PROPOSED TOTAL MAXIMUM DAILY LOAD (TMDL)

For

Dissolved Oxygen and Nutrient In

Six Mile Creek (WBID 1536F), Palm River (WBID 1536E),

And McKay Bay (WBID 1584B)

Prepared by:

US EPA Region 4 61 Forsyth Street SW

Atlanta, Georgia 30303

September 30, 2009

TMDL Report: Six Mile Creek (WBID 1536F), Palm River (WBID 1536E), and McKay Bay (WBID 1584B) - DO and Nutrients (Chla)

Acknowledgments

EPA would like to acknowledge that the contents of this report and the total maximum daily load (TMDL) contained herein were developed by the Florida Department of Environmental Protection (FDEP). Many of the text and figures may not read as though EPA is the primary author for this reason, but EPA is officially proposing the TMDL for dissolved oxygen and nutrients for Palm River and McKay Bay and soliciting comment. EPA is proposing this TMDL in order to meet consent decree requirements pursuant to the Consent Decree entered in the case of Florida Wildlife Federation, et al. v. Carol Browner, et al., Case No. 98-356-CIV-Stafford. EPA will accept comments on this proposed TMDL for 60 days in accordance with the public notice issued on September 30, 2009. Should EPA be unable to approve a TMDL established by FDEP for the 303(d) listed impairment addressed by this report, EPA will establish this TMDL in lieu of FDEP, after full review of public comments. This TMDL analysis could not have been accomplished without significant contributions from staff in the Florida Department of Environmental Protection’s Southwest District Office, Hillsborough County, and the Watershed Evaluation and TMDL (WET) Section. Editorial assistance provided by Jan Mandrup-Poulsen. For additional information on the watershed management approach and impaired waters in the Tampa Bay Basin, contact: Terry Hansen 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: terry.hansen@dep.state.fl.usPhone: (850) 245–8561 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 Evaluation and TMDL Section 2600 Blair Stone Road, Mail Station 3555 Tallahassee, FL 32399-2400 Email: kevin.petrus@dep.state.fl.usPhone: (850) 245–8459 Fax: (850) 245–8536

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TMDL Report: Six Mile Creek (WBID 1536F), Palm River (WBID 1536E), and McKay Bay (WBID 1584B) - DO and Nutrients (Chla)

Contents

Chapter 1: INTRODUCTION___________________________________1 

1.1 Purpose of Report ________________________________________________1 1.2 Identification of Waterbody _________________________________________1 

1.2.1 Waterbody Descriptions__________________________________________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 ______________________11 

3.1 Classification of the Waterbody and Criteria Applicable to the TMDL _____11 3.2 Applicable Water Quality Standards and Numeric Water Quality Targets __11 

3.2.1 Interpretation of Dissolved Oxygen Criterion _________________________11 3.2.2 Interpretation of Narrative Nutrient Criterion _________________________11 

Chapter 4: ASSESSMENT OF SOURCES_______________________13 

4.1 Types of Sources________________________________________________13 4.2 Point Sources __________________________________________________13 

4.2.1 NPDES Permitted Wastewater Facilities ___________________________13 4.2.2 Municipal Separate Storm Sewer System Permittees _________________15 

4.3 Land Uses and Nonpoint Sources__________________________________16 4.3.1 Land Uses___________________________________________________16 4.3.2 Estimating Nonpoint Loadings ___________________________________19 

Chapter 5: DETERMINATION OF ASSIMILATIVE CAPACITY_______23 

5.1 Determination of Loading Capacity_________________________________23 5.2 Analysis of Water Quality _________________________________________23 5.3 Attempts to Develop Empirical Relationships ________________________26 5.4 Percent Reduction Approach______________________________________26 5.5 Relationship Between Nutrients and DO ____________________________28 5.6 Current Restoration and Management Projects_______________________29 5.7 Critical Conditions_______________________________________________29 

Chapter 6: DETERMINATION OF THE TMDL ____________________30 

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TMDL Report: Six Mile Creek (WBID 1536F), Palm River (WBID 1536E), and McKay Bay (WBID 1584B) - DO and Nutrients (Chla)

6.1 Expression and Allocation of the TMDL _____________________________30 6.2 Wasteload Allocation ____________________________________________31 

6.2.1 NPDES Wastewater Discharges__________________________________31 6.2.2 NPDES Stormwater Discharges ________________________________3232 

6.3 Load Allocation _________________________________________________32 6.4 Margin of Safety_________________________________________________32 

Chapter 7: NEXT STEPS: IMPLEMENTATION PLAN DEVELOPMENT AND BEYOND _____________________33 

TMDL Implementation _______________________________________________33 

References __________________________________________ ____355 

Appendices _______________________________________________37 

Appendix A: Background Information on Federal and State Stormwater Programs__________________________________________________________37 

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TMDL Report: Six Mile Creek (WBID 1536F), Palm River (WBID 1536E), and McKay Bay (WBID 1584B) - DO and Nutrients (Chla)

List of Tables

Table 2.1 Verified Impairments for the TBC (WBID 1536F), Palm River (WBID 1536E) and McKay Bay (WBID 1584B) ____________________7

Table 2.2 Summary of Dissolved Oxygen Data Collected During Verification Period (January 2000 – June 2007)_____________________________8

Table 3.1 Statistical Summary of Data in Estuary WBIDs Not Impaired in the Tampa Bay Basin__________________________________________12

Table 4.1. Point Source Discharge Permit Information_________________________15 Table 4.2. Classification and Percent Distribution of Land Use Categories in the

TBC Gauged Watershed (2004) ______________________________17 Table 4.3. Classification and Percent Distribution of Land Use Categories in the

Ungauged Watershed (2004)________________________________199Table 4.4. Land Use Runoff Concentrations (Event Mean Concentrations) in

Southwest Florida _________________________________________20 Table 4.5. Total N Estimates for the TBC, Palm River and McKay Bay

Watershed _______________________________________________21 Table 5.1 Percent Reduction Calculations for Total Nitrogen____________________27 Table 5.2 TSI Calculation for the TBC (WBID 1536F) _________________________28 Table 5.3. SWIM Stormwater Retrofit Projects in the TBC, Palm River and

McKay Bay Watershed _____________________________________29 Table 6.1.a. TMDL Components Expressed as a Daily Load____________________31 Table 6.1.b. TMDL Components Expressed as an Annual Load _________________31

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TMDL Report: Six Mile Creek (WBID 1536F), Palm River (WBID 1536E), and McKay Bay (WBID 1584B) - DO and Nutrients (Chla)

List of Figures

Figure 1.1 Location of Sixmile Creek, aka Tampa Bypass Canal, (WBID1536F), Palm River (WBID 1536E) and McKay Bay (WBID 1584B) with Major Geopolitical Features in the Tampa Bay Basin _____3

Figure 1.2 Location of the Tampa Bypass Canal, Palm River and McKay Bay with Major Hydrologic Features ________________________________4

Figure 2.1 Annual Average Chlorophyll-a Values in the Lower TBC Segment in the Cycle 2 Verification Period (January 2000 – June 2007)________8

Figure 2.2 Annual Average Chlorophyll-a Values in the Palm River and McKay Bay in the Cycle 2 Verification Period (January 2000 – June 2007) ________________________________________________9

