HomeMy WebLinkAboutHydrology of the Shallow Ground-Water Reservoir TOS 1961 STATE OF NEW YORK
DEPARTMENT OF CONSERVATION
WATER RESOURCES COMMISSION
Hydrology of the Shallow Ground-Water
Reservoir of the Town of Southold,
Suffolk County, Long Island, NeW York
By
JOHN F. HOFFMAN
U. S. Cmeologic~l Survey
Prepared by the
U. S. GEOLOGICAL SURVEY
in caoperation with the
NEW YORK STATE WATER RESOURCES COMMISSION
SUFFOLK COUNTY BOARD OF SUPERVISORS
and the
SUFFOLK COUNTY WATER AUTHORITY
BULLETIN GW-45
ALBANY, N. Y.
1961
STATE OF N~w'YORK
DEPARTMENT OF CONSERVATION
WATER RESOURCES COMMISSION
Harold G. Wllm ..................................... Conservation Commissioner
J. Burch McMorran ............................. Superintendent of Public Works
Louis J. Lefkowltz ......................................... .Attorney General
Herman E. Hllleboe .......... ~,.. ....... ,..~ ........ ,.Commlsslon'er of~H~alth
Don J. Wlckham.... ................. ,;Commissioner of'Agrlc~l~u,re a~d Markets
John C, Thompson .... 0.... .... o ..................... .tt~.,.Executive Engineer
SUFFOLK COUNTY BOARD OF SUPERVISORS
H. Lee DenniSOn .... o..,. ............ ~ ....................... County Executive
SUFFOLK COUNTY WATER AUTHORITY
To Bayles Mlnuse,, ........ o ......................... , ........... ....Chairman
UNITED STATES
DEPARTMENT OF THE INTERIOR
Stewart L. Uda'll~ Secretary
GEOLOGICAL SURVEY
Thomas B. Nolan ..................................................... Director
Luna B. Leopold ..................................... Chief Hydraulic Engineer
O, Milton Hackett ................................. Chief, Ground Water Branch
Ralph C. Heath .............. o ............................. District Geologist
II
Figure 6,
7.
Table I.
2.
ILLUSTRATIONS (Continued)
Page
Idealized cross section of a peninsula showing the natural
movement of ground water in the vertical plane ............ 24
Comparison of the cumulative departure from mean annual
precipitation at New York City and the mean annual water
level in 14 selected wells on Long Island ................. 27
8. Idealized cross section showing the movement of ground
water toward a well being pumped .......................... 31
9. Idealized cross section of a peninsula showing vertical
movement of ground water around a well being pumped ....... 32'
10. Vertical sea-water encroachment caused by pumping ........... 38
Il. Effect of layers of low permeability on the encroachment of
sea water ................. 38
location of wells and irrigation ponds yielding salty'
water ..................................................... 40
13, Variation in chloride content of water pumped at Station 3,
v~llage of Greenport Water Supply, with monthly pumpage
and monthly rainfall during 1951 .......................... 42
14. Variation in chloride content of water pumped at Station 3,
village of Greenport Water Supply, with daily pumpage and
daily rainfall during October 1951 ........................ 43
TABLES
Population of Town of Southold and village of ~reenport,
1920-57 ................................................... 5
Estimated altitude and thickness of stratigraphic.,unlts
underlying Southold ....................................... ]2
Comparison of the average precipitation at gages located'in
Southold w~th the average precipitation at New York City
for various selected periods up to ]950 ................... 15
4. Estimated average annual recharge to the glacial deposits
underlying Southold during the 3-year period of minimum
rainfall .................................................. 18
5. Estimated fresh ground-water storage in the glacial deposits
of Southold, in millions of gallons, April 1950 ........... 25
6. Typical analysis of sea water off the coast of Long Island,
N. Y ..................................................... 36
7. Allowable chloride concentrations in water for various uses. 36
HYDROLOGY OF THE SHALLOW GROUND-WATER RESERVOIR OF
RE TOWN OF SOU]¥1OLD, SUFFOLK COUN]~¢, L. I., N. Y.
By
John F. Hoffman
ABSTRACT
The Town of Southold proper occupies 47 square miles of the NOrth Fork,
a peninsula extendlng 27 miles Into the Atlantic Ocean from the northeastern
end of Long Island, N. Y. Owing to the extensive withdrawal of ground water
for irrigation in Southold, sea-water contamination of the ground-water
reservoir is a potential problem. As sea water bounds the peninsula on
three sides and underlies the shallow ground water at depth, overpumping
the ground-water reservoir would sooner or later result in lateral or
vertical salt-water encroachment, or both.
Conditions for growlng potatoes are excellent in a major part of the
Town. Precipitation has been sufficient to produce a good potato crop In
nearly all of the-last few years. However, supplemental irrigation has in-
creased yields substantially during years of normal precipitation and has
decreased crop losses in drought years.
Most~ If not all, of the available fresh ground water of Southold is
contained In glacial~deposlts which constitute the shallow ground-water
reservoir. As the horizontal permeability of these deposits is greater than
the vertical permeability and as these deposlts are apparently underlain by
layers of very fine sand or clay~ the upward movement of salt water under
the present pattern of withdrawal has not been evldent~ if it is occurring
at all. Despite the fact that withdrawals have increased markedly in recent
years¢ sea-water encroachment has been restricted thus far to nearshore
areas of Southold where the altitude of the water table is less than 2 feet
above sea level.
Natural replenlshment of the ground-water reservoir Is derived solely
from precipitation that falls within the Town. However, only part of this
precipitation reaches the reservoir, mainly because of losses by evaporation.
Overland runoff losses, which are common In most hydrologic systems, are
small owing to the gentle slope of the terrain and the highly porous soil
cover.
-I-
The permissible perennial withdrawal from Southold~s ground-water reser-
voir is difficult to establish because of the ever-present possibility of
sea-water encroachment. The problem resolves Itself Into selection of a
conservatlve rate of annual withdrawal that will prevent serious overdraft
of the reservoir, both locally and areally~ under prevailing conditions of
recharge. Unless serious overdraft occurs~ the fresh-water head probably
will be sufficient to prevent the movement of sea water in large quantity
into the fresh water-bearing beds. In this report~ the permissible annual
withdrawal has been conservatively established as equal to the estimated
average replenishment during the consecutive 3-year period of least precipi-
tation since 1826. The estimates Indicate that about 30 percen%of the
average precipitation would replenish the water-bearing beds during such a
3-year dry period. On this basis~ the water-bearing beds of Southold can be
expected to yield perennially at least 7,000 million gallons per year or
about 19 million gallons per day. Additional water may be obtained by
temporarily "mining" ground water during brief periods of Iow replenishment;
however~ further study and closer evaluation of little known hydrologic and
geologic problems of the Town are required before such "mining" can be
practiced with impunity° Foremost among the problems requiring further
study is the relationship of fresh ground-water storage to precipitation
trends. A strong possibility exists that optimum conditions of storage
d~rlng the present period of study may obscure the problems that will result
from the reduged storage caused by long-term deficiencies in precipitation.
PURPOSE AND SCOPE OF REPORT
On the basis of data furnished by the New York Water Resources Commission
(prior to February 1960 the Commission was known as the New York Water Power
and Control Commission), it is estimated that in 1957 about 2,400 million
gallons of fresh water was pumped from the glacial deposits which constitute
the shallow ground-water reservoir underlying the Town of Southold. As the
welfare of the entire population depends on an adequate local supply of
ground water of good quality~ it is Important to know if the present /1958)
extensive withdrawal for irrlgatlon and other uses Is bringing about condi-
tions that would favor sea-water contamination of the ground-water reservoir.
This report is part of an~overall and continuing appraisal of ground-
water conditions on Long Island begun In 193~. The need for future manage-
ment of Long Island's water supply was recognized during the early
Since that time a continuing island-wide lnvestlgatlon of ground water has
been carried on by the U. S. Geological Survey In cooperation with the New
York Water Resources Commission~ the Nassau County Department of Public
Works~ the Suffolk County Water Authorlty~ and the Suffolk County Board of
Supervisors.
-2-
Work on a ground-water study of the Town of Southold was started by the
wrlter late In 1~8 in connection with fulfillment of thesis requirements
for a Master's degree and was completed in 1952o Later It was decided to
ampllfy the scope of the thesis Into a more comprehensive report and to
Include some additional data which had become available up to 1957. Thus,
the present report reviews data concerning the geology~ hydrol~ogy, and
ground-water conditions of Southold available up to the middle of 1957o The
chief objectives have been to appraise the eventuality of sea-water encroach-
ment~ to evaluate recharge to the ground-water reservoir, and to offer recom-
mendations for more complete investigation of the ground-wa~er resources.
ACKNOWLEDGMENTS
The author wishes to acknowledge the cooperation of Mr. Harry Monsell,
Superintendent of Public Works, village of Greenpor% and the New York State
Department of Conservatlo% Bureau of ~rine Fisheries in furnlshlng data
concerning the chloride concentrations of the waters of the Town of Southold.
The fleld work for this report was greatly expedited by Mr. Monsell's mak~i?g~
available to the Geological Survey much of the equipment and manpower un.d~
his jurisdlctlon.
GEOGRAPHIC FEATURES
The Town of Sou~hold, referred to In this report also as Southold, Is at
the extreme northeast end of Long Island, occupying the eastern 21 miles of
the North Fork, one of the two peninsulas that join the main part of eastern
Long Island at Rlverhead. Southold~s total land area of 53 square miles
comprises only slightly more than 3 percent of Long Island's total area of
1,373 square mlles. ~hls relationship Is shown in figure I. Included In
the area of Southold are the ~ square miles of Fishers Island, Plum Island,
and Robblns Island. However, these Islands are not considered In this
report.
Southold has a population density much below the average for Long Island~
for It contains less than O.I percent of the Island.s population (table I).
The village of Greenport contains slightly less than one-quarter of this
populatlon, making It the largest community in the Town of Southold. Summer
vacationers and fishermen seasonally increase the population of the village
of Greenport and the Town of Southold by approximately 50 percent.
U.S. GEOLOGICAL SURVEY.
Figure l.--Index map of Long Island, N. Y., showing the Ioca±ion of the Town of Southold.
Table I.--Populatlon of Town of Southold and village of Greenport, I920-57
Year village of Greenport Town of Southold ~/
1920 3,122 10,147
1930 3,062 ll,669
1940 3,259 12,046
1950 3,028 II,48~
1957 2,645 12,607
~/ Includes village of Greenport.
Southold's average annual air temperature is about 51°F (M. F. Woods,
U. $. Geological Survey, written communication, 1941), ranging from the
January average of 3I°F to the July average of 69°Fo The growing season,
which usually extends from April 20 to October 29, is normally about 192
days long, Precipitation varies considerably from place to place in
Southold. E~ased on records available up to 1950, precipitation ranges from
about 45 Inches at Cutchogue (51 years of record) and 3? Inches at Orient
(IO years of record), to 33 inches at Greenport (11 years of record).i,
According to Gustafson and Johnstone (1~1) the Sassafras slit-loam s~tl~'
averaging about 3 feet in thickness, covers most parts of Southold. ThiS:
soil is described as "light to light brown in color and only fairly wel
supplied with organic matter. Sassafras slit loam holds water and nutri-
ments fairly well." Cultivation loosens this soil sufficiently so that
durin9 the spring ~nd winter months a large part of the incident precipl-
tatlon seeps Into the ground. The Sassafras sandy loam, Haven loam,
Plymouth sandy loam, and Dukes sand also have been identified In the Town,
but they are unimportant because of their small areal extent (Gustafson and
Johnston% 1941). The Greenport clay, which occurs In the western part of
Greenport~ makes this section a relatively poor agrlcultural area and
retards recharge to the underlying ground-water reservoir.
