Draft Report

Task 3

Legacy P Abatement Plan 

For Project Entitled

Technical Assistance in Review and Analysis of Existing Data for
Evaluation of Legacy Phosphorus in the Lake Okeechobee Watershed

Prepared for

South Florida Water Management District 

by

Soil and Water Engineering Technology, Inc.

In association with

JGH Engineering

April 14, 2008

Technical Assistance in Review and Analysis of Existing Data for
Evaluation of Legacy Phosphorus in the Lake Okeechobee Watershed

Task 3: Legacy P Abatement Plan 

Table of Contents

  TOC \o "1-3" \h \z \u    HYPERLINK \l "_Toc195952375"  INTRODUCTION	 
PAGEREF _Toc195952375 \h  1  

  HYPERLINK \l "_Toc195952376"  DEFINITION OF LEGACY P	  PAGEREF
_Toc195952376 \h  1  

  HYPERLINK \l "_Toc195952377"  BACKGROUND OF LEGACY P	  PAGEREF
_Toc195952377 \h  2  

  HYPERLINK \l "_Toc195952378"  OVERALL ABATEMENT STRATEGY AND
ASSUMPTIONS	  PAGEREF _Toc195952378 \h  3  

  HYPERLINK \l "_Toc195952379"  LEGACY AND OTHER P SOURCES	  PAGEREF
_Toc195952379 \h  4  

  HYPERLINK \l "_Toc195952380"  PHOSPHORUS CONTROL PRACTICES	  PAGEREF
_Toc195952380 \h  4  

  HYPERLINK \l "_Toc195952381"  In-Field Agricultural BMPs	  PAGEREF
_Toc195952381 \h  10  

  HYPERLINK \l "_Toc195952382"  In-Field Soil Amendments	  PAGEREF
_Toc195952382 \h  10  

  HYPERLINK \l "_Toc195952383"  Edge-of-Field/Farm (EOF) Treatment
Technologies	  PAGEREF _Toc195952383 \h  12  

  HYPERLINK \l "_Toc195952384"  Residential and Urban	  PAGEREF
_Toc195952384 \h  12  

  HYPERLINK \l "_Toc195952385"  Facilities or Point Sources	  PAGEREF
_Toc195952385 \h  12  

  HYPERLINK \l "_Toc195952386"  Regional In-Stream Treatment
Technologies	  PAGEREF _Toc195952386 \h  13  

  HYPERLINK \l "_Toc195952387"  ESTIMATED IMPLEMENTATION LEVELS AND
COSTS TO ACHIEVE TMDL TARGETS	  PAGEREF _Toc195952387 \h  13  

  HYPERLINK \l "_Toc195952388"  IMPLEMENTATION SCHEDULE	  PAGEREF
_Toc195952388 \h  19  

  HYPERLINK \l "_Toc195952389"  REFERENCES	  PAGEREF _Toc195952389 \h 
20  

  List of Figures

  TOC \h \z \c "Figure"    HYPERLINK \l "_Toc195802534"  Figure 1. 
Northern Lake Okeechobee Watershed	  PAGEREF _Toc195802534 \h  1  

 

List of Tables

  TOC \h \z \c "Table"    HYPERLINK \l "_Toc195952390"  Table 1. 
Surface water inflows, TP concentrations, loading rates, and TMDL
targets for Lake Okeechobee Tributary Basins (1991-2005)	  PAGEREF
_Toc195952390 \h  5  

  HYPERLINK \l "_Toc195952391"  Table 2.  Assumed P mobility factors for
legacy, native, and anthrogenic P sources	  PAGEREF _Toc195952391 \h  6 


  HYPERLINK \l "_Toc195952392"  Table 3.  P loads from Soil Based Legacy
P for Various Land Uses	  PAGEREF _Toc195952392 \h  7  

  HYPERLINK \l "_Toc195952393"  Table 4.  P loads from Native and
Non-Soil Based Legacy P Anthropogenic Sources for Various Land Uses	 
PAGEREF _Toc195952393 \h  8  

  HYPERLINK \l "_Toc195952394"  Table 5.  Predicted P Source Loads to
Stream, In-stream Assimilation, and Net Basin Export (1991-2005)	 
PAGEREF _Toc195952394 \h  9  

