FINAL 4/18/2008 

FLORIDA DEPARTMENT OF ENVIRONMENTAL PROTECTION 

Division of Water Resource Management, Bureau of Watershed Management

CENTRAL DISTRICT • MIDDLE ST. JOHNS BASIN 

TMDL Report 

Nutrient TMDLs for the Wekiva River 

(WBIDs 2956, 2956A, and 2956C) and 

Rock Springs Run (WBID 2967) 

Xueqing Gao 

April 18, 2008 
ii 

Florida Department of Environmental Protection 

TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP

Acknowledgments 

This TMDL was based on the Pollutant Load Reduction Goal (PLRG) for nitrate and total 

phosphorus developed by the St. Johns River Water Management District. The Florida 

Department of Environmental Protection (the Department) appreciates the instrumental help 

provided by Rob Mattson, and valuable suggestions from Ed Lowe, Larry Battoe, and Eric 

Marzolf. Special thanks also go to Dr. Xufeng Niu, who helped to define the nitrate target using 

the change-point analysis. We deeply appreciate the kind help provided by the Department‘s 

Central District Office staff, especially Chris Ferraro, Dennise Judy, Pat Young, and Ali Kazi, 

who helped greatly in providing data, valuable insight, and understanding of the point sources 

identified in the Wekiva River drainage basin. We also deeply appreciate the help from Sarah 

Jozwiak (NPDES Stormwater Section of the department) in providing information related to MS4 

permits, and CDM, Inc for providing information about septic tanks for the Wekiva River 

Drainage basin. 

Editorial assistance provided by 

Daryll Joyner and Jan Mandrup-Poulsen 

For additional information on the watershed management approach and impaired waters 

in the Middle St. Johns Basin, contact 

Jennifer Gihring 

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: Jennifer.Gihring@dep.state.fl.us

Phone: (850) 245-8418; Suncom: 205-8418 

Fax: (850) 245-8434 

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

Xueqing Gao 

Florida Department of Environmental Protection 

Bureau of Watershed Management 

Watershed Assessment Section 

2600 Blair Stone Road, Mail Station 3565 

Tallahassee, FL 32399-2400 

Email: xueqing.gao@dep.state.fl.us

Phone: (850) 245-8464, SunCom: 205-8464 

Fax: (850) 245-8434 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

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Table of Contents 

Chapter 1: INTRODUCTION _____________________________________________1

1.1 Purpose of Report ________________________________________________1

1.2 Identification of Waterbody ________________________________________1

1.3 Background______________________________________________________2

Chapter 2: DESCRIPTION OF WATER QUALITY PROBLEM __________________4

2.1 Statutory Requirements and Rulemaking History ______________________4

2.2 Information on Verified Impairment__________________________________4

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 Target ___9

3.2.1 Interpretation of Narrative Nutrient Criterion __________________________9

Chapter 4: ASSESSMENT OF SOURCES _________________________________25

4.1 Types of Sources________________________________________________25

4.2 Potential Sources of pollutants in Watersheds of the Wekiva River and 

 RSR __________________________________________________________25

4.2.1 Point Sources ________________________________________________25

4.2.2 Nonpoint Sources _____________________________________________33

Chapter 5: DETERMINATION OF ASSIMILATIVE CAPACITY _________________47

Chapter 6: DETERMINATION OF THE TMDL ______________________________50

6.1 Expression and Allocation of the TMDL _____________________________50

6.2 Load Allocation _________________________________________________53

6.3 Wasteload Allocation ____________________________________________53

6.3.1 National Pollutant Discharge Elimination System Wastewater 

Discharges __________________________________________________53

6.3.2 National Pollutant Discharge Elimination System Stormwater 

Discharges __________________________________________________56

6.4 Margin of Safety_________________________________________________57

6.5 Recommendations for Further Studies______________________________57

Chapter 7: NEXT STEPS: IMPLEMENTATION PLAN DEVELOPMENT AND 

BEYOND __________________________________________________59

7.1 Basin Management Action Plan____________________________________59
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References 60