The Town's favorable climate and soll make It one of the major potato-
producing areas of Suffolk County~ which itself ranks high among the other
potato producing areas In the Nation. Although the acreage under cultiva-
tlon has been relatively codstant since 1899, the main crop cultivated has
shlfted gradually from grain to potatoes. Of the 13,614 acres planted In
vegetables In Southold In 1948~ more than ?6 percent was used for the culti-
vation of potatoes (U. S. Department of Agriculture,
Besides agriculture, the economy of Southold also depends to some extent
on the summer tourist trade~ the numerous oyster beds off the southern shore
of the peninsula, and the fishlng boats, both commercial and pleasure, that
use Its harbor facllltles.
-5-
WATER UTILIZATION
Water for public supply, Irrigation, and domestic use in Southold is
obtained from the only source available -- ground water. In 1957 ground-
water withdrawals for these uses amounted to an estimated ~,400 million
gallons. This water comes solely from the glacial (upper Pleistocene) de-
posits which constitute the shallow ground-water reservoir as most, If not
all, of the water stored In the deeper Magothy(?) formation of Late Creta-
ceous age may be salty, aod very little is known about the wa~er in the stl
deeper Raritan formation, also of Late Cretaceous ag% underlying the area.
Methods of Withdrawal
~lore than 1,000 wells have been drilled, driven, or jetted into the
water-bearing deposits underlying Southold. For the most part, these wells
have steel casings ranging In diameter from 1¼ Inches to about 12 inches and
extend to depths ranging from a few feet to about 200 feet. Screens are a
necessary part of well construction. These range in length from 2-foot well-
point screens on domestic wells to screens 30 feet or more in major public-
supply wells. An Important part of the well construction Is development~
which Involves the removal of the finer grained particles from around the
screen. Were It not for development, many wells screened In unconsolidated
materlal could be pumped only at very iow rates.
Artlfl~lal ponds also are used as a source of irrlgation water where the
water table Is less than about 8 feet below the land surface. These are
co~on In the eastern part of Southold. ponds generally average about SO
feet square and 6 feet deep~ but may differ conslderab y from these d men-
slons according to individual needs.
Deep-well turbines are the most commonly used type of pump in Southold.
Centrlfugal pumps are used to a small extent where the suction lift Is less
than about 15 feet. A modification of the deep-well turbine pump that Is
coming into more popular use is the submersible pump. All the worklng parts
of this type of pump~ including the electric motor, are contained inside the
well~ and are submerged below the water level. Where small-capacity pumps
are required, such as for household us% and the d~pth to water is beyond
suction lift, jet pumps are commonly used.
public Supply
Formerly, there were two public water supplies In Southold, the North
Fork Water Co. and Village of Greenport Water Supply. However~ in 1957 the
facllltles of the North Fork Water Co. were purchased by the village which
-6-
presently (1958) operates both systems. Besides supplying water for
domestic and commercial use, these systems supply water for flreflghtlng and
other munlclpal requirements.
Annual wlthdrawals from wells of the North Fork Water Co. system, to
serve 225 homes In the Town of Southoid, have been relatively constant at
about 20 million gallons. As shown In flgure 2, annual withdrawals from the
municlpal system of the village of Greenport, to serve about 800 homes, have
Increased gradually from about 61 million gallons in i932 to 150 million
gallons In 1957. The peak annual pumpage of 167 million gallons was reached
tn 1955. Pumpage during the months of June, July, August, and Septem§er re-
flects In large degree the Increased seasonal use for sprinkling and for the
tourist population. It amounts to more than 40 percent of the annual with-
drawal.
The water supplies for the North Fork Water Co. system are drawn from
4 wells at~a pumping station located at the intersection of South Harbor
· Road and I~ute 25 (pl. I). The village of Greenport currently (1958) oper-
ates three well flelds, Two of these fields (stations I and 9) are located
In the western part of Greenport less than half a mile apart. Another well
field (station 2), located between stations I and 9, has been shut down
since 1956 owing to the presence of undesirable concentrations of Iron and
bacteria In the water. The third active well field (station 4) Is located
in the eastern part of Greenport near the East Marion village line and about
I mile east of statlons I and 2.
Irrigation
Southold ls one of the two most intensively irrigated Towns of Long
Island~ the second being the Town of Riverhead, Immediate y to the west. n
1957 approximately 1,907 million gallons, or about ~ ...... ~'~ ...... I
estimated annual ground-water withdrawal in Southold was used ~or Irrigation.
The Irrlgatlon withdrawal was made during a 107-day period starting In the
middle of June and extending through October. The record maximum annual
wlthdrawal for irrigation occurred In 1949 when an estimated 4,600 million
gallons of water was pumped during the growing season.
Water for Irrigation Is pumped through portable aluminum pipe to oscil-
lating sprinklers, which spray it In a circular pattern. A common type of
sprinkler dlstrlbutes about 15 gpm (gallons per minute) through each sprin-
kler head. Another type distributes 400 gpm through one sprinkler head.
The amount of water used and the frequency of application vary widely.
Some farmers irrigate when the soil no longer cakes upon being squeezed.
Others follow the recommendations of the Long Island Research Farm at
Baltlng Itollow, N. Y., and supplement the rainfall with enough water to In-
sure the application of an average of t Inch of water per week to the land.
Still other farmers have little equlpment and are short of manpower; conse-
quently their Irrigation procedures are adjusted to these limitations.
-7-
170
160
150
._1
'~ 130
o110
~0
70
~100
Figure 2.--Annual pumpage for vi lage of Greenport Wafer Supply, 1932-57.
-8-
Domestic Use
About 9,000 persons In Southold are not served by a public supply and
private domestic'wells 4 Inches or less in diameter constitute the source of
supply. Based on an estimated d~lly water requirement of IOO gallons pet
[ap:!~, ground-water withdrawal for domestic use would amount to about 0.9
million gallons per day, or about 33O million gallons annually.
Nethod of Disposal of Used Water
Water pumped for household use in Southold generally is discharged to
septic tanks and cesspools whence it returns to the water-bearing deposits.
An exceptlon to thls practice is found in the village of Greenport, where
sewage effluent Is discharged, after treatment, directly to Long Island
Sound.
Water used for lrrlgation In Southold is applied to crops by sprinkling,
and most of the water probably Is evaporated from soil and plant surfaces.
'i At times, however, excessive amounts of water may be applied to the soil,
and a part of the applied water will be returned to the water table. In
§eneral~ probably only a small part of the water pumped for Irrigation re-
i turns to the water-bearing deposits. Pumping for Irrigation, therefore,
results In a net loss from the ground-water reservoir.
GEOLOGY
The geology of Southold is closely related to the hydrology of the
ground-water reservolr. Besides forming the medium In whlch the fresh water
Is stored, the glacial and older unconsolidated deposits that underlle
$outhold govern many of the factors affecting Inflltratlon, recharge~ and
dlschargeo On the one hand, the permeable facies of these deposits provide
conduits through whlch salty water may encroach inland~ but on the other
hand the Impermeable facles form barriers agatnst such encroachment. The
Ical and lateral distribution of permeable and Impermeable facies In
these deposits do much to determine the position of the water level in the
ground-water reservoir under given recharge-dlscharge conditions and thereby
affect the depth at which salty water Is first encountered In wells.
Physical Geology
The present topography of Southold is largely the result of marine ,~n
subaerlal erosion of unconsolidated deposlts of late Pleistocene age th.~?
were laid down by glacial Ice and its melt water. The backbone of the 'Fo
consists of Iow hills of the Harbor Hill terminal moraln% which genera[I
lie close to the north shore of the peninsula and in places end abruptl/
preclpltous cliffs facing Long Island Sound. The crest of this moraine I
gently undulatlng~ approaches sea level in some places~ and extends eashv
along the entire length of Southold. its maximum altitude In both the .~a
ern and western parts of the Town Is about 100 feet above sea level, A
glacial outwash plain slopes gradually southward from the base of the
ralnal hills to the tidal waters on the south shore of the peninsula wh.~r
se98r~].;embayments fringed with marshy areas form an indefinite shoreline
Subsurface Geology
Relatlveiy little Is known directly about the subsurface geology of
Southold¢ fbr most wells terminate at shallow depth In upper Plelstocen.~
poslts. Only three deep wells~ SI89, S490 (V892)~ and S3123, have been
drilled on the North Fork peninsula. Of these¢ two penetrated the LloyJ
sand member of the Rarltan formation and reached bedrock; the third well ~
drilled into the ~agothy(?) formation above the Raritan. The log of well
SI89 is published in Bulletin GW-4 (p. 93-9?) of the New York State Wat.~r
Resources Commission and that of well S~90 (V892) In a report by Veatch
(1906, p~ 330). As data from the three deep wells and other shallow well:
suggest a general correspondence between the subsurface geology of Sout~o
and that of the rest of Long Island¢ some estimate of the character of
various formations may be made by a review of Long Islandrs subsurface ~e(
ogy~ whlch has been described In some detail by deLaguna and Perlmutter
The Rarltan formatlon¢ deepest of the u~consolldated deposits on Lo3g
Island¢ rests unconformably on a basement of crystalline bedrock~ which
erally slopes at about 80 feet per mile in a southeasterly direction.
Rarltan is composed of two members -- an upper clay member and a lower
sand member. The clay member beneath most of Long Island generally consl~
of beds of silty and solld clay and some sandy layers. The Lloyd sand
ber is predominantly coarse sand and some gravel~ but Is Intercalated wi'hi
thin layers of slit and clay. As the overlying clay member has a very Io~
permeabillty¢ the water In the Lloyd sand member ls generally confined ~n(
arteslan pressure.
The Magothy(?) formation Is considerably thicker than the underlyln.~
Paritan formation In most places on Long Island. It consists of layers ot
fine sand¢ silt~ and clay Interbedded with several zones of coarse sand ar
-lO-
ne and
that
le Town
~ral ly
.tly In
ina Is
eastward
~e east-
A
where
al Ina
of
-ene de-
:en
Ioyd
· ,'el I was
well
~ater
ich
wel Is
~utho I d
~f the
:e geol-
er
Long
ch gan-
The
~r Lloyd
ons Ists
,d mem-
with
y
~d under
gravel~ Preglaclal erosion of the Magothy(?) formation developed consider-
I~ able relief on the upper surface. Consequently, the depth at which this
]i surface Is first penetrated by wells is quite variable. The water In the
] Magothy(?) formation Is generally under artes an pressure but locally Is Un-
,:ii confined.
~i The Jameco gravel, the oldest recogn zed glac al depos t underlying Long
~.~'~ Island, generally rests unconformably on the hlagothy(?) formation, but where
B[~! erosion has removed the Magothy(?) It may rest directly on the Rarltan or
even on bedrock. The Jameco gravel s composed ch efly of coarse sand and
m' 9ravel, but some enses of clay and s It are present. Conflnement.b the
Bi overlying Gardlners clay causes the water stored In the Jameco to beYgener-
Ri-. a y under artesian pressure. A though extensive deposits of the Jameco are
~]] known to occur in western Long s and, the formation or Its equivalent has
!!: not been yet (1958) identified in eastern Long Island or In Southold.