  HYPERLINK \l "_Toc195952395"  Table 6.  Measured and Estimated P
Source Loads to Stream and Net Basin Exports with TMDL Targets	  PAGEREF
_Toc195952395 \h  9  

  HYPERLINK \l "_Toc195952396"  Table 7.  Phosphorus Control Practices -
Assumed Effectiveness and Costs	  PAGEREF _Toc195952396 \h  11  

  HYPERLINK \l "_Toc195952397"  Table 8.  Northern Lake Okeechobee Basin
P Control Practices Implementation Plan for Meeting the Tributary TMDL	 
PAGEREF _Toc195952397 \h  15  

  HYPERLINK \l "_Toc195952398"  Table 9.  Upper Kissimmee Basin P
Control Practices Implementation Plan for Meeting the Tributary TMDL	 
PAGEREF _Toc195952398 \h  16  

  HYPERLINK \l "_Toc195952399"  Table 10.  Lake Istokpoga Basin P
Control Practices Implementation Plan for Meeting the Tributary TMDL	 
PAGEREF _Toc195952399 \h  17  

  HYPERLINK \l "_Toc195952400"  Table 11.  Estimated Additional Regional
Treatment Required to Meet Lake Okeechobee TMDL with and without Meeting
Tributary TMDLs	  PAGEREF _Toc195952400 \h  18  

 

List of Abbreviations

BAT 		Best Available Technologies

BMAP 	Basin Management Action Plan

BMP 		Best Management Practice

CERP 		Comprehensive Everglades Restoration Plan

cm 		Centimeters

EPA		Environmental Protection Agency

FDACS	Florida Department of Agriculture and Consumer Services

FDEP		Florida Department of Environmental Protection

Fe		Ferric

ha		Hectares

IFAS 		Institute of Food and Agricultural Sciences

kg		Kilograms

mg		Milligrams

mt 		Metric Tons

NRCS 		Natural Resources Conservation Service

P		Phosphorus

ppm		Parts per million

RASTA 	Reservoir Assisted Stormwater Treatment Area

SFER 		South Florida Environmental Report

SFWMD 	South Florida Water Management District

TMDL		Total Maximum Daily Load

TP 		Total Phosphorus

yr		Year

 INTRODUCTION

The goal of this final task 3 report is to present a legacy phosphorus
(P) abatement plan for the northern Lake Okeechobee watershed (Figure 1)
based on the findings of the first two tasks of this project.  Tasks 1
and 2 quantified, mapped, assessed mobility of, and identified abatement
practices for the legacy P within the watershed based on the available
field and literature data obtained during a comprehensive review
process.  

Figure   SEQ Figure \* ARABIC  1 .  Northern Lake Okeechobee Watershed

The Statement of Work for this final task provided for two options
depending on the adequacy of the findings for developing a meaningful
legacy P abatement plan at this time.  Even though more information
would obviously be useful, it was determined that the current legacy P
knowledge base was sufficient for developing an abatement plan.  If the
current information had been deemed insufficient, then a research and
data acquisition plan would have been developed to obtain the additional
information needed before an abatement plan could be developed.  

The specific objectives of this legacy P abatement plan were to outline
specific P control practices and strategies at different spatial scales,
anticipated P reduction performances, implementation costs, and a
general implementation schedule.   

DEFINITION OF LEGACY P

Legacy phosphorus (P) is defined as phosphorus within the watershed that
is present as the result of anthropogenic activities and has transport
potential to Lake Okeechobee.  Antecedent P is defined as the P that
occurs naturally in soils based on the native properties of the soils
and atmospheric deposition and rainfall.  Anthropogenic activities in
the Lake Okeechobee watershed have resulted in more imported P into the
watershed, as fertilizer, animal feed, and domestic goods, than has been
exported resulting in the accumulation of P in soils, waste storage
facilities, and landfills.  

