DRAFT 

 

FLORIDA DEPARTMENT OF ENVIRONMENTAL PROTECTION 

Division of Water Resource Management, Bureau of Watershed Management

SOUTHWEST DISTRICT • SARASOTA BAY BASIN 

TMDL Report 

Nutrient TMDL for Roberts Bay 

(WBID 1968D) 

Kevin Petrus 

Aaron Lassiter

October, 2005 

 

Florida Department of Environmental Protection i 

 

 

Acknowledgments 

This study could not have been accomplished without significant contributions from staff in the 

Florida Department of Environmental Protection’s (Department) Watershed Assessment 

Section. Richard Wieckowicz, Katrina Sanders, and Jessica Rich-Zeisler gathered data and 

calculated the nutrient loadings, and Barbara Donner provided the basin delineations. The 

Department also recognizes the support and assistance of staff from Sarasota County and the 

Sarasota Bay National Estuary Program, particularly their contributions towards understanding 

the issues, history, and processes at work in the Roberts Bay watershed. 

Editorial assistance provided by Linda Lord. 

Map production assistance provided by Barbara Donner. 

For additional information on the watershed management approach and impaired waters 

in the Sarasota Bay, Peace River, and Myakka River Basin, contact: 

Tom Singleton 

Florida Department of Environmental Protection 

Bureau of Watershed Management 

Watershed Planning and Coordination Section 

2600 Blair Stone Road, Mail Station 3565 

Tallahassee, FL 32399-2400 

Email: thomas.singleton@dep.state.fl.us

Phone: (850) 245-8561; Suncom: 205-8561 

Fax: (850) 245-8434 

Access to all data used in the development of this report can be obtained by contacting:

Kevin Petrus 

Florida Department of Environmental Protection 

Bureau of Watershed Management 

Watershed Assessment Section 

2600 Blair Stone Road, Mail Station 3555 

Tallahassee, FL 32399-2400 

Email: kevin.petrus@dep.state.fl.us

Phone: (850) 245-8459; Suncom: 205-8459 

Fax: (850) 245-8536 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients

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Florida Department of Environmental Protection 

Contents 

Chapter 1: INTRODUCTION___________________________________1

1.1 Purpose of Report _______________________________________________1

1.2 Identification of Waterbody_________________________________________1

1.3 Background ____________________________________________________5

Chapter 2: DESCRIPTION OF WATER QUALITY PROBLEM ________6

2.1 Statutory Requirements and Rulemaking History ______________________6

2.2 Information on Verified Impairment__________________________________6

Chapter 3. DESCRIPTION OF APPLICABLE WATER QUALITY 

STANDARDS AND TARGETS _______________________9

3.1 Classification of the Waterbody and Criteria Applicable to the TMDL______9

3.2 Applicable Water Quality Standards and Numeric Water Quality 

Targets_____________________________________________________________9

3.2.1 Interpretation of Narrative Nutrient Criterion __________________________9

Chapter 4: ASSESSMENT OF SOURCES_______________________10

4.1 Types of Sources________________________________________________10

4.2 Point Sources __________________________________________________10

4.2.1 NPDES Permitted Wastewater Facilities ___________________________10

4.2.2 Municipal Separate Storm Sewer System Permittees _________________11

4.3 Land Uses and Nonpoint Sources__________________________________12

4.3.1 Land Uses___________________________________________________12

4.3.2 Estimating Nonpoint Source Loadings _____________________________15

Chapter 5: DETERMINATION OF ASSIMILATIVE CAPACITY_______21

5.1 Determination of Loading Capacity_________________________________21

5.2 Attempts to Develop Empirical Relationships ________________________22

5.3 Current Restoration and Management Projects_______________________22

5.4 Critical Conditions_______________________________________________23

Chapter 6: DETERMINATION OF THE TMDL ____________________24

6.1 Expression and Allocation of the TMDL _____________________________24 

6.2 Load Allocation _________________________________________________15 

6.3 Wasteload Allocation ____________________________________________25

6.3.1 NPDES Wastewater Discharges__________________________________25

6.3.2 NPDES Stormwater Discharges __________________________________26
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Florida Department of Environmental Protection 

6.4 Margin of Safety_________________________________________________26

Chapter 7: NEXT STEPS: IMPLEMENTATION PLAN 

DEVELOPMENT AND BEYOND _____________________27

7.1 Basin Management Action Plan____________________________________27

References _______________________________________________28

Appendices _______________________________________________29

Appendix A: Background Information on Federal and State Stormwater 

Programs__________________________________________________________29

Appendix B: Chlorophyll a Raw Data __________________________________30 

Appendix C: Chlorophyll a and Total Nitrogen Graphs of Sample Results____44 

Appendix D: Total Nitrogen Loading Estimates by Source (pounds/year)____45

List of Tables 

Table 2.1. Verified Impairment in Roberts Bay, WBID 1968D ____________________8

Table 2.2. Summary of Chlorophyll a Data for Roberts Bay, WBID 1968D __________8

Table 4.1. Point Sources in the Roberts Bay Watershed, WBID 1968D____________11

Table 4.2. Classification of Land Use Categories in the Roberts Bay Watershed, WBID 

1968D (1999)_____________________________________________13

Table 4.3. Septic System Load Estimates by Subbasin and Year ________________18

Table 4.4. Land Use Runoff Concentrations (Event Mean Concentrations) in 

Southwest Florida _________________________________________20

Table 6.1. TMDL Components for Roberts Bay Watershed, WBID 1968D _________25
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Florida Department of Environmental Protection 

List of Figures 

Figure 1.1: Location of Roberts Bay Water Segment, WBID 1968D, and Major 

Geopolitical Features in the Sarasota Bay, Peace River, and Myakka 

River Basin Group__________________________________________3

Figure 1.2. Roberts Bay Water Segment, Monitoring Locations, and Wastewater 

Facilities with Surface Water Discharges_________________________4

Figure 2.1. Chlorophyll a Annual Averages for Roberts Bay (1992-2004) __________8

Figure 4.1. Principal Land Uses in the Roberts Bay Water Segment, WBID 1968D, in 

1999____________________________________________________14

Figure 5.1 Annual Average Total Nitrogen Loads in the Roberts Bay 

Watershed_______________________________________________22

Web sites 

Florida Department of Environmental Protection, Bureau of 

Watershed Management 

TMDL Program 

http://www.dep.state.fl.us/water/tmdl/index.htm

Identification of Impaired Surface Waters Rule 

http://www.dep.state.fl.us/water/tmdl/docs/AmendedIWR.pdf

STORET Program 

http://www.dep.state.fl.us/water/storet/index.htm

2002 305(b) Report 

http://www.dep.state.fl.us/water/docs/2002_305b.pdf

Criteria for Surface Water Quality Classifications 

http://www.dep.state.fl.us/legal/rules/shared/62-302t.pdf

Basin Status Report for the Tampa Bay Basin 

http://www.dep.state.fl.us/water/tmdl/stat_rep.htm

Water Quality Assessment Report for the Tampa Bay Basin 

http://www.dep.state.fl.us/water/tmdl/stat_rep.htm

Allocation Technical Advisory Committee (ATAC) Report 

http://www.dep.state.fl.us/water/tmdl/docs/Allocation.pdf
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients

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Florida Department of Environmental Protection 

U.S. Environmental Protection Agency 

Region 4: Total Maximum Daily Loads in Florida 

http://www.epa.gov/region4/water/tmdl/florida/

National STORET Program 

http://www.epa.gov/storet/

Florida Department of Environmental Protection 1 

 

 

Chapter 1: INTRODUCTION 

1.1 Purpose of Report 

This report presents the Total Maximum Daily Load (TMDL) for total nitrogen to address the 

nutrient impairment for Roberts Bay, located in the Sarasota Bay Basin in the City of Sarasota, 

and part of the larger Sarasota Bay, Peace River, and Myakka River Basin Group. The estuary 

was verified as impaired for nutrients, based on exceedances of the historic chlorophyll a

threshold, using the methodology described in the Identification of Impaired Surface Waters 

Rule (IWR), Chapter 62-303, Florida Administrative Code (F.A.C.). Roberts Bay was included 

on the Verified List of impaired waters for the Sarasota Bay, Peace River, and Myakka River 

Basin Group, that was adopted by Secretarial Order in June, 2005. The TMDL establishes the 

allowable loadings to Roberts Bay that would restore the waterbody so that it meets the 

applicable water quality standards for nutrients. 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 ambient water 

quality conditions. 

1.2 Identification of Waterbody 

Roberts Bay is located within the Sarasota Bay Basin, in northwest Sarasota County, Florida, 

bordering the southern side of the City of Sarasota (Figure 1.1). Roberts Bay receives drainage 

from the urbanized Phillippi Creek Basin, the Matheny Creek Basin, and the area draining 

directly to the bay. The watershed area draining to Roberts Bay covers approximately 65 

square miles. Roberts Bay is bounded by Sarasota Bay to the north and Little Sarasota Bay to 

its south. Big Sarasota Pass located in the southern portion of Sarasota Bay flushes bay water 

to the Gulf of Mexico. Extensive navigable canals and bayous on Siesta Key, located on the 

west side of Roberts Bay bring recreational boaters into this small, shallow bay that includes 

undeveloped islands and mangrove forests. 

The U.S. Environmental Protection Agency (EPA) designated the Sarasota Bay system, 

including Roberts Bay, as an Estuary of National Significance in 1988, and initiated the 

Sarasota Bay National Estuary Program (SBNEP) in 1989. The Florida Department of 

Environmental Protection (Department) has also designated the estuary as an Outstanding 

Florida Water (OFW). In 1995, the South Florida Water Management District (SWFWMD) 

placed Sarasota Bay on its Surface Water Improvement and Management (SWIM) Program list 

of priority waterbodies for protection or restoration. 

Residential areas make up about half of the land use in the Roberts Bay watershed. The 

northwest part of the watershed is within the city limits of Sarasota. The most intensely 

developed areas of the watershed are west of Interstate 75, and development is continuing to 

move eastward. Other urban areas in the Sarasota Bay system near Roberts Bay include the 

Cities of Longboat Key and Bradenton to the north and the City of Venice to the south. In 2000, 

the population of Sarasota County was 325,957. Additional information about the regions 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

hydrology and geology are available in the Basin Status Report for the Sarasota Bay–Peace–

Myakka Basin (Florida Department of Environmental Protection [Department], June 2003). 

For assessment purposes, the Department divided the Sarasota Bay Basin into water 

assessment polygons with a unique waterbody identification (WBID) number for each water 

segment or stream reach. Roberts Bay is designated WBID 1968D. Figure 1.2 shows the 

watershed, as well as the locations of monitoring stations used to assess the bay’s condition. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Figure 1.1. Location of Roberts Bay Water Segment, WBID 1968D, and 

Major Geopolitical Features in the Sarasota Bay, Peace 

River, and Myakka River Basin Group 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Figure 1.2. Roberts Bay Water Segment, Monitoring Locations, 

and Wastewater Facilities with Surface Water 

Discharges 
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Florida Department of Environmental Protection 

1.3 Background 

This report was developed as part of the Department’s watershed management approach for 

restoring and protecting state waters and addressing TMDL Program requirements. The 

watershed approach, which is implemented using a cyclical management process that rotates 

through the state’s 52 river basins over a 5-year cycle, provides a framework for implementing 

the TMDL Program–related requirements of the 1972 federal Clean Water Act and the 1999 

Florida Watershed Restoration Act (FWRA, Chapter 99-223, Laws of Florida). 

A TMDL represents the maximum amount of a given pollutant that a waterbody can assimilate 

and still meet water quality standards, including its applicable water quality criteria and its 

designated uses. TMDLs are developed for waterbodies that are verified as not meeting their 

water quality standards. TMDLs provide important water quality restoration goals that will guide 

restoration activities. 

This TMDL Report will be followed by the development and implementation of a Basin 

Management Action Plan, or BMAP, to reduce the amount of nutrients that caused the verified 

impairment of Roberts Bay. These activities will depend heavily on the active participation of 

the Southwest Florida Water Management District (SWFWMD), local governments, local 

businesses, and other stakeholders. The Department will work with these organizations and 

individuals to undertake or continue reductions in the discharge of pollutants and achieve the 

established TMDL. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Chapter 2: DESCRIPTION OF WATER QUALITY 

PROBLEM 

2.1 Statutory Requirements and Rulemaking History 

Section 303(d) of the federal Clean Water Act requires states to submit to the U.S. 

Environmental Protection Agency (EPA) a list of surface waters that do not meet applicable 

water quality standards (impaired waters) and establish a TMDL for each pollutant causing the 

impairment of the listed waters on a schedule. The Department has developed these lists, 

commonly referred to as 303(d) lists, since 1992. The list of impaired waters in each basin is 

also required by the FWRA (Subsection 403.067[4)] Florida Statutes [F.S.]); the list is amended 

annually to include updates for each basin statewide. 

Florida’s 1998 303(d) list included 84 waterbodies in the Sarasota Bay, Peace River, and 

Myakka River Basin Group. However, the FWRA (Section 403.067, F.S.) stated 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 rulemaking process, the Environmental Regulation Commission adopted the new 

methodology as Chapter 62-303, F.A.C. (Identification of Impaired Surface Waters Rule, or 

IWR), in April 2001. The list of waters for which impairments have been verified using the 

methodology in the IWR is referred to as the Verified List. 

2.2 Information on Verified Impairment 

The Department used the IWR to assess water quality in Roberts Bay and verified the 

impairment for nutrients, based on exceedances of the historic chlorophyll a threshold value 

(Table 2.1). Table 2.2 summarizes the data collected during the verification period (January 1, 

1997, to June 30, 2004). The IWR methodology uses chlorophyll a measurements (a measure 

of algal biomass) to interpret Florida’s narrative nutrient criterion. The IWR listing methodology 

provides two ways that an estuary can be listed for nutrient impairment. If the annual average 

chlorophyll a value exceeds the estuarine threshold of 11 micrograms per liter (ug/L) in any of 

the last three years of the verified period the segment is listed for nutrients. Additionally, if 

annual average values during the verified period have increased by more than 50% for at least 

2 consecutive years over historical values, an estuarine segment is identified as impaired for 

nutrients. The bay was verified as impaired for nutrients because annual mean chlorophyll a

values in the verified period were more than 50% above historic levels in two or more 

consecutive years. The bay annual average chlorophyll a values were more than 50% above 

the historic chlorophyll a value of 4.8 ug/L in 1997, 1998, 1999, 2001, 2003, and 2004 (Figure 

2.1). The historic chlorophyll a value is based on the average of the annual average chlorophyll 

a values in the 1992 to 1996 period. 