Figure 4.1. Location of the Point Source Facility Outfalls ______________________14 Figure 4.2. Principal Land Uses in the Gauged Watershed (Upstream of S-160)

and the Ungauged Watershed (Downstream of S-160), 2004________18 Figure 4.3. Distribution of Onsite Sewage Systems (Septic Tanks) in the

Watershed _______________________________________________22 Figure 5.1 Monitoring Locations in the Watershed Area of the TBC, Palm River

and McKay Bay ___________________________________________24 Figure 5.2 Annual Average Chlorophyll a Concentrations at the Hillsborough

County EPC Estuary and Freshwater Stations ___________________25 Figure 5.3 Annual Average Total Nitrogen Concentrations at the Hillsborough

County EPC Estuary and Freshwater Stations ___________________25 Figure 5.4 Annual Average Total Phosphorus Concentrations at the

Hillsborough County EPC Estuary and Freshwater Stations_________26

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TMDL Report: Six Mile Creek (WBID 1536F), Palm River (WBID 1536E), and McKay Bay (WBID 1584B) - DO and Nutrients (Chla)

Web sites

Florida Department of Environmental Protection, Bureau of Watershed Restoration

TMDL Program http://www.dep.state.fl.us/water/tmdl/index.htmIdentification of Impaired Surface Waters Rule http://www.dep.state.fl.us/water/tmdl/docs/AmendedIWR.pdfSTORET Program http://www.dep.state.fl.us/water/storet/index.htm2008 305(b) Report http://www.dep.state.fl.us/water/docs/2008_Integrated_Report.pdfCriteria for Surface Water Quality Classifications http://www.dep.state.fl.us/water/wqssp/classes.htmBasin Status Report for the Tampa Bay Basin http://www.dep.state.fl.us/water/tmdl/stat_rep.htmWater Quality Assessment Report for the Tampa Bay Basin http://www.dep.state.fl.us/water/tmdl/stat_rep.htm

U.S. Environmental Protection Agency

Region 4: Total Maximum Daily Loads in Florida http://www.epa.gov/region4/water/tmdl/florida/ National STORET Programhttp://www.epa.gov/storet/

vii

Chapter 1: INTRODUCTION

1.1 Purpose of Report

This report presents the Total Maximum Daily Load (TMDL) for dissolved oxygen and nutrients for Six Mile Creek, aka the Tampa Bypass Canal, (WBID 1536F), the Palm River (WBID 1536E), and McKay Bay (WBID 1584B) located in the Tampa Bay Basin – Coastal Hillsborough Bay Tributary Planning Unit (Figure 1.1). The waterbody segment named Six Mile Creek (WBID 1536F) is more commonly referred to as the Tampa Bypass Canal (TBC) and will be referred to throughout the rest of this report as the TBC. This system of freshwater and estuarine waterbody segments were verified as impaired for dissolved oxygen and nutrients (chlorophyll-a), and are included on the latest Verified List of impaired waters for the Tampa Bay Basin that was readopted by Secretarial Order on May 19, 2009. The TMDL establishes the allowable loadings to the three waterbody segments that would restore the waterbody so that it meets its applicable water quality criteria for dissolved oxygen and nutrients.

1.2 Identification of Waterbody

To provide a smaller-scale geographic basis for assessing, reporting, and documenting water quality improvement projects, FDEP divides basin groups into smaller areas called planning units. Planning units help organize information and management strategies around prominent sub-basin characteristics and drainage features. To the extent possible, planning units were chosen to reflect sub-basins that had previously been defined by the Southwest Florida Water Management District (SWFWMD). The TBC, Palm River, and McKay Bay are located within the Coastal Hillsborough Bay Tributary Planning Unit. For assessment purposes, the Department has divided the Coastal Hillsborough Bay Tributary Planning Unit into water assessment polygons with a unique waterbody identification (WBID) number for each water segment. The three segments which are the subject of this report are identified as WBID 1536F (TBC), WBID 1536E (Palm River), and WBID 1584B (McKay Bay), Figure 1.2.

1.2.1 Waterbody Descriptions

The TBC, Palm River, and McKay Bay water segments are hydrologically connected in series and are included in a watershed that encompasses 32,235 acres (50.3 square miles). The watershed is an intensively urbanized basin located in north-central Hillsborough County. The southwestern portion of the watershed lies within the city limits of Tampa, Figure 1.1. The upper portion of the watershed is drained by the TBC, which was created by excavation of the Six Mile Creek and Palm River channels between 1966 and 1981 to divert water from the Hillsborough River to McKay Bay, to provide for flood control in Tampa and Temple Terrace. The TBC consists of a series of freshwater pools created by the construction of water control structures that maintain water levels. The freshwater portion of the canal extends from Cow House Creek to the Palm River, a distance of about 10.7 miles. Structure S-160 controls water levels in the lower part of the canal and prevents saltwater intrusion into the canal from the Palm River. The lower pool of the canal lies between control structures S-162 and S-160 and is the

canal water segment identified as WBID 1536F. This section of the canal is about 300 feet wide and is approximately 2.2 miles long. Downstream of structure S-160 is the Palm River tidal segment that extends for approximately 3.3 miles and flows into McKay Bay. The Palm River channel was dredged during construction of the canal and has a width of about 400 feet. McKay Bay is a shallow estuary, with large open-water areas averaging 6 feet in depth and shallow open-water areas along the shoreline. A channel connecting to the Palm River has been dredged to an average depth of 25 feet (Stoker et al., 1995). The 22nd Street causeway separates the shallow McKay Bay to the north from the much deeper East Bay to the south; the latter is the center of shipping activity in Tampa Bay. Tidal mudflats along the northern bay shores become exposed at low tide. Most of the areas surrounding the open-water portions of the bay are poorly drained lowland mudflats, gradually sloping mangrove forest, and salt marshes (McKay Bay Water Quality Management Plan, December 1998). The TBC is a major freshwater inflow to McKay Bay and the Palm River. The watershed area for the TBC, Palm River, and McKay Bay drains to the south into Hillsborough Bay. Excavation of the canal system cut into the confining bed that separates the Upper Floridan aquifer from the overlying surficial aquifer and in several places breached the upper Floridan aquifer. Baseflow discharge from the canal area after 1978 was about twice the amount before canal construction (Knutilla and Corral, 1984). The climate in the watershed is sub-tropical with annual rainfall averaging approximately 44.9 inches, although rainfall amounts can vary greatly from year to year (CLIMOD, 2009). Based on data from a 30-year period (1971 – 2000), the average summer temperature is 89.9oF, and the average winter temperature is 72.8oF (CLIMOD, 2009). The topography of the Palm River watershed reflects its location within the Southwestern Florida Flatwoods or Southwestern Coastal Plains ecoregion. Elevations range in the southern part of the watershed from around 5 – 10 feet above sea level, and in the northern part of the watershed around 35 – 40 feet above sea level (FDEP, 2008). The predominant soil type is sandy clay and clay (FDEP, 2008).

