TOTAL MAXIMUM DAILY LOAD (TMDL)
For
Fecal Coliforms
In
C-25 Canal West
(WBID 3160) and
C-25 Cowbone Creek (WBID 3189)
Prepared by:
US EPA Region 4
61 Forsyth Street SW
Atlanta, Georgia 30303
October 2008
SEPA
United States
Environmental Protection
Agency
In compliance with the provisions of the Federal Clean Water Act, 33 U.S.C §1251 et. seq., as
amended by the Water Quality Act of 1987, P.L. 400-4, the U.S. Environmental Protection
Agency is hereby establishing Total Maximum Daily Loads (TMDLs) for fecal coliforms in the
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C-25 Canal West (WBID 3160) and C-25 Cowbone Creek (WBID 3189). Subsequent actions
must be consistent with these TMDLs.
James D. Giattina Date
Director
Water Management Division
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Page Intentionally Blank
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TABLE OF CONTENTS
1. INTRODUCTION 6
2. PROBLEM DEFINITION 9
3. WATERSHED DESCRIPTION 9
4. WATER QUALITY STANDARD AND TARGET IDENTIFICATION 12
5. WATER QUALITY ASSESSMENT 13
6. SOURCE ASSESSMENT 16
6.1. Point Sources 17
6.2. Nonpoint Sources 17
6.3. Wildlife 17
6.4. Agricultural Animals 18
6.5. Onsite Sewerage Treatment and Disposal Systems (Septic Tanks) 18
6.6. Urban Development 19
7. ANALYTICAL APPROACH 20
7.1. Percent Reduction Approach for TMDL Development 20
8. DEVELOPMENT OF TOTAL MAXIMUM DAILY LOADS 21
8.1. Critical Conditions 22
8.2. Margin of Safety 22
8.3. Determination of TMDL, LA and WL A 22
8.4. Waste Load Allocations 22
8.5. Load Allocations 23
8.6. Seasonal Variation 23
8.7. Recommendations 23
REFERENCES 24
APPENDIX A: Water Quality Data 25
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LIST OF TABLES
Table 1: Land Cover Distribution for WBID 3160 12
Table 2: Land Cover Distribution for WBID 3189 12
Table 3: Monitoring Stations used in the Fecal Coliform TMDL for WBID 3160 13
Table 4: Monitoring Stations used in the Fecal Coliform TMDL for WBID 3189 14
Table 5. Summary of Fecal Coliform Monitoring Data 14
Table 6. Livestock Inventory by County (source: USDA, 2002) 18
Table 7. County Estimates of Septic Tank Installations 19
Table 8. Summary of Fecal Coliform TMDL Components 22
Table 9: Guide to Water Quality Remark Codes (Rcode column in data tables) 25
Table 10. Fecal Coliform Data Collected in WBID 3160 (Source: IWR Run 32) 25
Table 11. Calculation of Percentiles 26
LIST OF FIGURES
Figure 1: FDEP Group 2 River Basins 7
Figure 2: St. Lucie / Loxahatchee River Basin 8
Figure 3: C-25 Basin 1 Planning Unit 11
Figure 4: Water Quality Monitoring Stations in WBID 3160 15
Figure 5. Comparison between fecal coliform concentrations in C-25 Canal and rainfall..16
in
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LIST OF ABBREVIATIONS
AFO Animal Feeding Operation
BMP Best Management Practices
BPJ Best Professional Judgment
CAFO Concentrated Animal Feeding Operation
CFS Cubic Feet per Second
CWA Clean Water Act
DMR Discharge Monitoring Report
EPA Environmental Protection Agency
F.A.C. Florida Administrative Code
GIS Geographic Information System
LA Load Allocation
MGD Million Gallons per Day
MOS Margin of Safety
MPN Most Probable Number
MS4 Municipal Separate Storm Sewer Systems
NASS National Agriculture Statistics Service
NLCD National Land Cover Data
NPDES National Pollutant Discharge Elimination System
NRCS Natural Resources Conservation Service
OSTD Onsite Sewer Treatment and Disposal Systems
RM River Mile
SFWMD South Florida Water Management District
SLE St. Lucie Estuary
S TA Storm water Treatm ent Area
STORET STORage RETrieval database
TMDL Total Maximum Daily Load
USD A United States Department of Agriculture
USGS United States Geological Survey
WBID Water Body Identification
WCD Water Control District
WLA Waste Load Allocation
WQS Water Quality Standard
WWTF Wastewater Treatment Facility
IV
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SUMMARY SHEET
Total Maximum Daily Load (TMDL)
1. 303(d) Listed Waterbody Information
State: Florida
Major River Basin: St. Lucie River Basin
Impaired Waterbodies for TMDLs (1998 303(d) List):
WBID
3160
3189
Segment Name and
Type
C-25 Canal West
C-25 Canal West
River Basin
St. Lucie
St. Lucie
County
St. Lucie, Indian River
and Okeechobee
St. Lucie, Indian River
and Okeechobee
Constituent(s)
Fecal Coliform
Fecal Coliform
2. TMDL Endpoints (i.e., Targets) for Class III Waters (fresh and marine):
Fecal Coliform: 400 MPN/lOOml and 800 MPN/lOOml
3. Fecal Coliform Allocations:
Stream Name /
WBID
C-25 Canal (3 160)
C-25 Canal (3 189)
Criterion used to
develop TMDL
800 MPN/lOOml
400 MPN/lOOml
WLA
Continuous
N/A
N/A
MS4
95%
reduction
N/A
LA
95%
reduction
97%
reduction
TMDL
95%
reduction
97%
reduction
Notes: 1) To meet the 400 MPN/lOOml criterion in WBID 3160, a 67 percent reduction is
required and to meet the 800 MPN/lOOml criterion in WBID 3189, a 95 percent reduction is
needed (see Section 7.1); and 2) margin of safety is implicit in both TMDLs.
