario 1 rates.] 

Scenario Public-supply pumpage Public-supply return flow Miscellaneous pumpage Agricultural pumpage 

Scenarios based on average-recharge conditions

1 1998 rates 1998 rates 1994 rates 1999 rates 

2 186-percent increase 121-percent increase no increase no increase

3 268-percent increase 141-percent increase no increase no increase

4 365-percent increase 165-percent increase 157-percent increase no increase

Scenarios based on drought conditions 

Drought was applied to each of the above scenarios as a 20-percent decrease in long-term rate of recharge and a 20- percent increase in 1999 

agricultural pumpage during years 2011-15. 

Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface 37
Scenario 1 represents no change in the rates of water 

use from either the 1998 public-supply pumpage and return 

flow, the 1993-95 miscellaneous pumpage, or the 1999 rate 

of agricultural withdrawal. These years and rates were chosen 

because they provide the most reliable estimates of conditions 

during the projected period.

Scenario 2 incorporated two planned wells at Alvah’s 

Lane and five proposed public-supply wellfields, and applied 

public-supply pumpage and return flow at 186 percent of 

the 1998 rates (table 11). Return flow of public-supply 

pumpage was applied to areas shown in figure 2E. The rates of 

miscellaneous pumpage and agricultural withdrawal were not 

changed. 

Scenario 3 incorporated two planned wells at Alvah’s 

Lane and five proposed public-supply wellfields, and applied 

public-supply pumpage and return flow at 268 percent of 

the 1998 rates (table 11). Return flow of public-supply 

pumpage was applied to areas shown in figure 2E. The rates of 

miscellaneous pumpage and agricultural withdrawal were not 

changed. 

Scenario 4 incorporated two planned wells at Alvah’s 

Lane and five proposed public-supply wellfields, and applied 

public-supply pumpage and return flow at 365 percent of 

the 1998 rates and miscellaneous pumpage at 157 percent of 

the 1993-95 rates (table 11). Return flow of public-supply 

pumpage was applied to areas shown in figure 2E.

 Limitations of Analysis

Several factors affect the reliability of conclusions drawn 

about the system and the certainty of predictions. Coarse 

model discretization entails averaging over large areas, 

depth intervals, and time intervals and therefore limits the 

precision of the simulated interface position and results in 

underestimation of its movement in response to localized 

stresses. The SHARP method inherently underestimates the 

movement of the potability interface through its method of 

representing freshwater and saltwater mixing, especially 

in the vicinity of pumped wells. As a result, a relatively 

small interface movement to within 50 ft of a well screen 

is a cause for concern, as is a large percent change in the 

distance between the interface and the well screen, or upward 

movement of an interface through a confining unit. 

Results of Average-Recharge Simulations

The four water-supply scenarios that simulated averagerecharge conditions used the long-term (1959-99) rate of 

recharge from precipitation, which is slightly smaller than 

the 1996-98 rate used for the 10-year period corresponding 

to 1996-2005. As a result, the model-generated water levels 

decreased, and interface positions moved upward and 

landward, in all four average-recharge scenarios. These 

changes were greater in scenarios 2, 3, and 4 than in scenario 

1 as a result of the applied increases in pumpage (table 11). 

Results of simulation of the four scenarios under averagerecharge conditions are summarized below, and results for the 

first three scenarios are depicted in figures 30A-C; the results 

of simulation of the drought scenarios are discussed in the next 

section and depicted in figures 30D, E.

Average-Recharge Scenario 1

Wellfields at Brecknock Hall and Inlet Drive (locations 

shown in fig. 3C) were the most susceptible to saltwater 

intrusion in this scenario. Saltwater intrusion at well 1A 

(appendix 7) of Inlet Drive (S-105669, redeveloped as S108347) is indicated to begin around 1998 (fig. 30A); here 

the saltwater interface moves through the upper confining 

unit and enters the unconfined aquifer in which the well is 

screened. The confined aquifer is shown to contain freshwater 

and saltwater until the crossover (1996), after which it is fully 

salty. The interface position thereafter is indicated to be above 

the bottom of the upper aquifer. 

Average-Recharge Scenario 2

Wellfields shown to be susceptible to saltwater intrusion 

in scenario 2 were those at Inlet Drive, Brecknock Hall, Main 

Bayview Road, and Islands End (locations shown in fig. 3C). 

The response of the Islands End wellfield at Well 8 (S15795) 

is depicted in figure 30B. Interface movement reverses from 

downward to upward in 2006. The interface travels only about 

15 ft, but interface movement throughout this area is expected 

to cause additional localized upconing. 

Average-Recharge Scenario 3

Upward movement of the saltwater interface at well 

S105669 during scenario 3 (fig. 30C) is more pronounced than 

in scenario 1. Capture of saltwater becomes evident at about 

year 2011, although chloride concentrations probably would 

begin to increase several years earlier because widespread 

interface movement generally causes additional localized 

upconing.

Average-Recharge Scenario 4

Simulation of scenario 4 indicated that wellfields at North 

Road and Alvah’s Lane, in addition to those indicated during 

scenarios 1, 2, and 3, show some upward interface movement 

toward the well screen. Wellfields that were not susceptible 

to saltwater intrusion during scenario 4 were those at Ackerly 

Pond, Kenney’s Road, Middle Road, North Road (Peconic), 

Rocky Point Road, and the hypothetical wellfield parcels 

shown in figure 3E.

Results of Drought Simulations

Simulation of drought conditions entailed application 

of a 20-percent decrease in the long-term rate of recharge 

38 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
from precipitation and an offsetting equivalent increase in 

the rate of agricultural withdrawal during the 5-year period 

corresponding to 2011-15. This period was chosen because it 

is the midpoint of the hypothetical period (2006-2020), and 

allows 5 years of recovery after the drought. The decreased 

rate of recharge during the hypothetical drought is essentially 

the same as that calculated for the study area during the 

drought of 1962-66, which affected most of the Northeast. The 

clearest indications of saltwater intrusion (scenarios 3 and 4), 

depicted in figures 30D and E, respectively, appear after the 

drought is over and normal recharge has resumed. This result 

indicates that these pumping rates may not be sustainable for 

the long term.

Drought Scenario 1

Upward movement of the saltwater interface in response 

to the addition of drought conditions to scenario 1 was greatest 

at well S-105669 at the Inlet Drive wellfield (fig. 3C), where 

the interface moved up 2 ft during the drought (not illustrated). 

Drought Scenario 2

Upward movement of the saltwater interface in response 

to the drought condition in scenario 2 was greatest at well 

S-15795 (Islands End, location shown in fig. 3C), where the 

interface moved up 2 ft during the drought (not illustrated).

Figure 30. Vertical sections showing model-generated heads and freshwater-saltwater-interface positions at selected wells in 

scenarios 1 through 4 under simulated average-recharge conditions in North Fork model, Suffolk County, N.Y.: A. Scenario 1: Well 

S105669 (redeveloped as S108347). B. Scenario 2: Well S15795. (Well locations are shown in figs. 3C-E; pumpage values for each 

scenario are given in table 11.) (Location is shown in fig. 1)

-125

-75

5 0

0

-5

-10

-50

-25

-100

5

0

-5

-10

-125

-75

0

-50

-25

-15 -100

-20

1941 1946 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006 2011 2016 2021

-15

-20

1941 1946 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006 2011 2016 2021

A. Scenario 1: Well S-105669 (redeveloped as S-108347)

B. Scenario 2: Well S-15795 

SIMULATED WATER LEVEL

WELL-SCREEN INTERVAL

SIMULATED INTERFACE

WELL-SCREEN INTERVAL

SIMULATED INTERFACE

SIMULATED 

WATER LEVEL

UPPER CONFINING LAYER

UPPER CONFINING LAYER

LOWER CONFINING LAYER

WATER LEVEL, NGVD 1929

INTERFACE AND CONFINING LAYER

 ALTITUDE AND WELL-SCREEN INTERVAL, 

NGVD 1929

WATER LEVEL, NGVD 1929

INTERFACE AND CONFINING LAYER

 ALTITUDE AND WELL-SCREEN INTERVAL, 

NGVD 1929

Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface 39
Figure 30. (continued) Vertical sections showing model-generated heads and freshwater-saltwater-interface positions 

at selected wells in scenarios 1 through 4 under simulated average-recharge conditions in North Fork model, Suffolk 

County, N.Y.: C. Scenario 3: Well S105669(redeveloped as S108347). D. Drought scenario 3: Well H19001. E. Drought 

scenario 4: Well S24851. (Well locations are shown in figs. 3C-E; pumpage values for each scenario are given in table 11.) 