Appendices _________________________________________________________62

Appendix A: Background Information on Federal and State Stormwater 

Programs__________________________________________________________62

Appendix B. Change Point Analysis of the Suwannee River Algal Data ________63
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List of Tables 

Table 2.1. Landuse of Juniper Creek and Alexander Springs Creek basins. ___ 5

Table 3.1. Ecological efficiencies and nitrate concentrations at test 

segments in WRMS, RSR, JC, and ASC.____________________ 14

Table 3.2. Percent stream bottom covered by vegetation of different 

functional groups at different test segments. _________________ 17

Table 3.3. Ecological efficiencies and TP concentrations at test segments 

in theWekiva River (WR), Rock Springs Run (RSR), Juniper 

Creek (JC), and Alexander Springs Creek (ASC)______________ 23

Table 4.1. NPDES permitted facilities identified in the drainage basin 

discharge to Wekiva River. _______________________________ 26

Table 4.2. Results of water quality monitoring in Sulfur Creek upstream and 

downstream of the effluent point and at the effluent point when 

flow appeared in the creek._______________________________ 28

Table 4.3. Long-term monthly average daily discharge rate, TP monthly 

average concentrations, and long-term TP monthly average 

loading for Altamonte Springs Regional Water Reclamation 

Facility. ______________________________________________ 29

Table 4.4. Long-term monthly average nitrate and TP concentrations and 

loadings for the effluent discharge from Wekiva Hunt Club 

WWTF in the period from 1999 through 2006. ________________ 31

Table 4.5. Nitrate concentrations at different sampling sites along the 

Sweetwater Creek – Cove Lake system_____________________ 32

Table 4.6. TP concentrations at different sampling sites along the 

Sweetwater Creek – Cove Lake system_____________________ 32

Table 4.7. Acreages and percent acreages of different landuse categories 

for the Wekiva River system draingage basin ________________ 36

Table 4.8. Classification of land use categories in the Wekiva River 

watershed ____________________________________________ 38

Table 4.9. Percent pollutant contribution from different landuse categories ___ 38

Table 4.10. Nutrient load for household wastewater discharged into septic 

tanks (kilograms/capita/year) (cited from Reckhow, 1980)_______ 41

Table 4.11. Characteristics of springs located in the Wekiva River drainage 

basin. _______________________________________________ 44

Table 4.12. Nitrate and TP loadings from springs located in the Wekiva 

River drainage basin and percent loadings from these springs ___ 45

Table 4.13. Summary of nitrate and TP loadings from possible nonpoint 

sources in the Wekiva River drainage areas. _________________ 46

Table 5.1. Existing and target nitrate concentrations for related stream

segments and percent concentration reduction required to 

achieve the nitrate target. ________________________________ 48
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Table 5.2. Existing and target TP concentrations for related stream 

segments and percent concentration reduction required to 

achieve the TP target.___________________________________ 49

Table 6.1. TMDL components for RSR, WRMS, and related WBIDs ________ 51

Table 6.2. Daily maximum for target nitrate concentration (mg/L) __________ 52

Table 6.3. Daily maximum for target TP concentration (mg/L) _____________ 52
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List of Figures 

Figure 1.1. Locations of Wekiva Parkway Protection Area (WPPA), main 

stem of the Wekiva River and Rock Springs Run, waterbody IDs 

(WBIDs) covered in this TMDL, and major cities located around 

the waterbodies under question.____________________________ 3

Figure 2.1. Locations of the two reference creeks used in this TMDL.________ 6

Figure 3.1-A Relationship between mean nitrate concentration and mean 

periphyton cell density from sampling sites on the Suwannee, 

Santa Fe, and Withlacoochee Rivers (Mattson et al. 2006). _____ 11

Figure 3.1-B Relationship between mean nitrate concentration and mean 

periphyton biomass from sampling sites on the Suwannee, 

Santa Fe, and Withlacoochee Rivers (Mattson, 2006). _________ 11

Figure 3.2. Locations of water quality stations from which nitrate and 

periphyton abundance samples were collected and used for the 

change-point analysis ___________________________________ 12

Figure 3.3. Wekiva River and Rock Springs Run stream segments for 

ecological evaluations. This figure was cited from Wetland 

Solution, Inc. (2005).____________________________________ 15

Figure 3.4. Juniper Creek stream segments for ecological evaluations. 