2

Figure 1.1 Location of Sixmile Creek, aka Tampa Bypass Canal, (WBID1536F), Palm River (WBID 1536E) and McKay Bay (WBID 1584B) with Major Geopolitical Features in the Tampa Bay Basin

3

Figure 1.2 Location of the Tampa Bypass Canal, Palm River and McKay Bay with Major Hydrologic Features

4

1.3 Background

This report was developed as part of the Florida Department of Environmental Protection’s (Department) 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 fifty-two river basins over a five-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 may be followed by the development and implementation of a Basin Management Action Plan (BMAP) that would restore the waterbody so that it meets its applicable water quality criteria for dissolved oxygen and nutrients (Chlorophyll a). These activities will depend heavily on the active participation of the Southwest Florida Water Management District, local governments, 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 TMDLs for impaired waterbodies.

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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) lists of surface waters that do not meet applicable water quality standards (impaired waters) and establish a TMDL for each pollutant causing impairment of listed waters on a schedule. The Department has developed such lists, commonly referred to as 303(d) lists, since 1992. The list of impaired waters in each basin, referred to as the Verified List, is also required by the FWRA (Subsection 403.067[4], Florida Statutes [F.S.]); the state’s 303(d) list is amended annually to include basin updates. Florida’s 1998 303(d) list included several waterbodies in the Tampa Bay Basin. The Palm River (WBID 1536E) and McKay Bay (WBID 1584B) are on the 1998 303(d) list. 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 Rule 62-303, Florida Administrative Code (F.A.C.) (Identification of Impaired Surface Waters Rule, or IWR), in April 2001; the rule was modified in 2006 and 2007.

2.2 Information on Verified Impairment

The Department used the IWR to assess water quality impairments and has verified the impairments for low dissolved oxygen (DO) and elevated nutrient concentrations in the TBC, Palm River, and McKay Bay (Table 2.1). Table 2.2 provides the assessment results for dissolved oxygen following the IWR methodology for the three water segments. The lower TBC water segment (WBID 1536F) was verified as impaired for DO because more than 10 percent of the values were below the Class III fresh water criterion value of 5.0 milligrams/liter (mg/L) over the course of the Cycle 2 verified period (January 2000 to June 2007). The Palm River (WBID 1536E) and McKay Bay (WBID 1584B) water segments were verified as impaired for DO because more than 10 percent of the values were below the Class III marine criterion minimum value of 4.0 milligrams/liter (mg/L) over the course of the Cycle 2 verified period. For nutrients, annual average chlorophyll-a values serve as the primary measurement for assessing nutrients in streams and estuaries under the IWR. Under the IWR, nutrient impairment for freshwater streams is primarily assessed by determining if annual average chlorophyll-a values exceed 20 micrograms per liter (ug/L), or if they are more than 50 percent greater than the historical value for at least 2 consecutive years. In the lower TBC segment (WBID 1536F), the annual mean chlorophyll-a values exceeded the stream threshold in all years of the Cycle 2 verified period (2000-2006). Annual average values ranged from a low of 25.3 ug/L in 2004 to a high of 57.8 ug/L in 2000, Figure 2.1.

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For the estuary segments of waterbodies tributary to Hillsborough Bay, the Hillsborough Bay chlorophyll a target of 15 ug/L, developed by the Tampa Bay Estuary Program to protect and restore seagrass, is used as the alternative chlorophyll a threshold. The chlorophyll a target was developed as part of the nitrogen management strategy to protect and restore seagrass meadows in the bay. The Department uses this water quality target as a site specific alternative chlorophyll a threshold for Hillsborough Bay (and the estuary segments tributary to the bay, including the Palm River and McKay Bay) to perform nutrient assessments following the IWR methodology. In the Palm River (WBID 1536E) and McKay Bay (WBID 1584B) estuary segments, the annual average chlorophyll-a values were above the site specific chlorophyll a threshold of 15 μg/L in at least one year in the Cycle 2 verified period. According to the IWR, if the annual mean chlorophyll-a for any one year in the verified period is greater than the chlorophyll-a threshold, the water is verified as impaired. In the Palm River, annual average values exceeded the chlorophyll a threshold in the 2001 to 2005 period, and ranged from a low of 16.2 ug/L in 2001 to a high of 24.9 ug/L in 2002, Figure 2.2. In McKay Bay, 2002 was the only year in the verified period when the annual average, 17.1 ug/L, exceeded the chlorophyll-a threshold, Figure 2.2.

Table 2.1 Verified Impairments for the TBC (WBID 1536F), Palm River (WBID 1536E) and McKay Bay (WBID 1584B)

WBID Waterbody Segment Name

Parameters Included on the 1998 303(d) List

Parameter Causing

Impairment

Projected Year for TMDL

Development 1536F Sixmile Creek

(TBC) Nutrients Nutrients (Chla) 2008A

1536F Sixmile Creek (TBC)

Dissolved Oxygen Nutrients, BOD 2008A

1536E Palm River Nutrients Nutrients (Chla) 2008A Palm River Dissolved Oxygen Nutrients, BOD 2008A 1536E

1584B McKay Bay Nutrients Nutrients (Chla) 2003B

McKay Bay Dissolved Oxygen Nutrients 2003B 1584B A The projected year for TMDL development was 2008, but the Settlement Agreement between EPA and Earthjustice, which drives the TMDL development schedule for waters on the 1998 303(d) list, allows an additional nine months to complete the TMDLs. As such, these TMDLs are to be proposed by September 30, 2009. B EPA proposed TMDL to meet consent decree schedule. This TMDL development is an update to the TMDL previously proposed.

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Table 2.2 Summary of Dissolved Oxygen Data Collected During Verification Period (January 2000 – June 2007)

Total Number of Samples

IWR-required number of

exceedances for the Verified

List

Number of observed

exceedances

Number of observed

nonexceedances

Number of seasons data

was collected

Waterbody Segment Name

Sixmile Creek ( TBC) 154 21 55 99 4

Palm River 1331 159 743 588 4

McKay Bay 1023 122 243 780 4

Figure 2.1 Annual Average Chlorophyll-a Values in the Lower TBC Segment in the Cycle 2 Verification Period (January 2000 – June 2007)

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Figure 2.2 Annual Average Chlorophyll-a Values in the Palm River and McKay Bay in the Cycle 2 Verification Period (January 2000 – June 2007)

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As part of the verified 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. Determining the limiting nutrient in a waterbody can be accomplished by calculating the ratio of nitrogen to phosphorus in the waterbody. Water column ratios of total nitrogen (TN) to total phosphorus (TP) of less than 10 suggest that nitrogen is limiting growth. Ratios between 10 and 30 suggest there is co-limitation, and ratios above 30 suggest that phosphorus is the limiting nutrient. In the lower TBC segment, the median TN to TP ratio is 5.2 (computed from n=96 values), indicating that nitrogen is the limiting nutrient. 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 over enrichment in coastal systems (National Research Council, 1993) and an analysis of the data from the Palm River and McKay Bay estuary segments support this conclusion. In the Palm River the median TN to TP ratio is 3.6 (computed from n=378 values), and the median ratio in McKay Bay is 2.9 (computed from n=199 values).

Since nitrogen is the limiting nutrient, reductions in TN loadings would be expected to result in decreases in algal growth, which are measured as decreases in chlorophyll a levels. Reductions in TN loading are also expected to result in additional benefits, including improvement in DO conditions and decreases in biochemical oxygen demand (BOD). BOD is defined as the amount of oxygen required by bacteria while stabilizing decomposable organic matter under aerobic conditions (Sawyer & McCarty, 1967). Reductions in nutrients will result in lower algal biomass levels in the water column, and lower algal biomass levels will result in smaller diurnal fluctuations in DO, fewer algal-based total suspended solids, and reduced BOD.

