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
Task 2 – Legacy P ii

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

INTRODUCTION .......................................................................................................................... 1

DEFINITION OF LEGACY P ....................................................................................................... 1

BACKGROUND OF LEGACY P.................................................................................................. 2

OVERALL ABATEMENT STRATEGY AND ASSUMPTIONS................................................ 3

LEGACY AND OTHER P SOURCES.......................................................................................... 4

PHOSPHORUS CONTROL PRACTICES .................................................................................... 4

In-Field Agricultural BMPs...................................................................................................... 10

In-Field Soil Amendments........................................................................................................ 10

Edge-of-Field/Farm (EOF) Treatment Technologies............................................................... 12

Residential and Urban............................................................................................................... 12

Facilities or Point Sources ........................................................................................................ 12

Regional In-Stream Treatment Technologies........................................................................... 13

ESTIMATED IMPLEMENTATION LEVELS AND COSTS TO ACHIEVE TMDL TARGETS

....................................................................................................................................................... 13

IMPLEMENTATION SCHEDULE............................................................................................. 19

REFERENCES ............................................................................................................................. 20

List of Figures

Figure 1. Northern Lake Okeechobee Watershed.......................................................................... 1
Task 2 – Legacy P iii

List of Tables

Table 1. Surface water inflows, TP concentrations, loading rates, and TMDL targets for Lake 

Okeechobee Tributary Basins (1991-2005).................................................................. 5

Table 2. Assumed P mobility factors for legacy, native, and anthrogenic P sources.................... 6

Table 3. P loads from Soil Based Legacy P for Various Land Uses ............................................. 7

Table 4. P loads from Native and Non-Soil Based Legacy P Anthropogenic Sources for Various 

Land Uses...................................................................................................................... 8

Table 5. Predicted P Source Loads to Stream, In-stream Assimilation, and Net Basin Export 

(1991-2005)................................................................................................................... 9

Table 6. Measured and Estimated P Source Loads to Stream and Net Basin Exports with TMDL

Targets........................................................................................................................... 9

Table 7. Phosphorus Control Practices - Assumed Effectiveness and Costs............................... 11

Table 8. Northern Lake Okeechobee Basin P Control Practices Implementation Plan for Meeting 

the Tributary TMDL ................................................................................................... 15

Table 9. Upper Kissimmee Basin P Control Practices Implementation Plan for Meeting the 

Tributary TMDL......................................................................................................... 16

Table 10. Lake Istokpoga Basin P Control Practices Implementation Plan for Meeting the 

Tributary TMDL......................................................................................................... 17

Table 11. Estimated Additional Regional Treatment Required to Meet Lake Okeechobee TMDL 

with and without Meeting Tributary TMDLs............................................................. 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
Task 3 – Legacy P 1

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. 

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. 

Figure 1. Northern Lake Okeechobee Watershed
Task 3 – Legacy P 2

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.
Task 3 – Legacy P 3

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 
Task 3 – Legacy P 4

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 instream 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:

1. In-Field – Field practices that address the legacy P and its mobility within the 

soil/plant environment.

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

field or farm.

3. Residential – Practices applied within residential areas.

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

5. Facilities – Practices used in non soil-based areas that potentially discharge P into 

runoff, such as industrial sites, packing houses, old land fills, etc. 

6. Regional – Practices that treat and/or retain stream flows within the tributary system 

where multiple upstream landowners drain to the system.
Task 3 – Legacy P 5

Table 1. Surface water inflows, TP concentrations, loading rates, and TMDL targets for 

Lake Okeechobee Tributary Basins (1991-2005)
Task 3 – Legacy P 6

Table 2. Assumed P mobility factors for legacy, native, and anthrogenic P sources
Task 3 – Legacy P 7

Table 3. P loads from Soil Based Legacy P for Various Land Uses
Task 3 – Legacy P 8

Table 4. P loads from Native and Non-Soil Based Legacy P Anthropogenic Sources for Various Land Uses
Task 3 – Legacy P 9

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

Table 6. Measured and Estimated P Source Loads to Stream and Net Basin Exports with TMDL Targets
Task 3 – Legacy P 10

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 sitespecific 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 
Task 3 – Legacy P 11

Table 7. Phosphorus Control Practices - Assumed Effectiveness and Costs
Task 3 – Legacy P 12

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. 
Task 3 – Legacy P 13

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 
Task 3 – Legacy P 14

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.
Task 3 – Legacy P 15

Table 8. Northern Lake Okeechobee Basin P Control Practices Implementation Plan for Meeting the Tributary TMDL
Task 3 – Legacy P 16

Table 9. Upper Kissimmee Basin P Control Practices Implementation Plan for Meeting the Tributary TMDL
Task 3 – Legacy P 17

Table 10. Lake Istokpoga Basin P Control Practices Implementation Plan for Meeting the Tributary TMDL
Task 3 – Legacy P 18

Table 11. Estimated Additional Regional Treatment Required to Meet Lake Okeechobee TMDL with and without Meeting 

Tributary TMDLs
Task 3 – Legacy P 19

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 
Task 3 – Legacy P 20

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

Bottcher, A. B. 2006. Phosphorus Reduction Performance and Implementation Costs under 

BMPs and Technologies in the Lake Okeechobee Protection Plan Area. Letter report provided to 

the South Florida Water Management District.