4 Endangered Species (yes or blank): Yes
5 EPA Lead on TMDL (EPA or blank): EPA
6. TMDL Considers Point Source, Nonpoint Source, or both: Both
7. Major NPDES Discharges to surface waters addressed in TMDLs:
St. Lucie County MS4 (FLR04E029)
Indian River County MS4 (FLR04E068)
Larson Dairy Barn #3 (FLA139254)
Note: MS4 permittees will only be responsible for reducing the anthropogenic loads
associated with stormwater outfalls they own or otherwise has responsible control over.
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
TOTAL MAXIMUM DAILY LOAD (TMDL)
FECAL COLIFORM IN C-25 CANAL WEST (WBIDS 3160 AND 3189)
1. INTRODUCTION
Section 303(d) of the Clean Water Act (CWA) 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 in-stream water quality conditions, so that states can
establish water quality based controls to reduce pollution from both point and nonpoint sources
and restore and maintain the quality of their water resources (USEPA, 1991).
The State of 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 watershed management approach is the framework FDEP
uses for implementing TMDLs. The state's 52 basins are divided into 5 groups. Water quality is
assessed in each group on a rotating five-year cycle. The Group 2 basin is shown in Figure 1 and
includes the St. Lucie and Loxahatchee River Basin (Figure 2). The St. Lucie and Loxahatchee
Basin encompasses many square miles. To provide a smaller-scale geographic basis for
assessing, reporting, and documenting water quality improvement projects, the FDEP subdivided
the Group 2 area into smaller areas called planning units. Planning units help organize
information and management strategies around prominent subbasin characteristics and drainage
features. To the extent possible, planning units were chosen to reflect subbasins that had
previously been defined by the South Florida Water Management District (SFWMD). The St.
Lucie and Loxahatchee Basin contains eight planning units: C-25/Basin 1, North St. Lucie, C-24,
C-23, South St. Lucie, C-44, Loxahatchee, and Coastal. Water quality assessments were
conducted on individual waterbody segments within planning units. Each waterbody segment is
assigned a unique waterbody identification (WBID) number. Waterbody segments are the
assessment units or polygons that have historically been used by the FDEP to define waterbodies
in their biannual inventory and reporting of water quality to EPA under Section 305(b) of the
federal Clean Water Act. The same WBIDs are also the assessment units identified in the FDEP's
biannual lists of impaired waters submitted to EPA as part of their reporting under Section 303(d)
of the Clean Water Act.
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
Apalachicola -Chipol
Mid die St. Johnsj
Tampa Bay TributariesL
I V
| Charlotte Harbor |
St. Lucia - Loxahatehe
Figure 1: FDEP Group 2 River Basins
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
St. Lucie - Loxahatchee
Group 2 Verified Listed
Waters
Interstates
US Routes
Major Rivers (lines)
Major Rivers
TMDL by Year
| 12005
1 WBID I |2Q1n
j 1998303d
I Planning Units
County Boundaries
Figure 2: St. Lucie / Loxahatchee River Basin
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
2. PROBLEM DEFINITION
Florida's final 1998 Section 303(d) list identified WBIDs 3160 and 3189 in the St. Lucie River
Basin as not supporting water quality standards (WQS) due to coliform bacteria. After assessing
all readily available water quality data, EPA determined fecal coliform TMDLs are needed in
WBIDs 3160 and 3189. The locations of these WBIDs are shown in Figure 2. The TMDLs
addressed in this document 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).
WBIDs 3160 and 3189 are designated as a Class III fresh water. The designated use of Class III
waters is recreation, propagation and maintenance of a healthy, well-balanced population offish
and wildlife. Class III waters are further categorized based on fresh or marine waters. Water
quality criteria for fecal and total coliform do not vary between Class III fresh or marine waters.
3. WATERSHED DESCRIPTION
FDEP manages water resources based on river basins. The river basins are organized from large
groups of major river basins to smaller watersheds called planning units, and finally to small
waterbody polygons called WBIDs. The following information is from FDEP's Basin Status
Report for St. Lucie and Loxahatchee (FDEP, 2003).
In the St. Lucie Basin, most of the land in non-coastal areas is used for the production of citrus
crops and beef cattle. The extensive network of canals that drain these agricultural areas transport
stormwater runoff containing nutrients, sediment, bacteria, and other pollutants. These reach the
natural drainage-ways (such as the North and South Forks of the St. Lucie River) and ultimately
the St. Lucie Estuary and the South Indian River Lagoon. The St. Lucie Canal (C-44), the inland
waterway that connects Lake Okeechobee to Florida's east coast, transports regulated releases of
water from Lake Okeechobee and runoff from agricultural areas within the C-44 basin. Other
major canals also transport storm-water from inland agricultural areas to the estuary. Canals C-23
and C-24 discharge water into the North Fork of the St. Lucie River and the C-25 Canal
discharges to the Indian River Lagoon. Urban and residential areas continue to expand in the
coastal areas, with polluted urban stormwater runoff and seepage from septic tanks also
contributing to the water quality problems in streams and canals. As a result, portions of the St.
Lucie Estuary (SLE) appear to be impaired by nutrients, copper, and low levels of DO. Other
evidence of impairment was gathered for the SLE segments in a FDEP South East District
biological survey (Graves et al., 2002). Sediment accumulation, decline of sea-grasses and
oysters, algal blooms, fish kills, and low diversity of benthic macroinvertebrates in the SLE
comprise this body of evidence.
WBIDs 3160 and 3189 are in the C-25 Canal planning unit of the St. Lucie Basin. These two
WBIDs are covered by this TMDL report since WBID 3189 is surrounded by and flows into
WBID 3160. The planning unit includes the watershed of the C-25 Canal (also known as Belcher
Canal), which transports water eastward across northern St. Lucie County from near the St.