This figure was cited from Wetland Solution, Inc. (2005). _______ 16

Figure 3.5. Alexander Springs Run stream segments for ecological 

evaluations. This figure was cited from Wetland Solution, Inc. 

(2005)._______________________________________________ 16

Figure 3.6. Correlation between ecological efficiency and nitrate 

concentration in WR, RSR, ASC, and JC. ___________________ 18

Figure 3.7. Monthly variation of nitrate concentration in upstream WRMS____ 20

Figure 3.8. Sampling stations used by the GreenWater Labs for attached 

algal studies in the Wekiva River and Rock Springs Run 

(GreenWater Labs, 2005) ________________________________ 22

Figure 3.9. Relationship between TP concentration and percent biovolume 

of blue-green and green algae in the Wekiva River and Rrock 

Springs Run (Mattson et al. 2006) _________________________ 23

Figure 3.10. Correlation between ecological efficiency and TP 

concentration in the Wekiva River, Rock Springs Run, 

Alexander Springs Creek, and Juniper Creek. ________________ 24

Figure 4.1. NPDES permitted facilities located in the Wekiva River 

drainage area._________________________________________ 27

Figure 4.2. Influence of the Altamonte Springs Regional WRF on the 

spatial distribution of TP concentration in the Little Wekiva 

River.________________________________________________ 30
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Figure 4.3. Locations of water quality stations along the Sweetwater Creek 

– Cove Lake systems for Wekiva Hunt Club WWTF. ___________ 34

Figure 4.4. Long-term spatial trend of nitrate and TP concentration at 

different sampling sites along the Sweetwater Creek – Cove 

Lake system.__________________________________________ 35

Figure 4.5. Principal land uses in the drainage basin of Wekiva River. ______ 37

Figure 4.6. Location of septic tank-using land parcels in the Wekiva Study 

Area. ________________________________________________ 40

Figure 4.7. Locations of springs in the Wekiva River drainage area. ________ 43
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Web sites 

Florida Department of Environmental Protection, Bureau of 

Watershed Management 

Total Maximum Daily Load (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

2004 305(b) Report 

http://www.dep.state.fl.us/water/docs/2004_Integrated_Report.pdf

Criteria for Surface Water Quality Classifications 

http://www.dep.state.fl.us/water/wqssp/classes.htm

Basin Status Reports 

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

Water Quality Assessment Reports 

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

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/

Chapter 1: INTRODUCTION 

1.1 Purpose of Report 

This report presents the nutrient Total Maximum Daily Loads (TMDLs) for Rock Springs Run 

(RSR) and the Wekiva River, in the Middle St. Johns River Basin. These waters were verified 

as impaired due to total phosphorus (TP) and nitrate based on evidence of imbalance in aquatic 

flora provided by the St. Johns River Water Management District (SJRWMD) and were added to 

the Verified List of impaired waters for the Middle St. Johns River Basin by Secretarial Order on 

January 3, 2007. The purpose of this TMDL is to establish the allowable loadings of pollutants 

to RSR and Wekiva River that would restore these waterbodies such that they meet their 

applicable water quality criteria for nutrients. 

1.2 Identification of Waterbody 

The Wekiva River Study Area (“WSA”; Figure 1-1) is located in central Florida. The boundary 

of the area was delineated in the Wekiva Parkway and Protection Act (WPPA, 2004) and 

encompasses 473 square miles. The river is a major hydrological feature of the WSA, which 

receives discharges from thirty springs and several major tributaries, including Little Wekiva 

River from the south, Rock Springs Run in the middle, and Blackwater Creek from the north, 

and discharges into the St. Johns River downstream of Lake Monroe. The eastern and 

southern parts of the WSA are highly urbanized areas occupied by several municipalities, 

including the City of Orlando, Winter Park, Casselberry, Winter Spring, Lake Mary, and Sanford. 

More rural areas are located in the northwestern part of the WSA. 