BACKGROUND OF LEGACY P

Over the last three decades, Lake Okeechobee has experienced accelerated
eutrophication due to excessive phosphorus inputs from anthropogenic
activities, particularly agricultural land uses that dominate in its
watershed.  Lake Okeechobee’s northern watershed consists of 21
summary basins covering more than 2.65 million acres or 4,100 square
miles (Figure 1).  From 1991 to 2005 P loads to Lake Okeechobee from the
northern drainage area were 457 metric tons per year (mt/yr), which were
about 83% of the total P load of 549 mt/yr to the lake including 35
mt/yr from atmospheric deposition.  These P loads are higher than the
established Total Maximum Daily Load (TMDL- FDEP Rules Chapter 62-304)
target by 160 mt/yr.  The northern Lake Okeechobee watershed exceeds its
TMDL target by 112 mt/yr.   An EPA proposed Lake Okeechobee tributary
TMDL will likely set in-stream P concentration targets somewhere between
77 to 120 ppb.  Despite the long history of regulatory and voluntary
incentive-based programs to control P inputs into Lake Okeechobee,
current P loadings to the lake and P concentrations in the watershed
north of the lake remain high.  Intensive P management strategies will
be needed to lower P loadings sufficiently to meet the TMDL target by
2015. 

Though the process of P accumulation has been occurring since the late
eighteen hundreds, the majority of the accumulation has occurred over
the past fifty years.  The first major import of P was as fertilizer
used for a developing vegetable crop industry around 1915 to 1920, but
the vegetable farms disappeared after a brief time due to hard freezes
and therefore little P accumulation occurred (VanLandingham and 
Hetherington, 1978).  From 1930 to 1940, a significant increase in the
cattle business occurred with beef cattle going from 17,000 head in
Okeechobee County in 1930 to 45,000 in 1940.  Phosphorus fertilizer was
used on beef pasture at this time, but was fairly limited due to costs
and low animal densities.  Beef cattle pastures were fertilized more
aggressively starting in the 1940s and up through the 1980s, which is
the period of the greater legacy P build up.  Phosphorus fertilization
on beef pastures was essentially stopped during the 1990s.

The period starting in the late 1940s through the early 1960s saw dairy
farms from the southeast coast of Florida move into the area.  At their
peak during the 1970s there were more than 45 dairies in the northern
Okeechobee basins.  More than half of these dairies have since closed as
part of the Dairy Buyout Program in the mid to late 1980s and economic
pressures.  Most of these dairies operated without waste management
systems until the 1960s when the US Soil Conservation Service
constructed lagoons and seepage fields on most of the dairies.  Other
best management practices, such as stream fencing, were started on the
dairies in 1979.  By 1988, all of the dairies were operating under FDEP
Dairy Rule permits that required BMPs on all dairies.  As these permits
were transferred to NPDES (EPA) permits, starting about the year 2000,
each dairy was required to show nutrient balancing across the dairy,
which in some cases required additional BMPs.

Residential and urban development also increased in the basin with its
most rapid growth occurring during the last 20 years.  The legacy P
associated with residential and urban development is from landscape
fertilization, the accumulation of P in drain fields and septic tanks,
municipal sludge from wastewater treatment plants, and landfills.

The findings of Tasks 1 and 2 provided a good picture of where the
legacy P is located within the watershed and its relative mobility for
eventually washing into the streams and ultimately to Lake Okeechobee. 
The P transport processes and associated practices that influence P
transport were also identified.  The purpose of this report is to use
these data and information to formulate an abatement plan that will meet
the TMDL target of 140 mt/y of P going to Lake Okeechobee by 2015 and an
assumed tributary P TMDL for the watershed.

  

OVERALL ABATEMENT STRATEGY AND ASSUMPTIONS

The overall approach for controlling the legacy P within the northern
Lake Okeechobee watershed from entering its tributaries and Lake
Okeechobee was to identify where the legacy P is being stored and then
identifying practices that could most cost efficiently limit its
mobility.  Establishing where they are to be implemented however depends
on where the TMDL P target levels are to be met.  The Lake Okeechobee
target has been set at 140 mt (112 mt for the northern Lake Okeechobee
watershed), however the tributary TMDL has not been finalized.  The
tributary TMDL target and its associated BMAP will be critical because
they directly influence the legacy P control measures and ultimately the
costs to meet the P reduction goals.   Obviously designing an abatement
program with an unknown target is difficult, therefore for this
assessment a tributary TMDL of 100 ppb TP was assumed.  It is also
important to known how rigorously the BMAP would enforce this target
within tributaries, i.e. would it extend to the limits of the Waters of
the State designation or would some flexibility be provided within the
secondary and tertiary reaches for more efficient practices?  For this
assessment, it was assumed that reason would prevail and upland
tributary practices would allow limited use of designated waters for
treatment systems.  In summary, it was assumed for this project that a
tributary TMDL will be established at 100 ppb TP, but that P control
measures could use Waters of the State for conveyance within
predominately agricultural areas or individual property boundaries. 