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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, well-

balanced 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)

3.2 Applicable Water Quality Standards and Numeric Water Quality Targets

The lower TBC freshwater segment (WBID 1536F) and the Palm River (WBID 1536E) and McKay Bay (WBID 1584B) marine segments are Class III waterbodies, with a designated use of recreation, propagation, and maintenance of a healthy, well-balanced population of fish and wildlife. The Class III freshwater and marine water quality criteria applicable to the impairment addressed by this TMDL are for the DO and the narrative nutrient criteria.

3.2.1 Interpretation of Dissolved Oxygen Criterion

The DO criterion for Class III freshwater waterbodies, applicable to the lower TBC segment, states that DO shall not be less than 5.0 mg/L. Normal daily and seasonal fluctuations above these levels shall be maintained. The DO criterion for Class III marine waterbodies, applicable to the Palm River and McKay Bay, states that the DO shall not average less than 5.0 mg/L in a 24 hour period and shall never be less than 4.0 mg/L. Normal daily and seasonal fluctuations above these levels shall be maintained.

3.2.2 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 streams and estuaries based on annual average chlorophyll a levels, these thresholds are

11

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. The freshwater segments of the TBC, although classified as stream segments, are actually ponded areas that have hydrologic characteristics similar to lakes. In recognition of this, the Trophic State Index (TSI) developed to assess nutrients in lakes was selected as the tool for establishing a nutrient target for TMDL development in WBID 1536F. The TMDL for nutrients in the lower TBC was based on using the TSI calculation method and reducing the nutrient and chlorophyll-a concentrations to levels that would produce an annual average TSI of less than 60. A chlorophyll based TSI of 60 equates to a chlorophyll a value of 20 ug/L. A reference approach was used to determine a nutrient level in estuaries that would be expected to allow the impaired estuaries to meet the applicable criteria for DO and nutrients. Data analysis was performed on Class III coastal and estuarine waters not impaired for DO and nutrients in the Tampa Bay Basin to develop a total nitrogen target for TMDL development for the Palm River and McKay Bay. A summary of the concentrations for nutrients, BOD, DO, and chlorophyll a from stations located in the reference WBIDs that are not impaired for DO and nutrients are summarized in Table 3.1. The reference WBIDs are 1603, 1609, 1709, 1676, 1558D, 1558E, 1661G, 1709F, 1797B, and 8049.

Table 3.1 Statistical Summary of Data in Estuary WBIDs Not Impaired in the Tampa Bay Basin

Total Phosphorus 

(mg/L) BOD ‐ 5 

Day (mg/L) Chlorophyll a 

(ug/L) 

Dissolved Oxygen (mg/L) 

Total Nitrogen (mg/L) 0.62  0.181  1.5  7.58  6.11 

Table 3.1 shows that estuary WBIDs not impaired in the Tampa Bay Basin have an average median sample station TN concentration of 0.62 mg/L, along with an annual median dissolved oxygen concentration of 6.11 mg/L, and a median chlorophyll a concentration of 7.58 ug/L. A total nitrogen of 0.62 mg/L should then be protective of the estuary chlorophyll a target of 15 ug/L and the marine dissolved oxygen criteria and serve as a reasonable target to achieve in order for the Palm River and McKay Bay to meet the applicable DO and nutrient criteria.

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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 two permitted wastewater treatment facilities that discharge nutrient loads and other wastewater constituents to surface waters in the watershed; these consist of one domestic wastewater facility and one industrial wastewater facility. The location of the surface water outfalls for the facilities are displayed in Figure 4.1. The Falkenburg Road Wastewater Treatment Facility is a domestic wastewater facility with an advanced wastewater treatment (AWT) system and a permitted discharge of 6.0 million gallons per day (MGD) to the Palm River, which flows into McKay Bay. The facility also has an existing land application system permitted for 0.116 MGD. The Falkenburg Road facility is owned by the Hillsborough County Water Department and is part of the county’s master reuse plan in the Brandon area. Conceptually, the reuse plan will have a capacity of 21.3 MGD, including current

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Figure 4.1. Location of the Point Source Facility Outfalls and potential users. Currently, the reuse capacity is limited to 10.0 MGD, based on the combined permitted capacities of the Falkenburg Road and Valrico facilities.

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The industrial wastewater facility is Trademark Nitrogen Corporation, a fertilizer manufacturer. The facility has a design flow of 25 MGD, but the typical average daily flow is only 0.08 MGD. Facility discharge monitoring reports show monthly flow averages ranging from 0.02 to 0.54 MGD in the 2000-2007 period. Process water and stormwater are treated in a retention ditch for the uptake and settling of solids. The wastewater can be recycled by manual pumping back into the system. Further treatment through aeration and pH control is performed prior to discharge. The effluent outfall discharges to an unnamed ditch, which flows to the Palm River and then to McKay Bay. Table 4.1 provides the permitted wastewater flows and nitrogen limits for both facilities. Based on discharge monitoring data collected between 2000 and 2007, the combined point source TN loading from the facilities contributes approximately 6 to 18 percent of the annual TN loading to the Palm River and McKay Bay. The majority of the point source load is from the Falkenburg Road AWWTP facility. (Table 4.5 provides the annual loads calculated for each facility.) To calculate the loads, discharge monitoring report data from the treatment facilities were used to create a time-varying input dataset for effluent flow and nitrogen concentrations. Monthly monitoring data for water quality concentrations were multiplied by monthly average flow data to determine the monthly load. The annual loads are calculated as the sum of the monthly loads.

Table 4.1. Point Source Discharge Permit Information

NPDES Permit Discharge Point

Design Flow (mgd)

Flow (mgd)

Annual TN Effluent Limits

Maximum Load

(lbs/year)1Facility

Trademark Nitrogen Corporation FL0000647 Tributary to Palm River 25.02 0.083 3 mg/L4 730

Falkenburg Road FL0040614 Palm River 6.0 6.0 3 mg/L 54,720

Combined Load 55,450

1 Annual Load = Monthly Average Flow * Concentration * 8.34 pounds/gallon * 12 months/year 2 The design capacity was not used to develop effluent limitations. 3 Average daily flow of existing discharge. 4 Effluent limit is monthly average.

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, 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. Within the watershed under study, several Phase I MS4 permits have been issued. Hillsborough County and Co-Permittees Plant City and the Florida Department of Transportation

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District 7 are copermittees under Permit FLS000006. The city of Tampa and the city of Temple Terrace have individual permits, FLS000008 and FLS000009, respectively. Most of the watershed lies within the jurisdiction of these three permits.

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 McKay Bay watershed is primarily urban, wildlife and agricultural animals/livestock sources are not expected to contribute significantly to the TN load. The total nonpoint source loads for each pollutant were quantified based on land use areas in the watershed. The loadings include runoff from urban areas and transportation and utility areas. Part of the surface runoff loads come from atmospheric deposition that falls directly onto the land surface. Although not specifically quantified, the runoff from residential areas includes leachate from septic systems. 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 2001, Hillsborough County has roughly 100,483 septic systems (Florida Department of Health, 2003). This total does not reflect systems removed from service going back to 1970.