The Wekiva River and RSR and their headsprings currently provide a variety of recreational 

opportunities, including canoeing, swimming, snorkeling, tubing, boating, and fishing. In 

addition to being protected under the WPPA, the Wekiva River system (including the main stem 

and Rock Springs Run) is designated as an Outstanding Florida Water (OFW). The river is also 

in the Wekiva River Aquatic Preserve, first designated by the Florida Legislature (Chapter 

258.36, FS) in 1975. Most recently, the Wekiva River and portions of its major tributaries were 

designated Florida’s third National Wild and Scenic River system (U.S. House of 

Representatives Bill H. R. 3155). This is a federal designation applied to rivers considered 

worthy of protection due to their ecological and aesthetic attributes and recreational value. 

The Wekiva River basin is also part of the SJRWMD’s Surface Water Improvement and 

Management (SWIM) program for the Middle St. Johns River Basin. The SJRWMD was 

required to develop a pollutant load reduction goal (PLRG) for the river, and the PLRG 

development schedule was expedited per the WPPA. 

The area that includes the Wekiva River surface water basin and “springshed” lies within 

portions of the Marion Upland, Orlando Ridge, and Osceola Plain physiographic regions 

(Schmidt 1997). Land elevations range from 175 feet above mean sea level (MSL) in the 

western part of the region to about 10 feet above MSL at the confluence of the Wekiva River 

and Blackwater Creek (WSI 2004). In the western and southern portions of the region, the land 

is a series of high (>75 feet above MSL) terraces and ridges, with well-draining sandy soils. In 
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the eastern and northeastern portions of the region, land elevations are generally < 25 feet 

above MSL, with poorly draining wetland and flatwoods soils. 

The Wekiva River basin and springshed lie in a karst-influenced landscape. The Floridan 

Aquifer is the main water source for springs that discharge to the Wekiva River and its 

tributaries (Toth and Fortich 2002; Osburn et al. 2002). The principal recharge areas to the 

Floridan Aquifer are in the western and southern portions of the region (Osburn et al. 2002), 

with recharge of up to 12” of rainfall annually. Much of the lengths of the Wekiva River and 

Rock Springs Run lie within the discharge zone of the Floridan Aquifer, resulting in a 

predominance of spring flow in these streams. Based on Hupalo et al. (1994), spring flow 

represents at least 67% of the base flow of the Wekiva River. Because of the predominance of 

spring flow in these streams, the water quality in the springs exerts a major influence on water 

quality in the spring-run streams. 

More detailed information regarding the physiogeography, hydrology, hydrogeology, and climate 

of the WPPA area can be obtained by consulting the “Wekiva River and Rock Springs Run 

Pollutant Load Reduction Goals” developed by the SJRWMD (Mattson, et al. 2006). 

For assessment purposes, the Department has divided the Middle St. Johns Basin into water 

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

watershed or stream reach. This TMDL report addresses four WBIDs: WBIDs 2956 and 2956A 

for the main stem of the Wekiva River, WBID 2956C for Wekiva Spring, and WBID 2967 for 

Rock Springs Run. Figure 1.1 shows the locations of the WBIDs covered in this TMDL report. 

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 FWRA. 

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, and 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 Wekiva River and RSR. These activities will depend heavily on the active 

participation of the SJRWMD, 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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Figure 1.1. Locations of Wekiva Parkway Protection Area (WPPA), main stem 

of the Wekiva River and Rock Springs Run, waterbody IDs 

(WBIDs) covered in this TMDL, and major cities located around 

the waterbodies under question.
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Chapter 2: DESCRIPTION OF WATER QUALITY 

PROBLEM 

2.1 Statutory Requirements and Rulemaking History 

Section 303(d) of the Clean Water Act requires states to submit to the EPA a list of surface 

waters that do not meet applicable water quality standards (impaired waters) and establish a 

TMDL for each pollutant source in each of these impaired 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.]), and the list is amended annually to include updates for each basin 

statewide. 

Florida’s 1998 303(d) list included 22 waterbodies in the Middle St. Johns River Basin. 