The assumption that meeting tributary TMDL targets will be required has
its greatest impact on those areas that have existing downstream P
abatement systems, such as large lakes, extended sloughs, or regional
treatment systems.  For example for the lakes in the upper Kissimmee
basin, particularly Lake Kissimmee, are currently assimilating most of
the P entering them from their watersheds, and therefore from the Lake
Okeechobee TMDL perspective upland P control practices in this watershed
would not be very effective.  The same is true for the Lake Istokpoga
basin and the extensive slough system in Fisheasting Creek, though to a
lesser extent.  A tributary TMDL within these basins obviously negates
this advantage and directly affects the P abatement strategies.  An
additional issue associated with the downstream systems, which have been
assimilating P for years, is that when their inflow P concentrations
decrease due to upland P control practices they will likely become
sources of P.  This means that there can be significant delays between
the P load reductions in upland tributaries and the P loads entering the
Lake Okeechobee, particularly for these upper basins.  

Since the tributary TMDLs targets will be higher than the Lake
Okeechobee TMDL targets and the in-stream accumulated legacy P could
start washing out, there be need for additional P removal before
discharging to the lake.   Therefore, it will be necessary to integrate
upland P control practices with regional treatment systems on the lower
tributaries in order to meet the lake TMDL.  The approach taken for this
abatement plan was to first meet the tributaries TMDL and then to do
regional treatment to obtain the additional P reductions needed to meet
the Lake Okeechobee TMDL.  

LEGACY AND OTHER P SOURCES

In order to develop an abatement plan it was first necessary to
understand and quantify where the P is coming from and how it is moving
through the stream system.   The 2008 SFER provided the flow and P loads
from 1991 through 2005 for all of the basins that drain to Lake
Okeechobee.  This information was reordered in Table 1 to separate out
the northern Lake Okeechobee watershed data and to compare these data to
the Lake Okeechobee TMDL and the assumed tributary TMDL targets.  The
measured data were used to verify the assessment tool developed as part
of this project.  This assessment tool predicts the P loads to streams
by land use and P source category for the three primary basins within
the northern Lake Okeechobee watershed based on the assumed mobility
factors shown in Table 2.  Table 3 provides the predicted P loads based
on the soil based legacy P information developed during task 2 of this
project, while Table 4 provides the predicted native and other
anthropogenic P loads from the various land uses.  These land use based
P source data were then combined with estimated assimilation rates
within the streams, sloughs, and lakes to predict net basin outflows
(Table 5).  These predicted net basin P loads were then compared to
measured data and the Lake Okeechobee and tributary TMDL targets (Table
6).  Table 6 is useful because it provides an indication of the
percentage reductions required to meet the TMDLs.  These results also
make it clear that meeting the tributary TMDL targets will not be
sufficient to meet the lake TMDL targets, and therefore either the land
sourced P loads will have to be reduced significantly below tributary
TMDL targets or additional in-stream treatment will be needed or a
combination of both.  

 

PHOSPHORUS CONTROL PRACTICES

This section describes the P control practices that are integral to the
abatement plan.  The P control practices used in the plan can be
categorized into one of the following spatial groupings that define the
scale and type of P source to be addressed:

In-Field – Field practices that address the legacy P and its mobility
within the soil/plant environment.

Edge-of-Field/Farm (EOF) – Practices that treat and/or retain runoff
as it is leaving a field or farm.

Residential – Practices applied within residential areas. 

Urban – Practices applied within
transporation/urban/commercial/industrial areas

Facilities – Practices used in non soil-based areas that potentially
discharge P into runoff, such as industrial sites, packing houses, old
land fills, etc. 