(Location is shown in fig. 1)

5

0

-5

-10 -125

-75

0

-50

-25

-100

10

1941 1946 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006 2011 2016 2021

E. Drought scenario 4: Well S-24851

SIMULATED WATER LEVEL

WELL-SCREEN INTERVAL

SIMULATED INTERFACE

UPPER CONFINING LAYER

WATER LEVEL, NGVD 1929

INTERFACE AND CONFINING LAYER

 ALTITUDE AND WELL-SCREEN INTERVAL, 

NGVD 1929

LOWER CONFINING LAYER

10

0

5

-10

-300

-250

-200

-175

-275

-15

-5

1941 1946 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006 2011 2016 2021

D. Drought scenario 3: Well H-190001

SIMULATED WATER LEVEL

SIMULATED INTERFACE

WATER LEVEL, NGVD 1929

INTERFACE ALTITUDE AND

WELL-SCREEN INTERVAL, 

NGVD 1929

WELL-SCREEN INTERVAL

-225

5

0

-5

-10

-125

-75

0

-50

-25

-15 -100

-20

1941 1946 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006 2011 2016 2021

C. Scenario 3: Well S-105669 (redeveloped as S-108347)

SIMULATED WATER LEVEL

WELL-SCREEN INTERVAL

SIMULATED INTERFACE

UPPER CONFINING LAYER

WATER LEVEL, NGVD 1929

INTERFACE AND CONFINING LAYER

 ALTITUDE AND WELL-SCREEN INTERVAL, 

NGVD 1929

40 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Drought Scenario 3

Upward movement of the saltwater interface in response 

to the drought condition in scenario 3 was greatest at well 

S-190001 at the Alvah’s Lane wellfield (fig. 30D), where the 

interface moved up 3 ft during the drought. 

Drought Scenario 4

A breakthrough of the saltwater interface through the 

lower confining unit (fig. 30E) occurs in 2018 at well S24851 

at the North Road wellfield (fig. 3D). The upper confining unit 

is not present at this location; thus, the main impediment to 

movement of the interface to the well screen has been crossed.

Summary and Conclusions

Ground water, the sole source of drinking water on 

the North Fork of eastern Long Island, occurs only in a 

series of hydraulically isolated freshwater lenses of varying 

thickness. Future increases in the demand for drinking water 

and irrigation water could, in a prolonged drought, cause 

drawdowns that induce saltwater intrusion and upconing at 

public-supply wells. As the demand for the limited supply of 

freshwater increases, information on the effects of current and 

future pumping and drought on ground-water levels within 

the freshwater systems, and especially on the position of 

the freshwater-saltwater interface, will be needed by watersupply managers. This need for information on the ability 

of the freshwater systems to meet future increased demands 

prompted a study by the USGS, in cooperation with SCWA, to 

develop a ground-water-flow model of the North Fork aquifer 

system and to analyze the effects of simulated pumping 

and recharge rates on water levels and the position of the 

freshwater-saltwater interface. 

The modeled area encompasses all of the Town of 

Southold and the easternmost part of the Town of Riverhead. 

The hydrogeology of the North Fork was evaluated from 

published information and from exploratory drilling of 

five deep wells during this study. The hydraulic properties 

of hydrogeologic units were compiled from previous 

investigations of unconsolidated deposits on Long Island and 

those in similar settings on western Cape Cod, Massachusetts.

The code used for the model was SHARP, a quasithree dimensional, finite-difference method of simulating 

freshwater and saltwater flow simultaneously. The position 

of the freshwater-saltwater interface was simulated in four 

hydrogeologic units: (1) the unconfined part of the upper 

glacial aquifer, (2) the part of upper glacial aquifer that 

underlies an upper confining unit, (3) the part of the upper 

glacial aquifer that underlies a lower confining unit, and (4) 

the Magothy aquifer. The active model boundary extends 

vertically through all layers and coincides with natural 

hydrologic boundaries where possible, or is specified at 

locations at sufficient distance from points of stress so as not 

to affect simulation results. 

The model was calibrated under a quasi-steady-state 

simulation of 1994 average annual conditions. Modelgenerated water levels were compared statistically with 

water levels measured in March-April 1994, and the modelgenerated freshwater-saltwater interface position was 

compared with long-term estimated equilibrium positions. 

Model-generated water levels based on the transient-state 

simulation of 1941-2005 seasonal conditions were plotted as 

time series along with historical hydrographs.

Ground-water levels and the freshwater-saltwater 

interface were simulated initially for a long-term (250-year) 

period under average annual pumping and recharge conditions 

that generally corresponded to those of 1994. When the 

simulated heads and interface positions reached a quasi-steady 

state deemed representative of 1994 conditions, a long-term 

(250-year) simulation under average annual predevelopment 

(nonpumping) conditions was run. Simulated predevelopment 

heads and interface positions were then used as initial 

conditions for a simulated 65-year period (1941-2005) at 

seasonal pumping and recharge rates. The simulated heads and 

interface positions obtained at the end of this period were then 

used as initial conditions for a simulated 15-year period under 

seasonal conditions corresponding to years 2006-20. Two sets 

of four water-supply scenarios—one set with average-recharge 

conditions, the other with the same conditions except for a 

5-year simulated drought (2011-15)—were run in which future 

water-use projections were applied. The simulated drought 

conditions were represented as a 20-percent decrease in the 

long-term rate of recharge from precipitation and a 20-percent 

increase in the 1999 agricultural pumpage during the 5-year 

drought.

Upward movement of the freshwater-saltwater interface 

during the hypothetical scenarios should be considered a 

cause for concern if there is a potential for saltwater intrusion; 

namely, if the interface reaches a position within 50 ft of a 

well screen, if a large percent change occurs in the distance 

between the interface and the well screen, or if the interface 

moves through a confining unit. Simulations predict there 

is a potential for saltwater intrusion at the wellfields of Inlet 

Drive, Brecknock Hall, Main Bayview Road, Islands End, 

North Road and Alvah’s Lane. Wellfields that did not show a 

potential for saltwater intrusion were those at Ackerly Pond, 

Kenney’s Road, Middle Road, Rocky Point Road, and the 

hypothetical-wellfield parcels. 

Summary and Conclusions 41
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42 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
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44 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York

Appendix

 1. Estimated 1957 annual and seasonal pumpage on the North Fork, Suffolk County, N.Y., by water-supply district . . . . . . . . . . 45

 2. Estimated 1994 public-supply pumpage on the North Fork, Suffolk County, N.Y., by water-supply district . . . . . . . . . . . . . . . . . 46

 3. 1998 pumpage by public water-supply districts on the North Fork, Suffolk County, N.Y. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

 4. Reported and estimated annual 1993-95 pumpage by commercial-supply wells on the North Fork, Suffolk County, N.Y. . . . . 50

 5. Annual, seasonal, and long-term precipitation at Bridgehampton, Greenport, and Riverhead, Suffolk County, N.Y., and 

corresponding recharge from land surface and lakes, 1955-99 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

 6. Modeled public water-supply pumpage and return-flow rates for 1957, 1994, 1998, and 2020 on the North Fork, Suffolk 

County, N.Y. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

 7. Pumpage at present, planned, and proposed public water-supply wellfields on the North Fork, Suffolk County, N.Y, 

Scenario 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

 8. Pumpage at present, planned, and proposed public water-supply wellfields on the North Fork, Suffolk County, N.Y., 

Scenario 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

 9. Pumpage at present, planned, and proposed public water-supply wellfields on the North Fork, Suffolk County, N.Y., 

Scenario 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

 10. Pumpage at present, planned, and proposed commercial-supply wells on the North Fork, Suffolk County, N.Y., 

Scenario 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Appendix 1. Estimated 1957 annual and seasonal pumpage on the North Fork, Suffolk County, N.Y., by water-supply district 

[Well locations are shown in fig. 21. gal/min, gallons per minute. ft3/s, cubic feet per second. Dash (--) indicates no data available.] 

