PROPOSED
TOTAL MAXIMUM DAILY LOAD (TMDL)
For
Biochemical Oxygen Demand, Dissolved Oxygen, Nutrients
and Unionized Ammonia
In the
Lake Okeechobee Tributaries
Osceola, Polk, Okeechobee, Highlands, Glade, Hendry, Palm
Beach, Martin, and St. Lucie Counties, Florida
Prepared by:
US EPA Region 4
61 Forsyth Street SW
Atlanta, Georgia 30303
September 2006
TABLE OF CONTENTS

1
INTRODUCTION.............................................................................................................. 1
1.1
Purpose of Report ............................................................................................................. 6
1.2
Previous Studies in the Lake Okeechobee Watershed ..................................................... 6
1.3
Identification of Impaired Waterbodies............................................................................ 9
1.3.1
Lake Okeechobee Basin ................................................................................................ 9
1.3.2
Kissimmee River Basin ............................................................................................... 15
1.3.3
Fisheating Creek Basin .............................................................................................. 17
1.3.4
Caloosahatchee River Basin ....................................................................................... 21
1.3.5
L-8 Basin..................................................................................................................... 21
1.3.6
Everglades Agricultural Area ..................................................................................... 22
2
STATEMENT OF WATER QUALITY PROBLEM ................................................... 24
3
WATER QUALITY STANDARDS ............................................................................... 25
3.1
Nutrient Criterion ........................................................................................................... 25
3.2
Dissolved Oxygen Criterion ........................................................................................... 25
3.3
Biochemical Oxygen Demand Criterion ........................................................................ 26
3.4
Unionized Ammonia Criterion ....................................................................................... 26
4
TARGET IDENTIFICATION ....................................................................................... 26
4.1
Basis and Rationale For Nutrient Targets ...................................................................... 27
4.2
Nutrient Target Development ......................................................................................... 31
4.2.1
Approach #1: Reference condition value from reference streams dataset (FDEP) ... 31
4.2.2
Approach #2: Reference condition value from an all streams dataset (EPA Region 4)32
4.2.3
Approach #3: A modeling approach removing land disturbance (EPA Region 4) .... 33
4.3
Nutrient Target Application ........................................................................................... 34
4.4
DO and BOD Target....................................................................................................... 36
i
4.5
Unionized Ammonia Target ........................................................................................... 36
5
WATER QUALITY RESULTS ..................................................................................... 38
6
SOURCE ASSESSMENT ............................................................................................... 46
6.1
Background Loads .......................................................................................................... 46
6.2
Permitted Point Sources ................................................................................................. 46
6.2.1
Inventory of Point Sources ......................................................................................... 46
6.2.2
Estimating Point Source Loads .................................................................................. 47
6.2.3
Municipal Separate Storm Sewer System Permittees ................................................. 48
6.3
6.3.1
Agriculture .................................................................................................................. 50
6.3.2
Sediment...................................................................................................................... 51
6.3.3
Septic Systems ............................................................................................................. 52
6.3.4
Stormwater Runoff ...................................................................................................... 52
7
DEVELOPMENT OF THE TMDL ............................................................................... 53
7.1
Nutrient TMDL .............................................................................................................. 53
7.2
Unionized Ammonia TMDL .......................................................................................... 59
7.3
BOD TMDL ................................................................................................................... 59
8
9
Nonpoint Sources ........................................................................................................... 50
TMDL ALLOCATION ................................................................................................... 59
8.1
Allocation ....................................................................................................................... 60
8.2
Load Allocation .............................................................................................................. 67
8.3
Wasteload Allocations.................................................................................................... 67
8.4
Margin of Safety............................................................................................................. 67
8.5
Seasonal Variability ....................................................................................................... 68
TMDL IMPLEMENTATION ........................................................................................ 68
REFERENCES ............................................................................................................................ 69
APPENDIX A: Water Quality Plots......................................................................................... 72
ii
Appendix B: Flow Records from DBHYDRO for WBIDs 3238 and 3238E ........................ 76
Appendix C: Derivation of WLA for Clewiston STP (FL0040665) ..................................... 77
Appendix D: Calculation of Limiting Nutrient ...................................................................... 81
Appendix F: Modeling Results of Natural Landuse Conditions ........................................... 91
Appendix G. Rationale for Controlling Nitrogen in Impaired WBIDs ................................ 93
LIST OF TABLES

Table 1. Planning Unit and Basin Group of Impaired WBIDs ...................................................... 2
Table 2. Comparison of SWIM Basins and Impaired WBIDs ....................................................... 7
Table 3. Summary of Total Phosphorus Loads Discharging into Lake Okeechobee ................... 10
Table 4. Summary of Land Cover in Impaired WBIDs ............................................................... 18
Table 5. Existing Limiting Condition in Impaired WBIDs (based on TP and TN data) ............. 30
Table 6. Summary of Nutrient and Unionized Ammonia Data for Impaired WBIDs ................. 39
Table 7. Summary of DO and BOD Data in WBIDs Impaired For DO ...................................... 41
Table 8. Permitted Wastewater Facilities Discharging in Impaired WBIDs ................................ 47
Table 9. Proposed Permit Limits for Clewiston WWTP (FL0040665) ....................................... 48
Table 10. MS4 Permittees in the Drainage Basins of Impaired WBIDs ...................................... 50
Table 11. Area and Inflows for Impaired WBIDs and LOPP Basins (Baseline Conditions) ....... 54
Table 12. Summary of Existing Conditions for Total Nitrogen .................................................. 57
Table 13. TMDL Components for Total Phosphorus ................................................................... 60
Table 14. TMDL Components for Total Nitrogen ....................................................................... 63
Table 15. TMDL Components for Unionized Ammonia............................................................. 65
Table 16. TMDL Components for BOD ...................................................................................... 66
Table 17. TP Allocations for LOPP Basins Expressed as Daily Loads ....................................... 66
iii
LIST OF FIGURES

Figure 1. Location of Horseshoe Creek (WBID 1436) in the Upper Kissimmee River Basin ...... 4
Figure 2. Location of Impaired WBIDs Below Lake Kissimmee .................................................. 5
Figure 3. Control Structures and Sampling Stations in Lake Okeechobee .................................. 13
Figure 4. Taylor Creek and Nubbin Slough Basins ..................................................................... 15
Figure 5. Location of WBIDs and Monitoring Stations Used to Calculate a Nutrient Target per
Section 4.2.2.......................................................................................................................... 37
Figure 6. Distribution of Average TP Concentrations ................................................................. 43
Figure 7. Distribution of Average TN Concentrations................................................................. 44
Figure 8. DO Distribution in the Area Surrounding Lake Okeechobee ....................................... 45
LIST OF ABBREVIATIONS
BMP
BOD
CFS
Best Management Practices
Biochemical Oxygen Demand
Cubic Feet per Second
DMR
DO
F.A.C.
GIS
HUC
LA
LOPP
MGD
MOS
MS4
Discharge Monitoring Report
Dissolved Oxygen
Florida Administrative Code
Geographic Information System
Hydrologic Unit Code
Load Allocation
Lake Okeechobee Protection Plan
Million Gallons per Day
Margin of Safety
Municipal Separate Storm Sewer Systems
Mton
NLCD
NPDES
SOD
TN
TP
WBID
WLA
WWTP
Metric Ton
National Land Cover Data
National Pollutant Discharge Elimination System
Sediment Oxygen Demand
Total Nitrogen
Total Phosphorus
Water Body Identification
Waste Load Allocation
Wastewater Treatment Plant
iv
SUMMARY SHEET
1. Florida 1998 303(d) Listed Waterbody Information
WBID
Segment Name
Classification Constituent
County
HUC
3186B Kissimmee River
3F
DO, BOD
Osceola
03090101
3186C Blanket Bay Slough
3F
Nutrients, DO
Osceola
03090101
3186D Eight Mile Slough
3F
DO
Polk
03090101
3F
Nutrients, DO
Okeechobee
03090101
3188A Chandler Slough
3F
Nutrients, DO
Okeechobee
03090101
3192C Oak Creek
3F
Nutrients, DO
Okeechobee
03090101
Nutrients, DO
Okeechobee
3188
3199B
Farm Area
Chandler Hammock
Slough
3F
03090102
3203A Nubbin Slough
3F
Nutrients, DO
Okeechobee
03090102
3203B Mosquito Creek
3F
Nutrients, DO
Okeechobee
03090102
3204
Harney Pond Canal
3F
Nutrients, DO
Highlands/Glade
03090103
3205
Taylor Creek
3F
Nutrients, DO
Okeechobee
03090101
3F
Nutrients, DO
Okeechobee
03090101
3205D Otter Creek
3206
Indian Prairie Canal
3F
Nutrients, DO
Highlands/Glade
03090103
3209
Kissimmee River
3F
Nutrients, DO
Glades
03090101
3213A Lettuce Creek
3F
Nutrients, DO
3213B Henry Creek
3F
Nutrients, DO
Okeechobee
03090102
3213C S-135
3F
Nutrients, DO
Martin
03090102
3213D Myrtle Slough
3F
Nutrients, DO
Martin
03090102
Okeechobee/Martin 03090102
3233
L-8
3F
Nutrients, DO
Palm Beach
03090202
3238
W. Palm Beach Canal
3F
Nutrients, DO
Palm Beach
03090202
M Canal
3F
Nutrients, DO
Palm Beach
03090202
3238E
v
3F
Nutrients, DO,
Unionized Ammonia
Palm Beach
East Caloosahatchee
3F
Nutrients, DO
Hendry
3247
715 Farms
3F
Nutrients, DO,
Unionized Ammonia
Palm Beach
3248
N. New River Canal
3F
Nutrients, DO
Palm Beach
03090202
3F
Nutrients, DO
Palm Beach
03090202
Nutrients
Palm
Beach/Hendry
03090202
3244
East Beach
3246
3248A Hillsboro Canal
3F
03090202
03090202
03090202
3250
S-236
3251
S-3
3F
Nutrients, DO
Palm Beach
03090202
3253
South Bay
3F
Nutrients, DO
Palm Beach
03090202
1436
Horseshoe Creek
3F
Nutrients, DO
Polk
03090101
2. Water Quality Standards:
BOD (62-302.530(12)): Levels shall not be increased to exceed values which would
cause dissolved oxygen to be depressed below the limit established for each class and, in
no case shall it be great enough to produce nuisance conditions.
DO (62-302.530(31)): Dissolved oxygen shall not be less than 5.0 mg/l. Normal daily
and seasonal fluctuations above these levels shall be maintained. The water quality
standard for DO also considers the definition of natural background and the directive not
to abate natural conditions (62-302.200(15) FAC and 62-302.300(15) FAC).
Nutrients (62-302.530(48)(a)): The discharge of nutrients shall continue to be limited as
needed to prevent violations of other standards contained in this chapter. Man induced
nutrient enrichment (total nitrogen and total phosphorus) shall be considered degradation
in relation to the provisions of Section 62-302.300, 62-302.700, and 62-4.242, FAC.
62-302.530(48)(b) In no case shall nutrient concentrations of a body of water be altered
so as to cause an imbalance in natural populations of aquatic flora or fauna.
Unionized Ammonia (62-302.530(3)): Ammonia (unionized) levels shall be less than or
equal to 0.02mg/l.
3. TMDL Approach
Nutrients: The TMDLs target both Total Phosphorus (TP) and Total Nitrogen (TN)
based on three approaches as described in Section 4 of this report. Results of the three
approaches indicate an appropriate TP target range between 70 and 90 ppb and a TN
target between 1.04 and 1.3 mg/l. The averages of these values were selected as the
vi
target TP and TN concentrations and are equal to 77 ppb and 1.2 mg/l, respectively. The
TMDL targets were developed to support the State of Florida’s narrative water quality
standard for nutrients by not causing an imbalance in natural populations of aquatic flora
and fauna and also to not produce or contribute to conditions that violate the State’s
standard for dissolved oxygen. Control of both nutrients, N and P, in upstream waters
provides additional assurance that excess productivity will remain in control, and avoids
pollutant caused depressions of dissolved oxygen. The TMDL will ensure protection for
aquatic life both in the tributary WBIDs, as well as not contribute to water quality
impairments in the downstream waters of Lake Okeechobee and its subsequent drainage
to the coastal estuaries of the St. Lucie and the Caloosahatchee.
Dissolved Oxygen: TMDLs for dissolved oxygen are addressed through controlling
nutrients. When BOD data are available and a correlation can be determined between
DO and BOD, the TMDL targets BOD. Many of the impaired waterbodies have been
channelized or are canals and it may be difficult to consistently meet the statewide DO
standards even after controlling pollutant concentrations. In such circumstances
calculating allocations would be targeted to achieve the natural background loading and
natural instream pollutant concentrations in the waterbody. Any allowance of increased
loadings beyond natural background would likely cause other than natural dissolved
oxygen levels, which would not be a proper application of the Florida definition.
Because the standard prevents abatement of natural conditions, the TMDL can provide an
allocation, where necessary, that results in natural conditions. A site specific criterion
needs to be established to target a condition other than natural concentrations of
pollutants.
BOD: A regression analysis correlating BOD to DO was developed to determine the
BOD concentration necessary to maintain DO levels above the water quality standard
(see the DO discussion above).
Unionized Ammonia: The TMDL for unionized ammonia is based on the numerical
criteria (0.02 mg/l) and an estimate of flow. Existing conditions are based on the 95th
percentile concentration measured in the WBID.
4. TMDL Allocation for Total Phosphorus in WBIDs:
Lake Basin/WBIDs
WLA
LA
(ppb)
MOS
TMDL
Lake
Load
(Mton/yr)
S-65A ,B, C, D, E
% Reduction
WBID
Conc. (ppb)
19.25
Lake
WBID
76%
3188
0
77
Implicit
77
84%
3188A
0
77
Implicit
77
58%
3186B
0
77
Implicit
77
4%
3186C
0
77
Implicit
77
80%
vii
Lake Basin/WBIDs
WLA
LA
(ppb)
MOS
TMDL
Lake
Load
(Mton/yr)
% Reduction
WBID
Conc. (ppb)
Lake
WBID
3186D
0
77
Implicit
77
6%
3192C
0
77
Implicit
77
72%
Taylor Creek / Nubbin Slough (S-191)
19.01
76%
3205
0
77
Implicit
77
84%
3205D
0
77
Implicit
77
88%
3203A
0
77
Implicit
77
84%
3203B
0
77
Implicit
77
92%
3213A
0
77
Implicit
77
82%
3213B
0
77
Implicit
77
83%
3213D
0
77
Implicit
77
93%
0.41
715 Farms
3247
0
77
Implicit
C-40 Basin (S-72)
77
2.32
3206
0
77
Implicit
C-41 Basin (S-71)
0
77
77
Implicit
East Beach DD (Culv 10)
77
77
Implicit
L59-E
0
77
77
Implicit
S-135 Basin
3213C
77
77
Implicit
S-154 Basin
28%
76%
77
5.72
viii
72%
76%
0.82
0
49%
76%
0.36
3209
58%
76%
2.12
72%
Reduction
24%
76%
6.17
3204
3244
75%
29%
76%
Lake Basin/WBIDs
WLA
LA
(ppb)
MOS
TMDL
Lake
Load
(Mton/yr)
3199B
0
77
Implicit
S-2 Basin
% Reduction
WBID
Conc. (ppb)
Lake
77
1.98
WBID
95%
76%
3248
43%
Reduction
77
Implicit
77
43%
3248A
31%
Reduction
77
Implicit
77
31%
S-3 Basin
3251
0.56
0
77
Implicit
S-4 Basin
3246
0.15
(Mton/yr)
77
Implicit
0
77
10%
Reduction
1.07
76%
77
77
21%
76%
10%
1.89
0
33%
Implicit
L-8 (Culv 10A)
3233
76%
0.26
77
8%
77
Implicit
South Shore / South Bay DD (Culv 4A)
3253
77
1.67
South FL Conservancy DD (S-236) & Industrial Canal
3250
76%
Implicit
S-5A Basin
76%
77
0
43%
N/A
3238
59%
Reduction
77
Implicit
77
59%
3238E
0
77
Implicit
77
25%
S-65 (Lake Kissimmee)
1436
16.96
0%
Reduction
77
Implicit
76%
77
0%
Note: A daily TP concentration of 77 ppb should be achieved based on an annual average of the
measured days recognizing natural variability; the WLA for WBID 3246 is equivalent to 0.96
lb/day.
ix
5. TP Allocations for Lake Okeechobee Basins Expressed as Daily Loads:
Basin
WLA
(lb/day)
LA
(lb/day)
TMDL
(lb/day)
S-65A, B, C, D, E
0
116.19
116.19
Taylor Creek / Nubbin Slough (S-191)
0
114.74
114.74
715 Farms
0
2.47
2.47
C-40 Basin (S-72)
0
14
14
C-41 Basin (S-71)
0
37.24
37.24
77% Reduction
12.8
12.8
L59-E
0
2.17
2.17
S-135 Basin
0
4.95
4.95
S-154 Basin
0
34.50
34.50
S-2 Basin
76% Reduction
11.95
11.95
S-3 Basin
0
3.38
3.38
S-4 Basin
0.96
9.11
10.07
South FL Conservancy DD (S-236) &
Industrial Canal
0
2.05
2359
South Shore/ South Bay DD (Culv 4A)
76% Reduction
1.57
1.57
L-8 (Culv 10A)
0
11.41
11.41
S-5A Basin
0
0
0
S-65
0
102.37
102.37
East Beach DD (Culv 10)
lb/day = Mton/yr * yr/365.25 day * 2204.623 lb/Mton.
Note: Achievement of the annual load would imply achievement of the daily load averaged through
the year; therefore, implementation should target the annual load.
6. TMDL Allocation for Total Nitrogen:
x
WBID
WLA
(lb/day)
LA
(lb/day)
MOS
TMDL
(lb/day)
%
Reduction
3188
0
600.09
Implicit
600.09
32%
3188A
0
65.08
Implicit
65.08
15%
3186B
0
412.44
Implicit
412.44
8%
3186C
0
98.73
Implicit
98.73
35%
3186D
0
149.39
Implicit
149.39
0%
3192C
0
62.98
Implicit
62.98
39%
3205
0
400.12
Implicit
400.12
34%
3205D
0
74.48
Implicit
74.48
43%
3203A
0
115.64
Implicit
115.64
25%
3203B
0
50.72
Implicit
50.72
54%
3213A
0
23.65
Implicit
23.65
35%
3213B
0
120.90
Implicit
120.90
42%
3213D
0
123.41
Implicit
123.41
54%
3247
0
107.61
Implicit
107.61
66%
3206
0
145.32
Implicit
145.32
31%
3204
0
444.90
Implicit
444.90
39%
3244
70%
Reduction
105.56
Implicit
105.56
70%
3209
0
57.13
Implicit
57.13
27%
3213C
0
170.44
Implicit
170.44
29%
3199B
0
115.19
Implicit
115.19
60%
3248
69%
Reduction
172.84
Implicit
172.84
69%
3248A
44%
Reduction
106.52
Implicit
106.52
44%
3251
0
87.50
Implicit
87.50
43%
xi
WBID
WLA
(lb/day)
LA
(lb/day)
MOS
TMDL
(lb/day)
%
Reduction
3246
15.02
lb/day
251.89
Implicit
266.91
48%
3250
0
92.42
Implicit
92.42
67%
3253
62%
Reduction
72.82
Implicit
72.82
62%
3233
0
467.39
Implicit
467.39
44%
3238
53%
Reduction
1397.25
Implicit
1397.25
49%
3238E
0
3074.29
Implicit
3074.29
60%
1436
30%
Reduction
240.37
Implicit
240.37
30%
Note: The expressed daily TN load should be achieved based on an annual average of the
measured days recognizing natural variability.
6. TMDL Allocation for Unionized Ammonia:
WBID
TMDL
(lb/day)
WLA
(lb/day)
LA
(lb/day)
Percent
Reduction
3244
1.76
0
1.76
60%
3247
1.79
0
1.79
29%
7. TMDL Allocation for BOD:
WBID
TMDL
(lb/day)
WLA
(lb/day)
LA
(lb/day)
Percent
Reduction
3186B
811.13
0
811.13
38%
3246
433.90
25.03
408.87
48%
8. Endangered Species (yes or blank): Yes
9. EPA Lead on TMDL (EPA or blank): EPA
10. TMDL Considers Point Source, Nonpoint Source, or both: Both
11. Major NPDES Discharges to surface waters:
xii
Annual Average Permit Limits based on WLA
Name of Facility
Impacted WBID
City of Clewiston WWTP
3246
(FL0040665)
Permitted Flow
(MGD)
BOD (mg/l)
TN (mg/l)
TP (mg/l)
1.5
2
1.2
0.077
Note: A Site Specific Alternative Criterion for DO may be necessary to adjust the permit limits.
WLA is designed to meet the natural background concentrations. Annual Average Loads
corresponding to permit limits shown above are: BOD: 25.05 lb/day; TN: 15.03 lb/day; and TP:
0.964 lb/day.
MS4 Allocations:
MS4
City of Pahokee/ Palm Beach
County
City of Belle Glades/Palm
Beach County
City of South Beach/ Palm
Beach County
City of Davenport/Polk County
Impacted WBID
NPDES ID
3244, 3238
FLS000018
3248A
FLS000018
3248, 3253
FLS000018
1436
FLS000015
% Reduction in
Nutrient Load
TP: 74%
TN: 72%
TP: 30%
TN: 44%
TP: 41%
TN: 69%
TP: 0%
TN: 29%
Note: When an MS4 covers more than one WBID, the largest percent reduction calculated for an
impaired WBID is assigned to the MS4. The MS4 is responsible for controlling pollutant loads
from the urban areas within its jurisdiction.
xiii
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
1
US EPA Region 4
INTRODUCTION
Section 303(d) of the Clean Water Act requires each state to list those waters within its boundaries
for which technology based effluent limitations are not stringent enough to protect any water quality
standard applicable to such waters. Listed waters are prioritized with respect to designated use
classifications and the severity of pollution. In accordance with this prioritization, states are required
to develop Total Maximum Daily Loads (TMDLs) for those water bodies that are not meeting water
quality standards. The TMDL process establishes the allowable loadings of pollutants or other
quantifiable parameters for a waterbody based on the relationship between pollution sources and instream water quality conditions, so that states can establish water quality based controls to reduce
pollution from both point and non-point sources and restore and maintain the quality of their water
resources (USEPA, 1991). The TMDLs described in this report are being proposed pursuant to EPA
commitments in the 1998 Consent Decree in the Florida TMDL lawsuit (Florida Wildlife Federation,
et al. v. Carol Browner, et al., Civil Action No. 4: 98CV356-WS, 1998).
Florida Department of Environmental Protection (FDEP) developed a statewide, watershed-based
approach to water resource management. Under the watershed management approach, water
resources are managed on the basis of natural boundaries, such as river basins, rather than political
boundaries. The state’s 52 basins are divided into 5 groups. Water quality is assessed in each group
on a rotating five-year cycle. The Lake Okeechobee Watershed includes the Lake Okeechobee Basin
located in group 1, the Caloosahatchee and Lake Worth Lagoon-West Palm Beach Coast Basins
located in group 3, the Fisheating Creek Basin and the Kissimmee Basin located in group 4 and the
Everglades Basin located in group 5. FDEP established five water management districts (WMD)
responsible for managing ground and surface water supplies in the counties encompassing the
districts. The Lake Okeechobee Watershed Tributaries addressed in this TMDL report are managed
through the South Florida Water Management District (SFWMD).
For the purpose of planning and management, the WMDs divided the district into planning units
defined as either an individual primary tributary basin or a group of adjacent primary tributary basins
with similar characteristics. These planning units contain smaller, hydrological based units called
drainage basins, which are further divided into “water segments”; each assigned a unique Waterbody
IDentification (WBID) number. A water segment usually contains only one unique waterbody type
(stream, lake, cannel, etc.).
EPA is proposing TMDLs for many of the impaired WBIDs in the Lake Okeechobee watershed in
advance of the Consent Decree schedule. The purpose for deviating from the Consent Decree
schedule is to encourage implementation of the TMDLs through a watershed approach. The
planning unit and Basin group of the impaired WBIDs discussed in this report are identified in Table
1. All segments are classified as freshwater streams. The locations of impaired WBIDs in the Upper
Kissimmee River basin are shown in Figure 1. Impaired WBIDs located below Lake Kissimmee are
shown in Figure 2.
