&EPA
United States
Environmental Protection
Agency
Calvert County, Maryland's
Success in Controlling
Sprawl
Rapid population growth and suburban development, and the resultant change in
land use and land cover were affecting the Calvert County landscape.
The extent of the County's ability to build a strong
economy, while protecting and maintaining its rural
character, depends largely upon three factors - the amount
of increase in population, the rate of new construction,
and the location of future development sites. The County
prepared a Comprehensive Plan which recommends a
four-step implementation strategy to achieve maximum
results: (1) reduce total build-out; (2) reduce the rate
of residential growth; (3) preserve the County's prime
farms, forests, historic resources and sensitive areas; and
(4) direct all growth to appropriate locations. The County
Commissioners were then faced with the decision of
how and where to limit the location and amount of new
construction. This increase in new construction and its
location would also affect the amount of increase in point
and non-point source pollution. Models of how anew
comprehensive zoning plan would affect water quality in
Calvert County were essential in designing ways to meet
the environmental goals in the Comprehensive Plan.
Calvert County Population Growth 1970-2000
Population Projections 2000-2020
Before and After Comprehensive Rezoning
125000
0
^^^
/
^r^
1 970 1 980 1 990 2000 201 0 2020
I
Maryland
Bunting Creek IE
Watershed \, -
The Institute for Ecological Economics (IEE)
at the University of Maryland was awarded
a Science to Achieve Results (STAR) Grant
from the U.S. EPA, Office of Research and
Development. The purpose of this grant was
to develop an ecological, economic model to
evaluate the driving forces and the ecological
consequences of land-use change. The project
goal was to create a dynamic, ecological,
economically-linked model and make it available
to resource managers for the effective
management of ecosystems at the watershed
scale. The approach designed by IEE estimates
the impact of economic development on
environmental conditions in a watershed. Various
watershed data were combined to produce a
spatially-explicit model. The IEE model was
used to demonstrate how changes in zoning
would affect water quality in Calvert County.
The Hunting Creek watershed was used in the
model as a representative area of the County.
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For the Hunting Creek model, IEE compared nine different zoning alternatives (Figure 1) and their resulting water
quality. The water quality was determined for each scenario in terms of the concentration of nitrogen (Figure 2).
-
la
I
Fig
con
|T| Build-out = dwelling units 1 997 zoning plans
[2] Build out = 25% density reduction plan
[3] Build out = 50% density reduction plan
[4] Same as 1 with improved septics
[5] Same as 2 with improved septics
[6] Same as 3 with improved septics
IT] Same as 4 with no development in river buffer zones
[8] Same as 4 with random choice of protected areas (random clustering)
0 Same as 4 with forest preservation and reforestation of the watershed
16.00
14.00-
12.00-
10.00-
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Results:
The nitrogen content in the watershed is sensitive to the
increase in the amount of dwelling units. The existing
design of septic drainage fields effectively removes
nitrogen from the active root zone and allows it to
accumulate in the ground water that eventually finds
its way into the river system (Figure 3). Scenarios 4-6
in Figure la employ septic systems that discharge in
the near-surface vegetative layer (Figure 3, Alternative
Design). In these scenarios, the nitrogen from the
septic systems is considerably lower, and there is little
difference among zoning strategies 4, 5, and 6. However,
preservation of an extended river buffer zone (200 m)
further diminishes the amount of nutrients entering the
estuary (Scenario 7). If a similar totally-preserved area is
chosen randomly, the gain is significantly less (Scenario
8). Furthermore, if the maximum build-out is assumed,
but on a totally-forested watershed (Scenario 9), the
pollution of the estuary relative to the current conditions
can actually decrease, even for the maximum projected
population growth in the watershed. It is hardly possible
to implement Scenario 9; however, it is important to
stress that environmental and management practices
associated with development may be more important
than the actual amount of build-out.
Evaporation
Overland
low
SURFACE WATER
1
^Surface -
Saturated
exchanges i
Percolation
& upflow
' ~~
»-| SATURATED WATER^^
* Groundwater
flow
Figure 4. Hydrologic cycle used in the model.
