# TOTAL MAXIMUM DAILY LOAD (TMDL)

For Nutrients, Dissolved Oxygen,

and Coliforms

In
Sarasota Bay/Charlotte Harbor Basin Groups

(WBIDs 1982A, 1984, 1984A, 2009A, 1975A, 1975, 2049, 2039, 2042, and 2030)

Prepared by:

US EPA Region 4 61 Forsyth Street SW Atlanta, Georgia 30303

March 2006

### ii 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 the Total Maximum Daily Load (TMDL) for nutrients, dissolved oxygen, and coliforms in the Sarasota Bay/Charlotte Harbor Basin (WBIDs1982A, 1984, 1984A, 2009A, 1975A, 1975, 2049, 2039, 2042, and 2030). Subsequent actions must be consistent with this TMDL.

__________________________________________ ___________
James D. Giattina, Director Date Water Management Division

### iii 

### TABLE OF CONTENTS

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯


### 1. INTRODUCTION ................................................................................................................... 1

2. PROBLEM DEFI NITION........................................................................................................2

3. WATERSHED DESCRIPTION ..............................................................................................4

3.1 S ARASOTA B AY P LANNING U NIT ..................................................................................................................4 3.2 L EMON B AY P LANNING U NIT ........................................................................................................................5



### 4. WATER QUALITY STANDARD AND TARGET IDENTIFICATION .......................................9

5. WATER QUALITY ASSESSMENT AND D EVIATION FROM TARGET..............................10

5.1 D ISSOLVED O XYGEN D ATA ........................................................................................................................12 5.2 C HLOROPHYLL D ATA

............................................................................................................................... ..14 5.3 A LGAL G ROWTH P OTENTIAL D ATA ............................................................................................................19 5.4 T OTAL C OLIFORM D ATA .............................................................................................................................20 5.5 F ECAL C OLLIFORM D ATA ...........................................................................................................................22



### 6. SOURCE ASSESSMENT....................................................................................................24

6.1 P OINT S OURCES

............................................................................................................................... .........24 6.1.1 NPDES Fa cilitie s............................................................................................................... ....................24 6.1.2 MS4 ar eas ...................................................................................................................... ........................24 6.2 N ONPOINT S OURCES

............................................................................................................................... ..25 6.2.1 Wild life....................................................................................................................... ............................25 6.2.2 Agricultura l anima ls ........................................................................................................... ...................25 6.2.3 Onsite Sewerage Treatment and Dis posal Systems (S eptic T anks)........................................................26
6.2.4 Urban Devel opment.............................................................................................................. .................27



### 7. ANALYTICAL APPROACH..................................................................................................27

7.1. N UTRIENT AND B IOLOCHEMICAL O XYGEN D EMAND (BOD) ......................................................................27
7.1.1 Determination of Pollu tant Loadi ng Capac ity.................................................................................... ...28
7.1.1.1. Hydrologic Data and Runoff Gene ration .......................................................................................... 28
7.1.1.2. Pollutant Loading Rates fo r Land Use Ca tegorie s............................................................................29
7.1.1.3. Load Attenuati on Fact ors....................................................................................................... ...........30
7.1.1.4. Computations of Runoff Volu mes and Pollutant Loadi ngs ................................................................31
7.1.2 Determination of Target Loads.................................................................................................. ............33 7.2. C OLIFORMS

............................................................................................................................... .................36
7.1.2.1. Percent Reducti on Appr oach..................................................................................................... ........37



### 8. DEVELOPMENT OF TOTAL MAXIMUM DAIL Y LOAD.......................................................38

8.1. W ASTE L OAD A LLOCATIONS ......................................................................................................................39
8.1.1 NPDES Wastewater Discharges .................................................................................................... ........39
8.1.2 NPDES Stormwater Discharges .................................................................................................... ........39 8.2. L OAD A LLOCATIONS

............................................................................................................................... ....40 8.3. M ARGIN OF S AFETY (MOS) .......................................................................................................................40 8.4. C RITICAL CONDITIONS AND S EASONAL V ARIATIONS .................................................................................42



### 9. CONCLUSION AND RE COMMENDATIONS ......................................................................42

REFERENCES ..................................................................................................................... ......44

APPENDIX A PHOTOS OF IMPAIRED WBIDS .....................................................................1

APPENDIX B TMDL DEVELOPMENT FOR SARASOTA BAY/LEMON BAY WBIDS USING

### iv THE REFERENCE WATE RSHED APPR OACH............................................................................I

### v 

### LIST OF TABLES

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ Table 1. TMDLs Developed By EPA in Sarasota Bay/Charlotte Harbor Basins ...........................2 Table 2. Current Land Use/Cover Distribution in Impaired WBIDs 1 

### .............................................6 Table 3. Aggregate Land Use/Cover Categories Derived from the Florida Land Use, Cover, and Forms Classification System (FLUCCS). ..............................................................................7 Table 4. Water Quality Monitoring Stations in the impaired WBIDs...........................................11 Table 5. Summary of Dissolved Oxygen Data (mg/l) for Impaired WBIDs.................................13 Table 6. Summary of Chlorophyll Data ( μ g/l) for Impaired WBIDs. ...........................................15 Table 7. Results of Algal Growth Potential Tests.......................................................................19 Table 8. Total Coliform Data for Impaired WBIDs......................................................................21 Table 9. Fecal Coliform Data for Impaired WBIDs.....................................................................22 Table 10. Livestock Inventory for Sarasota County, Florida. .....................................................26 Table 11. Estimates of Septic Tanks and Repair Permits for Sarasota County.........................27 Table 12. Percent Impervious and DCIA by Land Use for Impaired WBIDs..............................29 Table 13. Nutrient and BOD Concentrations in Stormwater by Land Use .................................29 Table 14. Treatment Potential Factors.......................................................................................30 Table 15. Stormwater System Attenuation Factors ...................................................................31 Table 16. Conveyance System Attenuation Factors..................................................................31 Table 17. Annual Total N Loads by Land Use Under Existing Conditions.................................32 Table 18. Annual BOD Loads by Land Use Under Existing Conditions.....................................33 Table 19. Land Cover Distribution in the Impaired WBIDs Under Natural Conditions ...............34 Table 20. Annual Total N Loads by Land Cover Under Natural Conditions...............................35 Table 21. Annual BOD Loads by Land Cover Under Natural Conditions ..................................36 Table 22. Fecal Coliform Measurements for Elligraw Bayou .....................................................37 Table 23. TMDL Components for Nutrient-Impaired Waters. ....................................................40 Table 24. TMDL Components for Waterbodies Impaired by DO ...............................................41 Table 25. TMDL Components for Waterbodies Impaired by Coliform. ......................................41



### LIST OF FIGURES

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ Figure 1. Location of 303(d) listed WBIDs in the Sarasota Bay and Lemon Bay Basins.............3 Figure 2. Dissolved Oxygen Measurem ents in Gottfried Creek, WBID 2049.............................14 Figure 3. Dissolved Oxygen Measurement s in Elligraw Bayou, WBID 1975. ............................14 Figure 4. Chlorophyll measurements in WBID 1975 (Elligraw Bayou)........................................15 Figure 5. Chlorophyll measurements in WBID 1975A (Clowers Creek)......................................16 Figure 6. Chlorophyll measurements in WBID 1982A (South Creek). .......................................17 Figure 7. Chlorophyll measurements in WBID 1984A (North Creek).........................................17 Figure 8. Chlorophyll measurements in WBID 1984 (Catfish Creek).........................................18 Figure 9. Chlorophyll measurements in WBID 2030 (Alligator Creek)........................................18 Figure 10. Total Coliform Measurements in WBID 1975 (Elligraw Bayou). ...............................21 Figure 11. Total Coliform Measurements in WBID 1975A (Clowers Creek). .............................22 Figure 12. Fecal Coliform Measurements in WBID 1975 (Elligraw Bayou)................................23 Figure 13. Fecal Coliform Measurements in WBID 1975A (Clowers Creek). ............................23

### vi LIST OF ABBREVIATIONS

________________________________________________________________________________________



### AWT Advanced Waste Treatment
BMP Best Management Practices
BPJ Best Professional Judgment
CFS Cubic Feet per Second
CFU Colony Forming Units
DEM Digital Elevation Model
DMR Discharge Monitoring Report
EPA Environmental Protection Agency

FAC Florida Administrative Code
GIS Geographic Information System
HUC Hydrologic Unit Code

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

PLRG Pollutant Load Reduction Goal

Rf3 Reach File 3

RM River Mile
STORET STORage RETrieval database
TMDL Total Maximum Daily Load
USDA United States Department of Agriculture
USGS United States Geological Survey
WBID Water Body Identification
WCS Watershed Characterization System

WLA Waste Load Allocation
WMP Water Management PlanDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basins September 2005 Page 

### v



### SUMMARY SHEET Total Maximum Daily Load (TMDL)

1. 303(d) Listed Waterbody Information State: Florida County: Sarasota Major River Basin: Sarasota Bay Basin (HUC 03100201)

WBID Segment Name Type Constituents 1975 Elligraw Bayou Freshwater Nutrients, Dissolved Oxygen (DO), Coliforms 1975A Clowers Creek Freshwater Coliforms 1982A South Creek Estuarine Nutrients 1984 Catfish Creek Estuarine Nutrients 1984A North Creek Estuarine Nutrients 2009A Curry Creek Estuarine Nutrients 2030 Alligator Creek Estuarine Nutrients 2039 Forked Creek Estuarine Nutrients

2042 Direct Runoff to Bay Estuarine Nutrients
2049 Gottfried Creek Estuarine Nutrients, Dissolved Oxygen

2. TMDL Development Approach and Modeling - Nutrient and DO Impairment Because of insufficient and/or lack of recent monitoring data of nutrients and DO for impaired WBIDs, pollutant loading capacity and target loads were determined using the Lemon Bay Watershed Model. The model used pollutant loading rates typical for land uses in these WBIDs and runoff volumes to compute long-term average annual loads of TN and BOD. The target loads were assumed to be those that existed under “natural conditions”, that is prior to anthropogenic influences in the impaired WBIDs.

- Coliforms Due to the lack of long-term record of bacteria samples and flow data to establish the relationship between bacterial concentrations and flow using load duration curves, coliform TMDLs were expressed as percent reductions.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basins September 2005 Page 

### vi

3. TMDL Endpoints and Load Allocations (LAs) - Total N for Waterbodies Impaired by Nutrients

WLA 2

Waterbody Parameter 1 Existing Load (kg/year) Target Load-LA (kg/year) Continuous (kg/year) MS4 (Percent reduction) MOS 4 (kg/year) Percent Reduction 5

Elligraw Bayou TN 2525.86 1799.13 N/A 3 28.8 Implicit 28.8

Curry Creek TN 1300.99 482.60 N/A 3 62.9 Implicit 62.9

North Creek TN 1116.10 589.95 N/A 3 47.1 Implicit 47.1

Catfish Creek TN 2279.7 1110.0 N/A 3 51.3 Implicit 51.3

South Creek TN 1816.58 941.89 N/A 3 48.2 Implicit 48.2

Gottfried

Creek TN 3025.13 2965.58 N/A 3 2.0 Implicit 2.0

Forked Creek TN 4234.90 3386.74 N/A 3 20.0 Implicit 20.0

Direct Runoff to Bay TN 1414.23 640.51 N/A 3 54.7 Implicit 54.7

Alligator

Creek TN 5370.41 3857.43 N/A 3 28.2 Implicit 28.2



### Notes: 1 TN = total nitrogen 2 WLA component is separated into load from continuous NPDES facilities (e.g., WWTPs) and load from MS4s. 3 N/A = not applicable
4 Margin of Safety is implicit due to conservati ve assumptions made in determining TMDL targets. 5 Percent reduction from current conditions to achi eve the target concentration for that nutrient.


### - TN and BOD Loads for Waterbodies Impaired by DO

Target LoadLA (kg/year) WLA 2

Waterbody Parameter 1 Existing Load (kg/year) Anthropogenic Natural Continuous (kg/year) MS4 (Percent reduction) MOS 4 (kg/year) Percent Reduction 5

TN 2525.86 0 1799.13 N/A 3 28.8 Implicit 28.8 Elligraw Bayou BOD 12931.64 0 3800.00 N/A 3 70.6 Implicit 70.6

TN 5370.41 0 3857.43 N/A 3 28.2 Implicit 28.2 Alligator Creek BOD 15727.53 0 6632.32 N/A 3 57.8 Implicit 57.8

1 TN = total nitrogen, BOD = Biochemical Biological Demand
2 WLA component is separated into load from continuous NPDES facilities (e.g., WWTPs) and load from MS4s. 3 N/A = not applicable
4 Margin of Safety is implicit due to conservati ve assumptions made in determining TMDL targets. 5 

### Percent reduction from current conditions to achieve the target concentration for that nutrient.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basins September 2005 Page 

### vii

- Coliforms: Endpoints: Fecal Coliform: 400 MPN/100ml Total Coliform: 2400 MPN/100ml

For Waterbodies Impaired by Coliform

WLA 2

WBID Parameter 1 TMDL (MPN/day) LA (MPN/day) Continuous MS4 (percent reduction Percent Reduction 3

TCOLI 3910 3910 N/A 39 39 Elligraw Bayou FCOLI 1323 1323 N/A 70 70

TCOLI 2615 2615 N/A 85 85 Clowers

Creek FCOLI 1678 1678 N/A 76 76



### Notes: 1. WLA component is separated into load from continuous NPDES facilities and load from MS4s. 2. N/A = not applicable 3. Percent reduction from current conditions to ac hieve the target concentration for that nutrient.



### 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 EPA TMDL: NoneDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 1



### TOTAL MAXIMUM DAILY LOAD (TMDL) FOR NUTRIENTS, D.O., FECAL AND TOTAL COLIFORMS in WBIDs 1975, 1975A, 1982A, 1984, 1984A, 2009A, 2030, 2039, 2042, 2049 (SARASOTA BAY/CHARLOTTE HARBOR BASINS)

1. 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 in-stream 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 State of Florida Department of Environmental Protection (FDEP) has developed 303(d) lists since 1992. The process by which Florida implement s section 303(d) requirements is set forth in the Florida Watershed Restoration Act (FWRA) of 1999 (s. 403.067, Florida Statutes). The FDEP list of impaired waters in each basin, referred to as the “Verified List”, is also adopted pursuant to the FWRA (Subsection 403.067[4], Florida Statutes). However, the FWRA also states that all previous Florida 303(d) lists were for planning purposes only and directed the Department to develop, and adopt by rule, a new science-based methodology to identify impaired waters. After a long-rule-making process, the Florida Environmental Regulation Commission adopted the new methodology as Chapter 62-303, Florida Administrative Code (Identification of Impaired Surface Waters Rule, or IWR), in April 2001. These TMDLs are being established pursuant to EPA commitments in the 1998 Consent Decree in the Flor ida TMDL lawsuit (Florida Wildlife Federation, et al. v. Carol Browner, et al., Civil Action No. 4: 98CV356-WS, 1998).