The verified impairments were based on data collected by the Mote Marine Lab and Sarasota 

County. Sampling was conducted at two fixed stations by Mote Marine Lab in 1992 and 1993. 

In 1995, Sarasota County Environmental Services began monthly randomized sampling in fixed 

grids located in Roberts Bay. Figure 1.2 shows the locations of the sampling sites, and 
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Florida Department of Environmental Protection 

Appendix B tabulates all available chlorophyll a data for the water segment collected from 1992 

to 2004. Appendix C presents time series graphs of the individual chlorophyll a and total 

nitrogen results.

As part of the listing process, the Department attempts to identify the limiting nutrient or 

nutrients for the impaired waterbody. The limiting nutrient, generally nitrogen or phosphorus, is 

defined as the nutrient that limits plant growth when it is not available in sufficient quantities. A 

limiting nutrient is a chemical that is necessary for plant growth, but available in quantities 

smaller than those needed for algae, represented by chlorophyll a, and macrophytes to grow. 

Once the limiting nutrient in a waterbody is exhausted, algae stop growing. If more of the 

limiting nutrient is added, larger algal populations will result until nutrients or other 

environmental factors again limit their growth. 

In Florida waterbodies, nitrogen and phosphorus are most often the limiting nutrients, and 

nitrogen is typically the limiting nutrient in most Florida estuaries. There is a general 

understanding in the marine scientific community that nitrogen is the principal cause of nutrient 

overenrichment in coastal systems (National Research Council, 1993) and an analysis of the 

data from Roberts Bay supports this conclusion. 

Determining the limiting nutrient in a waterbody can be accomplished by calculating the ratio of 

nitrogen to phosphorus in the waterbody, with water column ratios of total nitrogen (TN) to total 

phosphorus (TP) of less than 10 indicating nitrogen limitation. The median TN to TP ratio of 

each sampling event during the verified period is 2.4, indicating that nitrogen is the limiting 

nutrient in the Roberts Bay estuary. Since nitrogen is the limiting nutrient, reductions in TN 

loadings would be expected to result in decreases in algal growth. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Table 2.1. Verified Impairment in Roberts Bay, WBID 1968D

Parameter Causing 

Impairment 

Priority for TMDL 

Development 

Projected Year for TMDL 

Development 

Nutrients (Historic 

Chlorophyll a) High 2004 

Table 2.2. Summary of Chlorophyll a Data for Roberts Bay, 

WBID 1968D, January 1997 to June 2004

Parameter Causing 

Impairment 

Total 

Number of 

Samples 

Percent 

Chlorophyll a 

Samples > 11 

ug/L 

Minimum 

Concentration 

(ug/L) 

Maximum 

Concentration 

(ug/L) 

Chlorophyll a 439 20 1 48 

Roberts Bay - WBID 1968D 

Annual Average Chlorophyll a

0.0

2.0

4.0

6.0

8.0

10.0

12.0

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Year

Chlorophyll a (ug/L)

 Chlorophyll a Chlorophyll a Threshold 50 % Above Historic Chlorophyll a Value

Figure 2.1. Chlorophyll a Annual Averages for Roberts Bay 

(1992 – 2004) 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Chapter 3. DESCRIPTION OF APPLICABLE WATER 

QUALITY STANDARDS AND TARGETS 

3.1 Classification of the Waterbody and Criteria Applicable to 

the TMDL 

Florida’s surface waters are protected for five designated use classifications, as follows: 

Class I Potable water supplies 

Class II Shellfish propagation or harvesting 

Class III Recreation, propagation, and maintenance of a healthy, wellbalanced population of fish and wildlife 

Class IV Agricultural water supplies 

Class V Navigation, utility, and industrial use (there are no state 

waters currently in this class) 

The Roberts Bay water segment is a Class III marine waterbody, with a designated use of 

recreation, propagation, and maintenance of a healthy, well-balanced population of fish and 

wildlife. The Class III water quality criteria applicable to the observed impairment addressed in 

this TMDL is the narrative nutrient criteria. 

3.2 Applicable Water Quality Standards and Numeric Water Quality Targets 

3.2.1 Interpretation of Narrative Nutrient Criterion 

Florida’s nutrient criterion is narrative only, i.e., nutrient concentrations of a body of water shall 

not be altered so as to cause an imbalance in natural populations of aquatic flora or fauna. 

Accordingly, a nutrient-related target was needed to represent levels at which an imbalance in 

flora or fauna is expected to occur. While the IWR provides a threshold for nutrient impairment 

for estuaries based on annual average chlorophyll a levels, these thresholds are not standards 

and need not be used as the nutrient-related water quality target for TMDLs. In fact, in 

recognition that the IWR thresholds were developed using statewide average conditions, the 

IWR (Section 62-303.450, F.A.C.) specifically allows the use of alternative, site-specific 

thresholds that more accurately reflect conditions beyond which an imbalance in flora or fauna 

occurs in the waterbody. 

Roberts Bay was listed as impaired for nutrients because annual mean chlorophyll a values in 

the verified period were more than 50% above the historic chlorophyll a value of 4.8 ug/L in two 

or more consecutive years. The objective of the TMDL development is to reduce the annual 

average values to less than 50% above the historic value, therefore the chlorophyll a target for 

this TMDL is 7.2 ug/L. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Chapter 4: ASSESSMENT OF SOURCES 

4.1 Types of Sources 

An important part of the TMDL analysis is the identification of pollutant source categories, 

source subcategories, or individual sources of the pollutant of concern in the watershed and the 

amount of pollutant loading contributed by each of these sources. Sources are broadly 

classified as either “point sources” or “nonpoint sources.” Historically, the term point sources 

has meant discharges to surface waters that typically have a continuous flow via a discernable, 

confined, and discrete conveyance, such as a pipe. Domestic and industrial wastewater 

treatment facilities (WWTFs) are examples of traditional point sources. In contrast, the term 

“nonpoint sources” was used to describe intermittent, rainfall driven, diffuse sources of pollution 

associated with everyday human activities, including runoff from urban land uses, agriculture, 

silviculture, and mining; discharges from failing septic systems; and atmospheric deposition. 

However, the 1987 amendments to the Clean Water Act redefined certain nonpoint sources of 

pollution as point sources subject to regulation under the EPA’s National Pollutant Discharge 

Elimination System (NPDES) Program. These nonpoint sources included certain urban 

stormwater discharges, including those from local government master drainage systems, 

construction sites over 5 acres, and a wide variety of industries (see Appendix A for 

background information on the federal and state stormwater programs). 

To be consistent with Clean Water Act definitions, the term “point source” is used to describe 

traditional point sources (such as domestic and industrial wastewater discharges) and

stormwater systems requiring an NPDES stormwater permit when allocating pollutant load 

reductions required by a TMDL. However, the methodologies used to estimate nonpoint source 

loads do not distinguish between NPDES stormwater discharges and non-NPDES stormwater 

discharges, and as such, this chapter does not make any distinction between the two types of 

stormwater. 

4.2 Point Sources 

4.2.1 NPDES Permitted Wastewater Facilities 

There are three active permitted domestic wastewater treatment facilities and one inactive 

facility that discharge or have discharged nutrient loads and other wastewater constituents 

directly into the Roberts Bay watershed (Figure 1.2). Siesta Key Utilities Authority, Inc. 

(NPDES No. FL0025755) is a domestic wastewater treatment facility with an advanced 

wastewater treatment (AWT) system and a permitted discharge of 2.7 million gallons per day 

(mgd) annual average daily flow (AADF). Its outfall discharge is to Grand Canal, which is a 

tributary to Roberts Bay. South Gate (NPDES No. FL0032808) is an advanced wastewater 

treatment facility with a 1.36 MGD 12-Month Average Daily Flow. This facility discharges to 

Phillippi Creek, a Class III waterbody, approximately 500 feet northwest of the facility, which 

then travels approximately 3 miles to Roberts Bay. Gulf Gate (NPDES No. FL0032816) is an 

advanced wastewater treatment facility with an existing 1.78 MGD AADF permitted discharge to 

Matheny Creek, a Class III waterbody, approximately 3000 ft. west of the facility, thence flows 
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Florida Department of Environmental Protection 

approximately 2000 feet before entering the Bay. The maximum allowable TN load that can be 

discharged to surface waters from all the active facilities is 53,332 pounds/year (Table 4.1). 

American General, previously known as Tameron Utilities, (permit number FL0028411) was 

permitted to discharge wastewater to the Roberts Bay watershed from January 1993 to October 

1996, but is no longer operational. 

Table 4.1. Point Sources in the Roberts Bay Watershed, 

WBID 1968D 

Facility NPDES 

Permit Discharge Point Design Flow (MGD) 

Permitted 

Flow 

 (MGD) 

Annual TN 

Effluent 

Limit 

 (mg/L) 

Maximum 

Annual TN 

Load 

(lbs/year) 

Gulf Gate FL0032816 Tributary to 

Roberts Bay 1.78 1.78 3.0 16,255 

South Gate FL0032808 Tributary to 

Roberts Bay 1.36 1.36 3.0 12,420 

Siesta Key 

Utilities 

Authority, Inc. 

FL0025755 Tributary to 

Roberts Bay 2.7 2.7 3.0 24,657 

1

 Annual Load = Permitted Flow * TN Concentration * 8.34 pounds/gallon * 365 days/year 

Estimating Point Source TN Loadings 

TN loads were calculated for each of the four facilities that discharged into the Roberts Bay 

watershed during the period of 1992 to 2004. Loads were calculated by multiplying the TN 

monthly average concentrations by the corresponding flow, then by a conversion factor (8.34) to 

achieve a load in pounds/day. The TN load for each month was calculated by multiplying the 

TN load by the corresponding number of days in a given month. The sum of the TN load for 

each month of the year produced the annual TN load value. 

Each facility had missing effluent discharge data, so a method was used to estimate the missing 

values. When data were missing for 1 to 3 months, the values previous to and after the missing 

value would be averaged to insert for the missing value. For four or more months of missing 

values, an average was taken using all the available data to fill in the data gaps. 

The annual loading estimates for each facility are provided in Appendix D. Since 1997, the 

annual TN loading from the three active facilities has been between 40 to 78 percent of the 

maximum allowable annual load. 

4.2.2 Municipal Separate Storm Sewer System Permittees 

Municipal separate storm sewer systems (MS4s) may also discharge nutrients to waterbodies in 

response to storm events. To address stormwater discharges, the EPA developed the NPDES 

stormwater permitting program in two phases. Phase I, promulgated in 1990, addresses large 

and medium MS4s located in incorporated places and counties with populations of 100,000 or 

more. Phase II began in 2003. Regulated Phase II MS4s are defined in Section 62-624.800, 
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Florida Department of Environmental Protection 

F.A.C., and typically cover urbanized areas serving jurisdictions with a population of at least 

10,000 or discharge into Class I or Class II waters, or Outstanding Florida Waters. 

The stormwater collection systems in the Roberts Bay watershed, which are owned and 

operated by Sarasota County in conjunction with the Florida Department of Transportation 

(FDOT), are covered by a Phase I MS4 Permit. Currently, no local governments in the 

watershed have applied for coverage under the Phase II NPDES MS4 permit. 

The Roberts Bay watershed falls under the Sarasota County Phase I MS4 Permit (Number 

FLS000004). The City of Sarasota, and the FDOT District 1, are co-permittees with portions of 

their jurisdictions located within the bay’s watershed. 

4.3 Land Uses and Nonpoint Sources 

Nutrient loading from urban areas is most often attributable to multiple sources, including 

stormwater 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. Because the Roberts Bay watershed is primarily urban, wildlife and agricultural 

animals/livestock sources are not expected to contribute significantly to the TN load. 

Onsite sewage treatment and disposal systems (OSTDSs), including septic tanks, are 

commonly used where providing central sewer is not cost-effective or practical. When properly 

sited, designed, constructed, maintained, and operated, OSTDSs are a safe means of disposing 

of domestic waste. The effluent from a well-functioning OSTDS is comparable to secondarily 

treated wastewater from a sewage treatment plant. When not functioning properly, however, 

OSTDSs can be a source of nutrients (nitrogen and phosphorus), pathogens, and other 

pollutants to both ground water and surface water. As of 2004, Sarasota County has a 

cumulative registry of 74,774 septic systems (Florida Department of Health Web site, 2005). 

This total does not reflect systems removed from service going back to 1970. The Department 

does not have information on the percentage of the population using septic systems in Sarasota 

County, nor does it have estimates of countywide failure rates to determine the daily discharge 

of wastewater from septic tanks. 

4.3.1 Land Uses 

The spatial distribution and acreage of different land use categories were identified using the 

SWFWMD’s 1999 land use coverage (scale 1:40,000) contained in the Department’s 

geographic information system (GIS) library (Florida Department of Environmental Protection, 

2004). The Roberts Bay watershed drains about 41,491 acres (65 square miles). Land use 

categories in the watershed were aggregated using the Level 1 and Level 2 residential Florida 

Land Use and Cover Classification System (FLUCCS) codes which are tabulated in Table 4.2. 

Figure 4.1 shows the acreage of the principal land uses in the watershed. The predominant 

land use in the watershed is urban and built-up, which comprises 67 percent of the area. The 

next largest land uses are water and wetlands, which make up 12 percent of the watershed 

area. 
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Florida Department of Environmental Protection 

Table 4.2. Classification of Land Use Categories in the 

Roberts Bay Watershed 

Code Land Use Acreage Percentage of Total 

1000 Urban Open 6,899 17 

1100 Residential Low Density < 2 Dwelling Units/Acre 3,343 8 

1200 Residential Med Density 2 - 5 Dwelling Units/Acre 13,398 32 

1300 Residential High Density 6 or more Dwelling Units/Acre 4,013 10 

2000 Agriculture 4,665 11 

3000 Rangeland 295 1 

4000 Upland Forests 2,423 6 

5000 Water 2,933 7 

6000 Wetlands 1,893 5 

7000 Barren Land (Disturbed Land) 104 0 

8000 Transportation, Communication and Utilities 1,523 4 

Totals 41,491 100 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Figure 4.1. Principal Land Uses in the Roberts Bay Water 

Segment, WBID 1968D, in 1999 
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Florida Department of Environmental Protection 

4.3.2 Estimating Nonpoint Source Loadings 

The nonpoint source loading of TN in the Roberts Bay watershed, between 1992 to 2004, were 

estimated for atmospheric deposition, stream baseflow, ground water seepage to the bay, septic 

systems, and surface water runoff. The following describes the methods used to develop the 

loading estimates. 