The Gardlners clay, an interg ac al marine clay, Is commonly composed of
~'] silty clay and some layers of coarse sand. The Gardlners clay is believed
'It~.. to be present in Southold but ts th ckness and areal extent are not t
I~] clear y daf ned. In western Long Is and, however, wells nd cate tha~lt
~]' under les an area of cons derab e extent (deLaguna and Perlmutter, I~).
Glacial deposits of late Pleistocene age mantle the older formations in
~ractlcally all places on Long Island. They also form the present land sur-
face and surficlaI deposits of Southold. Two types of materials of differ-
ent geologic origin are recognized In the deposits -- till and outwash.
II Is commonly a heterogeneous mlxture of sand, clay, and boulders depos-
Ited from glacial Ice. Generally It is poorly sorted, and the presence of
~;.ictay, In some pl~ces, causes this materia to have rather Iow permeability.
~.i ~ln other places, the till s near y free of clay and is quite sandy, and
~'ilocally may have a high permeabll ty. 0utwash was deposited from glacial
t~ melt water and is moderately to well sorted. It is largely composed of sand
I!! and some gravel, and has a relatively high permeability. Strat flcation,
E: however, and the presence of lenses of clay and silt Interbedded w th the
~]sand and gravel usually cause the hoclzonta permeab Ilty of outwash to ax-
ECeed the vertical permeabll ty.
The estimated altitude and thickness of the various formatlons under-
lng Southold, listed in table 2 below, are based largely on the geologic
contour maps assembled by deLaguna and Perlmutter (19~), and partly on the
of wells S18~ S~90, and S3123.
lng
:rs of
nd and
Table 2.--Estimated altitude and thickness of stratlgraphic units under-
lying Southold /after deLaguna and Perlmutter, 1949/
Estlmated altitude a/ of Estimated
Age Formation fop of strati~raphi~ unlt average
Western Eastern thlckness
part part /feet/
Pleistocene Upper Pleistocene ~/ lO0 ~/ I00 225
deposits
Do. Gardiners clay ? ? ?
Do. Jameco gravel c/ ? ? ?
Cretaceous Magothy(?) formation -150 d/-208 ~50
Do. Raritan formation -
Clay member -700 Above cl/-387 I00
Lloyd sand member -825 Above ---400 150 .
Precambrtan Bedrock -1050 Above -500
a/ In feet, with reference to mean sea leveJo
~/ Maximum altitude In Southold; minimum altitude is sea level.
c/ This formation, or Its equivalent, as yet has not been positively
IdenTified in Southold.
~/ Based on the log of well S189.
HYDI~3LOGY
Natural recharge to Southold~s shallow ground-water reservolr Is derived
solely from the inflltratlon of precipitation on the Town. Only part of the
precipitation recharges the reservoir, for a sizable amount Is returned to
the atmosphere by evaporation and transpiration. Overland runoff ls small,
however~ owing to the porous soll cover and the gentle slope of the terrain.
Natural discharge takes place by ground-water outflow and evapotranspIratlon
In marshy tracts in the near-shore zone. Ground-water outflow comprises
spring discharge along the shore~ which is Vlslble mainly at Iow tlde~ and
nearly continuous upward seepage In the bottoms of adjacent salt-water
bodles.
Southold~ because of its topography and dlvlslon by tidal Inlets (pl.
can be conveniently grouped Into three separate or nearly separate hydro-
logic areas or units. This facilitates the understanding of discussions of
the relatlonshlps of preclpltatlon~ evapotranspiration, runof~and recharge
to storage in the ground-water reservoir. The first and largest hydrologic
unit consldered~ termed area I in this report~ covers about 29 square miles
and Is bordered on the west by Mattltuck inlet and on the east by Hashamomuck
Inlet (pl. I). The villages of Mattltuck, Cutchogue, Peconlc, and Southold
are Included in this area. Another hydrologic unit, designated area 2, con-
tains about 7 square miles and Is bordered on the west by Hashamomuck Inlet
and on the east by Orient Harbor. The village of Greenport and the hamlet
of East Marion are In this area. The third unit, termed area 3, ls about 4½
square miles in extent. Orient Harbor forms the western limit and Orient
Point~ the eastern. The village of Orient and environs are included In this
unit. A fourth area of about ? square miles In the extreme western part of
Southold Is not discussed for lack of relevant data.
Preclpltatlon
,ely
~er i ved
of the
~d to
~mal ly
~rra 1 n.
ration
.es
and
ns of
harge
logic
miles
amomuck
thold
, con-
Inlet
mlet
For this report precipitation studies have been made to estimate minimum
rates of recharge to and storage in the ground-water reservoir during the
period of precipitation record up throqgh 1950. Comparison of present
ground-water recharge and storage with the estimated long-term minimum re-
charge and storage gives insight into the possibility of sea-water encroach-
ment under present conditions of ground-water withdrawal.
The closest gage to Southold having long-term precipitation records is
that at the Battery in New York Cltyy about 80 miles west of the west edge
of the Town. Precipitation trends at gages in Southold with shorter records
resemble those of the Battery gag% and for this reason the New York City
records have been used as a long-term base. in Southoldy standard 8-inch
rain gages are located at Cutchogu% Greenpor% and Orien% and precipita-
tion records for these statlons are considered representative for hydrologic
areas ly 2y and ~y respectively. Precipitation data for these gages are
summarized In table 3. A similarity exists In the preclpltatlon trend meas-'
ured at these gages~ but the amount of catch differs appreciably (table 3)°
Part of thls dlff&rence may be attributed to an expected variation caused by
local topography and may be due to gage exposure and location. It is not
possible at thls time to evaluate the accuracy of each gagey and therefore
the precipitation measured at each was considered to be representative of
condltlons In its hydrologic area.
Comparison of water levels In wells with precipitation Indicates that in
$outhold there is only a general relationship between the preclpltatlon In
any one year and contemporaneous ground-water levels. Although water levels
during a year may decline markedly as the result of large deflolencles In
precipitation ( fig. 3), it is doubtful that such short term deflclencies
would be a direct cause of significant sea-water encroachment. Consequentlyy
precipltatlon records were analyzed by groups of years. Signiflcantly, re~
view of the precipitation records for Cutchogue shows that a 3-year term is
the longest during which precipltation has been substantially below normal
every year. Any period of 4 years or more was found to have at least I year
i of substantially above-normal precipitation. For Cutchogue this 3-year aver-
ag% which Was ~9.~2 inches~ occurred during the period 1924-26 and Is 87
percent of the average computed for a 52-year record (1899-1950) at Cutchogue.
For New York City this y-year average, which was 34.25 Inches, occurred
!during the period 1862-64 and Is 80 percent of the average computed for New
i York City's 125-year record (1826-1950). Relating the minimum precipitation
New York City to a base that is more convenient for purposes of compar-
Ison, it is 78 percent of the average for the 9-year period July 1941 to
-13-
7
6
~ S 6542, CUTCHOGUE
hJ 4 ~
~" S 6552, SOUTHOLD
hi
2
S 7283, ORIENT
Figure 3.--Hydrographs of water levels in wells S6542, Cu±chogue;
S65~2, Sou?hold; and S7283, Orient.
-14-
Table 3.~-Comparison of the average precipitation at gages located in Southold with the average precipitation
at New York City for various selected periods up to 1950 (From records of the U. S. Weather Bureau)
arecipi- Period Length Average precipitation, in inches
ration of of
station record period July
(years) Jan. Feb. IV~ar;I Apr. May June Aug. Sept. Oct. Nov. Dec. TOTAL
New York 1826-1950 126 3.66 3.82 3.64 3.23 3.24 3.33 4.24 4.33 3.39 3.53 3.56 3.62 42.99
City
New York 1899-1950 52 3.37 3.33 3.64 3.36 3.31 3.60 4.11 4.30 3.50 3.34 2.74 3.32 41.92
City
Cutchogue 1899-1950 52 4.06 3.50 4.32 3.92 3.26! 3.46 3.46 4.10 3.55 3.45 3.85 4.27 45.20
New York July 1941- 9 3.65 2.69 3.90 3.09 4.39 3.72 4.45 4.44 3.25 2.84 3.73 3.59 43.75
City June 195C
Cutchogue July 1941- 9 4.57 3.37 4.73: 4.17 4.30 3.00 3.23 4.42 2.46 3.16 5.94 4.70 48.05
June 1950
Greenport, July 1941- 9 2.80 2.03 3.06 2.89 3.20 2.09 2.51 3.72 1.78 2.1[ 3.90 3.23 33.38
a/ June 1950
Orient July 1941- 9 3.52 2.75 3.60 3.08 3.54 2.09 2.46 3.84 2.06 2.19 4.59 3.58 37.30
June 1950
a/ Records of the Village of Greenport Water Supply.
II
June 1950. On this basis the 3-year minimum average annual preclpltatlc~
Cutchogue (area I) becomes 97.5 Inches, at Greenport (area 2) 26 inches~ ~
at Orient (area 3) 29 inches.
Evapotranspiratlon
Only part of the precipitation on land surface reaches the ground-wa
reservolr~ for a sizable amount Is returned directly by 'evaporation to t
atmosphere. Evaporation also "pumps".water by capillarity from the soil
zone and from zones of shallow water table and returns it to the atmosph~
A slmllar action occurs where the physiological proc. asses of plants retulr
water to the atmosphere by transpiration. The sum of these losses is kn¢~
as total evaporation, or evapotransplratlon.
Lack of essential data makes application of available formulas for
estimates of evapotranspiratlon in Southold only very approximate.
basls of studies In the north-central states, Meyer On t~
of curves (194~) evolved a seri!s
for estimating evaporation. These curves have as parameters t~
average monthly temperature and the average monthly precipitation. As
data are available for Southold, Meyer's curves have been applied to ~ ye~,-
of contrastlng.ralnfall condltlons recorded at Cutchogue gage during the
period through 1950. These years are 1908, the year during which the lea~ ~
annual precipitation occurred; ~48, the year during which the heaviest
annual precipitation occurred; and 1949, a year during which the annual p
clpltatlon closely approached the ong-term~average. Using a watershed
coefficient of 0.8 (Meyer, 1944, p. 457), the computed direct evaporation
for 1968 was I~ Inches; for 1948, I? inches; and for 1949, 14 inches.
concludes from his studies that the annual transpiration by agricultural
crops In the North Central States is about 9 to lO inches. For purposes
estimate In this report an annual transpiration rate of 9 Inches was used.
The estimated total annual evaporation (evapotranspiratlon) for Southold,
the sum ~f direct evaporation and plant transpiration, computed for the 3
contrasting years ranged from 21 to 26 inches. In 1908 it was RI Inches~ ~r
61 percent of the precipitation for that year; In 1948 It was ~6 inches, ¢.
4R percent of the precipitation; and in 1949 It was ~3 inches, or 51 perc~'t
of the precipitation.
These estimates differ considerably from those of Spear (19RI), who
draws the generalization that the total annual evaporatlon on ~ong Island
about 17 inches.
-16-
~ at
and
Runoff
The absence of streams gives evidence that only a small part of the pre-
cipitation on Southold returns to the sea directly by overland runoff.
