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IEPA
United States ;
Environmental Protection
Agency <,
EPA832-R-93-005J
September 1993
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A CASE HISTORY:
LAKELAND WETLAND TREATMENT SYSTEM
Introduction
The City of Lakeland (City)
operates a 1,400 acre wetland
treatment system located just least
of the town of Mulberry, Florida. The
wetland system serves as the final treat-
ment process for the City of Lakeland's
10.8 mgd Glendale Wastewater Treat-
ment Plant and their 4.0 mgd Northside
Wastewater Treatment Plant. These
treatment plants serve a combined
population of approximately 79,000
people within the city limits, as well
as portions of the unincorpo-
rated areas of Polk County.
Many of the natural
upland and wetland commu-
nities within Polk County
and the surrounding coun-
ties have been replaced by
agricultural and industrial
development. Citrus and
phosphate mining industries
have altered the landscape
around Lakeland to a
greater extent than any
other development activity.
The phosphate mines have
provided the most dramatic
changes to the lands in
Polk County by not only
eliminating the natural
ecosystems, but also by
significantly altering the
topographic nature of
these areas.
Restoration efforts within
most of the abandoned mine
sites have been limited hi
scope at best, since no real
efforts generally are made
to restore the original topography
and vegetative communities. Instead,
upland areas are normally replanted as
monoculture pine forests, while most
aquatic areas are comprised of lakes
formed in unfilled mine pits. Most
emergent wetland communities are
restricted to the littoral zones of the lakes
or are usually dominated by monocul-
ture stands of cattails (Typha spp.) and/
or Carolina willow (Salix caroliniana).
Figure 1. Plan view of the site
showing the relative locations
of the internal cells.
Wetlands Ponds
Cattails
Other Ponds
Tree Line
Service Roads
Flow
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Project Background
Originally, the City began treating
wastewater on the Glendale site
in 1926 using a 2.5 mgd primary
treatment plant. This plant began
discharging effluent to Banana Lake
via Stahl Canal, a practice that continued
for more than 65 years. In 1939 the City
upgraded the treatment plant with trick-
ling filters to achieve secondary treat-
ment. In the late 1950's and 1960's, the
City rebuilt the trickling filters and
expanded the facility to 10 mgd. The
City began diverting up to 5.5 mgd of
effluent from the Glendale treatment
plant to the newly constructed C.D.
Mclntosh Jr. Power Plant for use as
cooling water. In 1981 effluent pumped
to the power plant was further treated
on the power plant site and discharged
(rapid infiltration) to the surficial
aquifer adjacent to Lake Parker, thereby
reducing the flows and loadings to
Banana Lake. In 1988, the City
expanded the wastewater treatment
Figure 2. The influent
structure aerates the water
as it enters the wetland.
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system to include its newly constructed
4.0 mgd Northside plant. When the
Northside plant went on-line, it became
the primary source of cooling water for
the power plant.
The sustained effluent discharge to
Banana Lake, along with agricultural
development in the Banana Lake
watershed, severely degraded the water
quality of the lake and down stream
waterways. Early in 1983, the Florida
Department of Environmental Protec-
tion (FDEP) indicated that the City's
discharge permit to Banana Lake would
not be renewed due to water quality
problems in the lake. For this reason,
both FDEP and the U.S. Environmen-
tal Protection Agency (USEPA)
negotiated compliance schedules with
the City to cease discharging effluent
to Stahl Canal and Banana Lake.
Faced with compliance schedules to
cease discharging to Banana Lake, the
City retained Post, Buckley, Schuh &
Jernigan, Inc. (PBS&J) to develop and
evaluate viable effluent disposal alterna-
tives. Analysis of these alternatives
indicated that disposal via an artificial
wetland system would be the most cost
effective method of effluent disposal
for the existing Glendale plant. The
Glendale facility has since been rerated
to 10.8 MGD. The wetland site selected
includes 1,600 acres that were formally
used by W.R. Grace Inc. as a phosphate
settling area. The site is characterized
by a series of seven cells surrounded by
levees. (See Figure 1.) Process waters
from the previous mining operation were
recycled through the cells to settle solids
out of the water column. Overflow from
the recycle system is discharged to the
Alafia River. This process created a soil
gradient across the cells where course-
grained sands settled on the influent side
of cells 1,2, and 3, while fine clayey
sediments settled on the effluent side
of the cells. The settling process also
created a significant topographic gradi-
ent hi the first three cells that slope
downward from the influent to effluent
sides of the cell. The sediments in cells 4
through 7 are predominately nearly level
fine clayey soils. A shallow lake still
exists on the downstream side of Cell 5,
while cells 6 and 7 remain as deep lakes.