1
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Table 1. Planning Unit and Basin Group of Impaired WBIDs
WBID
Segment Name
Planning Unit
Basin Group
3186B Kissimmee River
Lower Kissimmee
4
3186C Blanket Bay Slough
Lower Kissimmee
4
3186D Eight Mile Slough
Lower Kissimmee
4
Lower Kissimmee
4
3188A Chandler Slough
Lower Kissimmee
4
3192C Oak Creek
Lower Kissimmee
4
CTP Complex
1
3203A Nubbin Slough
NHLMS Complex
1
3203B Mosquito Creek
NHLMS Complex
1
3188
3199B
Farm Area
Chandler Hammock
Slough
3204
Harney Pond Canal
Northwest Lake Okeechobee
4
3205
Taylor Creek
TOL63 Complex
1
TOL63 Complex
1
3205D Otter Creek
3206
Indian Prairie Canal
Northwest Lake Okeechobee
4
3209
Kissimmee River
Lower Kissimmee
4
3213A Lettuce Creek
NHLMS Complex
1
3213B Henry Creek
NHLMS Complex
1
3213C S-135
NHLMS Complex
1
3213D Myrtle Slough
NHLMS Complex
1
L-8
3
3233
L-8
2
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
3238
US EPA Region 4
W. Palm Beach Canal
Everglades Agricultural Area
5
M Canal
Everglades Agricultural Area
5
3244
East Beach
Everglades Agricultural Area
5
3246
East Caloosahatchee
East Caloosahatchee
3
3247
715 Farms
Everglades Agricultural Area
5
3248
N. New River Canal
Everglades Agricultural Area
5
Everglades Agricultural Area
5
3238E
3248A Hillsboro Canal
3250
S-236
Everglades Agricultural Area
5
3251
S-3
Everglades Agricultural Area
5
Everglades Agricultural Area
5
3252A Knights Farm Field 1
3253
South Bay
Everglades Agricultural Area
5
1436
Horseshoe Creek
Upper Kissimmee
4
3
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
N
W
E
S
Citrus Ridge
W BID 1436
Re
ed
yC
re e
k
Lake Rus sell
#
#
#
#
##
##
#
Osceola County
#
#
###
Lake Cypress
Davenport
Polk County
Lake Hatc hineha
Lake K issimmee
Ho rsesho e Creek
Mon itoring Station s
WBID 1436
Rivers and Lakes
LAK E/P OND
RES ERVOIR
SEA/O CEAN
STR EAM/RIVER
CANAL/D ITC H
SWA MP/MAR SH
Co un ty Bo un dary
Cities and To wn s (near WB ID 1436)
Up per K issim m ee Basin
#
5
0
5
10
15
Figure 1. Location of Horseshoe Creek (WBID 1436) in the Upper Kissimmee River Basin
4
20 Miles
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
N
W
E
S
S-65 A
318 6C
S-65 BC
318 6B
318 6D
S-65 D
S-19 1
05
D
318 8
B
99
31
320 3B
350 5
03
A
8A
318
35
319 2C
32
S-15 4
C-41
13B
32 321 3D
S-13 3
C-40
320 9
320 4
C
13
32
320 6
321 3A
S-13 5
L-59 E
323 3
324 4
L-8
323 8
323
8
324 7
E
S-5A
325 3
324 6
LOWP Basin
TMDL WBIDs
WBIDs (IWR Run 22)
Waterbody
LAKE/POND
RESERVOIR
SEA/OCEAN
STREAM/RIVER
CANAL/DITCH
SWAMP/MARSH
0
10
324 8
va
tio
325 1
nA
re
a
S-3
325 2A
S-2
W
10
324 8A
325 0
s
S-4
at
er
20
30
40
Co
ns e
rv
a ti on Areas
50
Figure 2. Location of Impaired WBIDs Below Lake Kissimmee
5
n
W a te r Co
60
70
r
se
80 Miles
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
1.1
US EPA Region 4
Purpose of Report
This document presents Total Maximum Daily Loads (TMDLs) for pollutants contributing to the
1998 listed impairments (i.e., nutrients, DO, BOD and unionized ammonia) in the Lake Okeechobee
Tributaries. The tributaries were identified as impaired by nutrients, BOD, DO, unionized ammonia
or a combination of the above. Pollutant load reductions to Total Phosphorus (TP) and Total
Nitrogen (TN) should result in reduced nutrient loadings to the tributaries and ultimately achieve the
designated use of the streams and not contribute to impairments in downstream waters (i.e., Lake
Okeechobee).. TMDLs are also established for unionized ammonia and BOD that would restore the
tributaries to meet applicable water quality criteria
1.2
Previous Studies in the Lake Okeechobee Watershed
Lake Okeechobee TMDL
The total phosphorus TMDL for Lake Okeechobee was adopted by FDEP in May 2001 and was
approved by EPA in October 2001. The TMDL establishes an annual load of 140 metric tons of
phosphorus to Lake Okeechobee to achieve an in-lake target phosphorus concentration of 40 ppb in
the pelagic zone of the Lake. The target was developed using chlorophyll a as an indicator of algal
biomass, which in turn acts as a surrogate for indicating excessive nutrient concentrations. The
TMDL is allocated to atmospheric deposition (35 Mtons) and to the sum of all nonpoint surface
water inputs to the Lake (105 Mtons). No portion of the TMDL was allocated to point sources.
Several point sources exist in the Lake Okeechobee watershed; however, none of these sources
discharge directly to Lake Okeechobee. The TMDL report states that attainment of the TMDL will
be calculated using a 5-year rolling average of monthly loads calculated from measured flow and
concentration values. Water entering Lake Okeechobee from the watershed should be established at
a level to ensure that the applicable water quality standards are met. The 40 ppb goal for the entire
pelagic zone is considered a conservative goal that introduces an implicit margin of safety into the
TMDL. This reflects the fact that under high lake conditions, total phosphorus concentrations are
relatively homogeneous across the open water region, but when lake stages are low, the near shore
area displays considerably lower total phosphorus than the open water zone. Hence if 40 ppb is met
at the pelagic stations (which represent mid-lake) total phosphorus concentrations below 40 ppb
should occur in the near shore area during certain years.
Lake Okeechobee Protection Program: Lake Okeechobee Protection Plan
The Lake Okeechobee Protection Act (LOPA, Chapter 00-103, Laws of Florida) was passed by the
2000 Legislature, to establish a restoration and protection program of Lake Okeechobee. This is to
be accomplished by achieving and maintaining compliance with State water quality standards in
Lake Okeechobee and its tributary waters, through a watershed-based, phased, comprehensive and
innovative protection program designed to reduce phosphorus loads and implement long-term
solutions, based upon the Lake’s phosphorus TMDL and considering the establishment of TMDLs
for the tributaries of Lake Okeechobee. This program set forth a series of activities and deliverables
for the coordinating agencies- the South Florida Water Management District, the Florida Department
6
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
of Environmental Protection, and the Florida Department of Agriculture and Consumer Services.
Elements specifically required by the legislation include a formal Lake Okeechobee Protection Plan
(LOPP). The LOPP identifies alternative plans, schedules and costs to meet the established TP
TMDL for Lake Okeechobee (LOPP, 2004). The TMDLs contained in this report are considered to
be consistent with the LOPP and, therefore, the established Lake Okeechobee TP TMDL.
The original LOPP Project Area was composed of thirty-four basins that define the Lake Okeechobee
watershed. The basins are essentially the same as the basins used in the Surface Water Improvement
and Management Plan (SWIM). In 2005, the project boundaries were extended to the north to
include the Upper Kissimmee River basin. The approximate project boundaries are shown in Figure
1. EPA hopes to obtain GIS coverages of the new project boundaries during the public comment
period. Often more than one WBID will be contained within an LOPP basin. The location of the
original basins relative to the impaired WBIDs is shown in Figure 2. A listing of impaired WBIDs
within each SWIM basin and the percent of area these WBIDs encompass is provided in Table 2. TP
loads allocated in the LOPP to the basins are summarized in Table 3. The column “Target Based on
Load” depicts the loading necessary to achieve the Lake Okeechobee TMDL.
Table 2. Comparison of SWIM Basins and Impaired WBIDs
Lake Okeechobee SWIM Basin SWIM Basin Impaired WBIDs
Area (acres)
Impaired WBID
Area
(percentage)
715 Farms
3295
3247
100%
C-40 Basin
43,964
3206
100%
C-41 Basin
94,928
3204
100%
East Beach Drainage Ditch
5275
3244
100%
L-59E
14,409
3209
100%
Taylor Creek/Nubbin Slough
120,754
3205, 3205D, 3203A, 99%
3203B, 3213A,
3213B, 3213D
S-135 Basin
25,408
3213C
75%
S-154 Basin
24,630
3199B
38%
S-2 Basin
31,399
3248, 3248A
100%
S-3 Basin
9794
3251
100%
7
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Lake Okeechobee SWIM Basin SWIM Basin Impaired WBIDs
Area (acres)
Impaired WBID
Area
(percentage)
S-4 Basin
29,164
3246
100%
S-65 A, B, C, D, E
427,913
3188, 3188A, 3186B, 53%
3186C, 3186D, 3192C
South Shore/South Bay Drainage 2364
Ditch
3253
100%
S-5A Basin
120,798
3238, 3238E
80%
L-8 Basin
108,402
3233
82%
S-65
1,021,674
1436
0.3%
Note: Impaired WBIDs listed for S-65 basin are Group 4 WBIDs in the Consent Decree schedule.
Comprehensive Everglades Restoration Plan (CERP)
The Comprehensive Everglades Restoration Plan (CERP) provides a framework and guide to restore
the south Florida ecosystem including the Everglades. The conceptual plan for the Lake Okeechobee
watershed consists of construction of stormwater treatment areas (STAs) and reservoirs; restoration
of wetlands; and removal of phosphorus-laden sediment from tributaries. The Taylor Creek/Nubbin
Slough (WBIDs 3505 and 3203A) Reservoir-assisted Stormwater Treatment Area (RaSTA) is one of
ten initially authorized projects. The SFWMD purchased pastureland located adjacent to Taylor
Creek and converted the land to a reservoir suitable for storage and water quality treatment. The
Taylor Creek RaSTA is estimated to remove about 3 to 5 metric tons of phosphorus each year. The
Nubbin Slough STA is constructed wetlands for treating stormwater runoff before it enters Lake
Okeechobee. The STA is estimated to remove about 22 to 24 metric tons of phosphorus per year.
Other phosphorus reduction projects are planned for the watershed and should result in improved
water quality in both the impaired waterbodies and Lake Okeechobee. Details on CERP projects can
be found on the CERP webpage (www.evergladesplan.org).
Florida Geological Study
Howard T. Odum investigated phosphorus levels in Florida streams in the 1950’s as part of a Florida
Geological Survey study (Odum, 1953). This was one of the first studies in Florida on the behavior
of phosphorus in water and the impact it has on aquatic growth. Water samples were collected
throughout the state from streams, lakes and springs for the purpose of correlating TP levels in water
to geological conditions and levels of pollution. A limited number of samples were collected in Lake
Okeechobee and Kissimmee River watershed as part of the canals and rivers of south Florida region.
8
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
In June 1952, TP concentrations based on a limited number of samples in the tributaries ranged from
0.031 ppm in Fisheating Creek; 0.057 ppm in Taylor Creek; 0.060 ppm in the Kissimmee River
below Lake Kissimmee; and 0.097 in St. Lucie Canal. While these values are informative, they are
too limited (spatially and temporally) to represent the water quality condition of the waterbodies.
1.3
Identification of Impaired Waterbodies
The Lake Okeechobee watershed consists of the entire area that contributes surface water flow and
total phosphorus (TP) and total nitrogen (TN) loads to Lake Okeechobee. This includes lands that
drain by gravity to the lake, as well as areas that are drained by pumping into the lake. The entire
watershed is being considered in the development of the Lake Okeechobee Watershed Tributary
TMDLs. The following watershed descriptions are taken from the Basin Status Reports developed
by FDEP.
Land cover distribution cited in the planning unit descriptions is from 1999 color infrared imagery
downloaded from the SFWMD web page. The LOPA requires that “Prior to authorizing a discharge
into works of the District, the District shall require responsible parties to demonstrate that proposed
changes in land use will not result in increased phosphorus loading over that of existing land uses.”
Table 4 is a summary of land cover in the impaired WBIDs.
1.3.1 Lake Okeechobee Basin
Lake Okeechobee is a large, shallow eutrophic lake located in south central Florida that is designated
a Class I water (potable water supply). The lake is the largest body of freshwater in the southeastern
United States and covers a surface area of 730 mi2 (1730 km2) with an average depth of 8.6 ft (2.7m).
The Lake is a major feature of the Kissimmee-Okeechobee-Everglades system, which is a continuous
hydrologic system extending from Central Florida south to Florida bay. The watershed of the Lake
stretches from just south of Orlando to areas that border the Lake on the south, east and west and
covers 3.5 million acres. The Lake provides a number of values to society and nature including
water supply for agriculture, urban areas, and the environment; flood protection; a multi-million
dollar sport fishery; and habitat for wading birds, migratory waterfowl, and the federally endangered
Everglades Snail Kite. These values of the lake have been threatened in recent decades by excessive
phosphorus (P) loading, harmful high water levels, and rapid expansion of exotic plants.
(SFWMD,2007) Two hundred years ago, a large percentage of the lake bottom may have been
covered with sand. Today organic mud overlies much of the bottom. The upper 10 centimeters of
that mud are estimated to contain more than 30,000 metric tons of phosphorus. The rate of mud
sediment accumulation and phosphorus deposition has increased significantly over the past 50 years.
9
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Table 3. Summary of Total Phosphorus Loads Discharging into Lake Okeechobee
Basin
715 Farms (Culv 12A)
C-40 Basin (S-72)
C-41 Basin (S-71)
S-84 Basin (C41A)
S-308C (St. Lucie-C-44)
East Beach DD (Culv 10)
East Shore DD (Culv 12)
Fisheating Creek
Industrial Canal
L-48 Basin (S-127)
L-49 Basin (S-129)
L-59E
L-59W
L-60E
L-60W
L-61E
L-61W
Taylor Creek/Nubbin
Slough (S-191)
S-131 Basin
S-133 Basin
S-135 Basin
S-154 Basin
S-2
LOWP Design Loads
(Mtons/yr)
Alt 1 through Alt 1 through 7
6 (Higher of
(Higher of
Remain.
Remain. Load,
Load,
Adjusted
Adjusted
Remain. Load,
Remain.
and targets)
Load, and
targets)
LOPP
Implementation
AREA (acres)
Average
Annual
Discharge
(1991-2000)
(Acre-ft)
Average Annual
P Load (19912000) (Mtons)
Target
Based
on Flow
Target
Based
on Load
Target
conc.
based
on flow
Target
conc.
based
on load
3,295
43,964
94,928
58,488
129,428
5,275
8,416
289,366
8,232
20,774
12,093
14,409
6,440
5,038
3,271
14,286
13,567
120,754
12,045
16,266
49,799
51,791
55,880
11,815
14,432
200,766
23,337
23,040
13,189
6,395
8,319
1,236
419
6,997
10,646
101,946
1.67
9.58
25.45
9.06
11.23
8.73
3.10
40.97
2.99
6.58
1.69
1.48
1.93
0.25
0.07
1.13
1.27
78.40
0.56
0.76
2.33
2.42
2.61
0.55
0.67
9.38
1.09
1.08
0.62
0.30
0.39
0.06
0.02
0.33
0.50
4.77
0.41
2.32
6.17
2.20
2.72
2.12
0.75
9.93
0.73
1.59
0.41
0.36
0.47
0.06
0.02
0.27
0.31
19.01
37.91
37.91
37.91
37.91
37.91
37.91
37.91
37.91
37.91
37.91
37.91
37.91
37.91
37.91
37.91
37.91
37.91
37.91
27.32
115.81
100.49
34.40
39.53
145.35
42.24
40.13
25.23
56.14
25.18
45.55
45.74
39.20
31.67
31.80
23.39
151.22
0.59
6.98
17.14
6.47
9.86
2.12
0.89
32.99
2.24
5.03
1.31
1.20
1.55
0.21
0.05
0.93
1.08
24.03
0.59
6.02
13.82
5.31
8.09
2.12
0.89
31.81
2.24
4.97
1.29
1.20
1.55
0.21
0.05
0.93
0.90
19.01
7,164
25,660
18,089
33,798
106,044
9,490
26,478
25,408
24,630
31,399
1.28
6.99
3.39
23.59
8.16
0.44
FALSE
1.19
1.15
1.47
0.31
1.69
0.82
5.72
1.98
37.91
0.00
37.91
37.91
37.91
26.58
51.92
26.25
188.33
51.12
0.89
5.13
2.62
8.36
1.98
0.83
4.62
2.29
5.72
1.98
10
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
Basin
S-3
S-4
S-65A,B,C,D,E
South FL Conservancy
DD (S-236)
South Shore/So. Bay DD
(Culv 4A)
Nicodemus Slough (Culv
5)
S65 (Lake Kissimmee) **
Lake Istokpoga (S-68)**
S5A Basin (S-352-WPB
Canal)
East Caloosahatchee (S77) ***
L-8 Basin (Culv 10A)
Total
US EPA Region 4
LOWP Design Loads
(Mtons/yr)
Alt 1 through Alt 1 through 7
6 (Higher of
(Higher of
Remain.
Remain. Load,
Load,
Adjusted
Adjusted
Remain. Load,
Remain.
and targets)
Load, and
targets)
LOPP
Implementation
AREA (acres)
Average
Annual
Discharge
(1991-2000)
(Acre-ft)
Average Annual
P Load (19912000) (Mtons)
Target
Based
on Flow
Target
Based
on Load
Target
conc.
based
on flow
Target
conc.
based
on load
64,630
39,673
427,913
2,364
9,794
29,164
291,845
10,345
2.33
6.87
79.41
1.42
0.46
1.36
13.64
0.48
0.56
1.67
19.25
0.34
37.91
37.91
37.91
37.91
46.73
46.35
53.50
26.92
0.56
1.67
25.02
0.57
0.56
1.67
19.25
0.57
2,947
8,151
1.07
0.38
0.26
37.91
25.87
0.40
0.40
25,641
3,371
0.25
0.16
0.06
37.91
14.54
0.20
0.20
1,021,674
393,276
120,798
856,146
247,718
11
69.95
14.95
0.00
40.02
11.58
0.00
16.96
3.62
0.00
37.91
37.91
37.91
16.07
11.87
59.91
52.46
14.95
0.00
52.46
14.95
0.00
200,993
205
0.01
0.01
0.00
37.91
12.13
0.01
0.01
108,402
3,451,087
63,865
2,246,336
7.81
433.09
2.99
103.76
1.89
105.00
37.91
37.46
24.06
37.91
6.98
236.49
6.53
213.03
11
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
The surface hydrology in the Lake Okeechobee watershed is largely governed by man-made systems.
A system of encircling levees impounds the Lake’s waters, creating a reservoir used for navigation,
water supply, flood control, and recreation. Pumping stations and control structures in the levees
along Lake Okeechobee are designed to move water either into or out of the Lake as needed,
permitting water levels to fluctuate greatly with flood and drought conditions and the demand for
water (see Figure 3). The major inflows into the Lake include rainfall (39 percent), the Kissimmee
River (31 percent), and numerous smaller inflows (all 5 percent or less) from Fisheating Creek, and
Taylor Creek/Nubbin Slough, and numerous smaller inflows, such as discharges from the Everglades
Agricultural Area. Major outflows include evapotranspiration (66 percent), the Caloosahatchee
River to the west (12 percent), the St. Lucie Canal (C-44) to the east (4 percent), and four major
agricultural canals (the Miami, New River, Hillsboro, and West Beach Canals) that drain south and
southeast (18 percent).
The Lake Okeechobee Tributaries that directly affect the Lake are included in the Lake Okeechobee
Basin, St. Lucie-Loxahatchee Basin, Upper Kissimmee and Fisheating Creek Basin, Caloosahatchee
River Basin and the Everglades Basin. The Lake Okeechobee Basin is divided into three planning
units: the CTP Complex, the TOL63 Complex and the NHLMS Complex. The following description
of the planning units is from the SFWMD Lake Okeechobee Basin Status Report (2001).
12
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Figure 3. Control Structures and Sampling Stations in Lake Okeechobee
NHLMS Complex
The NHLMS Complex includes Nubbin Slough (WBID 3203A), Henry Creek (WBID 3213B),
Lettuce Creek (WBID 3213A), Mosquito Creek (WBID 3203B), Myrtle Slough (WBID 3213D), and
waters within the drainages leading to the South Florida Water Management District’s structures S135 (WBID 3213C) and S-153 (WBID 3219). The NHLMS Complex covers about 131 square miles
and contains about 29 miles of streams. It consists of a collection of small tributary streams along
the northeast shore of Lake Okeechobee that once flowed directly into the lake but the tributaries are
now intercepted by canals prior to reaching the Hoover Dike/Levee. Land uses in all WBIDs include
dairies, pasture, and low-density residential housing.
Flows in Mosquito Creek, Nubbin Slough, Henry Creek, Lettuce Creek and Myrtle Slough are
intercepted by the L-63 Canal, which transport water to the rim canal and the S-191 structure, which
ultimately discharges into the lake (see Figure 4). Mosquito Creek is four miles long and flows from
northeast to southwest. Nubbin Slough is about 7 miles long and flows to the southwest. Henry
Creek is four miles long and flows from northeast to southwest. Lettuce Creek is located on the
13
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
northeast side of Lake Okeechobee and near the small community of Upthegrove Beach. The surface
of the shallow, turbid, eutrophic creek is covered with dense mats of aquatic plants. Myrtle Slough is
about 4 miles long and flows to the southwest. The slough is part of a network of interconnecting
small canals constructed to drain a low-lying area so that it may be used for agricultural purposes,
mostly pastures. High levels of inorganic nitrogen have been measured in the slough indicative of
runoff containing animal waste.
CTP Complex
The CTP Complex includes the S-154 basin and part of the S-133 basin. It covers about 86 square
miles and contains about 11 miles of streams. Chandler Hammock Slough (WBID 3199B) is the
only impaired WBID on the 1998 303(d) list within the CTP Complex. Chandler Hammock Slough
flows southward into Turkey Slough (WBID 3199A), which flows into Popash Slough (WBID
3205C). The rim canal around Lake Okeechobee collects the flow from these connected sloughs (see
Figure 3). Depending on lake stage, water can flow from the rim canal into the lake through
hurricane gate structure 6. Water can also be pumped through S-133 into the lake. Land cover in
Chandler Hammock Slough is predominately agriculture, accounting for approximately 83% (or
10,645 acres) of land, followed by wetlands (1584 acres or 12.3%) and pasture (491 acres or 3.8%).
TOL63 Complex
The TOL63 Complex covers 108 square miles and contains 45 miles of streams and canals. It
includes part of the S-191 basin and the eastern portion of the S-133 basin. Taylor Creek (WBID
3205) and Otter Creek (WBID 3205D) are the two impaired WBIDs within the complex. Otter
Creek flows about 3.5 miles southwesterly before joining Taylor Creek. Taylor Creek is 29 miles
long. Flows from Taylor Creek are diverted into the L-63 North Canal (WBID 3203C) at structure
S-192 north of the town of Okeechobee. The Taylor Creek channel below the S-192 diversion
carries flow in a southeast direction until it reaches the rim canal (C-59) and discharges by gravity
into Lake Okeechobee at structure S-191 (see Figure 4). Land cover in Taylor and Otter creeks is
predominately agriculture, followed by wetlands and pastures.
14
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Figure 4. Taylor Creek and Nubbin Slough Basins
1.3.2 Kissimmee River Basin
The Kissimmee River Basin flows into Lake Okeechobee and is part of the Everglades ecosystem.
The Kissimmee River Basin is 2,940 square-miles and extends from Orlando southward to Lake
Okeechobee. The Kissimmee River is the largest source of surface water to Lake Okeechobee, is
about 105 miles long and has a maximum width of 35 miles. The Kissimmee River Basin contains
four planning units: Upper Kissimmee, Lower Kissimmee, Lake Istokpoga, and Lake Placid. None
of the impaired WBIDs discussed in this report are within either the Lake Istokpoga or Lake Placid
basins. A discussion of water quality in these basins can be found in the Kissimmee River and
Fisheating Creek Basin Status Report (SFWMD, 2004).
Lake Kissimmee is the geographic divide between the Upper and Lower Kissimmee planning units.
Lake Kissimmee outflow is regulated through structure S-65. Based on flow data from 1972 through
April 30, 2005, the annual average outflow from the lake was 719,120 acre-ft (SFWMD, 2006).
15
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
During the 2004 hurricane season the flow volume from the lake was over 1.9 times the historical
average flow.
Upper Kissimmee Planning Unit
The Upper Kissimmee Planning Unit includes portions of Orange, Osceola, and Polk Counties from
Orlando southward to the southern tip of Lake Kissimmee. Hundreds of lakes, ranging in size from
small sinkholes to large lakes dot the planning unit. The many lakes and swampy areas in the
planning unit provide a relatively large storage capacity which retards drainage and results in
relatively slow runoff rates. Water in the planning unit generally flows southward to Lake
Kissimmee, then onward to Lake Okeechobee via the Kissimmee River (a.k.a. C-38 Canal).
Horseshoe Creek (WBID 1436) is the only WBID in the Upper Kissimmee Planning Unit addressed
in this report.
Horseshoe Creek is located west of Reedy Creek in the northeastern part of Polk County. The
upstream half of the creek is channelized, fed by a number of small canals dug to drain wetlands.
