HomeMy WebLinkAboutGround Water Supply Analysis 1983E~H-l~orth~-~zst
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JUL 6 1983
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ANALYSIS OF AVAILABLE
GROUND WATER SUPPLY
TOWN OF SOUTHOLD
Prepared for
Town of Southold Planning Board
May 1983
Prepared by
ERM-Northeast
88 Sunnyside Blvd.
Plainview, New York 11803
Korth t
INTRODUCTION
The Southold Town Planning Board is currently updating its
Master Plan. ERM-Northeast was retained by the Planning Board
to estimate the quantity of ground water available throughout
the Town. The availability of ground water in the central
portion of the Southold peninsula (water budget areas) was
estimated during the preparation of the North Fork Water Supply
Plan (ERM-Northeast, April 1983). The focus of this investiga-
tion is, therefore, to estimate the available ground water
yield in coastal areas of the Town.
BACKGROUND
Five ground water supply zones were delineated in the North
Fork Water Supply Plan (NFWSP). Three of these zones (3, 4 and
5) are wholly within Southold Town. Zone 3 extends from the
Mattituck Inlet to Hashamomuck Pond; Zone 4 extends from Hasha-
momuck Pond to Dam Pond; Zone 5 starts at Dam Pond and ends at
Orient Point. These three zones function as independent aqui-
fers. Zone 2 is partially within Southold; it extends from
Doctor's Path in the Town of Riverhead to the Mattituck Inlet
in Southold. Approximately 25 percent of Zone 2 is located
within Southold Town.
In each ground water supply zone, a water budget area was
delineated. In these areas, sufficient ground water exists to
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permit the development of public supply wells. In Zones 3, 4
and 5, the available ground water supply is rather limited.
The water budget areas in these zones were defined by the two
foot (above sea level) ground water contour. Areas within
those zones have a minimum of 80 feet of fresh ground water(1).
In Zone 2, the available supply is less limited and the water
budget area was defined by the five-foot ground water contour.
The budget area is, therefore, underlain by a minimum of 200
feet of fresh ground water.
The permissive sustained yield(2) for the water budget area
in each zone was estimated in the NFWSP using unit yield factors
(million gallons per day per square mile of area).obtained from
the Suffolk County Comprehensive Water Supply Plan (CPWS-24).
These factors vary from zone to zone depending on the thickness
of fresh water and aquifer parameters. It was estimated that a
permissive sustained yield of 6.4 mgd can be derived from the
water budget areas in Zones 2 (Southold portion) 3, 4 and 5.
No estimates were made in the North Fork Water Supply Study of
the available ground water yield outside of the water budget
areas.
~l)The Ghyben-Herzberg principal states that the depth ~f fresh
water below sea level is 40 times the height of fresh water
above sea level. The validity of this principal on the
North Fork, was confirmed in the North Fork Water Supply Plan.
(2)The permissive sustained yield is the maximum rate at which
water may be withdrawn from the aquifers perennially without
bringing about the undesirable effects of saltwater intrusion.
2
EP,~;-North~st
METHODOLOGY
During this analysis, the quantity of water available out-
side of the water budget areas was estimated as follows:
a.) The area was divided into two sub-areas: (1) between
the coastline and the one-foot ground water contour,
and (2) between the one-foot contour and the water
budget area. - ---
b.) Unit yield factors were then determined for these
areas by extrapolating the yield factors (for the
water budget areas) contained in CPWS-24.
c.) The unit yield factors were then applied to the
areas delineated in Step (a) and total permissive
sustained yields obtained.
The location of
mated based upon:
one-foot ground water contours was esti-
o the Suffolk County Department of Health Services
ground water monitoring network
o the United States Geological Survey's ground water
monitoring network
(SCDHS)
o data on home wells obtained from the files of the SCDHS
o the topography of the area
o the geological cross-section prepared in the North Fork
O
Water Supply Study
proximity with respect
tidal bays, inlets and
to saline water bodies (including
streams).
