vvEPA
United States
Environmental Protection
Agency
EPA832-R-93-005n
September 1993
                   Fort Deposit, Alabama

                   Constructed Wetland Treatment System
                   Case History

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SYSTEM DESCRIPTION
A
        s designed, the Fort Deposit wet-
        land treatment system includes
        the following main components:

   An 8.9-acre aerated pond

   Two 7.5-acre constructed wetland
    cells

   A 0.1-acre post-aeration pond
   The town s existing stabilization pond
 was modified to provide more effective
 pre-treatment. The modifications
 included relocating the influent and
 effluent points and adding floating
 mechanical aerators. Seven acres of the
 pond were aerated, leaving the remain-
 ing area to serve as a settling basin.
 These modifications improve 5-day
 biochemical oxygen demand (BOD5)
 and ammonia nitrogen (NH3-N)
 removal efficiency, reduce organic
 and solids loading to the wetland cells,
 and provide additional flexibility in
 the overall treatment process.
   The wetland cells are configured side
 by side. Each cell covers 7.5 acres and
 has an aspect ratio (length to width) of
 4.6:1. The cell floors are slightly sloped
 for easy draining during maintenance.
 Although most of the  15 acres of wet-
 land cells are less than 2 feet deep,  each
 cell has three "deep zones," which are
 4 feet deep and about 20 feet wide.
 The deep zones remain free of rooted
 marsh vegetation, thus allowing effluent
 to be redistributed through the system
 and providing atmospheric aeration.
The deeper water in these zones also
furnishes year-round habitat for aquatic
life, particularly mosquito fish and
wetland birds.
   The parallel operation of the two
wetland cells gives the town the ability
to direct all flow through a single cell
during wetland resting and maintenance
periods. Moreover, the rate of flow
to each cell can be varied to allow
flexibility in operations and to aid in
testing or research.
   The treated effluent enters a post-
aeration pond after passing through the
wetland cells. This system component
is used to meet the effluent  dissolved
oxygen limits specified in the permit.
This 75.000-gallon earthen pond is
equipped with a floating mechanical
aerator. Final effluent flow rate from
the post-aeration pond is continuously
measured by a Parshall flume.
                                                       Aerated
                                                       Lagoon
                                                                              The Fort Deposit constructed
                                                                              wetland treatment system
                                                                              uses an aerated lagoon for
                                                                              pretreatment followed by two
                                                                              parallel wetland cells.
                                                                             Wetland
                                                                             Cell 1
                                      Wetland
                                      Cell 2

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  Outlet weir structures allow
  water level control for
  adjustment of hydraulic
  retention time.
Dense stands of submerged
cattail stems and leaves
serve as growth media for
microorganisms that feed on
impurities in the influent. The
natural transfer of atmospheric
oxygen to these microbes is
essential in removing organic
matter and ammonia from
the wastewater.

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 BACKGROUND
      The town of Fort Deposit, located
      south of Montgomery, Alabama,
      has a population of slightly more
 than 1,500. Until 1985, the town's waste-
 water was treated in a 10-acre waste
 stabilization pond and consistently met
 discharge limits. In 1985, a new discharge
 permit was issued by the Alabama
 Department of Environmental Manage-
 ment. This permit required the town
 to meet more stringent standards based
 on water quality limitations in the
 receiving water. Since the town's
 stabilization pond was unable to meet
 the new standards, an administrative
 order requiring the town to upgrade
 its system was issued.
   An engineering analysis of treatment
 alternatives was conducted by the
 environmental consulting firm
 CH2M HILL to compare a variety of
 conventional and innovative technolo-
 gies. On the basis of an evaluation of
 environmental benefits, reliability, and
 cost, treatment by constructed wetlands
 was selected as the most cost-effective
 approach for compliance with the new
 permit limitations.
  The use of constructed wetlands to
 remove impurities in wastewater and
 to consistently achieve treatment levels
 that meet permit requirements was an
 emerging technology in 1985. To assist
 with funding their new system, the town
 applied for and was awarded a $610,000
 U.S. Environmental Protection Agency
 (EPA) Innovative/Alternative
Technology grant for its wetland project.
This additional funding, coupled with
low construction and maintenance costs
associated with the wetland system.
reduced the financial impact of the
upgrade on the community and provided
it with a system that would require only
slightly more maintenance than the
existing stabilization pond.
Post-aeration is essential for
compliance with the effluent
standard for dissolved oxvgen.