The lower half of the creek is unmodified. Discharge from the creek flows to a portion of the Reedy
Creek swamp known as the Huckleberry Islands, an extensive wetland area in Osceola County
connecting Reedy and Snell Creeks. The city of Davenport is located south of Horseshoe Creek.
The creek drains a predominantly agricultural area; however, urbanized areas, especially some
medium density residential areas, are primarily located in the southern part of the drainage basin.
Lower Kissimmee Planning Unit
The Lower Kissimmee Planning Unit is 722 square miles and encompasses portions of Polk,
Osceola, Highlands, and Okeechobee Counties. There are no significant urban areas in the planning
unit as the area is entirely rural in nature; however, portions of an active military bombing test range
(Avon Park Air Force Range) is located in the northern portion of the planning unit near the PolkHighland County line. Impaired WBIDs in the planning unit include: Kissimmee River (WBIDs
3209 and 3186B), Blanket Bay Slough (WBID 3186C), and Eight Mile Slough (WBID 3186D), Oak
Creek (WBID 3192C), Farm Area (WBID 3188), and Chandler Slough (WBID 3188A). Land cover
in these WBIDs is predominately agriculture followed by wetlands.
Historically, the Kissimmee River meandered approximately 103 miles with a 1- to 2-mile-wide
floodplain. During the historic period of hydrologic record (1934-1960) the river moved very
slowly, with normal river velocities averaging less than 2 feet per second. A severe hurricane
occurred within the basin in 1947 resulting in extensive property damage from flooding. The State
responded with a request to the federal government to design a flood control plan for central and
southern portion of the state. Between 1962 and 1971, the Kissimmee River was channelized and
transformed into a series of impounded reservoirs. Inflow from the basin was regulated by six water
control structures (S-65 and S-65 A, B, C, D, and E). The Upper Kissimmee Basin (S-65) and
Kissimmee River (S-65A through S-65E) contribute about 51 percent of the total surface water
inflow to Lake Okeechobee, over 1.1 million acre-feet per year. These basins also contribute 34
percent of the phosphorus load to the lake.
16
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
The Kissimmee River Restoration and the Kissimmee River Headwater Revitalization projects were
jointly authorized in the 1992 Water Resources Development Act (SFWMD, 2006). The primary
goal of the Kissimmee River Restoration project is to reestablish the ecological integrity of the riverfloodplain system. Restoration efforts require reconstruction of the physical form of the river and
reestablishment of pre-channelization hydrologic conditions. Once the project is complete water
quality improvements should be achieved in the WBIDs in the S-65 A, B, C, D, and E basins.
The primary purpose of the Kissimmee River Headwater Revitalization Project is to provide the
water storage and regulation schedule modifications needed to approximate the historical flow
characteristics of the Kissimmee River system. Structures and canals in the upper basin will be
modified to accommodate the increased capacity associated with the increased lake storage volumes
needed to fully meet the requirements of the restoration.
1.3.3 Fisheating Creek Basin
The Fisheating Creek Basin is located to the west of Lake Okeechobee, adjacent to the Kissimmee
River Basin and is part of the Everglades ecosystem. The basin is about 849 square miles and
extends from west central Highlands County southward into northern portion of Glades County, and
then east ward towards Lake Okeechobee. The basin includes two planning units: Fisheating Creek
and Northwest Lake Okeechobee. Of the five major basins draining into Lake Okeechobee,
Fisheating Creek is the least impacted by humans in terms of hydrology and land uses, and still
contains many areas suited for preservation (SFWMD, 2004).
There are two stream segments listed as impaired in the Fisheating Creek Basin. Both the Harney
Pond Canal (WBID 3204) and Indian Prairie Canal (WBID 3206) are tributaries to Fisheating Creek
and are located in the Northwest Lake Okeechobee Planning Unit. Fisheating Creek drains via
gravity flow into Lake Okeechobee on the west shore, near Moore Haven. Land cover in the
impaired WBIDs is predominately agriculture followed by wetlands.
17
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Acres
%
Acres
Transportation
& Utilities
Barren &
Extractive
Wetlands
Water
Forest
Rangeland
WBID
Agriculture
Residential
Commercial,
Industrial,
Public
Table 4. Summary of Land Cover in Impaired WBIDs
%
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
Total
(acres)
Lake Okeechobee Basin
3199B
106
0.8
0
0.0
10645
82.6
491
3.8
19
0.2
26
0.2
1584
12.3
0
0.0
21
0.2
12893
3203B
353
5.2
37
0.6
5352
79.6
136
2.0
55
0.8
15
0.2
644
9.6
3
0.0
128
1.9
6724
3213A
49
1.6
26
0.8
2618
83.5
77
2.4
71
2.3
73
2.3
109
3.5
70
2.2
42
1.3
3135
3213B
400
2.5
25
0.2
11410
71.2
151
0.9
832
5.2
246
1.5
2703
16.9
134
0.8
129
0.8
16030
3213C
109
0.8
0
0.0
10746
79.1
393
2.9
260
1.9
510
3.8
1056
7.8
508
3.7
0
0.0
13582
3213D
13
0.1
0
0.0
11945
73.0
856
5.2
1583
9.7
30
0.2
1767
10.8
20
0.1
146
0.9
16361
3203A
551
3.6
33
0.2
12676
82.7
510
3.3
44
0.3
121
0.8
1203
7.8
121
0.8
74
0.5
15332
3205
2003
3.8
792
1.5
41876
78.9
1958
3.7
1252
2.4
594
1.1
4402
8.3
96
0.2
76
0.1
53049
34
0.3
42
0.4
8499
86.1
263
2.7
97
1.0
48
0.5
405
4.1
87
0.9
400
4.0
9875
65
0.4
9723
67.5
88
0.6
51
0.4
805
5.6
2699
18.7
970
6.7
0
0.0
14414
3205D
Kissimmee River Basin
3209
14
0.1
18
Barren &
Extractive
Wetlands
Water
Transportation
& Utilities
US EPA Region 4
Forest
Rangeland
WBID
Agriculture
Residential
Commercial,
Industrial,
Public
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
Total
(acres)
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
3186B
1590
2.3
106
0.2
31778
46.9
10356
15.3
8165
12.1
521
0.8
14539
21.5
591
0.9
43
0.1
67689
3186C
6
0
0
0.0
12389
76.5
127
0.8
30
0.2
30
0.2
3622
22.4
0
0.0
0
0.0
16203
3186D
0
0
0
0.0
3059
12.5
8863
36.1
8385
34.2
4
0.0
4194
17.1
13
0.1
0
0.0
24518
3192C
0
0
0
0.0
8784
85.0
0
0.0
0
0.0
0
0.0
1551
15.0
0
0.0
0
0.0
10335
3188
297
0.3
2
0.0
57417
58.3
15793
16.0
1217
1.2
1216
1.2
21937
22.3
516
0.5
91
0.1
98485
3188A
29
0.3
6
0.1
7383
69.1
6
0.1
130
1.2
58
0.5
3005
28.1
52
0.5
12
0.1
10680
1436
255
8.5
6
0.2
1305
43.4
729
24.3
42
1.4
113
3.7
348
11.6
50
1.7
158
5.2
3004
Fisheating Creek Basin
3204
898
0.9
42
0.0
70990
73.9
4845
5.0
3177
3.3
783
0.8
13994
14.6
1258
1.3
126
0.1
96114
3206
36
0.1
8
0.0
37629
84.7
19
0.0
442
1.0
472
1.1
5406
12.2
388
0.9
6
0.0
44406
2.7
35397
82.9
679
1.6
437
1.0
673
1.6
1163
2.7
408
1.0
1000
2.3
42706
Caloosahatchee River Basin
3246
1815
4.3
1134
L-8 Canal
19
Barren &
Extractive
Wetlands
Water
Transportation
& Utilities
US EPA Region 4
Forest
Rangeland
Agriculture
Residential
WBID
3233
Commercial,
Industrial,
Public
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
Total
(acres)
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
Acres
%
5251
5.9
7
0.0
14199
16.0
4387
4.9
20143
22.7
5229
5.9
38786
43.7
777
0.9
20
0.0
88799
Everglades Agricultural Area
3238
318
0.4
343
0.5
70709
96.1
36
0.0
26
0.0
872
1.2
381
0.5
592
0.8
285
0.4
73561
3238E
15
0.1
39
0.2
21497
92.6
449
1.9
0
0.0
112
0.5
283
1.2
735
3.2
75
0.3
23205
3248
444
0.7
451
0.7
62306
95.4
168
0.3
4
0.0
476
0.7
454
0.7
439
0.7
593
0.9
65336
3248A
1450
3.6
982
2.4
36441
90.5
323
0.8
13
0.0
328
0.8
27
0.1
277
0.7
427
1.1
40268
3253
251
8.6
52
1.8
2504
85.9
28
1.0
0
0.0
7
0.3
0
0.0
11
0.4
62
2.1
2915
3244
699
13.3
122
2.3
4290
81.8
0
0.0
5
0.1
46
0.9
0
0.0
28
0.5
52
1.0
5243
3247
24
0.7
37
1.1
2903
85.0
3
0.1
3
0.1
139
4.1
6
0.2
93
2.7
209
6.1
3415
3250
175
1.6
55
0.5
9904
93.2
112
1.1
23
0.2
99
0.9
5
0.0
123
1.2
128
1.2
10623
3251
65
0.1
43
0.1
63148
97.7
39
0.1
43
0.1
397
0.6
335
0.5
513
0.8
56
0.1
64638
20
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
1.3.4 Caloosahatchee River Basin
The Caloosahatchee River Basin encompasses approximately 1,400 square miles of southern Florida
and serves as the major source of freshwater in the Lower West Coast Region. The entire basin
covers significant portions of four counties and is divided into five planning units: East
Caloosahatchee River, West Caloosahatchee River, Orange River, Telegraph Swamp, and
Caloosahatchee Estuary. The hydrology and land uses of the Caloosahatchee Basin have undergone
significant modification in the last century. Originally, the Caloosahatchee was a shallow,
meandering river that flowed westward from its headwaters near Lake Hicpochee to San Carlos Bay
in the Gulf of Mexico (Haag et al, 1996). Dredging activities connected the Caloosahatchee to Lake
Okeechobee in 1884. Today, the Caloosahatchee River is part of the Okeechobee Waterway that
links the Gulf of Mexico to the Atlantic Ocean. The freshwater portion of the river has been
channelized into the C-43 canal in order to accommodate navigation and provide flood control.
Starting in the 1930’s, three locks or water control structures were constructed: the Moore Haven
Lock (S-77), Ortona Lock (S-78), and the Franklin Lock (S-79). The Franklin lock also serves as a
salinity barrier dividing the upstream freshwater and downstream tidal portions of the
Caloosahatchee. Most freshwater entering the Caloosahatchee estuary flows through Franklin Lock.
Currently, approximately half of the water that reaches S-79 is water that had passed through S-77
from Lake Okeechobee (see Figure 3).
WBID 3246, East Caloosahatchee, was included on the 1998 303(d) list as impaired for nutrients and
DO. The WBID is within the channelized portion of the Caloosahatchee River known as C-43.
WBID 3246 is within LOPP basin S-4. Agriculture is the predominant land cover in the WBID
followed by residential. It is likely the percentage of residential land cover has increased since 1999
due to urban sprawl.
1.3.5 L-8 Basin
Drainage from WBID 3233 discharges into the L-8 Canal located on the southeastern shore of Lake
Okeechobee. The L-8 Canal starts at Sand Cut and ends at the intersection with the West Palm
Beach Canal. Before discharging into the West Palm Beach Canal, the L-8 Canal connects to several
other canals and waterways, including the M-Canal, the M-0 and M-1 canals, and the L-40 Canal.
Land cover in WBID 3233 is predominately wetlands (44%) and forest (23%). Agriculture accounts
for about 16 percent of the land cover, predominately citrus groves, sugarcane, and corn. Most of the
undeveloped area in the WBID is within the J.W. Corbett National Wildlife Refuge.
The L-8 canal is a conveyance for excess stormwater from Lake Okeechobee and agricultural areas.
The canal is undergoing dramatic changes to its flow and basin-drainage pattern, which may alter
future water quality conditions. WBID 3233 is listed for DO, nutrients and turbidity. Depressed DO
levels are common in constructed waterbodies having small surface to cross-sectional area ratio and
an aquatic weed control program necessary for the canal to efficiently transport water SFWMD,
1999).
21
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
1.3.6 Everglades Agricultural Area
The Everglades Agriculture Area (EAA) is located on the southern tip of Lake Okeechobee and is
one of the most productive agricultural regions in the State. Over 505,000 acres of the EAA are
under production with sugar cane that accounts for over 80 percent of total crop coverage. Farmers
grow vegetables, sod, and rice during the winter months. Six major canals were built in the 1920’s
to drain and irrigate the EAA, many of which are included on the 1998 303(d) list as impaired for
nutrients and DO. These canals underwent major renovations in the 1960’s as part of the central and
South Florida Project (C&SF Project). As part of the C&SF Project, the U.S. Army Corps of
Engineers (USCOE) constructed a network of canals, levees, control structures, and pumps to control
flooding and provide water supply to the EAA. This project resulted in the back pumping of nutrient
rich water into Lake Okeechobee, exacerbating water quality problems in the lake.
In 1979, the Florida Department of Environmental Regulation (now the Department of
Environmental Protect (DEP)) approved the Interim Action Plan (IAP), an operating permit issued to
the SFWMD to regulate back pumping into Lake Okeechobee. The IAP states that EAA drainage
water can only be discharged into the lake under declared emergency conditions for water supply or
flood control purposes. Runoff from the EAA produced by normal rainfall is discharged into Water
Conservation Areas (WCAs) to limit the amount of nutrient rich water being released into the lake.
Prior to the IAP the northern one third of the EAA was routinely back pumped directly into Lake
Okeechobee. Since implementation of the IAP, back pumping for water supply has occurred four
times, the most recent in 2001 (Audubon of Florida, 2005). Back pumping is associated with dry
periods. Water management during droughts is essential for preventing lake levels from getting too
low.
The 1994 Everglades Forever Act required EAA landowners to reduce the total phosphorus in the
runoff from their land by 25 percent (Rule 40E-63). Landowners are implementing Best
Management Practices (BMPs) to manage water, sediments, and nutrients that balance water quality
improvements and agricultural productivity. Since January 1995, EAA Basin reductions have
exceeded the state law required reductions. In December 2001, DEP proposed the first numerical
ambient water quality standard for phosphorus in the Everglades Protection Area at 10 parts per
billion (ppb).
There are 10 WBIDs in the EAA included on the 1998 303(d) list as impaired for nutrients and DO:
WBID 3238 (West Palm Beach Canal); 3238E (M Canal); 3248 (North New River Canal); 3248A
(Hillsboro Canal); 3253 (South Bay); 3244 (East Beach); 3247 (715 Farms); 3251 (S-3); 3250 (S236); and 3252A (Knights Farm Field 1). Land cover for the impaired WBIDs is predominately
agriculture. The following discussions of each WBID are summarized from Ecosummary reports
prepared by the Florida Southeast District Assessment and Monitoring Program.
The West Palm Beach Canal (WBID 3238), also known as the C-51 Canal, was originally dug in the
1900’s to lower Lake Okeechobee and drain a part of the Everglades in order to farm the land.
Today the canal is part of the Central and South Florida flood control system. The canal starts at
Lake Okeechobee at structure S-352 (S5A basin) and flows southeast before emptying into the Lake
22
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Worth Lagoon in Palm Beach County. This report addresses WBID 3238 located in the EAA.
About 96 percent of land cover in the WBID is agriculture and is used primarily for growing
sugarcane.
The M Canal (WBID 3238E) was constructed in the 1950’s by the City of West Palm Beach to
augment its water supply. The M Canal receives water from Lake Okeechobee via a short
interconnecting canal (the L-8 Tieback Canal) connecting the M Canal to the L-8 Canal. The L-8
Canal flows southeasternly from Lake Okeechobee to the West Palm Beach Canal. Water is pumped
upward from the Tieback Canal into the M Canal to create an artificially elevated condition,
protecting the quality of water by limiting inflows from external sources. WBID 3238E is the
portion of the M Canal flowing from the Tieback Canal through citrus groves before entering the
West Palm Beach Water Catchment Area. About 93 percent of land cover in the WBID is
agriculture and is used primarily for citrus groves.
The North New River Canal (WBID 3248) was created to provide drainage as well as a navigable
connection between the Gulf of Mexico via Lake Okeechobee and the Caloosahatchee River. The
North New River Canal is one of the major canals in Southeast Florida. The canal starts at the
southeastern corner of Lake Okeechobee at the lake’s Rim Canal at South Bay’s Pump Station S-2.
It then runs south through the EAA, WCA2 and WCA3. WBID 3248 includes the northern portion
of the canal and land cover in the area is primarily agriculture.
The Hillsboro Canal (WBID 3248A) is located on the southeast shore of Lake Okeechobee and
transports flow between WCA-1 and WCA-2. The canal also receives flow from the Closter Farms
Drainage System. The impaired portion of the canal is located within the EAA. Land cover within
the WBID is primarily agriculture.
South Bay (WBID 3253) is located at the southeastern tip of Lake Okeechobee southwest of Belle
Glade. The S-2 Pump Station at South Bay discharges into the North New River and Hillsboro
Canals. South Bay is located in the EAA and land cover is primarily agriculture. Due to the IAP the
S-2 Pump Station no longer back pumps water north into Lake Okeechobee, except under declared
emergencies.
East Beach (WBID 3244) is located on the southeast shore of Lake Okeechobee within the EAA.
There are four main canals, C-1 through C-4, in the WBID that are connected to a complex network
of smaller lateral canals. When excess amount of stormwater collects in the canal system, water can
be back pumped to Lake Okeechobee by Pump Station #1 or to the West Palm Beach Canal by Pump
Station #3. A component of the Everglades Forever Act required 80 percent of the drainage from
East Beach to be diverted away from Lake Okeechobee by December 2000. The East Shore
Drainage Canal was constructed to transport water away from Lake Okeechobee to the Hillsboro
Canal for discharge into Stormwater Treatment Area (STA) 1-West and 1-East at the northern tip of
WCA-1. East Beach is under permit to the SFWMD following Rule 40E-63. Land cover in WBID
3244 is primarily agriculture followed by residential.
23
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Closter Farms, also known as 715 Farms (WBID 3247), is located on the southeast shore of Lake
Okeechobee south of East Beach, within the EAA. There are approximately four miles of main draw
canals and 37 miles of lateral canals. A major element of the drainage works is a pump station at
culvert 12-A. The pump station contains three pumps and is used to back pump stormwater
collected by the network of canals to Lake Okeechobee whenever excessive water levels occur.
Closters Farms Drainage System is included in the Everglades Best Management Practices Program
and was issued a 40E-63 permit. Under the permit, Closter Farms discharges into the EAA and
STAs through the North New River and Hillsboro Canals with discharge going into Lake
Okeechobee only as a backup. Land cover in the WBID is primarily agriculture.
WBID 3251 (S-3) includes the S-3 pump station located on the southern end of Lake Okeechobee at
Lake Harbor. The S-3 pump station constitutes the beginning of the Miami Canal at the lake’s Rim
Canal. Prior to implementation of the IAP, the northern one third of the EAA was routinely back
pumped directly into Lake Okeechobee through pump stations S-2, S-3, and S-4. Under the current
IAP the S-2 and S-3 basins are routed south to the WCAs. Land cover in the S-3 basin is primarily
agriculture.
WBID 3250 (S-236) is located on the southern tip of Lake Okeechobee in the EAA. Stormwater
runoff from the WBID discharges into the Caloosahatchee River. The SFWMD is proposing to
construct a reservoir for storing water originating from S-236 as well as other basins and releases
from Lake Okeechobee. Land cover in the WBID is primarily agriculture.
2 STATEMENT OF WATER QUALITY PROBLEM
Section 303(d) of the Clean Water Act requires states to submit to the Environmental Protection
Agency (EPA) lists of waters that are not fully meeting their applicable water quality standards.
FDEP has developed such lists, commonly referred to as § 303(d) lists, since 1992. As part of that
process, tributaries in the Lake Okeechobee watershed were included on Florida’s 1998 § 303(d) list
as impaired by excess nutrients, depressed dissolved oxygen (DO), unionized ammonia, and BOD.
The most common water quality problems in the Lake Okeechobee Basin are elevated levels of
nutrients and low DO. TP and TN levels are higher than statewide medians, and most of the DO
observations fall below the 5.0 mg/l water quality criterion. Many of the impaired waterbodies have
been channelized or are canals. In constructed waterbodies it is difficult to consistently meet DO
standards developed for natural water systems. In addition, there is an ongoing aquatic weed control
program in the basin, which is necessary to allow the waterbodies to efficiently transport water;
however, this exacerbates DO problems due to the decaying plant material. In the EAA, the
impaired WBIDs are located in areas of wetlands and organic soils where low DO concentrations
occur naturally.
In addition to nutrients and BOD, water temperature, flow velocity, and sediment oxygen demand
(SOD), can influence the DO concentration in a creek. Temperature can influence DO concentration
by influencing the solubility of DO in the water, the metabolic activities of organisms (for example,
24
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
respiration rate), and to a lesser extent, rate at which oxygen consumption chemical reactions are
taking place (organic materials oxidization). Theoretically, the difference in water temperature at
different stations can be caused by differences in canopy coverage. SOD data were not available in
the impaired WBIDs. Flow velocities can influence the accumulation of organic sediments, the DO
reaeration, and water residence time in a given creek. Many of the impaired WBIDs are
characterized as wide swampy areas, which diminish the momentum of the stream flow and cause
the flow velocity to decrease resulting in depressed DO concentrations.
Several of the WBIDs are impaired for unionized ammonia. In ambient water, unionized ammonia is
in a chemical equilibrium with ammonia, and the equilibrium coefficient is primarily controlled by
pH, water temperature, and sometimes ionic strength, especially water pH (Wetzel, 2001). Usually,
a higher fraction of the ammonia is in the form of unionized ammonia under a high pH condition.
The photosynthetic consumption of carbon dioxide (CO2) and bicarbonate (HCO3-) creates hydroxide
ions (OH-) in the water and increases the pH of the water, which in turn raises the portion of
unionized ammonia in the equilibrium. Controlling TP and TN should decrease the total algal
biomass in a waterbody and photosynthetic activity should decrease. This decreases the pH of the
water and therefore decreases the concentration of unionized ammonia.
3 WATER QUALITY STANDARDS
Water quality criteria established by the State of Florida are described in the Florida Administrative
Code (F.A.C.), Section 62-302.530. The individual criteria should be considered in conjunction with
other provisions in water quality standards, including Section 62-302.500 F.A.C. [Surface Waters:
Minimum Criteria, General Criteria] that apply to all waters unless alternative or more stringent
criteria are specified in F.A.C. Section 62-302.530.
Lake Okeechobee tributaries are Class III water bodies, with a designated use of recreation,
propagation and maintenance of a healthy, well-balanced population of fish and wildlife. The Class
III water quality criteria applicable to the impairment addressed by this TMDL are DO criterion,
BOD criterion, unionized ammonia criterion and the narrative nutrient criterion.
3.1
Nutrient Criterion
Florida’s nutrient criterion is narrative only - nutrient concentrations in a body of water shall not be
altered so as to cause an imbalance in natural populations of aquatic flora or fauna. Accordingly, a
nutrient related target was needed to represent levels at which an imbalance in flora or fauna is
expected to occur.
3.2
Dissolved Oxygen Criterion
The statewide default Class III DO criterion for predominantly fresh waters is a minimum DO of
5 mg/l. The narrative nutrient criterion is also controlling as it related to dissolved oxygen [62302.530(48)(a)]. The discharge of nutrients shall continue to be limited as needed to prevent
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Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
violations of other standards contained in this chapter.
The water quality standard for DO also considers the definition of natural background and the
directive not to abate natural conditions. Florida standards (62-302.200(15) FAC) states that,
“’Natural Background’ shall mean the condition of waters in the absence of man-induced alterations
based on the best scientific information available to the Department. The establishment of natural
background for an altered waterbody may be based upon a similar unaltered waterbody or on
historical pre-alteration data.” Florida standards also state at 62-302.300(15) FAC, “Pollution which
causes or contributes to new violations of water quality standards or to continuation of existing
violations is harmful to the waters of this State and shall not be allowed. Waters having water
quality below the criteria established for them shall be protected and enhanced. However, the
Department shall not strive to abate natural conditions.”
In the TMDL context, without a SSAC, calculating allocations would be targeted to achieve the
natural background loading and instream concentrations in the waterbody. Any allowance of
increased pollutant loadings beyond natural background would likely cause other than natural
dissolved oxygen levels which would not be a proper application of the Florida definition. Because
the standard prevents abatement of natural conditions, the TMDL can provide an allocation, where
necessary, that results in natural conditions. Therefore, the allocations are being established so that
all loading results in natural condition concentrations in the waterbody.
3.3
Biochemical Oxygen Demand Criterion
Florida’s BOD criterion is narrative stating BOD values shall not be increased to exceed values
which would cause DO to be depressed below the limit established for each class or a natural
condition concentration and, in no case shall it be great enough to produce nuisance conditions [62302.530(12)].