3
E P, t-1 -
Table 1
SUMMARY OF AVAILABLE WATER SUPPLY
(Ail Figures Rounded)
PERMISSIVE
UNIT YIELD SUSTAINED
AREA FACTOR YIELD
ZONE LOCATION (sq. miles) (mgd/sq. mile) (mgd)
2 Water Budget Area 0.60 0.4 0.2
(Southold
Portion) Between 1' & 5' _
Contour 5,0 0.35 1.8
Between Coastline
and 1' Contour 1.0 0.15 0.2
Total .... 2.2
3 Water Budget Area 14 0.35 4.9
Between 1' & 2'
Contour 6.2 0.20 1.2
Between Coastline
and 1' Contour 4.9 0.15 1.1
Total .... 7.2
4 Water Budget Area 3.4 0.25 0.9
Between 1' & 2'
Contour 1.5 0.20 0.3
Between Coastline
and 1' Contour 2.1 0.15 0.3
Total .... 1.5
5 Water Budget Area 1.6 0.25 0.4
Between 1' & 2'
Contour 2.2 0.20 0.4
Between Coastline
and 1' Contour 1.2 0.15 0.2
Total .... 1.0
EP.H- i o,-th st
Creek. Along
end of Orient,
inland.
To further
It was found that the one-foot ground water contour was
in close proximity to the coastline along the north shore
(except the eastern end of Orient) and the banks of Mattitock
the south shore and the north shore of the east
the one-foot ground water contour was further
assist in the development of the Master Plan,
the yields in Zones 3 and 4 were subdivided into a number of
discrete geographic sub-areas. Zone 3 was subdivided into
eight sub-areas including Nassau Point, Bayview and New Suffolk.
These areas are underlain by aquifer systems which function in-
dependently from each other and the main aquifer beneath Zone 3.
The remaining area in Zone 3 was divided (east/west) based upon
major physical features (water bodies) in the zone. The Long
Island Railroad tracks were used as the dividing line between
the north and south shore boundary between sub-areas. Table 2
provides the permissive yields for these areas.
Zone 4 was subdivided into two sub-areas utilizing the
east boundary of the Greenport Water District as the line of
demarcation. This line was used to delineate the sub-areas
because new development within the Greenport Service District
should utilize public supply from the Village of Greenport
(consistent with the capacity of the Greenport system). The
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CPWS-24 provides unit yield factors for water budget areas
throughout the County including the North Fork. CPWS-24, how-
ever, does not provide these factors for locations outside of
the water budget areas. To obtain these, the factors provided
in CPWS-24 were extrapolated dox~ward. The unit yield factor
for areas between the coastline and the one-foot contour was
estimated to be 150,000 gallons per day per square mile; a
yield of 200,000 gallons per day per square mile was estimated
for the area between the one and two foot contours. A yield
of 350,000 was estimated for the area in Zone 2 between the
one and five foot ground water contours. For comparison, the
unit factors in the water budget area in Zone 5 (Orient Point)~
is 250,000 gallons per day per square mile.
RESULTS
The results of this analysi's indicate that the total per-
missive sustained yield in Southold Town is 11.9 mgd. Of this
total, 6.4 mgd (54 percent) can be obtained from within the
water budget areas, and 5.5 mgd (46 percent) between the coast-
line and the budget areas.
Table 1 provides a summary of the results organize~ by
water supply zone. As indicated in Table 1, 60% of the total
yield can be obtained from Zone 3, with lower percentages from
Zones 2, 4 and 5 (listed in order of decreasing available
yield).