Occasional heavy storms may cause some ephemeral streamflow, but in compar-
ison with the amount of precipitation the overland runoff Is small. However~
ground-water outflow, or natural lateral outflow from the shallow ground-
water reservolr~ occurs along extensive seepage lines, or from numerous
small springs along the shores of Southold, and through the floors of the
bounding salt-water bodies. Such discharge probably constitutes the ~reater
part of the total discharge of liquld water from the Town. Ground-water
outflow Is considered more completely under the subsequent section "Ground-
water budget."
According to estimates in the Burr, Herlng, Freeman report (1904) total
runoff from Long island as a whole amounts to 20 percent of drought-year pre-
elpltation (35 inches) and 39 percent of average-year precipitation (45
inches). Again, Leggette (as cited by Paulsen, I~O) has estimated that
even during hurricanes direct overland runoff to Long Island streams is less
than 5 percent of the storm precipitation. Qualitative evldence~ such as
that listed below, favors use of an estimate approximating Leggette~s for
the overland runoff in Southoldr
I. The comparatively Iow moisture-retention capacity of the prevailing
silty loam soil.
2. Excellent subsoil drainage of the silty loam of Southold by the
underlying sand.
were eonsldered to be about I0
Retardation of overland runoff in the furrows of cultivated flelds.
The flatness of the terrain.
The absence of visible runoff during most storms.
For a conservative estimate In this repor% losses by overland runoff
~ercent of the annual precipitation.
Recharge
Recharge to the ground-water reservoir of Southold Is the difference
between precipitation and losses by evapotranspiratlon and overland runoff.
From the precedlng, it is estimated that about 70 percent of the annual pre-
clpitatlon during very dry years Is dissipated by these losses. The remain-
lng 30 percent, therefore, replenishes ground-water storage. According to
Spear (1912), "for a dry period the amount of percolation would be .
probably not greater than 17 or 18 Inches, or 50 percent of an annual rain-
fall of 35 inches." During years having average preclpltatlo% it is
-17-
estimated that about 40 Dercent of the annual precipitation replenishes
ground-water storage. These estimates are somewhat lower than those of
Spear's report (1912) wherein It ls stated that recharge "for the Long
Island watersheds during a year of average rainfall Is probably not more
than 50 percent of the mean annual rainfall or 22 Inches."
The estimated average recharge at the rate of 30 percent of the 3-year
minimum precipitation for hydrologic Area I would, be about 11.3 inches per
year, for Area 2 about 7.8 inches per year, and for Area 3 about 8.7 Inches
per year. On this basis, the estimated probable minimum annual recharge to
the glacial deposits underlying the three hydrologic areas of Southold would
be as glven In table 4 below:
Table 4.--Estlmated average annual recharge to the glaclal deposits under-
lying Southold during the 3~year period of minimum rainfall
Hydro- Annual recharge
logic Locality Land area
area (sq. miles) Million Million Million gallons
gallons gallons per sq. mile
per sq. mile per day
Mattltuck
I Cutchogue
Peconic 29.2 5,750 197 0.5~
.Southold
2 Greenport 3.6 a/ 165 136 ,37
East Marion 3.1 - 420 136 -37
East Orient 2.4 365 152 .42
3 W~st Orient 2.3 350 152 .42
I, 2, and 3 40.6 7,050 174 0.47
t Totals Averages
~/ On assumption that 75 percent of area Is effective for recharge,
owing to paving. Area of 2 square miles west of Chapel Lane, Sreenport, Is
directly underlaln by clay and Is not considered in estimate.
Annual recharge to the ground-water reservoir during a series of years
of normal precipitation might be 50 percent greater than that shown In
table 4, or about IO,5OO mllllon gallons. This would be distributed as
follows: area I, about 8,600 million gallons; area 2, about 860 million
gallons; and area 3, about I,IOO million gallons.
-18-
ear
per
ches
e to
~ould
Some doubt exists as to the applicability of either Meyer~s method or
Spear's estimate to the Southo[d area, owing mainly to the lack of control
data for the Town. Meyer~s method needs sufficient cllmato[ogic data for
checking the validity of the method and the magnitude of the watershed co-
efficient. Spear's estimate, on the other hand, generalized the results of
a relatlvely few local observations in other parts of Long Island.
GROUND WATER
Occurrence and Storage
i$
The available fresh ground water In Southold, for purposes of this
report, is considered to be water, which occurs in the pore spaces of the
upper Plelstocene glacial deposits. The three wells that penetrated the
underlylng Magothy(?) formation in Southold yielded salty water. Thus,
there is a possibility that the water contained In this formation Is salty
beneath most of the Town. Few data are available relatlve to the salinity
of water in the Lloyd sand member of the Rarltan formation. In some parts
of the Town the water may be fresh, but in other parts it Is definitely
salty. This concluslon Is based on data for two deep wells that penetrated
the formation. The first well, S490 (V892) a/, drilled in 1903 in Greenport
for the vltlage of Greenport, yielded a smalT amount of fresh water under
artesian pressure, but this supply was considered insufficient for pumping
(Veatch, 1906). ~nother well, SI89, drilled In 1935 Into the Lloyd sand
member for the Long Island State Park Commission at Orient Beach State Park,
about Io miles to the east, reportedly ylelded salty water from top to
bottom and had to be abandoned (Hoffman and Spiegel, 1958).
The total amount of water stored In saturated deposits depends chiefly
upon the volume of material containing the water and the poroslty of this
material. Only part of the stored water Is recoverable; some of It Is held
by ~lecular attraction against the force of gravity. The ratio of the
yolume of water that can be drained by gravity from a unit volume of satu-
rated material to the unit volume Is termed "specific yield." The speclflc
yield of water-bearing materials varies greatly and depends upon such
factors as grain size, sorting, the orientation of constituent grains, and
the compactlon of the material. Evaluation of the results of a pumping test
at Irrlgatlon well S7905 (see section on Movement), indicates that the
glacial deposits locally have a specific yleld of O. 17o
The water in the glacial deposits Is largely unconfined and the upper
limit of the saturated material in the unconfined deposits Is marked by the
water table. A map of the water table In Southold in April 1950 is shown In
plate I (Lusczynski and Hoffman, 1950). The water table fluctuates markedly
with changes in ground-water storage. The fluctuation in turn reflects
~See well-numbering system described at end of report,
varlatlons In recharge and discharge. This is evldent from the hydrographs
of wells S6532, S6542, and S7283~ shown in figure 3- Also~ from I0 years of
water-level records for these and many other wells screened at shallow depth,
It Is evldent that the water table in Southold was at a near-minimum stage
in April 1950 for the period December 1948 to October 1956.
The shape and thickness of the shallow fresh ground-water body that
overlies salty water beneath the Southold peninsula can only be conjectured~
for very few deep-well data are available, Theoretically, if the contact
between the fresh and the underlying salty water Is considered to be sharply
deflned and a hydrostatic balance Is considered to exlst~ the following for-
mula can be written for the depth of the contact below sea level:
df
h = ds df hf (I)
where h = the depth below sea level to a selected point on the fresh water-
salty water Interface~
hf = the height above sea level of the water table directly above the
selected point~
~.oo~ df = the density of the fresh water~ and
~°'~ ds = the denslty of the salty water.
This relationship, which is sometimes referred to as the Ghyben-Herzberg ~
ratlo~ Is shown in an Idealized cross section through a peninsula in figure 4.
An actual.cross section through the Southold peninsula at Cutchogue showing
the profile of the water table in April 1950 Is given in figure 5. The re-
semblance between the idealized profile of the water table In figure 4 and
wlth the actual one shown In figure 5 ls quite apparent.
The density of Southold's uncontaminated fresh ground water Is close to
IoOO0o The density of the bay and ocean water bounding the Southold penin-
sula dlffers from place to place~ depending on the point of sampling. The
density of samples from the embayments collected by the U. S. Geological
Survey and by the New York State Bureau of Marine Flsheries have ranged from
I.Ol9 to 1oO25. In certain embayments where large volumes of ground water
are discharged and become more or less trapped~ the density of the water may
be as Iow as I.OIO. However~ if the salty water underlylng the fresh ground
water of the Southold penlnsula Is considered to have the maximum density of
I.O25~ then for every foot of fresh water above sea level about 40 feet of
fresh water exlsts In below-sea-level storage. For a minimum denslty of
salty water of I.OIO the ratio becomes I:100. It Is known that the contact
between the fresh and salty water, at least in the case under consideratlon~
Is not sharply defined, and that a transitional zone~ termed "zone of diffu-
sions" exists. The dissolved solids and chloride In the water in this zone
gradually Increase In concentration toward the salty-water side. For exam-
ple, in 1957, data concerning the zone of diffusion were obtained in the
village of Greenport, located In hydrologic area 2. Here~ a well point was
driven into glacial sand and gravel to a depth of 70 feet. The altitude of
land surface at the site was about IO feet above mean sea level, and that of
phs
s of
e@th,
~ge
red~
t
rply
for-
ter-
the
lng
id
may
~ulld
of
~f
~ct
fu-
'as
of
of
salt water
Figure ~.--Idealized cross section of a peninsula showing the relation
of fresh and salt water according to the
Ghyben-Herzberg principle.
-21-
NW ~ SE
~ oJ -70
60- -60
'rio
40-
~ ~n _ o ~: ~ -~
level b .... ~ ~ ~----~------------X~ L-_I ~ /s,~
-I0- ~ Fresh J wofer ql Self --I0
.oter X
-5o
I I/2 0 I 2 MILES
-30
SCALE
the water table was about 1.1 feet above mean sea level. Water samples were
taken about every [0 feet and analyzed for chloride concentration. The data
are given below:
Depth of well screen
below land surface
(feet)
33-36
54-57
58-61
67-70
Chloride
concentration
(ppm)
82
33~
51o
6,800
12,500
The maximum normal chloride concentration of shallow ground water of
$outhold IS generally estimated to be about 25 ppm (Hoffman and Spiegel,
1958). At the Greenport site chloride concentrations down to a depth of 57
feet may represent residual contamination from a break In the sanitary sewer
In about 1950 or from the disposal of salty water about 500 feet from the
slte durlng a dewaterlng operation of many years ago. Another possibility
ls that the chloride concentrations may represent a part of the zone of dif-
fusion. The denslty of a water sample from a depth of 42 feet was I.OOO and
from a depth of 70 feet was I.O21. According to the Ghyben-Herzberg princi-
ple, the fresh water-salty water contact should be 48 feet below sea level,
or 58 feet below land surface. Thus, there I$ a reasonable correspondence
between observed conditions and the theoretical relatlonshlp.
As ground water, is in motion (flg. 6), Hubbert (19~0, p. 924-26) sug-
gests that the hydrostatic relationship assumed by the Ghyben-Herzberg for-
mula although orlglnally determined empirically, gives approximately correct
results at Iow hydraullc gradients. At higher gradlent$ Hubbert suggests
that Its use Is Incorrect. Aisc, a recent appraisal of the relationship
between fresh water a~d the underlying salty water In southwestern Nassau
County (Perlmutter, Geraghty, and Upson, 1959) has led to the modification
of the Ghyben-Herzberg formula (I), to read as follows:
ds df
Z = ds df ~ hs ds df ' hf (2)
where Z
= altitude, in feet, of a polnt on the fresh water-salt water
Interface,
df = density of fresh water,
ds = denslty of salt water,
hf = altitude, In feet, of the water level In a well terminated in
fresh water of density df, at or near the contact, and
hs = altltude, In feet, of the water level In a well terminated In
salt water of density ds, at or near the contact.