Atmospheric Deposition 

The rainfall and wet deposition nitrogen data, available at the National Atmospheric Deposition 

Program web site, for the Verna Well Field monitoring station (FL41) in northeast Sarasota 

County, were used to derive the deposition of TN directly onto the surface of Roberts Bay. 

Annual wet deposition rates for NH4 (KG/HA) and NO3 (KG/HA) were converted to TN, (where 

TN = (14/62)*NH4 + (14/62)*NO3). To obtain a total deposition rate, dry deposition was 

assumed to equal wet deposition, therefore total deposition is equal to 2.0*Wet Deposition. The 

annual loading estimates are provided in Appendix D. 

Groundwater 

Baseflow

Baseflow represents groundwater discharge to streams. The annual baseflow discharge and 

load were computed for each of the subbasins that drain to Roberts Bay (not including the bay 

itself) based on flow information for Phillippi Creek. The flow duration curve for Phillippi Creek 

was first determined from Phillippi Creek measured data and correlation with Walker Creek 

flows to cover the 1992-2004 period. The baseflow, identified using the lower 10th percentile 

flow value, was determined to be about 6.2 cfs at the Phillippi Creek gage. This flow to 

drainage area ratio was then used to determine the flow at each of the other ungaged subbasins 

in the watershed. 

The correlation of the natural log of TN with the natural log of flow measured at the Phillippi 

Creek gage was determined. The concentration of TN (at the lower 10th percentile flow) times 

the flow yields the annual TN load. The annual loading estimates are provided in Appendix D.

Ground Water Seepage to Bay

The load from groundwater seepage directly to Roberts Bay was estimated based on the 

seepage flow measured in Roberts Bay at several sites as part of Florida State University 

Oceanography Research studies. An average flow value of 26 liters/square meter/day was 

used (Margaret Murray personal communication, 2005). Ground water nutrient data from 12 

monitoring wells in the area were obtained from the Florida DEP Hydroport ground water 

database and used in the loading calculation. The annual loading estimates are provided in 

Appendix D.

Septic Systems

A total load generated for septic systems in the watershed was calculated; however, the load 

estimate was not included in the total annual TN loadings to Roberts Bay because the septic 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

16 

Florida Department of Environmental Protection 

system load reaching surface waters is included in the load estimated for baseflow and ground 

water seepage to the bay. 

The number of septic systems in Sarasota County were provided in a GIS coverage by the 

County. The Department then assigned the septic systems from this coverage to each of the 

subbasins in the Roberts Bay watershed. The flow assigned to each septic tank was computed 

per the EPA TMDL manual, Protocol for Developing Pathogen TMDLs (EPA-841-R-00-002). 

This equates to 70 gal/capita/day* 2.6 capita/tank. The TN concentration discharged from 

septic tanks was determined from Table 3-7 of the EPA Onsite Wastewater Treatment Systems 

Manual (EPA/625/R-00/008). The median of the range of values presented in the manual was 

used to calculate the TN loading. The total load generated from septic systems in each 

subbasin are provided in Table 4.3. 

Surface Water Runoff 

A spreadsheet model developed by the Department’s Watershed Assessment Section, using 

methods comparable to the Watershed Management Model, was used to estimate the 

watershed surface water runoff loads associated with rainfall. The model is designed to 

estimate annual or seasonal pollutant loadings from a given watershed (User’s Manual: 

Watershed Management Model, 1998). 

The fundamental assumption of the model is that the amount of stormwater runoff from any 

given land use is in direct proportion to annual rainfall. The quantity of runoff is controlled by the 

fraction of the land use category that is characterized as impervious and the runoff coefficients 

of both pervious and impervious areas. The governing equation is as follows: 

(1) RL = [Cp + (CI – Cp) IMPL] * I 

Where: 

RL = total average annual surface runoff from land use L (inches/year), 

IMPL = fractional imperviousness of land use L, 

I = long-term average annual precipitation (inches/year), 

CP = pervious area runoff coefficient, and 

CI = impervious area runoff coefficient. 

The model estimates pollutant loadings based on nonpoint pollution loading factors (expressed 

as pounds/acre/year) that vary by land use and the percent imperviousness associated with 

each land use. The pollution loading factor, ML, is computed for each land use L by the following 

equation: 

(2) ML = EMCL * RL * K 

Where: 

ML = loading factor for land use L (pounds/acre/year), 

EMCL = event mean concentration of runoff from land use L (mg/L); EMC varies by land use 

and pollutant, 

RL = total average annual surface runoff from land use L computed from Equation (1) 

(inches/year), and 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

K = 0.2266, a unit conversion constant. 

The data required for applying the spreadsheet model include the following: 

• Area of all the land use categories, 

• Percent impervious area of each land use category, 

• EMC for each pollutant type and land use category, 

• Percent EMC of each pollutant type that is in suspended form, and 

• Annual precipitation. 
Florida Department of Environmental Protection18

Table 4.3. Septic System Load Estimates by Subbasin and Year 

Subbasin 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 Runoff to Roberts Bay N 1.438E+04 1.438E+04 1.438E+04 1.438E+04 1.438E+04 1.438E+04 1.438E+04 1.438E+04 1.438E+04 1.438E+Runoff to Roberts Bay S 1.293E+04 1.293E+04 1.293E+04 1.293E+04 1.293E+04 1.293E+04 1.293E+04 1.293E+04 1.293E+04 1.293E+Matheny Creek 1.673E+04 1.673E+04 1.673E+04 1.673E+04 1.673E+04 1.673E+04 1.673E+04 1.673E+04 1.673E+04 1.673E+Phillippi Creek (gaged) 1.044E+05 1.044E+05 1.044E+05 1.044E+05 1.044E+05 1.044E+05 1.044E+05 1.044E+05 1.044E+05 1.044E+Phillippi Creek (ungaged) 2.348E+05 2.348E+05 2.348E+05 2.348E+05 2.348E+05 2.348E+05 2.348E+05 2.348E+05 2.348E+05 2.348E+Total Load 3.833E+05 3.833E+05 3.833E+05 3.833E+05 3.833E+05 3.833E+05 3.833E+05 3.833E+05 3.833E+05 3.833E+
Florida Department of Environmental Protection19 

 

 

Data Required for Estimating TN Loadings. To estimate TN loadings from the Roberts Bay 

watershed using the spreadsheet model, the following data were obtained: 

A. Rain precipitation data were obtained from the National Atmospheric Deposition Program 

Verna Well Field monitoring site (Station FL41) located in northeastern Sarasota County. 

Annual total rainfall were used to estimate the surface water runoff load. 

B. Areas of different land use categories were obtained by aggregating GIS land use 

coverage based on the simplified Level 1 code. The land use coverage was delineated for each 

of the following subbasins in the Roberts Bay watershed. 

 Phillippi Creek above the flow gage 

 Phillippi Creek below the flow gage 

 Matheny Creek 

 Direct Runoff to bay, North 

 Direct Runoff to bay, South 

C. Percent impervious area of each land use category is a very important parameter in 

estimating surface runoff. Nonpoint pollution monitoring studies throughout the United States 

over the past 15 years have shown that annual per-acre discharges of urban stormwater 

pollution are positively related to the amount of imperviousness in land use (User’s Manual: 

Watershed Management Model, 1998). Ideally, the impervious area is the area that does not 

retain water; therefore, 100 percent of the precipitation falling on the impervious area should 

become surface runoff. In practice, however, the runoff coefficient for impervious area typically 

ranges between 95 and 100 percent. Impervious runoff coefficients lower than this range were 

observed in the literature, but usually the number should not be lower than 80 percent. 

For pervious area, the runoff coefficient usually ranges between 10 and 20 percent. However, 

values lower than this range were also observed (User’s Manual: Watershed Management 

Model, 1998). In this report, the values for impervious and pervious runoff coefficients were 

obtained from the Watershed Management Model User's Manual (Camp Dresser McKee, 1998) 

and Brown, 1988. 

D. Local event mean concentrations (EMCs) of TN for different land use categories were 

obtained from the report, Evaluation of Alternative Stormwater Regulations for Southwest 

Florida (Harper and Baker, 2003), and are presented in Table 4.4. 

The annual TN load estimated from surface runoff for each of the five subbasins is provided in 

Appendix D. 

The total annual TN loadings to the Roberts Bay watershed presented in Appendix D were computed 

by summing the point source loads and the nonpoint source loads calculated for atmospheric 

deposition, stream baseflow, ground water seepage to the bay, and surface water runoff. The total 

annual TN load to Roberts Bay varied from a low of approximately 550,000 pounds/year in 2000 to a 

high of almost 795,000 pounds/year in 1997. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

20 

Florida Department of Environmental Protection 

Table 4.4. Land Use Runoff Concentrations (Event Mean 

Concentrations) in Southwest Florida1 

FLUCCS ID Land Use BOD 

(mg/L) 

Total N 

(mg/L) 

Total P 

(mg/L) 

4000 Forest/rural open 1.23 1.09 0.046 

1000-(1100+1200+1300) Urban open 7.4 1.12 0.18 

2000 Agriculture 3.8 2.32 0.344 

1100 Low-density residential 4.3 1.64 0.191 

1200 Medium-density residential 7.4 2.18 0.335 

1300 High-density residential 11.0 2.42 0.49 

8000 Communication and transportation 6.7 2.23 0.27 

3000+7000 Rangeland 3.8 2.32 0.344 

5000 Water 1.6 1.60 0.067 

6000 Wetlands 2.63 1.01 0.09 

 1

 Source: Harper and Baker, 2003. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Chapter 5: DETERMINATION OF ASSIMILATIVE 

CAPACITY 

5.1 Determination of Loading Capacity 

The goal of the TMDL development process is to identify the maximum allowable TN loading to 

the Roberts Bay watershed, so that the bay will meet the nutrient water quality criteria and 

maintain its function and designated use as a Class III water. The Department initially 

attempted to determine the bay’s assimilative capacity through a statistical comparison of 

nitrogen loading estimates and chlorophyll a data, but these efforts were not successful (see the 

next section). Because a statistically significant relationship between TN loading and 

chlorophyll a levels was not found, the assimilative capacity for TN loading to the bay was 

based on the annual average load estimated for the 1992 to 1996 period, which is used to 

define the historic chlorophyll a value. Maintaining the TN loading at levels during this period is 

expected to prevent annual average chlorophyll a values from exceeding the target of 7.2 ug/L. 

Using this approach to develop the TMDL also provides a margin of safety (MOS) because the 

average annual chlorophyll a level was 4.8 ug/L in the 1992 to 1996 period. The annual 

average TN loading for this period is 679,090 pounds per year, as presented in Figure 5.1. The 

annual average load estimated for the verified period (1997 to 2004) is 683,219 pounds per year 

(Figure 5.1) and will need to be reduced by 0.6 percent to achieve the nutrient TMDL. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Roberts Bay WBID 1968D 

Total Nitrogen Load from Point and Nonpoint Sources

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000

900,000

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

Year

Total Nitrogen Load (lbs/year)

Point and Nonpoint Source Load Average Annual TN Load 1992 - 1996 Average Annual TN Load 1997 - 2004

Figure 5.1. Annual Average Total Nitrogen Loads in the 

Roberts Bay Watershed 

5.2 Attempts to Develop Empirical Relationships 

Attempts were made to identify relationships between the watershed TN loading to Roberts Bay 

and the chlorophyll a values measured in the bay. No significant correlation between loadings 

and receiving water quality was found. This lack of a relationship is at least partially due to the 

limited information available to derive the loading estimates. There are limited flow and nitrogen 

concentration data available from Phillippi Creek and Matheny Creek to develop loading 

estimates from the watershed to the bay. The surface water runoff from each subbasin was 

calculated using a spreadsheet model, which is designed to estimate annual pollutant loadings 

from a watershed. Relationships between TN loading and chlorophyll a levels may exist at less 

than annual time frames, however, the existing data are insufficient for making such 

comparisons. Additionally, other factors such as water residence time in the bay, which has not 

yet been accounted for, can influence the growth of algae. 

 

5.3 Current Restoration and Management Projects 

Sarasota County has initiated the Phillippi Creek Septic System Replacement Program 

(PCSSRP) to improve wastewater treatment/disposal by connecting approximately 14,000 

homes and businesses from septic systems to central sewer in the Phillippi Creek watershed. 

These parcels represent approximately 3 MGD of wastewater flows. Design and construction of 

sewer systems is being performed in eight phases. Several phases are either in design or 

being bid for construction at this time. Approximately 8,170 (58%) septic tanks will be removed 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

23 

Florida Department of Environmental Protection 

by 2007, and the remaining 42% are anticipated to be removed by 2012. Approximately 1,500 

septic tanks have been removed to date. 

5.4 Critical Conditions 

The Roberts Bay TMDL was based on annual average conditions rather than critical/seasonal 

conditions because of the following: 

a) The methodology used to determine assimilative capacity does not lend itself very well 

to short-term assessments, 

b) The net change in overall primary productivity, which is better addressed on an annual 

basis, is generally a better indicator of an imbalance in flora or fauna, and 

c) The methodology used to determine impairment is based on an annual average and 

requires data from all four quarters of a calendar year. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Chapter 6: DETERMINATION OF THE TMDL 

6.1 Expression and Allocation of the TMDL 

The objective of a TMDL is to provide a basis for allocating acceptable loads among all of the 

known pollutant sources in a watershed so that appropriate control measures can be 

implemented and water quality standards achieved. A TMDL is expressed as the sum of all 

point source loads (Waste Load Allocations, or WLAs), nonpoint source loads (Load Allocations, 

or LAs), and an appropriate margin of safety (MOS), which takes into account any uncertainty 

concerning the relationship between effluent limitations and water quality: 

TMDL = ∑ WLAs + ∑ LAs + MOS

As discussed earlier, the WLA is broken out into separate subcategories for wastewater 

discharges and stormwater discharges regulated under the NPDES Program: 

TMDL ≅ ∑ WLAswastewater + ∑ WLAsNPDES Stormwater + ∑ LAs + MOS 

It should be noted that the various components of the revised TMDL equation may not sum up 

to the value of the TMDL because (a) the WLA for NPDES stormwater is typically based on the 

percent reduction needed for nonpoint sources and is also accounted for within the LA, and (b) 

TMDL components can be expressed in different terms (for example, the WLA for stormwater is 

typically expressed as a percent reduction, and the WLA for wastewater is typically expressed 

as mass per day). 