Regional – Practices that treat and/or retain stream flows within the
tributary system where multiple upstream landowners drain to the system.

Table   SEQ Table \* ARABIC  1 .  Surface water inflows, TP
concentrations, loading rates, and TMDL targets for Lake Okeechobee
Tributary Basins (1991-2005)

Table   SEQ Table \* ARABIC  2 .  Assumed P mobility factors for
legacy, native, and anthrogenic P sources

Table   SEQ Table \* ARABIC  3 .  P loads from Soil Based Legacy P for
Various Land Uses

Table   SEQ Table \* ARABIC  4 .  P loads from Native and Non-Soil
Based Legacy P Anthropogenic Sources for Various Land Uses



Table   SEQ Table \* ARABIC  5 .  Predicted P Source Loads to Stream,
In-stream Assimilation, and Net Basin Export (1991-2005)

Table   SEQ Table \* ARABIC  6 .  Measured and Estimated P Source Loads
to Stream and Net Basin Exports with TMDL Targets

The following sections will describe the individual P control practices
within each of these categories and provided estimated P removal
efficiencies in terms of dollars per pound of P removed.

In-Field Agricultural BMPs

Previous studies and reports have estimated the effectiveness and cost
of agricultural BMPs for the Okeechobee basin as described in the task 2
report.  FDACS has been instrumental in the development and
implementation of agricultural BMP around the Lake Okeechobee watershed
and the rest of Florida.  They have a series of BMP manuals for a
variety of commodities.  These manuals, however, do not provide specific
information on P reduction performances or costs.  Therefore, the letter
report (Bottcher, 2006) entitled:  “Phosphorus Reduction Performance
and Implementation Costs under BMPs and Technologies in the Lake
Okeechobee Protection Plan Area” was used for providing the
agricultural BMP response and cost data.  This letter report summarizes
the available BMPs and provides ranges and typical condition
implementation costs and estimated P reductions.  The typical condition
was developed to account for that fact that some farms already have BMPs
and for the fact that BMPs effectiveness also varies due to
site-specific conditions, such as soils.  Because of the complexity and
diversity of the northern Lake Okeechobee basins the following
assumptions had to be made to complete this assessment.  First it was
assumed that an integrated BMP program would be implemented instead of
trying to deal with individual BMPs implementation strategies, i.e. the
typical BMP implementation condition developed in the letter report was
be used.  Secondly, to roughly account for variable soil conditions
between the three primary basins, the northern Lake Okeechobee basins
were categorized as being predominately flatwood soils while the other
two basins were categorized as ridge soil dominated.  This adjustment
was done because the well drained ridge soils have considerably less P
transport potential than flatwood soils, thus reducing the legacy P
influences on P losses.  Table 7 summarizes of the assumed BMP reduction
performance and relative costs for the agricultural land uses used for
this plan’s development.

In-Field Soil Amendments

A few studies have looked at the benefits of applying soil amendments to
reduce the mobility of the accumulated legacy P in the soils.  The soil
amendments evaluated have been lime, gypsum, silica, aluminum and iron
salts, and water treatment residuals.  The intent of these compounds is
to either raise pH to enhance P binding or to directly bind P to the
applied compounds.  Though these soil amendments can significantly
reduce P they have three disadvantages that greatly limit their
effectiveness for controlling P.  First, soil amendments attempt to
treat the entire legacy P pool within the soil, which is about 50 to 200
times larger than the P being discharged per year.  This means large
amounts of chemicals have to be applied at high cost.  Second, it is
very difficult to get the amendments mixed into the soil adequately to
maximize there effectiveness.  Finally, soil amendments do not reduce
the amount of legacy P in the soil and over time many of the amendments
can lose their binding properties and the legacy P can become mobile
again.  Lime Table   SEQ Table \* ARABIC  7 .  Phosphorus Control
Practices - Assumed Effectiveness and Costs

and iron salts are particularly vulnerable to remobilization. 
Therefore, soil amendments were not considered a viable P control
practice in this plan.