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, 

Florida Administrative Code (F.A.C.) (Identification of Impaired Surface Waters Rule, or IWR), in 

April 2001, and modified in 2006. 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 Wekiva River (WBIDs 2956 and 2956A for the main stem and WBID 2956C for Wekiva 

Spring) and Rock Springs Run (WBID 2967) were not on the Verified List signed by Secretarial 

Order on May 27, 2004 because annual average Chl a concentrations of these WBIDs did not 

exceed the 20 μg/L threshold for eutrophication assessment at the time these waters were 

assessed. However, the Florida Impaired Waters Rule (Chapter 62-303, F.A.C) allows the use 

of information other than Chl a concentration to verify nutrient impairment. Recently, the 

SJRWMD provided to the Department several lines of evidence, indicating that these waters are 

impaired for nutrients, with the causative pollutants being nitrate1

 and phosphorus compounds. 

According to the basin rotation schedule, when waterbodies in the Middle St. Johns River basin 

are assessed in the second water quality assessment cycle in 2008, these waters could be 

included on the Verified Listed, based on the evidence provided by the SJRWMD. However, the 

Florida Legislature passed the Wekiva Parkway and Protection Act (WPPA) in 2004 (Chapter 

369, Part III, FS), which requires that: 

“By December 1, 2005, the St. Johns River Water Management District shall establish 

pollution load reduction goals for the Wekiva Study Area to assist the Department of 

Environmental Protection in adopting total maximum daily loads for impaired waters 

 1

 Nitrate is typically measured and reported as NO3+NO2. However, because the majority of this measurement is in 

the form of nitrate, NO3+NO2 is referred to as nitrate in this report. 
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within the Wekiva Study Area by December 1, 2006” (Chapter 369.318 [8], FS) 

Because Rock Springs Run and the Wekiva River main stem are both located within the 

boundary of the Wekiva Study Area defined by the WPPA, based on the expedited timeline 

required by the WPPA, the Department conducted an off-cycle water quality assessment for 

these waterbodies using the recent information provided by the SJRWMD and verified their 

impairments for nutrients (TP and nitrate). According to the 1999 Florida Watershed 

Restoration Act (FWRA), Chapter 99-223, Laws of Florida, once a waterbody is included on the 

Verified List, a TMDL must be developed. 

One way that the SJRWMD and its contractors used to identify the impairment was to compare 

the distribution of periphyton in the Wekiva River and Rock Springs Run with periphyton in two 

reference spring creeks [Alexander Springs Creek (ASC) and Juniper Creek (JC)]. These two 

reference creeks are located about 32 to 54 km (20 to 33 miles) north of the Wekiva River 

System in south Marion and north Lake Counties. Juniper Creek receives inflows from Juniper 

Springs and Fern Hammock Springs and travels for about 9 km (5.6 miles) before entering the 

southwest corner of Lake George. Alexander Springs Creek receives inflow from Alexander 

Springs and travels for about 17 km (10.5 miles) before entering the St. Johns River near Lake 

Dexter. Figure 2.1 shows the location of these two creeks. Table 2.1 shows the landuse 

categories in the watershed of these two creeks. The dominant landuse in watersheds of both 

reference creeks is upland forest. Development is insignificant in these watersheds. 

Table 2.1. Landuse of Juniper Creek and Alexander Springs Creek basins. 

Juniper Creek Alexander Springs Creek Landuse Description Acreage Percent Area Acreage Percent Area 

Urban and Built-Up 98 0.2% 197 1.7% 

Rangeland 488 1.1% 4.0 0.0% 

Upland Forest 39495 85.5% 7679 68.1% 

Water 457 1.0% 131 1.2% 

Wetlands 5603 12.1% 3261 28.9% 

Barren Land 3 0.0% 0 0.0% 

Transportation, 

Communication, and 

Utilities. 

23 0.1% 0 0.0% 

Total 46,167 100.0% 11,272 100.0% 

The SJRWMD compared the percent of stream bottom covered by periphyton2

 in the Wekiva 

River and Rock Springs Run to the two reference creeks and found that periphyton was more 

abundant in the Wekiva River and Rock Springs Run than in the two reference creeks. 