FDEP developed a statewide, watershed-based approach to water resource management. Following this approach, water resources are ma naged on the basis of natural boundaries, such as river basins, rather than political boundaries. The watershed management approach is the framework DEP 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 3 basin includes waters in the basins of the Caloosahatchee River, Choctawhatchee Bay and River, Saint Andrews Bay, Peace River, Sarasota Bay, Myakka Ri ver, Lake Worth Lagoon/Palm Beach Coast, and Saint Johns River. Group 3 waters were first assessed in 2002 with plans to revisit water management issues in 2007.

FDEP established five water management districts (WMD) responsible for managing ground and surface water supplies in the counties encompassing the districts. 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”. A water segment usually contains only one unique waterbody type (stream, lake, cannel, etc.) and is about 5 square miles. Unique numbers or waterbody identification (WBIDs) numbers are assigned to each water segment.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 2



### 2. PROBLEM DEFINITION

Florida’s final 1998 Section 303(d) list identified numerous WBIDs in the Sarasota Bay/Charlotte Harbor basin groups as potentially not supporting water quality standards (WQS). After assessing all readily available water quality data, EPA is responsible for determining whether TMDLs are needed for coliforms, nutrients and/or dissolved oxygen (D.O.) in various WBIDs of the basin. The TMDLs described in this report are listed in Table 1, and the geographic location of each listed WBID is provided in Figure 1. A request to de-list WBID 1975A (Clowers Creek) for nutrients and turbidity will be approved.

Table 1. TMDLs Developed By EPA in Sarasota Bay/Charlotte Harbor Basins

WBID Segment Name Type Planning Unit Parameter(s) of Concern
1975 Elligraw Bayou Freshwater Sarasota Bay Nutrients, Dissolved Oxygen, Coliforms 1975A Clowers Creek Freshwater Sarasota Bay Coliforms 1982A South Creek Estuarine Sarasota Bay Nutrients 1984 Catfish Creek Estuarine Sarasota Bay Nutrients 1984A North Creek Estuarine Sarasota Bay Nutrients 2009A Curry Creek Estuarine Sarasota Bay Nutrients 2030 Alligator Creek Estuarine Lemon Bay Nutrients 2039 Forked Creek Estuarine Lemon Bay Nutrients 2042 Direct Runoff to Bay Estuarine Lemon Bay Nutrients 2049 Gottfried Creek Estuarine Lemon Bay Nutrients, Dissolved Oxygen

The waterbodies listed in Table 1 are Class III waters with the designated use of recreation, and propagation and maintenance of a healthy, well-balanced population of fish and wildlife. Class III waters are further categorized as either freshwater or marine.

To determine the status of surface water quality in the state, 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 the threshold for determining if waters should be included on the state’s planning list and verified list. Potential impairments are determined by assessing whether a waterbody meets the criteria for inclusion on the planning list. Once a waterbody is on the planning list, additional data and information will be collected and examined to determine if the water should be included on the verified list.

The format of the remainder of this report is as follows: Chapter 3 is a general description of the impaired watersheds; Chapter 4 describes the water quality standard and target criteria for the TMDLs; and Chapter 5 describes the development of the TMDLs.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 3

# S # S # S

# S # S # S
# S

# S # S # S # S

# S

# S # S # S

#

S

# S # S # S # S

# S 

### Sarasota

North Port



### Port Charlotte Venice

Charlotte Harbor L i t t l e

S

a r a s o t a

B a y

L e

m

o

n

B

a y 

### Gulf

of Mexico

Englewood 2049 2039 2042 2030 2009A 1982A 1984A 1975A 1975

1984



### 7 0 7 14 Miles

Catalog Units Cities and Towns Counties Sarasota B./Charlotte H. WBIDs Rivers and Streams # S 

### NPDES Facilities N

E W

S



### area of detail 

# LEGEND

Figure 1. Location of 303(d) listed WBIDs in the Sarasota Bay and Lemon Bay BasinsDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 4



### 3. WATERSHED DESCRIPTION

The Sarasota Bay basin is defined by USGS Hydrologic Unit Code (HUC) 03100201. The following description of the impaired watersheds in the Sarasota Bay Planning Unit is from the Basin Status Report for Sarasota Bay and Peace and Myakka Rive rs (FDEP, 2003). The descriptions of the four WBIDs that drain to Lemon Bay are from the Charlotte Harbor Basin Status Report (FDEP, 2002). These documents should be consulted for additional details. Pictures of the impaired WBIDs in Sarasota and Lemon Bay Planning Units may be found in Appendix A.

3.1 Sarasota Bay Planning Unit The Sarasota Bay watershed is located in southwest Florida near the cities of Sarasota and Venice. The basin includes several important estuaries as well as many wetlands and small coastal streams that are predominantly tidal in nature. A few freshwater streams are also located in the basin. Sarasota Bay itself is the largest estuary in the basin, with 52 square miles of open water (FDEP, 2003). The total watershed draining to Sarasota Bay, from its northern extent at Anna Maria Sound to its southern extent at Venice Inlet, has been estimated at 150 square miles (SWFWMD, 2002).

Six of the estuaries in the Sarasota Bay watershed have been designated Estuaries of National Significance by the U.S. Environmental Protec tion Agency (EPA) and Outstanding Florida Waters (OFWs) by the Florida Department of Environment al Protection (FDEP). These include Anna Maria Sound, Palma Sola Bay, Sarasota Bay, Roberts Bay, Little Sarasota Bay, and Blackburn Bay. In 1995, the South Florida Water Management District (SWFWMD) named Sarasota Bay as a priority water body for its Surface Water Improv ement and Management (SWIM) Program.

Population in the Sarasota Bay watershed has grown rapidly in recent decades, especially during the 1980's. Between 1980 and 1990, Manatee County's population grew 43%, Sarasota County's grew 37%, and Charlotte County's went up 90% (FDEP, 2003). Continued population growth in these counties is anticipated.

Near the coast and along the barrier islands, the land use is largely urban and residential. There are several major urban areas in the watershed including the cities of Sarasota, Venice and Bradenton. The eastern portion of the watershed contains more agricultural uses such as range land, pasture, and row crops. Freshwater and saltwater wetlands and open waters are also important landuses, although the acreage of tidal and freshwater wetlands has declined significantly since World War II (SWFWMD, 2002).

North Creek, WBID 1984A, is located in Sarasota County near the city of Osprey. It is a Class III Marine waterbody that was listed on the 1996 303(d) list for nutrients (FDEP, 2003). North Creek is also considered potentially impaired for D.O. and coliforms. The creek is divided into freshwater (WBID 1984) and marine (WBID 1984A) segments.

Catfish Creek, WBID 1984, is located near the City of Vamo. It also drains into Little Sarasota Bay. It is also Class III Marine waterbody that was listed on the 1996 303 (d) list for nutrients.

South Creek, WBID 1982A, is located in Sarasota County near the city of Laurel. South Creek is one of the series of creeks and bayous on the mainland that drains stormwater runoff to the bay. South Creek is a Class III Marine water that was included on the 1996 303(d) list for nutrients (FDEP, 2003). The freshwater portion of South Creek is in WBID 1982, while WBID 1982B, SouthDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 5



### Creek in Park, is a small, elongate piece of WBID 1982A that was cut out along the creek as it flows through Oscar Scherer State Park. South Creek then empties into Dryman Bay. There are a number of nonforested freshwater wetlands in the upper South Creek watershed.

Curry Creek, WBID 2009A, is located in Sarasota County near the cities of Venice and Nokomis. Curry Creek was included on the 1996 303(d) list for nutrients (FDEP, 2003). It is also considered potentially impaired for D.O. Curry Creek terminates at Roberts Bay (the Roberts Bay located more to the south, near Dona Bay). Curry Creek pr ovides hydraulic connection between the Myakka River and Roberts Bay during periods of high flow.

Elligraw Bayou, WBID 1975, and Clowers Creek, WBID 1975A, are both Class III freshwater streams located in Sarasota County near the city of Sarasota. Elligraw Bayou is 303(d)-listed for coliforms, nutrients, and dissolved oxygen, and Clowers Creek is listed for coliforms. The estuarine portion of Clowers Creek is covered by WBID 1975AA.

3.2 Lemon Bay Planning Unit The 97 square miles of the Lemon Bay planning unit are encompassed by Sarasota and Charlotte Counties. The bay itself extends from South Veni ce to the southern end of Gasperilla Island. The watershed includes a system of interconnected em bayments and their watersheds. Four of these estuarine creeks have been identified as impaired by nutrients and/or dissolved oxygen: Alligator Creek, Direct Runoff, Gottfried Creek, and Forked Creek.

The Lemon Bay Estuarine System is designated an Outstanding Florida Water (OFW) by the FDEP, and there is a 7,667 acre state aquatic preserve in the bay. Lemon Bay is one of five individual preserves that make up the Charlotte Harbor Aquatic Preserves. Each preserve has a management plan to assess its condition and re source management needs. The management plan for Lemon Bay was adopted in April 1992. Although Lemon Bay is included in the Sarasota Bay hydrologic unit, FDEP has decided to consider it part of the Charlotte Harbor Basin because of Lemon Bay’s direct connection through Placida Harbor (FDEP, 2002). Table 2 contains the land use/cover distribution of the Sarasota and Lemon Bay WBIDs.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 6



### Table 2. Current Land Use/Cover Distribution in Impaired WBIDs 1

Land Use/Cover Area (Acres)

Land Use Clowers Creek Elligraw Bayou Curry Creek North Creek Catfish Creek South Creek Gottfried Creek Forked Creek Alligator Creek Direct Runoff to Bay

Agriculture 0 186 102 13 96 2 584 1,272 0 0

Commercial 118 307 63 40 164 152 197 94 423 15

Extractive 0 0 0 0 0 0 0 15 0 0

Industrial 0 332 0 0 1 0 0 19 0 3 Low-Density Residential 10 153 25 79 37 102 344 459 72 166MediumDensity Residential 8

1,758 66 417 121 316 559 947 1,566 807 High-Density Residential 198 451 509 202 871 364 202 480 1,610 110 Transportation 20 64 18 17 21 37 6 63 153 0

Institutional 13 163 25 0 3 47 70 7 129 0 Open 111 418 78 258 250 1,168 3,589 2,446 692 298

Recreational 0 209 38 347 304 7 231 114 187 5

Wetland 5 97 111 106 291 214 1,024 1,093 478 186 Water (Ponds and Lakes) 9 158 26 113 256 70 300 303 399 27 Water (Conveyance) 38 92 70 60 11 44 120 65 51 65

Total 530 4,390 1,131 1,651 2,426 2,524 7,227 7,375 5,761 1,683
1 Data source is 1995-Land cover from the SWFWMD . The land use classes in the Table were obtained by aggregating detailed land use categories of Land Use, Co ver, and Forms Classificati on System (FLUCCS) as shown in Table 3.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 7



### Table 3. Aggregate 

### Land Use/Cover Categories Derived from the Florida Land Use, Cover, and Forms Classification System (FLUCCS)



### . 

### Land Use/Cover FLUCCS Code Description FLUCCS Code Low-Density Residential Residential Low Density < 2 Dwelling Units 110 Medium-Density Residential Residential Med Density 2->5 Dwelling Unit 120 High-Density Residential Residential High Density 130 Commercial Commercial And Services 140
Industrial Industrial 150
Extractive 160 Beaches Other Than Swimming Beaches 710 Sand Other Than Beaches 720 Exposed Rock 730 Extractive

Disturbed Land 740
Institutional Institutional 170
Recreational Recreational 180 Cropland and Pastureland 210 Row Crops 214 Tree Crops 220 Feeding Operations 230 Nurseries And Vineyards 240 Vineyards 244 Specialty Farms 250 Tropical Fish Farms 255 Agriculture

Other Open Lands <rural> 260
Herbaceous 310 Shrub and Brushland 320 Mixed Rangeland 330 Upland Coniferous Forest 410
Pine Flatwoods 411 Longleaf Pine – Xeric Oak 412 Upland Hardwood Forests - Part 1 420 Xeric Oak 421 4300 Upland Hardwood Forests - Part 2 430
Tree Plantations 440 Open Land

Open land 190
Lakes 520 WATER (Ponds and Lakes)
Reservoirs 530

Bays And Estuaries 540 Water (Conveyance) Streams And Waterways 510Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 8

Land Use/Cover FLUCCS Code Description FLUCCS Code

Wetland Hardwood Forests 610 Bay Swamps 610 Mangrove Swamps 612 Titi Swamps 614 Stream And Lake Swamps (bottomland) 615 Wetland Coniferous Forests 620 Cypress 621
Wetland Forested Mixed 630 Vegetated Non-forested Wetlands 640
Freshwater Marsh 641 Saltwater Marshes 642
Wet Prairies 643 Emergent Aquatic Vegetation 644 Non-Vegetated 650 Tidal Flats/submerged Shallow Platform 651 Shorelines 652 Wetlands

Intermittent Ponds 653 Transportation 810 Communications 820 Transportation

Utilities 830Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 9



### 4. WATER QUALITY STANDARD AND TARGET IDENTIFICATION

The waterbodies addressed in this document are Class III waters, with a designated use of recreation, propagation and maintenance of a healthy, well-balanced population of fish and wildlife. 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: Mi nimum Criteria, General Criteria] that apply to all waters unless alternative criteria are specified in F.A.C. Section 62-302.530. In addition, unless otherwise stated, all criteria express the maximum not to be exceeded at any time. While the State of Florida does not have numeric criteria for nutrients, a narrative criterion exists as described below. The specific criteria for the impaired WBIDs addressed in this TMDL are as follows:

Nutrients (Class III Waters- Fresh and Marine) The discharge of nutrients shall continue to be limited as needed to prevent violations of other standards contained in this chapter [Section 62.302 F.A.C.]. 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 and fauna [Section 62.302.530 F.A.C.]