Lucie-Okeechobee County border. It includes the C-25, Basin 1, and C-25 East subbasins that are
defined by SFWMD. The USGS includes all of these but Basin 1 in the Southeast Florida Coast
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
hydrologic unit. Basin 1 lies in the Indian River South hydrologic unit, as defined by USGS. The
planning unit includes a complex network of canals primarily for agricultural drainage that has
created a conveyance for discharge to the IRL. Runoff from the western part of the planning unit
can discharge southward to the C-24 Canal via the C-25 extension (C-25 EXT). Runoff from the
eastern and central portions of this subbasin is conveyed eastward through the S-99 structure on
the C-25 Canal. Basin 1, east of S-99, receives drainage from the Ft. Pierce Farms Water Control
District (WCD) that was established under Chapter 298, Laws of Florida. The Ft. Pierce Farms
WCD Canal #1 is the primary surface water conveyance for Basin 1, providing drainage of the
agricultural area and inhibiting saltwater intrusion. Canal #1 and C-25 discharge into the South
IRL through the mouth of Taylor Creek at Ft. Pierce. The eastern part of this planning unit
includes the northern edge of the Ft. Pierce city limits. Figure 3 is a composite map of this
planning unit that shows potentially impaired waters and potential point sources of pollution.
Approximately 10 percent of the planning unit area is defined as wetland and 15 percent listed as
pine flatwoods. The largest contiguous wetland area, an extension of the St. Johns Marsh, is
located in the northwestern corner of St. Lucie County. One state-managed natural area exists in
the C-25/Basin 1 planning unit. The Green Swamp Preserve is located in the northwestern
corner. Most waterbodies within this planning unit are agricultural canals used for drainage
and/or irrigation that feed the conveyance system provided by C-25 and other SFWMD canals.
Although classified as Class III waters, canals are not capable of supporting the diverse
ecosystems characteristic of natural streams.
The C-25/Basin 1 planning unit is primarily an agricultural area. Efforts to reduce pollutant
loadings to storm-water from individual agricultural land holdings are tied to the active
participation of local citrus growers and cattlemen in agricultural best management practices
(BMP). These actions are assisted by Department of Agriculture and Consumer Services,
University of Florida Institute of Food and Agricultural Science, U.S. Department of Agriculture
Natural Resources Conservation Service and the FDEP Under the Indian River Lagoon South
Feasibility Study, a regional water storage reservoir and a storm-water treatment area (STA) are
proposed within this unit. This project will include a 741-acre aboveground reservoir and a 163-
acre STA at the S-99 structure on the C-25 Canal. The system will be used to capture local runoff
from the C-25 subbasin and the Ft. Pierce Farms WCD. The purpose of this component is to
provide peak flow attenuation, a water supply for irrigation, and reductions in concentrations of
nutrients, pesticides, and other contaminants. Water quality will be improved in the canal east of
the STA and the southern Indian River Lagoon.
WBID 3160 is a large polygon of over 96,000 acres that surrounds the much smaller WBID 3189
that contains only 741 acres. Cowbone Creek is a channelized stream system in the western part
of the planning unit that makes up WBID 3189. Land cover in WBIDs 3160 and 3189 is mostly
agriculture and wetlands, with about 81 and 52 percent agriculture and 12 and 43 percent
wetlands, respectively. The land cover distribution for this and other cover types is shown in
Table 1 for WBID 3160 and Table 2 for WBID 3189. Land cover is based on a 1999 coverage
provided by the SFWMD. WBID 3160 includes most of the C-25 Canal planning unit.
10
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
* Oomestc and industrial
waslewattff facilliv
discharging to surface water
* Domestic and industrial
waslewater facility
discharging to ground water
O Wastewater facility greater
than 0,1 MGO
4- Aciiva landfill (Class I, II, III, CSDj
Q State-funded hazardous wasfe siie
Superfund hazardous waste site
n SFWMD structure
Area o( toown ground wator
contamination
C-25/Basin 1 Planning Unit
Walsrbody identification boundary
Outstanding Florida Waters
303d listed waterbody segment
PotenlBly impaired waterbotfy s^menl Sasec! on
lmf>aimd Waters Ryle evaluatkm
ftote: Featyms from legend not shown on this
planning ynii m^j were not reported as
being present.
~^r
Figure 3: C-25 Basin 1 Planning Unit
11
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
Table 1: Land Cover Distribution for WBID 3160
Land Cover
Residential (1100-1390)
Commercial, Industrial, Public (1400, 1500, 1800)
Agriculture (2000 series)
Rangeland (3000 series)
Forest (4000 series)
Water (5000 series)
Wetlands (6000 series)
Barren & Extractive (7000, 1600)
Transportation & Utilities (8000 series)
TOTAL (acres)
Acreage
260
42
78448
686
1074
3022
11278
1063
563
96436
Percentage
0%
0%
81%
1%
1%
3%
12%
1%
1%
Table 2: Land Cover Distribution for WBID 3189
Land Cover
Residential (1100-1390)
Commercial, Industrial, Public (1400, 1500, 1800)
Agriculture (2000 series)
Rangeland (3000 series)
Forest (4000 series)
Water (5000 series)
Wetlands (6000 series)
Barren & Extractive (7000, 1600)
Transportation & Utilities (8000 series)
TOTAL (acres)
Acreage
0
0
386
0
21
12
322
0
0
741
Percentage
0%
0%
52%
0%
3%
2%
43%
0%
0%
4. WATER QUALITY STANDARD AND TARGET IDENTIFICATION
The water quality criteria for protection of Class III waters are established by the State of Florida
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.
Fecal coliforms are a subset of the total coliform group and indicate the presence of fecal
material from warm-blooded animals. Total coliform bacteria generally indicate the presence of
soil-associated bacteria and result from natural influences on a water body such as rainfall runoff
as well as sewage inflows. The most probable number (MPN) or membrane filter (MF) counts
per 100 milliliter (ml) of fecal coliform bacteria shall not exceed a monthly average of 200, nor
exceed 400 in 10 percent of the samples, nor exceed 800 on any one day. Monthly averages shall
be expressed as geometric means based on a minimum of 10 samples taken over a 30-day period.
The geometric mean criteria reflect chronic or long-term water quality conditions whereas the
400 and 800 values reflect acute or short-term conditions. The target for these TMDLs are is the
12
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
daily 800 MPN/100 ml and the "not to exceed 400 in 10 percent of the samples" criteria, since
insufficient monthly data were collected to evaluate the monthly average 200 criteria.