 

Edge-of-Field/Farm (EOF) Treatment Technologies

Edge-of-field/farm (EOF) P control practices are grouped together
because they use identical technologies and only differ in the physical
location of their implementation.  The concept behind EOFs is that they
need only treat the P leaving the field or farm and not the entire pool
of legacy P in the field or farm.  This means that all of the natural P
assimilation processes upstream of the EOF can be taken advantage of
before treatment.  The Dairy BAT project discussed in the Task 2 report
evaluated and ranked EOF technologies and then constructed and tested
four systems in the northern Lake Okeechobee basin.  This project found
that EOF systems for high P source areas are the most cost effective P
control practice that can be implemented.  However, the relative cost
effectiveness of EOF systems decreases as the P concentration in the
field or farm runoff decreases, where 2.0 ppm P runoff will cost about
$20 /lb-P removed/yr as compared to about $120 /lb-P removed/yr for 0.35
ppm P runoff.  Table 7 summarizes the assumed reduction performance and
relative costs for EOF systems for various land uses used for this
plan’s development.

Residential and Urban 

Residential P control practices include site level and EOF systems. 
Site level practices are typically landscape management BMPs, such as
fertility and water management practices.  The EOF systems include
standard stormwater retention/detention practices and possible chemical
treatment for pass-thru waters.  The estimated responses and costs are
based on Harvey Harper’s work included in the 2006 letter report
(Bottcher, 2006).  Table 7 summarizes the assumed P reduction
performance and relative costs for EOF systems for various urban land
uses used for this plan’s development.

Facilities or Point Sources 

Direct discharges from point sources and other industrial and commercial
operations were considered in the overall P balance for the watershed,
but were not included as a control option within this plan because these
sources typically do not include the mobility of accumulated legacy P
and are assumed to be under existing FDEP permits, so additional
modifications to these facilities were assumed unlikely.  Therefore, no
practices were applied to these sources; however it is strongly
encouraged that these sources be periodically reviewed for their
relative contributions and control practices.  

Regional In-Stream Treatment Technologies

The final option for controlling P loads going into Lake Okeechobee is
to treat the water flowing within the stream network at selected
regional locations.  The primary advantage of regional treatment,
particularly nearest to the lake, is that only the P that is headed into
the lake would be treated, thus taking full advantage of the other
assimilative processes within the watershed.  The two primary
disadvantages are that tributary TMDLs upstream of the regional systems
are not addressed and the fact that treatment of mixed or diluted flows
will be less efficient than treating closer to the higher P source
areas.  Two regional treatment technologies were considered for this
project, which were a reservoir assisted stormwater treatment areas
(RASTAs) that use a reservoir to buffer flows and depths within a
wetland treatment areas that provide P removal treatment and a
retention/detention reservoir system using chemical treatment for its
pass-thru waters.  Even though the chemical treatment system was found
to be more cost efficient, it was not included in the plan due to a
directive from the District that chemical treatment at the regional
scale would not be acceptable.  However, it is recommended that because
of its high efficiencies and lower cost, further investigations be
conducted to verify or disprove the stated concerns over chemical
treatment. 

The release and assimilation of legacy P within the stream network is an
important issue to address when considering the placement of regional
treatment systems.  Wetland sloughs and lakes can assimilate and release
P depending on the difference between current inflow P concentrations
and long term historical inflow P concentrations.  Over time these
wetlands and lakes will trend toward an equilibrium with inflow P
concentration, but in the case of large lakes and slough systems it is
unlikely that they have reach such an equilibrium and therefore are
still assimilating P.  However, as inflow P concentrations are reduced
these sloughs and lakes might begin to release either native or legacy
accumulated P.  Therefore placing regional treatment system upstream of
such systems could greatly reduce its effectiveness especially in the
short term.  In time the accumulated P in these systems will wash out to
establish a new equilibrium with the inflow P levels.  Sloughs will
likely respond within five to twenty years as compared to the larger
lakes taking perhaps five to ten times longer to establish a new
equilibrium.  Therefore it recommended the regional treatment systems
not be placed upstream of sloughs and lakes.    Table 7 summarizes the
assumed reduction performance and relative costs for the regional
treatment systems used for this plan’s development.