Dissolved Oxygen (Class III Waters) For Fresh Water: Dissolved Oxygen (D.O.) shall not be less than 5.0 (milligrams/liter) in a 24-hour period. Normal daily and seasonal fluctuations above these levels shall be maintained.

For Marine Water : Dissolved Oxygen (D.O.) shall not aver age less than 5.0 (milligrams/liter) in a 24-hour period and shall never be less than 4.0 (mg/l). Normal daily and seasonal fluctuations above these levels shall be maintained. All the waterbodies are estuarine creek systems and therefore fall in this category.

Biochemical Oxygen Demand (Class III Waters- Fresh and Marine) Biochemical Oxygen Demand (B.O.D.) 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.

Fecal Coliform Bacteria (Class III Waters- Fresh and Marine) The most probable number (MPN) or membrane filter (MF) counts per 100 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.

When flow data are available in the waterbody, fe cal coliform TMDLs are typically expressed as daily loads in units of counts per day. The target for the TMDLs is 400 MPN/100ml, which is the level not to be exceeded in more than 10 percent of the data, as this is the more stringent of the acute criteria. Fecal coliform TMDLs may also expressed in terms of the percent reduction required to achieve water quality standards when flow data are not available in the WBID or due to hydrologic and/or geologic conditions it is not possible to estimate flow (i.e., tidal influence or karst geologic formation). The percent reduction is calculated based on those observations exceeding the 400 MPN criteria.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 10



### It is appropriate to use the 10 percentile and maximum-based criteria for fecal coliform TMDL development as the data indicates violations of t he standard are typically related to storm events, which are short-term in nature. Violations of the geometric mean criteria are typically associated with point sources or non-point source continuous discharges (e.g., leaking septic systems) and typically occur during all weather conditions. Targeting the 10 percentile and maximum-based criteria should be protective of the chronic criteria.

Total Coliform Bacteria (Class III Waters- Fresh and Marine) The MPN per 100 ml of total coliform bacteria shall be less than or equal to 1,000 as a monthly average nor exceed 1,000 in more than 20 percent of the samples examined during any month, and less than or equal to 2,400 at any time. Monthl y averages shall be expressed as geometric means based on a minimum of 10 samples taken over a 30-day period.

The target for the total coliform TMDLs is the one-day maximum concentration of 2400 counts/100mL, as less than 10 sample s were collected in a 30-day period to determine violations of the geometric mean. 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 (i.e., acute conditions). By protecting the acute criteria (i.e., one-day maximum) bacteria concentrations in the stream should meet t he chronic criteria. The not to exceed criteria is not selected as the target because there are no known health risks associated with soil-born bacteria and using this criterion for the target would likely result in overly conservative reductions.

5. WATER QUALITY ASSESSMENT AND DEVIATION FROM TARGET

FDEP maintains ambient monitoring stations throughout the Sarasota Bay and Lemon Bay drainage basins. Table 4 provides a list of these monitoring stations. Each station is identified, and the time period of record for the individual stations is provided. Data collected during the Group 3 listing cycle (i.e. January 1997 through December 2003) and any more recent data, if available, areconsidered in the data assessment. However, for those instances where no (or insufficient) post1997 data are available for a particular parameter, older data are considered in the assessment. Additional tables of water quality data measured in these WBIDs are provided in Appendix A.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 11



### Table 4. Water Quality Monitoring Stations in the impaired WBIDs.

WBID WATERBODY STATION STATION NAME PERIOD OF RECORD

1975 Elligraw Bayou 21FLMML 271433082303100/ 21FLSARA24010644 Elligraw Bayou@ US41 Bridge NEPWQ-82 2003

1975A Clowers Creek 21FLTPA 27134838230100 Clowers Creek at Brooks House 2003

21FLTPA 27135458229507 TP190- Clowers Creek 2003-2004 1984A North Creek 21FLMML 271234082292500 North Creek @ US41 Bridge NEPWQ-92 1992-1994

1984 Catfish Creek 21FLMML 271301082292600 CATFISH CREEK @ VAMO WAY BRIDGE NEPWQ-88 2003

21FLSARA24010587 North Ck US 41 Bridge 1992

21FLMML 271004082283800 South Creek @ US41 Bridge NEPWQ-95 1992-1994 1982A South Creek

21FLSARA24010588 South Ck US 41 Bridge 1992

SC1 South Creek @ Canoe Launch in Oscar Sherer Park 2005

21FLGW FLO0099 / 21FLSWFDFLO0099 Curry Creek @ Albee Farm 1995-1998

21FLSARA24010617 Curry Creek @ Albee Farm Rd. Bridge 1992 2009A Curry Creek

21FLTPA 27070318226004 TP197- Curry Creek 2003

CC1 Curry Creek at US 41 2005

21FLSARA24010620 Alligator Creek at US 41 1991-1992 2030 Alligator Creek

21FLSARA24010676 Alligator Crk at Jacaranda Blvd. 1991-1992

21FLCHARLBV001 Alligator Crat Yacht Club Dr. Venice 1998-2000

21FLA 56112SEAS Canal West of ICWW 31 1991-1998

21FLSARA24010567 Lemon B Up Forked CR 1991-1992

21FLSARA24010623 Forked Crk at RT #775 Bridge 1991-1992 2039 Forked Creek

21FLCHARLBFOR1 Forked Creek at 775 Bridge 2000Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 12



### WBID WATERBODY STATION STATION NAME PERIOD OF RECORD

FC1 Forked Creek @ SR 776 (Englewood Rd.) 2005

21FLSARA24010621 Alligator Crk at Shamrock Blvd. 1991-1992 2042 Direct Runoff to Bay

WC1 Woodmere Creek @ Ponderosa Rd. Gauging Station 2005

AC1 Outlet of small creek (Woodmere Cr.?) to Bay 2005

21FLA 24010591 Gottfried Crk at 775-776-45A Brd 1991-1998

21FLSARA24010593 Gottfried Crk at End Wentworth S 1991-1992

21FLSARA24010624 Deer Creek at Norton Av Englewood 1991-1992

21FLCHARLBGOT2 Gottfried Creek at SR77 1998-2000 2049 Gottfried Creek

CHNEPLLB515 CHNEP515POR 2002-2003

GC1 Gottfried Creek @ Dearborn Avenue 2005



### 5.1 Dissolved Oxygen Data Although the State of Florida does not have numeric criteria for nutrients, a narrative criterion exists as described in the Water Quality Standards section of this report. Chlorophyll and dissolved oxygen are generally used to indicate whether nutrients are present in excessive amounts. However CHLA and DO monitoring data in the waterbodies are old and/or insufficient to perform a defendable analysis/modeling of current water quality condition.

Natural dissolved oxygen (D.O.) levels in a water body are a function of water temperature, water depth and velocity, and relative contribution of groundwater. Oxygen can be introduced to streams by wind, diffusion, tributaries, and photosynthesis. Warm water holds less oxygen than cool water, and slower-flowing, less turbulent water has less diffu sion of atmospheric oxygen into it. Because it is not in contact with air, groundwater naturally has lower concentrations of oxygen dissolved in it. D.O. levels naturally fluctuate over the course of a day. During the daylight, aquatic plants produce oxygen as a by-product of photosynthesis. At night, respiration may consume dissolved oxygen from the water. Decomposition of organic matter, such as dead plants and animals, also uses up dissolved oxygen.

For Class III marine waters, the water quality criter ia state that dissolved oxygen should not be less than 5.0 mg/l in a 24-hour period, and should never be less than 4.0 mg/l. For Class III fresh waters, the dissolved oxygen should not be less than 5.0 mg/l. Table 5 summarizes the D.O. data for the Sarasota Bay and Lemon Bay (Charlotte Harbor) WBIDs.

The available D.O. data indicate that dissolved oxy gen concentrations in many of the Sarasota Bay and Charlotte Harbor WBIDs are frequently below the Class III Water Quality Criterion that appliesDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 13



### to them (Table 5). In Clowers Creek, WBID 1975A, D.O. is potentially impaired, ranging from 1.1 to 7.8 mg/l and averaging 4.2 mg/l. Thirty eight percent of the data from Clowers Creek is below the Class III Fresh Water Criterion of 5 mg/l D.O. Although there are no D.O. data available for South Creek, WBID 1982A, D.O. was measured betw een 1992 and 1994 in WBID 1982B of South Creek. WBID 1982B is located entirely within the boundaries of WBID 1982A. Those D.O. data range from 1.5 to 7.6 mg/l and average 5.4 mg/l, with 26% of the values below the 4 mg/l standard. In North Creek, WBID 1984A, the only D.O. concentrations available are from 1992-1994. Those data range from 2.6 mg/l to 13.5 mg/l, and average 5.0 mg/l, with about 40% of the available data below the standard of 4 mg/l. More recent data are available for Curry Creek, WBID 2009A. The D.O. measurements range from 1.34 to 7.57 mg/l and av erage 4.54 mg/l. This represents an excursion rate of about 54%.

Table 5. Summary of Dissolved Oxygen Data (mg/l) for Impaired WBIDs.

WBID Waterbody Time Period Obs Min Max Mean StDev Median WQC %

1975 Elligraw Bayou 2003 20 2.1 10.8 5.8 3.1 5.6 5 55%

1975A Clowers Creek 2003 13 1.1 7.8 4.2 2.4 3.7 5 38%

1982A 1 South Creek 1992-1994 19 1.5 7.6 5.4 1.9 5.3 4 26%

1984 Catfish Creek 2003 25 3.1 15.4 7.4 6.6 3.4 4 80%

1984A North Creek 1992-1994 15 2.6 13.5 5.0 2.8 4.2 4 40%

2009A Curry Creek 1997-2003 13 1.3 7.6 4.5 2.0 4.5 4 54%

2030 Alligator Creek 1998-2000 28 1.2 6.0 3.4 1.0 3.2 4 75%

2039 Forked Creek 2000 9 3.2 6.4 4.5 1.2 4.4 4 33%

2049 Gottfried Creek 1998-2000 27 1 8.7 3.7 1.8 3.3 4 68%



### Notes: Obs= number of observations; Min= minimum value in the dataset; Max= maximum value in the dataset; Mean= average of all values in the dataset; StDev= st andard deviation; Median= median of all values in the dataset; WQC= applicable water quality criterion (marine or fresh); % = percentage of samples below the applicable water quality criterion for D.O.

1 Data summary for South Creek is from WBID 1982B, South Creek in Park.



### In Alligator Creek, WBID 2030, the dissolved oxy gen concentrations range from 1.2 to 6.0 mg/l and average only 3.4 mg/l. Fully 75% of the measurements are below the Class III Marine Water Quality Criterion of 4 mg/l. In Forked Creek, WBID 2039, one-third of the data are below the criterion. The D.O. concentrations in Forked Creek range from 3.2 to 6.4 mg/l and average 4.5 mg/l. Dissolved oxygen could not be assessed for WBID 2042, Direct Runoff to Bay, because no D.O. data are available.

Gottfried Creek and Elligraw Bayou have been forma lly 303(d)-listed for dissolved oxygen. In Gottfried Creek, WBID 2049, the D.O. data range from 1 mg/l to 8.7 mg/l, and average at 3.7 mg/l. Over two-thirds of the measured D.O. values in WBID 2049 are below the applicable standard of 4 mg/l. The D.O. data for Gottfried Creek are plotted in Figure 2

. In Elligraw Bayou, WBID 1975, D.O. ranges from 2.1 to 10.8 mg/l, and averages 5.8 mg/l. Approximately 55% of the data is below the water quality criterion (Figure 3).Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 14



### WBID 2049 Water Quality Data

0 2 4 6 8 10

1/5/ 1 998

7/24/ 1 9

98

2/9/ 1 99

9 8/28/19 99 3/15/20 00 10/1/20 0 0 4/19/ 2 0

01

11

/ 5/20 01 5/24/20 02 12/

1 0/

2

002

6/28/20 03 Dissolved Oxygen (mg/l) WaterQualityCriteria



### Figure 2. Dissolved Oxygen Measurements in Gottfried Creek, WBID 2049.



### WBID 1975 Water Quality Data

0 2 4 6 8 10 12

01

/ 29/03 03/20/03
05 / 09

/ 03 06/28/03 08/17/03
10 / 06

/ 0

3 11/25/03

0 1/

14

/ 0

4 Dissolved Oxygen Water Quality Criteria



### Figure 3. Dissolved Oxygen Measurements in Elligraw Bayou, WBID 1975.

5.2 Chlorophyll Data Chlorophyll is the green pigment in plants that allows them to create energy from light. In a water sample, chlorophyll is indicative of the presence of algae, and chlorophyll-a is simply a measure of the active portion of total chlorophyll. There are limited chlorophyll data for many of the Sarasota Bay and Charlotte Harbor WBIDs that are 303(d)-listed for nutrients. Table 6 summarizes theDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 15



### available chlorophyll data.

Table 6. Summary of Chlorophyll Data ( μ g/l) for Impaired WBIDs.

WBID Waterbody Time Period Obs Min Max Mean StDev Median 1975 Elligraw Bayou 1992-1993 7 10.4 47.3 19.9 12.8 15.3
1975A Clowers Creek 2003 10 1 58 11.9 21.8 1.55 1982A South Creek 1992-93, 2005 9 3.1 46.1 10.1 13.7 6.1
1984A North Creek 1992-1993 8 3.8 30.5 14.4 11.5 11.1 2009A Curry Creek 2003-2005 3 1 5.4 2.5 2.5 1 2030 Alligator Creek 1998-2000 25 1 48.7 9.5 10.1 6.0
2039 Forked Creek 2005 1 - - 9.3 - 9.3 2042 Direct Runoff to Bay 2005 2 2.0 2.5 2.25 0.35 2.25
2049 Gottfried Creek 2002-2005 3 1 13.1 6.1 6.3 4.2
Notes: Obs= number of observations; Min= minimum val ue in the dataset; Max= maximum value in the dataset; Mean= average of all values in the datas et; StDev= standard deviation; Median= median of all values in the dataset.
1 μ g/l is the lower quantification limit.



### Chlorophyll measurements available for Elligra w Bayou (WBID 1975) were collected in 2003. Those concentrations range from 1.0 to 56.0 μ g/l, and average 19.9 μ g/l (Figure 4). Based on this data, it appears that Elligraw Bayou may not be subject to algal blooms.



### WBID 1975 Water Quality Data

0 10 20 30 40 50 60

06/28/03 07

/ 18

/ 03 08/07/0 3

0 8 /27/0 3

09

/ 16

/ 03
10

/ 06

/0

3

10/26/03 11/15/03
12

/ 05

/ 03

1 2 /2

5 /0

3 Chlorophyll A Water Quality Criteria

Figure 4. 

