WATER QUALITY AND POLLUTION — SOUTH FORK OF LONG ISLAND, NEW YORK

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  • WATER RESOURCES BULLETIN VOL. 10, NO. 4 AMERICAN WATER RESOURCES ASSOCIATION AUGUST 1974

    WATER QUALITY AND POLLUTION -- SOUTH FORK OF LONG ISLAND, NEW YORK

    C. W. Fetter, Jr.

    ABSTRACT. The South Fork of Long Island, New York is an area which relies enthely on ground water for water supply. Most of the water which is pumped is artifically recharged, without treatment, via cesspools. The natural quality of the ground water is very high. Some areas show increasing nitrate in the ground water. This comes from both cesspools and agricultural fertilizer. Saline water intrusion is a potential problem in coastal areas. High ammonia in surface ponds may result in eutrophication. (KEY TERMS: water quality; nitrate pollution; ground water pollution)

    INTRODUCTION

    The South Fork of Long Island, New York is separated by a sea level canal from the remainder of Long Island, thus rendering it a distinct hydrogeographical area (figure 1) of 131.5 square miles. Ground water provides the only supply of potable water for the entire South Fork. This supply is susceptible t o contamination, both from the land surface and the saline ground water which surrounds and underlies the fresh water body.

    The present study presents an evaluation of the native ground water quality in the area, and a survey of ground water contamination. The principle sources of contamina- tion are saline water encroachment, agricultural fertilizers and wastewater disposal through cesspools.

    The permanent population of the area was established t o be 32,300 in 1965, with a large influx of summer residents and tourists (Holzmacher, McLendon and Murrell, 1968). Except for about 2,000 people in the Village of Sag Harbor, domestic wastewater from the remainder of the population is discharged, untreated, t o the subsurface through cesspools. The Village of Sag Harbor has a sewer system and discharges treated wastes into Sag Harbor. Water pumpage for all uses was less than 4 million gallons per day in 1965 (Hobmacher, McLendon and Murrell, 1968).

    If the population of the South Fork grows at a rate similar t o that of western Long Island, steps will be necessary to protect the ground water reservoir from saline water encroachment and surface sources of pollution.

    Paper No. 7401 6 of the Wafer Resources Bulletin. Discussions are open until February 1,1975. Assistant Professor of Geology, University of Wisconsin-Oshkosh, Oshkosh, Wisconsin 54901. 779

  • 780 Fetter, Jr.

    Figure 1. Location of the South Fork of Long Island, New York.

    I

    Long Island is the northward extension of the Atlantic Coastal Plain. A series of

    GEOLOGY

    unconsolidated Pleistocene and Cretaceous deposits extending to as much as 1600 feet below sea level underlie the area. The surficial deposits are Pleistocene and recent in age and consist of ice contact stratified glacial drift and outwash, dune sand and marsh (Fuller, 1914).

    Pleistocene deposits of coarse sand and gravel have been identified as extending as much as 251 feet below sea level and are at least 322 feet thick (Fetter, 1971). The underlying beds have been designated as the Magothy Formation and Matawan Group, indlfferentiated. The water-bearing layers of fine sand and silt are known as the Magothy aquifer. The Magothy Formation-Matawan Group extends to as much as 1100 feet below sea level in the area. The Raritan Formation of Cretaceous age is the lowest of the unconsolidated strata. Beneath western Long Island it is divided into two members. Such a division was not apparent in a test boring made just to the west of the South Fork area (Fetter, 1971). A basement complex of crystalline rock underlies all of the un- consolidated deposits.

    The fresh ground water is contained in two geohydrologic units. The uppermost is called the Glacial Aquifer. It consists of all the sand and gravel deposits of Pleistocene age. Underlying this is the Magothy Aquifer of Cretaceous age. Thin layers of fine to very fine sand are interbedded with lenses of silty and sandy clay. However, the permeable layers are interconnected and the entire thickness of the Magothy Formation and Matawan Group acts as a single, anisotropic aquifer. The vertical permeability is much less

  • WATER QUALITY AND POLLUTION 781

    than horizontal. The lower layers of the Magothy Aquifer and the Raritan Formation contain saline water.

    HYDROLOGY

    The sole source of natural recharge to the aquifer system is the precipitation whch falls on the South Fork. A secondary source of recharge is the artificial recharge of sanitary wastewater through subsurface disposal units. There are a limited number of basins for the inland recharge of storm water runoff from highways and subdivisions.