Wellfield 

name

Well 

no.

Well

identifier

Well 

capacity

(gal/min)

Estimated 

annual

pumpage

(gal x 103)

Average annual

pumpage

Monthly pumping rate 

June through August Septe

Rate Percent of 

capacity

Rate Percent of 

capacity

R

gal/min ft 

3/s gal/min ft3/s gal/min 

FORMER VILLAGE OF GREENPORT WATER SUPPLY (wellfield names are those associated with former Greenport Water District)

Plant no. 1 -- S-1668 a150 19,950 38.0 0.085 25.30 57.7 0.129 38.46 31.4 

-- S-1669 a150 19,950 38.0 0.085 25.30 57.7 0.129 38.46 31.4 

Plant no. 3 1 S-1673 167 22,167 42.2 0.094 25.30 64.1 0.143 38.46 34.9 

2 S-1674 167 22,167 42.2 0.094 25.30 64.1 0.143 38.46 34.9 6 S-1678 167 22,167 42.2 0.094 25.30 64.1 0.143 38.46 34.9 

Plant no. 4 6 S-3697 200 26,600 50.6 0.113 25.30 76.9 0.171 38.46 41.8 

7 S-3698 200 26,600 50.6 0.113 25.30 76.9 0.171 38.46 41.8 

subtotalb 1,201 159,601 303.7 0.677 461.6 1.028 251.1 

FORMER NORTH FORK WATER COMPANY

Plant no. 5 1 S-169 250 6,250 11.9 0.026 4.76 18.1 0.040 7.23 9.8 

2 S-170 a250 6,250 11.9 0.026 4.76 18.1 0.040 7.23 9.8 3 S-3045 250 6,250 11.9 0.026 4.76 18.1 0.040 7.23 9.8 4 S-4163 50 1,250 2.4 0.005 4.76 3.6 0.008 7.23 2.0 

subtotalb 800 20,000 38.1 0.085 57.89 0.129 31.5 

TOTALb 2,001 179,600 341.7 0.761 519.4 1.157 282.5 

aEstimated well capacity.b Total may not equal the sum of values because of rounding to significant digits.
Appendix 2.. Estimated 1994 public-supply pumpage on the North Fork, Suffolk County, N.Y., by water-supply district

[Well locations are shown in fig. 21. cap., capacity. Dash (--) indicates no data available. SCWA, Suffolk County Water Authority] 

Monthly pumpage (thousands of gallons)

Wellfield 

name

Well 

no.

Well 

identifiera

Well 

capacity.

(gal/min) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov 

FORMER VILLAGE OF GREENPORT WATER SUPPLY (wellfield names are those associated with former Greenport Water District)Plant no. 3 1 1673 167 30 0 33 0 0 3 0 54 0 39 Plant no. 4 6 3697 200 3 0 22 0 18 18 0 56 6 0 

7 3698 200 30 0 44 0 20 18 0 282 24 0 8 15795 300 27 0 24 0 20 18 0 111 12 0 

Plant no. 6 1 24850 500 3,705 3,719 3,055 988 862 5,936 3,956 285 316 942 

2 24851 500 3,875 2,120 1,413 3,366 3,161 5,668 5,464 1,224 1,193 5,236 2

Plant no. 7 1 33775 500 4,205 5,196 5,940 4,379 3,099 6,139 5,529 6,429 4,494 4,715 3

2 93794 500 5,116 4,244 5,737 3,953 4,792 6,399 4,189 9,466 6,703 3,178 4

Plant no. 8 1 71873 500 0 0 21 0 0 36 5 14 13 0 Plant no. 9 1 76772 500 0 0 22 0 0 541 1,214 2,002 2,508 2,661 2Plant no. 12 1 97501 500 2,567 1,218 3,449 5,165 7,969 8,737 15,244 10,984 9,694 5,541 5Plant no. 15 1 97502 500 4,698 3,821 3,758 6,172 9,489 9,483 15,304 9,768 6,191 3,745 2Subtotalc 4,867 24,256 20,318 23,518 24,023 29,430 42,996 50,905 40,675 31,154 26,057 21SUFFOLK COUNTY WATER AUTHORITY--MATTITUCK ZONEInlet Drive 1 6513 200 755 798 594 483 0 0 0 0 0 0 

1A 105669 200 0 0 0 0 0 0 331 1,238 1,101 2,048 

2 17835 200 0 11 22 26 6 17 217 15 29 0 

Sunset Dr. 1 94138 130 702 545 473 563 1,485 3,362 3,740 1,889 1,374 122 

Subtotalc 730 1,457 1,354 1,089 1,072 1,491 3,379 4,288 3,142 2,504 2,170 1

SUFFOLK COUNTY WATER AUTHORITY--SOUTHOLD ZONEb

Main 

Bayview Road

1 89754 30 -- -- -- -- -- -- -- 7 36 19 2 94274 30 -- -- -- -- -- -- -- 72 27 14 3 89756 25 -- -- -- -- -- -- -- 23 16 27 

Subtotalc 85 -- -- -- -- -- -- -- 102 79 60 

TOTALc 5,682 25,713 21,672 24,607 25,095 30,921 46,375 55,193 43,919 33,737 28,287 22

TOTAL PUMPAGE, BY SEASONGreenport Water District- May through October 221,217 SCWA--Southold Zoneb - May thr

November through April 133,693 November 

Subtotalc 354,910 

SCWA--Mattituck Zone- May through October 16,974

November through April 8,095

Subtotalc 25,069

a Prefix S for Suffolk County is omitted.b Pumpage subtotals for Suffolk County Water Authority--Southold zone include only 5 months of pumpage data. c Total may not equal the sum of values because of rounding to significant digits.
Appendix 2.. (continued) Estimated 1994 public-supply pumpage on the North Fork, Suffolk County, N.Y., by water-supply district 

[gal/min, gallons per minute; ft3/s, cubic feet per second] Wellfield name

Well 

no.