3.4
Unionized Ammonia Criterion
Florida’s criteria for unionized ammonia requires levels must be less than or equal to 0.02mg/l [62305.530(3)].
4 TARGET IDENTIFICATION
TMDLs must provide a remedy for listed impairments and return the subject waterbody to a
condition that is fully supporting the applicable water quality standard. Additionally, allocations in a
TMDL must not result in, or contribute to, any violation of other water quality standards for the
waterbody or water quality standards downstream.
This presents a special challenge for developing nutrient TMDLs, given the very nature of nutrients
and their interaction in aquatic systems. Nutrients are only a driver of a process, and that process,
known as primary productivity, is ubiquitous. Since that process can generally be assumed to occur
26
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
throughout an entire network of interconnected waterbodies, nutrient TMDLs should consider the
near-field, intermediate, and far-field impacts of nutrients and associated biomass.
4.1
Basis and Rationale For Nutrient Targets
Numeric targets for this TMDL are required to provide for a level of nutrients in the tributaries that
will ensure protection for aquatic life in the tributary WBIDs. Additionally, the allocations of those
TMDLs must not impact, but protect, downstream waters of Lake Okeechobee and its subsequent
drainage to the coastal estuaries of the St. Lucie and the Caloosahatchee. The demonstration that
allocations do not contribute to downstream problems is often dependent on the technical ability to
make such assessment. The targets of this TMDL were developed to support the State of Florida’s
narrative water quality standard for nutrients by not causing an imbalance in natural populations of
aquatic flora and fauna and also to not produce or contribute to conditions that violate the Dissolved
Oxygen standard, including natural conditions clauses.
Aquatic life becomes impaired by nutrients when excess amounts of nutrients are expressed in
excess primary productivity. Primary productivity refers to the collective actions of plants
(autotrophs) to utilize the energy of sunlight through the process of photosynthesis to fix carbon and
available nutrients into biomass of living organisms. This is, of course, an essential process on
which all plants and animals depend, and it serves as an intersection of the global cycles of critical
elements carbon, hydrogen, oxygen, nitrogen, and phosphorus (C, H, O, N, & P).
In aquatic systems, the normal cycles of C, H O, N, and P can be distorted by anthropogenic
activities in the watershed which generate extra N & P that can enter adjacent waterbodies by surface
runoff and ground water inflow. These excess nutrients then drive excess primary productivity, and
the extra accumulated biomass is seen as an over-abundance of aquatic plants, i.e., algal blooms
and/or increased macrophyte vegetation. This produces nuisance conditions which affect aesthetic
values and recreation. When certain algal species are involved which are able to produce toxins, as
in Harmful Algal Blooms (HABs), human health can be affected by exposure through drinking
water, direct contact, or inhalation.
Aquatic life use can be impacted directly by excess algal blooms and/or macrophyte abundance
through loss of habitat or other competitive disadvantages. But even more widespread impact occurs
indirectly through depression or depletion of dissolved oxygen that occurs when excess primary
production eventually decomposes and creates a great demand for dissolved oxygen. This lowers the
available oxygen for other aquatic life. Most aquatic life becomes stressed by chronic low oxygen
conditions and is virtually eliminated when oxygen depletion persists for a significant period of time.
Impairment of aquatic life use is the common result of excess eutrophication of a waterbody.
Since excess primary production is what creates the problem in the waterbody, and that results
directly from excess available nutrients, protection of aquatic life requires control of available
nutrients, in order to restrict primary productivity. But it should be kept in mind that resultant
productivity may lag introduction of nutrients in space and time, and that fact must be considered
when correlating nutrient levels and response. Proximal production may be temporarily suppressed
27
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
by limitation of light, the amount of one nutrient, high velocity/turbulence, or lack of substrate, but
transported bio-available nutrients will be utilized at some point. When these excess nutrients are
expressed, they will drive excess productivity and adversely affect aquatic life in that location. The
frequency and extent of these low oxygen events affects organisms differently, with non-motile and
long-lived organisms among the most sensitive.
Primary productivity as a process is driven by a number of factors, and moderated by others. The
major nutrients, nitrogen and phosphorus (N & P), along with certain minor nutrients, are required as
inputs for intermediary metabolic steps associated with photosynthesis. Since these steps are a series
of chemical reactions, their net stoichiometry is what ultimately determines the utilization of the
inputs to the process. These stoichiometric relationships provide some explanation for the ratios
originally reported by Redfield, and widely used today to interpret aquatic nutrient dynamics and
manage water quality.
The Redfield ratio for nitrogen and phosphorus is given as N : P = 16 : 1 (or N : P = 7.2 : 1 by
weight). In general practice, a functional range is used with a ratio greater than 30 considered P
limited, between 30 and 10 considered co-limited, and less than 10 considered nitrogen limited. This
practice allows for a wide mid-range of co-limitation where neither nutrient conclusively controls
primary production. Limiting nutrient analysis by Redfield ratio comparison can be a useful tool for
insight into nutrient limitation, but it should be applied with understanding of its limitations.
Appendix D contains calculations of the limiting nutrient in each WBID as well as a figure showing
the geographic distribution of the results.
Limiting nutrient analysis is based on “Liebig’s Law of the Minimum,” which is strictly applicable
only under steady-state conditions, that is, when inflows balance outflows of energy and materials.
The practice of identifying only a single nutrient target to address a problem of excess cultural
eutrophication presumes that the system is, and will remain, in steady state equilibrium, an
oversimplification whose weakness has been noted before. In 1971, Dr. Eugene P. Odum in
Fundamentals of Ecology, stated “Since cultural eutrophication usually produces a highly
“unsteady” state, involving severe oscillations (i.e., heavy blooms of algae followed by die-offs,
which in turn trigger another bloom on release of nutrients), then the “either/or” argument may be
highly irrelevant because phosphorus, nitrogen, carbon dioxide and many other constituents may
rapidly replace one another as limiting factors during the course of transitory oscillations.
Accordingly, there is no theoretical basis for any “one factor” hypothesis under such transient-state
conditions.”
It is important to realize that the Redfield ratio is a generalization that is thought to capture
stoichiometry of reactions that occur inside of cells, and that actual uptake of nutrients by cells (or
organisms), may be moderated by adaptation for things like storage capability or alternative
biochemistry. These adaptations can be particularly effective in highly enriched situations. In
addition, aquatic macrophytes can respond differently than algae to nutrient limitation ratios in the
water column, and often exactly opposite. This could be very important in cases where impairment
can involve either, and the overall effect on nutrient dynamics should not be underestimated.
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Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Calculation of Redfield ratios from an existing data set of ambient grab samples by averaging over
time and space tends to over-simplify the system. While this will effectively characterize the
prevailing pattern of nutrient limitation, it may not reflect periods or events of shorter duration when
very different nutrient conditions exist. Nutrient dynamics in aquatic systems are complex, with
often considerable fluctuation in the water column concentrations of nutrients, and therefore, the
ratio of nutrient concentrations varies. As previously noted, over-enriched aquatic systems are not
steady state systems; they are dynamic systems, and a complex dynamic at that.
Traditionally, many nutrient TMDLs have relied on comparing calculated nutrient ratios to Redfield
ratios to identify the limiting nutrient as a target and then to manage that nutrient over an averaging
period to control productivity. Doing so, mistakenly assumes a steady state for the diagnosis, and
then again for the application of the remedy. This increases the risk that excess productivity will not
always be controlled, and during shifts in limitation short term events would be allowed within the
averaging period that would not sufficiently protect aquatic life use. To illustrate this point, a daily
Redfield Ratio was calculated for each WBID where both TP and TN measurements were taken.
The percent of time the ratio was P-limited, Co-limited, and N-limited was calculated by dividing the
number of times the WBID was limited by the total number of sampling events. Results of this
analysis for existing conditions are shown in Table 5. A similar analysis was performed using a
single nutrient control (i.e., TP) and is shown in Appendix D.
When the limiting nutrient is identified, by default the other nutrient is identified as the excess
nutrient. Transport of un-reacted nutrients, as well as products of excess production, must be
considered when determining appropriate protection of downstream waterbody conditions,
immediate and long distance. Expression of bio-available nutrients in primary productivity may be
delayed. Conditions change over space and time, and nutrient limitation shifts. Even short duration
events of excess production can significantly affect aquatic life that cannot be sustained over long
term averaging periods.
While controlling one nutrient can prevent productivity, control of both nutrients, N and P, in
upstream waters can also provide additional assurance that excess productivity will remain in
control. In a highly enriched system, it is important to avoid even brief episodes that can escape the
prevailing control during periods of weakened limitation of one nutrient. This additional biomass is
the product of excess productivity initially driven by excess nutrients and should not be ignored.
Even if less significant locally, it will be transported downstream and because it represents an
additional biomass to be processed instream, it may continue to burden the normal dynamics as it
cycles, and recycles downstream. This spiraling effect can be underestimated in its effect on aquatic
life in the intermediate and far-field.
Under conditions of phosphorus limitation, even if local excess primary productivity is controlled to
a large extent by phosphorus reduction alone, there will be consequent export of the excess nutrient,
nitrogen, because the excess of that nutrient would not have the opportunity for uptake into biomass.
The larger the excess of nitrogen, the greater the contribution to nitrogen sensitive downstream
systems; therefore, concurrent reduction of nitrogen in the basin is often warranted in order to protect
downstream use. But there may also be an additional near-field justification for nitrogen reduction,
29
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
arising from the fact that at those times when local primary productivity is being effectively
suppressed by phosphorous limitation, biological uptake of N is restricted, which may leave the
chemically reduced constituents of the nitrogen series, i.e., ammonia and organic N, to directly exert
their oxygen demand in a setting that is already under oxygen stress.
Table 5. Existing Limiting Condition in Impaired WBIDs (based on TP and TN data)
WBID
No. of
Observations
Average
Condition
Limiting Condition (% of time)
Phosphorus
Nitrogen
Co-Limited
3186B
520
P-Limited
83%
3%
14%
3186C
46
Co-Limited
4%
50%
46%
3186D
37
P-Limited
73%
8%
19%
3188
689
N-Limited
19%
40%
42%
3188A
150
Co-Limited
25%
9%
66%
3192C
18
Co-Limited
28%
11%
61%
3199B
50
N-Limited
2%
86%
12%
3203A
2681
N-Limited
6%
67%
27%
3203B
583
N-Limited
1%
82%
18%
3205
433
N-Limited
2%
62%
36%
3205D
492
N-Limited
8%
58%
34%
3213A
201
N-Limited
0.5%
40.3%
59.2%
3213B
231
Co-Limited
15%
37%
48%
3213D
179
N-Limited
2%
83%
16%
3204
273
Co-Limited
61%
0%
39%
3213C
107
Co-Limited
67%
1%
32%
3233
229
P-Limited
66%
0%
34%
30
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
WBID
No. of
Observations
Average
Condition
US EPA Region 4
Limiting Condition (% of time)
Phosphorus
Nitrogen
Co-Limited
3238
448
Co-Limited
35.5%
0.4%
64.1%
3238E
339
P-Limited
92%
0%
8%
3244
124
P-Limited
71%
1%
28%
3246
545
P-Limited
85.9%
0.2%
13.9%
3247
252
P-Limited
98%
0%
2%
3248
270
P-Limited
95%
0%
5%
3248A
153
P-Limited
92%
0%
8%
3250
99
P-Limited
99%
0%
1%
3251
168
P-Limited
91%
0%
9%
3253
133
P-Limited
99%
0%
1%
3206
291
Co-Limited
34%
4%
62%
3209
1307
P-Limited
70%
2%
27%
1436
48
P-Limited
98%
0%
2%
4.2
Nutrient Target Development
The Lake Okeechobee drainage basin is a highly enriched system with elevated levels of both TP and
TN throughout and conditions of low dissolved oxygen are somewhat common. In this situation,
control of both TP and TN as nutrient inputs may be necessary to prevent adverse impacts in both
near-field and far-field waters.
Potential targets for phosphorus and nitrogen that reflect least impacted conditions were derived
from three independent approaches developed by FDEP and EPA. A summary of each approach is
discussed below. The results of these approaches were averaged to provide values supported by a
convergence of three lines of evidence. Those values are 0.077 mg/L TP and 1.2 mg/L TN.
4.2.1 Approach #1: Reference condition value from reference streams dataset (FDEP)
In this approach candidate reference sites were selected in the Central Peninsula bioregion based on
31
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
the Landscape Development Intensity (LDI) Index. LDI scores were calculated at individual stations
within a WBID and those stations having LDI scores less than 2 were considered to represent
minimally disturbed areas. Currently, insufficient data are available at the candidate WBIDs to
correlate low LDI scores with biological health. A number of candidate WBIDs identified on the
Verified List as impaired due to nutrients or DO were removed as potential reference sites.
Statistical outlier analyses using standard statistical methods (i.e., 75th percentile +1.5 * interquartile
range) were performed on the individual candidate data points to exclude any data not characteristic
of the bioregion (i.e., natural phosphate deposits). The annual geometric mean was calculated for
each WBID having four or more samples collected in a year. This dataset was reduced to one value
by calculating the 75th percentile of the lognormal distribution of the annual TP and TN
concentrations. The resulting TP and TN concentrations calculated using this method are 90 ppb and
1.3 mg/l.
FDEP continues to develop this approach to nutrient criteria development and plans to seek the
input of the Nutrient Technical Advisory Committee regarding the approach. Should the
outcome of that process provide a value that is sufficiently supported by the technical rationale,
EPA may use this value as the endpoint of the TMDL upon finalization. EPA recognizes that
this approach more closely compares nutrient concentrations to unimpacted streams which
should fully support an aquatic life use. Given technical support regarding the approach, EPA
would prefer to target such a value. While the other approaches have merit, they are more
related to conditions expected to approximate background and not related to an actual biological
condition. Given EPA’s interest, we specifically request comment on the method of targeting
this line of evidence at the exclusion of the others.
FDEP continues to develop this approach to nutrient criteria development and plans to seek the
input of the Nutrient Technical Advisory Committee regarding the approach. Should the
outcome of that process provide a value that is sufficiently supported by the technical rationale,
EPA may use this value as the endpoint of the TMDL upon finalization. EPA recognizes that
this approach more closely compares nutrient concentrations to unimpacted streams which
should fully support an aquatic life use. Given technical support regarding the approach, EPA
would prefer to target such a value. While the other approaches have merit, they are more
related to conditions expected to approximate background and not related to an actual biological
condition. Given EPA’s interest, we specifically request comment on the method of targeting
this line of evidence at the exclusion of the others.
4.2.2 Approach #2: Reference condition value from an all streams dataset (EPA Region 4)
A reference condition approach consistent with EPA’s peer-reviewed nutrient criteria guidance was
used to develop a local (i.e., WBID) target (USEPA, 2000). Depending on the type and extent of
available data, EPA suggests three methods for determining nutrient targets: 1) directly determined
32
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
from an unimpacted reference site; 2) empirically determined from a dataset from unimpacted
reference sites (similar to FDEP’s approach described in Section 4.2.1); or 3) empirically determined
from an all stream dataset. Application of these methods requires robust datasets consisting of
multiple stations, samples, seasons, and years.
A sufficient number of unimpacted reference sites with sufficient datasets was not available to EPA
in the Lake Okeechobee watershed to establish targets based on reference stream measurements.
EPA’s guidance manual encourages selecting a reference condition from a smaller geographic scale
(i.e., watershed versus state-wide) with a robust dataset as this improves similarity and comparability
of the streams. Information from all streams in the Lake Okeechobee watershed provides a
sufficiently robust dataset representing a range of conditions that approximates a normal distribution.
The spatial distribution of WBIDs and monitoring stations used to calculate the TP and TN targets is
shown in Figure 5 .
EPA developed a target for these TMDLs using the all stream approach by considering all WBIDs in
the Lake Okeechobee watershed having TP and TN measurements. Data stored in IWR Run 24 for
all streams (listed and non-listed) in the Lake Okeechobee watershed were considered in the analysis.
The all stream dataset considered in the analysis includes 113 WBIDs containing about 550 stations
where TP and TN samples were collected over a 13 year period. This robust dataset of 32,242 TP
measurements and 18,422 TN measurements was collapsed to station median values and statistically
ranked. When plotted, the TP data approximates a normal distribution. According to EPA nutrient
criteria guidance the 25th percentile concentration should correspond to an inherently protective
value. The 25th percentile annual average concentrations for TP and TN are 70 ppb and 1.23 mg/l,
respectively.
A limitation of this approach is that it does not factor in the aquatic condition of streams used in the
dataset. Therefore it is not clear whether the value inherently protects aquatic life. However, given
the distribution of data values and the expected levels resulting from taking the 25th percentile of the
dataset, it is expected that the value generated from this approach is inherently protective.
4.2.3 Approach #3: A modeling approach removing land disturbance (EPA Region 4)
A modeling approach was used where disturbed landuse was changed in select WBIDs to reflect
natural conditions (i.e., forest and wetlands). A spreadsheet based on EPA’s Pollutant Load
(PLOAD) model (EPA, 2001) was used to develop TP and TN targets. The spreadsheet was used to
calculate nonpoint source loadings for nutrients as the product of the water quality concentration and
runoff volume associated with certain land use practices. Seven WBIDs representing headwater
tributaries in the Lake Okeechobee watershed were selected to calculate the TP and TN target
concentrations based on undisturbed conditions. Landuses classified in the 1999 SWFWMD
coverage as urban, agriculture, pasture, commercial, industrial, extractive or barren were considered
disturbed categories and were changed to undisturbed categories (i.e., forest and wetlands). Runoff
volumes were calculated using estimates of annual average rainfall and Event Mean Concentrations
(EMCs) for the various landuses. Annual average rainfall for the Lake Okeechobee area is about 60
inches (University of Florida, 2001). Event Mean Concentrations (EMCs) assumed for each land use
33
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
type in Florida were selected from those compiled by Harper and Baker (2003). Model results from
the seven WBIDs indicate TP concentrations for natural conditions range from 70 to 74 ppb, with an
average value equal to 71 ppb. Model results for TN range from 1.04 to 1.05 mg/l, with an average
concentration of 1.04 mg/l. Model calculations are provided in Appendix F.
This procedure is designed to estimate loading to the stream. It does not contain any water quality
dynamics or a link to aquatic life use support. Aquatic life use support is assumed under natural
conditions. The utility of this tool is best used to predict background, or undisturbed, loading to the
stream which is then used to estimate natural resulting concentrations.
4.3
Nutrient Target Application
The averages of existing nutrient values for each WBID were used to provide the ratio for
comparison to the Redfield ratio to determine the prevailing nutrient limitation condition of that
WBID. There were 14 P limited WBIDs, eight co-limited WBIDs, and eight N limited WBIDs.
After the P target was applied, all WBIDs were P limited with existing levels of N (see Appendix F).
However, it is understood that with variation in nutrient concentration the ratio will change and
limitation will shift accordingly. Targeting only the limiting nutrient, without addressing the other
can be expected to restrain primary production only as long as that nutrient is clearly limiting.
If P is targeted in all WBIDs at a level that will maintain or establish P limitation in each, then excess
primary production should be controlled over the averaging period, as long as clear P limitation is
maintained throughout the WBID. Under those circumstances, the WBID should be protected in the
near-field and P transport reduced downstream to Lake Okeechobee (where primary productivity is
to be controlled by a TMDL for P). However, this approach would be incomplete without an
assessment of N for several reasons. Forms of N available for primary productivity can remain in
excess and directly exert a negative influence on dissolved oxygen.
High levels of excess N can have a direct effect on DO. During the majority of the time under P
limitation, when local primary productivity is being effectively suppressed by control of P, biological
uptake of N is restricted. This may leave the chemically reduced constituents of the nitrogen series,
i.e., ammonia and organic N, to more directly exert their oxygen demand in WBIDs that are already
under oxygen stress. In many of these WBIDs with high ambient N concentrations there is
significant animal agriculture in the watershed, which could be expected to increase the organic N
and ammonia fractions of total N delivered to the waterbody. News reports of oxygen depletion fish
kills associated with agricultural runoff are easy to find. This potential for increased nitrogenous
oxygen demand and allochthonous carbonaceous oxygen demand under P limitation provides
justification for concurrent reduction of N.
In the near field, with P only control, there may also be high levels of N present. Many WBIDs have
such significant P limitation precisely because of existing high levels of N. Allowing these high
ambient levels of N increases the risk of failure of the control scheme. The strength of P limitation
34
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
can be expected to vary during the averaging period, and shifts to co-limiting conditions with high N
present may result in loss of control of primary production. And during these times, events of short
duration could significantly affect aquatic life. In order to minimize the risk of water quality
standards violation, concurrent control of N may be warranted in these WBIDs.
Additionally, N can, or will be, the excess nutrient in all P limited WBIDs, and as such remains in
the watershed for transportation downstream while productivity is restrained by P control. The farfield effects of exported N from WBIDs under P only control must be considered if downstream uses
are to be adequately protected. Under conditions of P limitation, with local excess primary
production controlled to a large extent by P reductions alone, there will be consequent export of the
excess nutrient, N, which will impact nitrogen sensitive downstream systems. And without
concurrent control, the larger the excess of N, the greater will be the impact. There are documented
nutrient impairments in the downstream estuaries of the St. Lucie (see Proposed Nutrient TMDL for
St. Lucie Estuary TMDL, USEPA, 2006) and the Caloosahatchee River (SFWMD, 2005) with
excess nitrogen loading attributed to discharge from Lake Okeechobee. To avoid establishing, or
failing to establish, allocations that allow contribution to violations of water quality standards in
these downstream waters, concurrent control of N may be warranted. With control targets for
tributaries based upon estimations of least impacted conditions, levels may approach a natural
background condition which would be acceptable for transport to Lake Okeechobee.
As a result of the considerations described above, a dual nutrient approach will be followed in
assigning nutrient targets to each impaired WBID in the Lake Okeechobee watershed. The decision
rationale for controlling nitrogen in a particular WBID is summarized below. Additional detail can
be found in Appendix G.
Step one: If the DO is not meeting the water quality standard for the WBID based on the
verified list binomial test or, if the data set is too small, greater than 10% of the samples
violate, then a regression analysis is run to determine if nitrogen has an effect on DO. If so,
nitrogen will be controlled. If not, step two is applied (which would also apply if the DO
were meeting the water quality standard because it targets control of primary productivity
throughout the year).
Step two: If a phosphorus only TMDL results in phosphorus limitation for less than 90% of
the time using the TMDL target concentration as the phosphorus condition, nitrogen will be
controlled. This avoids the risk associated with dependence on a single nutrient control
approach where that condition would be expected for less than 90% of the time. Inherent
fluctuation in phosphorus levels will still be observed post TMDL implementation.
Step three: A third check will be made to ensure that excess nitrogen, post TMDL
implementation, is not delivered downstream recognizing that there are documented nitrogen
caused impairments in the St. Lucie and Caloosahatchee Bay. This will be done by using the
reductions necessary from the Lake Okeechobee watershed in the St. Lucie TMDL being
concurrently proposed by EPA to calculate a target condition for Lake Okeechobee. If the
target condition in Lake Okeechobee expressed as a median is less than the median of
35
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
existing TN concentrations in the WBID, nitrogen will be controlled. As expected, the
concentrations of nitrogen in Lake Okeechobee inflows are not significantly different, after
mixing, than those in Lake Okeechobee outflows.
4.4
DO and BOD Target
In waterbodies listed for both nutrients and DO, controlling nutrients should result in improved DO
conditions. In most of the WBIDs, insufficient data are available to correlate elevated BOD
concentrations with depressed DO levels, with the exception of WBID 3186B which is listed for DO
and BOD and not nutrients. In that case, a regression analysis between DO and BOD was performed
using the limited data available in the WBID. The analysis was conducted at both a single station
and using all data collected in the WBID. The correlation is stronger at a single station rather than
the results obtained when all data are used in the analysis. Although DO and BOD measurements are
collected at several stations within the WBID, only data collected at Station 21FLSFWMKRFNC38
include times when DO criteria are achieved in the stream. This station is located upstream of
Kissimmee River Restoration project restoration activities and was the only station where a range of
BOD and DO measurements were collected. The data were filtered to remove non-detect samples.
Using the trendline equation shown on this plot, the BOD concentration corresponding to the DO
criterion of 5 mg/l is about 2.36 mg/l and is used as the target in this WBID. Details of the BOD
target calculation are provided in Appendix E.
Elevated chlorophyll levels are an indication of nutrient productivity; however, insufficient data are
available in most WBIDs to indicate a correlation between these parameters. An assumption in these
TMDLs is DO conditions should improve when management strategies are implemented to return
nutrients loadings to natural background levels.
4.5
Unionized Ammonia Target
WBIDs 3244 and 3247 are listed for unionized ammonia. The TMDL targets the numerical criteria
of 0.02 mg/l in calculating allowable loads. Achieving the nutrient targets in these WBIDs should
result in lower unionized ammonia concentrations.