    Natural recharge can be considered to be the recharge of precipitation as opposed to the artificial recharge of wastewater. Highway drainage into recharge basins is by this defmition natural recharge. The water balance equation (Recharge = Precipitation - Evapotranspiration - Direct Runoff) can be used to compute the amount of natural recharge.

    The average annual precipitation is between 44 and 45 inches for the South Fork. By using the Thomthwaite method for computing evapotranspiration, the average actual evapotranspiration was computed as 23 inches. Because of the very permeable surface soils, there is very little direct runoff of precipitation, less than one inch a year. Thus the average annual recharge for the South Fork is about 21 to 22 inches. From 1951 to 1969 it ranged between 12 and 37 inches, primady because of fluctuations in precipitation.

    The homes and businesses of most of the area have cesspools for waste disposal. Because of the preponderance of this method of waste disposal, an estimated 4 million gallons per day of domestic water usage is presently being artifically recharged. Since this water was pumped from the aquifers, the artificial recharge does not represent a net addition to the total recharge.

    The recharged water moves downward through the unsaturated zone until it reaches the water table. Then it begins to move in a direction dependent upon the slope of the water table. The fresh ground water reservoir is a classic freshwater lens floating on denser satme water which underlies the entire area. In this situation groundwater moves downward and laterally away from the high portions of the water table. It then moves upward along the coast and discharges as small springs and streams, diffusion along the salt water interface and upflow into the bottom of the ocean or tidal estuaries. The shape and position of the fresh water reservoir beneath the South Fork area have been described by Fetter (1972).

    WATER QUALITY

    Ground Water

    Natural Quality

    Water quahty analyses are available for a number of public supply wells in either the Glacial or Magothy Aquifer. Manditory and recommended limits for the concentrations of a number of chemical and physical properties of drinking water are established by the U. S. Public Health Service. Water quality data for the Glacial Aquifer and the Magothy Aquifer are given in tables 1 and 2. These tables are a compendium of unpublished data obtained from the Suffolk County Water Authority, private water companies and the Suffolk County Health Department.

  • TABL

    E 1.

    Gro

    und

    Wat

    er Q

    ualit

    y of

    the

    Gla

    cial

    Aqu

    ifer

    Con

    stitu

    ent

    P.H

    .S.

    Lim

    it M

    axim

    um

    Min

    imum

    M

    a

    Num

    ber

    Con

    cent

    ratio

    n C

    once

    ntra

    tion

    Con

    cent

    ratio

    n of

    Wel

    ls

    Chr

    omiu

    m

    Sie

    r Le

    ad

    Cad

    miu

    m

    Cop

    per

    Zinc

    C

    obal

    t N

    icke

    l A

    rsen

    ic

    Boro

    n C

    yani

    de

    Flor

    ide

    Det

    erge

    nt

    Man

    gane

    se

    Iron

    PH

    T

    otal

    Sol

    ids

    Chl

    orid

    e A

    Jkat

    inity

    H

    ardn

    ess

    Nitr

    ate

    Free

    Am

    mon

    ia

    0.05

    ppm

    0.

    05 p

    pm

    0.05

    ppm

    0.

    01 p

    pm

    1.0

    ppm

    5.

    0 pp

    m

    0.01

    ppm

    1.

    0 pp

    m

    0.01

    ppm

    1.

    4 to

    2.

    4 pp

    m

    0.5

    ppm

    MBA

    S 0.

    3 pp

    m

    0.3

    ppm

    500

    ppm

    25

    0 pp

    m

    - p

    pm C

    aCO

    3 - p

    pm C

    aCO

    3

    - P

    Pm N

    20 p

    pm N

    0.00

    0 pp

    m

    0.00

    3 pp

    m

    0.01

    8 p

    pm

    0.00

    7 pp

    m

    0.96

    3 pp

    m

    0.20

    1 pp

    m

    0.01

    3 p

    pm

    0.01

    8 p

    pm

    0.00

    0 pp

    m

    0.11

    9 pp

    m

    0.00

    ppm

    0.14

    ppm

    0.

    32 p

    pm

    0.91

    ppm

    20

    .0 p

    pm

    7.4 251

    ppm

    18

    9 pp

    m

    90 p

    pm

    174

    ppm

    12

    .0 p

    pm

    0.11

    4 pp

    m

    0.00

    0 pp

    m

    0.00

    0 pp

    m

    0.00

    0 pp

    m

    0.00

    0 pp

    m

    0.02

    8 pp

    m

    0.01

    0 pp

    m

    0.00

    0 pp

    m

    0.00

    0 pp

    m

    0.00

    ppm

    0.