Well

identifiera

Average annual

pumpage

June through August 

pumpage

September through May 

pumpage

Rate Percent of 

capacity

Rate Percent of 

capacity

Rate Percent of 

gal/min ft capacity 3/s gal/min ft3/s gal/min ft3/s

FORMER VILLAGE OF GREENPORT WATER SUPPLY (wellfield names are those associated with former Greenport Water District)

Plant no. 3 1 1673 0.3 0.001 0.19 0.4 0.001 0.26 .03 0.001 0.17Plant no. 4 6 3697 0.3 0.001 0.14 0.6 0.001 0.28 0.2 0.000 0.09

7 3698 0.9 0.002 0.43 2.3 0.005 1.13 0.4 0.001 0.198 15795 0.5 0.001 0.15 1.0 0.002 0.32 0.3 0.001 0.09

Plant no. 6 1 24850 45.9 0.102 9.19 76.8 0.171 15.36 35.5 0.079 7.11

2 24851 71.2 0.159 14.24 93.3 0.208 18.65 63.8 0.142 12.76

Plant no. 7 1 33775 110.1 0.245 22.02 136.6 0.304 27.32 101.2 0.225 20.24

2 93794 118.8 0.265 23.76 151.4 0.337 30.27 107.8 0.240 21.57

Plant no. 8 1 71873 0.2 0.001 0.05 0.4 0.001 0.08 0.2 0.000 0.03Plant no. 9 1 76772 26.1 0.058 5.21 28.4 0.063 5.67 25.3 0.056 5.06Plant no. 12 1 97501 151.3 0.337 30.26 263.9 0.588 52.79 113.4 0.253 22.67Plant no. 15 1 97502 149.6 0.333 29.93 260.8 0.581 52.17 112.2 0.250 22.43Subtotalc 675.2 1.504 1,015.8 2.263 560.5 1.249

SUFFOLK COUNTY WATER AUTHORITY--MATTITUCK ZONE

Inlet Drive 1 6513 5.0 0.011 2.50 0.0 0.000 0.00 6.7 0.015 3.35

1A 105669 12.4 0.028 6.18 11.8 0.026 5.92 12.5 0.028 6.272 17835 0.8 0.002 0.40 1.9 0.004 0.94 0.4 0.001 0.22

Sunset Dr. 1 94138 29.5 0.066 22.71 67.9 0.151 52.21 6.6 0.037 12.78Subtotalc 47.7 0.106 81.6 0.182 36.3 0.081

SUFFOLK COUNTY WATER AUTHORITY--SOUTHOLD ZONEb

Main

 Bayview 

 Road 1 89754 0.6 0.001 1.92 0.2 0.000 0.53 0.7 0.002 2.27

2 94274 0.8 0.002 2.74 1.6 0.004 5.43 0.6 0.001 2.063 89756 0.5 0.001 2.06 0.5 0.001 2.08 0.5 0.001 2.06

Subtotalc 1.9 0.004 2.3 0.005 1.8 0.004TOTALc 724.9 1.615 1,099.7 2.450 598.6 1.334
 Appendix 3. 1998 pumpage by public water-supply districts on the North Fork, Suffolk County, N.Y. 

[Wellfield locations are shown in fig. 3. cap., capacity; %, percent; gal/min, gallons per minute; ft3/s, cubic feet per second]

Monthly pumpage (thousands of gallons)

Wellfield 

name

Well 

no.

Well

identifier

Well cap.

(gal/min) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov 

SUFFOLK COUNTY WATER AUTHORITY - MATTITUCK ZONEInlet Drive 1A S-105669 200 831 436 402 863 417 974 2,332 1,953 1,399 1,074 962 

2A S-108347 200 189 386 440 301 1,207 1,240 1,708 1,653 1,279 1,100 936 

Laurel Lake 1 S-101755 250 39 39 20 58 17 33 34 17 49 16 16 

2 S-106415 250 911 771 1,030 1,572 1,483 1,997 2,736 2,793 1,691 994 844 

Sunset Drive 1 S-94138 130 18 18 0 0 946 25 170 732 804 425 226 

 Subtotala 1,030 1,988 1,650 1,892 2,794 4,070 4,269 6,980 7,148 5,222 3,608 2,985 

SUFFOLK COUNTY WATER AUTHORITY - SOUTHOLD ZONEAckerly 

Pond 1 S-33775 340 346 764 507 510 2,366 2,356 5,447 2,734 1,071 0 0 

2 S-93794 500 207 592 1,175 1,869 72 0 1,047 6,887 2,366 2,815 2,746 

Brecknock 

Hall 1 S-76772 200 3,495 3,278 3,180 2,562 3,282 3,168 3,132 2,946 1,770 2,568 2,922 

Kenneys 

Road 1 S-97501 500 8,977 7,668 7,154 7,843 11,059 10,899 16,539 13,007 11,255 9,488 10,418 

Main 

Bayview 

Road. 1 S-89754 30 27 15 54 59 111 106 151 148 30 4 3 

2 S-94274 30 12 9 15 3 18 20 24 69 114 32 12 3 S-89756 25 0 4 38 1 3 3 2 27 126 6 2 

Middle Road 1 S-97502 500 8,012 5,156 7,512 7,650 10,119 12,286 13,138 11,431 13,819 10,131 5,845 Mill Lane 

(Peconic) 1 S-103522 300 0 0 0 0 0 594 377 450 450 923 393 

2 S-103523 300 0 0 0 0 0 260 363 320 1,067 796 641 

North Road 1 S-24850 500 141 443 543 533 1,893 2,523 4,196 4,366 1,830 818 831 

3 S-83475 425 23 89 1,222 622 0 0 29 5,405 2,007 2,059 1,090 

 Subtotala 3,650 21,240 18,017 21,400 21,652 28,923 32,215 44,444 47,789 35,905 29,640 24,903 

 TOTALa 4,735 23,471 19,873 23,524 24,697 33,453 36,930 52,091 55,773 41,723 33,737 28,253 Suffolk County Water Authority - Mattituck Zone May through October Suffolk County Water Authority - Mattituck Zone November through April Suffolk County Water Authority - Mattituck Zone total 
Average annual pumpage June through August September 

Wellfield 

name

Well 

no.

Well

identifier

Rate

% of cap.

Rate

% of cap.

Rate

gal/min ft 

3/s gal/min ft3/s gal/min ft

SUFFOLK COUNTY WATER AUTHORITY - MATTITUCK ZONEInlet Drive 1A S-105669 23.1 0.051 11.56 39.7 0.088 19.85 17.5 0

2A S-108347 20.7 0.046 10.37 34.7 0.077 17.37 16.0 0

Laurel Lake 1 S-101755 0.7 0.001 0.27 0.6 0.001 0.25 0.7 0

2 S-106415 34.1 0.076 13.66 56.8 0.127 22.73 26.5 0

Sunset Drive 1 S-94138 6.5 0.014 5.00 7.0 0.016 5.38 6.3 0

Subtotala 85.2 0.190 138.9 0.309 13.48 67.1 0

SUFFOLK COUNTY WATER AUTHORITY - SOUTHOLD ZONEAckerly Pond 1 S-33775 30.6 0.068 9.01 79.5 0.177 23.39 14.2 0

2 S-93794 43.7 0.097 8.74 59.9 0.133 11.98 38.2 0

Brecknock 

Hall 1 S-76772 67.1 0.149 33.53 69.8 0.155 34.90 66.1 0

Kenneys 

Road 1 S-97501 235.9 0.526 47.18 305.3 0.680 61.06 212.5 0

Main 

Bayview Rd. 1 S-89754 1.4 0.003 4.67 3.0 0.007 10.17 0.8 0

2 S-94274 0.7 0.002 2.48 0.9 0.002 2.84 0.7 03 S-89756 0.5 0.001 2.08 0.2 0.001 0.97 0.6 0

Middle Road 1 S-97502 210.2 0.468 42.05 278.2 0.620 55.64 187.4 0Mill Lane 

(Peconic) 1 S-103522 7.0 0.016 2.35 10.7 0.024 3.58 5.8 0

2 S-103523 7.3 0.016 2.42 7.1 0.016 2.37 7.3 0

North Road 1 S-24850 36.3 0.081 7.26 83.7 0.186 16.73 20.3 0

3 S-83475 25.1 0.056 5.91 41.0 0.091 9.65 19.7 0

 Subtotala 665.9 1.484 939.4 2.093 573.8 1

 TOTALa 760.8 1.695 1,092.9 2.435 648.8 1

a Total may not equal the sum of values because of rounding to significant digits.

Appendix 3. (Continued)1998 pumpage by public water-supply districts on the North Fork, Suffolk County, N.Y. 
Appendix 4. Reported and estimated annual 1993-95 pumpage by commercial-supply wells on the North Fork, 

Suffolk County, N.Y.