Table 2
AVAILABLE WATER SUPPLY
ZONE 3
PE~,~ISSIVE
TOTAL UNIT SUSTAINED
AREA YIELD YIELD
SUB-AREA _ (Sq. Miles) (mgJ/Sq~ Hile) (mgd)
North Shore - West of
Goldsmith Inlet
Water Budget Area 5.4 0.35 1.9
Between 1' and 2'
Contour 1.3 0.20 0,26
Between Coastline and
1' Contour 0.6 0.15 0.09
Total Area 7.3 -- 2.25
North Shore Between
Goldsmith Inlet and
Hashamomack Pond
Water Budget Area 2.4 0.35 0.84
Between 1' and 2'
Contour 1.3 0.2 0.26
Between Coastline and
1' Contour 0.9 0.15 0.14
Total Area 4.6 -- 1.24
South Shore - Between
Matt. Creek and East
Creek (Contiguous Areas
Water Budget Area 3.2 0.35 1.1
Between 1' and 2'
Contour 0.65 0.20 0.13
Between Coastline and
1' Contour 2.15 0.15 0.32
Total Area 6.0 -- 1.55
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ERH- [~orth~-~st
Table 2 (cont'd)
AVAILABLE WATER SUPPLY
ZONE 3
PE~,IISSIVE
TOTAL UNIT SUSTAINED
AREA YIELD YIELD
SUB-AREA (Sq ~__Miles) __(m~d/Sq. Hile) (mgd)
South Shore - Between
East Creek and Jockey
Creek
Water Budget Area 2.2 0.35 0.77
Between 1' and 2'
Contour 1.5 0.20 0.30
Between Coastline and
1' Contour 1.8 0.15 0.27
Total Area 5.5 -- 1.34
South Shore - Between
Jockey Creek and Hasha-
momack Pond
Water Budget Area 0.4 0.35 0.14
Between 1' and 2'
Contour 0.3 0.20 0.06
Between Coastline and
1' Contour 0.4 0.15 0.06
Total Area 1.3 -- 0.26
New Suffolk
Water Budget Area 0.0 N/A 0.0
Between 1' and 2'
Contour 0.18 0.20 0.04
Between Coastline and
1' Contour 0.19 0.15 0.03
Total Area 0.37 -- 0.07
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E~F~- North~-~st
Table 2 (cont'd)
AVAILABLE WATER SUPPLY
ZONE 3
PErmISSIVE
TOTAL UNIT SUSTAINED
AREA YIELD YIELD
SUB-AREA __ (Sq. Miles) _(mgd/Sq. Mile) (mgd)
Nassau Point
Water Budget Area 0.0 N/A 0.0
Between 1' and 2'
Contour 0.38 0.20 0.08
Between Coastline and
1' Contour 0.37 0.15 0.06
Total Area 0.75 -- 0.14'
Bayview
Water Budget Area 0.40 0.35 0.14
Between 1' and 2'
Contour 0.40 0.20 0.08
Between Coastline and
1' Contour 1.0 0.15 0.15
Total Area 2.3 -- 0.37
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area east
(0.39 mgd)
Site
of the Greenport service area has only 25 percent
of the total yield of Zone 4 (see Table 3).
specific investigations and field measurements are
required to accurately determine the availability of the area.
The yields obtained in this analyses however, are judged to
be conservative estimates suitable for general planning put-
poses.
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ERFi-i~:~rth~st
Table 3
AVAILABLE WATER SUPPLY
ZONE 4
PErmISSIVE
TOTAL UNIT SUSTAINED
AREA YIELD YIELD
SUB-AREA (Sq_. Mi]es) (mgd/~. Mi]e) (mgd)
West of Greenport Water
~rvice Area
Water Budget Area 2.6 0.25 0.65
Between 1' and 2'
Contour 1.3 0.20 0.26
Between Coastline and
1' Contour 1.1 0.15 0.17
Total Area 5.0 -- 1.08
East of Greenport Water
Service Area
Water Budget Area 0.8 0.25 0.2
Between 1' and 2'
Contour 0.2 0.20 0.04
Between Coastline and
1' Contour 1.0 0.15 0.15
Total Area 2.0 -- 0.39
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