The nonpoint sources addressed in this report primarily include loadings from surface runoff. TN loadings from nonpoint sources were estimated using the loadings calculated at the SWFWMD gage at control structure S-160 and by the use of a spreadsheet to calculate the surface runoff load generated from the area below the gage which is based on the imperviousness and event mean concentrations (EMCs) from different land use types in the watershed. The spatial distribution and acreage of different land use categories were identified using the SWFWMD’s 2004 land use coverage (scale 1:40,000) contained in the Department’s geographic information system (GIS) library (Florida Department of Environmental Protection, 2004).

4.3.1 Land Uses

The TBC, Palm River and McKay Bay watershed drains about 32,235 acres (50.3 square miles). Land use categories in the watershed were aggregated using the Level 1 Florida Land Use and Cover Classification System (FLUCCS) and are tabulated in Table 4.2 for the gauged area upstream of structure S-160 and in Table 4.3 for the ungauged area downstream of structure S-160. The gauged watershed is 17,498 acres in size, Table 4.2. The predominant land use in the TBC gauged watershed is urban and built-up, which comprises about 60 percent of the area. Residential areas make up about 33 percent of the urban land use. The next largest land use is agriculture (12 percent) followed by wetlands and water, which comprise about 15 percent of the watershed area. Land use categories were aggregated using the

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simplified Level 1 codes and are tabulated in Tables 4.1. Figure 4.2 shows the principal land uses in the both the gauged and ungauged watershed areas. Table 4.2. Classification and Percent Distribution of Land

Use Categories in the TBC Gauged Watershed (2004)

Landuse Acreage Percent of

Total Level 1 Code 1000  Urban Open  4,688 26.8 1100  Low Density Residential  2,406 13.8 1200  Medium Density Residential  1,577 9.0 1300  High Density Residential  1,770 10.1 2000  Agriculture  2,115 12.1 

3000+4000  Rangeland + Forest/Rural Open  924 5.3 5000  Water  1,081 6.2 6000  Wetlands  1,595 9.1 7000  Barren Land (Transportation)  38 0.2 8000  Communication and Transportation  1,304 7.5 

   17,498 100 Total The ungauged area of the watershed 14,737 acres in size, Table 4.3. The predominant land use in the ungauged watershed is urban and built-up, which comprises about 69 percent of the area. Residential areas make up about 24 percent of the urban land use. The next largest land cover is communication and transportation which comprises about 17 percent of the watershed area.

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Figure 4.2. Principal Land Uses in the Gauged Watershed (Upstream of S-160) and the Ungauged Watershed (Downstream of S-160), 2004

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Table 4.3. Classification and Percent Distribution of Land Use Categories in the Ungauged Watershed (2004)

Landuse Acreage Percent of

Total Level 1 Code 1000  Urban Open  6,620 44.9 1100  Low Density Residential  343 2.3 1200  Medium Density Residential  583 4.0 1300  High Density Residential  2,668 18.1 2000  Agriculture  43 0.3 

3000+4000  Rangeland + Forest/Rural Open  380 2.6 5000  Water  902 6.1 6000  Wetlands  597 4.1 7000  Barren Land (Transportation)  34 0.2 8000  Communication and Transportation  2,567 17.4 

   14,737 100 Total

4.3.2 Estimating Nonpoint Loadings

The nonpoint source loading of TN generated in the McKay Bay watershed was calculated using two methods. First, the loadings at the SWFWMD control structure S-160, formerly a U.S. Geological Survey (USGS) gauging station (U.S.G.S. 02301802, Tampa Bypass Canal at S-160, at Tampa, Florida, Latitude 27°57’21”, Longitude: 82°22’15”), were calculated based on flow data collected at the existing gage and water quality data collected upstream of the gage. Second, the loadings from the ungauged portion of the watershed were estimated using a spreadsheet method. The sum of the loads from these two methods was the estimate of the total nonpoint load generated in the watershed. The loads were calculated for the 2000 to 2007 period.

Estimating TN Loadings at SWFWMD Gage S-160 For the 2000 to 2007 period, monthly loads were calculated using the TN data collected at HCEPC Station 147, located in the Tampa Bypass Canal, and the monthly average flow at Gage S-160, which was provided by the SWFWMD. The monthly loads in each year were then summed to obtain annual TN loadings, which are shown in Table 4.5.

Estimating TN Loadings Using Spreadsheet Method The spreadsheet method was used to estimate the nonpoint source loadings downstream of SWFWMD Gage S-160. The spreadsheet is designed to estimate monthly and annual from a given watershed. The fundamental assumption of the method is that the amount of stormwater runoff from any given land use is in direct proportion to 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 area.

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The data required for applying the spreadsheet calculation 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,

• Runoff coefficients,

• Rainfall data Rainfall data from the weather station located at Tampa International Airport (NWS Station 88788) were used in the calculation. The rainfall amounts for the 2000 to 2007 period were obtained from the Tampa Bay Estuary Program. Areas of different land use categories were obtained by aggregating GIS land use coverage based on the simplified Level 1 code. The drainage area below the gage encompasses 23.0 square miles. Table 4.3 lists these areas and the percent of each land use category. Local event mean concentrations (EMCs) of TN for different land use categories were obtained from studies performed in Florida the results of which are summarized in stormwater reports by (Harvey and Baker, 2003 and Harper and Baker, 2007), and are presented in Table 4.4.

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

Land Use Total N (mg/L) FLUCCS ID

1000-(1100+1200+1300) Urban Open1 1.18

1100 Low Density Residential1 1.61

1200 Medium Density Residential1 2.07

1300 High Density Residential1 2.32

2000 Agriculture1 2.79

3000 Rangeland1 1.15

4000 Forest/Rural Open1 1.15

5000 Water2 1.60

6000 Wetlands2 1.01

7000 Barren Land **

Communication and Transportation1 1.64 8000

1 Harper, H. H. and D.M. Baker. 2007. Evaluation of Current Stormwater Design Criteria within the State of Florida. Environmental Research & Design, Inc. (Table 4-17) 2 Harper, H. H. and D.M. Baker. 2003. Evaluation of Alternative Stormwater Regulations for Southwest Florida.

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Environmental Research & Design, Inc. (Table 7)

Table 4.5 summarizes the annual average TN loadings to the Palm River and McKay Bay watershed from the gauged area, ungauged area, and point sources. Annual TN loadings from all sources varied from a low of 110,729 pounds in 2000 to a high of 809,838 pounds in 2004. The year 2000 was also the year with the lowest rainfall, 29.9 inches, while rainfall in 2004 was above average at 59.3 inches. Table 4.5. Total N Estimates for the TBC, Palm River and

McKay Bay Watershed

Nonpoint Source Loading Point Source Loading

Gauged TN Load

(lbs)

Ungauged TN Load

(lbs)

Percent Nonpoint Source

Falkenburg Road

AWWTP TN Load

(lbs)

Trademark Nitrogen TN Load

(lbs)

Percent Point

Source

Total TN Load

(lbs)

Year

2000 7,410 89,576 87.6 13,542 201 12.4 110,7292001 157,516 119,286 92.3 23,027 190 7.7 300,0192002 188,234 186,269 93.1 27,792 74 6.9 402,3692003 258,575 156,018 94 26,517 129 6 441,2392004 606,550 177,984 96.9 25,071 233 3.1 809,8382005 183,194 116,887 89.7 34,367 103 10.3 334,5512006 38,102 169,912 85.1 36,436 56 14.9 244,5062007 11,841 126,008 81.9 30,293 86 18.1 168,227

Septic Tanks Septic tanks are another potentially important source of pollution. Information on the location of septic systems was obtained from Hillsborough County, which is based on an ongoing study to identify septic tanks. The septic tank database was developed from records obtained from the Florida Department of Health and sewer billing records (David Glicksberg, personal communication). The septic tanks located in the watershed are displayed in Figure 4.3. Currently, the number of septic tanks in this watershed area is estimated to be 1,815.