### Chlorophyll measurements in WBID 1975 (Elligraw Bayou).
The chlorophyll concentrations measured in Clowers Creek (WBID 1975A) range from 1 to 58 μ g/l, and average 11.9 μ g/l. The high range and standard deviation of the data indicates that chlorophyll concentrations are frequently low in Clowers Creek, but the stream is subject to occasional algal blooms that increase chlorophyll concentrations considerably (Figure 5).Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 16



### WBID 1975A Water Quality Data

0 10 20 30 40 50 60 70

1 /29/20 0 3

3 /2

0 / 2 0 0 3 5/9/2 0 03

6/ 2 8 / 2003

8 /17/ 2 0 0 3

1 0/

6 / 2 0 0 3

1 1 /25/ 2

0 0 3 1/14 / 2004 Chlorophyll Corrected (ug/l)



### Figure 5. Chlorophyll measurements in WBID 1975A (Clowers Creek).

Most of the chlorophyll measurements available for South Creek (WBID 1982A) were collected in 1992-1993 (Figure 6). In March, EPA collected another sample in South Creek and measured its chlorophyll concentration. Only one of the 9 chlorophyll measurements appears elevated. In Curry Creek (WBID 2009A), there are only three measurements for corrected chlorophyll, two of which were at the lower quantification limit of 1 μ g/l. The third value was also low (5.4 μ g/l). The chlorophyll concentrations for both of these streams do not indicate the presence of algal blooms. However, nutrient TMDLs are provided for both st reams, because their chlorophyll data are limited, median nutrient levels in both streams are higher than FDEP’s program threshold, both have low dissolved oxygen, and both are potentially influenced by urban stormwater runoff.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 17



### WBID 1982A Water Quality Data

0 10 20 30 40 50

5/7/ 1 990 1/31/19 93

1 0/

2 8/

1 995 7/24/19 9 8 4/19/20 01 1/14/20 04 10/10/ 2

006 Chlorophyll (ug/l) Water Quality Comparison



### Figure 6. Chlorophyll measurements in WBID 1982A (South Creek).

The only chlorophyll concentrations available for North Creek (WBID 1984A) were eight measurements made in 1992-1993. Those concentra tions appear elevated, ranging from 3.8 to 30.5 ` μ g/l and averaging 14.4 μ g/l (Figure 7).



### WBID 1984A Water Quality Data

0 5 10 15 20 25 30 35

12

/ 28

/ 19

91 4/6/1992 7/15/19 92

10/23/1992 1/31/19 9 3

5/11/19 9 3

8/19/19 93

11/27/1993

3/ 7 /1

99

4 Chlorophyll (ug/l) Water Quality Comparison



### Figure 7. Chlorophyll measurements in WBID 1984A (North Creek).Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 18



### There were eight measurements for chlorophyll concentrations made in 2003 for Catfish Creek (WBID 1984). Five of those measurements were higher than 11 μ g/l. Concentrations ranged from
0.9 to 40.0 μ g/l and averaged 12.6 μ g/l (Figure 8).



### WBID 1984 Water Quality Data

0 5 10 15 20 25 30 35 40 45

5/9/ 2 003

6/ 2 8/

2 00

3 8/17/ 2 00

3

10 / 6/200 3

1 1/

2 5/

2

003 1/14/200 4 Chlorophyll (ug/l) Water Quality Comparison



### Figure 8. Chlorophyll measurements in WBID 1984 (Catfish Creek).

In Alligator Creek (WBID 2030), chlorophyll concentrations ranged from 1 to 48.7 μ g/l. The average
concentration was 9.5 μ g/l. Many of the observations appear to be elevated, indicating the likely presence of algal blooms (Figure 9).



### WBID 2030 Water Quality Data

0 10 20 30 40 50 60

4/15/199 8 7/24/ 1 998

11

/ 1/19 98

2 / 9/1999

5 / 20

/ 19

99 8/28/1999

12

/ 6/199 9 3/15/2000 6/23/20 00 10/1/2000 1/9/200 1 4/19/2001 Chlorophyll (ug/l) Water Quality Comparison



### Figure 9. Chlorophyll measurements in WBID 2030 (Alligator Creek).Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 19



### There is only one recent measurement of chlorophyll in Forked Creek (WBID 2039). This sample was collected in March 2005, and had a value of 9.3 μ g/l. Two measurements of chlorophyll were made in WBID 2042 (Direct Runoff to Bay) in March 2005. The sample taken from Woodmere Creek (which is a freshwater stream) had a chlorophyll concentration of 2.0 μ g/l, and the sample taken from a small, unnamed watercourse entering the bay had a concentration of 2.5 μ g/l. Three recent measurements of chlorophyll are available for Gottfried Creek (WBID 2049). These concentrations range from 1 to 13.1 μ g/l, and average 6.1 μ g/l.

5.3 Algal Growth Potential Data Algal Growth Potential (AGP) tests measure the levels of biologically available nutrients by determining the maximum amount of algal growth that nutrients in the water can support. This indicates the potential for algal blooms or nuisance aquatic weed growth, which can lead to eutrophication. Studies have shown that algal dry weight concentrations exceeding 6.1 mg/l are associated with highly productive waters (Miller et. al., 1974) and algal dry weight concentrations exceeding 10 mg/l are associated wi th eutrophic waters which are subject to nuisance algal blooms (EPA, 1975; and Raschke, et. al., 1987).

Table 7 summarizes the results of the algal growth potential tests for the impaired WBIDs. Results of AGP tests in WBID 2009A (Curry Creek), WBID 1982A (South Creek), and WBID 2049 (Gottfried Creek) yielded algal dry weight concentrations of 5.4 mg/l, 5.0 mg/l, and 5.1 mg/l, respectively. These values are slightly lower than the threshold considered to indicate highly productive waters. The AGP test result for WBID 1975 (Elligraw Bayou) wa s just above this threshold. Algal dry weight concentrations for WBID 2030 (Forked Creek) and both samples for WBID 2042 (Direct Runoff to Bay) are above 10 mg/l, indicating that those waters are very productive and may be eutrophic.

Table 7. Results of Algal Growth Potential Tests

WBID Waterbody Date AGPT (mg/l) 1975 Elligraw Bayou (McGraw Creek) 3/22/2005 6.1 (7.1 for duplicate)

1982A South Creek 3/22/2005 5.0

2009A Curry Creek 3/22/2005 5.4

2039 Forked Creek 3/22/2005 12.4 A

2042 Direct Runoff to Bay (outlet creek) 3/22/2005 11

2042 Direct Runoff to Bay (Woodmere Creek) 3/22/2005 16.8 A

2049 Gottfried Creek 3/22/2005 5.1 NOTES: A = Analyte analyzed in replicate. Reported value is “average” of replicates. AGPT= maximum standing crop (dry weight)



### Based on the available data for chlorophyll, nutrients, and algal growth potential, etc, TMDLs are provided for nutrients in the following 303(d)-listed waters: Elligraw Bayou (WBID 1975), South Creek (WBID 1982A), North Creek (WBID 1984A), Curry Creek (WBID 2009A), Alligator Creek (WBID 2030), Forked Creek (WBID 2039), Direct Runoff to Bay (WBID 2042), and Gottfried Creek (WBID 2049). The D.O. listings for Elligraw Bayou (WBID 1975) and Gottfried Creek (WBID 2049) will also be addressed. EPA will accept the delis ting request for nutrients in WBID 1975A (Clowers Creek).Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 20



### 5.4 Total Coliform Data Total coliform bacteria generally indicate the presence of soil-associated bacteria. One sub-group of total coliforms is fecal coliform bacteria, which are used as indicators of fecal contamination since they are abundant in the intestines and feces of animals and people. As such, total coliform bacteria concentrations may result from natural influences on a water body, as well as unnatural influences such as sewage inflows.

In Elligraw Bayou (WBID 1975), 4 of the 20 samples (25%) were above the 2400 MPN/100ml standard that is not to be exceeded at any time. The data are illustrated in Figure 9.

In Clowers Creek (WBID 1975A), 5 of the 20 samples (20%) were above the 2400 MPN/100ml standard that is not to be exceeded at any time (Figure 10).

Summary statistics for total coliforms in both WBIDs are provided below in Table 8.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 21



### Table 8. Total Coliform Data for Impaired WBIDs.

WBID Waterbody Time Period Obs Min Max Mean StDev Median Percent Excursions

1975 Elligraw Bayou 2003 20 1 5800 1325 1685 690 20

1975A Clowers Creek 2003 20 1 3700 1107 1139 780 25

Notes: Obs= number of observations; Min= minimum value in the dataset; Max= maximum value in the dataset; Mean= average of all values in the dataset; StDev= st andard deviation; Median= median of all values in the dataset.



### WBID 1975 Water Quality Data

0 1000 2000 3000 4000 5000 6000 7000

0

1 / 29

/ 0

3

0 3/20/03

0 5 / 0 9/03

0 6/28 / 03

0 8 / 17

/ 0

3

1 0/06/03

1 1 / 2 5/03

0 1/14 / 04 

### Total Colifirm Water Quality Criteria



### Figure 10. Total Coliform Measurements in WBID 1975 (Elligraw Bayou).Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 22



### WBID 1975A Water Quality Data

0 500 1000 1500 2000 2500 3000 3500 4000

1/

2 9/

2 0

03 3/20/20 0 3 5/9/ 2 003 6/28/20 03

8/ 1 7/

2 0

03 10/6/2003 11/25/2003 1/14/20 04 Total Coliform (/100ml) WaterQualityCriteria



### Figure 11. Total Coliform Measurements in WBID 1975A (Clowers Creek).

5.5 Fecal Colliform Data The fecal coliform data for Elligraw Bayou (WBID 1975) and Clowers Creek (WBID 1975A) are summarized in Table 9.

In Elligraw Bayou (WBID 1975), 8 of the 20 samples (40%) were above the 800 MPN/100ml standard that is not to be exceeded at any time, and 70% of the data were above 400 MPN/100ml. The data are illustrated in Figure 12. In Clowers Creek (WBID 1975A), 7 of the 10 samples (35%) were above the 800 MPN/100ml standard that is not to be exceeded at any time and 70% of all the data are above 400 MPN/100 ml (Figure 13).

Table 9. Fecal Coliform Data for Impaired WBIDs.

WBID Waterbody Time Period Obs Min Max Mean StDev Median Percent Excursions 1

1975 Elligraw Bayou 2003 20 65 2500 758 575 602 70

1975A Clowers Creek 2003 20 75 4400 975 986 628 70

NOTES: Obs= number of observations; Min= minimum val ue in the dataset; Max= maximum value in the dataset; Mean= average of all values in the dataset; StDev= standard deviation; Median= median of all values in the dataset. 1. Percent excursions above the TMDL target of 400 MPN/100ml.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 23



### WBID 1975 Water Quality Data

0 500 1000 1500 2000 2500 3000

01

/ 29

/ 03 03/20/03 05/09/03 06/ 2 8/

0

3 08 / 17

/ 03 10/06/03 11/25/03 01/14/ 0

4 Fecal Coliform Water Quality Criteria



### Figure 12. Fecal Coliform Measurements in WBID 1975 (Elligraw Bayou).



### WBID 1975A Water Quality Data

0 1000 2000 3000 4000 5000

1/29/2003 3/20/2003

5/ 9/

2003

6/ 28/

20

03

8/ 17/

20

03

10 /6/2003
11/ 25/

2003

1/ 1 4/2004 Fecal Coliform (/100mll) WaterQualityCriteria



### Figure 13. Fecal Coliform Measurements in WBID 1975A (Clowers Creek).

Based on the available data for coliforms, TMDLs are needed for total and fecal coliforms in Elligraw Bayou (WBID 1975) and Clowers Creek (WBID 1975A).Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 24



### 6. SOURCE ASSESSMENT

An important part of the TMDL analysis is the identification of source categories, source subcategories, or individual sources of pollutants in the watershed and the amount of loading contributed by each of these sources. Sources are broadly classified as either point or non-point sources. Nutrients enter surface waters from both point and 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 and treated sanitary wastewater must be authorized by Na tional Pollutant Discharge Elimination System (NPDES) permits. NPDES permitted facilities, in cluding certain urban stormwater discharges such as municipal separate stormwater systems (MS4s) , certain industrial facilities, and construction sites over one acre, are storm-water driven sources that are considered “point sources” in this report.

Non-point sources of pollution are diffuse sources that cannot be identified as entering a waterbody through a discrete conveyance at a single location. These include runoff of agricultural fields, golf courses, and lawns, septic tanks, and residential developments outside of MS4 areas. These sources generally, but not always, involve accumulation of nutrients and/or bacteria on land surfaces and wash off as a result of storm events.

6.1 Point Sources A wasteload allocation (WLA) is given only to NPD ES facilities discharging to surface waters and to permitted Municipal Separate Storm Sewer Systems (MS4s). It should be noted that permits for wastewater facilities authorize a discharge only if the applicant provides reasonable assurance that the discharge will not cause or contribute to violations of the water quality criteria.

6.1.1 NPDES Facilities Although many of the 303(d)-listed WBIDs in the Sarasota Bay and Lemon Bay planning units contain domestic and industrial wastewater facilities, most of them do not discharge directly to surface water and therefore, do not have NPDES permits (although they may have state permits). Only one facility, Snowbirdland Vistas (FL0041785), currently discharge a pollutant of concern in the listed WBIDs. Snowbirdland Vistas is a mobile home site that discharges to Curry Creek (WBID 2009A), which is 303(d)-listed for nutrients. It is a minor facility that has an annual average discharge limit of only 20,000 gallons per day (gpd). Its permit (#FL0041785) also contains limits for dissolved oxygen (D.O.), pH, radium 226 + radi um 228, and alpha- gross particle activity. In addition, Snowbirdland Vistas is required to conduct to xicity testing. There are no specific limits for any nutrient. The limit for D.O. is a daily minimum of 4 mg/l. This is an end-of-pipe limit equivalent to the applicable water quality standard for Curry Creek, the receiving waterbody.

