HomeMy WebLinkAboutCluster vs Sprawl re: Contamination of Ground Water 1982
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Cluster vs Sprawl:
An example of tand use effects on nitrate
. contamination of ground water
REPORT S1
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CENTER FOR ENVIRONMENTAL RESEARCH
CORNELL UNIVERSITY
ITI<Ar.A, NFW YORK HRS:!
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Cluster YS Sprawl:
An Example Of Land Use Effects On Nitrate
Contamination Of Ground Water
Report 51
Working Paper I
August 1982
Computer Wor!< and Documentation By:
Nancy M. Trautmann
Mary Jane Heather
Keith S. Porter
With Graphics By:
Donna C. Curtin
Center for Environmental Research
Cornell University
Ithaca, New York 14853
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Preface
The Town of Southold is coming under increasing pressure for conversion
of farm land to housing development. The Southold Citizen's Advisory
Committee (C.A.C.) requested tllat we apalyzethe effects on ground water of
clustering houses along the shoreline in order to preserve inland areas for
farming. The subarea of Southold used for detailed simulation was chosen by
members of the C.A.C. and by t1enry Raynor representing the Southold Planning
Board.
The work was conducted under the auspices of the New York State
Department of Environmental Conservation as part of the Fertilizer, Herbicide,
and Pesticide Demonstration Project funded by the U.S. Environmental
Protection Agency.
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Land uses play a major role in determining the nitrate concentrations of
water recharging Southold's ground-water supply (Figure O. Many wells' in
Southold have water near or above the nitrate drinking water standard of 10
mg/l, so nitrate concentrations of recharge water need to be considered
carefully in land use planning decisions.
FIGURE 1
EFFECT OF LAND USES ON GROUND WATER aUAlITY
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. Potato Field
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Influence of potato field on saturated zone
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Infl~ence of forest on saturated zone _--... .
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As an example of how this consideration can be built into land use
planning in Southold, we chose a subarea of the town for detailed analysis of
effects of various land uses on recharge quality. Bounded by Reeves Avenue,
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Middle Road, Henry's Lane, and the Long Island Sound, this subarea is portrayed
in Figure 2.
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fiGURE 2
SUBAREA Of TOWN OF IOUTHOlD. LONG ISLAND, N. Y.
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Using the Water and Land Resource Analysis System. (W ALRAS), we
simulated inputs and outputs of nitrogen from the root zone. Nitrate leaving
the root zone leaches through the unsaturated zone and into the ground water,
as shown in Figure 3.
In residential areas, nitrogen inputs include on-site sewage disposal, lawn
fertilization, pet wastes, and precipitation. For agriculture, the primary
nitrogen source is the fertilizer-application. Outputs from both sources include
leaching, runoff, gaseous loss, and export of plant materials.
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FIGURE 3
MOVEMENT OF NITRATE TO AND THROUGH THE GROUND WATER
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Figure 4a shows the simulated recharge quality for the Southold subarea
under existing land uses. Seventy-seven percent of the land in this subarea is in
potato production, and because of current fertilization practices the nitrate
leaching is high. For purposes of this report, fertilization was assumed to be
192 kg N/ha (175 Ib N/Ac) at planting as a representative practice in Southold.
Loss of nitrate to ground water is high under these conditions but could be
reduced through split application of smaller amounts of fertilizer, as discussed
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in Report S2 of this series (Center for Environmental Research, 1982).
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NITRATE LEACHING = 10.0mg II
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NITRATE LEACHING = 1.5mg/ I
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NITRATE LEACHING = 2.0mg / I
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NITRATE LEACHING ~ 4.6mg/1
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FIGURE 4: The effect ot housing density on the "itrale concentration ot .e';ha~ge water.
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For the three residential densities analyzed here (2-acre, I-acre, and 1/4-
acre zoning), nitrate leaching becomes higher with increasing housing density
(Figure 4 b-d). The contributions from on-site sewage disposal rise in
proportion to the number of people living in the area, and make up a
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progressively larger portion of the total : nitrogen leached as the development
becomes more dense. Nitrogen inputs from lawn fertilization and pet wastes
also increase with the increased residential density, while concentrations in
precipitation remain unchanged.