36
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
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Monitoring Stations
County
Target Setting WBIDs
Waterbody
LAKE/POND
RESERVOIR
SEA/OCEAN
STREAM/RIVER
CANAL/DITCH
SWAMP/MARSH
0
10
20
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30
40
50
60
70
80
90
100 Miles
Figure 5. Location of WBIDs and Monitoring Stations Used to Calculate a Nutrient Target per Section 4.2.2
37
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
5 WATER QUALITY RESULTS
Data collected during the Group 4 listing cycle were used to assess water quality in the impaired
waterbodies. Data compiled in IWR Run 24 were used in the data analysis and is summarized in
Table 6 and Table 7. This covers data collected between 1993 and 2004. For WBIDs listed for
nutrients, TN, TP, chlorophyll-a and unionized ammonia, data are reported. A summary of BOD and
DO data for WBIDs listed for DO is shown in Table 7. The spatial distributions of average TP,
TN, and DO values are shown in Figure 6, Figure 7, and Figure 8, respectively. As shown in these
figures, areas of high nutrient concentrations correspond to areas of depressed DO concentrations.
WBIDs 3186B and 3186D are listed for DO and/or BOD. Samples collected at the same station and
on the same day and analyzed for DO, BOD, Chl-a, TP TN, and temperature are plotted to determine
a correlation, if any, between these parameters. Select correlation plots for WBID 3186B and 3186D
are provided in Appendix A. As expected, DO has a positive correlation with temperature, most
likely a benefit of tree canopy. In these WBIDs, DO does not have a strong correlation with Chl-a or
any of the nutrient parameters.
WBID 3186D does not have sufficient data collected at any station to correlate depressed DO
concentrations with either BOD or chlorophyll-a. Chlorophyll concentrations measured in the WBID
are low (maximum value is 6 g/l) and would not be indicative of nutrient rich waters. WBID
3186D is predominately forest and rangeland. The correlation between DO and TN for WBID
3186D is shown in Appendix A. The correlation is weak, but in general as TN concentrations
decrease, DO concentrations increase.
WBIDs 3244 and 3247 are listed for unionized ammonia, nutrients, and DO. The 95th percentile
concentration of unionized ammonia data is selected to represent existing conditions. This percentile
concentration (i.e., 0.05 mg/l for WBID 3244 and 0.0283 mg/l for WBID 3247) is considered
conservative, as the average concentrations measured in WBIDs 3244 and 3247 are 0.02 and
0.01mg/l, respectively, which are equivalent to or less than the water quality standard. Plots of
unionized ammonia data collected in the WBIDs and percentile calculations are provided in
Appendix A.
38
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
Table 6.
US EPA Region 4
Summary of Nutrient and Unionized Ammonia Data for Impaired WBIDs
WBID
TP (mg/l)
Obs
TN (mg/l)
Mean Min
Max
Obs
Mean
Min
Chlorophyll -a(µg/l)
Max
Obs
Mean
Min
Unionized Ammonia (mg/l)
Max
Obs
Mean
Min
Max
3186B
1,904
0.08
0
3.39
586
1.31
-0.49
6.97
320
24.24
1
293.8
164
0
0
0.02
3186C
46
0.39
0.01
1.49
45
1.86
0.84
9.51
20
29.17
1.4
365.07
1
0
0
0
3186D
45
0.07
0.01
1.08
43
1.08
0.33
3.8
17
2.4
1
6.3
-
-
-
-
3188
711
0.47
0
3.92
258
1.77
0.5
8.4
23
7.24
1
74
13
0
0
0
3188A
152
0.19
0.03
1.19
108
1.42
0.52
4.64
6
83.02
1
480
-
-
-
-
3192C
18
0.27
0.04
1.3
18
1.98
1.11
4.71
12
30.03
1
150
-
-
-
-
3199B
104
1.587
0.05
5.78
92
2.99
0.92
11.00
14
157.77
6.00
979.36
-
-
-
-
3203A
2,869
0.484
0.01
15
557
1.6
0.78
11.36
3
13.78
3.89
26.67
191
0
0
0.02
3203B
591
0.943
0.19
3.72
203
2.6
1.04
9.68
3
5.28
4.41
6.17
2
0
0
0
3204
988
0.15
0
0.73
987
1.96
0.07
6.41
21
51.55
1
440
399
0
0
0.01
3205
567
0.48
0.02
1.47
405
1.83
0.51
7.91
23
50.32
1
370
1
0.01
0.01
0.01
3205D
500
0.63
0.02
5.83
369
2.1
0.57
27.85
21
12.52
1
210
2
0.02
0.01
0.03
3206
444
0.185
0.04
1.93
444
1.73
-0.44
5.07
23
24.72
1
62
199
0
0
0.07
3209
3,453
0.107
0
2.59
1588
1.64
-0.47
13.62
233
10.28
1
69.3
552
0
0
0.01
203
0.455
0.07
1.76
200
1.86
0.48
3.87
8
19.83
1
67
2
0.01
0.01
0.01
3213A
39
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
WBID
TP (mg/l)
Obs
US EPA Region 4
TN (mg/l)
Mean Min
Max
Obs
Mean
Chlorophyll -a(µg/l)
Min
Max
Obs
Mean
Min
Unionized Ammonia (mg/l)
Max
Obs
Mean
Min
Max
3213B
272
0.438
0
2.11
245
2.07
-0.37
23.38
65
38.65
3.8
144.8
34
0
0
0
3213C
422
0.109
0
2.11
397
1.69
-0.37
23.38
68
39.43
3.8
144.8
89
0
0
0.01
3213D
179
1.096
0.09
3.92
8
2.6
0.8
3.68
4
3.98
1
8.92
1
0.01
0.01
0.01
3233
346
0.135
0.01
0.85
320
2.14
0.95
8.4
18
11.8
4.27
27.3
106
0
0
0.03
3238
467
0.186
0.01
1.7
382
2.34
0.63
11.2
27
38.07
1
120.93
101
0.01
0
0.03
3238E
362
0.103
0
0.43
300
3
-0.1
9.94
60
9.65
2.3
30.1
78
0.01
0
0.04
3244
173
0.277
0.05
1.43
173
4
1.28
22.4
-
-
-
-
60
0.02
0
0.06
3246
738
0.115
0.02
0.59
739
2.3
-0.48
7.93
1
7.9
7.9
7.9
306
0
0
0.05
3247
324
0.101
0
0.45
324
3.54
0.5
17
-
-
-
-
130
0.01
0
0.06
3248
308
0.135
0.01
1.22
305
3.87
0.51
35.97
34
30.49
3.1
187
88
0.01
0
0.03
3248A
167
0.112
0.01
0.88
154
2.15
-0.43
13.57
13
38.52
13.9
107.6
1
0.03
0.03
0.03
3250
149
0.097
0.03
0.27
149
3.62
1.4
5.99
-
-
-
-
56
0.01
0
0.05
3251
195
0.084
0.02
0.49
168
2.11
0.8
7.93
26
48.7
5.7
566.1
-
-
-
-
3253
171
0.086
0.04
0.24
171
3.13
1.17
22.95
-
-
-
-
67
0.01
0
0.05
1436
56
0.068
0.01
0.24
56
1.71
0.59
4.42
16
3.06
1
15.65
10
0
0
0
40
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Table 7. Summary of DO and BOD Data in WBIDs Impaired For DO
WBID
DO (mg/l)
Obs
Mean
Min
BOD (mg/l)
Max
Obs
Mean
Min
Max
3186B
616
4.42
0.01
12.81
60
3.81
-2
14.6
3186C
46
4.11
0.61
7.6
16
2.91
0.7
7.4
3186D
43
4.49
0.13
9.16
15
2.05
2
2.2
3188
608
3.53
0.11
14.02
23
2.23
0
8.5
3188A
137
3.18
0.42
8.43
6
2.43
0
8.3
3192C
19
2.46
0.17
7.6
12
5.72
1
20.1
3199B
92
2.57
0.18
8.61
-
-
-
-
3203A
1050
3.38
0
15.43
-
-
-
-
3203B
519
3.76
0.44
9.41
-
-
-
-
3204
949
4.31
0.2
11.63
19
3.55
0
19.2
3205
413
4.24
0.33
11.3
-
-
-
-
1079
3.76
0.1
12.6
13
1.31
0.41
3.8
3206
435
4.19
0.13
10.69
29
2.21
0
6.1
3209
1379
5.34
0
13.42
8
2.49
2
3.4
3213A
197
4
0.69
10.5
-
-
-
-
3213B
240
3.98
0.09
10.8
-
-
-
-
3213C
400
4.67
0.09
13.93
-
-
-
-
3213D
168
2.57
0.3
9.16
-
-
-
-
3233
360
4.83
0.2
12.91
-
-
-
-
3238
311
5.95
0.3
15.03
-
-
-
-
3238E
275
4.39
0.8
11.13
-
-
-
-
155
4.3
0.2
14.9
-
-
-
-
3205D
3244
41
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
WBID
DO (mg/l)
Obs
Mean
Min
US EPA Region 4
BOD (mg/l)
Max
Obs
Mean
Min
Max
3246
695
7.37
0.9
11.00
-
-
-
-
3247
305
4.08
0.1
13.72
-
-
-
-
3248
223
4.97
0.3
13.06
-
-
-
-
3248A
80
5.99
0.4
10.53
-
-
-
-
3251
94
5.85
0.1
14.11
-
-
-
-
3253
161
3.89
0
9.9
-
-
-
-
1436
68
3.75
0.14
8.9
25
2.01
1.1
3.6
42
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Average TP Values
N
W
E
S
TMDL WBID
TP (ppb)
0 - 25th Percentile
25th - 50th Percentile
50 - 75th Percentile
75 - 95th Percentile
> 95th Percentile
Waterbody
LAK E/POND
RESER VOIR
SEA/OCE AN
STREAM/R IV ER
CANAL/DITCH
SWAMP/MAR SH
60
70
80
12
0
940
390
80
70
30
30
50
410
470
290
63
0
70 270
1590 480
60
150
190
50
39
0
0
#
100
#
110
30
1100
80
0
16
140
190
10
0
90
100
90
80
70
10
0
10
20
30
40
110
100
50
60
Figure 6. Distribution of Average TP Concentrations
43
70
130
80
90
100 Miles
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
N
Average TN Values
W
E
S
TMDL WBIDs (2)
TMDL WBID
TN (mg/l)
0 - 25th Percentile
25 - 50th Percentile
50 - 75th Percentile
75 - 95th Percentile
> 95th Percentile
Waterbody
LAKE/POND
RESERVOIR
SEA/OCEAN
STREAM/RIVER
CANAL/DITCH
SWAMP/MARSH
1.67
1.86
0.9
0
1.07
1.31
2.36
1.49
2.13
1.56
1.87
2
2. .00
02
2.97
1.68
1.71
1.
90
1.94
2.21
1.92
1.90
#
2.12
2.56
#
#
2.98
2.31
#
2.15
#
2.11
8.63
3.87
4.28
3.69
20
0
20
40
60
Figure 7. Distribution of Average TN Concentrations
44
80
100 Miles
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
N
W
E
S
LOWP Basin
TMDL WBID
DO (mg/l)
5 - 25
4.01 - 4.99
0.1 - 4
Waterbody
LAKE/POND
RESERVOIR
SEA/OCEAN
STREAM/RIVER
CANAL/DITCH
SWAMP/M ARSH
10
0
10
20
30
40
50
60
70
80
Figure 8. DO Distribution in the Area Surrounding Lake Okeechobee
45
90
100 Miles
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
6 SOURCE ASSESSMENT
An important part of the TMDL analysis is the identification of source categories and the amount of
pollutant loading contributed by these sources. Sources are broadly classified as either point or
nonpoint sources. Phosphorus originating from atmospheric deposition is allocated to background
loads. Several of the WBIDs are also impaired for dissolved oxygen and unionized ammonia. The
sources contributing to nutrient impairment also contribute to the low DO and elevated unionized
ammonia levels. Low DO concentrations can also be attributed to hydromodification associated with
channelization.
6.1
Background Loads
Dry and wet atmospheric deposition of phosphorus is considered background. Phosphorus loading
in South Florida is monitored through the Florida Atmospheric Mercury Study (FAMS). Wet
deposition phosphorus loading rates average about 10 mgP/m2-yr, while dry deposition phosphorus
loading rates range from 10 mgP/m2-yr to 20 mgP/m2-yr (FDEP, 2001). The Lake Okeechobee
Technical Advisory Committee recommended that 18 mgP/m2-yr is an appropriate atmospheric
loading of phosphorus over the open lake. This rate is used to estimate background loads of
phosphorus in the impaired tributaries in the Lake Okeechobee watershed. The LOPP allocates 35
Mtons to atmospheric deposition.
6.2
Permitted Point Sources
A point source is defined as a discernable, confined, and discrete conveyance from which pollutants
are or may be discharged to surface waters. Point source discharges of industrial wastewater and
treated sanitary wastewater must be authorized by National Pollutant Discharge Elimination System
(NPDES) permits. NPDES permitted facilities discharging treated sanitary wastewater or
stormwater are typically considered primary sources of nutrients.
6.2.1 Inventory of Point Sources
Several domestic and industrial wastewater point sources exist in the watershed; however, most of
them do not discharge to surface waters. Animal Feeding Operations (AFOs) are located in WBIDs
3505 and 3505D but they land apply the wastewater and do not discharge to surface waters.
Stormwater Treatment Areas (STAs) are large parcels of wetlands planted with specific species that
act as filters to remove nutrients. Within the life cycle of these plants, plant litter will accumulate
and become peat through a natural anaerobic process. The peat will trap pollutants in agricultural
stormwater runoff, facilitating restoration of downstream waterbodies. STA 1 West (STA1W) is
located in WBID 3238E and is permitted through the NPDES program with monitoring requirements
only. Permitted facilities located in the impaired WBIDs are shown in Table 8.
FDEP regulates dairy farms and other confined animal operations located in the Lake Okeechobee
watershed under State Law, Chapter 62-670.500, F.A.C. (Dairy Rule). The purpose of the rule is to
46
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
control pollution of waters of the state due to the discharge of wastewater and runoff from dairies
and other confined animal operations. Additionally, EPA reinterpreted its federal rules regarding
NPDES permitting of Concentrated Animal Feeding Operations (CAFOs). The state was required to
implement these federal rules by December 2004. Based on the EPA rules, all of the dairies and
some of the CAFOs located within the Lake Okeechobee watershed must obtain NPDES permits.
The permitting requirements include the development and implementation of a nutrient management
plan, record keeping, transfer of waste to third parties, and annual reporting (SFWMD, 2006).
Table 8. Permitted Wastewater Facilities Discharging in Impaired WBIDs
Name of Facility
City of Clewiston WWTP
H W Rucks Dairy Barn #1
H W Rucks Dairy Barn #2
Okeelanta Power L P Cogeneration
Osceola Power L P Cogeneration
Palm Beach Aggregates
Everglades STA1W
Annual Average Nutrients
Limits (existing)
Permitted
Flow
TN
TP
Facility ID WBID (MGD)
(mg/l)
(mg/l)
FL0040665 3246
FLA139173 3205
FLA139165 3505D
FL0043737 3248
FL0043745 3238
FL0169081 3238E
FL0177962 3238E
1.5
5
0.7
Land application of wastewater
Land application of wastewater
0.423
Discharges to percolation pond
0.33
Discharges to percolation pond
5
Discharges to settling pond
Monitoring requirements only
6.2.2 Estimating Point Source Loads
Waste Load Allocations (WLAs) are assigned to all NPDES permits discharging to surface waters.
The City of Clewiston WWTP (FL0040665) uses extended aeration to treat wastewater before
applying it to an isolated sprayfield. Underdrains from the sprayfield discharge into a perimeter
canal that is continuously pumped to the Class III freshwaters of an irrigation canal. This canal
ultimately discharges to the Caloosahatchee River. A WLA is assigned to this facility as its
wastewater has been shown to impact water quality in the Class III irrigation canal (FDEP, 2002). A
WLA is calculated for TP, TN and BOD and expressed in units of Metric tons (Mtons) based on the
following equation.
WLA = concentration (mg/l) * flow (gal/day) * 3.785 l/gal * Mton/109 mg = Mton/day (Equation 1)
The WLA for the City of Clewiston WWTP is calculated using design flow and annual average
concentrations that reflect natural conditions for TP, TN and BOD (see Table 9). The NPDES
permit for the Clewiston facility should be revised to reflect these new limits. If these concentrations
are achieved in the effluent, the facility should not cause or contribute to water quality impairment in
the WBID because the regulatory concentration in the waterbody would reflect natural conditions
[62-302.200(15) FAC]. Details on the derivation of the WLA values are provided in Appendix C.
47
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Table 9. Proposed Permit Limits for Clewiston WWTP (FL0040665)
Parameter
Total Nitrogen
Total Phosphorus
Biochemical Oxygen Demand
Concentration
(mg/l)
Annual Average Load
(lb/day)
1.2
15.02
0.077
0.96
2.0
25.03
Note: The expressed daily load and concentration should be achieved based on an annual
average of the measured days.
Dissolved Oxygen concentrations reported in DMRs between 1998 and 2004 indicate numerous
violations of the water quality criteria between 1998 and 2001. Many of these violations coincide
with violations measured in the Industrial Canal (see Figure C- 3 in Appendix C). This TMDL
requires the City of Clewiston WWTP to comply with its permit limit for DO and to comply with
revised permit limits for nutrients and BOD based on this TMDL. Site specific criteria may need to
be developed for DO if the reductions proposed to achieve natural background conditions can be
adjusted and still result in attainment of the designated use.
6.2.3 Municipal Separate Storm Sewer System Permittees
Like other nonpoint sources of pollution, urban stormwater discharges are associated with land use
and human activities, and are driven by rainfall and runoff processes leading to the intermittent
discharge of pollutants in response to storms. The 1987 amendments to the Clean Water Act
designated certain stormwater discharges from urbanized areas as point sources requiring NPDES
stormwater permits. The three major components of the NPDES stormwater regulations are:
 Municipal Separate Storm Sewer Systems (or MS4) permits that are issued to entities that own
and operate master stormwater systems, primarily local governments. Permittees are required to
implement comprehensive stormwater management programs designed to reduce the discharge
of pollutants from the MS4 to the maximum extent practicable.
 Stormwater Associated with Industrial Activities, which is regulated primarily by a multisector
general permit that covers various types of industrial manufacturing facilities and requires the
implementation of stormwater pollution prevention plans.
 Construction activity generic permits for projects that disturb one or more acres of land and
which require the implementation of stormwater pollution prevention plans to provide for
erosion and sediment control during construction and the treatment and management of
stormwater to minimize pollution and flooding.
48
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
In October 2000, USEPA authorized FDEP to implement the NPDES stormwater program in all
areas of Florida except Indian Tribal lands. FDEP’s authority to administer the NPDES program is
set forth in Section 403.0885, Florida Statutes. The Stormwater Rule was established as a
technology-based program that relies on the implementation of BMPs that are designed to achieve a
specific level of treatment (i.e., performance standards) as set forth in Chapter 62-40, F.A.C.
The Stormwater Rule requires the state’s water management districts (WMDs) to establish
stormwater pollutant load reduction goals (PLRGs) and adopt them as part of a SWIM plan, other
watershed plan, or rule. Stormwater PLRGs are a major component of the load allocation part of a
TMDL. To date, stormwater PLRGs have been established for Tampa Bay, Lake Thonotosassa, the
Winter Haven Chain of Lakes, the Everglades, Lake Okeechobee, and Lake Apopka.
The NPDES stormwater program was implemented in phases, with Phase I MS4 areas including
municipalities having a population above 100,000. Because the master drainage systems of most
local governments in Florida are interconnected, EPA implemented Phase 1 of the MS4 permitting
program on a countywide basis, which brings in all cities, Chapter 298 urban water control districts,
and the Florida DOT throughout the fifteen counties meeting the population criteria. Phase II of the
NPDES Program was expanded in 2003 and requires stormwater permits to construction sites
between one and five acres, and to local governments with as few as 10,000 people.
An important difference between federal and state stormwater permitting programs is the federal
program covers both new and existing discharges, while the state program focuses on new
discharges. Although MS4 discharges are technically referred to as “point sources” for the purpose
of regulation, they are still diffuse sources of pollution that cannot be easily collected and treated by
a central treatment facility. Most MS4 permits issued in Florida include a re-opener clause allowing
permit revisions for implementing TMDLs once they are formally adopted by rule.
MS4 entities covering the drainage basins of the impaired WBIDs are shown in Table 10. The cities
of Pahokee, South Bay, and Belle Glade are urban areas located south of Lake Okeechobee covered
by a Palm Beach County Phase I MS4 permit (FLS000018). The City of Pahokee is located in
portions of WBIDs 3244 and 3238, South Bay is located in portions of WBIDs 3248 and 3253 and
the City of Belle Glade is located within WBID 3248A. Polk County and the City of Davenport in
the Horseshoe Creek basin (WBID 1436) are covered by a Phase I MS4 permit (FLS000015). Polk
County is the “unofficial” lead permittee. The Department of Transportation is a co-permittee to this
permit. There are no urban areas in the impaired WBIDs of sufficient populations in Polk, Osceola,
or Martin counties covered by an MS4 permit.
MS4 permittees will only be responsible for reducing the anthropogenic loads associated with
stormwater outfalls that it owns or otherwise has responsible control over, and it is not responsible
for reducing other nonpoint source loads in its jurisdiction. All future areas with populations
meeting the MS4 requirements will be required to achieve the allocations presented in the TMDL.
49
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Table 10. MS4 Permittees in the Drainage Basins of Impaired WBIDs
County
Permit/Co-Permit Name
Permit ID Number
MS4 Type
Polk
Polk County
FLS000015
Phase I
Osceola
Osceola County
FLR04E063
Phase II
Martin
Martin County
FLR04E013
Phase II
Palm Beach
Palm Beach County ERM
FLS000018
Phase I
6.3
Nonpoint Sources
Unlike traditional point source effluent loads, nonpoint source loads are diffuse sources that cannot
be identified as entering a waterbody through a discrete conveyance at a single location. These
sources generally, but not always, involve accumulation of nutrients on land surfaces and wash off as
a result of storm events. Nonpoint sources of phosphorus and nitrogen loadings in the Lake
Okeechobee watershed include: agriculture (cattle and crops), wildlife, septic systems, and
stormwater runoff. The single greatest contributor to increased N in most ecosystems is fertilizer
use, with other factors including deforestation, fossil fuel burning, increased planting of nitrogen
fixing crops, and oxidation of organic soils (SFWMD, 2003).
Major outflows from Lake Okeechobee include evapotranspiration (66 percent), the Caloosahatchee
River to the west (12 percent), St. Lucie Canal to the east (4 percent) and the four major agricultural
canals (the Miami, New River, Hillsboro, and West Palm Beach Canals) that drain south and
southeast (18 percent). The lake contributes poor water quality to these waterbodies.
Implementation of control strategies outlined in the Lake Okeechobee Protection Plan should result
in improved water quality discharging from the lake.
Depressed DO concentrations in the EAA are a result of nutrient-rich waters transported in the
canals. Despite reductions in the organic load carried in the canals, the physical nature of the canals
and their position in an area of wetlands and organic soils, DO concentrations should continue to be
depressed below Class III water quality criteria.
A summary of anthropogenic nonpoint sources found in the Lake Okeechobee watershed is presented
below. A detail discussion of these sources and remediation actions planned for the watershed can
be found on FDEP’s webpage.
6.3.1 Agriculture
Agricultural activities are the principle land uses in the impaired WBIDs and are responsible for
discharging large quantities of nutrients to the waterbodies through stormwater runoff. Cattle and
50
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
dairy pasturelands are the primary agriculture activities north and northwest of Lake Okeechobee,
while cropland (sugarcane and vegetables) dominates to the south and east of the lake. The most
intensive land use in the watershed is dairy farming, which began in the 1950’s.
In 1987, FDEP adopted Chapter 62-670 to establish treatment requirements to reduce total
phosphorus concentrations in runoff originating from AFOs and dairy farms in the Lake Okeechobee
watershed. Waste treatment systems were to be constructed to treat runoff and wastewater from
barns and high-intensity milk herd holding areas. According to the Dairy Rule, all 49 dairies in the
Lake Okeechobee drainage basin had to sell and remove their cattle or else comply with the rule by
1991. The Dairy Buy-Out-Program allowed owners of dairies to sell their dairy if they were unable
or unwilling to comply with the rule. In 1997, 23 dairies were eliminated, while 26 came into
compliance with the rule.
The importation of phosphorus as feed, fertilizer and detergents, to support agricultural activities is a
major source of phosphorus, nitrate, nitrite, and ammonia to the watershed. Ninety-eight percent of
the phosphorus imported to the watershed supports agricultural activities while the remaining two
percent supports human activities. Land use activities that are responsible for the largest percentage
of annual phosphorus imports to the watershed include: improved pasture, sugar mills, dairies,
sugarcane fields, and truck crops. FDEP has demonstrated a high correlation between phosphorus
imports (animal feed and fertilizers) to the watershed and phosphorus loadings to Lake Okeechobee.