6.1.2 MS4 areas According to 40 CFR 122.26(b)(8), a municipal separate storm sewer (MS4) is “a conveyance or system of conveyances (including roads with dr ainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains): (i) Owned or operated by a State, city, town, borough, county, parish, district, association, or other public body (created by or pursuant to State law)...including special districts under State law such as a sewer district, flood control district or drainage district, or similar entity,Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 25



### or an Indian tribe or an authorized Indian tribal organization, or a designated and approved management agency under section 208 of the Clean Water Act that discharges into waters of the United States. (ii) Designed or used for collecting or conveying storm water; (iii) Which is not a combined sewer; and (iv) Which is not part of a Publicly Owned Treatment Works.”

Municipal Separate Storm Sewer Systems (MS4s) may discharge nutrients, coliform bacteria, and other pollutants to waterbodies in response to storm events. Large and medium MS4s serving populations greater than 100,000 people are required to obtain a NPDES storm water permit under the Phase I storm water regulations. After March 2003, small MS4s serving urbanized areas were required to obtain a permit under the Phase II storm water regulations. An urbanized area is defined as an entity with a resi dential population of at least 50,000 people and an overall population density of 1,000 people per square mile.

The Phase I MS4 permit #:FL000004, which covers Sarasota County, FDOT District 1 and the cities of North Port, Sarasota, and Venice, and Longboat Key, may affect listed WBIDs in the Sarasota Bay watershed. A requirement of the MS4 permit is the development of a Master Stormwater Management Plan. Implementation of this plan addresses water quality and flooding problems according to a priority list.

6.2 Nonpoint Sources Nonpoint sources that ultimately contribute to depletion of in-stream dissolved oxygen include sources of nutrients such as animal waste, waste-lagoon sludge, fertilizer application to agricultural fields, lawns, and golf courses, and malfunctioning onsite sewage treatment and disposal systems or septic tank systems. Many of these sources are also potential contributors of coliform bacteria.

The major landuses in the Sarasota Bay Planning Unit WBIDs are residential and commercial/industrial, along with lesser amounts of open water and wetlands (Table 2). Residentialand commercial/industrial developments are also important in the Lemon Bay Planning Unitespecially in WBIDs 2042 (Alligator Creek) and 2030 (Direct Runoff to Bay). Agriculture and rangeland are significant portions of WBIDs 2049 (Gottfried Creek) and 2039 (Forked Creek).

6.2.1 Wildlife Wildlife deposits their feces onto land surfaces where it can be transported during storm events to nearby streams. Water fowl (e.g., egrets, ducks, wood storks, herons) often frequent stormwater ponds. Generally, the nutrient and bacterial load from wildlife is assumed to be background, as the contribution from this source is small relative to the load from urban and agricultural areas in most watersheds.

6.2.2 Agricultural animals Agricultural activities, including fertilizer application and runoff from pastureland and cattle in streams, can impact water quality. Between 1997 and 2002, Sarasota County experienced a 6% decline in farmland. Many of the waterbodies listed for nutrients and/or coliforms are located in urban areas and livestock are not a relevant source of impairment. However, agriculture and rangeland are significant landuses in some of the impaired watersheds, including WBIDs 2049 (Gottfried Creek) and 2039 (Forked Creek).

The Florida Department of Agriculture and Consumer Services (FDACS), Office of AgriculturalDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 26



### Water Policy developed a manual outlining best management practice for cow/calf operations (FDACS, 1999). In this report the authors state “implementation of the practices described in this manual provides a good argument that you have m ade reasonable efforts to reduce pollutants from your ranch by the maximum practicable amount”. The manual acknowledges “after implementation of these BMPs it may be necessary to add more stringent guidelines for site specific areas that continue to exceed water quality standards”.

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) di rects 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. Livestock inventory from the 1997 and 2002 Census of Agriculture reports for Sarasota County are listed in Table 10. As shown in this table, cattle and beef cows are the predominate livestock. Confined Animal Feeding Operations (CAFOs) are not known to operate in the county.

Table 10. Livestock Inventory for Sarasota County, Florida.

Livestock Number of Farms 1 Inventory
1997 2002 1997 2002
Cattle and calves 276 176 26,248 22,741
Beef Cows 240 161 16,368 15,147
Dairy Cows 21 4 377 9

Swine 47 15 526 181
Poultry (broilers sold) - - - -
Sheep 10 7 46 68

Goats - 5 - 23

Horses and Ponies - 126 - 882 Notes: (D) – data withheld to avoid di sclosing data for individual farms. 1. A farm is defined as any place from which $1,000 or more of agricultural products were produced and sold, or normally would have been sold, during the census year.



### In 2002, NASS reported 371 farms in Sarasota County covering an area of 121,310 acres, as compared to 463 farms in 1997 covering an area of 129,311 acres. The average size farm in Sarasota County in 2002 was 327 acres. In bot h 1997 and 2002, farms in Sarasota County applied more commercial fertilizer to cropland, pastureland, and rangeland, as compared to manure. Despite the decline in the number of farms and their total acreage, use of chemical fertilizers in Sarasota County increased between 1997 and 2002. In 1997, 3,416 acres of pastureland and rangeland were treated with chemical fertilizer, compared to 4,237 acres in 2002.

6.2.3 Onsite Sewerage Treatment and Disposal Systems (Septic Tanks) Onsite sewage treatment and disposal systems (OSTDs) including septic tanks are commonly used where providing collection and central treatment are 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-functi oning OSTD is comparable to secondarily treated wastewater from a sewage treatment plant. When not functioning properly, OSTDs can be a source of nutrients (nitrogen and phosphorus), pathogens, and other pollutants to both ground water andDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 27



### surface water.

The State of Florida Department of Health (www.doh.state.fl.us/environment/ostds/statistics/) publishes septic tanks data on a county basis. Tabl e 11 summarizes the number of septic systems installed in Holmes County since the 1970 census and the total number of repair permits issued between 1997-98 and 2003-04. The data does not reflect septic tanks removed from service.

Table 11. Estimates of Septic Tanks and Repair Permits for Sarasota County.

County Number of Septic Tanks (2002) Number of Repair Permits Issued (1997 – 2004)

Sarasota 74,774 3,491



### 6.2.4 Urban Development Nutrient 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.

In 1982, Florida became the first state in the count ry to implement statewide regulations to address the issue of nonpoint source pollution by requi ring new development and redevelopment to treat stormwater before it is discharged. The Stormwater Rule, as outlined in Chapter 403 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 hav ing 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 62-4-.432 (5)(c), F.A.C.).

Nonstructural and structural BMPs are an integral part of the State’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.

7. ANALYTICAL APPROACH

7.1. Nutrient and Biolochemical Oxygen Demand (BOD) In order to develop nutrient TMDLs, the narrative nutrient criterion must first be translated to numeric targets using appropriate analytical tools. Because of the lack of sufficient and/or recent nutrient and flow data to allow appr opriate calibration/validation of a distributed model, a watershed loading model, the Lemon Bay Watershed Model (LBMW), was used to determine existing andDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 28



### target loads of total nitrogen and BOD for the impaired WBIDs. Nitrogen is the only nutrient addressed in these TMDLs because it is the limiting factor for phytoplankton productivity in Sarasota, Charlotte Harbor, and Lemon Bay ecos ystems (Dixon and Kirkpatrick, 1991, SWFWMD, 1999). The next section describes watershed loading models in general and the LBWM modeling application to generate loads for the impaired WBIDs.

7.1.1 Determination of Pollutant Loading Capacity During the last fifteen years, several WQ modeling efforts were undertaken to estimate pollutant loadings originating from upland watersheds to several Florida bays including Hillsborough Bay (Johansson, 1991), Charlotte Harbor (Squires et al., 1998), Sarasota Bay (Heyl, 1992), Tampa Bay (Harper, 1991), and Lemon Bay (ERD, 2004). These modeling activities were carried out by Watershed Management Districts often in collaboration with national estuaries programs in these areas, Florida Department of Environmental Protection, and local counties. These models are simple loading functions in which annual average runoff and loadings to bays are derived using simple algorithms and land use loading rates to generate long term annual averages of runoff volumes and pollutant loadings to the Bay.

The Lemon Bay Watershed Model is an excel worksheet that estimates total annual runoff stormwater runoff volumes and pollutant loadings from seven watersheds draining to Lemon Bay (ERD, 2004). First, Runoff volumes are estimated using site specific land use and hydrologic soil groups, percent impervious, and percent directed connected impervious areas (DCIA) calculated as a percent of the total impervious area. Then pollutant concentrations specific to each land use are used with runoff volumes to generate pollutant loads. Finally, attenuation factors are applied to total generated runoff volumes and pollutant loads to account for losses in stormwater and conveyance systems. The model is an improv ement of previous similar efforts in Sarasota, Charlotte and Lemon Bays (Heyl, 1992, Squires et al., 1998, Tomasko et al., 2001) because land use loading rates and attenuation factors used in this model are considered to be more accurate. When compared to measured data from contributing wa tersheds, modeled results differed only by 11%, 24%, 1%, and 7%, respectively for total N, total P, BOD and TSS. More information on the model is provided in Environmental Research and Design, Inc. (2004).

7.1.1.1. Hydrologic Data and Runoff Generation This section presents hydrologic data used for runoff generation in the impaired WBIDs using the LBWM model. Land use and soil information were obtained from the SWFWMD GIS data (http://www.swfwmd.state.fl.us/data/gis/). FLUCCS were consolidated into 14 land use categories as shown in Table 12 and are the same as those presented in Table 3. Percent impervious for each land use in a WBID was determined based on measurements from 1999 1-meter resolution orthophoto quads. Percent DCIA is computed as a percentage of impervious areas using values typical for the given land use (Table 12). Wet and dry season rainfall distributions used in the model were derived from the National Climatic Data Center (NCDC) hourly rainfall for St. Petersburg and Ft. Myers, and daily rainfall from Englewood and Cape Haze. Weighted seasonal curve numbers (CNs) under average an tecedent moisture conditions (AMC II), dry (AMC I) and wet conditions (AMCIII) are computed using the fraction of events falling into each AMC, hydrologic soil group (HSG) and land use/cover distributions in WBIDs.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 29



### Table 12. Percent Impervious and DCIA by Land Use for Impaired WBIDs.

LAND USE PERCENT IMPERVIOUS % IMPERVIOUS THAT IS DCIA Agriculture 0 0 Commercial 65 75 Extensive 50 25 Industrial 50 25 Low-Density Residential 15 20 Medium Density Residential 40 40 High-Density Residential 60 65 Transportation 50 90 Institutional 45 60 Open 0 0 Recreational 6 0 Wetlands 0 0

7.1.1.2. Pollutant Loading Rates for Land Use Categories LBWM uses loading concentrations in runoff emanating from each land use. Nutrient and BOD concentrations in stormwater were primarily based on long-term monitoring data that were obtained as part of the model development and on data colle cted by counties, universities, and private agencies in Lemon Bay, Sarasota and Charlotte Bay contributing watersheds (ERD, 2004). Loading rates for total N and BOD used in this analysis are presented in Table 13.

Table 13. Nutrient and BOD Concentrations in Stormwater by Land Use

Typical Loading Rates (mg/l) Land Use
Total N BOD

Agriculture 1.24 2.40
Commercial 0.88 2.30
Extractive 1.18 9.60
Industrial 1.64 9.60 Low-Density Residential 0.94 1.50 Medium-Density Residential 1.17 2.00 High-Density Residential 1.17 3.10 Transportation 2.23 6.70
Institutional 1.17 2.00Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 30

Open 0.70 1.00
Recreational 1.17 2.00
Wetland 1.44 2.63 Water (Ponds and Lakes) 0.31 2.00 Water (Conveyance) 0.31 2.00



### 7.1.1.3. Load Attenuation Factors A series of load attenuation factors is used in the model for each land use to represent the effect of stormwater system treatment. The first attenuation factor is the treatment potential value of each land use. It is the ratio of water (ponds, lakes, and reservoirs) falling in each land use to that land use area in the watershed. The attenuation values for this factor are presented by land use for the 8 impaired WBIDs in Table 14. The second factor is the stormwater attenuation factor (Table 15). It is applied to pollutant load to represent load losses over the watershed landscape and load reductions associated with in-stream processes. The third factor is the conveyance attenuation factor which is applied to the entire watershed and is function of the ratio of conveyance system (streams, estuaries) area to total watershed area (Table 16).

Table 14. Treatment Potential Factors

Land Use Ratio Land Use Area to Treatment Area

Elligraw Bayou Curry Creek North Creek Catfish Creek South Creek Gottfried Creek Forked Creek Alligato r Creek Direct Runoff to Bay Agriculture 0.05 0.02 0.00 --- --- 0.20 0.13 --- --- Commercial 0.03 0.10 0.00 0.40 --- 0.03 0.05 0.05 --- Extractive --- --- --- --- --- --- --- --- --- Industrial 0.04 --- --- --- --- --- --- 0.00 --- Low-Density Residential 0.00 --- 0.03 0.05 0.05 0.06 0.02 0.48 ---MediumDensity Residential 0.06 0.23 0.04 0.02 0.05 0.04 0.02 0.02 High-Density Residential 0.04 0.00 0.20 0.40 0.08 0.02 0.03 0.11 0.14 Transportatio

n --- --- --- --- --- --- --- --- --- Institutional 0.01 --- --- --- 0.15 0.00 0.75 0.03 --- Open 0.00 0.03 --- 0.05 0.02 0.03 0.02 0.13 --- Recreational 0.03 0.00 0.16 0.20 0.00 0.11 0.09 0.08 --- Wetland --- --- --- 0.10 --- --- --- --- --- Water (Ponds and Lakes) 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Water (Conveyance ) 0.02 0.06 0.04 0.00 0.02 0.02 0.01 0.01 0.04Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 31



### Table 15. Stormwater System Attenuation Factors

Land Use Runoff Volume Total N BOD

Agriculture 0.00 0.00 0.00
Commercial 0.10 0.25 0.20
Extractive 0.00 0.25 0.20
Industrial 0.10 0.25 0.20 Low-Density Residential 0.15 0.25 0.00 Medium-Density Residential 0.15 0.25 0.20 High-Density Residential 0.15 0.25 0.20 Transportation 0.10 0.25 0.20
Institutional 0.15 0.25 0.20 Open 0.00 0.00 0.00
Recreational 0.15 0.25 0.20
Wetland 0.00 0.00 0.00 Water (Ponds and Lakes) 1.00 1.00 1.00