WLAs for stormwater discharges are typically expressed as “percent reduction” because it is 

very difficult to quantify the loads from MS4s (given the numerous discharge points) and to 

distinguish loads from MS4s from other nonpoint sources (given the nature of stormwater 

transport). The permitting of stormwater discharges also differs from the permitting of most 

wastewater point sources. Because stormwater discharges cannot be centrally collected, 

monitored, and treated, they are not subject to the same types of effluent limitations as 

wastewater facilities, and instead are required to meet a performance standard of providing 

treatment to the “maximum extent practical” through the implementation of BMPs. 

This approach is consistent with federal regulations (40 CFR § 130.2[I]), which state that TMDLs 

can be expressed in terms of mass per time (e.g., pounds per day), toxicity, or other 

appropriate measure. The TMDL for Roberts Bay is expressed in terms of pounds/year and 

percent reduction, and represents the long-term annual average TN load the estuary can 

assimilate to maintain chlorophyll a annual averages below the threshold of 7.2 ug/L (Table 

6.1). 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Table 6.1. TMDL Components for Roberts Bay Watershed, WBID 1968D 

WLA 

Parameter Wastewater1

(lbs/year) 

NPDES Stormwater 

(percent reduction) 

LA 

(lbs/year) 

MOS 

(lbs/year

TMDL 

(lbs/year) 

Percent 

Reduction2

TN 53,332 8.4 625,758 Implicit 679,090 0.6 

1

 The allowable annual load is the sum of the permitted point source loads shown in Table 4.1. 2 Represents the reduction needed in the total existing load to meet the TMDL. 

6.2 Load Allocation 

The LA was determined by subtracting the WLA from the total maximum load allowed. The 

estimated allowable TN loading was the annual average of the sum of point source loads and 

nonpoint source loads for the 1992 to 1996 period. The total maximum allowable loading was 

calculated to be 679,090 pounds/year. Subtracting the WLA of 53,332 pounds/year gives a LA 

of 625,758 pounds/year. The existing annual average total load for the 1997 to 2004 period is 

683,219. Therefore to meet the LA, the nonpoint source loading will need to be reduced by 8.4 

percent ((683,219 pounds/year – 625,758 pounds/year) / 683,219 pounds/year) * 100. 

6.3 Wasteload Allocation 

6.3.1 NPDES Wastewater Discharges 

The final WLA was established according to recommendations in A Report to the Governor and 

the Legislature on the Allocation of Total Maximum Daily Loads in Florida (Florida Department 

of Environmental Protection, February 1, 2001). Because the three facilities have made 

significant reductions in their permitted discharge (see Section 4.2.1) and have provided 

treatment beyond technology-based effluent treatment levels for TN, each facility was given 

their current maximum permittable load (based on permit concentration and flow limitations). 

The three domestic facilities are advanced wastewater treatment plants (AWTP), having effluent 

limits that are greater than the technology-based treatment levels for domestic wastewater 

facilities (secondary treatment). To allocate the maximum permitted load to each facility and still 

meet the TMDL limit, the nonpoint source load allocation was reduced to offset the allowable 

point source load increase. The WLA was determined by summing the permitted annual TN 

load for each facility as shown in Table 4.1. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

6.3.2 NPDES Stormwater Discharges 

As noted in Chapter 4, loadings from stormwater discharges permitted under the NPDES 

stormwater program are placed in the WLA, rather than the LA. Since it is difficult to quantify 

the load from this source, the allocation is expressed as a percent reduction. Since the 

nonpoint source component of the TMDL needs to be reduced by 8.4 percent, this percent 

reduction is applied to the NPDES stormwater WLA. This includes loads from MS4s. It should 

be noted that any MS4 permittee is only responsible for reducing the loads associated with 

stormwater outfalls that it owns or otherwise has responsible control over, and it is not 

responsible for reducing other nonpoint source loads in its jurisdiction. 

6.4 Margin of Safety 

Consistent with the recommendations of the Allocation Technical Advisory Committee Report 

(Florida Department of Environmental Protection, February 1, 2001), an implicit margin of safety 

(MOS) was used in the development of this TMDL. An implicit MOS was provided by the 

conservative decision associated with the TMDL development approach, which established the 

TMDL at a load that is expected to maintain the annual average chlorophyll a value below the 

chlorophyll a target of 7.2 μg/L. The TMDL is based on the estimated TN load during the 

historic baseline period when the annual average chlorophyll a values were less than 7.2 ug/L. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

27 

Florida Department of Environmental Protection 

Chapter 7: NEXT STEPS: IMPLEMENTATION PLAN 

DEVELOPMENT AND BEYOND 

7.1 Basin Management Action Plan 

Following the adoption of this TMDL by rule, the next step in the TMDL process is to develop an 

implementation plan for the TMDL, which will be a component of a Basin Management Action 

Plan (BMAP). This document will be developed over the next year in cooperation with local 

stakeholders and will attempt to reach consensus on more detailed allocations and on how load 

reductions will be accomplished. The BMAP will include the following: 

• Appropriate allocations among the affected parties, 

• A description of the load reduction activities to be undertaken, 

• Timetables for project implementation and completion, 

• Funding mechanisms that may be utilized, 

• Any applicable signed agreement, 

• Local ordinances defining actions to be taken or prohibited, 

• Local water quality standards, permits, or load limitation agreements, and 

• Monitoring and follow-up measures. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

28 

Florida Department of Environmental Protection 

References 

Brown, M. T. 1988. The South Dade Watershed Project. Miami, Florida: Center for Urban and 

Community Design. 

Camp Dresser and McKee. 1998. The Watershed Management Model User's Manual. 

Florida Administrative Code. Chapter 62-302, Surface Water Quality Standards.

Florida Administrative Code. Chapter 62-303, Identification of Impaired Surface Waters. 

Florida Department of Environmental Protection. February 1, 2001. A Report to the Governor 

and the Legislature on the Allocation of Total Maximum Daily Loads in Florida. 

Tallahassee, Florida: Bureau of Watershed Management. 

—. June 2003. Sarasota Bay, Peace River, and Myakka River, Basin Status Report. 

Tallahassee, Florida. Available: http://www.dep.state.fl.us/water/basin411/sbpm/status.htm

Florida Department of Health Web site. 2005. Available at http://www.doh.state.fl.us/ and 

http://www.doh.state.fl.us/environment/OSTDS/statistics/ostdsstatistics.htm

Harper, H. and Baker, D. 2003. Evaluation of Alternative Stormwater Regulations for 

Southwest Florida, Final Report. Orlando, Florida: Environmental Research and Design, 

Inc. 

National Research Council, 1993. Managing Wastewater in Coastal Urban Areas. National 

Academy Press, Washington, DC.

Southwest Florida Water Management District. 2000. Southern Coastal Watershed 

Comprehensive Watershed Management Plan. Brooksville, Florida. 

U. S. Environmental Protection Agency. 1999. Protocol for Developing Nutrient TMDLs. 

Washington, D.C.: Office of Water. EPA 841-B-99-007. 

U. S. Environmental Protection Agency. 2001. Protocol for Developing Pathogen TMDLs. 

Washington, D.C.: Office of Water. EPA 841-R-00-002. 

U. S. Environmental Protection Agency. 2002. Onsite Wastewater Treatment Systems Manual. 

Washington, D.C.: Office of Water. EPA/625/R-00/008. 

User’s Manual: Watershed Management Model, Version 4.1. 1998. Rouge River National Wet 

Weather Demonstration Project. Wayne County, Michigan. PRO-NPS-TM27.02. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Appendices 

Appendix A: Background Information on Federal and State 

Stormwater Programs 

In 1982, Florida became the first state in the country to implement statewide regulations to 

address the issue of nonpoint source pollution by requiring new development and 

redevelopment to treat stormwater before it is discharged. The Stormwater Rule, as authorized 

in Chapter 403, F.S., was established as a technology-based program that relies on the 

implementation of BMPs that are designed to achieve a specific level of treatment (i.e., 

performance standards) as set forth in Chapter 62-40, F.A.C. 

The rule requires the state’s water management districts (WMDs) to establish stormwater 

pollutant load reduction goals (PLRGs) and adopt them as part of a SWIM plan, other 

watershed plan, or rule. Stormwater PLRGs are a major component of the load allocation part 

of a TMDL. To date, stormwater PLRGs have been established for Tampa Bay, Lake 

Thonotosassa, the Winter Haven Chain of Lakes, the Everglades, Lake Okeechobee, and Lake 

Apopka. No PLRG has been developed for Newnans Lake at the time this study was 

conducted. 

In 1987, the U.S. Congress established Section 402(p) as part of the federal Clean Water Act 

Reauthorization. This section of the law amended the scope of the federal NPDES stormwater 

permitting program to designate certain stormwater discharges as “point sources” of pollution. 

These stormwater discharges include certain discharges that are associated with industrial 

activities designated by specific Standard Industrial Classification (SIC) codes, construction 

sites disturbing five or more acres of land, and master drainage systems of local governments 

with a population above 100,000, which are better known as municipal separate storm sewer 

systems (MS4s). However, because the master drainage systems of most local governments in 

Florida are interconnected, the EPA has implemented Phase 1 of the MS4 permitting program 

on a countywide basis, which brings in all cities (incorporated areas), Chapter 298 urban water 

control districts, and the Florida Department of Transportation throughout the fifteen counties 

meeting the population criteria. 

An important difference between the federal and state stormwater permitting programs is that 

the federal program covers both new and existing discharges, while the state program focuses 

on new discharges. Additionally, Phase 2 of the NPDES Program will expand the need for 

these permits to construction sites between one and five acres, and to local governments with 

as few as 10,000 people. These revised rules require that these additional activities obtain 

permits by 2003. While these urban stormwater discharges are now technically referred to as 

“point sources” for the purpose of regulation, they are still diffuse sources of pollution that 

cannot be easily collected and treated by a central treatment facility similar to other point 

sources of pollution, such as domestic and industrial wastewater discharges. The Department 

recently accepted delegation from the EPA for the stormwater part of the NPDES Program. It 

should be noted that most MS4 permits issued in Florida include a re-opener clause that allows 

permit revisions to implement TMDLs once they are formally adopted by rule. 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

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Florida Department of Environmental Protection 

Appendix B: Chlorophyll a Raw Data 

WBID Station Time Date Parameter Result 

1968D 21FLMML 271529082320400 1307 2/4/1992 CHLA 2.2 

1968D 21FLMML 271716082324500 1402 2/4/1992 CHLA 2.1 

1968D 21FLMML 271803082323400 1415 2/4/1992 CHLA 4.9 

1968D 21FLMML 271529082320400 930 5/12/1992 CHLA 4.9 

1968D 21FLMML 271716082324500 1025 5/12/1992 CHLA 4.7 

1968D 21FLMML 271803082323400 1045 5/12/1992 CHLA 4.5 

1968D 21FLMML 271529082320400 1032 8/11/1992 CHLA 10.2 

1968D 21FLMML 271716082324500 1140 8/11/1992 CHLA 11.9 

1968D 21FLMML 271803082323400 1212 8/11/1992 CHLA 8.5 

1968D 21FLMML 271529082320400 1216 11/10/1992 CHLA 8.7 

1968D 21FLMML 271716082324500 1335 11/10/1992 CHLA 4.5 

1968D 21FLMML 271803082323400 1355 11/10/1992 CHLA 3.9 

1968D 21FLMML 271529082320400 1302 2/9/1993 CHLA 5 

1968D 21FLMML 271716082324500 1422 2/9/1993 CHLA 1.5 

1968D 21FLMML 271803082323400 1452 2/9/1993 CHLA 2.6 

1968D 21FLMML 271529082320400 1022 5/4/1993 CHLA 3.5 

1968D 21FLMML 271716082324500 1122 5/4/1993 CHLA 3.7 

1968D 21FLMML 271803082323400 1141 5/4/1993 CHLA 3.5 

1968D 21FLMML 271529082320400 1223 8/3/1993 CHLA 13.9 

1968D 21FLMML 271716082324500 1334 8/3/1993 CHLA 12.3 

1968D 21FLMML 271803082323400 1352 8/3/1993 CHLA 5.8 

1968D 21FLMML 271529082320400 1325 11/2/1993 CHLA 5.2 

1968D 21FLMML 271716082324500 1445 11/2/1993 CHLA 5.8 

1968D 21FLMML 271803082323400 1500 11/2/1993 CHLA 13.6 

1968D 21FLSARA950125-13-5 1230 1/25/1995 CHLA 1 

1968D 21FLSARA950125-13-4 1300 1/25/1995 CHLA 1 

1968D 21FLSARA950125-13-3 1330 1/25/1995 CHLA 1 

1968D 21FLSARA950125-13-2 1345 1/25/1995 CHLA 1 

1968D 21FLSARA950125-13-1 1400 1/25/1995 CHLA 1 

1968D 21FLSARA950214-13-5 1115 2/14/1995 CHLA 1 

1968D 21FLSARA950214-13-4 1230 2/14/1995 CHLA 1 

1968D 21FLSARA950214-13-3 1300 2/14/1995 CHLA 1 

1968D 21FLSARA950214-13-2 1325 2/14/1995 CHLA 1 

1968D 21FLSARA950214-13-1 1350 2/14/1995 CHLA 1.1 

1968D 21FLSARA950314-13-5 1305 3/14/1995 CHLA 1.1 

1968D 21FLSARA950314-13-4 1325 3/14/1995 CHLA 1.6 

1968D 21FLSARA950314-13-3 1340 3/14/1995 CHLA 1.6 

1968D 21FLSARA950314-13-2 1350 3/14/1995 CHLA 1 

1968D 21FLSARA950314-13-1 1400 3/14/1995 CHLA 1 

1968D 21FLSARA950419-13-4 1220 4/19/1995 CHLA 4.8 

1968D 21FLSARA950419-13-5 1240 4/19/1995 CHLA 4.3 

1968D 21FLSARA950419-13-3 1300 4/19/1995 CHLA 4.3 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