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 ANCILLARY BENEFITS
   In addition to improving the quality
   of the effluent discharged to the
   receiving stream, the creation of
the Fort Deposit constructed wetland
treatment system has significantly
increased wildlife. This new habitat
provides cover and food for various
types of wetland-dependent vertebrate
and invertebrate life including a
variety of ducks and wading birds and
their prey.
  As a result of the wetland's success
and the desire of others to adopt similar
technology, the town is receiving
visitors from other areas of the state
and the nation.
                                                                            The Fort Deposit wetlands
                                                                            continue to diversify as new
                                                                            plant species colonize the cells.

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    In the Fort Deposit wetland system,
    wastewater is treated by the naturally
    occurring bacteria and fungi that
 colonize the sediments on the bottom
 of the cells and the stems and leaves of
 the wetland vegetation below the water
 level. These microorganisms help trans-
 form and remove organic matter and
 nutrients that might otherwise degrade
 adjacent surface waters.
   The vegetation in the two wetland
 cells was selected to simulate a natural
 wetland and included an initial planting
 of 68,000 cattail and bulrush plants.
   Influent from the aerated pond is
 distributed to the cells by pipes with
 1-inch holes drilled at 10-foot intervals.
 This method of distributing  influent
 starts the flow through the treatment
 system and reduces the buildup of solids
 at the head of the wetland cells.
   The system is designed so that the
 effluent takes up to 30 days to flow
 through the wetland cells. The actual
 retention time varies seasonally to
 account for changes in the reaction
 rate of microorganisms in the cells.
 Because the microorganisms react more
 quickly at higher temperatures, the
 retention time can be decreased during
 the summer and still provide the
 required contact time for effective
 removal of impurities. Conversely,
 during the winter's colder temperatures,
 the reaction rate of the microorganisms
 is lower and the retention time is
 increased by raising water levels.
   Aluminum stop logs, located in three
outlet structures along the width of each
wetland cell, control cell water depth
and promote the flow of effluent
through the treatment system.
  After treatment by the wetland cells,
effluent is conveyed to the post-aeration
pond, where it receives supplemental
aeration from a floating aerator.
Influent distribution to the
wetland cells is enhanced by
perforated pipes on a rip-rap
slope across the width of the
wetland cells.

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 ACKNOWLEDGEMENTS
The Waterworks and Sewer Board of
the Town of Fort Deposit

    Henry Crenshaw, Chairman

    Leo Goldsmith, Board Member

    WO. Ward, Board Member

    David Edwards, Manager


Consulting Engineers

    Dennis A. Sandretto,
    CH2M HILL
    Project Manager

    Robert L. Knight,
    CH2M HILL Project
    Environmental Scientist
Alabama Department of
Environmental Management
   Truman Green,
   Chief, Municipal Branch,
   Water Division
U.S. Environmental Protection Agency
   Robert Freeman,
   Municipal Grants Program,
   Region IV
This brochure was prepared by
CH2M HILL for the
U.S. Environmental Protection Agency.

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PERFORMANCE
       Construction of the cells began in
       June 1989, with planting starting
       during May 1990. By August
1990, the vegetation provided almost
complete cover, and operation of the
wetland cells began. Since then, with
only one exception for NH3, the Fort
Deposit constructed wetland treatment
system has consistently achieved permit
compliance and has caught the  attention
of others seeking a low cost, dependable
natural treatment system. Because of
its outstanding contribution to water
resource conservation, the Fort Deposit
system received several awards including
                the Alabama 1991 Governor's Conserva-
                tion Achievement Award, the Alabama
                Engineering Excellence Award, and
                the Grand Award from the American
                Consulting Engineers Council.
       Month
        December
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                                             Deep zones in the wetlands
                                             provide open water for ducks
                                             and wading birds, enhance
                                             flow distribution in the
                                             wetland cells, serve as a sump
                                             for settling solids, and provide
                                             additional hydraulic residence
                                             time in the wetland cells.

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