 [gal/min, gallons per minute; ft3/s, cubic feet per second; --, no data reported] 

1993-95 mean annual pumpage

Well 

Identifier Well use

Well 

capacity 

(gal/min)

Total pumpage (gallons) Total 

(gallons)

Flow rate Percent of 

1993 1994 1995 gal/min ft capacity 3/s

REPORTED PUMPAGE

S-31448 Irrigation 600 21,126,000 21,989,000 14,332,000 19,149,000 36.4 0.081 6.07

S-52086 Industrial 65 1,727,000 1,814,000 1,855,000 1,798,667 3.4 0.008 5.26

S-93628 Domestic 80 -- 0 2,611,000 1,305,500 2.5 0.006 3.10

S-94491 Irrigation 60 2,353,000 10,189,000 1,178,000 4,573,333 8.7 0.019 14.50

Subtotala 805 25,206,000 33,992,000 19,976,000 26,826,500 51.0 0.114

ESTIMATED PUMPAGE

S-11362 Irrigation 60 -- -- -- 1,999,491 3.8 0.008 6.34

S-11699 Domestic 25 -- -- -- 833,121 1.6 0.004 6.34

S-26049 Domestic 20 -- -- -- 666,497 1.3 0.003 6.34

S-33990 Domestic 30 -- -- -- 999,745 1.9 0.004 6.34

S-36799 General 200 -- -- -- 6,664,969 12.7 0.028 6.34

S-45809 Domestic 20 -- -- -- 666,497 1.3 0.003 6.34

S-45810 Domestic 20 -- -- -- 666,497 1.3 0.003 6.34

S-45811 Domestic 20 -- -- -- 666,497 1.3 0.003 6.34

S-45812 Domestic 20 -- -- -- 666,497 1.3 0.003 6.34

S-84076 Domestic 20 -- -- -- 666,497 1.3 0.003 6.34

S-98991 Irrigation 500 -- -- -- 16,662,422 31.7 0.071 6.34

S-101947 Domestic 20 -- -- -- 666,497 1.3 0.003 6.34

Subtotala 955 -- -- -- 31,825,227 60.6 0.135

TOTALa 1,760 25,206,000 33,992,000 19,976,000 58,651,727 111.6 0.249

a

Total may not equal the sum of values because of rounding to significant digits.

50 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Appendix 5. Annual, seasonal, and long-term precipitation at Bridgehampton, Greenport, and Riverhead,

Suffolk County, N.Y., and corresponding recharge from land surface and lakes, 1955-99

[Precipitation values are in inches. Boldface values are means for multiple years. --, no data available. Locations are shown in fig. 1.]

a Long-term precipitation data incomplete for 1 or more years; data for those years were not used to compute long-term mean value.

b Greenport recharge data for 1955-57 and 1998 estimated from Bridgehampton records and from the ratio of 1959-99 values. 

c Precipitation data for the following years and stations were unavailable; annual values for the stated months were estimated

from Bridgehampton records: Greenport - September 1994 and October 1997. Riverhead - September 1957 and April 1998.

Station Period a

P r e c i p i t a t i o n

Calendar year October 15 through May 15 Calculated recharge

Total

50 percent

of total Total

75 percent 

of total

90 percent 

of total Land Lakes

BRIDGEHAMPTON 1955 43.26 21.63 26.10 19.58 23.49 21.53 9.56

1956 45.27 22.64 32.25 24.19 29.03 26.61 11.57

1957 35.79 17.90 22.87 17.15 20.58 18.87 2.09

1955-57 mean 41.44 20.72 27.07 20.31 24.37 22.34 7.74

1962 46.61 23.31 25.61 19.21 23.05 21.13 12.91

1963 38.23 19.12 22.74 17.06 20.47 18.76 4.53

1964 38.16 19.08 29.49 22.12 26.54 24.33 4.46

1965 30.67 15.34 25.04 18.78 22.54 20.66 -3.03

1966 37.28 18.64 15.23 11.42 13.71 12.56 3.58

1962-66 mean 38.19 19.10 23.62 17.72 21.26 19.49 4.49

1992 45.11 22.56 20.36 15.27 18.32 16.80 11.41

1993 45.46 22.73 30.56 22.92 27.50 25.21 11.76

1994 47.97 23.99 35.43 26.57 31.89 29.23 14.27

1992-94 mean 46.18 23.09 28.78 21.59 25.91 23.75 12.48

1996 67.54 33.77 36.95 27.71 33.26 30.48 33.84

1997 47.47 23.74 36.19 27.14 32.57 29.86 13.77

1998 55.79 27.90 47.63 35.72 42.87 39.29 22.09

1996-98 mean 56.93 28.47 40.26 30.19 36.23 33.21 23.23

1959-99 mean 46.08 23.04 28.81 21.61 25.93 23.77 12.38

GREENPORT b1955-57 mean -- -- -- 18.69 22.43 20.56 7.01

1962 42.03 21.02 21.46 16.10 19.31 17.70 8.33

1963 35.34 17.67 20.68 15.51 18.61 17.06 1.64

1964 44.31 22.16 26.95 20.21 24.26 22.23 10.61

1965 25.94 12.97 21.33 16.00 19.20 17.60 -7.76

1966 36.63 18.32 16.25 12.19 14.63 13.41 2.93

1962-66 mean 36.85 18.43 21.33 16.00 19.20 17.60 3.15

1992 43.82 21.91 20.82 15.62 18.74 17.18 10.12

1993 42.34 21.17 27.39 20.54 24.65 22.60 8.64 c1994 33.07 16.54 24.11 18.08 21.70 19.89 -0.63

1992-94 mean 39.74 19.87 24.11 18.08 21.70 19.89 6.04

1996 56.39 28.20 34.04 25.53 30.64 28.08 22.69 c1997 35.16 17.58 30.10 22.58 27.09 24.83 1.46

b1998 -- -- -- -- -- 36.17 20.01

1996-98 mean 45.78 22.89 32.07 24.05 28.86 29.70 14.72

1959-99 mean 44.91 22.46 26.52 19.89 23.87 21.88 11.21

RIVERHEAD 1955 40.92 20.46 24.55 18.41 22.10 20.25 7.22

1956 44.64 22.32 31.11 23.33 28.00 25.67 10.94 c1957 43.15 21.58 23.89 17.92 21.50 19.71 9.45

1955-57 mean 42.90 21.45 26.52 19.89 23.87 21.88 9.20

1962 45.03 22.52 23.48 17.61 21.13 19.37 11.33

1963 36.09 18.05 22.13 16.60 19.92 18.26 2.39

1964 41.31 20.66 28.92 21.69 26.03 23.86 7.61

1965 33.71 16.86 24.99 18.74 22.49 20.62 0.01

1966 36.71 18.36 14.37 10.78 12.93 11.86 3.01

1962-66 mean 38.57 19.29 22.78 17.08 20.50 18.79 4.87

1992 45.09 22.55 17.22 12.92 15.50 14.21 11.39

1993 45.58 22.79 28.85 21.64 25.97 23.80 11.88

1994 42.51 21.26 31.41 23.56 28.27 25.91 8.81

1992-94 mean 44.39 22.20 25.83 19.37 23.24 21.31 10.69

1996 57.46 28.73 32.76 24.57 29.48 27.03 23.76

1997 38.38 19.19 33.20 24.90 29.88 27.39 4.68 c1998 52.66 26.33 42.47 31.85 38.22 35.04 18.96

1996-98 mean 49.50 24.75 36.14 27.11 32.53 29.82 15.80

1959-99 mean 45.33 22.66 27.12 20.34 24.41 22.37 11.63

Appendix 51
Appendix 6. Modeled public water-supply pumpage and return-flow rates for 1957, 1994, 1998, and 2020 on the North Fork, 

Suffolk County, N.Y.

[est., estimated. SWCA, Suffolk County Water Authority. --, no data available]

Pumpage (thousands of gallons) Estimated return flow 

Water-supply 

district

Service 

area (est.)