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Figure 4.3. Distribution of Onsite Sewage Systems (Septic Tanks) in the Watershed

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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 watershed, so that the TBC, Palm River and McKay Bay will meet the applicable DO and nutrient criteria and maintain their function and designated use as Class III waters. The Trophic State Index (TSI) was used as the tool for establishing a nutrient target for TMDL development in the TBC. For the Palm River and McKay Bay, the TMDLs were developed by applying a reference approach, where a nutrient target was selected based on results from Tampa Bay Basin waters that are not impaired for DO and nutrients. In each case, the TMDLs were established by calculating the percent reduction needed in existing TN concentrations to meet the water quality target.

5.2 Analysis of Water Quality

Water quality monitoring data collected in the watershed that are available to the Department have been performed by a variety of agencies and the sampling locations are shown in Figure 5.1. The majority of data collection in the lower freshwater segment of the TBC has been performed by the Hillsborough County Environmental Protection Commission (HCEPC), along with some limited data collection by the Florida DEP Southwest District Office. THE HCEPC collects samples near the upstream end of WBID 1536F at the location identified as station 147. In the estuarine segments of the Palm River and McKay Bay, the majority of data collection has been performed by the HCEPC and by Tampa Bay Water. The HCEPC collects samples at two fixed locations in the Palm River, Station 110 and Station 109 and at one location in McKay Bay, Station 58. The county also samples monthly in East Bay at Station 54 located near the boundary with McKay Bay. Tampa Bay Water conducts water quality sampling in the estuarine areas as part of the Hydrobiological Monitoring Program (HBMP). The HBMP consists of using a probabilistic design in which sampling is randomized within strata along the longitudinal axis of the waters. Data collection within each stratum occurs on a monthly basis. Water quality trends in chlorophyll a, total nitrogen, and total phosphorus at the HCEPC stations in the watershed are presented in Figures 5.2, 5.3, and 5.4, respectively. Some temporal and spatial patterns can be seen in the annual average results. The annual average chlorophyll a values suggest a decreasing trend over time at each sampling location and the chlorophyll a values decrease moving downstream, Figure 5.2. The TBC freshwater segment typically exhibits the highest annual average chlorophyll a values and the largest variation between years. Moving downstream, the annual average chlorophyll a values tend to decrease and exhibit less variation between years. The annual average total nitrogen values exhibit a decreasing trend at the estuary stations, particularly showing a decline after 2002, whereas the nitrogen average in the TBC freshwater segment has not declined, Figure 5.3. The annual average total phosphorus concentrations exhibit a declining trend between 1989 and 1999 at the estuarine stations, and after 1999 remain fairly constant, with the exception of averages at Station 109 in the Palm River, Figure

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5.4. The TBC freshwater segment average annual phosphorus values exhibit little, if any, trend over time.

Figure 5.1 Monitoring Locations in the Watershed Area of the TBC, Palm River and McKay Bay

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Figure 5.2 Annual Average Chlorophyll a Concentrations at the Hillsborough County EPC Estuary and Freshwater Stations

Figure 5.3 Annual Average Total Nitrogen Concentrations at the Hillsborough County EPC Estuary and Freshwater Stations

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Figure 5.4 Annual Average Total Phosphorus Concentrations at the Hillsborough County EPC Estuary and Freshwater Stations

5.3 Attempts to Develop Empirical Relationships

The Department initially attempted to determine the receiving water’s assimilative capacity through a statistical evaluation of available nutrient data and chlorophyll a data, but these efforts were not successful. Attempts were made to identify relationships with the response variable, chlorophyll a, and water column TN concentrations and watershed TN loadings, but no strong correlations were found. This lack of a relationship is at least partially due to the limited information used to derive the loading estimates. For example, the freshwater monitoring site available for calculating the gauged load to the estuary was located at HCEPC Station 147 (Latitude: 27°58’54”, Longitude: 82°21’16”), approximately 2 miles upstream of the SWFWMD Gage S-160. Differences in water quality between Station 147 and the gage need to be investigated. Additionally, the TN load calculated for the ungauged area of the watershed is a course estimate, that with further data collection and adjustment could be calibrated to actual measurements.

5.4 Percent Reduction Approach

The TMDL calculation was performed using the “percent reduction” approach. For this method, the selected water quality target for TMDL development is the average median sample station TN concentration of 0.62 mg/L for Tampa Bay Basin estuary WBIDs not impaired for DO and nutrients. These stations have an annual median dissolved oxygen concentration of 6.11 mg/L, and a median chlorophyll a concentration of 7.58 ug/L. Achieving this nutrient target in the impaired segments is expected to allow them to meet the applicable DO and nutrient criteria.

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The percent reduction for each waterbody was determined by calculating the reduction needed in the average of the annual average TN concentrations during the verified period in the TBC, Palm River, and McKay to meet the target of 0.62 mg/L.

[measured exceedance – target] X 100 measured exceedance

The percent reduction calculations are displayed in Table 5.1. The percent reductions in the TN concentrations needed to meet the target in the TBC, Palm River, and McKay Bay are 32 percent, 35 percent, and 22 percent, respectively. Annual average values were used in establishing the TMDL in this case as the IWR nutrient assessment is performed using annual average chlorophyll a values.

Table 5.1 Percent Reduction Calculations for Total Nitrogen

Year TBC (WBID 1536F) Average TN

(mg/L)

Palm River (WBID 1536E) Average TN

(mg/L)

McKay Bay (WBID 1584B) Average TN

(mg/L)

2000 0.94 1.14 1.07 2001 0.92 1.09 0.85 2002 0.87 1.07 0.93 2003 1.04 0.80 0.63 2004 0.98 0.87 0.67 2005 0.77 0.82 0.64 2006 0.86 0.94 0.77

Average 0.91 0.96 0.79 Water Quality

Target 0.62 0.62 0.62

Percent Reduction

32 35 22

As discussed in Chapter 3, the TSI threshold for lakes of 60, was applied for setting the nutrient target for the TBC, as this water has hydrologic characteristics similar to lakes. The TSI is calculated based on concentrations of TP, TN, and chlorophyll a as follows: CHLATSI = 16.8 + 14.4 * LN(Chl a) Chl a in μg/L TNTSI = 56 + 19.8 * LN(N) N in mg/L

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TN2TSI = 10 * [5.96 + 2.15 * LN(N + 0.0001)] TPTSI = 18.6 * LN(P * 1000) – 18.4 P in mg/L TP2TSI = 10 * [2.36 * LN(P * 1000) – 2.38] If N/P > 30, then NUTRTSI = TP2TSI

If N/P < 10, then NUTRTSI = TN2TSI

if 10< N/P < 30, then NUTRTSI = (TPTSI + TNTSI)/2 TSI = (CHLATSI + NUTRTSI)/2 (TSI has no units) An annual average TSI for the TBC was calculated based on using the average of the annual average TN and TP concentrations during the Cycle 2 verified period. Average concentrations for this period are a chlorophyll a of 44.4 μg/L, a TN of 0.91 mg/L, and a TP of 0.19 mg/L. These concentrations result in a TSI of 64.5 (Table 5.2).

