United States
Environmental Protection
Agency
Office of Water
(4504F)
EPA842-F-95-001C
September 1995
vvEPA
Georgetown Stormwater
Management Project
Demonstrating Practical Tools For Watershed
Management Through The National Estuary Program
Delaware Inland Bays,
Delaware
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Introduction To Delaware Inland Bays
Delaware's southeastern coast, between Rehoboth
Bay and Fenwick Island, lie three interconnected bodies of
water known as the Delaware Inland Bays. Historically, the
Inland Bays were a natural, primarily freshwater, estuarine
environment capable of supporting a wide variety of wildlife.
Large, thriving beds of submerged aquatic vegetation (S AV),
such as eelgrass, provided a home for numerous waterfowl,
shellfish, and finfish.
Although a few areas of the Bays are still considered healthy,
products of industry and development, mainly the nutrients
nitrogen and phosphorus, have caused a noticeable decline in
water quality and a loss of habitat. This, in turn, has shaken the
fragile lines connecting the health of the Inland Bays to the plant
and animal life existing within and around the estuaries. As a
result, Delaware's Inland Bays have suffered.
Excessive amounts of nitrogen and phosphorus have robbed
the once healthy waterbodies of oxygen. This has led to either
fish kills or movement offish to other areas. The high levels of
nitrogen and phosphorus have also inhibited the growth of SAV
in the Inland Bays, eliminating the freshwater habitat needed by
wildlife such as scallops, white perch, and striped bass. Pres-
ently, no substantial SAV beds exist in the Bays, and previously
existing soft clam, bay scallop, and oyster fisheries are, for the
most part, extinct.
A 1988-1990 study of nutrient loads indicated that the
nitrogen and phosphorus inputs to the Bays come from both
point and nonpoint sources; nonpoint sources, especially
stormwater runoff, however, are the
primary source of nutrients to the Bays.
It has been estimated that nonpoint
sources contribute 1,040 tons of
nitrogen per year and 30 tons of
phosphorus per year to Indian River
and Rehoboth Bay. Loadings have
increased in areas with a large amount
of impermeable surfaces, such as
roadways or parking lots.
and phosphorus-laden stormwater eastward to the Delaware
Inland Bays.
The Georgetown Industrial Park was chosen as a demonstra-
tion project because it typifies the problem of stormwater-carried
nutrients in an urban watershed. In addition, the demonstration
project provided the perfect arena for testing the new and unique
method of using a constructed wetland for stormwater control.
EPA joined forces with the Delaware Department of Natural
Resources and Environmental Control, the Soil Conservation
Service, the Sussex Conservation District, and the Sussex
County government to develop a plan to demonstrate the use of
an artificial wetland for stormwater management and habitat
creation.
Project Objectives
L he objectives of the project were to reduce nitrogen and
phosphorus loads entering the Bays, create additional habitat for
wildlife, and demonstrate the effectiveness of using an artifi-
cially constructed wetland for stormwater management.
Implementing The Project
L he Georgetown Industrial Park site was selected as the
demonstration site in 1990. Because the industrial park is owned
by the County of Sussex, acquisition of property was not
necessary. The County and State of Delaware negotiated a lease
agreement for the 2-acre project site for $1 a year. Design and
construction of the pond was completed in fall 1991. The pond
was planted with emergent wetland plants in spring 1992. The
Overview Of Georgetown
Industrial Park
Cjeorgetown Industrial Park,
located in and owned by Sussex
County, Delaware, is a highly urban-
ized 200-acre site. An airport occupies
about one-half the site, whereas the
other half contains light industrial
businesses. The entire 200-acre
industrial park drains past an open field
by way of drainage ditches.
Stormwater and nutrients are trans-
ported directly into Peterkins Branch, a
tributary of the Indian River. The
Indian River then carries the nitrogen
25% of pond
perimeter
open grass
Maintenance
bench
Inflow
Pipe
Splash boards
provide
flexibility in
depth control
Waterfowl island
Use of wetland mulch
to create diversity
25 foot wetland buffer
landscaped with native
trees/shrubs for habitat
A shallow marsh system wetland similar in design to the Georgetown wetland.
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design and construction phases of the project involved a number
of steps:
• Staff wetland biologists field verified that there were no
natural wetlands at the project site.
• The constructed wetland was designed as an "off line"
treatment system. Flow diversions were designed for
placement in the two existing drainage ditches to direct the
first inch of runoff from the industrial park to the wetland.
This "off line" approach would divert the first flush to the
wetland, while larger flows could continue unimpeded.