31 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA950419-13-2 1350 4/19/1995 CHLA 2.7 

1968D 21FLSARA950419-13-1 1410 4/19/1995 CHLA 1.6 

1968D 21FLSARA950516-13-5 1310 5/16/1995 CHLA 4.3 

1968D 21FLSARA950516-13-3 1335 5/16/1995 CHLA 2.7 

1968D 21FLSARA950516-13-2 1345 5/16/1995 CHLA 2.7 

1968D 21FLSARA950516-13-1 1410 5/16/1995 CHLA 3.2 

1968D 21FLSARA950620-13-5 1235 6/20/1995 CHLA 7.5 

1968D 21FLSARA950620-13-4 1255 6/20/1995 CHLA 8 

1968D 21FLSARA950620-13-3 1320 6/20/1995 CHLA 6.9 

1968D 21FLSARA950620-13-2 1345 6/20/1995 CHLA 6.9 

1968D 21FLSARA950620-13-1 1400 6/20/1995 CHLA 3.2 

1968D 21FLSARA950711-13-5 1305 7/11/1995 CHLA 3.2 

1968D 21FLSARA950711-13-4 1330 7/11/1995 CHLA 3.2 

1968D 21FLSARA950711-13-3 1345 7/11/1995 CHLA 2.7 

1968D 21FLSARA950711-13-2 1400 7/11/1995 CHLA 3.7 

1968D 21FLSARA950711-13-1 1415 7/11/1995 CHLA 2.1 

1968D 21FLSARA950828-13-4 1200 8/28/1995 CHLA 13.9 

1968D 21FLSARA950828-13-5 1225 8/28/1995 CHLA 19.2 

1968D 21FLSARA950828-13-3 1320 8/28/1995 CHLA 11.2 

1968D 21FLSARA950828-13-2 1345 8/28/1995 CHLA 9.1 

1968D 21FLSARA950828-13-1 1400 8/28/1995 CHLA 10.1 

1968D 21FLSARA950919-13-5 1115 9/19/1995 CHLA 12.3 

1968D 21FLSARA950919-13-4 1135 9/19/1995 CHLA 11.2 

1968D 21FLSARA950919-13-3 1155 9/19/1995 CHLA 9.1 

1968D 21FLSARA950919-13-2 1220 9/19/1995 CHLA 9.1 

1968D 21FLSARA950919-13-1 1235 9/19/1995 CHLA 9.1 

1968D 21FLSARA951016-13-5 1150 10/16/1995 CHLA 7.5 

1968D 21FLSARA951016-13-4 1220 10/16/1995 CHLA 6.9 

1968D 21FLSARA951016-13-3 1240 10/16/1995 CHLA 4 

1968D 21FLSARA951016-13-2 1300 10/16/1995 CHLA 4.8 

1968D 21FLSARA951016-13-1 1325 10/16/1995 CHLA 5.3 

1968D 21FLSARA951114-13-5 1130 11/14/1995 CHLA 2.7 

1968D 21FLSARA951114-13-4 1150 11/14/1995 CHLA 1.6 

1968D 21FLSARA951114-13-3 1210 11/14/1995 CHLA 1.6 

1968D 21FLSARA951114-13-2 1230 11/14/1995 CHLA 1.6 

1968D 21FLSARA951114-13-1 1245 11/14/1995 CHLA 1.6 

1968D 21FLSARA951211-13-5 1150 12/11/1995 CHLA 6.4 

1968D 21FLSARA951211-13-4 1215 12/11/1995 CHLA 4.3 

1968D 21FLSARA951211-13-3 1245 12/11/1995 CHLA 9.1 

1968D 21FLSARA951211-13-2 1305 12/11/1995 CHLA 5.9 

1968D 21FLSARA951211-13-1 1330 12/11/1995 CHLA 4.8 

1968D 21FLSARA960123-13-5 1230 1/23/1996 CHLA 1.1 

1968D 21FLSARA960123-13-4 1255 1/23/1996 CHLA 2.7 

1968D 21FLSARA960123-13-3 1330 1/23/1996 CHLA 2.7 

1968D 21FLSARA960123-13-2 1345 1/23/1996 CHLA 1 

1968D 21FLSARA960123-13-1 1400 1/23/1996 CHLA 1.1 

1968D 21FLSARA960214-13-5 1135 2/14/1996 CHLA 1.1 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

32 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA960214-13-4 1155 2/14/1996 CHLA 1.1 

1968D 21FLSARA960214-13-3 1220 2/14/1996 CHLA 1.1 

1968D 21FLSARA960214-13-2 1250 2/14/1996 CHLA 1 

1968D 21FLSARA960214-13-1 1305 2/14/1996 CHLA 1 

1968D 21FLSARA960321-13-5 1130 3/21/1996 CHLA 1.1 

1968D 21FLSARA960321-13-4 1205 3/21/1996 CHLA 1.1 

1968D 21FLSARA960321-13-3 1220 3/21/1996 CHLA 1 

1968D 21FLSARA960321-13-2 1245 3/21/1996 CHLA 1 

1968D 21FLSARA960321-13-1 1305 3/21/1996 CHLA 1.6 

1968D 21FLSARA960408-13-1 940 4/8/1996 CHLA 1 

1968D 21FLSARA960408-13-2 1000 4/8/1996 CHLA 1 

1968D 21FLSARA960408-13-3 1020 4/8/1996 CHLA 1 

1968D 21FLSARA960408-13-4 1035 4/8/1996 CHLA 2.1 

1968D 21FLSARA960408-13-5 1050 4/8/1996 CHLA 3.2 

1968D 21FLSARA960510-13-5 1030 5/10/1996 CHLA 2.1 

1968D 21FLSARA960510-13-3 1100 5/10/1996 CHLA 2.7 

1968D 21FLSARA960510-13-2 1120 5/10/1996 CHLA 1.6 

1968D 21FLSARA960510-13-1 1135 5/10/1996 CHLA 1.1 

1968D 21FLSARA960619-13-5 1125 6/19/1996 CHLA 5.8 

1968D 21FLSARA960619-13-4 1140 6/19/1996 CHLA 6.5 

1968D 21FLSARA960619-13-3 1150 6/19/1996 CHLA 4.8 

1968D 21FLSARA960619-13-2 1215 6/19/1996 CHLA 2.7 

1968D 21FLSARA960619-13-1 1230 6/19/1996 CHLA 2.1 

1968D 21FLSARA960716-13-5 1110 7/16/1996 CHLA 4.8 

1968D 21FLSARA960716-13-4 1145 7/16/1996 CHLA 5.1 

1968D 21FLSARA960716-13-3 1215 7/16/1996 CHLA 2.7 

1968D 21FLSARA960716-13-2 1230 7/16/1996 CHLA 1.6 

1968D 21FLSARA960716-13-1 1245 7/16/1996 CHLA 2.7 

1968D 21FLSARA960820-13-5 1130 8/20/1996 CHLA 5.3 

1968D 21FLSARA960820-13-4 1145 8/20/1996 CHLA 4.3 

1968D 21FLSARA960820-13-3 1215 8/20/1996 CHLA 4.8 

1968D 21FLSARA960820-13-2 1230 8/20/1996 CHLA 5.3 

1968D 21FLSARA960820-13-1 1245 8/20/1996 CHLA 6.9 

1968D 21FLSARA960926-13-5 1125 9/26/1996 CHLA 1.1 

1968D 21FLSARA960926-13-4 1210 9/26/1996 CHLA 1.6 

1968D 21FLSARA960926-13-3 1235 9/26/1996 CHLA 1.6 

1968D 21FLSARA960926-13-2 1250 9/26/1996 CHLA 2.1 

1968D 21FLSARA960926-13-1 1305 9/26/1996 CHLA 1 

1968D 21FLSARA961024-13-5 1140 10/24/1996 CHLA 1.1 

1968D 21FLSARA961024-13-4 1210 10/24/1996 CHLA 1 

1968D 21FLSARA961024-13-3 1235 10/24/1996 CHLA 1.1 

1968D 21FLSARA961024-13-2 1255 10/24/1996 CHLA 1.1 

1968D 21FLSARA961024-13-1 1320 10/24/1996 CHLA 1.6 

1968D 21FLSARA961119-13-5 1105 11/19/1996 CHLA 1.1 

1968D 21FLSARA961119-13-4 1120 11/19/1996 CHLA 1 

1968D 21FLSARA961119-13-3 1135 11/19/1996 CHLA 1.1 

1968D 21FLSARA961119-13-2 1150 11/19/1996 CHLA 1.1 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

33 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA961119-13-1 1205 11/19/1996 CHLA 1.6 

1968D 21FLSARA961210-13-5 1230 12/10/1996 CHLA 1 

1968D 21FLSARA961210-13-4 1250 12/10/1996 CHLA 1.1 

1968D 21FLSARA961210-13-3 1310 12/10/1996 CHLA 3.2 

1968D 21FLSARA961210-13-2 1320 12/10/1996 CHLA 1.1 

1968D 21FLSARA961210-13-1 1330 12/10/1996 CHLA 2.7 

1968D 21FLSARA970109-13-5 1100 1/9/1997 CHLA 2.7 

1968D 21FLSARA970109-13-4 1115 1/9/1997 CHLA 2.7 

1968D 21FLSARA970109-13-3 1140 1/9/1997 CHLA 2.7 

1968D 21FLSARA970109-13-2 1150 1/9/1997 CHLA 1.6 

1968D 21FLSARA970109-13-2 1150 1/9/1997 CHLA 1.6 

1968D 21FLSARA970109-13-1 1200 1/9/1997 CHLA 1.6 

1968D 21FLSARA970109-13-1 1200 1/9/1997 CHLA 1.6 

1968D 21FLSARA970210-13-5 1140 2/10/1997 CHLA 4.8 

1968D 21FLSARA970210-13-4 1155 2/10/1997 CHLA 2.7 

1968D 21FLSARA970210-13-3 1210 2/10/1997 CHLA 3.2 

1968D 21FLSARA970210-13-2 1245 2/10/1997 CHLA 1.1 

1968D 21FLSARA970210-13-1 1305 2/10/1997 CHLA 2.1 

1968D 21FLSARA970311-13-5 1120 3/11/1997 CHLA 3.2 

1968D 21FLSARA970311-13-4 1200 3/11/1997 CHLA 7.5 

1968D 21FLSARA970311-13-3 1215 3/11/1997 CHLA 1.1 

1968D 21FLSARA970311-13-2 1230 3/11/1997 CHLA 1.6 

1968D 21FLSARA970311-13-1 1245 3/11/1997 CHLA 1 

1968D 21FLSARA13-1-04 1010 4/23/1997 CHLAC 1.6 

1968D 21FLSARA13-2-04 1040 4/23/1997 CHLAC 2.1 

1968D 21FLSARA13-3-04 1105 4/23/1997 CHLAC 3.2 

1968D 21FLSARA13-4-04 1125 4/23/1997 CHLAC 2.1 

1968D 21FLSARA13-5-04 1150 4/23/1997 CHLAC 2.1 

1968D 21FLSARA970519-13-5 1130 5/19/1997 CHLA 3.7 

1968D 21FLSARA970519-13-3 1200 5/19/1997 CHLA 3.7 

1968D 21FLSARA970519-13-2 1220 5/19/1997 CHLA 1.6 

1968D 21FLSARA970519-13-1 1235 5/19/1997 CHLA 2.1 

1968D 21FLSARA970618-13-5 1120 6/18/1997 CHLA 35.2 

1968D 21FLSARA970618-13-4 1130 6/18/1997 CHLA 17.6 

1968D 21FLSARA970618-13-3 1145 6/18/1997 CHLA 19.2 

1968D 21FLSARA970618-13-2 1200 6/18/1997 CHLA 21 

1968D 21FLSARA970618-13-1 1220 6/18/1997 CHLA 39.2 

1968D 21FLSARA970715-13-5 1105 7/15/1997 CHLA 4.4 

1968D 21FLSARA970715-13-4 1115 7/15/1997 CHLA 4.8 

1968D 21FLSARA970715-13-3 1130 7/15/1997 CHLA 5.2 

1968D 21FLSARA970715-13-2 1145 7/15/1997 CHLA 7 

1968D 21FLSARA970715-13-1 1200 7/15/1997 CHLA 4.4 

1968D 21FLSARA970818-13-1 1000 8/18/1997 CHLA 4.2 

1968D 21FLSARA970818-13-2 1020 8/18/1997 CHLA 5.6 

1968D 21FLSARA970818-13-3 1040 8/18/1997 CHLA 6.8 

1968D 21FLSARA970818-13-4 1110 8/18/1997 CHLA 5.7 

1968D 21FLSARA970818-13-5 1130 8/18/1997 CHLA 4.6 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

34 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA970916-13-5 1105 9/16/1997 CHLA 16.4 

