HomeMy WebLinkAboutNassau Point Ground Water Qualityv
INVESTIGATION OF GROUND WATER QUALITY OF THE
NASSAU POINT PENINSULA
TOWN OF SOUTHOLD, SUFFOLK COUNTY
SUFFOLK COUNTY DEPARTMENT OF HEALTH
Herbert W. Davids, Director
Division of Environmental Health Services
· · · Nassau Potnt ......'..:..;.'.'..i...'. ... '-.'..'~,
X '. '," · ~ '.'~;'¢-'./ ~'~'. '.':.'~ ..... :.."4-"
~.~ X '.. ~.';.~" . / ~.~'.- ~ ~:' ~ '.:~:.- ...... v'
,. :.:...~' ~...,.,.4.~ r,.-~.~..,~ '~~[... ,.
.. -. ~ .... ~:'.~.~"' X , ~....,,..-. .,,-s, ..
~r~, -..~ .. :...; .... . -. ;:-.~.M'. _ 4-.~..* .%. '- · .'...'. '.' '.... ~'%
ocEAN
Fig. 1 Nassau Point - Little Nog Neck - Town of Southold
Location: Nassau Point, also known as Little Hog Neck, ts.a peninsula
located on 'the south shore of the North Fork In the Town of Southold,
Suffolk County (Fig. 1). The peninsula has an approximate land area
of 0.75 sq. mi. and ts surrounded by salt water bodies. Great Peconic
Bay borders the peninsula on the west and the Little Pecontc Bay on
the east. Haywaters and Broadwaters separate the peninsula from the
mainland on the north. A causeway, approximately 1500 feet tn length
by 150 feet in width, connects the peninsula to the mainland.
Geology: Underlying soil conditJons of Nassau Point consist of
primarily glacial outwash deposits. These deposits are chiefly sands
and gravels of Upper Pliestocene age. An area, near Wunneweta Pond,
consists of ground moraine deposits which are a mixture of clay, sand
and pebbles to boulder sized gravel. Shoreline deposits of.recent
geologic age comprise the east coast of the Point. Thts formatfon ts
well sorted sand and gravel deposited by currect and wave action.
The topography elevations range .from sea level to over 50 feet.
~limate: The predominate climate for the area is temperate marine.
Temperatures are moderate and precipitation is abundant during the
fall, winter and spring. Summer usually is dry.
The mean annual precipitation is 44.S inc'hes. The April-September
mean precipitation is 20.5 inches.
Fig. 2 - Cross Section from L.I. Sound to Little
Pecontc Bay
-2-
Ground Water: A small body of fresh water underlies Nassau Point
(Fig. 2). Precipitation provides the only source of replenishment
of the ground water reservior. A part of the precipitation flows
overland to the surrounding salt water bodies and fresh water ponds.
A part is returned to the atmosphere by evaporation and by trans-
piration of plants. The remainder of the precipitation seeps into
the ground. Some of the seepage into the ground eventually reaches
the ground water reservtor and becomes available for withdrawal by
wells (Fig. 3).
At the present time, all the homes
Information supplied by individual
depths vary l0 to 100 feet.
on the peninsula use private wells.
homeowners indicate that well
It is estimated that approximately 5 inches of the annual precipitation
enters the surface waters as direct runoff and 17 inches is lost throug~
the combined effects of evaporation and transpiration {evapotranspir-
ation).
Recharge to the ground water reservior is the difference between the
amount of precipitation and the sum of direct runoff and evapotrans-
piration.
The annual recharge for the Nassau Point area is 160 million gallons.
A lO~ reduction is included to allow for local clay soil conditions,
paving, and residential homes.
All the fresh ground water available for use on the
contai ned
Since the
peninsula is
under water table conditions in upper Pliestocene deposits.
Point is virtually surrounded by salt water, the area is
\
\
,,,
Ffg. 4 Ghyben-Herzberg Principle
Fig. 5 - Vertfcal Hovemenb of Salty Ground Water Toward
a Pumping ~el1
-3-
treated as an island of ground water or
The specific gravity of the fresh water
underlying salt water, therefore, the fresh
the salt water within the boundaries of the
to the Ghyben-Herzberg principle {Fig. 4).
a discrete fresh water lens.
is less than that of the
water tends to float on
island genera'lly according
This principle states that equilibriun, the depth of fresh water below
sea level at any point on the island, is proportional to the fresh
water head above sea level and dependent on the relation of the specific
gravities of fresh and salt water. Generally, the relationship shows
that fresh water would extend 40 feet below sea level for each foot
it extends above sea level. This theory does not take into account
the zone of mixed water around the fresh water lens.
Little Hog Neck, based on 1963 report, contains a fresh water mound
with a crest altitude of slightly more than 1 foot. A report by the
Geological Survey of water tabJe elevations as of March lg20 was not
of sufficient detail to include Nassau Point since the contour map
developed had elevations shown at 5' intervals.
The movement of the ground water moves toward the surrounding salt
water bodies along flow lines whose direction is normal or perpendicular
to the water table contopr.
It is estimated by the USGS that there is 600 million cubic feet of
deposits satuated with fresh water. This water is not totally availabl(
The specific yield of the aquifer is assumed to be about 22% based on
studies performed in the Town. This would leave the peninsula with
an estimated volume of fresh water in storage as 1,O00 million gallons.