ESTIMATED IMPLEMENTATION LEVELS AND COSTS TO ACHIEVE TMDL TARGETS

This section spatially assigns P control practices across the watershed
to achieve both the Lake Okeechobee and assumed tributary TMDL targets
based on the 2006 land use GIS coverage and assumed P control
practices’ performances and costs.  The approach taken was to apply P
control practices for meeting the tributary TMDLs first, and then to
apply additional practices as needed to meet the Lake Okeechobee TMDL. 
The method of applying P control practices was to apply the most cost
effective practice first, and then to add practices as needed to meet
the TMDL targets for each land use.    

The implementation of a modest “typical” BMP program was found to be
the most cost effective initial P control practice for the watershed,
and therefore was applied first across the watershed.  To keep the
logistics of BMP implementation to a manageable level, site or field
level BMPs were applied as a suite of BMPs as previously identified as
the most appropriate combination by Bottcher (2006).  The next P control
practice implemented was stormwater retention, which includes wetland
restoration and water reuse, as well as standard urban R/D systems. 
Finally, chemical treatment was added to the retention based systems if
the first two practices were not sufficient to meet TMDL targets.  

Tables 8 through 10 show the existing P loads to the tributaries, the
tributary TMDL target, required P load reduction, P load reductions by P
control practices, and annual costs for each land use category within
the three primary basins.  The TMDL targets for the individual land uses
were adjusted to account for the dilution effect of runoff from lower P
concentration sources, such as native areas, groundwater contributions,
and reduced P concentrations due to long term P assimilation in lakes
and sloughs.  These adjustment factors are provided as a footnote in the
tables.  They clearly show that the northern Lake Okeechobee basins have
the least dilution effect thus requiring greater relative P reductions
than for similar land uses for the other two primary basins,
particularly compared to the Upper Kissimmee regional basin that had the
greatest P dilution advantage.  

These tables also show that the relative importance of the various land
uses with improved beef pastures being the dominant source of P in the
watershed.  Nearly 80% of the P load reduction needed in the northern
Lake Okeechobee basin is associated with improved beef pasture while
about 60% and 70% P reductions are needed for improved beef pasture for
the Lake Istokpoga and Upper Kissimmee basins, respectively.  It was
also found that BMPs and retention practices alone were not sufficient
for improved beef pastures to meet tributary TMDL targets except within
the Upper Kissimmee basin because of the lower P load reductions
required in this basin.  As anticipated only the more intensive dairy
and vegetable land uses required EOF chemical treatment to meet
tributary TMDL targets.  

The cost for implementing the P control practices to meet the tributary
TMDL are also show in Tables 8 through 10.  These costs include both the
amortized capital costs and annual operation and maintenance costs so
that a direct comparison can be made as to the long term investment
required to meet the TMDL targets.  The annual costs are obviously
closely related to the P load reductions, but the lower P load sources
do have higher relative costs compared to high P load sources on a cost
per pound of P removed basis.  The estimated total annual cost for
meeting the tributary TMDL throughout the northern Lake Okeechobee
watershed is about $54 million with about half going to O&M costs and
the remaining being the 20-year amortized initial outlay of capital
expenses including land, equipment, and construction.  This means about
$270 million of initial capital expenditures would be needed for all
three primary basins to meet the tributary TMDL target.

Table   SEQ Table \* ARABIC  8 .  Northern Lake Okeechobee Basin P
Control Practices Implementation Plan for Meeting the Tributary TMDL

 Table   SEQ Table \* ARABIC  9 .  Upper Kissimmee Basin P Control
Practices Implementation Plan for Meeting the Tributary TMDL

 Table   SEQ Table \* ARABIC  10 .  Lake Istokpoga Basin P Control
Practices Implementation Plan for Meeting the Tributary TMDL

 

Table   SEQ Table \* ARABIC  11 .  Estimated Additional Regional
Treatment Required to Meet Lake Okeechobee TMDL with and without Meeting
Tributary TMDLs