Annual total

May -

October

NovemberApril

Average 

annual

May through 

October

November 

through April

Acres inches inches inches 

1957 Conditionsa

Former Village of Greenport 

Water Supply 964 154,400 -- -- 5.01 6.25 3.78

Former North Fork Water 

Company 376 20,000 -- -- 1.66 2.30 1.03

1994 Conditionsb

Former Greenport Water 

District 2,729 354,910 221,217 133,693 4.07 5.07 3.07

Riverhead Water District 15,549 1,453,478 1,004,587 448,891 2.93 4.05 1.81

SWCA--Laurel Zone 54 -- -- -- 2.93 4.05 1.81

SWCA--Mattituck Zone 157 25,069 16,974 8,095 5.00 6.77 3.23

SWCA--Southold Zone 60 419 241 178 0.52 0.50 0.56

1998 Conditionsc

Riverhead Water District 15,549 1,453,478 1,004,587 448,891 2.93 4.05 1.81

SWCA--Mattituck Zone 752 44,768 31,296 13,472 1.86 2.61 1.12

SWCA--Southold Zone 3,572 350,004 218,917 131,087 3.07 3.84 2.30

2020 Conditionsc - Scenario 1

Riverhead Water District 15,549 1,453,478 1,004,587 448,891 2.93 4.05 1.81

SWCA--Mattituck Zone 806 44,768 31,296 13,472 1.74 2.43 1.05

SWCA--Southold Zone 3,946 350,004 218,917 131,087 2.78 3.47 2.08

2020 Conditionsc,d - Scenario 2

Riverhead Water District 15,549 1,453,478 1,004,587 448,891 2.93 4.05 1.81

SWCA--Southold Zone 10,810 734,560 465,576 268,984 2.13 2.70 1.56

2020 Conditionsc,d - Scenario 3

Riverhead Water District 15,549 1,453,478 1,004,587 448,891 2.93 4.05 1.81

SWCA--Southold Zone 10,810 1,056,186 669,428 386,758 3.06 3.88 2.24

2020 Conditionsc,d - Scenario 4

Riverhead Water District 15,549 1,453,478 1,004,587 448,891 2.93 4.05 1.81

SWCA--Southold Zone 10,810 1,441,151 913,425 527,726 4.17 5.29 3.06

a Pumpage and estimated 1957 monthly return flow for former Village of Greenport Water Supply excludes 5,200,000 gallons pumped for irrigation. 

Estimated 1957 return flows for former Village of Greenport Water Supply are based on ratio of May through October to 1994 annual total pumgage 

by former Greenport Water District.

b Pumpage and estimated monthly return flows in 1994 for SWCA - Laurel Zone are from Riverhead Water District. 

Estimated monthly return-flow rates in 1994 for SWCA - Southold zone are estimated from 5 months of pumpage data. 

c 1998 and 2020 pumpage and estimated monthly return-flow rates for Riverhead Water District are from 1994 data for this system. 

d Estimated monthly return flow for SWCA 2020 scenarios 2-4 are based on ratio of May through October 

to 1998 annual total pumgage for this system.

52 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York
Appendix 7. Pumpage at present, planned, and proposed public water-supply wellfields on the North Fork, Suffolk County, N.Y, Scenario 2 

[Well identifier between 190000 and 199999 denotes planned well; identifier with number greater than 200000 denotes proposed well. Well-identifier prefix “S” 

is omitted.] 

Monthly pumping rate

Wellfield name

Well 

no.

Well

 identifier

Well 

capacity

(gal/min)

Annual

total 

pumpage

(gal x 103)

Average annual June through August September through May

Flow rate

Percent 

of 

capacity

Flow rate

Percent 

of 

capacity

Flow rate

Percent 

of 

gal/min ft capacity 3/s gal/min ft3/s gal/min ft3/s

Scenario 2--Increase number of connections to 8,930, serving 67 percent of 13,313 housing units in 1998.

SUFFOLK COUNTY WATER AUTHORITY--SOUTHOLD ZONE

Ackerly Pond 1 33775 340 28,281 53.8 0.120 15.83 77.5 0.173 22.79 45.9 0.102 13.50

2 93794 500 41,590 79.1 0.176 15.83 113.9 0.254 22.79 67.5 0.150 13.50

Alvah’s Lane 1 190001 50 4,159 7.9 0.018 15.83 11.4 0.025 22.79 6.8 0.015 13.50

2 190002 100 8,318 15.8 0.035 15.83 22.8 0.051 22.79 13.5 0.030 13.50

Brecknock Hall 1 76772 200 16,636 31.7 0.071 15.83 45.6 0.102 22.79 27.0 0.060 13.50

Inlet Drive 1A 105669 200 16,636 31.7 0.071 15.83 45.6 0.102 22.79 27.0 0.060 13.50

2A 108347 200 16,636 31.7 0.071 15.83 45.6 0.102 22.79 27.0 0.060 13.50

Island’s End 6 3697 200 16,636 31.7 0.071 15.83 45.6 0.102 22.79 27.0 0.060 13.50

7 3698 200 16,636 31.7 0.071 15.83 45.6 0.102 22.79 27.0 0.060 13.50

8 15795 300 24,954 47.5 0.106 15.83 68.4 0.152 22.79 40.5 0.090 13.50

Kenneys Road 1 97501 500 41,590 79.1 0.176 15.83 113.9 0.254 22.79 67.5 0.150 13.50

Laurel Lake 1 101755 250 20,795 39.6 0.088 15.83 57.0 0.127 22.79 33.8 0.075 13.50

2 106415 250 20,795 39.6 0.088 15.83 57.0 0.127 22.79 33.8 0.075 13.50

Main Bayview Road 1 89754 30 2,495 4.7 0.011 15.83 6.8 0.015 22.79 4.1 0.009 13.50

2 94274 30 2,495 4.7 0.011 15.83 6.8 0.015 22.79 4.1 0.009 13.50

3 89756 25 2,079 4.0 0.009 15.83 5.7 0.013 22.79 3.4 0.008 13.50

Middle Road 1 97502 500 41,590 79.1 0.176 15.83 113.9 0.254 22.79 67.5 0.150 13.50

Mill Lane (Peconic) 1 103522 300 24,954 47.5 0.106 15.83 68.4 0.152 22.79 40.5 0.090 13.50

2 103523 300 24,954 47.5 0.106 15.83 68.4 0.152 22.79 40.5 0.090 13.50

Moore’s Lane 1 1673 167 13,891 26.4 0.059 15.83 38.1 0.085 22.79 22.6 0.050 13.50

2 1674 167 13,891 26.4 0.059 15.83 38.1 0.085 22.79 22.6 0.050 13.50

6 1678 167 13,891 26.4 0.059 15.83 38.1 0.085 22.79 22.6 0.050 13.50

North Road 1 24850 500 41,590 79.1 0.176 15.83 113.9 0.254 22.79 67.5 0.150 13.50

2 24851 500 41,590 79.1 0.176 15.83 113.9 0.254 22.79 67.5 0.150 13.50

3 83475 425 35,351 67.3 0.150 15.83 96.9 0.216 22.79 57.4 0.128 13.50

North Road (Peconic) 1 113387 150 12,477 23.7 0.053 15.83 34.2 0.076 22.79 20.3 0.045 13.50

Parcel number 1 1 200001 150 12,477 23.7 0.053 15.83 34.2 0.076 22.79 20.3 0.045 13.50

Parcel number 7 1 200007 150 12,477 23.7 0.053 15.83 34.2 0.076 22.79 20.3 0.045 13.50

Parcel number 10 1 200010 300 24,954 47.5 0.106 15.83 68.4 0.152 22.79 40.5 0.090 13.50

Parcel number 15 1 200015 150 12,477 23.7 0.053 15.83 34.2 0.076 22.79 20.3 0.045 13.50

Parcel number 16 1 200016 300 24,954 47.5 0.106 15.83 68.4 0.152 22.79 40.5 0.090 13.50

Rocky Point Road 1 115103 50 4,159 7.9 0.018 15.83 11.4 0.025 22.79 6.8 0.015 13.50

South Harbor Road 1 169 250 20,795 39.6 0.088 15.83 57.0 0.127 22.79 33.8 0.075 13.50

3 3045 250 20,795 39.6 0.088 15.83 57.0 0.127 22.79 33.8 0.075 13.50

4 4163 50 4,159 7.9 0.018 15.83 11.4 0.025 22.79 6.8 0.015 13.50

Sunset Drive 1 94138 130 10,813 20.6 0.046 15.83 29.6 0.066 22.79 17.6 0.039 13.50

The Long Way 1 71873 500 41,590 79.1 0.176 15.83 113.9 0.254 22.79 67.5 0.150 13.50

TOTALa 8,831 734,560 1,397.6 3.114 2,012.5 4.484 1,192.6 2.657

a Total may not equal the sum of values because of rounding to significant digits.