    000

    ppm

    0.

    00 p

    pm

    0.1

    ppm

    0.

    02 p

    pm

    0.00

    1 pp

    m

    0.02

    ppm

    5.5

    55

    PPm

    5

    ppm

    4

    PPm

    13

    PPm

    0.

    02 p

    pm

    0.00

    2 pp

    m

    0.00

    0 pp

    m

    0.00

    1 pp

    m

    0.00

    8 pp

    m

    0.00

    1 pp

    m

    0.19

    4 pp

    m

    0.03

    7 pp

    m

    0.00

    3 pp

    m

    0.00

    8 pp

    m

    0.00

    ppm

    0.

    020

    ppm

    0.

    00 p

    pm

    0.1

    ppm

    0.

    03 p

    pm

    0.01

    1 pp

    m

    1.1

    ppm

    6.

    4 11

    6 pp

    m

    20 P

    Pm

    23 P

    Pm

    53 P

    Pm

    1.6

    ppm

    0.

    014

    ppm

    ~~

    ~

    18

    18

    18

    18

    18

    18

    18

    18

    6 6 6 18

    24

    38

    38

    38

    10

    31

    3

    1

    38

    37

    15

  • TA

    BL

    E 2

    . G

    roun

    d W

    ater

    Qua

    lity

    of th

    e M

    agot

    hy A

    quife

    r

    Con

    stitu

    ent

    P.H

    .S.

    Lim

    it M

    axim

    um

    Con

    cent

    ratio

    n M

    inim

    um

    Con

    cent

    ratio

    n

    ~ ~~

    ~~

    Mean

    Con

    cent

    ratio

    n Number

    of W

    ells

    Chl

    orid

    e Iron

    Man

    gane

    se

    PH

    Har

    dnes

    s A

    lkal

    inity

    N

    itrat

    e

    250

    ppm

    19

    PPm

    0.

    3 pp

    m

    2.2

    ppm

    0.

    3 pp

    m

    0.05

    ppm

    6.

    4 - p

    pm C

    aCO

    3 42

    ppm

    - p

    pm C

    aCO

    3 24

    PPm

    10

    ppm

    N

    2.0

    ppm

    8 PP

    m

    0.04

    ppm

    0.

    05 p

    pm

    5.8

    10 P

    Pm

    8 P

    P~

    0.

    02 p

    pm

    Tot

    al S

    olid

    s 30

    0 pp

    m

    106

    ppm

    20

    PPm

    13 P

    P~

    0.

    49 p

    pm

    0.05

    ppm

    6.

    1 23

    PPm

    15

    PPm

    0.

    47 p

    pm

    67 P

    Pm

    6 s a s

    Y

    Figu

    re 2

    . N

    itrat

    e an

    d ir

    on in

    the

    goun

    dwat

    er o

    f th

    e G

    laci

    al A

    quife

    r.

    hb

    lr S

    uppl

    y W

    enlr

    ld W

    ith L

    OW

    Ir

    on I

    n Tn

    e G

    lacl

    al

    Aqu

    ifer

    p?ppyI

    L A

    rea

    W

    itn

    Gen

    eral

    ly A

    ccep

    tabl

    e C

    on

    cen

    trat

    ims

    of N

    itra

    te

    Are

    a

    With

    M

    arg

    inal

    Wat

    erO

    Lalit

    y D

    ue

    To

    Nit

    rate

    Con

    tam

    inat

    ion

    4

    M

    ww

    A

    rea

    W

    tth

    Exc

    elle

    nt W

    ater

    Od

    ity

    With

    Res

    pect

    To

    N

    itra

    te

    w

  • 784 Fetter, Jr.

    The natural quality of the water is excellent in most cases. Of the constituents, only iron, manganese, chloride and nitrate ever exceed the drinking water standards.

    Iron concentration presents serious water quality problems in some areas of the South Fork. In 23 of the 38 wells for which iron analyses were available, there was at least one analysis where the iron standard of 0.3 ppm was exceeded.