### Table 16. Conveyance System Attenuation Factors

Land Use Runoff Volume Total N BOD

Water (Conveyance) 0.00 0.25 0.10



### 7.1.1.4. Computations of Runoff Volumes and Pollutant Loadings The runoff volume for each WBID was generated for wet and dry seasons using watershed area, percent impervious, DCIA, and CN for each combination of land use and hydrologic soil group. Total N and BOD loads for dry and wet seasons were computed by multiplying the land use pollutant concentrations in Table 14 with appropriate generated runoff volumes. Attenuated pollutant loads for each season were obtained by multiplying generated load pollutants by stormwater and conveyance attenuation factors respectively in Tables 15 and 16. Annual attenuated total N and BOD loads in the impaired WBIDs were obtained by summing loadsDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 32



### generated in wet and dry seasons and are presented in Tables 17 and 18, respectively.

Table 17. Annual Total N Loads by Land Use Under Existing Conditions

Land Use Annual Total N (kg)

Land use Elligraw Bayou Curry Creek North Creek Catfish Creek South Creek Gottfried Creek Forked Creek Alligator Creek Direct Runoff to Bay

Agriculture 42.9 16.4 1.7 41.7 0.2 120.5 248.9 0.0 0.0
Commercial 407.5 69.1 65.5 232.9 260.3 328.4 150.7 532.6 29.8
Extractive 0.0 0.0 0.0 0.0 0.0 0.0 25.1 0.0 0.0
Industrial 452.7 0.0 0.0 1.0 0.0 0.0 41.7 0.0 9.0 Low-Density Residential 60.2 10.5 30.7 13.6 35.0 142.4 213.3 15.9 82.0 Medium-Density Residential 1417.5 50.9 405.7 155.8 309.4 554.3 1078.1 1313.6 952.8 High-Density Residential 672.3 846.9 289.4 1405.5 579.6 398.2 947.5 2003.0 177.0 Transportation 213.5 61.5 64.5 92.5 144.6 26.0 257.6 511.4 0.0
Institutional 188.5 27.6 0.0 4.4 51.1 109.2 7.3 143.3 0.0 Open 51.1 6.5 47.6 41.2 173.9 466.1 317.3 73.5 47.9
Recreational 69.5 4.6 77.4 87.1 2.1 49.3 32.9 43.8 4.0
Wetland 49.2 115.8 87.6 187.7 192.2 738.6 786.4 252.8 129.3 Water (Ponds and Lakes) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Water (Conveyance) 73.8 105.4 90.8 16.3 72.0 132.0 127.0 75.3 89.8

Total 2525.9 1301.0 1116.1 2279.7 1816.6 3025.1 4234.9 5370.4 1414.2Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 33



### Table 18. Annual BOD Loads by Land Use Under Existing Conditions

Land Use Annual BOD (kg)

Land Use Elligraw Bayou Curry Creek North Creek Catfish Creek South Creek Gottfried Creek Forked Creek Alligator Creek Direct Runoff to Bay

Agriculture 104.9 36.9 3.4 82.0 0.4 236.6 499.0 0.0 0.0
Commercial 1370.7 223.9 175.1 660.6 725.8 884.1 418.5 1844.0 70.3
Extractive 0.0 0.0 0.0 0.0 0.0 0.0 211.5 0.0 0.0
Industrial 3417.4 0.0 0.0 6.2 0.0 0.0 253.1 0.0 47.4 Low-Density Residential 121.4 19.4 53.4 25.2 67.9 274.4 367.4 43.6 118.2 Medium-Density Residential 3162.0 107.9 722.9 271.0 569.7 991.4 1954.6 2924.4 1483.5 High-Density Residential 2301.8 2607.3 835.8 4041.6 1724.5 1079.2 2643.4 7289.4 452.2 Transportation 810.2 214.9 198.1 282.6 463.3 79.3 801.6 1978.6 0.0
Institutional 408.4 54.8 0.0 7.6 99.5 189.6 13.8 320.8 0.0 Open 91.7 10.7 69.2 59.6 263.9 672.4 467.5 134.6 61.6
Recreational 152.6 9.1 144.3 161.6 3.9 91.1 61.7 101.2 6.2
Wetland 113.5 245.7 163.6 348.8 374.5 1368.2 1487.7 594.4 213.5 Water (Ponds and Lakes) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Water (Conveyance) 877.0 648.3 555.4 106.4 423.1 1146.3 626.1 496.4 602.5

Total 12931.6 4178.8 2921.1 6053.4 4716.3 7012.5 9806.0 15727.5 3055.4



### 7.1.2 Determination of Target Loads Target loads for total N and BOD were determined using the same model (LBWM), loading rates , and attenuation factors except land cover distribution in the impaired WBIDs. Land cover categories used for determining target loads are those considered to have existed in the impaired WBIDs prior to anthropogenic influences. They are Open Land, Wetlands and Water (ponds, lakes, and conveyances), in addition to streams and rivers. This assumption is very conservative because impairement in these watersheds more likely occured sometime after the start of the human influence. This scenario was compared to the Reference Watershed Approach, a method considered as more approapriate for TMDL computations in the abscence of WQ criteria (See Appendix B).Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 34



### Soil properties are a good indicator of land cover prior to human influnces because soils are mapped in their ‘natural’ state. Therefore, pre-development land cover categories in each WBID was determined using primarily hydrologic soil groups (HSG) as follows:

First, agriculture and developed land (residential, commercial industrial, extractive, etc.) that presently occurs on HSG D have existed as Wetlands before human settlements. This assumption makes sense because all soil series with HSG D in the Sarasota County Soil survey Manual are hydric soils, one of the main indicators of wetlands.

Second, agriculture and developed land presently on soils with HSGs A, B and C was assigned to Open Land cover and are assumed to have occurred on same HSGs.

Third, agriculture and developed land presently on soils with HSGs B/D and C/D was assigned to Open Land cover or Wetlands with the assumption that 20% of these soils were initially wetlands with HSG D. The same assumption was used in the Lemon Bay Watershed Model (ERD, 2004). The Open land use currently on B/D and C/D was assumed to have existed on HSG D. This assumption is valid because soils with HSGs B/D and C/D, which existed as poorly drained soils (HSG D) in thei r original state are currently drained and as a result exhibit characteristics of soils with HSGs B and C. These soils are currently mapped in Florida as hydric soils.

Finally, agriculture and developed land occurring on HSG designation W existed as waterbodies such as lakes and ponds and therefore were assigned to Water (ponds and lakes).

The land cover categories estimated in each WBID for natural conditions are presented in Table 19. Results obtained using the LBWM model using these categories are pr esented in Tables 20 and 21 for total nitrogen and BOD respectively.

Table 19. Land Cover Distribution in the Impaired WBIDs Under Natural Conditions

Land Use Area (acres)

Land Use Elligraw Bayou South Creek Catfish Creek North Creek Curry Creek Gottfried Creek Forked Creek Alligato r Creek Direct Runoff to Bay
Agriculture 0 0 0 0 0 0 0 0 0
Commercial 0 0 0 0 0 0 0 0 0
Extractive 0 0 0 0 0 0 0 0 0
Industrial 0 0 0 0 0 0 0 0 0 Low-Density Residential 0 0 0 0 0 0 0 0 0 Medium-Density Residential 0 0 0 0 0 0 0 0 0 High-Density Residential 0 0 0 0 0 0 0 0 0 Transportation 0 0 0 0 0 0 0 0 0
Institutional 0 0 0 0 0 0 0 0 0Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 35

Open 2,984 1,950 1,304 1,198 740 5,324 4,947 3,736 1,141
Recreational 0 0 0 0 0 0 0 0 0
Wetland 1,126 451 843 281 287 1,461 2,022 1,574 449 Water (Ponds and Lakes) 188 79 267 112 35 322 341 399 28 Water (Conveyance) 92 44 11 60 70 120 65 51 65

Total 4,390 2,524 2,426 1,651 1,132 7,227 7,375 5,760 1,683



### Table 20. Annual Total N Loads by Land Cover Under Natural Conditions

Land Use Annual Total N (kg)

Land Use Elligraw Bayou South Creek Catfish Creek North Creek Curry Creek Gottfried Creek Forked Creek Alligator Creek Direct Runoff to Bay

Agriculture 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Commercial 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Extractive 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Industrial 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Low-Density Residential 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Medium-Density Residential 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 High-Density Residential 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Transportation 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Institutional 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Open 910.4 531.2 456.4 323.8 147.4 1683.8 1696.9 2430.1 278.1
Recreational 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Wetland 758.7 349.7 637.3 186.4 242.7 1110.3 1594.8 1351.9 276.4 Water (Ponds and Lakes) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Water (Conveyance) 130.0 61.1 16.3 79.7 92.5 171.5 95.1 75.4 86.0

Total 1799.1 941.9 1110.0 590.0 482.6 2965.6 3386.7 3857.4 640.5Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 36



### Table 21. Annual BOD Loads by Land Cover Under Natural Conditions

Land Use Annual BOD (kg)

Land Use
South Creek Catfish Creek North Creek Curry Creek Gottfried Creek Forked Creek Alligator Creek Direct Runoff to Bay

Agriculture 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Commercial 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Extractive 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Industrial 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Low-Density Residential 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Medium-Density Residential 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 High-Density Residential 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Transportation 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Institutional 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Open 850.4 660.5 541.1 250.3 2561.4 2497.9 3579.3 470.9
Recreational 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Wetland 718.8 1184.3 399.8 529.4 2168.5 3014.2 2556.6 600.8 Water (Ponds and Lakes) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Water (Conveyance) 417.6 106.4 555.5 649.0 1146.3 626.1 496.4 602.5

Total 1986.8 1951.3 1496.4 1428.7 5876.2 6138.3 6632.3 1674.2



### 7.2. Coliforms The approach for calculating coliform TMDLs depends on the number of bacteria samples and the availability of flow data. When long-term records of water quality and flow data are available, load duration curves, that establish a relationship between flow and concentration, are used to developDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 37



### TMDLs. Load duration curves utilize a mass balance approach to estimate loadings transported in the stream. Otherwise, when water quality and flow data are scarce or non-existent as it is the case here, TMDLs are expressed as percent reductions.

7.1.2.1. Percent Reduction Approach Coliform TMDLs for Elligraw Bayou and Clowers Creek WBIDs were developed using the Percent Reduction Approach. As shown in Tables 8 and 9, there is a limited number of coliform samples in these WBIDs. In addition, flow data for the two waterbodies is not available. Under this approach, the percent reduction needed to meet the applicable criterion is calculated based on the 90 th 

### percentile of all measured concentrations. The 90 th 

### percentile concentration represents existing conditions and implies that 90 percent of the measured values are lower than this concentration or 10 percent are higher. The percent reduction required to meet the coliform criteria is based on the following equation:

Percent Reduction (%) = (existing concentration – criteria) / existing concentration * 100

As an example, the calculated 90 th 

### percentile concentrati on and percent reduction r equired to meet the acute criterion for Elligraw Bayou WB ID is shown in Table 22. The 90 th 

### percentile concentration is MPN/100ml and a % reduction is necessary to meet the instream water quality target of 400 counts/100 ml.



### Table 22. Fecal Coliform Measurements for Elligraw Bayou

Station Date Concentration (MPN/100ml)

21FLTPA 27151668230388 6/9/2003 1200
3/4/2003 1300
7/22/2003 790
10/13/2003 65
4/8/2003 2500
5/20/2003 210
9/23/2003 30
8/25/2003 440
12/15/2003 940
12/1/2003 400
21FLTPA 27152258230197 5/20/2003 470
12/15/2003 1210
8/25/2003 1530
3/4/2003 235
12/1/2003 360
9/23/2003 680
7/22/2003 395
6/9/2003 480
10/13/2003 670
4/8/2003 1260 

### 90 th 

### Percentile Concentration 1323 Percent Reduction 70%Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 38



### 8. DEVELOPMENT OF TOTAL MAXIMUM DAILY LOAD

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), non-point source loads (Load Allocations), and an appropriate margin of safety (MOS), which takes into account any uncertainty concerning the relationship between effluent limitations and water quality:

TMDL = Σ WLAs + Σ LAs + MOS

The objective of a TMDL is to allocate loads among the known pollutant sources throughout a watershed so that appropriate control measures can be implemented and water quality standards achieved. 40 CFR §130.2 (i) states that TMDLs can be expressed in terms of mass per time (e.g. pounds per day), toxicity, or other appropriate measure . The TMDLs are expressed as the longterm annual average loads in units of kilograms (kg) per year. TMDL components for nutrientimpaired water are provided in Table 23. For water bodies impaired by DO, the process to allocate total N and BOD loads is described below.

TMDL established also a load for nutrients and BOD for Elligraw Bayou (WBID 1975) and Alligator Creek (WBID 230) to address DO-listed impairments. EPA has evaluated the waterbody to determine 1) existing loading to the waterbody and 2) loading to the waterbody with a natural condition land use (forested). T here are no point sources in the waterbody. Modeling results under the natural condition loading showed that the applicable dissolved oxygen criteria could not be achieved.

The water quality standards for Florida at 62-302.200(15) FAC state 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 Departmen t. 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 prot ected and enhanced. However, the Department shall not strive to abate natural conditions.”

The purpose of a TMDL is to allocate pollutant loading such that water quality standards are achieved. The Clean Water Act at Section 303(d)(1)(C) states, “Such load shall established at a level necessary to implement the applicable water quality standards ...” In expressing this TMDL, EPA must apply the applicable dissolved oxygen water quality standard while also considering the definition of natural background and the directive not to abate natural conditions.

The natural background definition established a narrative criteria in cases where there is an absence of man-induced alterations, but then states that a natural background level can be established (through 62-302.800 FAC) based on a similar unaltered waterbody, or on historical pre-Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 39



### alteration data. Therefore the Agency can apply a narrative natural background condition (unaltered) as the water quality criteria. In the TMDL context, without a site specific criteria, calculating allocations would be targeted to achieve the natural background. Using a model, this can be achieved by removing all anthropogenic loading. Any allowance of increased loading beyond natural background would likely cause other than natural, and likely lower, dissolved oxygen levels which would not be a proper application of the Florida definition. Therefore, the allocations must be established with no allowance for anthropogenic loading in order to properly “implement the applicable water quality standards.” However, because of the standard that prevents abatement of natural conditions (62-302.300(15) FAC), the TMDL must provide an allocation, where necessary, to allow for natural condition loading.

The TMDL was calculated to allow natural condition loading, but did not provide an allocation for anthropogenic loading. The Agency strongly encourages the development of site specific criteria such that anthropogenic loadings may be expressed as part of the TMDL. In the absence of site specific criteria, implementation of loading reducti ons should strive to achieve a natural background loading condition for the waterbody. Nutrient and BOD TMDL components to address DO impairment in Elligraw Bayou and Alligator Creek are presented in Table 24. Table 25 presents TMDL components for waterbodies impaired by coliforms.