Sugarcane has been grown commercially in southern Florida, primarily in the EAA, since the 1920s
and is one of the most economically important crops in the state. Sugarcane planting and harvesting
operations are conducted during the fall and winter. During the summer wet months area farms store
water by flooding vacant sugarcane fields or by growing paddy rice. Sugarcane is planted in rotation
with rice, sod, spring and fall corn, and other assorted vegetables. To maximize the efficient use of
plant nutrients in the soil, a rotation from higher to lower fertility requiring crops is normally
practiced. Like any other plant, sugarcane requires nutrients for optimum growth. In the EAA,
nutrients are provided from rainfall, irrigation water, organic soils, and fertilizer. Research studies
based on yield responses have been used to establish guidelines currently used for fertilizer rates.
Studies have shown that sugarcane biomass removes more phosphorus from the soil than the amount
applied as fertilizer.
6.3.2 Sediment
Another factor that controls phosphorus in the waterbodies involves the internal phosphorus loading
from sediments that accumulates in the waterbodies. Phosphorus is typically bound to calcium, other
organic matter, or iron at the surface of the sediments. The diffusive flux of phosphorus between the
surface and water column is controlled by iron solubility. Under conditions of low dissolved oxygen
(iron is in the form of Fe2+), phosphorus is released at high rates from the sediment in the water
column and could increase from 50 ppb to over 1 ppm. This condition could contribute to algal
blooms that occur in the summer months.
The largest amounts of N come from the EAA as these former soils of the Everglades are organic
51
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
and decompose under current agricultural practices. So much N is released through soil loss that
crops in the EAA do not need additional N fertilizer. Like P, plants and chemical interactions can
absorb large amounts of N. However, ecosystems can become N saturated, and once this happens, N
runoff accelerates.
Dairies and sludge applications are other significant sources of N in the Okeechobee watershed.
Most of the P control measures enacted in response to the Dairy Rule, especially holding more water
and containing cattle waste, yield significant N control. An estimated 11,914 tons of sludge was
applied in Okeechobee County in 1999, containing an estimated 275 tons of N and 133 tons of P.
Large chicken farms near Indiantown transported nitrogen-rich chicken manure into Okeechobee’s
watershed through 2001. A partial moratorium on sludge application was called in 2001 and BMPs
for sludge application for agriculture were developed by the Florida Department of Agriculture and
Consumer Services (FDACS, SFWMD, 2002).
Nutrient impairment in Lettuce Creek (WBID 3213A) is attributed to high dissolved phosphorus
fraction attached to sediment particles. Baffle boxes were installed in the creek as part of the
Tributary Sediment Removal Project to evaluate the phosphorus reduction benefits that could be
achieved by removing sediment loads from a stream. This type of traditional sediment trap was
ineffective at removing phosphorus due to the small diameter particles discharging into Lettuce
Creek. The study concluded a simple settling pond with chemical coagulation would be more
efficient and cost effective at removing particulate phosphorus than baffle boxes.
6.3.3 Septic Systems
Residential septic tank systems and small package plants deliver contaminants (bacteria and toxic
household chemicals) and nutrients to the impaired waterbodies. While urban areas comprise about
10 percent of the land uses in the basin, they only contribute 3 percent of the total phosphorus load in
the watershed (SFWMD, 2001). Wastewater master plans were completed in January 2004 to
address the need for connecting septic system and package plants to a central sewer system.
6.3.4 Stormwater Runoff
Stormwater runoff from agricultural and urban land cover represents a significant portion of the
nutrient loadings to the impaired streams. Numerous Best Available Technologies (BATs) projects
have been initiated in the Lake Okeechobee watershed to reduce phosphorus loadings in stormwater
runoff. In May 2004, the SFWMD completed constructed of edge-of-farm stormwater treatment
BATs on select dairy properties in the watershed, one of which was on property located in WBIDs
3213A and 3203A. Dairy BATs projects consist of capturing stormwater runoff from high nutrient
pasture areas; reusing the runoff onsite in current operations (if possible); and if offsite discharge is
necessary, chemically treating the runoff prior to its release.
Reducing nutrients entering stormwater in urbanized areas is essential to achieving the goals of the
LOPP. Public education through the Florida Yards and Neighborhood Program provides weekly
newspaper articles addressing proper lawn maintenance practices. The program encourages the use
52
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
of low- or no-phosphorus fertilizers for urban lawns and golf courses.
7 DEVELOPMENT OF THE TMDL
The TMDLs are based on achieving nutrient concentrations that protect the actual listed waterbodies
and also achieve the nutrient load to Lake Okeechobee consistent with the allocations outlined in the
Lake Okeechobee Protection Plan (LOPP) and the proposed St. Lucie TMDL. The LOPP allocates
an annual average load of 35 metric tons to background (i.e., atmospheric deposition) and 105 metric
tons/yr between point and nonpoint sources. To achieve the TP load in the lake, the basins
discharging into the lake are allocated a load such that the total load from all waterbodies (impaired
and not impaired) does not exceed 105 metric tons. Details of the development of the target TP load
for Lake Okeechobee can be found in the LOPP (SFWMD, 2004). The TMDLs also target TN as
described in Section 4 of this report.
For WBIDs listed for both nutrient and DO the TMDL targets reductions in nutrients to achieve
loadings representing natural background to achieve DO natural condition criteria. In addition to
being listed for nutrients and DO, WBIDs 3244 and 3247 are also listed for unionized ammonia. The
unionized ammonia TMDL is calculated using a mass balance approach based on the criterion (0.02
mg/l) and estimates of flow in the WBIDs (see Table 11). The TMDL for WBID 3186B allocates to
BOD loadings.
7.1
Nutrient TMDL
Nutrient enrichment and the resulting problems related to eutrophication tend to be widespread and
are frequently manifested some distance (in both time and space) from their source. Addressing
eutrophication involves relating water quality and biological effects (photosynthesis, decomposition,
nutrient recycling, etc.), as acted upon by hydrodynamic factors (flow, wind, tide, salinity, etc.) to the
timing and magnitude of constituent loads supplied from various categories of pollution sources.
Dynamic computer simulation models have become indispensable tools to describe these
relationships. Calibrated models also provide opportunities to predict water quality conditions under
alternative constituent loadings.
FDEP’s TMDL for Lake Okeechobee used the watershed model WAMVIEW to develop baseline
discharge and TP loads into the lake. The model time period was 1991-2003 and included the worst
drought in recent history (2000) and extremely wet years (1998 and 2003). The LOPP describes
how model results were used to assign annual TP loads to each of the 34 basins in the Lake
Okeechobee watershed. TP loads allocated to each basin were calculated by multiplying the annual
discharge (acre-ft) at each basin outflow structure, the observed flow-weighted TP concentration
(mg/l), and a conversion factor (1.233 x 10-3 m3 Mton acre-ft-1 mg-1).
Table 11 is a summary of impaired WBIDs located within each LOPP basin, the drainage area, and
the annual average discharge. These values represent baseline conditions (1991-2000) against which
alternative TP reduction plans are compared. Flows reported for WBIDs 3238 and 3238E are based
53
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
on discharge records obtained from DBHYDRO at structures S352_S and S5A_P, respectively.
These flows are measured at the downstream boundary of the WBID and represent annual average
flow for the period 1991-2000. Flow records from these structures are included in Appendix B. The
annual average flow for WBID 1436 is based on WAMVIEW model output at the downstream end
of the WBID. Flow from WBID 1436 drains to a swamp before entering Lake Kissimmee.
For all other WBIDs addressed in this report, the annual average discharge values assigned to each
WBID are area-weighted based on the percentage of area the WBID covers in an LOPP basin. For
example, the drainage area of WBID 3205 is about 44 percent of the total drainage area of the S-191
basin. This percentage is multiplied by the total flow from the S-191 basin to estimate flow in
WBID 3205. WBIDs may cover multiple basins. WBID 3250 watershed extends over the South FL
Conservancy DD (S-236) and Industrial Canal basins. The discharge assigned to WBID 3250 is the
sum of the values for the two LOPP basins.
In most cases WBID boundaries align with LOPP basins, but in some instances the areas differ. An
LOPP basin may include areas from WBIDs not on the 303(d) list. The impaired WBIDs in Basins
S-65 and S-65 A, B, C, D, E account for about 53 percent of the flow from the watershed. The
TMDL allocates loads to the impaired WBIDs but not to the non-listed waterbodies in the watershed.
The non-listed waterbodies are expected to meet the goals for TP reduction outlined in the LOPP.
The SFWMD developed a spreadsheet to evaluate the impact alternative BMPs would have on
achieving the TP TMDL for Lake Okeechobee. Criteria used to evaluate the BMPs included
protection of native flora and fauna in the lake and watershed, achievement of water quality
standards, and cost impacts on land owners and the regional economy. A summary of estimated load
reductions resulting from current BMP activities and future tools necessary to achieve the TMDL are
shown in Table 3.
Table 11. Area and Inflows for Impaired WBIDs and LOPP Basins (Baseline Conditions)
LOPP Basin
WBID
Drainage Area
Acres
S-65 A, B, C, D, E Basin
% of WBID
within Basin
427,913
Annual
average
Discharge
(acre-ft/yr)
291,845
3188
98,485
23.0%
67,169
3188A
10,680
2.5%
7284
3186B
67,689
15.8%
46,165
3186C
16,203
3.8%
11,051
54
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
LOPP Basin
WBID
Drainage Area
Acres
US EPA Region 4
% of WBID
within Basin
Annual
average
Discharge
(acre-ft/yr)
3186D
24,518
5.7%
16,722
3192C
10,335
2.4%
7049
Non-Listed Areas
200,003
46.7%
136,406
Taylor Creek/Nubbin Slough (S-191)
120,754
101,946
3205
53,049
43.9%
44,786
3205D
9875
8.2%
8337
3203A
15,332
12.7%
12,944
3203B
6724
5.6%
5677
3213B
16,030
13.3%
13,533
3213A
3135
2.6%
2647
3213D
16,361
13.5%
13,813
248
0.2%
209
Non-Listed Areas
715 Farm
3295
3247
C-40 Basin (S-72)
12,045
3415
100%
43,964
3206
C-41 Basin (S-71)
44,406
16,266
100%
94,928
3204
East Beach DD (Culv 10)
96,114
16,266
49,799
100%
5275
3244
12,045
49,799
11,815
5243
100%
55
11,815
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
LOPP Basin
WBID
Drainage Area
Acres
L-59E
% of WBID
within Basin
14,409
3209
S-135 Basin
14,414
Non-Listed Areas
S-154
100%
Non-Listed Areas
S-2
6395
25,408
13,582
75.1%
19,078
4,507
24.9%
6331
33,798
3199B
Annual
average
Discharge
(acre-ft/yr)
6395
18,089
3213C
US EPA Region 4
24,630
12,893
38.1%
9396
20,905
61.9%
15234
106,044
31,399
3248
65,336
61.6%
19,346
3248A
40,268
38.0%
11,923
S-3
64,630
3251
S-4
64,638
9794
100%
39,673
3246
South FL Conservancy DD (S-236)
and Industrial Canal
3250
South Shore/South Bay DD (Culv
4A)
3253
42,706
29,164
100%
10,596
10,623
9794
29,164
33,682
100%
2947
33,682
8151
2915
100%
56
8151
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
LOPP Basin
WBID
Drainage Area
Acres
L-8 (Culv 10A)
% of WBID
within Basin
US EPA Region 4
Annual
average
Discharge
(acre-ft/yr)
108,402
3233
Non-Listed Areas
S-5A
63,865
88,799
81.9%
52,316
19,603
18.1%
11549
120,798
3238
73,561
60.9%
156,397
3238E
23,205
19.2%
344,111
0.3%
26,905
S-65
1,021,674
1436
Other Areas (includes impaired
WBIDs not in the Group 4 Basin)
3004
862,069
Existing conditions for TP are expressed as concentrations and represent the mean value calculated
from all stations in the WBID (see Table 6). The TP baseline load assigned to each LOPP basin
represents existing conditions for all WBIDs discharging into that basin.
Existing conditions for TN are expressed as loads. TN loads are calculated using the mean
concentration measured in the WBID and area-weighted flows estimated from the LOPP.
Load (Mton/yr) = Flow (acre-ft/yr) * Conc. (mg/l) * 1.2326E-03
(Equation 2)
In the above equation, flow is the annual average flow estimated for the WBID and concentration is
the mean value calculated using all observation data collected in the WBID. Existing conditions for
total nitrogen are summarized in Table 12.
Table 12. Summary of Existing Conditions for Total Nitrogen
WBID
Average TN
Concentration (mg/l)
Flow
(acre-ft/yr)
TN Load
(lb/day)
3186B
1.31
46,165
450.24
3186C
1.86
11,051
153.03
57
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
WBID
US EPA Region 4
Average TN
Concentration (mg/l)
Flow
(acre-ft/yr)
TN Load
(lb/day)
3186D
1.08
16,722
134.45
3188
1.77
67,169
885.123
3188A
1.42
7284
77.01
3192C
1.98
7049
103.91
3199B
2.99
9396
287.01
3203A
1.60
12,944
154.19
3203B
2.60
5677
109.89
3205
1.83
44,786
610.18
3205D
2.10
8337
130.34
3213A
1.86
2647
36.65
3213B
2.07
13,533
208.56
3213D
2.60
13,813
267.38
3204
1.96
49,799
726.68
3213C
1.69
19,078
240.04
3233
2.14
52,316
833.51
3238
2.34
156,397
2724.64
3238E
3.00
344,111
7685.72
3244
4.00
11,815
351.85
3246
2.30
29,164
499.39
3248
3.87
19,346
557.40
3248A
2.15
11,923
190.85
58
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
WBID
7.2
US EPA Region 4
Average TN
Concentration (mg/l)
Flow
(acre-ft/yr)
TN Load
(lb/day)
3251
2.11
9794
153.85
3206
1.73
16,266
209.50
3209
1.64
6395
78.08
3247
3.54
12,045
320.14
3250
3.62
33,682
278.81
3253
3.13
8151
189.94
1436
1.71
26,905
342.53
Unionized Ammonia TMDL
Existing conditions for unionized ammonia is calculated using flow estimated for the WBID and the
95th percentile concentration. Calculations are provided in Table A- 2 of Appendix A. The existing
unionized ammonia load in WBID 3244 is 4.4 lb/day. The existing load in WBID 3247 is 2.54
lb/day.
7.3
BOD TMDL
A regression analysis using DO and BOD data collected in the upper portion of the WBID is used to
develop the DO TMDL for WBID 3186B. The data are graphed and a trendline is drawn through the
data points. The trendline equation is then used to determine the BOD concentration resulting in DO
of 5 mg/l. The TMDL is calculated using this BOD concentration of 2.36 mg/l and an estimate of
annual average flow in the WBID. Existing BOD load assigned to WBID 3186B is calculated using
the average BOD measurement collected from all stations in the WBID. Existing and TMDL loads
are 1309 and 811.13 lb/day, respectively. BOD load calculations are provided in Appendix E.
8 TMDL ALLOCATION
The TMDL process quantifies the amount of a pollutant that can be assimilated in a waterbody,
identifies the sources of the pollutant, and recommends regulatory or other actions to be taken to
achieve compliance with applicable water quality standards based on the relationship between
pollution sources and in-stream water quality conditions. The objective of a TMDL is to allocate
loads among all of the known pollutant sources throughout a watershed so that appropriate control
measures can be implemented and water quality standards achieved.
59
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
8.1
US EPA Region 4
Allocation
A TMDL can be expressed as the sum of all point source loads (Waste Load Allocations or WLA),
nonpoint source loads (Load Allocations or LA), and an appropriate margin of safety (MOS), which
accounts for uncertainty concerning the relationship between effluent limitations and water quality:
TMDL =  WLAs +  LAs + MOS
Federal regulations provide that TMDLs can be expressed in terms of mass per time (e.g. pounds per
day), toxicity, or other appropriate measure (40 C.F.R.§ 130.2(i)). TMDLs for the Lake Okeechobee
tributaries are expressed as annual average loads for consistency with the allocations in the LOPP.
Allocations are to both TP and TN to ensure complete protection of aquatic use support. Strategies
implemented in the watershed to achieve the nutrient TMDLs should achieve DO and BOD criteria.
The TMDL components for TP are expressed as concentration at the WBID scale and as loads in
metric-tons/year and pounds/day at the LOPP basin scale. Annual average LOPP basin loads are
divided by 365 days/yr to obtain daily loads. The TMDL components for TN, unionized ammonia
and BOD are expressed in terms of daily loads in lb/day. The target TP and TN concentrations
represent annual average values and the TMDLs should be implemented to achieve the annual
average concentrations and LOPP loads. Loads allocated to the impaired WBIDs are calculated by
multiplying the target concentrations and an estimate of annual flow. TMDL components for TP and
TN are provided in Table 13 and Table 14; for unionized ammonia in Table 15; and for BOD in
Table 16 . LOPP basin loads converted to daily loads are provided in Table 17. An implicit Margin
of Safety (MOS) is assumed in all TMDLs as described in Section 8.4. The percent reduction
required to achieve water quality standards is calculated using the following equation:
% Reduction = (existing load – TMDL) / (existing load) * 100
(Equation 3)
Table 13. TMDL Components for Total Phosphorus
Lake Basin/WBIDs
WLA
LA
(ppb)
MOS
TMDL
Lake
Load
(Mton/yr)
S-65A ,B, C, D, E
% Reduction
WBID
Conc. (ppb)
19.25
Lake
WBID
76%
3188
0
77
Implicit
77
84%
3188A
0
77
Implicit
77
58%
3186B
0
77
Implicit
77
4%
3186C
0
77
Implicit
77
80%
60
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
Lake Basin/WBIDs
WLA
LA
(ppb)
MOS
US EPA Region 4
TMDL
Lake
Load
(Mton/yr)
% Reduction
WBID
Conc. (ppb)
Lake
WBID
3186D
0
77
Implicit
77
6%
3192C
0
77
Implicit
77
72%
Taylor Creek / Nubbin Slough (S-191)
76%
19.01
3205
0
77
Implicit
77
84%
3205D
0
77
Implicit
77
88%
3203A
0
77
Implicit
77
84%
3203B
0
77
Implicit
77
92%
3213A
0
77
Implicit
77
82%
3213B
0
77
Implicit
77
83%
3213D
0
77
Implicit
77
93%
0.41
715 Farms
3247
0
77
Implicit
C-40 Basin (S-72)
77
2.32
3206
0
77
Implicit
C-41 Basin (S-71)
0
77
77
Implicit
East Beach DD (Culv 10)
77
77
Implicit
L59-E
0
77
Implicit
61
49%
76%
77
0.36
3209
58%
76%
2.12
72%
Reduction
24%
76%
6.17
3204
3244
75%
72%
76%
77
28%
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
Lake Basin/WBIDs
WLA
LA
(ppb)
MOS
TMDL
Lake
Load
(Mton/yr)
S-135 Basin
3213C
% Reduction
WBID
Conc. (ppb)
0.82
0
77
Implicit
S-154 Basin
3199B
US EPA Region 4
77
77
Implicit
S-2 Basin
WBID
76%
29%
76%
5.72
0
Lake
77
1.98
95%
76%
3248
43%
Reduction
77
Implicit
77
43%
3248A
31%
Reduction
77
Implicit
77
31%
S-3 Basin
3251
0.56
0
77
Implicit
S-4 Basin
3246
0.15
(Mton/yr)
77
Implicit
0
77
10%
Reduction
76%
77
0
77
21%
76%
10%
1.89
Implicit
S-5A Basin
3238
1.07
33%
Implicit
L-8 (Culv 10A)
3233
76%
0.26
77
8%
77
Implicit
South Shore / South Bay DD (Culv 4A)
3253
77
1.67
South FL Conservancy DD (S-236) & Industrial Canal
3250
76%
76%
77
43%
77
59%
0
59%
77
Implicit
62
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
Lake Basin/WBIDs
WLA
LA
(ppb)
MOS
US EPA Region 4
TMDL
Lake
Load
(Mton/yr)
% Reduction
WBID
Conc. (ppb)
Lake
WBID
Reduction
3238E
0
77
Implicit
S-65 (Lake Kissimmee)
1436
77
25%
16.96
0%
Reduction
77
Implicit
76%
77
0%
Notes:
1. Reduction proposed for WBIDs are based on achieving 77 ppb as an annual average of
measured days. Lake reduction based on achieving the load allocated in LOPP.
2. WBIDs in S-5 Basin discharge to the Water Conservation Areas and not into Lake
Okeechobee.
3. City of Clewiston WWTP is located in WBID 3246. WLA is based on facility design flow
and a TP concentration of 0.077 mg/l.
4. WLA values assigned to these WBIDs represent contributions from MS4s and are assigned a
percent reduction equivalent to the LA component necessary to protect the WBID.
5. Implicit MOS based on conservative assumptions including using all data collected in the
WBID to determine existing conditions rather than considering one time period (season or year).
Data represents all flow conditions including drought (1999-2002) and hurricane years (2004).
Table 14. TMDL Components for Total Nitrogen
WBID
WLA
(lb/day)
LA
(lb/day)
MOS
TMDL
(lb/day)
%
Reduction
3188
0
600.09
Implicit
600.09
32%
3188A
0
65.08
Implicit
65.08
15%
3186B
0
412.44
Implicit
412.44
8%
3186C*
0
98.73
Implicit
98.73
35%
63
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
WBID
WLA
(lb/day)
LA
(lb/day)
MOS
TMDL
(lb/day)
%
Reduction
3186D
0
149.39
Implicit
149.39
0%
3192C*
0
62.98
Implicit
62.98
39%
3205
0
400.12
Implicit
400.12
34%
3205D
0
74.48
Implicit
74.48
43%
3203A*
0
115.64
Implicit
115.64
25%
3203B*
0
50.72
Implicit
50.72
54%
3213A
0
23.65
Implicit
23.65
35%
3213B
0
120.90
Implicit
120.90
42%
3213D*
0
123.41
Implicit
123.41
54%
3247
0
107.61
Implicit
107.61
66%
3206*
0
145.32
Implicit
145.32
31%
3204*
0
444.90
Implicit
444.90
39%
3244
70%
Reduction
105.56
Implicit
105.56
70%
3209
0
57.13
Implicit
57.13
27%
3213C
0
170.44
Implicit
170.44
29%
3199B*
0
115.19
Implicit
115.19
60%
3248
69%
Reduction
172.84
Implicit
172.84
69%
3248A*
44%
Reduction
106.52
Implicit
106.52
44%
3251*
0
87.50
Implicit
87.50
43%
3246 *
15.02
lb/day
251.89
Implicit
266.91
48%
64
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
WBID
WLA
(lb/day)
LA
(lb/day)
MOS
TMDL
(lb/day)
%
Reduction
3250
0
92.42
Implicit
92.42
67%
3253
62%
Reduction
72.82
Implicit
72.82
62%
3233
0
467.39
Implicit
467.39
44%
3238
53%
Reduction
1397.25
Implicit
1397.25
49%
3238E
0
3074.29
Implicit
3074.29
60%
1436
30%
Reduction
240.37
Implicit
240.37
30%
Notes: 1. WLA for WBID 3246 is based on TN concentration of 1.23 mg/l and design flow.
2. The expressed daily TN load should be achieved based on an annual average of the
measured days recognizing natural variability.
Allocations provided for WBIDs marked with an asterisk are provided primarily for the purpose of
protecting downstream waterbodies. EPA recognizes that projects can legitimately be designed,
located, and implemented downstream in the future for treatment of nitrogen to address estuary
impairments in lieu of implementing reductions in the waterbodies. At such time, these allocations
can be modified to account for those projects. Implementation of this TMDL, or the St. Lucie
estuary TMDL, can include such treatment projects. Until then, reduction of nitrogen in these
WBIDs is provided by these allocations for the protection of those downstream waterbodies.
Practices for reduction of nitrogen in agricultural lands are identified in Section 9 TMDL
Implementation.
The allocations given to the sources (continuous and stormwater) in the above tables can also be
modified (i.e. trading/offsets) as long as the overall load does not exceed the TMDL WLA.
Table 15. TMDL Components for Unionized Ammonia
WBID
TMDL (lb/day)
WLA (lb/day)
LA (lb/day)
Percent
Reduction
3244
1.76
0
1.76
60%
3247
1.79
0
1.79
29%
Note: TMDL = 0.02 mg/l * flow (acre-ft/yr) * 1.2326E-03 (Mton/(acre-ft*mg/l))
65
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Table 16. TMDL Components for BOD
WBID
TMDL
(lb/day)
WLA
(lb/day)
LA
(lb/day)
Percent
Reduction
3186B
811.13
0
811.13
38%
3246
433.90
25.03
408.87
48%
Table 17. TP Allocations for LOPP Basins Expressed as Daily Loads
Basin
WLA
(lb/day)
LA
(lb/day)
TMDL
(lb/day)
S-65A, B, C, D, E
0
116.19
116.19
Taylor Creek / Nubbin Slough (S191)
0
114.74
114.74
715 Farms
0
2.47
2.47
C-40 Basin (S-72)
0
14
14
C-41 Basin (S-71)
0
37.24
37.24
77% Reduction
12.8
12.8
L59-E
0
2.17
2.17
S-135 Basin
0
4.95
4.95
S-154 Basin
0
34.50
34.50
S-2 Basin
76% Reduction
11.95
11.95
S-3 Basin
0
3.38
3.38
S-4 Basin
0.96
9.11
10.07
South FL Conservancy DD (S-236)
& Industrial Canal
0
2.05
2359
South Shore/ South Bay DD (Culv
4A)
76% Reduction
1.57
1.57
East Beach DD (Culv 10)
66
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
Basin
US EPA Region 4
WLA
(lb/day)
LA
(lb/day)
TMDL
(lb/day)
L-8 (Culv 10A)
0
11.41
11.41
S-5A Basin
0
0
0
S-65
0
102.37
102.37
8.2
Load Allocation
The LA includes nonpoint source loads from air deposition and unimpaired tributaries. The LA
assigns necessary reductions expected in the upstream load from areas above Lake Kissimmee.