One of the lakes located
at the downstream end
of the wetlands.
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WETLAND DESIGN
Since 1987, approximately 1,400
acres of the project site have
been used as part of the wetland
treatment system. This area provides a
permitted treatment capacity of 14 mgd
of secondary effluent, although the
current flows average approximately
8.0 mgd. Effluent is pumped from the
Glendale plant polishing ponds through
6.4 miles of force main to the wetland
system. In 1989, the influent to the
wetland system was augmented by
the inclusion of blow down waters from
the Unit No. 3 cooling tower at the
Mclntosh Power Plant, along with
periodic discharges from the ash ponds.
Blow down waters from the power
plant are mixed with effluent from the
wastewater treatment plants at the
Glendale plant and are then pumped
to the wetland.
The introduction of the cooling
waters and the ash pond effluent
has significantly increased the total
dissolved solids concentrations to the
wetland. As an example, the average
annual influent conductivity levels
have increased.
The influent enters the wetland
through a cascade inlet structure, as
shown in Figure 2. The inlet structure is
designed to aerate the influent waters
through turbulent fall down the struc-
ture's 13 steps. The flow is split at the
inlet structure between two Fabriform
lined ditches that lie along the eastern
boundary (influent side) of Cell 1.
Water is discharged from the distribution
ditches through weirs located every 100
feet along the ditch. Flow rates through
individual weirs can be controlled by the
addition or removal of flashboards. Once
the water passes through the cell it is
collected and discharged to Cell 2. This
general pass through and collection
system is repeated in cells 2 and 3. These
three cells have the greatest change in
topography. This system helps better
distribute flow in these cells.. Cells 4
through 7 do not have distribution
ditches. An H-flume outlet structure
located at the south end of Cell 7 is used
to monitor and control flows leaving the
wetland site. A meteorological station
provides data to assist in the preparation
of annual water budgets for the wetland.
Weirs located along berms
covered with grout-filled fabric
revetments distribute flow into
the cells 2 and 3.
The H-flume outlet structure
controls flows leaving the
wetlands.
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SITE CONDITIONS
When the City assumed control
of the wetland site, much of
the interior of cells 1 through
4 were covered by cattails and Carolina
willow. Upland islands within the cells
generally were vegetated by undesirable
grass/herbaceous species, and in some
areas by pine (Finns spp.) and live oak
(Quercus virginiana) tree species.
Vegetation in the upstream areas of Cell
5 was a mixture of cattails and Carolina
willow, while the downstream half of
the cell was a shallow lake system that
was ringed by a dense population of
water hyacinths (Eichhornia
crassipes). Densities of algal
populations in this lake often
created a lime green color in
the open water areas.
Although minimal disruption
of the existing wetland vegetation
within the treatment cells
resulted from the construction
activities, restoration grant
monies received by the City from
the Florida Department of
Natural Resources were used
to plant trees including black
gum, red maple, sweet bay,
swamp laurel oak, bald cypress,
dahoon holly, and pop ash, within
certain areas of cells 1 through 5.
Secondly, the water hyacinths
were removed from Cell 7 in
response to concerns, voiced by
the Polk County Environmental
Services Division, that operation
of the wetland system would
increase mosquito production in
areas covered by water hyacinths.
The areas along the eastern sides of
cells 1 and 2 were originally barren
sands or sparsely covered by upland
grass species. These were the only
areas planted with herbaceous wetland
vegetation during construction. In both
cells the pre-construction vegetation
was cleared to allow the site to be
graded. Initially, the highly permeable
sandy soils made it difficult to establish
wetland vegetation in these areas.