Appendix 53
Appendix 8. Pumpage at present, planned, and proposed public water-supply wellfields on the North Fork, Suffolk County, N.Y., Scenario 3 

[Well identifier between 190000 and 199999 denotes planned well; identifier with number greater than 200000 denotes proposed well. Well- identifier prefiix “S” is omitted.] 

Monthly pumping rate

Annual

total 

pumpage

(gal x 103)

Average annual June through August Septe

Wellfield name

Well 

no.

Well 

identifier

Well 

capacity

(gal/min)

Flow rate

Percent 

of capacity

Flow rate

Percent 

of capacity

Flow 

gal/min ft 

3/s gal/min ft3/s gal/min 

Scenario 3--Increase number of connections to 12,840, serving 96 percent of 13,313 housing units in 1998.SUFFOLK COUNTY WATER AUTHORITY—SOUTHOLD ZONEAckerly Pond 1 33775 340 40,664 77.4 0.172 22.75 111.4 0.248 32.77 66.0 

2 93794 500 59,800 113.8 0.253 22.75 163.8 0.365 32.77 97.1 

Alvah’s Lane 1 190001 50 5,980 11.4 0.025 22.75 16.4 0.037 32.77 9.7 

2 190002 100 11,960 22.8 0.051 22.75 32.8 0.073 32.77 19.4 

Brecknock Hall 1 76772 200 23,920 45.5 0.101 22.75 65.5 0.146 32.77 38.8 

Inlet Drive 1A 105669 200 23,920 45.5 0.101 22.75 65.5 0.146 32.77 38.8 

2A 108347 200 23,920 45.5 0.101 22.75 65.5 0.146 32.77 38.8 

Island’s End 6 3697 200 23,920 45.5 0.101 22.75 65.5 0.146 32.77 38.8 

7 3698 200 23,920 45.5 0.101 22.75 65.5 0.146 32.77 38.8 8 15795 300 35,880 68.3 0.152 22.75 98.3 0.219 32.77 58.3 

Kenneys Road 1 97501 500 59,800 113.8 0.253 22.75 163.8 0.365 32.77 97.1 Laurel Lake 1 101755 250 29,900 56.9 0.127 22.75 81.9 0.183 32.77 48.5 

2 106415 250 29,900 56.9 0.127 22.75 81.9 0.183 32.77 48.5 

Main Bayview Road 1 89754 30 3,588 6.8 0.015 22.75 9.8 0.022 32.77 5.8 

2 94274 30 3,588 6.8 0.015 22.75 9.8 0.022 32.77 5.8 3 89756 25 2,990 5.7 0.013 22.75 8.2 0.018 32.77 4.9 

Middle Road 1 97502 500 59,800 113.8 0.253 22.75 163.8 0.365 32.77 97.1 Mill Lane (Peconic) 1 103522 300 35,880 68.3 0.152 22.75 98.3 0.219 32.77 58.3 

2 103523 300 35,880 68.3 0.152 22.75 98.3 0.219 32.77 58.3 
Appendix 8. (Continued) Pumpage at present, planned, and proposed public water-supply wellfields on the North Fork, Suffolk County, N.Y., Scenario 

Wellfield name

Well 

no.

Well 

identifier

Well 

capacity

(gal/min)

Annual

total 

pumpage

(gal x 103)

Monthly pumping rate

Average annual June through August Septem

Flow rate

Percent 

of capacity

Flow rate

Percent 

of capacity

Flow 

gal/min ft 

3/s gal/min ft3/s gal/min 

Moore’s Lane 1 1673 167 19,973 38.0 0.085 22.75 54.7 0.122 32.77 32.4 

2 1674 167 19,973 38.0 0.085 22.75 54.7 0.122 32.77 32.4 6 1678 167 19,973 38.0 0.085 22.75 54.7 0.122 32.77 32.4 

North Road 1 24850 500 59,800 113.8 0.253 22.75 163.8 0.365 32.77 97.1 

2 24851 500 59,800 113.8 0.253 22.75 163.8 0.365 32.77 97.1 3 83475 425 50,830 96.7 0.215 22.75 139.3 0.310 32.77 82.5 

North Road (Peconic) 1 113387 150 17,940 34.1 0.076 22.75 49.2 0.110 32.77 29.1 

Parcel number 1 1 200001 150 17,940 34.1 0.076 22.75 49.2 0.110 32.77 29.1 Parcel number 7 1 200007 150 17,940 34.1 0.076 22.75 49.2 0.110 32.77 29.1 Parcel number 10 1 200010 300 35,880 68.3 0.152 22.75 98.3 0.219 32.77 58.3 Parcel number 15 1 200015 150 17,940 34.1 0.076 22.75 49.2 0.110 32.77 29.1 Parcel number 16 1 200016 300 35,880 68.3 0.152 22.75 98.3 0.219 32.77 58.3 Rocky Point Road 1 115103 50 5,980 11.4 0.025 22.75 16.4 0.037 32.77 9.7 

South Harbor Road 1 169 250 29,900 56.9 0.127 22.75 81.9 0.183 32.77 48.5 

3 3045 250 29,900 56.9 0.127 22.75 81.9 0.183 32.77 48.5 4 4163 50 5,980 11.4 0.025 22.75 16.4 0.037 32.77 9.7 

Sunset Drive 1 94138 130 15,548 29.6 0.066 22.75 42.6 0.095 32.77 25.2 The Long Way 1 71873 500 59,800 113.8 0.253 22.75 163.8 0.365 32.77 97.1 TOTALa 8,831 1,056,186 2,009.5 4.477 2,893.7 6.447 32.77 1,714.8 

a Total may not equal the sum of values because of rounding to significant digits.
Appendix 9. Pumpage at present, planned, and proposed public water-supply wellfields on the North Fork, Suffolk County, N.Y., Scenario 4 

{Well identifier between 190000 and 199999 denotes planned well; identifier greater than 200000 denotes proposed well. Prefix S is omitted.] 

Monthly pumping rate

Wellfield 

name

Well 

no.