However, the LA does NOT take into account changes in nonpoint source loads due to projected
changes in land use. The LOPA states changes in land use cannot result in increased phosphorus
loading over existing conditions.
Compliance with these load allocations can be measured in the WBIDs at locations commiserate
with implementation strategies. This can occur at locations in the WBID relative to reduction
schemes implemented for protection of the waterbody.
8.3
Wasteload Allocations
The WLA is a combination of the WLAs for all of the NPDES wastewater facilities and the
stormwater discharge from MS4 entities. To estimate the MS4 load, the urban stormwater
component of the nonpoint source loads was moved from the nonpoint source inventory to the WLA.
Urban stormwater from smaller municipalities not yet covered under Phase II of the NPDES
stormwater program was included in the LA component.
The City of Clewiston WWTP (FL0040665) discharges in WBID 3246 and is assigned WLA values
based on target TP, TN and BOD concentrations necessary to achieve background conditions. WLA
calculations are provided in Appendix C. All future point sources discharging to surface waters
impacting the impaired WBIDs will be required to meet the loads established in these TMDLs.
8.4
Margin of Safety
An implicit MOS was provided in the TMDL analysis through the selection of nutrient target
concentrations that incorporate natural background conditions. It is assumed that each waterbody
contains a certain amount of assimilative capacity above natural background before the standards are
exceeded. Including natural background as part of the averaging in developing a target provides an
implicit margin of safety.
67
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
An implicit MOS was provided in the TMDL analysis for unionized ammonia by representing
existing conditions as the 95th percentile concentration. This is considered conservative as less than
10 percent of the samples collected in the WBIDs exceed the target. In WBID 3244 four of 60
measurements, or 7 percent, exceed the 95th percentile concentration of 0.05 mg/l. In WBID 3247
seven of 130 measurements, or 5 percent, exceed the 95th percentile concentration of 0.0283 mg/l.
8.5
Seasonal Variability
Seasonal variability was addressed in the selection of the nutrient target concentrations by
considering data collected during all seasons. The data used in the TMDL analysis were collected
during both drought (2000-2001) and wet conditions (1998). South Florida experienced an
extremely rare occurrence of a series of hurricanes during August and September 2004. High
rainfall, high surface water flows, and rises in water levels in lakes were experienced during the
events and following months. Water quality data collected in the fall of 2004 reflects the devastation
caused by these events.
9 TMDL IMPLEMENTATION
The Clean Water Act [Section 303(d)(2)] directs that a TMDL established by the Environmental
Protection Agency be implemented by a State pursuant to subsection 303(e). A State can establish
its own procedures for implementation. Federal regulations provide direction on implementation of
TMDLs in the permitting process. At a minimum, NPDES permits must include a permit limit
consistent with the assumptions of an approved wasteload allocation. However, the State may also
establish a compliance schedule to provide time for implementation of effluent limits more stringent
than currently permitted.
Control of nonpoint sources is much more dependant on local efforts to reduce pollution. There are
many methods for controlling nonpoint sources. The predominant land uses in the areas covered by
this TMDL is agriculture. For guidance on controlling nonpoint loading into waterbodies from
agricultural sources, please refer to EPA's guidance, National Management Measures to Control
Nonpoint Source Pollution from Agriculture, http://www.epa.gov/owow/nps/agmm/index.html.
EPA also recently published a report, "Riparian Buffer Width, Vegetative Cover, and Nitrogen
Removal Effectiveness: A Review of Current Science and Regulations", which provides a synthesis
of existing scientific literature on the effectiveness of riparian buffers to improve water quality
through their inherent ability to process and remove excess anthropogenic nitrogen from surface and
ground waters (USEPA, 2005).
68
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
REFERENCES
Audubon of Florida, 2005. Lake Okeechobee: A synthesis of information and recommendations
for its restoration. P.N. Gray, C.J. Farrell, M.L. Krauss, and A.H. Gromnicki, Eds.,
Audubon of Florida, Miami. 106 pp. + appendices.
Chapra, Steven C. 1997. Surface Water-Quality Modeling. The McGraw-Hill Companies, Inc.,
New York, 840 pp.
Florida Administrative Code (F.A.C.) 62-302.530. Criteria for Surface Water Quality
Classifications.
FDEP, 2006. Water Quality Assessment Report, Kissimmee River and Fisheating Creek.
Division of Water Resources Bureau of Watershed Management. March 2006.
FDEP, 2005. 2005 South Florida Environmental Report, Chapter 3: Lake Okeechobee Annual
Report.
FDEP, 2004. Water Quality Status Report Kissimmee River and Fisheating Creek. Division of
Water Resource Management, South and Central Districts, Group 4 Basin, 2004.
FDEP, 2003. Basin Status Report, Caloosahatchee. Division of Water Resource Management,
South District, Group 3 Basin, June 2003.
FDEP, 2003. Water Quality Status Report, Lake Worth Lagoon – Palm Beach Coast. Division
of Water Resource Management, Southeast District, Group 3 Basin, July 2003.
FDEP, 2002. Biological Assessment of Clewiston WWTP, Hendry County, NPDES
#FL0040665, Sampled July 2001. FDEP, Biological Section, Bureau of Laboratories,
Division of Resource Assessment and Management, March 2002.
FDEP, 2001. Total Maximum Daily Load for Total Phosphorus – Lake Okeechobee, Florida.
Submitted to the USEPA Region 4. Tallahassee, FL.
FDEP, 2001. Basin Status Report, Lake Okeechobee. Division of Water Resource
Management, Southeast District, Group 1 Basin, 2001.
Harper, H. H. and D.M. Baker. 2003. Evaluation of Alternative Stormwater Regulations for Southwest
Florida. Environmental Research & Design, Inc.
Odum, Eugene P., 1971. Fundamentals of Ecology, Third Edition. WB. Saunders Company,
Philadelphia, PA.
Odum, Howard T., Dissolved Phosphorus in Florida Waters. Department of Biology, College of
Arts and Sciences, University of Florida, Report to Florida Geological Survey, January 9,
1953.
69
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
SFWMD, 2006. Comprehensive Everglades Restoration Plan: System-Wide Performance
Measures, RLG Review Draft, Central and Southern Project. March 16, 2006.
SFWMD, 2005. Caloosahatchee River/Estuary Nutrient Issues. White Paper prepared for the
South Florida Water Management District, October 10, 2005.
SFWMD, 2004. Lake Okeechobee Protection Plan (LOPP), South Florida Water Management
District, Florida Department of Environmental Protection, and Florida Department of
Agriculture and Consumer Affairs. January 1, 2004.
SFWMD, 2003. Lake Okeechobee Surface Water Improvement and Management Plan (SWIM),
Division of Water Resources Management, Southeast District, 2003.
SFWMD, 1999d. Ecosummary, East Beach Water Control District Palm Beach County. FDEP,
Southeast District, Assessment and Monitoring Program, December 1999.
SFWMD, 2000. Ecosummary, North New River Canal, West Palm Beach and Broward
Counties. FDEP, Southeast District, Assessment and Monitoring Program, June 2000.
SFWMD, 1999c. Ecosummary, South Bay, Palm Beach County. FDEP, Southeast District,
Assessment and Monitoring Program, October 1999.
SFWMD, 1999a. Ecosummary, L-8 Canal, Palm Beach and Martin Counties. FDEP, Southeast
District, Assessment and Monitoring Program, May 1999.
SFWMD, 1999e. Ecosummary, SFWMD Pump Station S-3, Palm Beach County. FDEP,
Southeast District, Assessment and Monitoring Program, December 1999.
SFWMD, 1999b. Ecosummary, West Palm Beach Canal. FDEP, Southeast District,
Assessment and Monitoring Program, July 1999.
SFWMD, 1999f. Ecosummary, Water Conservation Area 1, North Sector, Palm Beach County.
FDEP, Southeast District, Assessment and Monitoring Program, December 1999.
SFWMD, 1999g. Ecosummary, Closter Farms, Palm Beach County. FDEP, Southeast District,
Assessment and Monitoring Program, December 1999.
University of Florida, 2001. Florida Water Resources. University of Florida Extension Institute of
Food and Agricultural Sciences WQ101. Gainesville, FL April 2001.
USEPA, 2006. Proposed Total Maximum Daily Load (TMDL) for Dissolved Oxygen and
Nutrients in North St. Lucie River (WBID 3194), St. Lucie Estuary (WBID 3194B), and C24 Canal Watershed (WBID 3197), USEPA Region 4, Atlanta, GA. September 2006.
USEPA, 2005. Riparian Buffer Width, Vegetative Cover, and Nitrogen Removal Effectiveness:
A Review of Current Science and Regulations. USEPA, National Risk Management
Research Laboratory, Office of Research and Development, Cincinnati, OH EPA/600/R05/118, October 2005.
USEPA, 2000. Nutrient Criteria Technical Guidance Manual, Rivers and Streams. USEPA,
70
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Office of Water, Washington, DC EPA-822-B-00-002.
USEPA, 1991. Guidance for Water-Quality Based Decisions: the TMDL Process. USEPA,
Office of Water, Washington, DC EPA-440/4-91-001. April 1991.
71
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
APPENDIX A: Water Quality Plots
Sta 21FLSFWMKRFNC38
BOD (mg/l)
16
14
12
y = -1.6707x + 10.618
R2 = 0.401
10
8
6
4
2
0
0
1
2
3
4
5
6
7
DO (mg/l)
Figure A-1. Correlation Between DO and BOD in WBID 3186B
Correlation between DO and Chla(corrected) at
Sta 21FLSFWMKREA97
140
Chla (ug/l)
120
y = -1.1795x + 28.138
R2 = 0.017
100
80
60
40
20
0
0
2
4
6
8
10
12
DO (mg/l)
Figure A-2. Correlation Between DO and Chlorophyll-a in WBID 3186B
72
14
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Sta 21SFWMS65A
40
Temperature (C)
35
30
25
20
15
y = -1.1392x + 29.92
R2 = 0.2989
10
5
0
0
2
4
6
8
10
12
14
DO (mg/l)
Figure A- 3. Correlation Between DO and Temperature in WBID 3186B
Sta 21FLSFWMKREA97 in WBID 3186B
0.2
y = -0.003x + 0.0783
R2 = 0.0772
TP (mg/l)
0.15
0.1
0.05
0
0
2
4
6
8
10
DO (mg/l)
Figure A- 4. Correlation Between DO and TP in WBID 3186B
73
12
14
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
DO and TN Correlation Plot at Sta 21FLSFWMKREA 78
1.6
1.4
y = -0.0698x + 1.0378
R2 = 0.0244
TN (mg/l)
1.2
1
0.8
0.6
0.4
0.2
0
0
1
2
3
4
5
6
7
8
DO (mg/l)
Figure A- 5. Correlation Between DO and TN in WBID 3186D
Station 21FLSFWMKREA78 in WBID 3186D
35
Temperature (C)
30
25
y = -3.3585x + 42.694
R2 = 0.6885
20
15
10
5
0
0
1
2
3
4
5
6
7
DO (mg/l)
Figure A- 6. Correlation Between Temperature and DO in WBID 3186D
Unionized Ammonia in WBID 3244
Criteria
Figure A- 7. Unionized Ammonia Data in WBID 3244
74
11
/1
/9
8
4/
15
/9
8
9/
27
/9
7
3/
11
/9
7
8/
23
/9
6
2/
5/
96
7/
20
/9
5
1/
1/
95
Concentration (mg/l)
Unionized Ammonia
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
8
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Unionized Ammonia in WBID 3247
Unionized Ammonia
Criteria
Concentration (mg/l)
0.07
0.06
0.05
0.04
0.03
0.02
0.01
10
/2
/1
99
9
12
/6
/1
99
8
2/
9/
19
98
4/
15
/1
99
7
6/
19
/1
99
6
8/
24
/1
99
5
10
/2
8/
19
94
1/
1/
19
94
0
Figure A- 8. Unionized Ammonia Data in WBID 3247
Table A- 1. Percentile Concentrations for Unionized Ammonia in WBID 3244 and 3247
Percentile
WBID 3244
(mg/l)
WBID 3247
(mg/l)
10%
0.0023
0.0012
25%
0.0058
0.0045
50%
0.0143
0.0095
75%
0.027
0.0148
90%
0.042
0.011
95%
0.05
0.0283
Table A- 2. Calculation of TMDL and Percent Reduction for Unionized Ammonia
WBID
Flow (acre-ft/yr) Existing Conditions
Conc
(mg/l)
Load
(lb/day)
TMDL Conditions
Conc
(mg/l)
Percent
Reduction
Load
(lb/day)
3244
11,815
0.05
4.40
0.02
1.76
60%
3247
12,045
0.0283
2.54
0.02
1.79
29%
Load (lb/day) = flow (ac-ft/yr)*Conc(mg/l)*yr/365.25day*43560ft2/ac * 28.32 L/cf * lb/453592 mg
75
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Appendix B: Flow Records from DBHYDRO for WBIDs 3238 and 3238E
WBID 3238:
DBKEY
P0794
STATION AGENCY
S352_S
WMD
COUNTY TYPE
PAL
FLOW
UNITS
CFS
STAT
MEAN
FQ
DA
START
END
LAT
LONG
1965
2003
265150
803755
Period of Record Statistical Summary by Year For DBKEY P0794
For Period 19910101 to 20001231
DBKEY
Station
Data
----------------P0794
S352_S
FLOW
P0794
S352_S
FLOW
P0794
S352_S
FLOW
P0794
S352_S
FLOW
P0794
S352_S
FLOW
P0794
S352_S
FLOW
P0794
S352_S
FLOW
P0794
S352_S
FLOW
P0794
S352_S
FLOW
P0794
S352_S
FLOW
average annual flow (1991-2000):
WBID 3238E:
DBKEY STATION AGENCY
6739
S5A_P
WMD
Type
------
Year
---1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
216.0177 cfs
156396.8 acre-ft/yr
COUNTY TYPE
PAL
FLOW
Sample
------
Size
----365
366
365
365
365
366
365
365
365
366
UNITS
CFS
STAT
MEAN
Minimum Mean
Maximum Std. Dev.
------------- ------------- ------------- -----------0
38.419
636
109.3
0
225.492 1,050.00
313.28
0
265.94
910
304.99
0
109.641
924
240.2
0
334.784
962
341.65
0
270.38
798
277.74
0
123.123
755
207.56
0
251.303 1,100.00
370.64
0
305.013
921.22
310.33
-53
236.082
931
283.78
FQ
DA
START
END
LAT
LONG
1985
2006
264104
802203
Period of Record Statistical Summary by Year For DBKEY 06739
For Period 19850531 to 20060502
DBKEY Station
Data Type
Year
Sample Size Minimum Mean
Maximum Std. Dev.
------------------------------------------------ ------------- ------------- -----------6739
S5A_P
FLOW
1985
215
0
549.297 4,173.07
898.36
6739
S5A_P
FLOW
1986
364
0
266.296 3,502.01
582.21
6739
S5A_P
FLOW
1987
359
0
366.862 4,706.30
856.68
6739
S5A_P
FLOW
1988
365
0
303.989 3,635.56
712.94
6739
S5A_P
FLOW
1989
359
0
207.677 2,532.73
510.41
6739
S5A_P
FLOW
1990
365
0
137.51
2,600.84
390.23
6739
S5A_P
FLOW
1991
365
0
394.972 4,769.98
781.47
6739
S5A_P
FLOW
1992
366
0
571.772 4,503.82
950.58
6739
S5A_P
FLOW
1993
365
0
551.488 3,863.70
830.81
6739
S5A_P
FLOW
1994
365
0
753.22
4,724.50 1,074.84
6739
S5A_P
FLOW
1995
365
0
596.236 4,520.15
919.78
6739
S5A_P
FLOW
1996
366
0
284.581 3,361.20
608.87
6739
S5A_P
FLOW
1997
365
0
366.84
4,231.94
598.34
6739
S5A_P
FLOW
1998
365
0
353.673 4,778.59
851.67
6739
S5A_P
FLOW
1999
365
0
530.973 4,530.77
839.68
6739
S5A_P
FLOW
2000
366
0
349.165 4,275.48
677.62
6739
S5A_P
FLOW
2001
365
0
324.897 3,991.22
711.23
6739
S5A_P
FLOW
2002
365
0
764.04
3,736.14
820.35
6739
S5A_P
FLOW
2003
365
0
533.673 3,127.59
697.88
6739
S5A_P
FLOW
2004
366
0
596.881 4,837.29
979.74
6739
S5A_P
FLOW
2005
365
0
327.089 4,053.99
619.92
6739
S5A_P
FLOW
2006
122
0
133.344 3,663.61
517.21
average annual flow (1991-2000):
475.292 cfs
344111.4 acre-ft/yr
76
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Appendix C: Derivation of WLA for Clewiston STP (FL0040665)
Table C- 1. Summary of Effluent Data
Effluent Data Summary (5/31/98 - 6/30/04)
BOD
TP
TN
Ave. Annual Conc (mg/l)
3.260
0.203
2.620
Ave. Annual Load (lb/day)
55.842
3.235
44.977
Max. Daily Conc (mg/l)
4.280
0.305
3.323
Ave. Monthly Conc (mg/l)
3.057
0.199
2.417
142.889
6.133
59.728
Ave. Annual Conc (mg/l)
20
0.7
5
Ave. Monthly Conc (mg/l)
25
0.875
6.25
Max. Daily Conc (mg/l)
60
1.4
10
Ave. Annual Load (lb/day)
Report
Report
Report
Ave. annual load (lb/day, based on existing permit limits)
250.38
8.76
62.59
Ave. monthly load (lb/day, based on existing permit limits)
312.97
10.95
78.24
Ave. Monthly Load (lb/day)
Permit Limits
Note: DMR reports indicate annual average flow from the facility is about 2.18 MGD.
WLA using TMDL target values (TP=77ppb, TN=1.2mg/l, BOD=2 mg/l):
WLA (lb/day) = Flow (MGD) * Conc (mg/l) * 3.785 l/gal * 106 * lb/453,592.4 mg
WLA (Mton/yr) = lb/day * 365.25 day/yr * Mton/2204.623 lb
Using the design flow of 1.5 MGD and annual average TP conc. of 0.077 mg/l the WLA is:
WLA (for TP) = 1.5x106 * 0.077 mg/l * 3.785 l/gal * lb/453,592.4 mg = 0.96 lb/day
WLA (for TN) = 1.5x106 * 1.2 mg/l * 3.785 l/gal * lb/453,592.4 mg = 15.02 lb/day
77
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
WLA (for BOD) = 1.5x106 * 2 mg/l * 3.785 l/gal * lb/453,592.4 mg = 25.03 lb/day
In terms of Mton/yr, the WLA values are:
WLA (for TP) = 0.96 lb/day * 365.25 day/yr * Mton/2204.623 lb = 0.16 Mton/yr
WLA (for TN) = 15.02 lb/day * 365.25 day/yr * Mton/2204.623 = 2.49 Mton/yr
WLA (for BOD) = 25.03 lb/day * 365.25 day/yr * Mton/2204.623 = 4.15 Mton/yr
Table C- 2. TMDL Components for WBID 3246
Parameter
WLA (lb/day)
LA (lb/day)
TMDL (lb/day)
TP
0.96
9.11
10.07
TN
15.02
251.89
266.91
BOD
25.03
408.87
433.90
Note: The LA component is calculated as the difference between the TMDL load and the
WLA. The TMDL load is based on the allocation provided in the LOPP.
Verify Concentrations corresponding to LA values are achievable (using LOPP flows):
The LOPP states the annual average flow is 29,164 acre-ft/yr (or 40.3 cfs = 26 mgd); the
TP concentration corresponding to an LA of 1.51 Mton/yr (or 9.11 lb/day) is:
LA concentration = 9.11 lb/day * 453592.4 mg/lb / (26 mgd * 3.785 l/gal * 106)
TP Conc. = 0.042 mg/l = 42 ppb. This concentration is achievable.
The TN concentration corresponding to the LA component is calculated as follows:
LA = (41.73 Mton/yr * 2204.623 lb/Mton) / 365.25 day/yr = 251.89 lb/day
TN Conc = 251.89 lb/day * 453592.4 mg/lb /(26 mgd * 3.785 l/gal * 106) = 1.16 mg/l
BOD TMDL Calculation:
TMDL= (26 x 106 gal/day * 2 mg/l * 3.785 l/gal) / 453592.4 mg/lb = 433.90 lb/day = 71.89 Mton/yr
BOD reduction (from point sources) = (55.842 lb/day – 25.03 lb/day)/55.842 lb/day * 100 = 55%
In conclusion, permit modifications are required for BOD, TP and TN. The facility should not cause
or contribute to nutrient impairment in the WBID as the concentrations associated with these loading
values represent natural background conditions. Site specific alternative criteria may need to be
developed for DO as it may not be possible to achieve the statewide DO criteria of 5 mg/l after
controlling pollutant loading or concentrations to a natural pollutant condition in the waterbody.
78
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Annual TP Load for Clewiston WWTP
Existing
WLA
Load (lb/day)
6
5
4
3
2
1
1/
1/
1
7/ 99 8
20
/1
9
2/ 98
5/
1
8/ 99 9
24
/1
99
3/
11 9
/2
9/ 0 00
27
/2
00
4/
15 0
/2
11 0 01
/1
/2
00
5/
20 1
/2
12 0 02
/6
/2
00
6/
24 2
/2
1/ 0 03
10
/2
7/ 0 04
28
/2
00
4
0
Figure C- 1. Annual average TP Load in Effluent of FL0040665
12
/6
/2
00
2
10
/2
/2
00
3
7/
28
/2
00
4
10
/2
8/
19
98
8/
24
/1
99
9
6/
19
/2
00
0
4/
15
/2
00
1
2/
9/
20
02
100
90
80
70
60
50
40
30
20
10
0
1/
1/
19
98
Load (lb/day)
Annual TN Load for Clewiston WWTP
Figure C- 2. Annual average TN Load in Effluent of FL0040665
79
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
DO Measurements and DMR Data
DMR Data
Criteria
1/
1/
19
98
9/
8/
19
98
5/
16
/1
99
9
1/
21
/2
00
0
9/
27
/2
00
0
6/
4/
20
01
2/
9/
20
02
10
/1
7/
20
02
6/
24
/2
00
3
2/
29
/2
00
4
11
/5
/2
00
4
Concentration (mg/l)
WQ Data
20
18
16
14
12
10
8
6
4
2
0
Figure C- 3. Comparison of DO in Effluent of FL0040665 and DO Measured in Industrial Canal
Instream DO Concentrations and Effluent BOD and DO levels
Effluent DO (mg/l)
Instream DO Conc. (mg/l)
20
18
16
14
12
10
8
6
4
2
0
9/
30
/1
99
8
2/
27
/1
99
9
7/
27
/1
99
12
9
/2
4/
19
99
5/
22
/2
00
10
0
/1
9/
20
00
3/
18
/2
00
1
8/
15
/2
00
1
1/
12
/2
00
2
6/
11
/2
00
2
11
/8
/2
00
2
4/
7/
20
03
9/
4/
20
03
2/
1/
20
04
6/
30
/2
00
4
Concentration
Effluent Daily BOD (mg/l)
Figure C- 4. Comparison of Effluent DO and BOD Concentrations to Instream DO Concentrations
80
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Appendix D: Calculation of Limiting Nutrient
Table D- 1. Limiting Nutrient Conditions for Existing and TMDL Conditions
WBID
Existing Conditions (ave. values)
TN
TP
TMDL Conditions
Limiting
Nutrient/value
TN
TP
Limiting
Nutrient/value
3186B
1.31
0.08 Phosphorus / 36.26
1.2
0.077
Phosphorus / 34.5
3186C
1.86
0.39 Co-Limiting / 10.56
1.2
0.077
Phosphorus / 34.5
3186D
1.07
0.07 Phosphorus / 33.85
1.2
0.077
Phosphorus / 34.5
3188
1.49
0.47 Nitrogen / 7.02
1.2
0.077
Phosphorus / 34.5
3188A
1.42
0.19 Co-Limiting / 16.55
1.2
0.077
Phosphorus / 34.5
3192C
2.13
0.27 Co-Limiting / 17.47
1.2
0.077
Phosphorus / 34.5
3199B
2.97
1.59 Nitrogen / 4.14
1.2
0.077
Phosphorus / 34.5
3203A
2
0.5 Nitrogen / 8.86
1.2
0.077
Phosphorus / 34.5
3203B
2.18
0.94 Nitrogen / 5.14
1.2
0.077
Phosphorus / 34.5
3204
1.94
0.15 Co-Limiting / 28.64
1.2
0.077
Phosphorus / 34.5
3205
1.87
0.48 Nitrogen / 8.63
1.2
0.077
Phosphorus / 34.5
3205D
2.22
0.63 Nitrogen / 7.80
1.2
0.077
Phosphorus / 34.5
3206
1.71
0.19 Co-Limiting / 19.93
1.2
0.077
Phosphorus / 34.5
3209
1.68
0.11 Phosphorus / 33.82
1.2
0.077
Phosphorus / 34.5
3213A
1.86
0.45 Nitrogen / 9.15
1.2
0.077
Phosphorus / 34.5
3213B
2.02
0.39 Co-Limiting / 11.47
1.2
0.077
Phosphorus / 34.5
3213C
1.9
0.29 Co-Limiting / 14.51
1.2
0.077
Phosphorus / 34.5
3213D
1.92
1.2
0.077
Phosphorus / 34.5
1.1 Nitrogen / 3.86
81
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
WBID
Existing Conditions (ave. values)
TN
TP
US EPA Region 4
TMDL Conditions
Limiting
Nutrient/value
TN
TP
Limiting
Nutrient/value
3233
2.12
0.14 Phosphorus / 33.53
1.2
0.077
Phosphorus / 34.5
3238
2.56
0.19 Co-Limiting / 29.83
1.2
0.077
Phosphorus / 34.5
3238E
2.98
0.1 Phosphorus / 65.99
1.2
0.077
Phosphorus / 34.5
3244
4.28
0.3 Phosphorus / 31.59
1.2
0.077
Phosphorus / 34.5
3246
2.31
0.1 Phosphorus / 51.15
1.2
0.077
Phosphorus / 34.5
3247
3.77
0.1 Phosphorus / 83.48
1.2
0.077
Phosphorus / 34.5
3248
3.87
0.13 Phosphorus / 65.92
1.2
0.077
Phosphorus / 34.5
3248A
2.15
0.11 Phosphorus / 43.28
1.2
0.077
Phosphorus / 34.5
3250
3.69
0.1 Phosphorus / 81.71
1.2
0.077
Phosphorus / 34.5
3251
2.11
0.08 Phosphorus / 58.40
1.2
0.077
Phosphorus / 34.5
3253
3.3
0.08 Phosphorus / 91.34
1.2
0.077
Phosphorus / 34.5
1436
1.69
0.07 Phosphorus / 53.46
1.2
0.077
Phosphorus / 34.5
Limiting nutrient calculations are based on molar ratio of average TN to TP concentrations
measured at all stations in the WBID. Concentrations are converted to molar values by dividing
TN and TP concentrations by their molecular weight, or 14 for Nitrogen and 31 for Phosphorus.