5. WATER QUALITY ASSESSMENT
To determine the status of surface water quality in Florida, three categories of data, chemistry
data, biological data, and fish consumption advisories, were evaluated to determine potential
impairments. The level of impairment is defined in the Identification of Impaired Surface Waters
Rule (IWR), Section 62-303 of the Florida Administrative Code (F.A.C.). The IWR defines
FDEP's threshold for identifying water quality limited WBIDs to be included on the State's 303
(d) list. In addition, all waters on the 1998 303 (d) list that were not delisted remain on the
current 303 (d) list and require TMDLs. WBIDs 3160 and 3189 are on FDEP's planning list for
fecal coliform bacteria. EPA assessed these WBIDs using data reported in IWR Run 32 and
concluded that they are impaired and fecal coliform TMDLs are required (see Appendix A).
FDEP maintains ambient monitoring stations throughout the basin. Table 3 provides a list of the
monitoring stations in WBID 3160 used in the development of the TMDL. The spatial
distribution of the monitoring stations is shown in Figure 4. Data were not collected in WBID
3189; however, stations 21FLA26010429 and 21FLBRA3160-C are located downstream of
WBID 3189 and are the only data available to characterize WBID 3189 (see Table 4). Therefore,
the data collected at these two stations were used in the development of the TMDL for WBID
3189. Table 5 summarizes the fecal coliform monitoring data by station in the two WBIDs.
Violations of the fecal coliform criteria often occur in response to rainfall events. Precipitation
data collected at the St. Lucie County Airport (National Oceanic Atmospheric Administration
Station 12895) located near WBID 3160 was plotted with the fecal coliform results in WBID
3160 to identify conditions when violations occurred (see Figure 5). In most instances,
exceedances of the criteria occur in response to rain events while at other times exceedances
occur during dry conditions. Implementation of this TMDL should address controlling nonpoint
sources during both wet and dry weather conditions. Rainfall data were not available in WBID
3189, so a precipitation plot with fecal coliform correlations could not be developed for WBID
3189.
Table 3: Monitoring Stations used in the Fecal Coliform TMDL for WBID 3160
Station ID
21FLA 26010429
Station Name
COWBONE CREEK AT SR 68
Number of
Observations
12
Start Date
2/15/1996
End Date
8/4/1998
13
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
21FLBRA3160-A
21FLBRA3160-B
21FLBRA3160-C
21FLWPB28042331
21FLA 26010429
3 160 - Cowbone Creek -
Header Rd dead ends at canal
3 160 - Cowbone Creek - Bridge
W of Header Canal Rd station
3 160 - Cowbone Creek -
Cowbone Creek off 68
CC1 - C-25 @ N HEADER
CANALRD
COWBONE CREEK AT SR 68
10
9
1
5
12
3/28/2006
6/6/2006
10/19/2006
2/7/2007
2/15/1996
10/19/2006
10/10/2006
11/7/2007
8/4/1998
Table 4: Monitoring Stations used in the Fecal Coliform TMDL for WBID 3189
Station ID
21FLA 26010429
21FLBRA3160-C
Station Name
COWBONE CREEK AT SR 68
3 160 - Cowbone Creek -
Cowbone Creek off 68
Number of
Observations
12
1
Start Date
2/15/1996
10/19/2006
End Date
8/4/1998
Table 5. Summary of Fecal Coliform Monitoring Data
Number of Samples
21FLA 26010429
21FLBRA3160-A
21FLBRA3160-B
21FLBRA3160-C
21FLWPB28042331
% Samples >
400
(MPN/lOOml)
92%
0%
0%
100%
0%
% Samples >
800
(MPN/lOOml)
50%
0%
0%
100%
0%
Minimum
Concentration
(MPN/lOOml)
180
1
1
1000
2
Maximum
Concentration
(MPN/lOOml)
17100
315
036
1000
096
Notes: Insufficient data collected to evaluate geometric mean criterion
14
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
Figure 4: Water Quality Monitoring Stations in WBID 3160
15
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
Rainfall and Fecal Coliform Data in WBID 316ol
1400 T_
fecal coliform
nmifirr m M fl Pirn
1700 1 "1
E --MOOO
o E
S 800 -I
^ z Rnn
s 1
OĢ. 400
onn
r| |-ŧ
Rainfall
TP'ff "f"
'"
'I"
8/1/2003 9/4/2004 10/9/2005
a^n*
^^~^^~
11/13/2006
12/18/
0
2
a
o
4 "2
- o w
8fl^
"
10
2007
Figure 5. Comparison between fecal coliform concentrations in C-25 Canal and rainfall
6. SOURCE ASSESSMENT
An important part of the TMDL analysis is the identification of source categories, source
subcategories, or individual sources of coliform bacteria in the watershed and the amount of
pollutant loading contributed by each of these sources. Sources are broadly classified as either
point or nonpoint 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 (i.e., Phase I or II MS4 discharges) are considered primary point
sources of coliform. Figure 3 shows permitted wastewater treatment facilities, landfills, and
delineated ground water contamination areas in the planning unit. Most of the facilities are in the
eastern part of the planning unit and do not impact WBIDs 3160 or 3189.
Nonpoint sources of coliform 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 bacteria on land surfaces and wash off as a result of storm
events. Typical nonpoint sources of coliform include:
Wildlife
Agricultural animals
Onsite Sewer Treatment and Disposal Systems (septic tanks)
Urban development (outside of Phase I or IIMS4 discharges)
16
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
A geographic information system (GIS) tool was used to display, analyze, and compile available
information to characterize potential bacteria sources in the impaired WBID. This information
includes land use, point source dischargers, soil types and characteristics, population data
(human and livestock), and stream characteristics.
6.1. Point Sources
Larson Dairy Barn #3 (FLA139254) is a confined animal feeding operation (CAFO). The
facility discharges to a spray irrigation land application site in the Gomez Creek watershed
within WBID 3160. Gomez Creek is a tributary to Cowbone Creek, and therefore this facility is a
potential source of pollutants in both WBID 3160 and 3189.
CAFOs are point sources, as defined by the CWA [Section 502(14)]. To be considered a CAFO, a
facility must first be defined as an Animal Feeding Operation (AFO). Animal Feeding Operations
(AFOs) are agricultural operations where animals are kept and raised in confined situations.