Well 

identifier

Well 

capacity

(gal/min)

Annual

total pumpage

(gal x 103)

Average annual May through August Sep

Flow rate Percent of 

capacity

Flow rate Percent of 

capacity

Flo

gal/min ft 

3/s gal/min ft3/s gal/min 

Scenario 4 (Scenario 3 plus 4,680 connections serving 62 percent of 7,590 additional housing units at saturation)SUFFOLK COUNTY WATER AUTHORITY—SOUTHOLD ZONEAckerly Pond 1 33775 340 55,485 105.6 0.235 31.05 152.0 0.339 44.71 90.1 

2 93794 500 81,596 155.2 0.346 31.05 223.6 0.498 44.71 132.5 

Alvah’s Lane 1 190001 50 8,160 15.5 0.035 31.05 22.4 0.050 44.71 13.2 

2 190002 100 16,319 31.0 0.069 31.05 44.7 0.100 44.71 26.5 

Brecknock 

Hall 1 76772 200 32,638 62.1 0.138 31.05 89.4 0.199 44.71 53.0 

Inlet Drive 1A 105669 200 32,638 62.1 0.138 31.05 89.4 0.199 44.71 53.0 

2A 108347 200 32,638 62.1 0.138 31.05 89.4 0.199 44.71 53.0 

Island’s End 6 3697 200 32,638 62.1 0.138 31.05 89.4 0.199 44.71 53.0 

7 3698 200 32,638 62.1 0.138 31.05 89.4 0.199 44.71 53.0 8 15795 300 48,958 93.1 0.208 31.05 134.1 0.299 44.71 79.5 

Kenneys 

Road 1 97501 500 81,596 155.2 0.346 31.05 223.6 0.498 44.71 132.5 

Laurel Lake 1 101755 250 40,798 77.6 0.173 31.05 111.8 0.249 44.71 66.2 

2 106415 250 40,798 77.6 0.173 31.05 111.8 0.249 44.71 66.2 

Main 

Bayview Road 1 89754 30 4,896 9.3 0.021 31.05 13.4 0.030 44.71 7.9 

2 94274 30 4,896 9.3 0.021 31.05 13.4 0.030 44.71 7.9 3 89756 25 4,080 7.8 0.017 31.05 11.2 0.025 44.71 6.6 

Middle Road 1 97502 500 81,596 155.2 0.346 31.05 223.6 0.498 44.71 132.5 Mill Lane 

(Peconic) 1 103522 300 48,958 93.1 0.208 31.05 134.1 0.299 44.71 79.5 

2 103523 300 48,958 93.1 0.208 31.05 134.1 0.299 44.71 79.5 

a Total may not equal the sum of values because of rounding to significant digits.
Appendix 9. (continued) Pumpage at present, planned, and proposed public water-supply wellfields on the North Fork, Suffolk County, N.Y., Scen

Wellfield 

name

Well 

no.

Well 

identifier

Well 

capacity

(gal/min)

Annual

total pumpage

(gal x 103)

Monthly pumping rate

Average annual May through August Sep

Flow rate Percent of 

capacity

Flow rate Percent of 

capacity

Flo

gal/min ft 

3/s gal/min ft3/s gal/min 

Moore’s Lane 1 1673 167 27,253 51.9 0.116 31.05 74.7 0.166 44.71 44.2 

2 1674 167 27,253 51.9 0.116 31.05 74.7 0.166 44.71 44.2 6 1678 167 27,253 51.9 0.116 31.05 74.7 0.166 44.71 44.2 

North Road 1 24850 500 81,596 155.2 0.346 31.05 223.6 0.498 44.71 132.5 

2 24851 500 81,596 155.2 0.346 31.05 223.6 0.498 44.71 132.5 3 83475 425 69,357 132.0 0.294 31.05 190.0 0.423 44.71 112.6 

North Road 

(Peconic) 1 113387 150 24,479 46.6 0.104 31.05 67.1 0.149 44.71 39.7 

Parcel 

number 1 1 200001 150 24,479 46.6 0.104 31.05 67.1 0.149 44.71 39.7 

Parcel 

number 7 1 200007 150 24,479 46.6 0.104 31.05 67.1 0.149 44.71 39.7 

Parcel 

number 10 1 200010 300 48,958 93.1 0.208 31.05 134.1 0.299 44.71 79.5 

Parcel 

number 15 1 200015 150 24,479 46.6 0.104 31.05 67.1 0.149 44.71 39.7 

Parcel 

number 16 1 200016 300 48,958 93.1 0.208 31.05 134.1 0.299 44.71 79.5 

Rocky Point 

Road 1 115103 50 8,160 15.5 0.035 31.05 22.4 0.050 44.71 13.2 

South Harbor 

Road 1 169 250 40,798 77.6 0.173 31.05 111.8 0.249 44.71 66.2 

3 3045 250 40,798 77.6 0.173 31.05 111.8 0.249 44.71 66.2 4 4163 50 8,160 15.5 0.035 31.05 22.4 0.050 44.71 13.2 

Sunset Drive 1 94138 130 21,215 40.4 0.090 31.05 58.1 0.129 44.71 34.4 

The Long 

Way 1 71873 500 81,596 155.2 0.346 31.05 223.6 0.498 44.71 132.5 

TOTALa 8,831 1,441,151 2,741.9 6.109 3,948.4 8.797 2,339.8 
Appendix 10. Pumpage at present, planned, and proposed commercial-supply wells on the North Fork, Suffolk County, N.Y., Scenario 4

[Annual total pumpage for 1994 from appendix 4. Well capacity is in gallons per minute. Annual total pumpage is in thousands of gallons. Well identifier between 

190000 and 199999 denotes planned well; identifier with number greater than 200,000 denotes proposed well. Well-identifier prefix “S” is omitted.]

Monthly pumping rate

Well 

no.

Well 

use

Well 

capacity

(gal/min)

1994 Annual

total 

pumpage

(gal x 103)

Annual

total 

pumpage

(gal x 103)

Average annual June through August September through May

Flow rate

Percent of 

capacity

Flow rate

Percent of 

capacity

Flow rate

Percent of 

gal/min ft capacity 3/s gal/min ft3/s gal/min ft3/s

Scenario 4

S-11362 Irrigation 60 1,999 3,139 6.0 0.013 9.96 8.6 0.019 14.34 5.1 0.011 8.50

S-11699 Domestic 25 833 1,308 2.5 0.006 9.96 3.6 0.008 14.34 2.1 0.005 8.50

S-26049 Domestic 20 666 1,046 2.0 0.004 9.96 2.9 0.006 14.34 1.7 0.004 8.50

S-31448 Irrigation 600 19,149 30,066 57.2 0.127 9.53 82.4 0.184 13.73 48.8 0.109 8.14

S-33990 Domestic 30 1,000 1,570 3.0 0.007 9.96 4.3 0.010 14.34 2.5 0.006 8.50

S-36799 General 200 6,665 10,465 19.9 0.044 9.96 28.7 0.064 14.34 17.0 0.038 8.50

S-45809 Domestic 20 666 1,046 2.0 0.004 9.96 2.9 0.006 14.34 1.7 0.004 8.50

S-45810 Domestic 20 666 1,046 2.0 0.004 9.96 2.9 0.006 14.34 1.7 0.004 8.50

S-45811 Domestic 20 666 1,046 2.0 0.004 9.96 2.9 0.006 14.34 1.7 0.004 8.50

S-45812 Domestic 20 666 1,046 2.0 0.004 9.96 2.9 0.006 14.34 1.7 0.004 8.50

S-52086 Industrial 65 1,799 2,824 5.4 0.012 8.27 7.7 0.017 11.90 4.6 0.010 7.05

S-84076 Domestic 20 666 1,046 2.0 0.004 9.96 2.9 0.006 14.34 1.7 0.004 8.50

S-93628 Domestic 80 1,306 2,050 3.9 0.009 4.87 5.6 0.013 7.02 3.3 0.007 4.16

S-94491 Irrigation 60 4,573 7,181 13.7 0.030 22.77 19.7 0.044 32.79 11.7 0.026 19.43

S-98991 Irrigation 500 16,662 26,162 49.8 0.111 9.96 71.7 0.160 14.34 42.5 0.095 8.50

S-101947 Domestic 20 666 1,046 2.0 0.004 9.96 2.9 0.006 14.34 1.7 0.004 8.50

Totala 1,760 58,652 92,090 175.2 0.390 252.3 0.562 149.5 0.333

a Total may not equal the sum of values because of rounding to significant digits.

58 Simulated Effects of Pumping and Drought on Ground-Water Levels and the Freshwater-Saltwater Interface on the 

North Fork of Long Island, New York