The spatial distribution of the limiting nutrient in each impaired WBID is shown in Figure D- 1.
An example calculation is as follows:
WBID 3186B: TN/TP = (1.31/14) / (0.08/31) = 0.0936/0.0026 = 36.26
For TMDL conditions: TN/TP = (1.2/14) / (0.077/31) = 34.5
82
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
N
W
LOPP SWMM Basin
TN:TP Ratio
Nitrogen
Co-Limiting
Phosphorus
Waterbody
LAKE/POND
RESERVOIR
SEA/OCEAN
STREAM/RIVER
CANAL/DITCH
SWAMP/MARSH
E
S
S-65A
S-65D
S-65B
S-191
C-40
C-41
C-44
S-133
S-135
L-8
S-5A
S-4
S-2
S-3
10
0
10
20
30
40
50
60
70
80
Figure D- 1. Spatial Distribution of Limiting Nutrient (based on average conditions)
83
90
100 Miles
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Table D- 2. Post TMDL Conditions Using a Single Nutrient Approach (Phosphorus)
WBID
3186B
3186C
3186D
3188
3188A
Median TN
(mg/l)
1.20
161
1.03
1.55
1.37
Predicted
Concentration
Limiting Condition (% time)
P-Limited
Co-Limited
N-Limited
Low (58 ppb)
95%
4.7%
0.2%
Mean (77 ppb)
71%
29.2%
0.2%
High (98 ppb)
34%
66.2%
0.2%
Low (49 ppb)
100.0%
0.0%
0.0%
Mean (77 ppb)
96%
4%
0.0%
High (127 ppb)
36%
64%
0.0%
Low (63 ppb)
68%
27%
5%
Mean (77 ppb)
49%
46%
5%
High (152 ppb)
3%
84%
14%
Low (35 ppb)
99%
0%
0%
Mean (77 ppb)
84%
15%
0%
High (183 ppb)
17%
77%
6%
Low (53 ppb)
98%
2%
0%
Mean (77 ppb)
83%
17%
0%
High (122 ppb)
22%
77%
0%
84
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
WBID
3192C
3199B
3203A
3203B
3205
3205D
Median TN
(mg/l)
1.81
2.66
1.54
2.37
1.73
1.73
Predicted
Concentration
US EPA Region 4
Limiting Condition (% time)
P-Limited
Co-Limited
N-Limited
Low (44 ppb)
100.0%
0.0%
0.0%
Mean (77 ppb)
94%
6%
0.0%
High (122 ppb)
50.0%
50.0%
0.0%
Low (54 ppb)
100.0%
0.0%
0.0%
Mean (77 ppb)
98.0%
2.0%
0.0%
High (111 ppb)
88.0%
12.0%
0.0%
Low (53 ppb)
98.5%
1.4%
0.0%
Mean (77 ppb)
90.3%
9.7%
0.1%
High (96 ppb)
72.8%
27%
0.1%
Low (49 ppb)
100%
0%
0%
Mean (77 ppb)
99%
1%
0%
High (120 ppb)
83%
17%
0%
Low (54 ppb)
97%
3%
0%
Mean (77 ppb)
85%
15%
0%
High (111 ppb)
60%
40%
0%
Low (40 ppb)
100%
0%
0%
85
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
WBID
3213A
3213B
3213D
3204
3213C
Median TN
(mg/l)
1.79
1.75
2.14
1.76
Predicted
Concentration
US EPA Region 4
Limiting Condition (% time)
P-Limited
Co-Limited
N-Limited
Mean (77 ppb)
89%
11%
0%
High (121 ppb)
54%
46%
0%
Low (54 ppb)
99%
1%
0%
Mean (77 ppb)
98%
2%
0%
High (132 ppb)
50%
50%
0%
Low (39 ppb)
99.1%
0.5%
0.5%
Mean (77 ppb)
96.7%
2.8%
0.5%
High (121 ppb)
56.6%
42.5%
0.9%
Low (39 ppb)
100%
0%
0%
Mean (77 ppb)
96%
4%
0%
High (132 ppb)
68%
32%
0%
Low (52 ppb)
99%
1%
0%
Mean (77 ppb)
94%
6%
0%
High (123 ppb)
57%
43%
0%
Low (55 ppb)
100%
0%
0%
Mean (77 ppb)
100%
0%
0%
1.58
86
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
WBID
3233
3238
3238E
3244
3246
Median TN
(mg/l)
1.78
1.96
2.80
3.21
1.95
Predicted
Concentration
US EPA Region 4
Limiting Condition (% time)
P-Limited
Co-Limited
N-Limited
High (119 ppb)
47%
53%
0%
Low (58 ppb)
100%
0%
0%
Mean (77 ppb)
98%
2%
0%
High (104 ppb)
81%
19%
0%
Low (59 ppb)
100%
0%
1%
Mean (77 ppb)
99%
1%
1%
High (98 ppb)
93%
7%
1%
Low (57 ppb)
100%
0%
0%
Mean (77 ppb)
97%
3%
0%
High (106 ppb)
86%
14%
0%
Low (48 ppb)
100%
0%
0%
Mean (77 ppb)
100%
0%
0%
High (171 ppb)
58%
42%
0%
Low (55 ppb)
100%
0%
0%
Mean (77 ppb)
99%
1%
0%
High (110 ppb)
80%
20%
0%
87
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
WBID
3247
3248
3248A
3250
3251
Median TN
(mg/l)
3.15
3.47
1.71
3.55
1.65
Predicted
Concentration
US EPA Region 4
Limiting Condition (% time)
P-Limited
Co-Limited
N-Limited
Low (59 ppb)
100%
0%
0%
Mean (77 ppb)
99%
1%
0%
High (113 ppb)
88%
12%
0%
Low (53 ppb)
99%
1%
0%
Mean (77 ppb)
99%
1%
0%
High (118 ppb)
86%
14%
0%
Low (53 ppb)
99%
0%
0%
Mean (77 ppb)
99%
0%
1%
High (118 ppb)
75%
0%
25%
Low (55 ppb)
100%
0%
0%
Mean (77 ppb)
100%
0%
0%
High (120 ppb)
96%
4%
0%
Low (53 ppb)
100%
0%
0%
Mean (77 ppb)
97%
3%
0%
High (116 ppb)
60%
40%
0%
88
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
WBID
3253
3206
3209
1436
Median TN
(mg/l)
2.52
1.60
1.36
1.63
Predicted
Concentration
US EPA Region 4
Limiting Condition (% time)
P-Limited
Co-Limited
N-Limited
Low (62 ppb)
100%
0%
0%
Mean (77 ppb)
100%
0%
0%
High (117 ppb)
80%
20%
0%
Low (53 ppb)
98%
1%
1%
Mean (77 ppb)
91%
8%
1%
High (138 ppb)
30%
68%
2%
Low (54 ppb)
97.2%
2.6%
0.2%
Mean (77 ppb)
77.6%
22.1%
0.2%
High (116 ppb)
39.6%
60.1%
0.3%
Low (60 ppb)
94%
6%
0%
Mean (77 ppb)
88%
13%
0%
High (87 ppb)
81%
19%
0%
The low and high values in the table represent the expected fluctuations of phosphorus under a post
TMDL implementation scenario. Existing fluctuations were analyzed and applied to each WBID
under a post TMDL condition. Existing fluctuations were derived by applying the percent departure
from the median that is represented by the 75th and 25th percentile of existing data. Those same
percent departures were applied to the post TMDL concentration of 77 ppb to represent the low and
high end of natural variability. This analysis demonstrates the complexity of applying a limiting
nutrient only strategy in a non steady state environment.
89
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
DO and BOD Correlation at
Sta 21FLSFWMKRFNC38 in WBID 3186B
16
BOD (mg/l)
14
12
y = -1.6495x + 10.595
R2 = 0.3735
10
8
6
4
2
0
0
1
2
3
4
DO (mg/l)
5
6
7
The trendline equation shown in the above plot is used to determine the BOD target.
To maintain DO levels above 5 mg/l, BOD would need to be equal to or less than:
BOD = -1.6495x + 10.595
BOD = -1.6495 (5) + 10.595
BOD =
2.3655 mg/l
Average Annual Flow estimated for WBID 3186B is:
Average Annual BOD load is:
Daily BOD load is:
46165 acre-ft/yr
134.291 Mton/yr
811.1263 lb/day
[LOPP, 2003]
Conversion Factors: 2204.623 lb/Mton
Existing Conditions:
Existing BOD loads are calculated using the average concentration measured at all stations in the
WBID between 1998 and 2001. This concentration is multiplied by the annual average flow and
converted to load as follows:
Mean BOD concentration = 3.81 mg/l
Existing Load = 3.81 mg/l * 46165 acre-ft/yr * 0.0012326 = 216.8 Mton/yr
Existing Load (lb/day) = 216.8 Mton/yr * yr/365.25 day * 2204.623 lb/Mton = 1309 lb/day
Conversion Factor: mg/L*acre-ft/yr * 43560 ft2/acre*28.317 L/cf * Mton/109mg = 0.0012326
Percent Reduction:
% Reduction = (Existing Load – TMDL Load) / Existing Load * 100
% Reduction = (216.8 – 134.291) / 216.8 = 38%
90
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Appendix F: Modeling Results of Natural Landuse Conditions
EPA’s PLOAD spreadsheet was used to estimate annual average TP, TN and BOD concentrations
resulting from a natural landuse condition. In the analysis existing “disturbed” landuse were
changed to half wetland and half forest for purposes of representing “natural” or undisturbed
conditions. In the analysis disturbed lands ere assumed to be all landuse categories with the
exception of forest, water, and wetlands. Seven WBIDs representing headwater tributaries in the
Lake Okeechobee watershed were selected for this analysis. Results of the analysis are shown in
Table F- 1.
Table F- 1. Model Results of Nutrient and BOD Concentrations for a Natural Landuse Condition
WBID
BOD
Total Nitrogen
Total Phosphorus
Load (lb/yr) Conc (mg/l) Load (lb/yr) Conc (mg/l) Load (lb/yr) Conc (mg/l)
3246
49598
2
26091
1.05
1742
0.07
1436
3697
2.08
1853
1.04
129
0.073
3188
125197
2.13
60905
1.04
4365
0.074
3203A
18435
2.04
9434
1.04
646
0.071
3213A
3696
2.01
1926
1.05
130
0.07
3206
54256
2.07
27366
1.04
1898
0.072
3213D
19100
1.99
10041
1.05
671
0.07
Average:
1.044
0.071
Note: disturbed land = all categories with the exception of water, forest and wetlands
% Disturbed
49%
45%
43%
48%
48%
46%
44%
The PLOAD model uses annual average rainfall and event mean concentrations (EMCs) to estimate
the loading transported off a particular landuse. The model assumes all lands are connected to the
stream, resulting in a conservative estimate of the load. The PLOAD model is based on the
following equation:
RVU = 0.05 – (0.09 * IU)
Where: RVU = runoff coefficient for land use type u, in inches runoff/inches rain; and IU = percent
impervious.
The pollutant load is calculated with the following equation:
LP = Ó U (P * PJ* RVU * CU* AU * 2.72 / 12)
Where: LP = Pollutant load, lbs
P = Precipitation, inches/year
PJ = Ratio of storms producing runoff (default = 0.9)
RVU= Runoff Coefficient for land use type u, inchesrun/inchesrain
CU = Event Mean Concentration for land use type u, milligrams/liter
AU = Area of land use type u, acres (In BASINS areas calculated from GIS data are
in square meters. PLOAD converts areas from square meters to acres prior to
using the information in the above equation)
An annual average precipitation value of 60 in/yr was assumed for the selected WBIDs based on
91
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
information found on SFWMD web page. The precipitation and storm ratio values are entered by the
user interactively. The loading rates are derived from the EMC tables while the land use areas are
interpreted from readily available landuse and watershed GIS data. EMC values assumed for the
various landuses are shown in Table F- 2.
Table F- 2. Land Use Runoff Concentrations (Event Mean Concentrations) in Southwest Florida 1
FLUCCS ID
1000
1100
1200
1300
1400
1500
1600
1700
1800
2000
3000
4000
5000
6000
7000
8000
1
Land Use
Urban Open
Low Density Residential
Medium Density Residential
High Density Residential
Commercial and Services
Industrial
Extractive (mines)
Institutional
Recreational
Agriculture
Rangeland
Forest/Rural Open
Water/ Wetlands
Water/ Wetlands
Rangeland
Communication and Transportation
BOD
7.4
4.3
7.4
11.0
17.2
9.6
9.6
7.4
4.3
3.8
3.8
1.23
2.63
2.63
3.8
6.7
Total N
1.12
1.64
2.18
2.42
2.83
1.79
1.18
1.12
1.64
2.32
2.32
1.09
1.01
1.01
2.32
2.23
Total P
0.180
0.191
0.335
0.490
0.430
0.310
0.150
0.180
0.191
0.344
0.344
0.046
0.090
0.090
0.344
0.270
Source: Harper, H. H. and D.M. Baker. 2003. Evaluation of Alternative Stormwater Regulations for Southwest Florida.
Environmental Research & Design, Inc. (Table 7)
92
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
Appendix G. Rationale for Controlling Nitrogen in Impaired WBIDs
Three conditions were considered in determining whether to control nitrogen in the Lake
Okeechobee tributaries. Table G- 3 displays these conditions for each WBID. If any one of the three
conditions were true, controlling nitrogen was considered essential to meeting the designated use in
the WBID.
Table G- 3. Decision Rationale for Controlling Nitrogen in Lake Okeechobee Tributaries
WBID Does DO Correlate with
Nitrogen (see note 1)
Is
TP
Limiting Is TNWBID > Threshold TNLAKE
Condition LESS than (see note 3)
90% time (see note 2)
No
Yes – control N (TP No
limited 71% of time)
No
No
No
Yes – control N (TP No
limited 49% of time)
No
Yes – control N (TP Yes – control N (TN: 1.55 > 1.2)
limited 84% of time)
No
Yes – control N (TP Yes – control N (TN: 1.37 > 1.2)
limited 83% of time)
3192C
No
No
Yes – control N (TN: 1.81 > 1.2)
3199B
No
No
Yes – control N (TN: 2.66 > 1.2)
3203A
No
No
Yes – control N (TN: 1.54 > 1.2)
3203B
No
No
Yes – control N (TN: 2.37 > 1.2)
3204
No
No
Yes – control N (TN: 1.76 > 1.2)
No
Yes – control N (TP Yes – control N (TN: 1.73 > 1.2)
limited 85% of time)
No
Yes – control N (TP Yes – control N (TN: 1.73 > 1.2)
limited 89% of time)
3186B
3186C
3186D
3188
3188A
3205
3205D
Yes – control N (TN: 1.61 > 1.2)
93
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
WBID Does DO Correlate with
Nitrogen (see note 1)
US EPA Region 4
Is
TP
Limiting Is TNWBID > Threshold TNLAKE
Condition LESS than (see note 3)
90% time (see note 2)
Yes – control N (TN: 1.60 > 1.2)
No
No
No
Yes – control N (TP Yes – control N (TN: 1.36 > 1.2)
limited 78% of time)
3213A
Yes (control N)
No
Yes – control N (TN: 1.79 > 1.2)
3213B
Yes (control N)
No
Yes – control N (TN: 1.75 > 1.2)
3213C
Yes (control N)
No
Yes – control N (TN: 1.58 > 1.2)
3213D
No
No
Yes – control N (TN: 2.14 > 1.2)
3233
Yes (control N)
No
Yes – control N (TN: 1.78 > 1.2)
3238
Yes (control N)
No
Yes – control N (TN: 1.96 > 1.2)
3238E
Yes (control N)
No
Yes – control N (TN: 2.80 > 1.2)
3244
Yes (control N)
No
Yes – control N (TN: 3.21 > 1.2)
3246
No
No
Yes – control N (TN: 1.95 > 1.2)
3247
Yes (control N)
No
Yes – control N (TN: 3.15 > 1.2)
3248
Yes (control N)
No
Yes – control N (TN: 3.47 > 1.2)
3248A
No
No
Yes – control N (TN: 1.71 > 1.2)
3250
Yes (control N)
No
Yes – control N (TN: 3.55 > 1.2)
3251
No
No
Yes – control N (TN: 1.65 > 1.2)
3253
Yes (control N)
No
Yes – control N (TN: 2.52 > 1.2)
Yes (control N)
Yes – control N (TP Yes – control N (TN: 1.63 > 1.2)
limited 88% of time)
3206
3209
1436
1. Data indicates correlation with ammonia, nitrate-nitrite, and/or total nitrogen
2. TP limiting condition reflects Post TMDL condition for implementing TP controls only
94
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
3. WBID TN represents median value for the WBID (IWR 24); threshold TN for Lake
Okeechobee corresponds to the proposed TMDL for St. Lucie Estuary (USEPA, 2006).
WBIDs showing a correlation between DO and Nitrogen are illustrated below.
TKN
WBID 3213A
4
3.5
3
2.5
2
1.5
1
0.5
0
y = -0.1416x + 2.2542
R2 = 0.2153
0
2
4
6
8
10
12
DO
Figure G- 1. Correlation Between DO and TKN in WBID 3213A
TN
WBID 3213A
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
y = -0.1131x + 2.2973
R2 = 0.1374
0
2
4
6
8
DO
Figure G- 2. Correlation Between DO and TN in WBID 3213A
95
10
12
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
3213B
4
y = -0.1345x + 2.227
R2 = 0.1887
3.5
3
TKN
2.5
2
1.5
1
0.5
0
0
2
4
6
8
10
12
DO
Figure G- 3. Correlation Between DO and TKN in WBID 3213B
3213B
4.5
4
y = -0.1064x + 2.2722
R2 = 0.1184
3.5
3
TN
2.5
2
1.5
1
0.5
0
0
2
4
6
DO
Figure G- 4. Correlation Between DO and TN in WBID 3213B
96
8
10
12
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
3213C
0.3
y = -0.0099x + 0.104
2
R = 0.2062
0.25
Ammonia
0.2
0.15
0.1
0.05
0
0
2
4
6
8
10
12
14
16
-0.05
DO
Figure G- 5. Correlation Between DO and Ammonia in WBID 3213C
3233
3
2.5
y = -0.051x + 0.4128
R2 = 0.2025
Ammonia
2
1.5
1
0.5
0
0
2
4
6
8
-0.5
DO
Figure G- 6. Correlation Between DO and Ammonia in WBID 3233
97
10
12
14
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
3238
3.5
3
y = -0.107x + 0.8951
R2 = 0.3014
2.5
Ammonia
2
1.5
1
0.5
0
0
2
4
6
8
10
12
14
16
-0.5
-1
DO
Figure G- 7. Correlation Between DO and Ammonia in WBID 3238
3238E
12
10
y = -0.3794x + 4.7827
R2 = 0.2551
8
TN
6
4
2
0
0
2
4
6
-2
DO
Figure G- 8. Correlation Between DO and TN in WBID 3238E
98
8
10
12
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
3244
6
y = -0.1938x + 1.9526
R2 = 0.2851
5
4
Ammonia
3
2
1
0
0
2
4
6
8
10
12
14
16
14
16
-1
-2
DO
Figure G- 9. Correlation Between DO and Ammonia in WBID 3244
3244
12
y = -0.3509x + 5.0746
2
R = 0.2176
10
8
TKN
6
4
2
0
0
2
4
6
8
-2
DO
Figure G- 10. Correlation Between DO and TKN in WBID 3244
99
10
12
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
3247
6
5
y = -0.1625x + 1.461
R2 = 0.4101
4
Ammonia
3
2
1
0
0
2
4
6
8
10
12
14
16
14
16
-1
-2
DO
Figure G- 11. Correlation Between DO and Ammonia in WBID 3247
3247
10
9
y = -0.1884x + 3.9827
2
R = 0.1163
8
7
TKN
6
5
4
3
2
1
0
0
2
4
6
8
DO
Figure G- 12. Correlation Between DO and TKN in WBID 3247
100
10
12
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
3248
3
y = -0.0908x + 0.8094
R2 = 0.3609
Ammonia
2
1
0
0
2
4
6
8
10
12
14
12
14
-1
DO
Figure G- 13. Correlation Between DO and Ammonia in WBID 3248
3248
7
y = -0.1679x + 1.5396
R2 = 0.2006
6
5
4
NOx
3
2
1
0
0
2
4
6
8
10
-1
-2
DO
Figure G- 14. Correlation Between DO and Nitrate-Nitrite (NOx) in WBID 3248
101
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
3250
12
10
y = -0.3794x + 4.7827
R2 = 0.2551
8
TN
6
4
2
0
0
2
4
6
8
10
12
-2
DO
Figure G- 15. Correlation Between DO and TN in WBID 3250
3250
6
y = -0.3001x + 3.9095
R2 = 0.2912
5
4
TKN
3
2
1
0
0
2
4
6
-1
DO
Figure G- 16. Correlation Between DO and TKN in WBID 3250
102
8
10
12
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
3250
3.5
y = -0.1135x + 0.959
R2 = 0.2476
3
2.5
Ammonia
2
1.5
1
0.5
0
0
2
4
6
8
10
12
10
12
-0.5
DO
Figure G- 17. Correlation Between DO and Ammonia in WBID 3250
3253
7
y = -0.3028x + 3.8918
2
R = 0.4887
6
5
TKN
4
3
2
1
0
0
2
4
6
DO
Figure G- 18. Correlation Between DO and TKN in WBID 3253
103
8
Lake Okeechobee Tributaries – Nutrient Total Maximum Daily Load
US EPA Region 4
3253
3.5
y = -0.2294x + 1.7608
R2 = 0.5962
3
2.5
Ammonia
2
1.5
1
0.5
0
0
2
4
6
8
10
12
-0.5
-1
DO
Figure G- 19. Correlation Between DO and Ammonia in WBID 3253
1436
5
4.5
y = -0.1453x + 2.2419
R2 = 0.1591
4
3.5
TN
3
2.5
2
1.5
1
0.5
0
0
1
2
3
4
5
DO
Figure G- 20. Correlation Between DO and TN in WBID 1436
104
6
7
8
9
10