8.1. Waste Load Allocations Only facilities discharging directly into streams and MS4 areas are assigned a WLA. The WLAs, if applicable, are expressed separately for continuous discharge facilities (e.g., WWTP) and MS4 areas as the former discharges during all weather conditions whereas the later discharges in response to storm events.

8.1.1 NPDES Wastewater Discharges Snowbirdland Vistas is a mobile home site that di scharges to Curry Creek, which is 303(d)-listed for nutrients. However the facility does not have limits for nutrients.

8.1.2 NPDES Stormwater Discharges The WLA for the MS4s are expressed in terms of percent reduction. Given the available data, it is not possible to estimate loadings in units of MPN/day coming exclusively from the MS4 areas. Although the aggregate wasteload allo cations for storm water discharges are expressed in numeric form, i.e. percent reduction, based on the information available today, it is infeasible to calculate numeric WLAs for individual storm water outfalls because discharges from these sources can be highly intermittent, are usually characterized by ve ry high flows occurring over relatively short time intervals, and carry a variety of pollutants whose nature and extent varies according to geography and local land use. For example, municipal source s such as those covered by these TMDLs often include numerous individual outfalls spread over large areas. Water quality impacts, in turn, also depend on a wide range of factors, including the magnitude and duration of rainfall events, the time period between events, soil conditions, fraction of land that is impervious to rainfall, other land use activities, and the ratio of storm water discharge to receiving water flow.

These TMDLs assume for the reasons stated above that it is infeasible to calculate numeric water quality-based effluent limitations for storm water discharges. Therefore, in the absence of information presented to the permitting authority showing otherwise, these TMDLs assume that water quality-based effluent limitations for storm water sources of coliforms and/or nutrients derivedDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 40



### from this TMDL can be expressed in narrative form (e.g., as best management practices), provided that (1) the permitting authority explains in the permit fact sheet the reasons it expects the chosen BMPs to achieve the aggregate wasteload allocation for these storm water discharges; and (2) the state will perform ambient water quality monitoring for coliform and/or nutrients for the purpose of determining whether the BMPs in fact are achieving such aggregate wasteload allocation.

The percent reduction calculated for nonpoint sources is assigned to the MS4 as violations from both sources typically occur in response to storm events. Permitted MS4s will be responsible for reducing only the loads associated with stormwater outfalls which it owns, manages, or otherwise has responsible control. MS4s are not responsible for reducing other nonpoint source loads within its jurisdiction. All future MS4s permitted in the area are automatically prescribed a WLA equivalent to the percent reduction assigned to the LA.

8.2. Load Allocations The load allocations are expressed as the annual average loads nutrient and BOD less the MOS. In this analysis, load allocation equals the target load because MOS is implicit.

8.3. Margin of Safety (MOS) There are two methods for incorporating a MOS in the analysis: a) implicitly incorporate the MOS using conservative model assumptions to develop allo cations; or b) explicitly specify a portion of the TMDL as the MOS and use the remainder for allocations. An implicit MOS is incorporated in the conservative decision associated with the TMDL development approach used. This approach established TMDLs at loads that are expected to have existed under natural land cover conditions before human influences.

Table 23. TMDL Components for Nutrient-Impaired Waters.

WLA 2

Waterbody Parameter 1 Existing Loads (kg/year) Target Load-LA (kg/year) Continuous (kg/year) MS4 (Percent reduction) MOS 4 (kg/year) Percent Reduction 6
Elligraw Bayou TN 2525.86 1799.13 N/A 3 28.8 Implicit 28.8

Curry Creek TN 1300.99 482.60 N/A 3 62.9 Implicit 62.9

North Creek TN 1116.10 589.95 N/A 3 47.1 Implicit 47.1

Catfish TN 2279.7 1110.0 N/A 3 51.3 Implicit 51.3

South Creek TN 1816.58 941.89 N/A 3 48.2 Implicit 48.2

Gottfried

Creek TN 3025.13 2965.58 N/A 3 2.0 Implicit 2.0

Forked Creek TN 4234.90 3386.74 N/A 3 20.0 Implicit 20.0

Direct Runoff to Bay TN 1414.23 640.51 N/A 3 54.7 Implicit 54.7Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 41

WLA 2

Waterbody Parameter 1 Existing Loads (kg/year) Target Load-LA (kg/year) Continuous (kg/year) MS4 (Percent reduction) MOS 4 (kg/year) Percent Reduction 6
Alligator

Creek TN 5370.41 3857.43 N/A 3 28.2 Implicit 28.2



### Notes: 1 TN = total nitrogen 2 WLA component is separated into load from continuous NPDES facilities (e.g., WWTPs) and load from MS4s. 3 N/A = not applicable
4 Margin of Safety is implicit due to conservati ve assumptions made in determining TMDL targets. 5 Percent reduction from current conditions to achi eve the target concentration for that nutrient.



### Table 24. TMDL Components for Waterbodies Impaired by DO

Target LoadLA (kg/year) WLA 2

Waterbody Parameter 1 Existing Load (kg/year) Anthropogenic Natural Continuous (kg/year) MS4 (Percent reduction) MOS 4 (kg/year) Percent Reduction 5

TN 2525.86 0 1799.13 N/A 3 28.8 Implicit 28.8 Elligraw Bayou
BOD 12931.64 0 3800.00 N/A 3 70.6 Implicit 70.6

TN 5370.41 0 3857.43 N/A 3 28.2 Implicit 28.2 Alligator Creek
BOD 15727.53 0 6632.32 N/A 3 57.8 Implicit 57.8

1 TN = total nitrogen, BOD = Biochemical Biological Demand
2 WLA component is separated into load from continuous NPDES facilities (e.g., WWTPs) and load from MS4s. 3 N/A = not applicable
4 Margin of Safety is implicit due to conservati ve assumptions made in determining TMDL targets. 5 Percent reduction from current conditions to achi eve the target concentration for that nutrient.



### Table 25. TMDL Components for Waterbodies Impaired by Coliform.

Waterbody Parameter 1 TMDL LA WLA 2Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 42

(MPN/day) (MPN/day)

Continuous MS4 (percent reduction) Percent Reduction 3

TCOLI 3910 3910 N/A 39 39 Elligraw Bayou FCOLI 1323 1323 N/A 70 70

TCOLI 2615 2615 N/A 85 85 Clowers

Creek FCOLI 1678 1678 N/A 76 76



### Notes: 1. TCOLI= total coliforms; FCOLI= fecal coliforms 2. WLA component is separated into load from continuous NPDES facilit ies (e.g., WWT Ps) and load from MS4s. N/A = not applicable. MS4 load represen ted as percent reduction. If future residential development densities result in a change to the MS4 boundary, the MS4 will be required to meet the established TMDL in the form of BMPs. 3. Percent reduction from current conditions to achieve the target concentration.



### 8.4. Critical conditions and Seasonal Variations The critical conditions can be defined as the environmental conditions requiring the largest reduction to meet standards. By achieving the reduction for critical conditions, water quality standards should be achieved during all other times. Seasonal variation must also be considered to ensure that water quality standards will be met during all seasons of the year.

The critical condition for non-point source loadings is typically an extended dry period followed by a rainfall runoff event. During the dry weather period, pollutants 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. The expression of a nutrient impairment is more likely to occur during warmer months. However, because nutrients (especially phosphorus) can accumulate, nutrient loadings are usually considered over longer periods (e.g. annual instead of daily loads). Critical conditions and seasonal variation were incorporated into the TMDL development by using dry and wet seasonal variations of rainfall.

9. CONCLUSION AND RECOMMENDATIONS

Determining the source of nutrients in waterbodies is the initial step to implementing a nutrient TMDL. FDEP employs the Basin Management Ac tion 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 monitoringDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 43



### TMDLs for impaired WBIDs presented in this document were based on limited nutrient and BOD monitoring data. As a result, existing and target loads were computed using a conservative modeling approach in which long-term estimated loading rates rather than actual rates were used. A more robust modeling analysis, coupled with appropriate model calibration and verification, could have been used if sufficient monitoring data was available.

Sarasota County, in cooperation with Sarasota Bay National Estuary Program (SBNEP), is currently planning an aggressive water quality monitoring of these waterbodies as part of the development of its Basin Management Action Plan (B-MAP). The data collected as part of this monitoring program can be used to better assess site-specific allowable loads necessary to protect aquatic communities in these waterbodies. At the same time, new pollutant percent reductions may be computed and used to address these TMDLs during the B-MAP implementation phase.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 44



### REFERENCES

Dixon, L.K. and G.J. Kirkpatrick. 1999. Biological effects of atmospheric deposition on algal assemblages. Sarasota Bay National Estuary Program. Sarasota, FL.

Environmental Research and Design, Inc (ERD). 2004. Nonpoint source model development and basin management strategies for Lemon Bay. Final Report to Southwest Florida Water Management District. May 2004.

Florida Administrative Code (F.A.C.). Chapter 62-302, Surface Water Quality Standards.

Florida Department Agriculture and Consumer Services (FDACS), 1999. Water Quality Best Management Practices for Cow/Calf Operations in Florida , Office of Agricultural Water Policy, June 1999.

Florida Department of Environmental Protection (FDEP), 2002. Basin Status Report, Charlotte Harbor , FDEP Division of Water Resource Management, South District, Group 2 Basin, June 2002.

Florida Department of Environm ental Protection (FDEP), 2003. Basin Status Report, Sarasota Bay and Peace and Myakka Rivers, FDEP Division of Water Resource Management, Southwest District, Group 3 Basin, September 2003.

Harper, H. H. 1991. Estimation of loading rate parameters for the Tampa Bay Watershed. SWFWMD, Brooksville, FL.

Heyl, M.G. Point and nonpoint source pollutant loading assessment. P. 12.1-12.1. In P. Roat, C. Cicolella, H. Smith, and D. Tomasko (eds). Sarasota Bay Framework for Action. Sarasota Bay National Estuary Program, Sarasota, FL.

Johansson, J.O.R. 1991. Long-term trends in N loadings and biological indicators in Hillsborough Bay, Fl. P. 157-176. In S.F. Treat and P.A. Clark (eds). Proc. Tampa Bay Area Scient. Information Symposium. St Petersburg, FL.

Sarasota Bay Estuary Program, 2004. Sarasota Bay Watershed Management Plan for the Sarasota Bay Planning Unit, Florida , December 2004.

Southwest Florida Water Management District (SWFWMD), 2002. Sarasota Bay Surface Water Improvement and Management (SWIM) Plan , Resource Management Department, Tampa, Florida. December 2002.

Squires, A.P. et al. 1998. Loadings of TN, TP, and TSS to Charlotte Harbor. P. 187-200. In S.F. Treat (ed.). Proc. of the Charlotte Harbor Public Conference and Technical Symposium March 13-16, 1997. Punta Gorda, FL. NEP and SFWMD.

Tomasko, D.A., D.L. Bristol, and J.A. Ott. 2001. Assessment of present and future nitrogen loads, water quality, and seagrass depth distribution in Lemon Bay. Estuaries 24(6A): 925-938.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page 45



### United States Department of Agriculture (USDA). National Agricultural Statistics Service (NASS), 2002 Census of Agriculture , U.S. Department of Agriculture.

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.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page B- 

### 1



### APPENDIX A PHOTOS OF IMPAIRED WBIDSDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page B- 

### 2

Small Creek in WBID 1975 (Elligraw Bayou).

WBID 1982A, South Creek at US41 east, looking upstream.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page B- 

### 3

WBID 1984, Catfish Creek (Upstream)

WBID 1984A, North Creek at US41.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page B- 

### 4

WBID 2009A, Curry Creek at Colonia and Albee Farm

WBID 2030, Alligator Creek at US41, facing eastDraft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page B- 

### 5

WBID 2039, Forked Creek at mobile home park.

WBID 2042 (Direct Runoff to Bay), ditch behind residences, Florida and Rutgers Streets.Draft Nutrient/D.O. TMDLs Sarasota Bay/Charlotte Harbor Basin September 2005 Page B- 

### 6

WBID 2049, Gottfried Creek at Dearborn St., facing downstream.

### APPENDIX B TMDL Development for Sa rasota Bay/Lemon Bay WBIDs Using the

Reference Watershed Approach

## Watershed Loading Modeling and the Reference Watershed Approach

For

Nutrient/BOD/DO TMDLs

In

Sarasota Bay/Charlotte Harbor Basins



# A Comparison of Two Approaches:

Reference Watershed versus “N atural Conditions” Scenario

Prepared by:

US EPA Region 4 61 Forsyth Street SW Atlanta, Georgia 30303

September 2005

## Table of Contents
1. Introduction 1 2. Reference Watershed Approach (RWA) 1 2.1. Concept of a Reference Watershed Approach 1 2.2. Selection of a Reference Watershed 2 3. Water Quality Modeling for Reference Watersheds 2 4. TMDL Computations and Comparison of Approaches 6

References 7



## List of Tables
Table 1. Land Use/Cover distributions in the Reference Watersheds 3 Table 2. Comparison Between Impaired and Reference Watersheds/WBIDs 4 Table 3. Annual Total Nitrogen Loads by Land Cover for the Reference Watersheds 5 Table 4. Annual Biochemical Oxygen Demand (BOD) Loads by Land Cover for the Reference Watersheds 5 Table 5. TMDL Components Using the Reference Watershed Approach 6

Table 6. Percent Reductions Needed To Achieve Water Quality Objectives- Comparison of Approaches 7Loading Function Models and Reference Watershed Approach for TMDL Development Plans



### 1 

## 1. Introduction The Lemon Bay Watershed Model (LBWM) was used to generate long-term average nutrient and BOD loads from nine watersheds in the Sarasota and Lemon Bay Basins. These watersheds were selected to represent “reference“ conditions for TMDL development and their predicted loads are used as targets for impaired WBIDs in these basins. Existing loads for the impaired watersheds were derived using the same model and are presented in the main body of this document.

The present appendix describes t he Reference Watershed Approach (RWA) to TMDL development, computes nutrient and BOD TMDLs based on modeling results for impaired and reference watersheds in Sarasota/Charlotte Harbor Bay Basins, and finally compares the “natural conditions” scenario to RWA approach in terms of percent reductions needed to attain water quality objectives in impaired watersheds. In this analysis, the RWA approach is considered to be the most accurate since the impairment occurred sometimes after human influences started in the WBIDs.