AFOs generally congregate animals, feed, manure, dead animals, and production operations on a
small land area. Feed is brought to the animals rather than the animals grazing or otherwise
seeking feed in pastures. Animal waste and wastewater can enter water bodies from spills or
breaks of waste storage structures (due to accidents or excessive rain), and non-agricultural
application of manure to crop land. AFOs that meet the regulatory definition of a CAFO have the
potential of being regulated under the NPDES permitting program. The NPDES permit for a
CAFO does not allow discharge to surface waters except under extreme conditions.
Municipal Separate Storm Sewer Systems (MS4s) may also discharge bacteria to water-bodies in
response to storm events. Large, medium, and small MS4s serving populations greater than
50,000 people, or with an overall population density of 1,000 people per square mile, are
required to obtain a NPDES storm water permit. There are three MS4 permits in St. Lucie
County, five in Indian River County, and none in Okeechobee County. Only the St. Lucie County
MS4 (FLR04E029) and the Indian River County MS4 (FLR04E068) are near WBID 3160 and
are likely to discharge in the WBID. There are no MS4s near WBID 3189.
6.2. Nonpoint Sources
Based on Level I and Level II land use summary information (SFWMD, 1995), the predominant
land use in the C-25/ Basin 1 planning unit is agriculture (approximately 65 percent of area). The
agricultural lands are used for cultivation of citrus (approximately 34 percent of planning unit
area) and improved pasture (approximately 28 percent of area). Only 5 percent of the planning
unit area is designated as urban/built-up. These land uses can be associated with nonpoint
discharges of pollutants and eroded sediments.
6.3. Wildlife
Wildlife deposit bacteria in their feces onto land surfaces where it can be transported during
storm events to nearby streams. Bacteria load from wildlife is assumed background, since the
contribution from this source is small relative to the load from urban and agricultural areas.
Water fowl (e.g., egrets, ducks, wood storks, herons) often frequent storm-water ponds.
Depending on the number of birds, the contributions of fecal coliform could result in stream
17
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
concentrations above the criteria.
6.4. Agricultural Animals
Agricultural animals are the source of several types of coliform loadings to streams, that impact
water quality. This source includes agriculture runoff from pastureland and cattle in streams. The
land use within the impaired WBIDs is 81 and 52 percent agricultural (Table 1 and Table 2), so
this landuse likely discharges a significant amount of the bacteria load.
The USDA National Agricultural Statistics Service (NASS) compiles Census of Agriculture data
by county for virtually every facet of U.S. agriculture (USDA, 2002). The "Census of
Agriculture Act of 1997" (Title 7, United States Code, Section 2204g) directs the Secretary of
Agriculture to conduct a census of agriculture on a 5-year cycle collecting data for the years
ending in 2 and 7. In 2002, NASS reported 221,537 acres of farmland in St. Lucie County,
191,333 acres in Indian River County, and 392,495 acres in Okeechobee County. Livestock
inventory from the 2002 Census of Agriculture reports are listed in Table 6. Cattle and calves are
the predominate livestock. CAFOs are not known to operate in either St. Lucie or Indian River
County; however, dairy farm CAFOs, such as the Larson Dairy discussed previously, are present
in Okeechobee County.
Table 6. Livestock Inventory by County (source: USDA, 2002)
Livestock
(inventory)
Cattle and calves
Hogs and Pigs
St. Lucie
31,944
394
Okeechobee
142,656
82
Indian River
25,139
271
6.5. Onsite Sewerage Treatment and Disposal Systems (Septic Tanks)
Onsite sewage treatment and disposal systems (OSTDs) including septic tanks are commonly
used where providing central sewer is not cost effective or practical. When properly sited,
designed, constructed, maintained, and operated, OSTDs are a safe means of disposing of
domestic waste. The effluent from a well-functioning OSTD is comparable to secondarily treated
wastewater from a sewage treatment plant. When not functioning properly, OSTDs can be a
source of nutrient (nitrogen and phosphorus), pathogens, and other pollutants to both ground
water and surface water. The State of Florida Department of Health publishes septic tanks data
on a county basis (www.doh.state.fl.us/environment/ostds/statistics/ostdsstatistics.htm). Table 7
summarizes the cumulative number of septic systems installed since the 1970 census. The data
does not reflect septic tanks removed from service.
18
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
Table 7. County Estimates of Septic Tank Installations
County
St. Lucie
Indian River
Okeechobee
Number Septic Tanks
(1970-2002)
43,022
34,174
11,432
6.6. Urban Development
Fecal coliform loading from urban areas is attributable to multiple sources including storm-water
runoff, leaks and overflows from sanitary sewer systems, illicit discharges of sanitary waste,
runoff from improper disposal of waste materials, leaking septic systems, and domestic animals.
Urban land uses include residential, industrial, extractive and commercial categories. Fecal
coliform loading from urban areas (whether within an MS4 jurisdiction or not) is attributable to
multiple sources including storm water runoff, leaks and overflows from sanitary sewer systems,
illicit discharges of sanitary waste, runoff from improper disposal of waste materials, leaking
septic systems, and domestic animals.
In 1982, Florida became the first state in the country to implement statewide regulations to
address the issue of nonpoint source pollution by requiring new development and redevelopment
to treat stormwater before it is discharged. The Stormwater Rule, as outlined in Chapter 403 of
the Florida Statutes (F.S.), was established as a technology-based program that relies upon 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.
Florida's stormwater program is unique in having a performance standard for older stormwater
systems that were built before the implementation of the Stormwater Rule in 1982. This rule
states: "the pollutant loading from older stormwater management systems shall be reduced as
needed to restore or maintain the beneficial uses of water" (Section 62-40-.432 (5) (c), F.A.C.).
In 1994, state legislation created the Environmental Resource Permitting program to consolidate
stormwater quantity, stormwater quality, and wetlands protection into a single permit. Presently,
the majority of environmental resource permits are issued by the state's water management
districts, although DEP continues to issue permits for specific projects.