Table 11 provides estimates of the additional regional treatment
required to meet the Lake Okeechobee TMDL for three conditions; 1)
tributary TMDL not addressed, 2) tributary TMDL is met and existing
wetlands and lakes equilibrate to the TMDL levels, and 3) tributary TMDL
is met and existing wetlands and lakes will maintain current P discharge
levels.   It is assumed that the regional treatment is implemented
downstream of any significant P sinks or sources, such as lakes or
wetland sloughs to maximize their benefits.  As seen in Table 11 the
current P loads leaving the Lake Istokpoga and Upper Kissimmee basins
are already in compliance with the assumed tributary TMDL due to their
significant buffering effect in these basins.  This means that achieving
tributary TMDL targets within these basins will have a minimum benefits
for achieving the Lake Okeechobee TMDL.  In fact, since the assumed
tributary TMDL targets in these basins are actually higher than current
P discharges, it is possible that over time these lakes will ultimately
come into equilibrium with tributary TMDL.  To account for this
possibly, two tributary TMDL scenarios are presented in Table 11, which
reflect the future condition that the lakes do come into equilibrium
with TMDL or that the lakes will continue to buffer P concentrations in
their outflows to current levels.  A third scenario presented in Table
11 is for the condition where tributary TMDLs are not implemented, so
that only the Lake Okeechobee TMDL target has to be met.  The predicted
results indicate that current upstream P assimilation or buffering by
the large lakes is reducing the P load treatment needs by about 16 mt
per year, which translates into an annual savings of about $5.2 million.
 Assuming that the lakes continue to buffer P and the tributary TMDL
targets are met, then it would cost about $47 million per year to
provide the additional treatment needed to meet the Lake Okeechobee
TMDL.  However, if no tributary TMDL P control practices are
implemented, then it would take about $106 million per year (about $700
million of capital expenditures) to meet the Lake Okeechobee TMDL or
about $60 million per year more than if the tributary TMDL targets were
already met.  Comparing this to the estimated $54 million per year for
meeting the tributary TMDL means that it would be less expensive to meet
both TMDL targets together than it would be trying to meet the Lake
Okeechobee TMDL by just doing regional treatments.  

IMPLEMENTATION SCHEDULE

Previous sections presented the recommended P control practices required
to meet the tributary and lake TMDL targets based on the 1991-2005
discharge data and average implementation conditions over that period. 
This means that the P control practices implemented since 2000 were not
reflected in the presented results and therefore must be included in any
implementation plan based on these results.  Hence, the following
implementation schedule includes the period staring in 2000 and any
moneys spent on the P controls after this date would be included in the
cost estimates presented in the previous section, thus reducing future
expenditures.  

The plan development requires set goals for when both the tributary and
Lake Okeechobee TMDLs are to be met.  The stated goal for meeting the
Lake Okeechobee TMDL is 2015 where there is currently no set timeline
for the tributary TMDL.  The concern of different target compliance
dates for the TMDLs is that the relative response times of various P
controls practices will impact when and where TMDL targets can be met. 
The tributary or upland P controls, particularly BMPs, may take several
years for their full benefits to be realized while EOF and regional
treatment system will have much quicker P reduction responses.  This
means that even if the described tributary and regional P controls
practices are fully implemented by 2015, the Lake Okeechobee TMDL target
will likely not be fully met for another five to ten years.  Therefore,
to achieve compliance with the Lake Okeechobee TMDL in 2015, the quicker
response P controls, such as EOF and regional treatment, must be
implemented at levels greater than what would be needed when future
equilibrium conditions are realized.  If the compliance date for the
tributary TMDLs is also set to 2015, then the retention and EOF upland P
control practices would have to become the higher priority.  The
compelling argument for going with the more intensive upland EOF systems
is that you can obtain fast P reduction responses while not having to
temporary overbuild regional treatment systems while waiting for the
slower response BMPs to take their full effect.  

Making the assumption that meeting both tributary and Lake Okeechobee
TMDLs by 2015 would be the preferred goals and that temporarily
overbuilding regional treatment systems is not cost effective the
following a generalized implementation schedule is recommended.  The
highest priority should be placed on EOF systems on the highest P source
areas within the Northern Lake Okeechobee basin.  BMPs should also
remain as a very high priority because in the long run they provide the
most cost effective P reduction response.  Regional treatment must also
continue to be implemented, but only to the level needed to address the
equilibrium condition with the tributary TMDL.  

REFERENCES

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Task 2 – Legacy P

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Task 3 – Legacy P