1968D 21FLSARA970916-13-4 1120 9/16/1997 CHLA 14.5 

1968D 21FLSARA970916-13-3 1135 9/16/1997 CHLA 14.6 

1968D 21FLSARA970916-13-2 1145 9/16/1997 CHLA 8.1 

1968D 21FLSARA970916-13-1 1200 9/16/1997 CHLA 10.1 

1968D 21FLSARA971008-13-5 1055 10/8/1997 CHLA 11.5 

1968D 21FLSARA971008-13-4 1110 10/8/1997 CHLA 14.1 

1968D 21FLSARA971008-13-3 1125 10/8/1997 CHLA 11.3 

1968D 21FLSARA971008-13-2 1140 10/8/1997 CHLA 14.3 

1968D 21FLSARA971008-13-1 1200 10/8/1997 CHLA 11.6 

1968D 21FLSARA971111-13-5 1045 11/11/1997 CHLA 2.3 

1968D 21FLSARA971111-13-4 1100 11/11/1997 CHLA 2.1 

1968D 21FLSARA971111-13-3 1110 11/11/1997 CHLA 3.2 

1968D 21FLSARA971111-13-2 1130 11/11/1997 CHLA 3.2 

1968D 21FLSARA971111-13-1 1140 11/11/1997 CHLA 1.6 

1968D 21FLSARA971210-13-5 1135 12/10/1997 CHLA 7.9 

1968D 21FLSARA971210-13-4 1145 12/10/1997 CHLA 26.2 

1968D 21FLSARA971210-13-3 1205 12/10/1997 CHLA 12.3 

1968D 21FLSARA971210-13-2 1215 12/10/1997 CHLA 11.5 

1968D 21FLSARA971210-13-1 1230 12/10/1997 CHLA 10.5 

1968D 21FLSARA980225-13-5 1215 2/25/1998 CHLAC 10.2 

1968D 21FLSARA980225-13-4 1236 2/25/1998 CHLAC 9.9 

1968D 21FLSARA980225-13-3 1255 2/25/1998 CHLAC 12.2 

1968D 21FLSARA980225-13-2 1322 2/25/1998 CHLAC 7.9 

1968D 21FLSARA980225-13-1 1345 2/25/1998 CHLAC 6 

1968D 21FLSARA980317-13-5 1227 3/17/1998 CHLAC 3.3 

1968D 21FLSARA980317-13-4 1250 3/17/1998 CHLAC 2.3 

1968D 21FLSARA980317-13-3 1311 3/17/1998 CHLAC 3.1 

1968D 21FLSARA980317-13-2 1338 3/17/1998 CHLAC 3 

1968D 21FLSARA980317-13-1 1356 3/17/1998 CHLAC 2.3 

1968D 21FLSARA980414-13-5 1224 4/14/1998 CHLAC 3.1 

1968D 21FLSARA980414-13-4 1249 4/14/1998 CHLAC 4.8 

1968D 21FLSARA980414-13-3 1312 4/14/1998 CHLAC 4.8 

1968D 21FLSARA980414-13-2 1340 4/14/1998 CHLAC 5.6 

1968D 21FLSARA980414-13-1 1401 4/14/1998 CHLAC 5.3 

1968D 21FLSARA980415-16-2 1352 4/15/1998 CHLAC 3.1 

1968D 21FLSARA980505-13-5 1152 5/5/1998 CHLAC 5 

1968D 21FLSARA980505-13-4 1209 5/5/1998 CHLAC 4.1 

1968D 21FLSARA980505-13-3 1231 5/5/1998 CHLAC 6.8 

1968D 21FLSARA980505-13-2 1252 5/5/1998 CHLAC 8.1 

1968D 21FLSARA980505-13-1 1308 5/5/1998 CHLAC 9.6 

1968D 21FLSARA980610-13-5 1149 6/10/1998 CHLAC 9.4 

1968D 21FLSARA980610-13-4 1211 6/10/1998 CHLAC 6.6 

1968D 21FLSARA980610-13-3 1235 6/10/1998 CHLAC 5.4 

1968D 21FLSARA980610-13-2 1255 6/10/1998 CHLAC 3.1 

1968D 21FLSARA980610-13-1 1315 6/10/1998 CHLAC 3.7 

1968D 21FLSARA980715-13-5 1154 7/15/1998 CHLAC 10.3 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

35 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA980715-13-4 1209 7/15/1998 CHLAC 14.7 

1968D 21FLSARA980715-13-3 1241 7/15/1998 CHLAC 13.3 

1968D 21FLSARA980715-13-2 1300 7/15/1998 CHLAC 11.4 

1968D 21FLSARA980715-13-1 1319 7/15/1998 CHLAC 10 

1968D 21FLSARA980826-13-5 1158 8/26/1998 CHLAC 6.7 

1968D 21FLSARA980826-13-4 1220 8/26/1998 CHLAC 9 

1968D 21FLSARA980826-13-3 1300 8/26/1998 CHLAC 10.8 

1968D 21FLSARA980826-13-2 1324 8/26/1998 CHLAC 5.1 

1968D 21FLSARA980826-13-1 1347 8/26/1998 CHLAC 7.1 

1968D 21FLSARA980916-13-5 1211 9/16/1998 CHLAC 14.7 

1968D 21FLSARA980916-13-4 1238 9/16/1998 CHLAC 14.9 

1968D 21FLSARA980916-13-3 1305 9/16/1998 CHLAC 12.3 

1968D 21FLSARA980916-13-2 1329 9/16/1998 CHLAC 10.2 

1968D 21FLSARA980916-13-1 1352 9/16/1998 CHLAC 15.7 

1968D 21FLSARA981014-13-5 1211 10/14/1998 CHLAC 11.8 

1968D 21FLSARA981014-13-4 1227 10/14/1998 CHLAC 5.3 

1968D 21FLSARA981014-13-3 1252 10/14/1998 CHLAC 10.9 

1968D 21FLSARA981014-13-2 1314 10/14/1998 CHLAC 10.3 

1968D 21FLSARA981014-13-1 1329 10/14/1998 CHLAC 6.7 

1968D 21FLSARA13-5-11 1157 11/18/1998 CHLAC 6.3 

1968D 21FLSARA13-4-11 1216 11/18/1998 CHLAC 6 

1968D 21FLSARA13-3-11 1240 11/18/1998 CHLAC 6.5 

1968D 21FLSARA13-2-11 1343 11/18/1998 CHLAC 6.3 

1968D 21FLSARA13-1-11 1358 11/18/1998 CHLAC 5.1 

1968D 21FLSARA13-5-12 1144 12/9/1998 CHLAC 5.6 

1968D 21FLSARA13-4-12 1208 12/9/1998 CHLAC 4.9 

1968D 21FLSARA13-3-12 1227 12/9/1998 CHLAC 11.7 

1968D 21FLSARA13-2-12 1247 12/9/1998 CHLAC 3.5 

1968D 21FLSARA13-1-12 1302 12/9/1998 CHLAC 3.7 

1968D 21FLSARA13-5-01 1149 1/7/1999 CHLAC 1 

1968D 21FLSARA13-4-01 1222 1/7/1999 CHLAC 1.1 

1968D 21FLSARA13-3-01 1241 1/7/1999 CHLAC 1.8 

1968D 21FLSARA13-2-01 1302 1/7/1999 CHLAC 1.1 

1968D 21FLSARA13-1-01 1316 1/7/1999 CHLAC 2 

1968D 21FLSARA13-5-02 1155 2/10/1999 CHLAC 5.3 

1968D 21FLSARA13-4-02 1217 2/10/1999 CHLAC 4.4 

1968D 21FLSARA13-3-02 1240 2/10/1999 CHLAC 7.8 

1968D 21FLSARA13-2-02 1309 2/10/1999 CHLAC 5.7 

1968D 21FLSARA13-1-02 1337 2/10/1999 CHLAC 4.5 

1968D 21FLSARA13-5-03 1210 3/10/1999 CHLAC 2.3 

1968D 21FLSARA13-4-03 1243 3/10/1999 CHLAC 2.5 

1968D 21FLSARA13-3-03 1305 3/10/1999 CHLAC 2.7 

1968D 21FLSARA13-2-03 1330 3/10/1999 CHLAC 2.5 

1968D 21FLSARA13-1-03 1350 3/10/1999 CHLAC 2.9 

1968D 21FLSARA13-5-04 1201 4/14/1999 CHLAC 6.8 

1968D 21FLSARA13-4-04 1238 4/14/1999 CHLAC 5.7 

1968D 21FLSARA13-3-04 1256 4/14/1999 CHLAC 5.8 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

36 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA13-2-04 1321 4/14/1999 CHLAC 5.5 

1968D 21FLSARA13-1-04 1340 4/14/1999 CHLAC 5.3 

1968D 21FLSARA13-5-05 1148 5/12/1999 CHLAC 8.2 

1968D 21FLSARA13-3-05 1226 5/12/1999 CHLAC 12 

1968D 21FLSARA13-2-05 1247 5/12/1999 CHLAC 11.8 

1968D 21FLSARA13-1-05 1306 5/12/1999 CHLAC 8.7 

1968D 21FLSARA13-5-06 1212 6/16/1999 CHLAC 7.9 

1968D 21FLSARA13-4-06 1229 6/16/1999 CHLAC 6.7 

1968D 21FLSARA13-3-06 1251 6/16/1999 CHLAC 8.4 

1968D 21FLSARA13-2-06 1316 6/16/1999 CHLAC 5.6 

1968D 21FLSARA13-1-06 1333 6/16/1999 CHLAC 2.9 

1968D 21FLSARA13-1-07 1029 7/21/1999 CHLAC 6.4 

1968D 21FLSARA13-2-07 1048 7/21/1999 CHLAC 11.3 

1968D 21FLSARA13-3-07 1107 7/21/1999 CHLAC 9.5 

1968D 21FLSARA13-4-07 1130 7/21/1999 CHLAC 10.4 

1968D 21FLSARA13-5-07 1144 7/21/1999 CHLAC 6.5 

1968D 21FLSARA13-5-08 1208 8/10/1999 CHLAC 35.6 

1968D 21FLSARA13-4-08 1228 8/10/1999 CHLAC 20.4 

1968D 21FLSARA13-3-08 1331 8/10/1999 CHLAC 19.6 

1968D 21FLSARA13-2-08 1350 8/10/1999 CHLAC 28.6 

1968D 21FLSARA13-1-08 1406 8/10/1999 CHLAC 23.9 

1968D 21FLSARA13-5-09 1227 9/28/1999 CHLAC 19.6 

1968D 21FLSARA13-4-09 1247 9/28/1999 CHLAC 21 

1968D 21FLSARA13-3-09 1312 9/28/1999 CHLAC 25.5 

1968D 21FLSARA13-2-09 1344 9/28/1999 CHLAC 23.6 

1968D 21FLSARA13-1-09 1358 9/28/1999 CHLAC 21.2 

1968D 21FLSARA13-5-10 1152 10/20/1999 CHLAC 10.9 

1968D 21FLSARA13-4-10 1229 10/20/1999 CHLAC 11.4 

1968D 21FLSARA13-3-10 1247 10/20/1999 CHLAC 12 

1968D 21FLSARA13-2-10 1308 10/20/1999 CHLAC 13 

1968D 21FLSARA13-1-10 1325 10/20/1999 CHLAC 7 

1968D 21FLSARA13-5-11 1211 11/10/1999 CHLAC 6 

1968D 21FLSARA13-4-11 1237 11/10/1999 CHLAC 4.2 

1968D 21FLSARA13-3-11 1257 11/10/1999 CHLAC 5.6 

1968D 21FLSARA13-2-11 1323 11/10/1999 CHLAC 5.3 

1968D 21FLSARA13-1-11 1347 11/10/1999 CHLAC 5.6 

1968D 21FLSARA13-5-12 1205 12/15/1999 CHLAC 2 

1968D 21FLSARA13-4-12 1300 12/15/1999 CHLAC 6.5 

1968D 21FLSARA13-3-12 1326 12/15/1999 CHLAC 10.6 

1968D 21FLSARA13-2-12 1348 12/15/1999 CHLAC 2.4 

1968D 21FLSARA13-1-12 1403 12/15/1999 CHLAC 2.1 

1968D 21FLSARA13-5-01 1225 1/12/2000 CHLAC 6.9 

1968D 21FLSARA13-4-01 1313 1/12/2000 CHLAC 3.9 

1968D 21FLSARA13-3-01 1337 1/12/2000 CHLAC 2.9 

1968D 21FLSARA13-2-01 1358 1/12/2000 CHLAC 2.3 

1968D 21FLSARA13-1-01 1412 1/12/2000 CHLAC 2.4 

1968D 21FLSARA13-5-02 1211 2/16/2000 CHLAC 1.9 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

37 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA13-4-02 1246 2/16/2000 CHLAC 1.8 

1968D 21FLSARA13-3-02 1322 2/16/2000 CHLAC 1 

1968D 21FLSARA13-2-02 1344 2/16/2000 CHLAC 1.7 

1968D 21FLSARA13-1-02 1403 2/16/2000 CHLAC 1 

1968D 21FLSARA13-5-03 1245 3/15/2000 CHLAC 2.9 

1968D 21FLSARA13-4-03 1305 3/15/2000 CHLAC 3.2 

1968D 21FLSARA13-3-03 1326 3/15/2000 CHLAC 3.3 

1968D 21FLSARA13-2-03 1354 3/15/2000 CHLAC 5.4 

1968D 21FLSARA13-1-03 1408 3/15/2000 CHLAC 3.6 

1968D 21FLSARA13-5-04 1211 4/12/2000 CHLAC 4.5 

1968D 21FLSARA13-4-04 1248 4/12/2000 CHLAC 3.5 

1968D 21FLSARA13-3-04 1305 4/12/2000 CHLAC 3.5 

1968D 21FLSARA13-2-04 1329 4/12/2000 CHLAC 4.2 

1968D 21FLSARA13-1-04 1346 4/12/2000 CHLAC 3.5 

1968D 21FLSARA13-5-05 1158 5/10/2000 CHLAC 3.9 

1968D 21FLSARA13-3-05 1248 5/10/2000 CHLAC 5.1 

1968D 21FLSARA13-2-05 1309 5/10/2000 CHLAC 5 

1968D 21FLSARA13-1-05 1323 5/10/2000 CHLAC 3.6 

1968D 21FLSARA13-5-06 1219 6/14/2000 CHLAC 6.8 

1968D 21FLSARA13-4-06 1237 6/14/2000 CHLAC 6.5 

1968D 21FLSARA13-3-06 1255 6/14/2000 CHLAC 4 

1968D 21FLSARA13-2-06 1320 6/14/2000 CHLAC 5.2 

1968D 21FLSARA13-1-06 1336 6/14/2000 CHLAC 7 

1968D 21FLSARA13-5-07 1225 7/18/2000 CHLAC 11.3 

1968D 21FLSARA13-4-07 1305 7/18/2000 CHLAC 10.6 

1968D 21FLSARA13-3-07 1336 7/18/2000 CHLAC 12.9 

1968D 21FLSARA13-2-07 1412 7/18/2000 CHLAC 7 

1968D 21FLSARA13-1-07 1430 7/18/2000 CHLAC 2.6 

1968D 21FLSARA13-5-08 1206 8/8/2000 CHLAC 11.5 

1968D 21FLSARA13-4-08 1246 8/8/2000 CHLAC 10.2 

1968D 21FLSARA13-3-08 1331 8/8/2000 CHLAC 12 

1968D 21FLSARA13-2-08 1408 8/8/2000 CHLAC 20 

1968D 21FLSARA13-1-08 1441 8/8/2000 CHLAC 9.2 

1968D 21FLSARA13-5-09 1214 9/20/2000 CHLAC 26.4 

1968D 21FLSARA13-4-09 1251 9/20/2000 CHLAC 19 

1968D 21FLSARA13-3-09 1325 9/20/2000 CHLAC 21.4 

1968D 21FLSARA13-2-09 1402 9/20/2000 CHLAC 22.1 

1968D 21FLSARA13-1-09 1427 9/20/2000 CHLAC 25.4 

1968D 21FLSARA13-5-10 1202 10/17/2000 CHLAC 6.5 

1968D 21FLSARA13-4-10 1256 10/17/2000 CHLAC 2.7 

1968D 21FLSARA13-3-10 1328 10/17/2000 CHLAC 3.6 

1968D 21FLSARA13-2-10 1402 10/17/2000 CHLAC 5.5 

1968D 21FLSARA13-1-10 1427 10/17/2000 CHLAC 4.3 

1968D 21FLSARA13-5-11 1201 11/14/2000 CHLAC 4 

1968D 21FLSARA13-4-11 1317 11/14/2000 CHLAC 2.7 

1968D 21FLSARA13-3-11 1342 11/14/2000 CHLAC 3.7 

1968D 21FLSARA13-2-11 1413 11/14/2000 CHLAC 4.9 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