Any of these three residential densities would produce recharge water
with nitrate concentrations well below the drinking water ~tandard o.f 10 mg/l.
Currently this area is zoned at_ one house per acre, but Southold allows
clustering into 50% of the land area, so a net housing density of two houses per
acre would be allowed.
Usually in a cluster development the remaining land would be left as open
space covered by unmaintained vegetation rather than lawns or crops. This
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provides recreational space as well as a buffer area to help compensate for the
increased impact to ground water of spacing the houses more closely together.
In Southold, however, one of the reasons for considering clustered development
is to make it possible to preserve valuable agricultural land in inland areas by
clustering houses along the shoreline.
Figure 5 shows the results from simulations representing clustered housing
development at densities of either one or two houses per acre. When the
remaining half of the land area is left in unmaintained vegetation, the nitrate
leaching concentrations remain quite low (Figure 5 a and b). If this land is used
for agriculture instead, however; the concentrations increase three or four-fold,
to 7.6 or 8.3 mg/l depending on the housing density (Figure 5 c and d).
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NITRATE LEACHING = 1.3mg/l
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NITRATE LEACHING", 1.9 mg/l
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FIGURE 5: The ellect of clustered development on the nitrate concentration of recharge
water. Houses are clustered into 50 % of the land area. with either
agriculture or vacant land on the remaining acreage.
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Southold is considering changing its cluster ordinance to provide more
open space by allowing closer spacing' of houses, using 35% rather than 50%' of
the total land area. As shown in Figure 6, the nitrate leaching levels become
quite high if 35% of the land area is used for clustered housing and the
remaining 65% for agriculture.
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FIGURE 6
SOUTHOLD SUBAREA
NITRATE CONCENTRATIONS IN RECHARGE WATER
Land Use Patt.rn A~ AGRICULTURE
currenl land u... 'I Hz HOUSING
NO CLUSTERING :I' acr. VzVACANT
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CLUSTERED - 5O%H ~~V
2.ACRE ZONING 35~H. 65". ~
35"". (6% v
50"".50% A I
CLUSTERED -5O-.4H. 0" V
1- ACRE ZONING 35"4H 65" . ~
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For planning purposes, we suggest that an average concentration of 6 mg/l
be used as the highest acceptable average nitrate concentration so that the 10
mg/l standard will be exceeded' n~ more than ten percent of the time. This 6
mg/l average is exceeded by all of the alternatives considered here in which
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potato fields fill the open space portion of the cluster developments. When the
open spaces are left as unmaintained vegetation, however, then the nitrate
concentrations are well below this maximum acceptable level. Reduced
fertilization of the agricultural fields might make farming a compatible use as
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By creating a mass balance of nitrogen inputs and outputs, the W ALRA5
technique makes it possible to evaluate the effects of new patterns of land use
such as clustering of residential development. Protection of 50uthold's ground-
water supplies will rely on careful land use management based on analyses such
as these.
Possible courses of action include the following:
· Determine criteria for clustered development. (What types of land
use are appropriate for the open space portions of cluster
developments?)
· Incorporate ground-water considerations into land use planning and
management prQcesses in 50uthold. ~_.
· .C.Qnsider ways of reducing nitrate leaching from agricultural fields
(see Report 52 of this series) and from residential lawns.
· Analyze effects of increased residential development on other
ground-water contaminants such as coliform bacteria or organic
chemicals.
· Evaluate the effect of requiring advanced on-site sewage disposal
systems for houses in cluster developments.
· Assess the feasibility and desirability of importing drinking water
via a public water. supply system rather than using ground water
underlying the development through private wells.
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References
Center for Environmental Research, 1982. Effect of timing and rate of
fertilization on potato growth and nitrate leaching to ground water.
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Report 52. Cornell University, Ithaca, N.Y.
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