Specifically, periphyton (including benthic algae, filamentous algae, Nitella sp., and etc.) 

covered about 22.5% and 10.1% of the creek bottom in the Wekiva River and Rock Springs 

Run, respectively, while the percent of stream bottom covered by these algae was only about 

1.8% in the two reference creeks (WSI, 2005). While some amount of periphyton growth is 

ecologically beneficial, excessive periphyton growth can inhibit the growth of submerged aquatic 

vegetation (SAV), which is considered the most important aquatic habitat for fish and other 

 2 Periphyton refers to the community of attached organisms on submerged surfaces, which may include 

microsopic algae such as diatoms, green algae, blue-green algae, euglenophytes, as well as 

filamentous macrophytic algae (Mattson et al. 2006). 
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Figure 2.1. Locations of the two reference creeks used in this TMDL.
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aquatic organisms in these spring creeks. For the case of the Wekiva River and Rock Springs 

Run, these high values indicate an imbalance in the flora of the creeks under question. 

Another focus of the SJRWMD’s studies was to examine the existence of algal species in the 

creeks that may cause harmful effects to fish and wildlife populations or human health concerns. 

One algal group of major concern in Florida springs is the filamentous Cyanobacteria, primarily 

in the genus Lyngbya. Studies have shown that, with increased nutrient loading to a 

waterbody, it is frequently the Cyanobacteria that respond most prolifically (Komarek 2003, 

Bronmark and Hansson 1998). Increases in Lyngbya biomass is a management issue in many 

Florida Springs (Stevenson et al. 2004). Lyngbya, and other Cyanobacteria, produce toxins that 

may be associated with skin reactions and respiratory distress in humans. Large mats of 

filamentous Cyanobacteria may also adversely affect macroinvertebrate and fish habitat, water 

quality and SAV. 

Based on data collected by the Green Lab, Inc (contracted by the SJRWMD), Cyanobacteria 

were found to be the dominant or second largest contributors in the attached algal communities 

at the majority of the Wekiva River sites examined. The major Cyanobacteria species identified 

in the study were Heteroleibleinia sp, Lyngbya wollei, and Phormidium sp.1. Dominance of the 

attached algal communities by Cyanobacteria was also observed in Rock Springs Run, which 

was due primarily to the presence of Lyngbya wolli (Mattson, 2006). These observations are 

consistent with the conclusion that the Wekiva River and Rock Springs Run were impaired and 

the aquatic flora in these streams were imbalanced. 

Information from an ecosystem level study conducted by the Wetland Solution, Inc (WSI, 2005) 

also suggested that the Wekiva River and Rock Springs Run aquatic flora were impaired. In 

this study, several ecosystem level indices, including gross primary productivity, net primary 

productivity, system respiration rate, and ecological efficiency, were measured for segments of 

Wekiva River and Rock Springs Run and compared to those measured in the two reference 

creeks. It was found that all these system indices were depressed in the Wekiva River and 

Rock Springs Run compared to the reference creeks, suggesting impairment on the ecosystem 

functions of the streams under question. 

The SJRWMD provided several lines of evidences to show that nitrate and phosphorus 

compounds are the causative pollutants for observed impairments: 

1. Laboratory experiments (Cowell and Dawes, 2004) and field studies (Hornsby et al. 

2000) indicated that Lyngbya biomass and the biomass and diversity of Cyanobacteria 

population increased with elevated nitrate concentration, especially when the nitrate 

concentration increased above 0.30 mg/L. 

2. Field studies indicated that the percent biovolume of Cyanobacteria in the algal 

community increased with increased total phosphorus (TP) concentrations, especially 

when the TP concentration was higher than 0.090 mg/L (Potapova and Charles, 2005). 

3. The mean nitrate and TP concentrations in the Wekiva River and Rock Springs Run 

range between 0.60-0.70 mg/L and 0.12-0.14 mg/L, respectively, which are significantly 

higher than the threshold nitrate and TP concentrations identified in the above studies. 