38 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA13-1-11 1440 11/14/2000 CHLAC 4.4 

1968D 21FLSARA13-5-12 1151 12/5/2000 CHLAC 1 

1968D 21FLSARA13-4-12 1222 12/5/2000 CHLAC 1.3 

1968D 21FLSARA13-3-12 1253 12/5/2000 CHLAC 3.8 

1968D 21FLSARA13-2-12 1322 12/5/2000 CHLAC 2.1 

1968D 21FLSARA13-1-12 1346 12/5/2000 CHLAC 1.5 

1968D 21FLSARA13-5-01 1239 1/16/2001 CHLAC 1.7 

1968D 21FLSARA13-4-01 1313 1/16/2001 CHLAC 1 

1968D 21FLSARA13-3-01 1344 1/16/2001 CHLAC 1 

1968D 21FLSARA13-2-01 1415 1/16/2001 CHLAC 1 

1968D 21FLSARA13-1-01 1443 1/16/2001 CHLAC 1.2 

1968D 21FLSARA13-5-02 1212 2/21/2001 CHLAC 4.7 

1968D 21FLSARA13-4-02 1240 2/21/2001 CHLAC 3.8 

1968D 21FLSARA13-3-02 1302 2/21/2001 CHLAC 2.2 

1968D 21FLSARA13-2-02 1332 2/21/2001 CHLAC 2.1 

1968D 21FLSARA13-1-02 1352 2/21/2001 CHLAC 2 

1968D 21FLSARA13-5-03 1219 3/22/2001 CHLAC 1.9 

1968D 21FLSARA13-4-03 1314 3/22/2001 CHLAC 2.1 

1968D 21FLSARA13-3-03 1331 3/22/2001 CHLAC 2.5 

1968D 21FLSARA13-2-03 1352 3/22/2001 CHLAC 2.9 

1968D 21FLSARA13-1-03 1408 3/22/2001 CHLAC 5.2 

1968D 21FLSARA13-5-04 1215 4/25/2001 CHLAC 3 

1968D 21FLSARA13-4-04 1236 4/25/2001 CHLAC 3.6 

1968D 21FLSARA13-3-04 1254 4/25/2001 CHLAC 4.8 

1968D 21FLSARA13-2-04 1317 4/25/2001 CHLAC 4.5 

1968D 21FLSARA13-1-04 1333 4/25/2001 CHLAC 4.9 

1968D 21FLSARA13-5-05 1147 5/16/2001 CHLAC 2.2 

1968D 21FLSARA13-3-05 1225 5/16/2001 CHLAC 2.8 

1968D 21FLSARA13-2-05 1246 5/16/2001 CHLAC 5.1 

1968D 21FLSARA13-1-05 1304 5/16/2001 CHLAC 3.1 

1968D 21FLSARA13-1-06 1032 6/5/2001 CHLAC 7.1 

1968D 21FLSARA13-2-06 1105 6/5/2001 CHLAC 11.8 

1968D 21FLSARA13-3-06 1133 6/5/2001 CHLAC 7.5 

1968D 21FLSARA13-4-06 1153 6/5/2001 CHLAC 8 

1968D 21FLSARA13-5-06 1213 6/5/2001 CHLAC 3.9 

1968D 21FLSARA13-5-07 1203 7/26/2001 CHLAC 45.5 

1968D 21FLSARA13-4-07 1219 7/26/2001 CHLAC 43.2 

1968D 21FLSARA13-3-07 1242 7/26/2001 CHLAC 21.9 

1968D 21FLSARA13-2-07 1303 7/26/2001 CHLAC 21.6 

1968D 21FLSARA13-1-07 1325 7/26/2001 CHLAC 46.6 

1968D 21FLSARA13-5-08 1212 8/15/2001 CHLAC 31.55 

1968D 21FLSARA13-4-08 1227 8/15/2001 CHLAC 31.59 

1968D 21FLSARA13-3-08 1251 8/15/2001 CHLAC 34.9 

1968D 21FLSARA13-2-08 1312 8/15/2001 CHLAC 27.78 

1968D 21FLSARA13-1-08 1329 8/15/2001 CHLAC 19.1 

1968D 21FLSARA13-5-09 1158 9/20/2001 CHLAC 40.7 

1968D 21FLSARA13-4-09 1219 9/20/2001 CHLAC 34.2 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

39 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA13-3-09 1239 9/20/2001 CHLAC 39.35 

1968D 21FLSARA13-2-09 1306 9/20/2001 CHLAC 35.6 

1968D 21FLSARA13-1-09 1328 9/20/2001 CHLAC 33.23 

1968D 21FLSARA13-5-10 1154 10/24/2001 CHLAC 6.62 

1968D 21FLSARA13-4-10 1213 10/24/2001 CHLAC 1.01 

1968D 21FLSARA13-3-10 1242 10/24/2001 CHLAC 2.69 

1968D 21FLSARA13-2-10 1305 10/24/2001 CHLAC 3.55 

1968D 21FLSARA13-1-10 1317 10/24/2001 CHLAC 3.31 

1968D 21FLSARA13-5-11 1146 11/14/2001 CHLAC 5.58 

1968D 21FLSARA13-4-11 1207 11/14/2001 CHLAC 4.01 

1968D 21FLSARA13-3-11 1225 11/14/2001 CHLAC 4.55 

1968D 21FLSARA13-2-11 1250 11/14/2001 CHLAC 4.11 

1968D 21FLSARA13-1-11 1305 11/14/2001 CHLAC 3.42 

1968D 21FLSARA13-5-12 1222 12/12/2001 CHLAC 3.41 

1968D 21FLSARA13-4-12 1238 12/12/2001 CHLAC 5.8 

1968D 21FLSARA13-3-12 1304 12/12/2001 CHLAC 4.52 

1968D 21FLSARA13-2-12 1327 12/12/2001 CHLAC 3.65 

1968D 21FLSARA13-1-12 1340 12/12/2001 CHLAC 2.33 

1968D 21FLSARA13-5-01 1228 1/23/2002 CHLAC 2.17 

1968D 21FLSARA13-4-01 1251 1/23/2002 CHLAC 4.41 

1968D 21FLSARA13-3-01 1310 1/23/2002 CHLAC 4.4 

1968D 21FLSARA13-2-01 1332 1/23/2002 CHLAC 1.79 

1968D 21FLSARA13-1-01 1346 1/23/2002 CHLAC 3.67 

1968D 21FLSARA13-5-02 1247 2/5/2002 CHLAC 2.14 

1968D 21FLSARA13-4-02 1304 2/5/2002 CHLAC 2.23 

1968D 21FLSARA13-3-02 1323 2/5/2002 CHLAC 1.75 

1968D 21FLSARA13-2-02 1348 2/5/2002 CHLAC 2.76 

1968D 21FLSARA13-1-02 1405 2/5/2002 CHLAC 2.59 

1968D 21FLSARA13-1-03 1125 3/19/2002 CHLAC 1.96 

1968D 21FLSARA13-2-03 1141 3/19/2002 CHLAC 4.36 

1968D 21FLSARA13-3-03 1204 3/19/2002 CHLAC 5.06 

1968D 21FLSARA13-4-03 1219 3/19/2002 CHLAC 5.9 

1968D 21FLSARA13-5-03 1238 3/19/2002 CHLAC 7.91 

1968D 21FLSARA13-1-04 1131 4/16/2002 CHLAC 1.4 

1968D 21FLSARA13-2-04 1153 4/16/2002 CHLAC 2.5 

1968D 21FLSARA13-3-04 1218 4/16/2002 CHLAC 2.89 

1968D 21FLSARA13-4-04 1237 4/16/2002 CHLAC 3.22 

1968D 21FLSARA13-5-04 1301 4/16/2002 CHLAC 3.16 

1968D 21FLSARA13-1-05 1141 5/15/2002 CHLAC 1.43 

1968D 21FLSARA13-2-05 1153 5/15/2002 CHLAC 1.18 

1968D 21FLSARA13-3-05 1211 5/15/2002 CHLAC 1.55 

1968D 21FLSARA13-5-05 1244 5/15/2002 CHLAC 1.73 

1968D 21FLSARA13-1-06 1119 6/12/2002 CHLAC 3.28 

1968D 21FLSARA13-2-06 1138 6/12/2002 CHLAC 3.07 

1968D 21FLSARA13-3-06 1200 6/12/2002 CHLAC 3.56 

1968D 21FLSARA13-4-06 1216 6/12/2002 CHLAC 3.04 

1968D 21FLSARA13-5-06 1235 6/12/2002 CHLAC 3.44 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

40 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA13-5-07 1201 7/17/2002 CHLAC 8.15 

1968D 21FLSARA13-4-07 1215 7/17/2002 CHLAC 8.05 

1968D 21FLSARA13-3-07 1236 7/17/2002 CHLAC 10.26 

1968D 21FLSARA13-2-07 1254 7/17/2002 CHLAC 9.97 

1968D 21FLSARA13-1-07 1313 7/17/2002 CHLAC 10.64 

1968D 21FLSARA13-5-08 1147 8/14/2002 CHLAC 6.67 

1968D 21FLSARA13-4-08 1202 8/14/2002 CHLAC 5.91 

1968D 21FLSARA13-3-08 1230 8/14/2002 CHLAC 8.6 

1968D 21FLSARA13-2-08 1246 8/14/2002 CHLAC 7.26 

1968D 21FLSARA13-1-08 1301 8/14/2002 CHLAC 8.26 

1968D 21FLSARA13-5-09 1132 9/18/2002 CHLAC 18.33 

1968D 21FLSARA13-4-09 1154 9/18/2002 CHLAC 14.79 

1968D 21FLSARA13-3-09 1211 9/18/2002 CHLAC 20.16 

1968D 21FLSARA13-2-09 1232 9/18/2002 CHLAC 13.39 

1968D 21FLSARA13-1-09 1248 9/18/2002 CHLAC 13.46 

1968D 21FLSARA13-5-10 1153 10/16/2002 CHLAC 13.99 

1968D 21FLSARA13-4-10 1220 10/16/2002 CHLAC 10.88 

1968D 21FLSARA13-3-10 1240 10/16/2002 CHLAC 12.44 

1968D 21FLSARA13-2-10 1300 10/16/2002 CHLAC 16.06 

1968D 21FLSARA13-1-10 1322 10/16/2002 CHLAC 13.67 

1968D 21FLSARA13-5-11 1209 11/14/2002 CHLAC 3.62 

1968D 21FLSARA13-4-11 1230 11/14/2002 CHLAC 3.5 

1968D 21FLSARA13-3-11 1246 11/14/2002 CHLAC 4.35 

1968D 21FLSARA13-2-11 1306 11/14/2002 CHLAC 6.68 

1968D 21FLSARA13-1-11 1322 11/14/2002 CHLAC 6.36 

1968D 21FLSARA13-5-12 1153 12/11/2002 CHLAC 2.3 

1968D 21FLSARA13-4-12 1215 12/11/2002 CHLAC 2.29 

1968D 21FLSARA13-3-12 1237 12/11/2002 CHLAC 4.86 

1968D 21FLSARA13-2-12 1255 12/11/2002 CHLAC 3.8 

1968D 21FLSARA13-1-12 1307 12/11/2002 CHLAC 2.64 

1968D 21FLSARA13-5-01 1209 1/22/2003 CHLAC 2.3 

1968D 21FLSARA13-4-01 1247 1/22/2003 CHLAC 2.42 

1968D 21FLSARA13-3-01 1320 1/22/2003 CHLAC 7.31 

1968D 21FLSARA13-2-01 1343 1/22/2003 CHLAC 1.13 

1968D 21FLSARA13-1-01 1410 1/22/2003 CHLAC 1 

1968D 21FLSARA13-5-02 1213 2/12/2003 CHLAC 1.68 

1968D 21FLSARA13-4-02 1234 2/12/2003 CHLAC 2.51 

1968D 21FLSARA13-3-02 1255 2/12/2003 CHLAC 1.41 

1968D 21FLSARA13-2-02 1349 2/12/2003 CHLAC 1.68 

1968D 21FLSARA13-1-02 1408 2/12/2003 CHLAC 1.61 

1968D 21FLSARA13-5-03 1211 3/19/2003 CHLAC 3.57 

1968D 21FLSARA13-4-03 1230 3/19/2003 CHLAC 2.22 

1968D 21FLSARA13-3-03 1251 3/19/2003 CHLAC 2.77 

1968D 21FLSARA13-2-03 1313 3/19/2003 CHLAC 3.37 

1968D 21FLSARA13-1-03 1327 3/19/2003 CHLAC 2.67 

1968D 21FLSARA13-5-04 1155 4/22/2003 CHLAC 4.05 

1968D 21FLSARA13-4-04 1215 4/22/2003 CHLAC 2.61 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

41 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA13-3-04 1234 4/22/2003 CHLAC 2.66 

