Enwwra^Protocfcr Agmcy
  Constructed Wetlands for
  Wastewater Treatment and
      Wildlife Habitat
Fort Deposit, AL: Constructed Wetland Treatment
                  System Case History
            Fort Deposit, Alabama
            Canttrutfed W«U«nd Twrtnwm SyiMnt
Background


System Description


Operations and Management


Performance


Ancillary Benefits


Acknowledgements

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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 wastewater 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 Management. 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
technologies. 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
             oxygen.

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                              System Description
As designed, the Fort Deposit
wetland 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 remaining area
to serve as a settling basin. These modifications improve 5-day biochemical oxygen demand (BODS) 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 wetland 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 Fort Deposit constructed wetland treatment system uses an aerated
   lagoon for pretreatment followed by two parallel wetland cells.
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.

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                     Operations  and  Management
                                  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 transform 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.
Outlet weir structures allow water level
  control for adjustment of hydraulic
          retention time.
                                                         Influent distribution to the wetland cells is
                                                         enhanced by perforated pipes on a rip-rap
                                                            slope across the width of the wetland
                                                                        cells.
                                     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.

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Dense stands of submerged cattail stems

  and leaves serve as growth media for      A n       ,     . i   ,1     *T  j  n    f£\                t •   ±u
                                      After treatment by the wetland cells, effluent is conveyed to the
microorganisms matjeed on impurities in             .                                              .

   the influent.  The natural transfer of     post-aeration pond, where  it receives supplemental aeration

atomospheric oxygen to these microbes is   from a floating aerator.

essential in removing organic matter and

     ammonia from the wastewater.

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                                 Performance
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.
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 Conservation Achievement
Award, the Alabama Engineering Excellence Award,
and the Grand Award from the American Consulting
Engineers Council.
                                               Month   BOD5  TSS
                                  Nitrogen
                                                        In Out In Out    TKN In    NHsOut
1990August 102 5 137 10
September 27 8 101 18
October 30 3 168 18
November 27 3 127 10
December 15 4 71 9
1991 January 20 5 52 10
February 13 4 18 4
March 26 7 40 8
April 22 10 97 15
May 21 9 52 20
June 29 10 72 25
July 33 7 69 10
August 56 7 183 7
September 24 4 87 12
October 30 8 125 18
November 32 4 106 7
December 33 12 64 16
1992January 39 4 83 19
February 22 4 32 4
March 34 4 58 5
20.0
11.0
19.0
14.0
10.0
8.0
11.0
19.0
10.0
80.0
5.0
21
20.0
10.0
6.0
11.0
11.5
10.0
6.7
10.0
0.57
0.66
0.78
0.93
2.60
1.10
0.74
0.89
0.70
0.35
0.94
6.43
0.90
0.99
0.75
0.21
0.87
0.38
0.15
0.22

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     April      31  4 119  3       12.0       0.51

Wetland effluent BOD5 and total suspended solids
(TSS) are consistenly in compliance with permit limits
despite variable inflow quality to the wetland cells.
Total Kjeldahl nitrogen (TKN) is mineralized in the
wetland cells to NH3 and then nitrified to achieve the
low discharge limits.

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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 wetland1 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.

            Fort Deposit
            Wetland  Design Criteria
            Average Daily Flow 0.24 mgd
            Influent Quality
               BODs
               TSS
               TN
               NH3-N

            Effluent Criteria
               BODs
               TSS
               NH3-N
               pH
40 mg/L
lOOmg/L
20 mg/L
10 mg/L
10(18)amg/L
30 mg/L
2(5)a mg/L
6-9 units
                            The Fort Deposit wetlands continue to
                           diversify as new plant species colonize the
                                        cells.
            Areas
               Lagoon          10 acres
               Wetland Cells (2) 7.5 acres each
            ()a winter limits December-April

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                         Acknowledgements

The Waterworks and Sewer Board of the Town of Fort Deposit

     Henry Crenshaw, Chairman
     Leo Goldsmith, Board Member
     W.O. 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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