Table 5.2 TSI Calculation for the TBC (WBID 1536F)

Existing Condition

TMDL Reduction Condition

Total Nitrogen (mg/L) 0.91 0.62Total Phosphorus (mg/L) 0.19 0.19TN/TP 4.8 3.3Chlorophyll a (ug/L) 44.4 20.0TSI (Nitrogen Limited) 64.5 54.6

The TMDL for nutrients in the TBC was based on achieving a target TSI of 55, as a margin of safety, through reductions in both TN and chlorophyll a. Using the equations for calculating TSI, the TN was reduced to the target of 0.62 mg/L for the estuary segments. A large fraction of the TN load delivered to the Palm River and McKay Bay is from the TBC. A TN concentration of 0.62 mg/L, with the chlorophyll a value set at 20 ug/L, while maintaining the average annual TP value, results in a TSI of 54.6.

5.5 Relationship Between Nutrients and DO

Reductions in TN are also expected to result in additional benefits for other parameters of concern, including DO and BOD. Reduced algal biomass, as measured by chlorophyll a, should result in lower BOD and SOD levels as less algae would enter the organic carbon pool in the water column and sediment. The lower BOD and SOD levels would exert less of an oxygen demand in the water column and are expected to result in improved DO conditions. Additionally during daylight hours, algal photosynthesis consumes nutrients and organic matter. The organic matter acts as an energy reserve, and oxygen is released. The reverse process, respiration, may occur simultaneously and dominate during dark periods of the day. During respiration, algae consume oxygen and their energy reserve to produce carbon dioxide and water. Because photosynthesis creates oxygen and respiration depletes oxygen, the algae affect the oxygen sources in the impaired waters. With reduced algal biomass in the water column, the variation in DO over the course of a day would be reduced.

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5.6 Current Restoration and Management Projects

At least four stormwater projects that have been implemented in the McKay Bay watershed in recent years that have already reduced the TN loading to the watershed. The SWFWMD funded several stormwater retrofit projects through the Surface Water Improvement and Management (SWIM) Program. The primary goal of these projects was to reduce pollutant loadings to McKay Bay and ultimately to Tampa Bay, improving or maintaining estuarine water quality. Table 5.3 lists the projects and the estimated load reductions. As shown in Table 5.3, these projects are estimated to reduce annual TN loadings to the bay by over 12,105 pounds.

Table 5.3. SWIM Stormwater Retrofit Projects in the TBC, Palm River and McKay Bay Watershed

Estimated Load Reduction (lbs/year)) WBID Basin

Acreage TN TP TSS Completed Cooperator Project

30th Street Baffle Box* 1584A 14 - - - April 1998 City of Tampa

1584A 190 300 368 14,354 September 1998 City of Tampa Pond 56

1584B 600 944 317 69,697 September 2002

Florida Department of Transportation Melburne Pond

1579 1,200 9,982 809 256,157 December 2000 Hillsborough County East Lake Outfall**

Eastshore Commerce Park Stormwater Retrofit 1536A 1,000 880 586 27,591 Ongoing Tampa Bay Water,

Hillsborough County * Load reductions not estimated for this project. ** System operational from December 2000 to December 2002; expected to be back on line in June 2004 - No estimate provided.

5.7 Critical Conditions

The TMDL was based on annual average conditions (i.e., values from all four seasons in a calendar year) 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.

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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 total nitrogen TMDLs for the TBC, Palm River and McKay Bay are expressed in terms of pounds/day and percent reduction, Table 6.1.a, and pounds/year and percent reduction, Table 6.1.b, and represent the maximum TN load the surface waters can assimilate in order for them to attain the applicable chlorophyll a thresholds and DO criteria. The TMDLs to be implemented are those expressed on a mass per year basis, and the expression of the TMDL on a mass per day basis is for information purposes only.

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Table 6.1.a. TMDL Components Expressed as a Daily Load

WLA

TMDL (mg/L) Wastewater

NPDES Stormwater

LA (% Reduction)2

Parameter    (lbs/day)1 (% Reduction)2   

MOS

WBID

1536F Total N 0.62 NA 32% 32% Implicit

1536E Total N 0.62 51.0 35% 35% Implicit

1584B Total N 0.62 NA 22% 22% Implicit 1 The allowable average daily load for Falkenburg Road AWWTP is 49 pounds and for Trademark Nitrogen Corporation is 2 pounds. 2 As the TMDL represents a percent reduction, it also complies with EPA requirements to express the TMDL on a daily basis.

Table 6.1.b. TMDL Components Expressed as an Annual Load

WLA

TMDL (mg/L) Wastewater

NPDES Stormwater

LA (% Reduction)2

Parameter    (lbs/year)1 (% Reduction)2   

MOS

WBID

1536F Total N 0.62 NA 32% 32% Implicit

1536E Total N 0.62 18,365 35% 35% Implicit

1584B Total N 0.62 NA 22% 22% Implicit 1 The allowable annual load for Falkenburg Road AWWTP is 17,635 pounds and for Trademark Nitrogen Corporation is 730 pounds. 2 As the TMDL represents a percent reduction, it also complies with EPA requirements to express the TMDL on a daily basis.

6.2 Wasteload Allocation

6.2.1 NPDES Wastewater Discharges

The WLA was determined by calculating the allowable TN load for each facility and combining the loads as shown in Table 6.1.a and Table 6.1.b. The allowable combined WLA is 18,365 pounds/year of TN. The Trademark Nitrogen discharge was considered not to be a significant load to the receiving waters relative to the nonpoint source load and the existing Falkenburg Road AWWTP load, as the current TN load being discharged is less than one percent of the total load. The Trademark Nitrogen Corporation WLA of 730 pounds/year of TN was calculated using the annual average flow of 0.08 MGD and a monthly effluent limit of 3 mg/L. Although Trademark has a design

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capacity of 25.0 MGD, the effluent limit for TN was based on the average flow of the existing discharge in the 2000 to 2007 period. The existing load from the Falkenburg Road AWWTP was considered to be a significant load to surface waters, making up between 3 percent to 18 percent of the total nitrogen annual load generated in the watershed. In this case, the allowable TN load was determined by reducing the existing annual average load by the same percent reduction (35 percent) being applied to the nonpoint sources discharging to the Palm River. The WLA for the Falkenburg Road AWWTP is 17,635 pounds/year.

6.2.2 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 between 22 to 35 percent, this percent reduction is applied to the NPDES stormwater WLA. The MS4 permittees, including Hillsborough County and Co- Permittees (FDOT District 7 and the city of Plant City), the city of Tampa, and the city of Temple Terrace are covered by Phase I NPDES municipal separate storm sewer system (MS4) permits. Areas within their jurisdiction contributing loads to the watershed may be responsible for between a 22 to 35 percent reduction in current anthropogenic TN loading depending on the waterbody they discharge to. 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.