Sea level /
$
\ \ containing / /
salt water
Figure 6.--Idealized cross section of a peninsula showing the natural
movement of ground water in the vertical plane.
Much conjecture still exists abou
and salty water at depth. The prlncl~lumet~i~'~~ II
dlmensJonaJ changes of the zone of dl~nd dJmen~io~ []
changes of the overlying fresh-water lens under varylng condltions-;~"~;;;;;_ I
0f The water table, (3) the distribution of salinity and density of the
I..~ water stored In the zone of d ffuslon, and 4 a
i~ ' chan~^ ~- ........ - ( ) ny fluid movement or lnter-
I~:. ~ ~u~ SighT TaKe place within the zone of dlffus on.
I~ If fresh-water storage Is considered to conform according to the Ghyben-
Herzberg principle, for a ratio of 1:40 and a specific ¥1eld of 0ol?, th'e
fresh-waTer storage In the upper Pleistocene glacial deposits of The three
hydrologic areas o~ $outhold In April 1950 would approximate ~3,000 million ~.
gallons. The oreskdown of the estimate by hydrologic areas ]s shown In
table ~.
Table 5.--Estimated fresh ground-water storage In the glacial deposits of
Southold, in mllllons of gallons, April 1950
Hydro- Storage Storage
'. logic Locat Ion above below Tota I
sea leve sea leve storage
. i Mattituck Inlet, Mattltuck to 1~300 52,000 5I~000
Peconlc Lane, Peconlc
Pecon lc Lane~ .Pecon ic to 1;00 16,000 16~00
Hashamomuck Inlet, Southold
Subtota] I'~?O0 ~8~000 ~0,000
] 2 Chapel Lane, Gre, enport to Gull 40 1,600 1,600
~. . Pond Road, Greenport
!.. Gull Pond Road, Greenport to I10 ~,00 I+,500
· Causeway, East Mar Ion
· S ubtota I I ~0 ~, 000 ~, l O0
· 3 West Orient to 1½ miles east of 90 3,600 3,?00
Maln St., Orient .
: ~. East Or lent 80 3,200 3,300
~ S ubtota I 170 6,800 7,000
_ Total (rounded) 2,000 i 81,000 83,000
The estimated average annual recharge of 10,500 million gallons from the.
infiltration of precipitation previously discussed in the section on
"Recharge" is equivalent to slightly more than one-eighth of the estimat.~
volume of storage in the shallow ground-water reservoir In April 1950.
Major changes In ground-water storage on Long Island, N. Y., roughl~
follow a cumulative departure curve for precipitation at New York City.
Figure 7 shows the comparison between the mean annual water level in the
selected wells In central Long Island and the cumulative departure curw~
preclpltatlon from 1826 to 1950 at New York City. The mean monthly water
level In the 14 wells differed by less than about 2 fe~t from the mean
annual water level for any one year in the period of observation. As cli
matlc conditions In Southold are approximately similar to those of other-
parts of Long Island, ground-water storage in the shallow reservoir Is
assumed to follow qualitatively a trend somewhat similar to that shown In
figure 7o Comparison of the departure curve and the average water levels
the 14 selected wells Indicates that ground-water levels on Long Island
In Southold probably dld not approach a long-term minlmum during 1950.
the relationship shown in figure 7 is considered to hold throughout the
perlod shown, water levels were at a minimum, for the period 1826 to 1950~
sometime between 1852 and 1860. Few, If any, water-level data are on rec~;
for any area between 1852 and 1860. Therefore, storage determined for
Southold on the basis of water levels In April 1950 (see table 5), althou.:
representing a near-minimum for the period, December 1948 to October
cannot be considered to be a long-term minimum. During the period 1~48-5i~
the rate of recharge to the ground-water reservoir varied appreciably. Th
rate was very high during 19~8 when precipitation approached record high!s,
and very Iow during an extended dry period in the growing season of 1949.
Heavy. withdrawals for irrigation during the dry perlod caused water levels
to reach a marked Iow in early 1950.
During more recent years, water levels in most wells in Southold ap-
proached minimum stages In the latter part of 1957 as the result of below-
normal ~recipltatlon and recharge, and heavy withdrawals for Irrigation.
Heavy precipitation during late 1~57 and early 1~58, however, caused these
levels to approach record to near-record highs in the spring of 1958. Thi~
Is particularly evident In the hydrographs of $6532~ S6542, and S7283 showr
in figure 3.
Movement
The movement of water wlthln the sha]'low ground-water reservoir Is Impo
tant to the fresh ground-water supply of Southold and to the potential lm.-
palrment of its quality by sea-water encroachment. From an areal standpoln
the rate. of ground-water movement Is governed by the permeability of the
aqulfer in the direction of flow and by the factors that determine the hy-.
draullc gradlento The permeability depends on the characteristics of the
geologic medium through which the water moves and on the properties of the
-26-
+40
+2O
0
- 20
-40
-60
-80
-I00
CUMULATIVE DEPARTURE FROM AVERAGE PRECIPITATION RATE (1826-1950)
OF 42,90 INCHES PER YEAR
hi
hi
hi
51
49
47
45
43
41
39 1830 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950
MEAN ANNUAL WATER LEVEL IN 14 SELECTED WELLS
Figure 7.--Comparison of the cumulative departure from mean annual precipitation at New York City
and the mean annual water level in It selected wells on Long Island.
water itself, particularly temperature and density. Variations in the phys
ical character of the sediments cons?ltutlng the ground-water reservoir of
Southold have resulted in large differences in the permeability. Dlfferenc~
In temperature and concentration of dissolved salts In the water change the
vlscoslty and density of the water and have a similar effect. As a result.,
the average permeability of the reservoir Is not easily determined. In
problems involving sea-water contamination, the local permeability of the
sediments in the areas of heavy withdrawal Is sometimes more important to
the problem than the overall average permeability.
One method of determining the permeability of an aquifer Is by means of
pumping tests, or aquifer tests. These have been described by Theis (J935)~.
Wenzel (1942), and Ferrls (1949), among others. Using some of the methods
of analysis, a coefficient of permeability Is obtained directly. However,
In the case of the Thels nonequllibrlum formula, the transmlsslblllty of th~
entire thlckness of the aquifer Is obtained. Thls is equal to the coeffi-
cient of permeability multiplied by the thickness of the aquifer.
The evaluatlon of a test at Irrigation well S7905, north of the town of
Southold~ during which the well was pumped at about 325 gpm for IOO hours,
Indlcates that the coefficient of transmlsslblllty of the saturated glacial
deposits in this area is about 200,000 gpd (gallons per day) per foot.
Although the thickness of the saturated deposits cannot be established def-
Inltely, an estimate can be made from the log of the well. From this the
saturated thickness is known to be greater than 50 feet, but probably less
than 200 feet. Therefore~ the coefflclent of permeability may range between
I,oOO and 5,000 gpd per square foot.
Evaluation of one aquifer test gives a knowledge of the hydraulic char-
acteristics of only a comparatively small volume of sediments. This cover-
age may be extended throughout Southold, however, by comparing the specific
capacities of many other wells in the Town with that of well S7905. .The
specific capacity of a well ls computed by dividing the rate at which a well J
is pumped~ <In gallons per m!nute~ by the maximum resultant drawdown, In feet.
Although' the quantity obtained is a unit of gallons per minute per foot of
drawdown (gpm per ft), It is quite commonly referred to by the numerical
value only. The specific capacity of well S7905 Is 27 gpm per foot. Spe-
cific capacities for 77 other wells In Southold that were pumped at more
than IOO gpm range from 7 to 67 gpm per foot and the range is distributed as
follows: ~
Range In speclflc capacity
(gpm per ft)
40 or more
3o to 39
~0 to ~9
IO to 19
Less than
Total
Wells Investigated
Number Percent
Il
15
35
15
I
77
IOO
~e phys-
~ir of
ferencee
~ge the
esult,
In
the
,t to
aris of
thods
ever~
of the
effl-
own of
lacial
d def-
the
less
~etween
char-
:over-
~ciflc
he
a well
n feet.
~t of
al
Spe-
re
ted as
Correlation of the speclflc capacity and the pumping rate of these wells
shows a considerable scattering of the plotted points. Most of the specific
capacities were determined from 8-hour well-capacity (yield) tests. At the
end of 8 hours of pumping, the drawdown In well S7905 had reached more than
90 percent of the total drawdown for a IOO-hour period of pumping. Assuming
this to be true for most of the 7~ wells under consideration, the scattering
of polnts Is probably due to variations In the hydraulic characteristics of
the saturated deposlts. Although a number of factors preclude any precise
extrapolation~ the data suggest that the transmlsslblllty of the glaclal
deposlts underlying Southold ranges from values somewhat less than ~OO~OOO
gpd per foot to values somewhat greater. Further consideration of ?hls will
be glven In a later section concerning the "Ground-Water Budget."
The hydraullc gradient In areas where natural condltions prevall is
related to the llthology, slze~ and shape of the ground-water reservolr~ the
preclpltatlon pattern, and the proxlmlty to and the direction from a re-
gional "sink" where the continuous discharge of ground water can take place.
In Southold such a "sink" Is formed by the salty-water bodies that bound the
Town. Pumping wells and evaporation from ponds and marshy areas can alter
the hydraulic gradient locally and also affect the directlon of the ground-
water I~ovemento Based on an evaluation of the water table for April 1950'as
shown In plate I, the maximum gradient evldent Is about 4 feet per mile.
During tlmes of maximum storage this gradlent would probably be greater.
The relation of the factors Involved In the rate of ground-water move-
ment~ expressed in unlts used by the U. S. Geological Survey, is as follows:
PI (3)
where V = veloclty~ in feet per day,
P = permeabillty of the deposits In the direction of flow, in gallons
per day per square foot of aqulfer~ under a hydraulic gradlent
of [ fdot decline In head for each foot of travel, at 60° F,
! = the hydraulic gradient, in feet per foot, and
0 = poroslty~ which is dimensionless.
For exampl% the rate of ground-water movement in the shallow ground-
water reservoir underlying Southold~ based on a permeability of 5~OOO
gallons per day per square foot~ a hydraulic gradient of 4 feet per mile~
and a porosity of I/3, may be as much as 1½ feet per day.
The dlrectlon of horizontal movement of ground-water in Southold Is at
right angles to the water-table contours and is radially away from a series
of highs (pi. I) In the water table to the surroundlng salty-water bodles.
The role played by shorellne Irregularities In governing the dlrectlon of
ground-water movement Is evident from plate I. Owing to these Irregular-
ltles~ ground water may move from north to south In the northern part of the
Town and from south to north In the southern part. Similarly, on points or
necks~ the movement may be to the east or to the west.
-29-
Precise Information concerning the natural vertical movement of gro~r
water In Southold Is still lacking. Vertical movement through the grour(I.
water reservoir Is probably somewhat similar to the ideallzation shown
the cross section of figure 6. The Water recharged In the Inland hlghs
follows longer flow paths than the water recharged In nearshore areas. 7':
latter Is probably discharged at or just beyond the shoreline. This Ideal
Ization assumes a homogeneous, isotroDlc aquifer (one In which water
with equal facility In all dlrectlons~. The paths of ground-water movem~r
are altered by the presence of layers of slit, clay, and Cemented sand.
Where such layers occur in Southold, the actual flow pattern may be
erably distorted from the idealization shown.