However, after five years of operation
both areas now support dense commu-
nities of wetland vegetation.
In operation since 1987, the
Lakeland Wetland Treatment
System offers wildlife a
natural habitat.
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OPERATIONAL RESULTS
The original design objectives for
the wetland treatment system
were to improve the City's efflu-
ent quality beyond the secondary level
(shown in Table 1 as Original Goals).
Since start-up of the wetland system,
state legislation was enacted that
required the wetland to meet even
more advanced wastewater treatment
levels (also shown in Tablel as Existing
Permit Conditions). Table 1 provides a
summary of the influent BOD, TSS,
TN & TP concentrations, water quality
after passing through the first two cells
(represented by station G3) that are
primarily emergent wetlands, and the
final effluent discharge structure. The
average annual concentrations for the
first four years of operation are
presented, as well as the FDEP and
USEPA permit limits. As shown, the
wetland effluent quality has consistently
met the permit limits, with the exception
of TSS for 1990 and 1991. This can be at
least partially attributed to increased
algal populations in the last four cells
within the wetland. Cell 7 previously was
covered by water hyacinths, which
served to limit the concentration of
algae near the effluent structure. The
removal of the water hyacinths in
response to county concerns has allowed
the algal concentrations to increase
which appears to interfere with the
wetlands ability to maintain TSS
concentrations below permit limits. The
City currently is working with FDEP,
USEPA, and PBS&J to lower water
levels in cells 3 through 6, and to
increase the density and distribution of
macrophytic vegetation in cells
Table 1.
Water quality results for the
first four years of operation.
Parameter
BOD TSS TN TP
(mg/L) (mg/L) (mg/L) (mg/L)
Influent 3.88 5.60 10.36
G3 1.14 1.74 2.79
Existing
Permit
Conditions 5.0
4 through 7. Increased
densities of macrophytic
vegetation in the latter four
cells should help limit the
density of algae in these
cells and, consequently,
reduce their contribution
to TSS in the effluent.
The wetland also has
provided habitat for a variety of
wildlife species. Most notable are
the large rookeries formed by wood
storks (Mycteria americana), white
pelicans (Pelecanus eiythrorhynchos),
cormorants (Phalacrocorax auritus)
anhingas (Anhinga anhinga), white ibis
(Eudocimus albus), and several egret
and heron species on the upland islands
within cells 5, 6, and 7. In addition, there
are several bobcat (Felix rufus) and otter
(Lutra canadensis) families now living
within the boundaries of the wetland.
Effluent 3.12 4.70 1.99
Original
Goals
9.05
6.54
4.22
5.0 10.0 3.0 Exempt
5.0
3.0
mpt
* Effluent phosphorus limits are exempted
due to the high background phosphorus
levels in the receiving stream.
Project Capital
Costs
Wetland
Pipeline
Pump Station
Total
$3,100,000
$2,800,000
$780,000
$6,680,000
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Acknowledgements
Numerous individuals have contributed to the
success of the Lakeland Wetland Treatment
System. Listed below are some of the key
groups and individuals.
City of Lakeland
John K. Allison, former Public Works Director
Virgil Caballero, Wastewater Superintendent
David Hill, Project Biologist
FDEP
Edward G. Snipes Jr., Permit Coordinator
G J. Thabaraj, Engineer
Blnipendra Vora, Grants Coordinator USEPA
USEPA
Robert K. Bastian
Office of Wastewater Management
Washington, D.C.
Prepared by Post, Buckley,
Schuh & Jernigan, Inc.
1560 Orange Ave., Suite 700
Winter Park, FL 32789
(407) 647-7275
Editors:
Jon C. Dyer, P.E.
John S. Shearer, P.E.,
Director, Environmental Services
The wide variety of wildlife
inhabiting the wetlands
includes anhinga and
numerous other waterfowl.
PBS&J
R. Morrell, Project Director
M. Walch, Project Manager
K. Keefer, Project Engineer
J. Jackson, Project Engineer
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