Vegetation
Groundwater
Existing Design
Vegetation
Groundwater
Alternative Design
Figure 3. Comparison of existing and alternative septic system
designs. Additional nitrogen removal for septic systems in watersheds
that contribute heavily to the nitrogen load is under consideration in
Calvert County.
Conclusions:
Atmospheric deposition is a prime source of nitrogen
loading that should not be overlooked. Additional research
is needed to identify the contribution of local vs. distant
sources of atmospheric deposition.
Spatial distribution of the development is extremely
important for water quality in the estuary. By avoiding
land use change in the river buffers (-200 m), most of the
development in the watershed can be compensated for, even
under maximum build-out.
Even more important are the particular land use practices:
grow trees, not lawns.
Most important are the management practices. Nitrogen
removing septic tanks can remove 60% of the nitrogen
from septic effluent and when combined with redesigned
septic fields that deliver the effluent to the root zone (which
increases nitrogen retention by the plants) rather than to the
groundwater, these systems can be extremely effective.
Recommendations to Calvert County:
Consider alternative designs of septic tanks and drainage fields to make better use of biological
treatment and achieve greater nutrient removal (Figure 3, Alternative Design).
Continue to prioritize and implement preservation/conservation efforts before further growth
outstrips their positive effects.
Minimize clearing, maximize reforestation and encourage reduced lawn areas.
Support further analysis of the pathways of nutrients across the watershed.
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Region 3
Philadelphia, PA 19103
EPA/903/F-02/004
May 2002
Patricia Bradley
bradley.patricia@epa.gov
410-305-2744
U.S. Environmental
Protection Agency
Mid-Atlantic Integrated Assessment
Environmental Science Center
701 Mapes Road
Ft. Meade, MD 20755
www.eDa.pov/maia
Barbara Levinson
levinson.barbara@epa.gov
202-564-6911
U.S. Environmental Protection Agency
National Center for Environmental Research
(8723R)
Washington, DC 20460
www.epa.gov/ncer
David C. Brownlee
brownldc@co.cal.md.us
410-535-1600 ext. 338
Calvert County
Department of Planning and Zoning
150 Main Street
Prince Frederick, MD 20678
www.co.cal.md.us
Robert Costanza
costza@cbl.umces.edu
410-326-7213
Alexey Voinov
voinov@cbl.umces.edu
410-326-7207
University of Maryland
Institute for Ecological Economics
Center for Environmental Science
Chesapeake Biological Lab
PO Box 38
Solomons, MD 20688
iee.umces.edu
iee.umces.edu/PLM/HUNT
rt Ul MAJU LASH
Institute for
Ecological
Economics
Based on the recommendations to the County
by IEE and the reduction in the cost of
future school and road construction, the Board
of County Commissioners adopted a zoning
ordinance that provides for a major reduction
in future density and that directs the location
of future growth. The Commissioners feel that
these measures will improve the environment
and help to maintain the general quality
of life in Calvert County as described in
the Comprehensive Plan's implementation
strategy. Also, consistent with the
Comprehensive Plan, the County is exploring
the use of nitrogen-removing septic systems.
The spatial landscape model, funded by this
STAR Grant and developed by IEE, is very
flexible. It can be used to analyze the impacts
of a specific development or regulatory policy.
The model can be scaled down to represent small
watersheds (Hunting Creek) or up to represent
major drainage basins (Chesapeake Bay). The
parameters used in the model can be adjusted
to reflect the particular goals of the project.
Numerous scenarios can be run through the
model and the results compared, as was done
with Hunting Creek. Or, decision-makers can
formulate a goal that they want the system
to reach and then have the model sort the
parameters and pattern combinations to reach
that goal. This is an especially important tool
when many processes and factors with numerous
constraints must be accounted for to reach an
optimal decision. The kind of solutions required
determines the complexity of the model. That,
and the amount of available data determine
the speed and expense of applying and using
this modeling approach. However, if difficult
and numerous questions must be answered, the
complexity is appropriate and the model is more
economical than other solutions.
The results of this grant and other
STAR grants are available on the NCER
website. This research may further
assist other organizations in basing their
decision-making on sound science.
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