-4-
In an ideal hydrologic system, discharge equals recharge plus or min~
changes in ground water storage. Pumpage could be allowed to approach
\
the daily recharge from precipitation. However, withdrawal must be
kept lower than this amount to minimize demand on storage. On the
basis of conditions, withdrawal should not exceed 30% of annual recharge
Annual recharge = 160 mg - 0.44 mgZday
30% Annual recharge - 0.132 mg/D = Allowable Withdrawal
Assuming Use of lO0 gal/capita/day
132000 MGD
100 GPCD = 1320 People
Assuming 3.7 Persons Per Home
'1320
~ = 356 Homes.
Theroetically there ts sufficient water available based on 1963 data
to support 350 homes, however, several factors must be incorporated
into any allowable density in this area. These include salt water
intrusion and water quality.
Salt Water Intrusion: Fresh water generally has a chloride concen~
tration of less than 40 mg/1. The concentration within the zone of
diffusion varies from 40 to 1800 mg/1. The underlying body of salty
ground water has a chloride concentration of 1600 to 18,000 ppm.
Intrusion occurs when pumpage neat the interface draws the salty water
upward (Fig. 5). High tides and wave action can inundate the fresh
water lens by downward movement. Oredging also causes the inward move-
ment of the interface. In a USGS report (1963) four shoreline wells
had chloride concentration ranging from 103 to 1600 ppm. Drinking
Water Standards states a recommended limit of 250 mg/1. These wells
were within 500' of the shoreline.
Water Quality: On August 26, 1970, this Unit sampled sixteen wells
for partial chemical analysis. The analysis included ammonia, nitrates,
-5-
detergents, chlorides, tron and pH. Additional samples
March 2, lg71. One home was sampled on both occasions
seasonal variations. No variation was found.
were taken on
to determine
Nitrates find there way into water supplies from the decomposition
of organic nitrogen and ammonia, both of which are present in household
sewage.. Lawn and garden fertilizers are also a source of nitrates.
Maximum permissible levels of 10 mg/1
due to serious and occasionally fatal
waters containing nitrates.
nitrate nitrogen has been set
poisioning of infants ingesting
Detergents have
disposal system and therefore a good
entering an individual water supply.
gents is 0.5 mg or MBAS.
their orgin specifically from the household waste
indicator that sewage wastes are
The recommended limit for deter-
Chlorides are a dual indicator. High concentrations can be used to
indicate salt water intrusion while lower values show etther domestic
sewage pollution and/or salt water intrusion. The Drinking Water
Standard for ch]orides is 250 mg/1.
Iron concentrations in excess of the recommended Drinking Water
Standards is an esthetic problem causing discoloration, taste, and
clothes and fixture staining.
pH is 14 point range indicating the acidity or alkalinity of the
water with a value of 7 being neutral. 0-7 indicates a acidic condition.
.Samples - 20
Determination
Chiori~es 20
Detergent 13
~onst!tutent
NBAS
Chloride
Nitrate
Nitrate 13 Iron 13
Ammonia 13 pN 20
Range % Of Samples
Within Range
* 0.1 mg/1 g5
0.1-0.5 5
0-20 20.0
20-40 30.0
40-250 50.0
250 or greater 0
0-7 95
7-10 0
10 or greater 5
Iron 0-0.3 77
0.3 or greater 23
* indicates less than
appeared to be receiving detrect cesspool leach-
Only one shallow well
tngs.
There was no evidence of detergent in the aquifer except in the
aforementioned case.
were not found in a
concentrations were
except for the east
balance in the area
Fifty percent of the wells sampled showed varying degrees of salt water
intrusion. The chloride concentrations indicating possible intrusion
specific geographical area although the higher
found in the areas closer to the salt water bodies
bluff. It is obvious that there is a tenuous
between the salt and fresh water. Certainly any
large withdrawals will have drastic effects. The one case of nitrate
concentration exceeding standards was caused by cesspool leaching. The
generally low concentrations can be attributed to seasonal population
-7-
fluctuation and the sam11 percentage of land receiving fertilizers.
The 1ton concentrations tn excess of standards were probably caused
by well inactivity, plumbing or the well casings. ·
Conclusions
1. Nassau Point h~s a limited quantity of fresh water tn under-
ground storage due to the salt water of the Bay's existing
below the peninsula.
2. The only source of replenishment of the fresh ground water is
by natural precipitation of which only about one half finds
it way into the water table by the tnflitratton prOcess.
3. Chemical analyses (chlorides) indicated that salt water
intrusion is evident t.n 50~ of the wells surveyed while an
additional 30~ had chloride levels in which differentiation
between salt intrusion and cesspool pollution could not be
actually determined. Eighty percent of the homes are thus
experiencing chloride levels in their water supply greater
than normal accepted ground water concentrations although
none exceeded drinking water standards.
4. The rate of salt water intrusion cannot be accurately es-
tablished but the rate wi1'1 be a function of development,
population growth, ground water withdrawal and the amount
of natural precipitation. Another drought with the resultant
lowering of the ground water
fresh salt water balance and
deterioration.
table will further aggrevate the
increase the rate of ground water
-8-
R~Rommendations
1. Establish low density zontng tn the area.
Prevent any dredging of the shoreline
3. If the condition of the ground water shows detertoa'tto~, a
central water supply for the peninsula should be established
to provide management of the resource. Controlled move-
ment of the salt water interface could thus be achieved.
The feasibility of connecting to a central mainland public
supply shoulc be studied.
Prepared by:
~ames Hetl, P.E.
~ater Quality Section