1968D 21FLSARA13-2-04 1256 4/22/2003 CHLAC 2.59 

1968D 21FLSARA13-1-04 1315 4/22/2003 CHLAC 2.81 

1968D 21FLSARA13-5-05 1210 5/20/2003 CHLAC 8.5 

1968D 21FLSARA13-3-05 1249 5/20/2003 CHLAC 10.98 

1968D 21FLSARA13-2-05 1311 5/20/2003 CHLAC 9.33 

1968D 21FLSARA13-1-05 1324 5/20/2003 CHLAC 10.12 

1968D 21FLSARA13-5-06 1226 6/10/2003 CHLAC 7.47 

1968D 21FLSARA13-4-06 1300 6/10/2003 CHLAC 9.02 

1968D 21FLSARA13-3-06 1314 6/10/2003 CHLAC 7.47 

1968D 21FLSARA13-2-06 1334 6/10/2003 CHLAC 5.91 

1968D 21FLSARA13-1-06 1354 6/10/2003 CHLAC 4.65 

1968D 21FLSARA13-5-07 1140 7/22/2003 CHLAC 26.11 

1968D 21FLSARA13-4-07 1204 7/22/2003 CHLAC 41.05 

1968D 21FLSARA13-3-07 1221 7/22/2003 CHLAC 48.42 

1968D 21FLSARA13-2-07 1235 7/22/2003 CHLAC 43.12 

1968D 21FLSARA13-1-07 1250 7/22/2003 CHLAC 31.78 

1968D 21FLSARA13-3-08 1214 8/12/2003 CHLAC 9.76 

1968D 21FLSARA13-5-08 1215 8/12/2003 CHLAC 11.28 

1968D 21FLSARA13-4-08 1231 8/12/2003 CHLAC 7.46 

1968D 21FLSARA13-2-08 1328 8/12/2003 CHLAC 8.09 

1968D 21FLSARA13-1-08 1343 8/12/2003 CHLAC 10.96 

1968D 21FLSARA13-5-09 1244 9/16/2003 CHLAC 16.72 

1968D 21FLSARA13-4-09 1308 9/16/2003 CHLAC 16.4 

1968D 21FLSARA13-3-09 1338 9/16/2003 CHLAC 23.73 

1968D 21FLSARA13-2-09 1401 9/16/2003 CHLAC 17.34 

1968D 21FLSARA13-1-09 1416 9/16/2003 CHLAC 15.72 

1968D 21FLSARA13-1-10 947 10/21/2003 CHLAC 3.58 

1968D 21FLSARA13-2-10 1014 10/21/2003 CHLAC 1.71 

1968D 21FLSARA13-3-10 1045 10/21/2003 CHLAC 3.2 

1968D 21FLSARA13-4-10 1114 10/21/2003 CHLAC 3.48 

1968D 21FLSARA13-5-10 1135 10/21/2003 CHLAC 2.32 

1968D 21FLSARA13-5-11 1230 11/11/2003 CHLAC 7.64 

1968D 21FLSARA13-4-11 1251 11/11/2003 CHLAC 5.57 

1968D 21FLSARA13-3-11 1308 11/11/2003 CHLAC 9.02 

1968D 21FLSARA13-2-11 1344 11/11/2003 CHLAC 7.12 

1968D 21FLSARA13-1-11 1359 11/11/2003 CHLAC 7.97 

1968D 21FLSARA13-5-12 1201 12/9/2003 CHLAC 1.15 

1968D 21FLSARA13-4-12 1228 12/9/2003 CHLAC 1.18 

1968D 21FLSARA13-3-12 1253 12/9/2003 CHLAC 2.23 

1968D 21FLSARA13-2-12 1320 12/9/2003 CHLAC 1 

1968D 21FLSARA13-1-12 1337 12/9/2003 CHLAC 1 

1968D 21FLSARA13-5-01 1218 1/13/2004 CHLAC 1.51 

1968D 21FLSARA13-4-01 1239 1/13/2004 CHLAC 1.71 

1968D 21FLSARA13-3-01 1304 1/13/2004 CHLAC 1.81 

1968D 21FLSARA13-2-01 1325 1/13/2004 CHLAC 1.09 

1968D 21FLSARA13-1-01 1343 1/13/2004 CHLAC 1.32 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

42 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA13-5-02 1236 2/17/2004 CHLAC 8.05 

1968D 21FLSARA13-4-02 1258 2/17/2004 CHLAC 7.69 

1968D 21FLSARA13-3-02 1331 2/17/2004 CHLAC 8.62 

1968D 21FLSARA13-2-02 1409 2/17/2004 CHLAC 9.45 

1968D 21FLSARA13-1-02 1428 2/17/2004 CHLAC 7.9 

1968D 21FLSARA13-5-03 1219 3/23/2004 CHLAC 2.9 

1968D 21FLSARA13-4-03 1256 3/23/2004 CHLAC 4.5 

1968D 21FLSARA13-3-03 1313 3/23/2004 CHLAC 5.4 

1968D 21FLSARA13-2-03 1346 3/23/2004 CHLAC 5.3 

1968D 21FLSARA13-1-03 1404 3/23/2004 CHLAC 2.5 

1968D 21FLSARA13-5-04 1131 4/13/2004 CHLAC 3.2 

1968D 21FLSARA13-4-04 1152 4/13/2004 CHLAC 2.9 

1968D 21FLSARA13-3-04 1208 4/13/2004 CHLAC 3.1 

1968D 21FLSARA13-2-04 1229 4/13/2004 CHLAC 2.5 

1968D 21FLSARA13-1-04 1243 4/13/2004 CHLAC 2.2 

1968D 21FLSARA13-5-05 1217 5/11/2004 CHLAC 6.7 

1968D 21FLSARA13-3-05 1256 5/11/2004 CHLAC 6.7 

1968D 21FLSARA13-2-05 1318 5/11/2004 CHLAC 3.2 

1968D 21FLSARA13-1-05 1334 5/11/2004 CHLAC 3.1 

1968D 21FLSARA13-5-06 1238 6/22/2004 CHLAC 6.2 

1968D 21FLSARA13-4-06 1259 6/22/2004 CHLAC 7.1 

1968D 21FLSARA13-3-06 1316 6/22/2004 CHLAC 6.1 

1968D 21FLSARA13-2-06 1339 6/22/2004 CHLAC 4.3 

1968D 21FLSARA13-1-06 1357 6/22/2004 CHLAC 2.8 

1968D 21FLSARA13-5-07 1153 7/13/2004 CHLAC 8.40 

1968D 21FLSARA13-4-07 1206 7/13/2004 CHLAC 5.40 

1968D 21FLSARA13-3-07 1225 7/13/2004 CHLAC 8.90 

1968D 21FLSARA13-2-07 1251 7/13/2004 CHLAC 7.40 

1968D 21FLSARA13-1-07 1305 7/13/2004 CHLAC 4.00 

1968D 21FLSARA13-5-08 1202 8/17/2004 CHLAC 36.1 

1968D 21FLSARA13-4-08 1220 8/17/2004 CHLAC 33.9 

1968D 21FLSARA13-3-08 1255 8/17/2004 CHLAC 31.9 

1968D 21FLSARA13-2-08 1314 8/17/2004 CHLAC 13.4 

1968D 21FLSARA13-1-08 1331 8/17/2004 CHLAC 13.3 

1968D 21FLSARA13-5-10 1157 10/28/2004 CHLAC 6.4 

1968D 21FLSARA13-4-10 1221 10/28/2004 CHLAC 5.8 

1968D 21FLSARA13-3-10 1243 10/28/2004 CHLAC 9.7 

1968D 21FLSARA13-2-10 1305 10/28/2004 CHLAC 9.3 

1968D 21FLSARA13-1-10 1324 10/28/2004 CHLAC 7.7 

1968D 21FLSARA13-1-11 1023 11/10/2004 CHLAC 3.1 

1968D 21FLSARA13-2-11 1059 11/10/2004 CHLAC 2.7 

1968D 21FLSARA13-3-11 1123 11/10/2004 CHLAC 2 

1968D 21FLSARA13-4-11 1142 11/10/2004 CHLAC 1.4 

1968D 21FLSARA13-5-11 1204 11/10/2004 CHLAC 1 

1968D 21FLSARA13-5-12 1439 12/7/2004 CHLAC 1.9 

1968D 21FLSARA13-4-12 1455 12/7/2004 CHLAC 3.8 

1968D 21FLSARA13-3-12 1515 12/7/2004 CHLAC 2.1 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

43 

Florida Department of Environmental Protection 

WBID Station Time Date Parameter Result 

1968D 21FLSARA13-2-12 1530 12/7/2004 CHLAC 2 

1968D 21FLSARA13-1-12 1539 12/7/2004 CHLAC 2.8 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

44 

Florida Department of Environmental Protection 

Appendix C: Chlorophyll a and Total Nitrogen Graphs of 

Sample Results 

Roberts Bay - WBID 1968D 

 Chlorophyll a Sample Results

0

5

10

15

20

25

30

35

40

45

50

Jan-92Jan-93Jan-94Jan-95Jan-96Jan-97Jan-98Jan-99Jan-00Jan-01Jan-02Jan-03Jan-04

Date

Chlorophyll a (Mg/L)

Sarasota County Stations

Roberts Bay - WBID 1968D 

Total Nitrogen Sample Results

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Jan-92Jan-93Jan-94Jan-95Jan-96Jan-97Jan-98Jan-99Jan-00Jan-01Jan-02Jan-03

Date

Total Nitrogen (mg/L)

Sarasota County Stations
Florida Department of Environmental Protection 1

Appendix D: Total Nitrogen Loading Estimates by Source (pounds/year) 

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 

Point Sources FL0025755 Siesta Key UtilIsland Circle 9.83E+03 1.07E+04 9.77E+03 9.64E+03 9.06E+03 7.97E+03 9.33E+03 7.81E+03 8.35E+03 7.74E+03 FL1132816 FL Cities Water CoGulf Gate 8.64E+03 1.04E+04 9.83E+03 1.27E+04 8.96E+03 8.70E+03 1.13E+04 1.27E+04 1.51E+04 2.06E+04 FL0032808 FL Cities WaterSouth Gate 6.89E+03 7.18E+03 7.01E+03 6.08E+03 5.97E+03 6.05E+03 5.99E+03 5.43E+03 9.30E+03 1.31E+04 FL0042811 American Commonwealth 0.00E+00 2.83E+04 4.61E+02 6.54E+02 2.83E+03 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 Total Point Source Load 2.54E+04 5.66E+04 2.71E+04 2.90E+04 2.68E+04 2.27E+04 2.66E+04 2.59E+04 3.28E+04 4.15E+04 Nonpoint Sources Atmospheric Deposition 1.28E+04 1.54E+04 1.25E+04 1.30E+04 1.11E+04 1.15E+04 1.37E+04 1.03E+04 1.04E+04 1.24E+04 Baseflow Runoff to Roberts Bay N 1.61E+03 1.61E+03 1.61E+03 1.61E+03 1.61E+03 1.61E+03 1.61E+03 1.61E+03 1.61E+03 1.61E+03 Runoff to Roberts Bay S 6.89E+02 6.89E+02 6.89E+02 6.89E+02 6.89E+02 6.89E+02 6.89E+02 6.89E+02 6.89E+02 6.89E+02 Matheny Creek 9.88E+02 9.88E+02 9.88E+02 9.88E+02 9.88E+02 9.88E+02 9.88E+02 9.88E+02 9.88E+02 9.88E+02 Phillippi Creek (gaged) 1.16E+04 1.16E+04 1.16E+04 1.16E+04 1.16E+04 1.16E+04 1.16E+04 1.16E+04 1.16E+04 1.16E+04 Phillippi Creek (ungaged) 8.96E+03 8.96E+03 8.96E+03 8.96E+03 8.96E+03 8.96E+03 8.96E+03 8.96E+03 8.96E+03 8.96E+03 Total Baseflow 2.38E+04 2.38E+04 2.38E+04 2.38E+04 2.38E+04 2.38E+04 2.38E+04 2.38E+04 2.38E+04 2.38E+04 Groundwater Seepage to Bay 2.13E+05 2.13E+05 2.13E+05 2.13E+05 2.13E+05 2.13E+05 2.13E+05 2.13E+05 2.13E+05 2.13E+05 Surface Water Runoff Runoff to Roberts Bay N 3.88E+04 3.64E+04 3.33E+04 3.96E+04 3.06E+04 4.72E+04 3.86E+04 3.10E+04 2.43E+04 3.32E+04 Runoff to Roberts Bay S 1.89E+04 1.77E+04 1.63E+04 1.93E+04 1.49E+04 2.30E+04 1.88E+04 1.51E+04 1.19E+04 1.62E+04 Matheny Creek 1.88E+04 1.76E+04 1.61E+04 1.91E+04 1.48E+04 2.28E+04 1.86E+04 1.50E+04 1.18E+04 1.60E+04 Phillippi Creek (gaged) 1.87E+05 1.75E+05 1.60E+05 1.91E+05 1.47E+05 2.27E+05 1.86E+05 1.49E+05 1.17E+05 1.60E+05 Phillippi Creek (ungaged) 1.67E+05 1.57E+05 1.44E+05 1.71E+05 1.32E+05 2.04E+05 1.66E+05 1.34E+05 1.05E+05 1.43E+05 Total Surface Water Runoff 4.31E+05 4.04E+05 3.70E+05 4.39E+05 3.40E+05 5.24E+05 4.28E+05 3.44E+05 2.70E+05 3.68E+05 Total Nonpoint Source Load 6.80E+05 6.56E+05 6.19E+05 6.89E+05 5.87E+05 7.72E+05 6.78E+05 5.90E+05 5.17E+05 6.17E+05 
TMDL Report: Sarasota Bay Basin, Roberts Bay, WBID 1968D, Nutrients 

2 

Florida Department of Environmental Protection 

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 

Total Point and Nonpoint Source Load 7.05E+05 7.12E+05 6.46E+05 7.18E+05 6.14E+05 7.94E+05 7.05E+05 6.16E+05 5.50E+05 6.58E+05 
Florida Department of Environmental Protection 1 

 

 

Florida Department of Environmental Protection 

Division of Water Resource Management 

Bureau of Watershed Management 

2600 Blair Stone Road, Mail Station 3565 

Tallahassee, Florida 32399-2400 

(850) 245-8561 

http://www.dep.state.fl.us/water/