    Concentrations of iron in a given well can fluctuate. In Well S-184 at Sag Harbor, the iron content ranged from 0.3 ppm to 10.6 ppm, with a mean of 5.8 ppm for 12 analyses. High content is apparently related to specific areas. Glacial Aquifer wells with low iron content are all located in the central portion of the South Fork, and the wells with high iron content are located at the margins of the island. There are some wells with iron content about 0.3 ppm located intermediate between the high iron content and low iron content wells (figure 2). This distribution does not hold in the Magothy Aquifer where Magothy Aquifer test zones at Wells S-33922 and S-3 1037 had a high iron content and Glacial Aquifer test zones had low iron content.

    Appreciable amounts of ferrous iron cannot exist in water with significant amounts of dissolved oxygen which causes a high oxidation potential. Glacial Aquifer wells with low iron content are in ground water recharge areas where the shallow water presumably contains considerable dissolved oxygen. T h s implies conversely that a lack of dissolved oxygen (i.e., low oxidation potential) as well as an available iron source will result in more dissolved iron in the ground water, other factors remaining the same. Since none of the Magothy Aquifer test wells had detectable dissolved oxygen in the water, wells with high iron content can occur anywhere in this aquifer.

    Manganese is soluble as Mnt2 under similar conditions as ferrous iron, although it is somewhat less easily oxidized to its relatively insoluble higher oxidation states Mnt3 and MnC4. The occurrence of wells with high manganese content (four out of 28 wells) is much more limited than high iron content wells. It is probable that manganese is less abundant in the sediments than iron.

    On the basis of a limited number of anlayses, the water quality of the Magothy Aquifer appears to differ from that of the Glacial Aquifer. The deeper ground water has lower total solids as well as lower hardness, chloride and alkalinity (table 3). Data are lacking for other constituents. There is a significant amount of interstitial clay in the Magothy Aquifer so that anion and cation exchange with the clay minerals may cause the observed change in ground water quality.

    Changes in Ground Water Quality Due to the Activities of Man

    Of the constituents found in the ground water, nitrate, detergent (MBAS) and chloride show evidence of having been induced at least partly by man.

    Nitrate. Small quantities of nitrate can naturally be present in ground water from the microbial decomposition of organic matter at the surface. This is a rather low amount and 16 of the 38 public supply wells tested had a nitrate content of less than 1 .O ppm (as N). Wells with nitrate content above this level probably contain some nitrate from other sources.

    Human waste contains ammonia which can be nitrified by aerobic soil bacteria to nitrate. Almost all waste water on the South Fork is disposed via cesspools. Ammonia in the waste is converted to nitrate in the unsaturated soil zone. This nitrate is a potential source of ground water contamination.

  • WATER QUALITY AND POLLUTION 785

    TABLE 3. Comparative Ground Water Quality in the Glacial Aquifer and the Magothy Aquifer

    Chloride TotalSolids Hardness Alkalinity

    Average of All Wells Glacial Aquifer 28 PPm Magothy Aquifer 13

    Bridgehampton Test Well ($33922) Glacial Aquifer

    Magothy Aquifer

    Magothy Aquifer

    Depth 154 to 174 feet

    Depth 400 to 440 feet

    Depth 630 to 659 feet

    28

    12

    7

    Southampton Test Well ( S 3 1037) Glacial Aquifer

    Glacial Aquifer

    Magothy Aquifer

    Magothy Aquifer

    Depth 65 to 100 feet

    Depth 170 to 190 feet

    Depth 240 to 280 feet

    Depth 345 to 365 feet

    23

    12

    12

    12

    116 ppm 67

    25 1

    100

    106

    53 ppm CaC03 23

    120

    44

    22

    235 107

    55 26

    21 10

    20 12

    23 ppm CaC03 15

    28

    20

    24

    23

    26

    16

    16

    Large amounts of ammonia and nitrate are applied to crops as a fertilizer. Nitrate is extremely soluble in water and if not rapidly utilized by plants can pass through the root zone.

    On the above basis, one would expect to find ground water with high nitrate levels in both populous and agricultural areas. The public water supply wells are generally located in or near populous areas, and more than half have nitrate content greater than 1 .O ppm. Suffolk County Health Department records of water analyses of private wells for new homes are a source of abundant data on nitrate content of ground water. A statistical tabulation of 65 I wells was made (table 4). A nitrate concentration less than 1 .O ppm is considered to be natural, nitrate content from 1 .O to 4.9 ppm represents some pollution, nitrate content from 5.0 to 9.9 ppm represents considerable pollution and nitrate content greater than 10.0 p...

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