## 2. Reference Watershed Approach (RWA) 2.1. Concept of a Reference Watershed Approach Several states, including Florida, do not have water quality criteria for nutrients, sediments, and BOD. For this reason, a number of them (e.g., Pennsylvania, Maryland, New York) have adopted a reference watershed approach to identify TMDL endpoints or water quality objectives for these parameters in impaired watersheds. The general approach to TMDL development involves comparing pollutant loads of the impaired watershed to those (target loads) of a reference watershed. The procedure consists at reducing pollutant loadings in the impaired watershed to levels consistent with the reference watershed. Such load reductions will ensure that the aquatic life use in the impaired watershed is achieved and maintained as evidenced in the reference watershed. Further description and example of a Reference Watershed Approach and its use in TMDL development plans can be found in Nizeyimana-Louis et al. (2002).

The reference watershed approach can be used in TMDL determinations in three different ways depending on the availability of monitoring data:

1) If the reference watershed has sufficient monitoring data for the pollutant of interest, the target load (or TMDL) is determined by computing average annual loads (target) and comparing them to modeling results of impaired watersheds.

2) In most cases however, both reference and impaired watersheds do not have monitoring data. In this instance, impaired and reference watersheds are modeled the same way and the resulting predicted pollutant loads are compared to determine load reductions needed to remove the impairment.

3) Sometimes the time when the impairment took place and its cause are known based on expert and/or stakeholder knowledge. In this ca se, rather than using a reference watershed, the reference “target” is pollutant loads obtained by modeling the impaired watershed but using land use conditions before the impairment occurred (e.g., prior to urbanization) some time in the past (reference conditions). Load reductions are performed by comparing modeled loads obtained using “present” and “past” land use distributions.Loading Function Models and Reference Watershed Approach for TMDL Development Plans



### 2 

## 2.2. Selection of a Reference Watershed In general, three factors should be considered when selecting a suitable reference watershed. 1) A reference watershed should be a watershed that has been assessed by the State and has been determined to attain wate r quality standards or objectives. If not assessed yet, the reference watershed should exhibit lower levels of the pollutant for which TMDL (e.g., nutrient) is being determined and satisfy other indicators of impairment for that parameter. For example, if a nutrient TMDL is being determined, Chlorophyll A should be at acceptable levels and the watershed should not be impaired by dissolved oxygen (DO).

2) The reference watershed should closely resemble the impaired watershed in terms of proximity and physical properties such as land cover/land use, physiographic province, soils, and geology. However, the difference in land use distribution is not always taken into account because the land use change (e.g. from forest to agriculture or urban land) is often the cause of impairment. That is removing the impairment via the use of BMPs and engineering structures becomes equivalent to returning the impaired watershed to land use conditions similar to those of the reference watershed.

3) Finally, the size of the reference watershed should be within 0 to 30% of the impaired watershed area to minimize the impact of watershed size on loading differences.

The search for a reference watershed that would satisfy the above characteristics is commonly done by means of a desktop screening using several GIS coverages including land use distribution maps, State’s 305(b) assessed stream databases, soils, ecoregions, and geologic rock types. Since finding a suitable reference watershed for use each time a TMDL need to be developed may be time consuming, it is suggested that potential reference watersheds be identified ahead of time in different physiographic provinces, ecological regions, and geologic formations using statewide or regional spatial datasets (See an example in Evans et al., 2002). However, once potential reference watersheds are identified, a field investigation should be done to determine the most suitable reference watershed to use.



## 3. Water Quality Modeling for Reference Watersheds The LBWM was previously run for the impaired WBIDs for current and natural land use/cover conditions (see main body of the document). The modeling was also performed for the reference watersheds as part of this analysis using the same loading rates and attenuation factors as for the impaired watersheds. The watersheds used as references for the impaired WBIDs are shown in Table 2. A map showing the location of impaired reference watersheds in relation to impaired WBIDs is indicated in Figure 1. Detailed land use/cover distributions in the reference watersheds are presented in Table 1. All impaired and reference watersheds are located in Sarasota and Lemon Bay Basins and within the Southwestern Florida Flatwoods ecor egion, Lowlands, Gaps, and Valleys physiographic province, and Shelly Clays, and Sands geologic formation. The impaired and corresponding reference watersheds compare well exc ept in land use distributions as evidenced in Table 2.

LBWM modeling results are presented in Tables 3 and 4 respectively for total N and BOD.Loading Function Models and Reference Watershed Approach for TMDL Development Plans



### 3 Table 1. Land Use/Cover distributions in the Reference Watersheds

Land Cover Area (acres)

Land Use

Ainger Creek Coral Creek Unnamed Ditch Blackburn Canal Catfish Bayou

Agriculture 202 42 754 493 46
Commercial 85 36 32 56 0

Extractive 0 0 219 0 0
Industrial 25 2 0 0 0 Low-Density Residential 904 73 0 261 0 Medium-Density Residential 359 144 16 140 0

High-Density Residential 29 11 0 6 0 Transportation 11 0 0 38 24

Institutional 23 0 0 0 0 Open 3619 781 21 226 2,060
Recreational 7 89 0 26 0

Wetland 1133 246 223 37 2,471 Water (Ponds and Lakes) 135 64 74 72 354 Water (Conveyance) 104 251 0 0 101

Total 6637 1,740 1,339 1,355 5,055Loading Function Models and Reference Watershed Approach for TMDL Development Plans



### 4 Table 2. Comparison Between Impaired and Reference Watersheds/WBIDs

ATTRIBUTE IMPAIRED WBID REFERENCE WATERSHED/WBID Elligraw Bayou Catfish Bayou Area (acres) 4390 5055 Dominant Land Use/Covers Residential (54%), Open (10%) Wetland (49%); Open (41%) Dominant Hydrologic Soil Groups B/D (69%); D (15%) B/D (44); D (48%)

South Creek Coral Creek Area (acres) 2525 1740 Dominant Land Use/Covers Open (46%); Residential (31%) Open (45%); Wetlands (14%) Dominant Hydrologic Soil Groups B/D (60); C(18%) B/D (50); C (18%)

North Creek Blackburn Canal Area (acres) 1651 1355 Dominant Land Use/Covers Residential (41); Recreational (21) Agriculture (36%); Residential (30%) Dominant Hydrologic Soil Groups B/D (65%); D (15%) B/D (75%); D (19%)

Curry Creek Unnamed Ditch Area (acres) 1131 1339 Dominant Land Use/Covers Residential (53%); Agriculture (10%) Agriculture (56%); Wetlands (17) Dominant Hydrologic Soil Groups B/D (57%); A (18%) B/D (59%); D (35%)

Gottfried Creek Ainger Creek Area (acres) 7207 6637 Dominant Land Use/Covers Open (49%), Wetland (17%) Open (54%), Wetlands (17%) Dominant Hydrologic Soil Groups B/D (59%); D (23%) B/D (70%) and D (21%)

Forked Creek Ainger Creek Area (acres) 7360 6637 Dominant Land Use/Covers Open (32%); Residential (26%) Open (54%), Wetlands (17%) Dominant Hydrologic Soil Groups B/D (65%), D (20%) B/D (70%) and D (21%)

Alligator Creek Ainger Creek Area (acres) 5761 6637 Dominant Land Use/Covers Residential (56); Open (12%) Open (54%), Wetlands (17%) Dominant Hydrologic Soil Groups B/D (73%), D (14%) B/D (70%) and D (21%)

Direct Runoff to Bay Coral Creek Area (acres) 1683 1740 Dominant Land Use/Covers Residential (65%); Open (18%) Open (45%); Wetlands (14%) Dominant Hydrologic Soil Groups B/D (57%); C (18%) B/D (50); C (18%)Loading Function Models and Reference Watershed Approach for TMDL Development Plans



### 5 Table 3. Annual Total Nitrogen Loads by Land Cover for the Reference Watersheds

Total Nitrogen (Kg)

Land Use Ainger Creek Coral Creek Unnamed Ditch Blackburn Canal Catfish Bayou

Agriculture 140.8 4.7 147.1 99.4 9.4
Commercial 133.7 51.2 46.9 60.4 0.0

Extractive 0.0 0.0 285.3 0.0 0.0
Industrial 32.6 3.1 0.0 0.0 0.0 Low-Density Residential 547.4 34.8 0.0 94.4 0.0 Medium-Density Residential 292.6 148.6 22.4 106.2 0.0

High-Density Residential 43.9 19.6 0.0 9.6 0.0 Transportation 40.8 0.0 0.0 125.0 88.5

Institutional 23.9 0.0 0.0 0.0 0.0 Open 1228.9 116.5 3.7 26.6 272.2
Recreational 1.5 46.6 0.0 5.7 0.0

Wetland 825.7 144.3 123.1 17.7 1589.7 Water (Ponds and Lakes) 0.0 0.0 0.0 0.0 0.0 Water (Conveyance) 148.8 331.0 0.0 0.0 142.3

Total 3460.7 900.3 628.4 545.0 2102.1



### Table 4. Annual Biochemical Oxygen Demand (BOD) Loads by Land Cover for the Reference Watersheds

Annual BOD Loads (Kg)

Land Use Ainger Creek Coral Creek Unnamed Ditch Blackburn Canal Catfish Bayou

Agriculture 11.0 11.0 341.6 230.8 19.7
Commercial 160.4 160.4 147.0 202.2 0.0

Extractive 0.0 0.0 2898.8 0.0 0.0
Industrial 21.8 21.8 0.0 0.0 0.0 Low-Density Residential 66.6 66.6 0.0 201.7 0.0 Medium-Density Residential 304.9 304.9 45.9 224.3 0.0

High-Density Residential 62.2 62.2 0.0 30.5 0.0 Transportation 0.0 0.0 0.0 450.7 288.6

Institutional 0.0 0.0 0.0 0.0 0.0 Open 198.9 198.9 6.3 45.4 420.1
Recreational 95.6 95.6 0.0 12.5 0.0

Wetland 316.2 316.2 269.9 38.8 3150.7 Water (Ponds and Lakes) 0.0 0.0 0.0 0.0 0.0 Water (Conveyance) 2326.3 2326.3 0.0 0.0 957.8Loading Function Models and Reference Watershed Approach for TMDL Development Plans



### 6 Total 3563.8 3563.8 3709.3 1436.8 4837.0 

## 4. TMDL Computations and Comparison of Approaches Total N and BOD loads computed for the reference wa tersheds were used as target loads (Table 5, Column 4). A 10% margin of safety (MOS) was applied to compute load allocations (LAs). The existing loads from impaired watersheds (see main document) are presented in Table 5 Column 2, below. Total phosphorus loads were not computed since nitrogen is the limiting factor in these estuarine creek systems.

Table 6 compares predevelopment land use cover conditions and the Reference Watershed Approach in terms of percent reductions needed to meet water quality objectives for nutrient and water quality standard for DO. As it appears, the two approaches compare well. At the average, there is close agreement between total N percent reductions obtained using natural conditions (36.5%) and the Reference watershed Approach (32. 8%). The difference between the two methods for BOD, 16 percent, can be considered relatively low given the high uncertainty associated assessment assumptions used in the two approaches.

Table 5. TMDL Total N and BOD Components Using the Reference Watershed Approach

WLA 2

Waterbody (WBID) Parameter 1 Existing Load (kg/year) Target Load-TMDL (kg/year) LA (kg/year) Continuous (kg/year) MS4 (Percent reduction) MOS 4 (kg/year) Percent Reduction 5

TN 2525.9 2102.1 1891.8 N/A 3 25.1 210.2 25.1 Elligraw Bayou

6 BOD 12931.6 4837.0 4353.3 N/A 3 70.6 483.7 66.3

Curry Creek TN 1301.0 628.4 565.6 N/A 3 56.5 62.8 56.5

North Creek TN 1116.1 545.0 490.5 N/A 3 56.1 54.5 56.1

South Creek TN 1816.6 1740.0 1566.0 N/A 3 13.8 174 13.8

Gottfried Creek TN 3025.1 3460.7 3114.7 N/A 3 0.0 346.0 0.0

Forked Creek TN 4234.9 3460.7 3114.7 N/A 3 26.5 346.0 26.5

Direct Runoff to Bay TN 1414.2 900.30 810.3 N/A 3 41.7 90.3 41.7

TN 5370.4 3460.7 3114.7 N/A 3 42.0 346.0 42.0 A lligator Creek 6 BOD 15727.5 7200.4 6480.4 N/A 3 58.8 720.0 58.8



### Notes: 1 TN = total nitrogen; BOD = Biological Oxygen Demand
2 WLA component is separated into load from continuous NPDES facilities (e.g., WWTPs) and load from MS4s. 3 N/A = not applicable
4 Margin of Safety is implicit due to conservati ve assumptions made in determining TMDL targets. 5 Percent reduction from current conditions to achi eve the target concentration for that nutrient. 6 Elligraw Bayou and Alligator Creek are impaired by DO. Reducing nutrient and BOD as indicated in the table will assure that these waterbodies meet DO water quality standards.Loading Function Models and Reference Watershed Approach for TMDL Development Plans



### 7 Table 6. Percent Reductions Needed To Achieve Water Quality Objectives- Comparison of Approaches

Percent Reduction In Total Nitrogen (N) Loads Approach IMPAIRED WATERBODY Natural Conditions Reference Watershed

Elligraw Bayou 28.8 25.1

South Creek 48.2 13.8

North Creek 47.1 56.1
Curry Creek 62.9 56.5
Runoff to Bay 54.7 42.7

Gottfried 2.0 0.0

Forked 20.0 26.5 Alligator 28.2 42.0
- Mean 36.5 32.8

Percent Reduction in Biochemical Oxygen Demand (BOD) Loads Approach IMPAIRED WATERBODY Natural Conditions Reference Watershed

Elligraw Bayou 70.6 66.3

South Creek 57.9 32.0

North Creek 48.8 52.7
Curry Creek 65.8 20.1
Runoff to Bay 45.2 0.0

Gottfried 16.2 7.6

Forked 37.4 33.9 Alligator 57.8 58.8
- Mean 50.0 34.0



## References

Evans, B.M.. et al. 2003. A Comprehensive GIS-based modeling approach for predicting nutrient loads in watersheds. J. Spatial Hydrology. 2 (2). 234-264.

Nizeyimana-Louis, E. and B.M. Evans. 2002. Total maximum daily load (TMDL) development plans for urbanized watersheds in Pennsylvania. Case Study: Neshamin y watershed, Southeaster PA. 282 pp + appendices.