Water moves toward a pumped well in the manner shown In figure 8. W[~
a well is pumped~ two gradients influence the path of flow. One is cause~
by the presence of a natural regional "sink," and the other ls caused by ti
local ~sink" formed when the well is pumped. The resultant vertical flo~
pattern In the ground-water reservoir is shown in figure ~. Water particl~
close to the well move at a rate greater than those farther away. As the
distance from the pumped well increases, the effect of the natural gradieal
on a particle of water becomes greater and diverts a greater amount of fl.)!,
from a direct path toward the well. At still greater dlstance, the influ-
ence of the natural flow pattern is equal to that set up by the pumped well
and a ground-water divide Is created. Beyond this divide the effect of the
natural flow predominates, although the flow paths are distorted. As a r~-.
suit of this comblnatlon of influences, the water level In a pumped well ~
be below sea level locally without causing movement of sea water toward t~e
pumped well.
Ground-water budget
Wate~storage In the ground-water reservoir is a function of the more
basic variables of recharge and discharge that constitute the ground-water
budget~ Changes In the rate of recharge, the rate of discharge, or both
result In changes in ground-water storage. Fluctuations of water levels Jr
wells screened Immediately beneath the water table Indicate these changes In
storage. Decreased recharge resulting from below-normal precipitation may
result In a shrinkage in the volume of fresh Water In storage and cause
salty water to move Inland and upward. Ground-water withdrawal by pumping
from wells at a rate in excess of reservoir recharge Would have the same ent
result. Increased recharge from above-normal preclpltatlon has the opposlt~,
effect. However~ as soil-moisture conditions and consumptive losses vary
wlth the season of the year, precipitation trends do not necessarily di-
rectly reflect trends In ground-water storage.
Figure 3 shows the marked effect that evapotransplratlon has on ground-
Water storage. In most years storage is at a mlnlmum during the late summer
and fall and at a maximum during the spring. Even In summers of above-
normal precipitation, interception of rainfall by plant and soil surfaces
-30-
Land surface
Water level_prior_
to _ p u_m..pi_ng
Figure 8,--Idealized cross section showing the movement Of ground
water toward a well being pumped.
-31-
Pumping
(,..9
Z~
m~
Ground wale,
divide
Sand and gravel
containing
salt water
Figure 9.--Idealized cross sec±ion of a peninsula showing vertical
movement of ground water around a well being pumped,
-32-
usually prevents appreciable recharge to the ground-water reservoir. Rain-
fall which seeps into the topsoil replenishes the moisture deficiency of the
root zone. Water In storage in this zone is tapped by plants and returned
to the atmosphere by transpiration, or Is raised through the interstitial
spaces in the soil to the surface by capillarity and evaporated. During
late fall, water consumption by plants and direct evaporation diminish.
Thus, preclpltatlon in this period can replenish the ground-water reservoir
more effectively. When the resultant recharge exceeds discharge in the form
of lateral outflow and evaporation, water levels in wells begin to rise.
Storage Increases until evaporative and vegetative losses reduce ground-
water recharge to the point where the depleting effects of these Io~ses plus
these of lateral outflow and pumping predominate. Water levels in wells
then start to decline.
The net natural discharge from the ground-water reservoir by lateral
outflow to the surrounding salt-water bodies and by evaporation from marshy
areas probably ranges from 2,500 to 6,000 million gallons annually. This Is
based on a rate of recharge to the ground-water reservoir of at least 7,000
million gallons a year (see table 4) and annual withdrawals for irrigation
and other consumptive uses ranging from I,OO0 million gallons to 4,500
million gallons. If the recharge to and discharge from the ground-water
reservoir followed the same pattern exactly each year equlllbrium would be
established. Under such circumstances there would be little difficulty In
evaluating the ground-water budget on the basis of the recharge-discharge
relatlon shown below:
R = D
which may be written as:
(4)
P - cllmatologic losses = (U + e + Dw) +Z~S (5)
where R = recharge, D = discharge~
Z~S = change In storage,
P = precipitation incident upon land area,
U = lateral underflow,
e = evaporation from the ground-water reservoir exposed in marshy
areas, and
Dw = net discharge from wells.
Certain condltlons are thought to exist In the problem at hand which pre-
clude a simplified consideration of the ground-water budget. The complexity
arises not out of shortcomings In the theory but because sufficient data on
the unknown factors are not available. These factors are discussed below.
Recharge to the ground-water reservoir has been determined earlier In
this report on the basis of preclpltatlon less cllmatlc losses. The estl-
· m~te of lateral underflow and evaporat on from marsh
.~!.. y areas In a precedln~
i paragraph has been made on the basis of recharge in the consecutive 3-yea
period experiencing least precipitation since 1826 and a range in the with-
drawal of ground water. As a steady-state condition was assumed, the time
sequence of events In the approach could be Ignored.
During most years precipitation Is above the minimum value and both cli-
matic conditions and withdrawals for irrigation vary widely. In a year of
average precipitation recharge to the ground-water reservoir may be ],5OO
million gallons more than that in a year experiencing below average precipi-
tation. As previously discussed~ recharge during years with the same annual
precipitation may vary widely. Moreover, all the recharge may not reach the
zone of saturation during the calendar year in which the precipitation took
place. Some might be stored on land surface as snow and not reach the water
table until after the Spring thaw. Some might be retalned in ~he zone of
aeration and not reach the water table in the year being budgeted. If the
year In question has been preceded by a series of very dry years, the amount
of water retained In the Zone of aeration at the start of the year Is at
near-minimum. During the year a larger proportion of the recharge may be
stored temporarily in the zone of aeratlon than if the preceding years were
wet years~
After recharge has reached the Water table, changes in the rate of accre-
tlon to fresh-water storage are assumed to be lnd cated by changes In the
posltlon of the water table. Implicit In this assumption is the conslder-
atlon that such changes in storage take place above sea level. According to
the Ghyben-Herzberg principle, however, storage in a lens of fresh water
floating on salt water is dlvlded Into above- and below-sea level components.
Theoretically, a change in fresh-water storage above sea level would counter-
balance a change of at least forty times the amount In storage below sea
level. In the case of Southold Township the fine sand~ silt, and clay,
which are thought to underlie the area would inhibit any rapid expansion or
contractlon of fresh water storage below sea level. However, as these mate-
rials are permeable to some extent, it Is not unreasonable to assume that
changes in the posltlon of the water table would at least partly indicate a
transfer of storage. The volume of recharge not going Into storage would of
course be discharged as lateral underflow or be evaporated from marshy areas.
Such a conslderatlon suggests the possibility that the Iow point to which
the water levels in wells decline annually (fig. ]) lies J~ the surface of a
more or less "permanent, lens of fresh Water which Is recharged at a minimum
but more or less constant rate of recharge. Rates of recharge for rela-
tively short periods in excess of the amount necessary to sustain this stor-
age would tend to produce transient effects in the storage above sea level.
H~wever, the Influence of precipitation trends throughout a longer period
may modify the volume and shape of this '~permanent, lens.
Evaluation of a ground-water budget for an aquifer consisting of a lens
of fresh ground water floating on salt water is possible only when adequate
data are In hand. These data are more complex than for areas where only
fresh Water Is Involved and where the sediments are homogeneous, the direc-
tion of the ground-water flow in cross-sectional vlew essentially is parallel
to the water table, and the recharge-storage relationship of the aquifer Is
well-defined by the water levels In wells. In addltlon to the hydrologic
data discussed earlier In the report, Information concerning the relation-
ship of the rate of change in volume of both above- and below-sea level
storage with the rate of accretion to the Water table should be in hand.
Also, the relationship of this latter factor to precipitation throughout
selected periods is necessary for computing losses by natural discharge.
~llel
Is
A check of the order of magnitude of the lateral underflow may be made
by application of Darcy's law as reannotated by Ferris (1949):
=
where T = transmlsslblllty of the aqulfer~ In gallons per day per foot~ I = hydraulic gradient, in feet per foot, and
W = length, in feet, of trace In a horizontal plane of the vertical
surface through which flow takes place and at which the gradient
I exists.
On the basis of a transmlssiblllty of ~OO~O00 gallons per day per foot
determined from the aquifer performance test at well S7905, a hydraulic
gradient of ~ feet per mile, and a aggregate distance of 50 miles for the
trace of the vertical surface through which flow takes place and at which
the Indicated gradient is assumed to exis% the average annual outflow is
estimated at about 7,BOO million gallons. Comparison of this amount with
the values for the natural discharge described in the preceding pages sug-
gests that the average transmlsslbIlity of the shallow deposits of Southold
Township Is less than 200,000 gpd per foot. Owing to the complex inter-
relatlonshlp between the flow pattern and the permeability of the deposits
In the direction of flow and the lack of data, only approximate quantitative
slgniflcance can be attributed to such a comparison.
SEA-WATER ENCROACHMENT
The deleterlous effects of sea-water contamination on the fresh-water
supplies of coastal.areas are almost too obvious to mention. If present In
fairly large concen~ratlon~ salty water impairs the taste of drinking water,
destroys the utility of water for Irrigation, and corrodes metallic surfaces.
Magnesium and calcium salts of the contaminating sea water increase the
hardness of a water supply and increase soap consumption and costs by re-
tarding the lathering action of soap. In addition, these salts form boiler
scale. In extremely high concentrations, salt contamination can make a
water supply unfit for human consumption, for Industrial use, or for irri-
gation.
A typical analysis of sea water off the coast of Long Island is given in
table 6.
-35-
Table 6.--Typical analysis of sea water off the coast of Long Island, N. Y.
(after Burr, Herlng, Freeman,
Constituent Parts per million Percent of total sollds
Sodium chloride a/
Magnesium chlorite a/
t&~gneslum sulfate
Calcium sulfate
Silica
Calclum carbonate
Magnesium carbonate
Iron oxide
26,430
3,150
1,783
1,330
56
Trace
Trace
80.4
9.6
5.4
4.0
.4
a/ In this same report the ch
of sea water collected at various
I0,000 to 20,000 ppm.
Iorlde-ion concentration given for samples
locations around Long Island ranged from
Sodium chloride constitutes about 80 percent of the dissolved solids of
sea water In the Long Island area and magnesium and calcium salts almost 20
percent.
Well water havlng a chloride concentration in excess of 500 ppm /parts
per million) is not satisfactory for most uses. Although water having a
chloride concentration as hlgh as 500 ppm or even higher Is not harmful to
the human body, chloride concentrations in excess of 250 or 300 ppm impart a
salty tast~ to the water. Tabulated below are the maximum chloride concen-
trations desirable for various uses (Hoffman and Spiegel, 1958):
Table 7.-~Allowable chlorlde concentrations in water for various uses
Use
Public supply
Irrlgation
Carbonated beverages
Food-equipment washing
Sugar making
Textile processes
Paper making:
Groundwood pulp
Soda pulp
Kraft pulp
Maximum desirable
chloride concentratlo
(parts per million)
25o
IOO to 1,26o*
250 **
250 ~
2o,.x-
IOO ..x.,
75
75 **
200 ~-~
Source
U. S. Public Health Service
Callfornla State Water
Pollution Control Board
Publication No. 3,
"Water Quality Criteria"
Do.
DO.
Do.
Do.
Do.
Do.
* Varies with type of crop.
~-~ Recommended threshold or limiting concentration.