6.3 Load Allocation

A total nitrogen reduction of 32 percent, 35 percent, and 22 percent is required from nonpoint sources discharging to the TBC, Palm River, and McKay Bay, respectively. It should be noted that the load allocation includes loading from stormwater discharges that are not part of the NPDES Stormwater Program.

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 decisions associated with selecting the nutrient targets. For the freshwater segment of the TBC, the selected TSI target of 55 is less than the TSI of 60 used as an impairment threshold for lakes. For the Palm River and McKay Bay estuarine segments, the nutrient target was developed using data from reference waters that have annual average chlorophyll a values below the threshold of 15 ug/L.

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Chapter 7: NEXT STEPS: IMPLEMENTATION PLAN DEVELOPMENT AND BEYOND

TMDL Implementation

Following the adoption of this TMDL by rule, the Department will determine the best course of action regarding its implementation. Depending upon the pollutant(s) causing the waterbody impairment and the significance of the waterbody, the Department will select the best course of action leading to the development of a plan to restore the waterbody. Often this will be accomplished cooperatively with stakeholders by creating a Basin Management Action Plan, referred to as the BMAP. Basin Management Action Plans are the primary mechanism through which TMDLs are implemented in Florida [see Subsection 403.067(7) F.S.]. A single BMAP may provide the conceptual plan for the restoration of one or many impaired waterbodies. If the Department determines a BMAP is needed to support the implementation of this TMDL, a BMAP will be developed through a transparent stakeholder-driven process intended to result in a plan that is cost-effective, technically feasible, and meets the restoration needs of the applicable waterbodies. Once adopted by order of the Department Secretary, BMAPs are enforceable through wastewater and municipal stormwater permits for point sources and through BMP implementation for nonpoint sources. Among other components, BMAPs typically include:

• Water quality goals (based directly on the TMDL);

• Refined source identification;

• Load reduction requirements for stakeholders (quantitative detailed allocations, if technically feasible);

• A description of the load reduction activities to be undertaken, including structural projects, nonstructural BMPs, and public education and outreach;

• A description of further research, data collection, or source identification needed in order to achieve the TMDL;

• Timetables for implementation;

• Implementation funding mechanisms;

• An evaluation of future increases in pollutant loading due to population growth;

• Implementation milestones, project tracking, water quality monitoring, and adaptive management procedures; and

• Stakeholder statements of commitment (typically a local government resolution).

BMAPs are updated through annual meetings and may be officially revised every five years. Completed BMAPs in the state have improved communication and cooperation among local stakeholders and state agencies, improved internal communication within local governments, applied high-quality science and local information in managing water resources, clarified

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obligations of wastewater point source, MS4 and non-MS4 stakeholders in TMDL implementation, enhanced transparency in DEP decision-making, and built strong relationships between DEP and local stakeholders that have benefited other program areas. However, in some basins, and for some parameters, particularly those with fecal coliform impairments, the development of a BMAP using the process described above will not be the most efficient way to restore a waterbody, such that it meets its’ designated uses. Why? Because fecal coliform impairments result from the cumulative effects of a multitude of potential sources, both natural and anthropogenic. Addressing these problems requires good old fashioned detective work that is best done by those in the area. There are a multitude of assessment tools that are available to assist local governments and interested stakeholders in this detective work. The tools range from the simple – such as Walk the WBIDs and GIS mapping - to the complex such as Bacteria Source Tracking. Department staff will provide technical assistance, guidance, and oversight of local efforts to identify and minimize fecal coliform sources of pollution. Based on work in the Lower St Johns River tributaries and the Hillsborough River basin, the Department and local stakeholders have developed a logical process and tools to serve as a foundation for this detective work. In the near future, the Department will be releasing these tools to assist local stakeholders with the development of local implementation plans to address fecal coliform impairments. In such cases, the Department will rely on these local initiatives as a more cost-effective and simplified approach to identify the actions needed to put in place a roadmap for restoration activities, while still meeting the requirements of Chapter 403.067(7), F.S.

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References

Baker, D., and H. Harper, H. 1994. Evaluation of Alternative Stormwater Regulations for Southwest Florida, Final Report. Orlando, Florida: Environmental Research and Design, Inc.

Brown, M.T. (Add date.) The South Dade Watershed Project. Miami, Florida: Center for Urban and Community Design.

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.

—. 2003. Total Maximum Daily Load for Total Phosphorus for Lake Eustis and Haines Creek Reach, Lake County, Florida. Tallahassee, Florida: Bureau of Watershed Management.

—. 2003. Total Maximum Daily Load for Dissolved Oxygen Impairment for the Palatlakaha River, Lake County, Florida. Tallahassee, Florida: Bureau of Watershed Management.

—. September 2003. Tampa Bay Basin Status Report. Tallahassee, Florida. Available at http://www.dep.state.fl.us/water/tmdl/stat_rep.htm.

—. 2004. (Add rest of citation)

Florida Department of Health. 2003. (Add rest of citation)

Florida LakeWatch. Available at http://lakewatch.ifas.ufl.edu/. Florida Watershed Restoration Act. Chapter 99-223, Laws of Florida.

Harper, H. H. and D.M. Baker. 2003. Evaluation of Alternative Stormwater Regulations for Southwest Florida, Final Report. Orlando, Florida: Environmental Research and Design, Inc.

Harper, H. H. and D.M. Baker. 2007. Evaluation of Current Stormwater Design Criteria within the State of Florida. Orlando, Florida: Environmental Research and Design, Inc.

Knutilla, R.L. and M.A. Corral. 1984. Impacts of the Tampa Bypass Canal System on the Areal Hydrology, Hillsborough County, Florida. U.S. Geological Survey Water Resources Invetigations Report 84-4222.

McKay Bay Water Quality Management Plan. December 1998. (Add rest of citation)

National Research Council. 1993. Managing Wastewater in Coastal Urban Areas. National Academy Press, Washington, D.C.

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Roehl, J. W. 1962. Sediment Source Areas, Delivery Ratios, and Influencing Morphological Factors. International association of Scientific Hydrology. 59: 202-213. Symposium of Bari, October 1-8, 1962.

Stoker, Y.E., V.A. Levesque, and E.M. Fritz. 1996. Discharge, Water Quality Characteristics, and Nutrient Loads from McKay Bay, Delaney Creek, and East Bay, Tampa, Florida, 1991 – 1993. U.S. Geological Survey Water Resources Investigations Report 95-4167.

Southwest Florida Water Management District. 20__. Tampa Bay/Anclote River Watershed Comprhensive Watershed Management Report. Brooksville, Florida.

—. 1998. Tampa Bay Surface Water Improvement and Management Plan. Brooksville, Florida.

Tampa Bay Estuary Program. 1999. Progress Report, Partners for Progress, The Tampa Bay Nitrogen Management Consortium Action Plan, 1995 – 1999. Tampa, Florida.

U. S. Environmental Protection Agency. 1999. Protocol for Developing Nutrient TMDLs. Washington, D.C.: Office of Water. EPA841-B-99-007.

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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. 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.

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