Nonstructural and structural BMPs are an integral part of Florida's stormwater programs.
Nonstructural BMPs, often referred to as "source controls", are those that can be used to prevent
the generation of NPS pollutants or to limit their transport off-site. Typical nonstructural BMPs
include public education, land use management, preservation of wetlands and floodplains, and
minimizing impervious surfaces. Technology-based structural BMPs are used to mitigate the
increased stormwater peak discharge rate, volume, and pollutant loadings that accompany
urbanization.
19
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
7. ANALYTICAL APPROACH
The approach for calculating coliform TMDLs depends on the number of water quality samples
and the availability of flow data. When long-term records of water quality and flow data are not
available, the TMDL is expressed as a percent reduction. Load duration curves are used to
develop TMDLs when significant data are available to develop a relationship between flow and
concentration. Flow measurements are not available in either WBID 3160 or 3189, nor were
sufficient information available to estimate flow; therefore, these TMDLs are expressed as a
percent reduction.
7.1. Percent Reduction Approach for TMDL Development
Under this "percent reduction" method, the percent reduction needed to meet the applicable
criterion is calculated based on a percentile of all measured concentrations. The (p X 100)
percentile is the value with the cumulative probability of p. For example, the 90th percentile has a
cumulative probability of 0.90. The 90th percentile is also called the 10 percent exceedance event
because it will be exceeded with the probability of 0.10. Therefore, considering a set of water
quality data, 90 percent of the measured values are lower than the 90th percentile concentration
and 10 percent are higher. Since the water quality standard states the fecal coliform concentration
shall not exceed 400 counts per 100 ml in 10 percent of the samples, 400 should be targeted with
a percentile slightly larger than 90 to ensure less than 10 percent of the values exceed 400. For
this TMDL, 400 counts per 100 milliliter was targeted as the 95th percentile. This will meet the
water quality standard and provide a margin of safety by ensuring that only 5 percent of the data
exceed a concentration of 400. There are many formulas for determining the percentile and these
can be found in many text books on statistics. In these TMDLs the Hazen formula was used
since it is recommended in Hunter's Applied Microbiology (2002) article concerning bacteria in
water. Application of the Hazen formula to data collected in WBID 3160 is provided in
Appendix A and summarized below.
The percent reduction was also calculated using the maximum concentration measured in the
WBID and the 800 criterion. The larger of the two percent reduction values was selected as the
TMDL. The TMDL percent reduction required to meet the coliform criteria is based on the
following equation:
Percent Reduction = (existing 95th percentile concentration - criteria) / existing 95th percentile
concentration x 100 (Equation 1)
For WBID 3160, the existing 95th percentile concentration is 1,226 MPN/100 mL, and a 67
percent reduction is necessary to meet the water quality target of 400 MPN/100 mL 95 percent of
the time. The "not to exceed 800" standard would result in a reduction of about 95 percent
because of the maximum reported value of 17,100 counts per 100 mL. The 97 percent reduction
is selected for the TMDL to comply with both acute and the chronic criteria in the water quality
standards.
For WBID 3189, the existing 95th percentile concentration is 14,727 MPN/100 mL, and a 97
percent reduction is necessary to meet the water quality target of 400 MPN/100 mL 95 percent of
20
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
the time. The "not to exceed 800" standard would result in a reduction of about 95 percent
because of the maximum reported value of 17,100 counts per 100 mL. The 97 percent reduction
is selected for the TMDL to comply with both water quality standards.
8. DEVELOPMENT OF TOTAL MAXIMUM DAILY LOADS
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. A TMDL can be expressed as the sum
of all point source loads (Waste Load Allocations (WLA)), nonpoint source loads (Load
Allocations (LA)), and an appropriate margin of safety (MOS), which takes into account any
uncertainty concerning the relationship between effluent limitations and water quality:
TMDL = E WLAs + E LAs + MOS
As discussed earlier, the WLA is broken out into separate subcategories for wastewater
discharges and stormwater discharges regulated under the NPDES Program:
TMDL = X WLAswastewater+ Ģ WLASNPDES Stormwater + Ģ LAs + MOS
The various components of the TMDL equation may not sum up to the value of the TMDL
because: a) the WLA for NPDES stormwater is typically based on the percent reduction needed
for nonpoint sources and is also accounted for within the LA; and b) TMDL components can be
expressed in different terms (e.g., the WLA for stormwater is typically expressed as a percent
reduction, and the WLA for wastewater is typically expressed as mass per day).
WLAs for stormwater discharges are typically expressed as "percent reduction" because it is
very difficult to quantify the loads from MS4s (given the numerous discharge points) and to
distinguish loads from MS4s from other nonpoint sources (given the nature of stormwater
transport). The permitting of stormwater discharges also differs from the permitting of most
wastewater point sources. Because stormwater discharges cannot be centrally collected,
monitored, and treated, they are not subject to the same types of effluent limitations as
wastewater facilities, and instead are required to meet a performance standard of providing
treatment to the "maximum extent practical" through the implementation of BMPs. This
approach is consistent with federal regulations (40 CFR § 130.2(i)), which state that TMDLs can
be expressed in terms of mass per time (e.g., pounds per day), toxicity, or other appropriate
measure. TMDLs for the C-25 WBIDs 3160 and 3189 are expressed as a percent reduction.
The TMDLs are expressed as daily loads by multiplying the water quality target by an estimate
of flow in the WBID. The C-25 Canal is an ungaged waterbody and therefore it is not possible to
estimate flow with the available data. However, it is recommended that flow be measured at the
time of sampling to ensure compliance with the TMDLs. The maximum one day load the Canal
can transport in any 30-day period and maintain water quality standards is calculated by
multiplying 800 MPN/100 ml times the flow (in cubic feet per second) and a conversion factor to
obtain units of fecal coliform counts/day.
21
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
8.1. Critical Conditions
The critical condition for nonpoint source coliform loading is an extended dry period followed
by a rainfall runoff event. During the dry weather period, coliforms build up on the land surface,
and are washed off by rainfall. The critical condition for point source loading occurs during
periods of low stream flow when dilution is minimized. Water quality data have been collected
during both time periods. Most violations occur in response to rain events. Critical conditions
are accounted for in the analyses by using all water quality data available for the WBIDs.