-36-
Sea-water contamination of ground water, resulting In higher than normal
concentrations of chloride, can take place by (I) natural landward migration
cf the zone of diffusion between fresh water and salty water in the forma-
tion, (2) sea-water inundation of iow-lying shoreline areas as a result of
high tides and storm winds, or of high winds alone, and (3) the pumping of a
welt situated close to a zone of diffusion at such a rate that salty water
Is drawn Into the well.
At present, the nature, dlrectlon, and rate of movement of salty water
toward the pumped wells In Southold are not completely known. Some possible
ways by which salt-water encroachment may occur are illustrated in figures 9,
I0, and II.
In figure I0 the water is considered to be stored under hydrostatic con-
dltlons slmllar to that described by the Ghyben-Herzberg ratlo (see section
on "Occurrence and Storage"). The reduced head resulting from the lowering
of water level around the pumped well cannot balance the head of the salty
water at the fresh water-salty water contact, and salty water moves toward
the well. Cessation of the pumping theoretically permits the water to move
back to an equlllbrlum condition. Neither action Is Instantaneous, however,
owing to the slow movement of ground water and the need for the flushing of
water ahead of the advancing front. This slow response Is demonstrated by
the hydrograph of well S7283 in figure 3. The water level in this dug well
Is occasionally depressed to a position lower than 2 feet above sea level
for relatively long periods during the irrigating season. Theoretically,
wlth the It40 ratio, the fresh water-salt water contact should be less than
: . 80 feet below sea level; yet nearby wells screened at this depth yield water
of Iow chlorlde concentrations. This is because, as shown in figure 9,
short-term pumping m~y not change the natural movement of ground water
enough to establish a gradient from the salty water to the fresh water dur-
ing pumplng. Encroachment, therefore, would not occur even if the water
level in the pumped well were below sea level. With extensive ground-water
] ' withdrawal and Iong-te[m pumping, the ground-water divide shown in flgure 9
may extend to the zone'of diffusion and salty water may be drawn toward the
pumped well.
The Important controlling feature in the movement of salty water toward
pumped wells is the subsurface geology. Where the zone of diffusion and
salty water are In or below material of Iow permeability, the salty water
moves toward a pumped well at a very slow rate. If the layers of Iow perme-
ablJlty form a very tight, continuous seal, serious sea-water encroachment
I~ay occur only when the cone of depression of the pumped well has expanded
to the shorellne as shown In figure I1, or when a sufficiently high gradient
has been established across the layers of Iow permeability. If the layers
of Iow permeability are not continuous, are thin, or have been breached,
perhaps by eroslon during glacial time, encroachment may come largely from
beneath. Electrical-resistivity measurements and examination of cuttings
from drilled wells in Southold suggest that layers of fine sand and silt
Interbedded with lenses and layers of clay do occur at varying depths.
Additional test drilling and geophysical exploration will be needed to
establlsh a more complete knowledge of the lithology of the deposits under-
lying the shallo~ ground-water reservoir of Southold.
-37-
WELL BEING PUMPED
t Lond surfoce
Seo level ,~. ~-- ~ Water table
~ . contmning ~
fre,h woter/
~ / Sond?.nd, grovel
Cone of s~a wa~ [ ~ containing
intrusion ~ ~lt ~ter
Figure IO,--Vertlcal sea-water encroachment caused by pumping.
WELL BEING PUMPED
II.--Effect of layers of low permeabil.lty on the encroachment
of sea water.
-38-
Contamination by sea water has caused some of the unusually high chlo-
rld~ concentrations at a number of individual wells and certain irrigation
ponds in Southold -- at the villages of Orlen% Greenport, Southold, Nassau
Poi~lt, and Peconlc (Hoffman and Spiegel, t958). These well locations, shown
In ~:lgure 12 and plate I, are reviewed In the following sections.
Orient area
Contamination of wells and irrigation ponds by sea water Is In evidence
in the vicinity of Orient (hydrologic area 3), an intensively farmed and
irrigated area of about 4½ square miles at the eastern tip of the North Fork
(fig. 12).
This area Is almost entirely surrounded by the sea,.and salt marshes
fringe the shoreline portions of some of the outlying farms. Occasionally,
hurricanes and other severe storms cause tidal waters to flood the low, lying
lands. Because of the proximity of sea water and of the Iow fresh-water
head, it Is reasonable to assume that the fresh ground-water body is thin
and that salty water occurs at a relatively shallow depth. Moreover, be-
cause of the absence of industry In the area, the distance of the sampling
points from the roadways, and the Iow population density, wldespread above-
normal chloride concentrations in the ground water cannot be attributed to
Industry~ highway ~alntenance (spreading of salts to reduce dust or melt ice
and snow), or cesspools. Inasmuch as the use of fertilizer In other in-
tensely farmed areas of Suffolk County has produced chloride concentrations
of less than ~5 ppm in the ground water and presumably would produce a com-
parable effect in this ar~a, concentrations above ~5 ppm cannot readily be
attributed to ferti izer. Sea-water contamination Is the obvious remaining
choice.
High chloride has been recorded In some of the irrlgatlon ponds In
0rlent. The highest recorded is 5,810 ppm In pond P-6 on September 30, 19~8.
Samples taken from this pond on later dates showed a fairly consistent de-
crease to 60 ppm on June ~6, 1953~ During the summer of 1~8 heavy and
continuous withdrawals lowered the pond level and caused salty water to move
Into the pond either from the adjoining tidal inlet or from the ground be-
neath, or both. After 19~8, draft from this pond ceased and the water grad-
ually freshened. Most of the samples from the other ponds had chloride
concentrations of 90 ppm or more -- for example, I00 ppm in P-~ on October II,
1948; 124 ppm In P-5 in August 1949; and 202 ppm in P-9 on July 7, 1952.
The water level In all these ponds Is only I to 3 feet above sea level, and
the ponds are near salt marshes or tldal inlets. The high chloride may be
due In part to occasional see-water inundation; or, more Ilkely, to heavy
withdrawals. The heavy withdrawals lower the pond level and allow the adja-
cent salty surface water to move in or underlying salty water to move upward.
Figure.12.--Map of the eastern part of the Town of Southold showing location of wells
and irrigation ponds yielding salty wa~er.
Only three wells in Orient have shown high chloride -- SI89 (fig. 12,
H-2R), 7,600 ppm when drilled in 1935; S7176 (fig. IR, H-RR), I,OOO ppm on
September 30, 1948, but less .on later dates; and SI4597 (fig.
835 ppm on September 20, 1949, and 296 ppm on July 6, 1950. Well SI89 is
668 feet deep and reportedly yielded no fresh water when drilled. The well
is on a low~ narrow bar, which probably contains only a thin lens of fresh
water floating on salty water derived from the surrounding sea. Water sam-
pled from S7176, a group of 6 well points driven to a depth of I] feet,
contained so much chloride that In the absence of any other source these
concentrations are thought to represent admixture with sea water. At the
time of sampling on September 30, 1948, the water table at this s'ite was
less than a foot above sea level. The shortest lateral distance to a tidal
Inlet is about 700 feet. Thus, large irrigation withdrawals during the
summer of 1948 probably caused salt water to move in either laterally from
the nearby tidal Inlet or vertically from beneath, or both. This salty
water, when mixed in the well with the fresh ground water~ caused chloride
concentrations of I,OO0 ppm or posslbly higher. Well SI4597 is about 150
feet from the shore of Orient Harbor~ In the village of Orient. Prior to
the summer of 1949 a satisfactory water supply was obtained from this well.
However~ In September 1949 the chloride concentration of the water was 835
ppm~ and In July 1950 a second sample contained 296 ppmo The depth of the
well Is not known, but it seems likely that the hlgh chloride is due to
admlxture of salty water from the nearby bay or posslbly from the underlying
salty water.
Greenport-East ~tarlon area
At the village of Greenport~ about 4 miles east of Orient, some of the
public-supplY wells yield water having a detectable salty taster probably
due to the chloride content. Greenport and nearby East Marion, which lie In
hydrologic area 2, are virtually surrounded by sea water. The highest place
In the area, which contains about 7 square miles, Is about 60 feet above sea
level, but most of the area Is much less than 40 feet above sea level. The
water table in unpumped localities has a ~ximum altitude of about 3 feet
above sea level. A sewer system discharges domestl% commercial, and Indus-
trial wastes to Long Island Sound, so there is probably little contamination
of ground water from these sources.
Station 3 of the village of Greenport water system comprises 6 wells
(Sl673-78; fig. i2, H-21) about 55 feet deep. These are pumped together,
end the mixed water is pumped into the distribution system. Figure {3'shows
the monthly variation In the chloride concentration of the water from this
station together with the ~nthly pumpage and monthly precipitation. Figure
14 shows the same data on a dally basis for October 1951. Chloride concen-
trations of water pumped at this station throughout a period of years have
ranged from 123 to ~24 ppm~ the concentration being highest In the summer
when withdrawals are greatest. These concentrations are substantially
higher than that (45 ppm) determined In 1932 for the water pumped from well
7
6
~5
I
z MONTHLY PRECIPITATION
~300
0 0
0 0
o 0
Z Z Z
-~200
b.I
n I00
o
MONTH-END CHLORIDE
CONCENTRATION
6
J F M A M J J A .S 0 N D
MONTHLY PUMPAGE
Figure 13.--Variation in chloride content of water pumped at $'i'ation 3,
vi lage of Greenport Water Supply, with monthly pumpage
and monthly rainfall during 1951.
-42-
I.O
I
I
o.o ' -
DALLY PRECIPITATION
4OO
DALLY
CHLORIDE
CONCENTRATION
I ~1 II
I 5 I0 15 20 ?-5
DAY OF THE MONTH
31
DALLY PUMPAGE
igure 14.--Variation in chloride content of water pumped at Station 3,
village of Greenport Water Supply, with daily pumpage
and daily rainfall during October 1951.
-43-
SI78 at the same site. Extenslve spreadlng of water of lower chloride
concentrations during recent years has helped somewhat in reducing the
cc~ntamlnatlon.
Station I has two wells about 35i feet deep that are pumped separately.
Water from well SI668 (fig. 12, H-21) has had chloride concentrations rang-
lng from 76 to 94 ppm; and well SI669 (fig. 12, H-21) showed concentrations
of 135 and I53 ppm in the summers of 1949 and 1950, respectively. These
chlorlde concentrations Indicate an admixture of salty and fresh water.
Data obtalned during the drllllng of test well S490 (V892) a/, drll'led 690
feet to bedrock at station I In 1903, Indicated salty water-at a depth of
225 feet (Veatch, 1906). These data are incomplete, however, and neither
the salt-water level nor the actual chloride concentration Is known. During
the 1940's when the existing wells at Station I (SI668 and SI669) were
pumped for brief periods at a rate of 600 gpm, ~rked and rapid Increases in
the chloride concentration of the pumped water were observed (Harry Monsell,
Village of Greenport Department of Public Works, personal communication).
As these wells are about half a mile from any tidewater, this contamlnatlon
Is probably the result of upward movement of underlying salty water. In
1953, when wells S1668 and SI669 were pumped at a rate of about 50 gpm each,
they produced water having · chloride concentration ranging from 76 ppm to
153 ppm.
Other Southold areas
Other wells In Southold that are thought to have been contaminated by
salty water In nearshore areas are: S4091, Southold (918 ppm);
Peconlc (l,600 ppm); and S5475-76, Nassau Point (103 ppm).