• Construction was sequenced so that the wetland was built
from the outside-in, allowing the emerging pond to act as
its own sediment basin during construction. The actual
connection of the pond with the existing drainage ditches
was not done until the entire excavation was completed and
the site was stabilized by vegetation above the normal pond
elevation.
• To enhance wildlife benefits, the wetland was constructed
in an irregular shape, and 75 percent of the depths in the
pond were less than 2 feet. An island was built in the pond
to lengthen flow paths from inflow to outflow, providing a
secure location for nesting birds. The outlet consisted of a
weir structure with splash boards to control pond elevation
as needed.
• Approximately 30 percent of the pond surface area was
planted with emergent plants to accelerate the development
of the wetland. Although construction of the pond was
completed in fall 1991, wetland planting took place in
spring 1992, so that wetland grasses and brush could have a
full growing season to maximize planting success.
The project team organized a "Planting Picnic" offering
pizza and hamburgers to participants. The team enlisted the help
of 150 high school students who volunteered their green thumbs
for the planting event. While students were planting, small
group information sessions were held to explain the need for and
expectations of the project. Overall, 8,000 plants including
buttonbush shrubs, duck potato grass, and bald cypress trees
were planted in about 4 hours. The planting event was attended
by local officials and covered by news reporters and TV stations.
The Georgetown Industrial Park
Success Story
L he Georgetown Stormwater Management Demonstration
Project proved to be an innovative, successful, and attractive
way to control stormwater runoff. The project team found that,
much like a natural wetland, the constructed wetland acts like a
"sponge," soaking up and retaining stormwater runoff. While
holding the stormwater, the wetland removes nitrogen, phospho-
rus, and other pollutants through filtration by wetland plants,
microbial activity, and uptake by wetland plants and algae,
before gradually releasing stormwater to the Bays.
Although no funding has been made available for monitoring
actual pollutant load reductions, it is estimated that up to 60
percent of the nitrogen and up to 40 percent of the phosphorus
will be removed from the stormwater after flowing through the
wetland. In addition, the suspended sediments could be reduced
by up to 80 percent and trace metals by approximately 60
percent.
The wetland, which is maintained by the State of Delaware,
has also flourished as a habitat for plants, waterfowl, mammals,
insects, and fish. Vegetation as well as plant diversity is
booming, and many waterfowl have been sighted at the wetland.
Some species, such as duck and quail, have already established
nests.
Visually, the wetland adds scenic value to the industrial park.
The project has demonstrated that constructing an artificial
wetland would not only be an effective way to treat nutrient
loading from stormwater runoff, but an attractive one as well.
The Georgetown Stormwater Management Demonstration
Project successfully illustrates the ability to use an artificially-
constructed wetland to control stormwater and create additional
habitat. The applicability of project conditions and methods
used to other areas is widespread. Artificial wetlands can be
used quite successfully in other regions of the country to treat
stormwater, especially in coastal areas. However, conditions
change from region to region, so it is important to consider
factors such as soil types, available space, and baseflow or
groundwater supply.
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Lessons Learned
L he Georgetown Stormwater Management Demonstration
Project illustrated that constructed wetlands are an excellent
option for treating urban Stormwater runoff and its associated
pollutants. Additional lessons learned from the project include:
• Lease arrangements and memoranda of understanding can
take longer to put in place than actual design and construc-
tion. A strategy to facilitate the process helps minimize
delays in implementation.
• A major cost factor for any Stormwater management
project is the cost associated with removal and disposal of
earth excavated from the project site. Consideration should
be given to disposal locations close to the site. In the case
of the Georgetown Stormwater Management Demonstra-
tion Project, fill material was needed to extend a runway at
the nearby airport, so the materials had to be trucked only a
short distance.
• Plantings should be done at a time of year when the plants
have a full growing season to ensure rapid and lush growth.
In Delaware, planting should be done in spring so that
plants have a full growing season prior to dormancy.
Printed on recycled paper
For more information contact:
Earl Shaver, Environmental Engineer
Division of Soil and Water Conservation
Delaware Department of Natural Resources
and Environmental Control
89 Kings Highway
P.O. Box 1401
Dover, Delaware 19903
(302)739-4411
(302) 739-6724 FAX
Jim Butch
U.S. EPA Region 3
841 Chestnut Street
Philadelphia, Pennsylvania 19107
(215)597-9343
(215) 597-1850 EAX
V-/EPA
United States
Environmental Protection
Agency
(4504F)
Washington, DC 20460
Official Business
Penalty for Private Use
$300
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