8.2. Margin of Safety
TMDLs shall include a margin of safety (MOS) that takes into account any lack of knowledge
about the pollutant loading and in-stream water quality. In these TMDLs, lack of knowledge
concerns the data, how well it represents the true water quality in the WBIDs, and the estimation
of the exceedance probability. There are two methods for incorporating a MOS in the analysis: 1)
implicitly incorporate the MOS using conservative model assumptions to develop allocations; or
2) explicitly specify a portion of the TMDL as the MOS and use the remainder for allocations. In
these TMDLs, an implicit MOS was used by targeting reductions that will result in no more than
5 percent of the samples exceeding a concentration of 400 counts per 100 ml even though the
standard requires less than 10 percent exceedance. In addition, the TMDLs require very high
reductions.
8.3. Determination of TMDL, LA and WLA
The TMDL values represent the maximum daily load the stream can assimilate and maintain
water quality standards. The TMDLs are based on the daily 800 counts per 100 ml and the "not
to exceed 400 in 10 percent of the samples" Class III WQS, and are expressed as percent
reductions. TMDL components for the impaired water-bodies required to achieve the numerical
criterion are summarized in Table 8.
Table 8. Summary of Fecal Coliform TMDL Components
Stream Name /
WBID
C-25 Canal (3 160)
C-25 Canal (3 189)
Criterion used to
develop TMDL
SOOMPN/lOOml
400MPN/100ml
WLA
Continuous
N/A
N/A
MS4
95%
reduction
N/A
LA
95%
reduction
97%
reduction
TMDL
95%
reduction
97%
reduction
Notes: 1) To meet the 400 MPN/lOOml criterion in WBID 3160, a 67 percent reduction is
required and to meet the 800 MPN/lOOml criterion in WBID 3189, a 95 percent reduction is
needed (see Section 7.1); and 2) margin of safety is implicit in both TMDLs.
8.4. Waste Load Allocations
It is not applicable to assign a waste load allocation (WLA) to the Larson Dairy Barn #3
(FLA139254) because the CAFO permit does not allow the facility to discharge to surface
22
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
waters, except under extreme conditions. CAFOs have management plans that describe how the
waste will be treated so that no waste water is discharged.
The WLA for municipally separated storm sewer systems contributing pollutants to WBID 3160
is a 95 percent reduction from existing concentrations. There are two MS4 permits near WBID
3160: St. Lucie County MS4 (FLR04E029) and Indian River County MS4 (FLR04E068). It
should be noted that any MS4 permittee 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.
8.5. Load Allocations
There are two modes of transport for nonpoint source coliform bacteria loading into the stream.
First, fecal coliform loading from failing septic systems and animals in the stream are considered
direct sources of coliform to the stream, since they are independent of precipitation. The second
mode involves coliform loadings resulting from accumulation on land surfaces transported to
streams during storm events. Data from these WBIDs shows violations during wet weather and
dry weather, so both direct and indirect sources should be targeted by the reductions.
8.6. Seasonal Variation
Seasonality was addressed by using all water quality data associated with the impaired WBIDs,
which was collected during multiple seasons over several years.
8.7. Recommendations
It is recommended that flow be measured at the time of sampling so that loads can be calculated.
The available data indicates violations of the acute criteria occurred at the stations in Cowbone
Creek near State Route 68. Locating BMPs in the subbasins draining into these stations should
be a priority during implementation. Determining the source of bacteria in waterbodies is the
initial step to implementing a coliform TMDL. FDEP employs the Basin Management Action
Plan (B-MAP) as the mechanism for developing strategies to accomplish the necessary load
reductions. Components of a B-MAP are:
Allocations among stakeholders
Listing of specific activities to achieve reductions
Project initiation and completion timeliness
Identification of funding opportunities
Agreements
Local ordinances
Local water quality standards and permits
Follow-up monitoring
23
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
REFERENCES
Cleland, Bruce, 2003. TMDL development from the "bottom up " - Part III: Duration curves
and wet-weather assessments. America's Clean Water Foundation, Washington, DC. September
15,2003.
Florida Administrative Code (F. A.C.). Chapter 62-302, Surface Water Quality Standards.
FDEP, 2003. Basin Status Report, St. Lucie and Loxahatchee Basin, FDEP Division of Water
Resource Management, Group 2 Basin, February 2003.
Graves, Gregory A., Wan, Yongshan and Fike, Dana L., 2004. Water Quality Characteristics of
Storm Water From Major Land Uses in South Florida, Journal of the American Water Resources
Association, December 2004, 40(6): 1405-1419.
Hunter, P.R., 2002. The Society for Applied Microbiology, Letters in Applied Microbiology. 34.
283-286.
USDA, 2002. 2002 Census of Agriculture, Volume 1, Geographic Area Series, Part 9, U.S.
Department of Agriculture, National Agricultural Statistics Service. AC02-A-9, June 2004.
USDA, 1997. 7997 Census of Agriculture, Volume 1, Geographic Area Series, Part 42, U.S.
Department of Agriculture, National Agricultural Statistics Service. AC97-A-42, March 1999.
USEPA, 1991. Guidance for Water Quality -based Decisions: The TMDL Process. U.S.
Environmental Protection Agency, Office of Water, Washington, DC. EPA-440/4-91-001, April
1991.
24
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
APPENDIX A: WATER QUALITY DATA
Table 9: Guide to Water Quality Remark Codes (Rcode column in data tables)
Remark
Code
A
B
E
I
J
K
L
Q
T
U
<
Z
Definition
Value reported is mean of two or more
samples
Result based on colony counts outside the
acceptable range
Extra sample taken in compositing process
The value reported is less than the practical
quantification limit and greater than or equal
to the method detection limit.
Estimated. Value shown is not a result of
analytical measurement.
Off-scale low. Actual value not known, but
known to be less than value shown
Off-scale high. Actual value not known, but
known to be greater than value shown
Sample held beyond normal holding time
Value reported is less than the criteria of
detection
Material was analyzed for but not detected.