Well S4091 (flg~ 12j G-20) Is about 500 feet from the head of Town Creek,
a tldal Inlet near the village of Southold. This well, 45 feet deep, is
screened In a bed of sand and gravel 60 feet thick, which Is underlain by at
least 80 feet of clay and sandy clay. According to the driller's report the
water beneath the clay and sandy clay Is salty. Pumping the well at a rate
of about 225 gpm caused salty water to move either upward through the clay
or laterally from the Inlet. Thls waterj mixing In the well with the fresh
water, caused the chlorlde concentration of the well water to increase
steadily from 24 ppm on September 5, 1945~ to 918 ppm on July 9,
Owlng to the high chloride concentratlon In the water, the well was aban-
doned and another well, S4091R, was drilled about 500 feet to the west. The
chloride concentration In the water from this newer well was 34 ppm In
Well S6059 (pl. I, G~20), 78 feet de~p, Is approxlmately 500 feet from a
tidal ~arsh. The log of the well shows ~O feet of fine sand and some clay
overlying the 38 feet of sand and gravel in which the well Is screened. As
the water table at thls slte Is less than l½ feet above sea level, the well
---"~-/--_aSee well-numberlng system described at end of report.
is probably screened in or near the zone of diffusion separating the fresh
water and the salty water below. Contlnued pumping of the well at 350 gpm
resulted in a gradual increase in the chloride concentration of the water to
1,6OO ppm. Water having this concentration of chloride cannot be used for
irrigation in thls area, so the well was ultimately abandoned.
Wells S5475-76 (pl. I, F-20), drilled to a depth of 30 feet, are less
than 500 feet from sea water in Nassau Point, an Isolated colony of summer
homes. The altitude of the water table in the vicinity is not specifically
known, but it probably Is less than a foot above sea level, and the wells
may be screened near the zone of diffusion. Although the draft from these
wells Is small and the wells are used for domestic supply, the magnitude of
chloride concentration (37 ppm, t948; IO3 ppm, [950) is above the maximum
normally expected (~5 ppm) and suggests that pumping causes salty water to
move Into the wells. There Is also the posslbillty that contamination from
cesspools has contrlbuted to the chloride concentration. However, no addi-
tional data are now available, and further Inferences are not possible.
SUMMARY AND CONCLUSIONS
Approximately 83,000 mllllon gallons of usable water are stored In the
upper Pleistocene sand and gravel of Southold's shallow ground-water reser-
volr. The few pieces of available evidence confirm the supposltlon that
this reservoir Is underlain by salty water. Owing to the protective Influ-
ence of the clay of. the Rarltan formation and the pattern of ground-water
movement from the mainland part of Long Island, It is also possible that
Ilmlted supplies of fresh water may be stored at depths of over 600 feet in
parts of the Lloyd sand member. However, very little is known concerning
the characteristics of the water In the Raritan formation beneath Southold.
The shallow ground-water reservoir ts replenished by the infiltratlon of
preclp'ltatlon on the Town. During very dry years It Is estimated that the
replenishment is about %000 mllllon gallons annually, or about one-twelfth
of the fresh ground water In storage. During other years both replenishment
and storage are probably greater. This replenlshment Is held In storage
temporarily, for it Is being continuously discharged to the sea by lateral
movement of ground water. This lateral discharge, which takes place by
spring flow and evepotranspiratlon near the shorelines and by submarine out-
flow, may be as much as 6,000 milllon gallons annually.
As salty water forms both the lateral and the subsurface boundaries of
the shallow ground-water reservoir, impairment of the quality of the water
through pumping Is a constant threat. Serious salt-water contamination has
taken place at only a few wells, all of which were near the shore in areas
where the Water table was less than ~ feet above mean sea level. Perhaps
the most serious case of contamination Is that of the wells of the village
of Greenport's water supply, where chloride concentrations of the well water
have been higher than 400 ppm. Controlled pumping of the contaminated wells
and mixlng the pumped water wlth water of Iow chloride content from other
wells has kept the water supply potable.
Southold's present (1958) ground-water proolem is not so much general
sea-water encroachment that would result from ~er,eral overdraft by pumping
of the ground-water reservoir and lowering the water table areally, but
rather local contaminatlon resulting from mark.~d lowering of the water table
by sustained heavy withdrawals at one well or a cluster of wells. Despite
the fact that pumping wlll create a hydraulic .~radlent from the salty water
to the fresh water, the method and pattern of i~lthdrawals and the subsurface
geology largely determine the extent and rate of any encroachment that may
take place. Fortunately, withdrawals for Irri!]ation are seasonal and the
salty water drawn toward the wells during the summer months may be fJushed
out during the fall and winter months.
Past experience (1949) Indicates that irrigation withdrawals of 4,600
million gallons annually can be made occasionaJly with Impunity, if the
present pattern of pumping Is observed. As this Is only about two-thirds of
the average near-minimum replenishment, the allowable withdrawal can prob-
ably be doubled safely during most years. In near-~shore areas or areas~
where the water table is close to sea level and the fresh water in storage
does not rest on layers of Iow permeability, even moderate withdrawals may
result in sea-water contamination of the reservoir. Previous experience in-
dicates also that it is inadvisable to locate any irrigation pond or well
wlthln I,OOO feet of the shoreline or of any embayments containing sea water.
Nearshore wells and ponds located according to this rule generally can be
pumped intermittently at a maximum rate of about 250 gpm, or about I00 gpm
continuously. In the more inland parts of Southold an intermittent pumping
rate of 500 gpm has been found satisfactory.
Prior to further development of the ground-water reservoir of Southold,
test wells need to be drllled to depths of 200 feet or more to ascertain the
lower limits of the fresh-water reservoir, the nature of the underlying
salty water, and the physical character of any layers of Iow permeability
that may exlst.
Owing to the lack~of data, only brief consideration has been given in
thls report to the relation of trends in precipitation to the volume of
fresh ground water in storage. This relationship may prove to be the crit-
Ical factor governing the allowable withdrawal. Replenishment to and stor-
age In the ground-water reservoir during the perlod of study may represent
optimum conditions. Shrinkage of the volume of fresh water In storage as
the result of lowered replenishment for extende,~ periods may cause the base
of the fresh-water body to shift upward. Thus, the pattern of withdrawal
considered safe under present (1958) conditions may cause a relatively rapid
Intrusion of salty water under future conditions. On the other hand, the
zone of diffusion may lie in material of Iow permeability and respond very
slowly to changes In preclpltatlon. Future problems of sea-water encroach-
ment may appear only gradually.
The data in hand are sufficient to Indicate that a future problem may
arise and to suggest the relationship of the various factors Involved. More
detalled data must be collected, however~ to substantiate the conclusions
that have been made thus far and to permit a more complete analysis of the
-46-
geology and hydrology of the area. For example, detailed study of the
recharge to the ground-water reservoir necessitates consldarable Instrumen-
tation for determining precipitation and evaporation. Evaluation of storaga
in the reservolr requires a more complete appraisal of the hydraulic charac-
teristics of the reservoir and a detailed analysls of fluctuations in ground-
water levels. Further knowledge of the physical character of the ground-
water reservoir and the occurrence of fresh and salty water requires test
holes and possibly additional geophysical exploration. The evaluation of .
the dlscharge from the ground-water reservoir at various stages of the water
table requires Information on the hydraullc characteristics of the reservoir
and water-table contour maps. Correlatlng this discharge with various re-
charge conditions requ!res intensification of the water-level-measurement
program. Finally, study of the movement and dimensional changes of the zone
of diffusion requires detailed sampllng of selected wells for chloride con-
tent°
WELL-NUMBERING SYSTEM
Wells on Long Island, N. y., are Identified by a numbering system set up
by the New York Water Resources Commission. Each well is numbered serlally
and is prefixed by the initial letter of the Long Island county In which it
is located. Thus, for Suffolk County thls would be the letter "S~, as In
the well number S7~8]. For greater leglblllty the prefix "S" has been omit-
ted from well numbers shown on plate I and in figure 12.
Most walis that were drilled prior to 19]~ and that appeared In the
early publlshed reports of the Geological Survey have been subsequently
assigned numbers under the current system. Thus~ for example, the well num-
ber S490 Is the current number assigned to the well V89~, described by
Veatch (1906, p. 330)~
-47-
REFERENCES
Burr, W. H., Herlng, R., and Freeman, J. R.~ 190~, Report of commlsslon on
addltlonal water supply for City of New York: New York, Martin B.
Brown Co.
Ferrls~ J. G., 1949, Ground water, Chap. 7 in Wlsler, C. 0., and Brater,
E. F., Hydrology: New York, John Wlle~ Sons, p. 198-272.
Gustafson, A. F., and Johnstone, D. B., 1941, Soil and pasture management
for Long Island, New York: Cornell Univ. Agrlc. Expt. Sta. Bull.
~p.
Hoffman, J. F., 1959, Ground-water utilization, Suffolk County, L. I., N. Y.:
Am. Soc. Civil Engineers Proc., v. 85, Separate no. 2(:~0, p. 25-41.
Hoffman, J. F., and Spiegel, S. J., 1958, Chloride concentration and temper-
ature of water from wells In Suffolk County, Long Island, New York,
1928-53: New York State Water Power and Control Comm. Bull. GW-38, 55 p.
Hubbert~ M, King, I~0, The theory of ground-water motlon: Jour. Geology,
v. 48, no. 8, p. 92~-926.
Leggette, R. M., and others, 1938, Record of wells In Suffolk County, N. Y.:
New York State Water Power and Control Comm. Bull. GW-4, 108 p.
Lusczynskl, N. d., and Hoffman, J. Fo, 1951, The water table as of Aprll
1950 In Southold Township, Suffolk County, Long Island, N. Y.: U. So
Geol. Survey open-file report, 4 p.
Meyer, A.~ 194/~, The elements of hydrology: New York, John Wlley& Sons,
522 p.
Paulsen, C. G., and others, 1940, Hurricane floods of September 1938: U.S.
Gaol. Survey Water-Supply Paper 867, 562 p.
Perlmutter, N. M., Geraghty, J. J., and Upson, J. E°, 1959, The relation
between fresh and salty ground water in southern Nassau and southeastern
Queens Counties, Long Island, N. Y.: Econ. Geology, v. 54, p. 416-435.
Spear, W., 1912, Long Island sources -- An additional supply of water for
the City of New York: New York City Board of Water Supply, 2 vols.
Suter, Russell, deLaguna, Wallace, and Perlmutter, N. M., 19J~9, Mapping of
geologic formations and aqulfers of Long Island, N. Y.: New York State
Water Power and Control Commo Bull. GW-18, 212 p.
Thels, C. V., 1935, The relation between the Iowerlng of the plezometric
surface and the rate and duration of discharge of a well using ground-
water storage: Am. Geophys. Union Trans., p. 519-524.
-48-
REFERENCES (Continued)
S. Department of Agriculture, 1~8, Local marketing report no. I0, 1948,
Suffolk County, New York.
Veatch, A. C., and others, 1906, Underground water resources of Long Island,
New York: U. S. Geol. Survey Prof. Paper 44, 394 p.
Wenzel, L. ~i~ 1942, Metes for determining permeability of water-bearing
materials, with special reference to dlscharglng-well methods; with a
sectlon on direct laboratory methods, and bibliography on permeablllty
and laminar flow by V. C. Flshel: U. S. Geol. Survey Water-Supply
Paper 887, 192 p.
-49-