Value stored is the limit of detection.
NAWQA - actual value is known to be less
than the value shown
Too many colonies were present to count
(TNTC), the numeric value represents the
filtration volume
Use in TMDL
Data included in analysis as
reported
Data included in analysis as
reported
Data included as average
Data included in analysis as
reported
Data included in analysis as
reported
Data included in analysis as
reported
Data included in analysis as
reported
Data used in analysis - holding
samples on ice slows the
metabolism of the organisms
resulting in no appreciable
growth. Actual concentration is
expected to be at least as high as
the value reported.
Data included in analysis if the
reported value is below criteria;
otherwise, reported value is not
used in the analysis
Data not included in analysis
Data included in analysis
Data not included in analysis
Table 10. Fecal Coliform Data Collected in WBID 3160 (Source: IWR Run 32)
Station
Date
Depth
Result
Rcode
25
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21FLBRA3160-A
21FLBRA3160-A
21FLBRA3160-A
21FLBRA3160-A
21FLBRA3160-A
21FLBRA3160-A
21FLBRA3160-A
21FLBRA3160-A
21FLBRA3160-A
21FLBRA3160-A
21FLBRA3160-B
21FLBRA3160-B
21FLBRA3160-B
21FLBRA3160-B
21FLBRA3160-B
21FLBRA3160-B
21FLBRA3160-B
21FLBRA3160-B
21FLBRA3160-B
21FLBRA3160-C
21FLGW 20026
21FLGW 20105
21 FLWPB 28042331
21 FLWPB 28042331
21 FLWPB 28042331
21 FLWPB 28042331
21 FLWPB 28042331
2/15/1996
4/10/1996
8/1/1996
10/1/1996
11/20/1996
2/19/1997
7/8/1997
8/5/1997
11/5/1997
1/22/1998
6/2/1998
8/4/1998
3/28/2006
6/6/2006
6/15/2006
7/12/2006
7/20/2006
8/4/2006
8/20/2006
9/8/2006
10/10/2006
10/19/2006
3/28/2006
6/6/2006
6/15/2006
7/12/2006
7/20/2006
8/4/2006
8/17/2006
9/8/2006
10/10/2006
10/19/2006
8/19/2003
10/21/2003
2/7/2007
3/28/2007
8/1/2007
9/26/2007
11/7/2007
0.98
0.33
0.98
0.66
0.33
0.66
2.95
0.98
0.98
2.62
1.31
0.98
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.35
0.50
0.10
0.10
0.10
0.10
0.10
1280
1100
810
410
1010
950
610
520
17100
720
180
670
5.1
170
5.1
35
315
1
20
96
5.2
15
5.2
11
8.5
7.5
2
1
5.2
36
7.5
1000
880
10
11
2
96
78
14
J
J
U
B
B
B
Table 11. Calculation of Percentiles
Date
8/4/2006
8/4/2006
7/20/2006
3/28/2007
3/28/2006
6/15/2006
10/10/2006
Station
21FLBRA3160-A
21FLBRA3160-B
21FLBRA3160-B
21 FLWPB 28042331
21FLBRA3160-A
21FLBRA3160-A
21FLBRA3160-A
Result
1
1
2
2
5.1
5.1
5.2
Rcod
e
U
Rank
1
2
3
4
5
6
7
Percentile
by Hazen
method
1%
4%
6%
9%
12%
14%
17%
26
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
Date
3/28/2006
8/17/2006
7/12/2006
10/10/2006
6/15/2006
10/21/2003
6/6/2006
2/7/2007
11/7/2007
10/19/2006
8/20/2006
7/12/2006
9/8/2006
9/26/2007
9/8/2006
8/1/2007
6/6/2006
6/2/1998
7/20/2006
10/1/1996
8/5/1997
7/8/1997
8/4/1998
1/22/1998
8/1/1996
8/19/2003
2/19/1997
10/19/2006
11/20/1996
4/10/1996
2/15/1996
11/5/1997
Station
21FLBRA3160-B
21FLBRA3160-B
21FLBRA3160-B
21FLBRA3160-B
21FLBRA3160-B
21FLGW 20105
21FLBRA3160-B
2 1FLWPB 28042331
2 1FLWPB 28042331
21FLBRA3160-A
21FLBRA3160-A
21FLBRA3160-A
21FLBRA3160-B
2 1FLWPB 28042331
21FLBRA3160-A
2 1FLWPB 28042331
21FLBRA3160-A
21 FLA 26010429
21FLBRA3160-A
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21FLGW 20026
21 FLA 26010429
21FLBRA3160-C
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
21 FLA 26010429
Result
5.2
5.2
7.5
7.5
8.5
10
11
11
14
15
20
35
36
78
96
96
170
180
315
410
520
610
670
720
810
880
950
1000
1010
1100
1280
17100
Rcod
e
B
B
J
J
B
Rank
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
Percentile
by Hazen
method
19%
22%
24%
27%
29%
32%
35%
37%
40%
42%
45%
47%
50%
53%
55%
58%
60%
63%
65%
68%
71%
73%
76%
78%
81%
83%
86%
88%
91%
94%
96%
99%
In this TMDL the Hazen formula was used since it is recommended in Hunter's Applied
Microbiology (2002) article concerning bacteria in water. To use the Hazen formula to calculate
the percentile associated with the sample concentrations, the data are first sorted by
concentration, lowest to highest. A ranking is assigned to each sample, with the lowest
concentration having a rank of 1 and the highest concentration having a rank equivalent to the
total number of samples collected. The percentile is calculated as follows:
Percentile = (Rank - 0.5)/ (total number of samples collected)
For example, on October 19, 2006 a fecal coliform concentration of 1000 MPN/lOOml was
measured at station 21FLBRA3160-C. This concentration ranks number 35 out of 39 samples
collected in WBID 3160. The associated percentile is calculated as:
Percentile = (35-0.5)739 = 0.88 = 88%
27
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Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189)
September 2008
This implies that 88 percent of the time the instream concentration is less than 1000 MPN/lOOml.
28
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