4. The percent stream bottom covered by algae was higher and overall ecosystem 

metabolic activities were lower in the Wekiva River and Rock Springs Run where nitrate 

and TP concentrations were higher compared to the two reference creeks where nitrate 

and TP concentrations were lower. 
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5. The highest biomass of attached algae was found at sites in and around the springs of 

both the Wekiva River and Rock Springs Run. Filamentous Cyanobacteria (particularly 

Lyngbya wollei and Phormidium) were most abundant in terms of biomass at spring vent 

sites. These spring vents typically have significantly higher nitrate and TP 

concentrations than sites farther downstream of the vent. 

The above evidence indicated that the Wekiva River and Rock Springs Run are impaired and 

the causative pollutants are nitrate and phosphorus compounds. 
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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, 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) 

Both the Wekiva River and Rock Springs Run 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 water quality criteria applicable to the impairment addressed 

by this TMDL are for nutrients. 

3.2 Applicable Water Quality Standards and Numeric Water Quality Target 

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. A threshold commonly used for assessing the nutrient 

impairment in streams is the annual average Chl a concentration of 20 μg/L, which is defined in 

the Impaired Waters Rule (IWR, 62-303 F.A.C). In addition, the IWR also allows the use of 

other information indicating imbalance in flora or fauna due to nutrient enrichment, including, but 

not limited to, algal blooms, excessive macrophyte growth, decrease in the distribution (either in 

density or areal coverage) of seagrasses or other submerged aquatic vegetation, changes in 

algal species richness, and excessive dial oxygen swings. 

 

As indicted in SJRWMD’s PLRG (Mattson et al., 2006), the impairments of the Wekiva River 

and Rock Springs Run were primarily manifested through elevated algal biomass, dominance of 

benthic algal communities by blue-green algae such as Lyngbya wolli , and depressed 

ecosystem metabolic activities and that the impairments were due to the elevated nitrate and 

phosphorus concentrations. As such, target nitrate and TP concentrations are needed to 

address the imbalances of these structures and functions of aquatic communities. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

10

3.2.1.1 Setting the nitrate target 

The target nitrate concentration for the Wekiva River and Rock Springs Run was established 

based on several lines of evidence, including 1) laboratory nutrient amendment bioassays, 2) 

examining the relationship between periphyton biomass and cell density and the nitrate 

concentration in flow-through systems similar to the Wekiva River and Rock Springs Run, and 

3) comparing metabolic rates, specifically, ecological efficiency, of aquatic communities in the 

Wekiva River and Rock Springs Run with those in reference creeks. 

1) Laboratory nutrient amendment bioassays

The nutrient amendment bioassay work was conducted by Cowell and Dawes (2004), who 

examined the required nitrate concentration in the Rainbow River, Marion County, Florida to 

achieve a reduction of biomass of Lyngbya wollei. L. wollei is a nuisance blue-green benthic 

algal species that dominates the Rainbow River due to elevated nitrate concentrations, and is 

also frequently observed in the Wekiva River and Rock Springs Run where elevated nitrate 

concentrations exist (Mattson et al. 2006). Using Lyngbya cultures incubated in a series of 

nitrate amendments, Cowell and Dawes (2004) found that, at the end of the nutrient amendment 

experiments, both the biomasses and growth rates were low in treatment groups with nitrate 

concentration at or below 300 μg/L, while the growth rates and biomass were significantly higher 

in treatments with nitrate concentrations at or higher than 600 μg/L. In addition, the experiment 

also showed that the biomass and growth rate in 300 and 70 μg/L treatment groups were 

similar, suggesting that further reduction of nitrate concentration below the 300 μg/L level 

probably would not achieve dramatic further reduction of L. wollei. A nitrate concentration of 

300 μg/L should be appropriate in controlling L. wollei. 

2) Relationship between periphyton biomass and cell density and nitrate concentration

The nitrate target suggested by the Rainbow River study was corroborated by the findings of 

Hornsby et al. (2000), who evaluated periphyton and water quality data collected from the 

Suwannee River and two tributaries including the Withlacoochee River and Santa Fe River. 

Much of the length of the Suwannee River was heavily influenced by spring inflow, and the algal 

communities appeared to be generally similar in composition to those in the Wekiva River and 

Rock Springs Run. Therefore, results from this river were considered applicable to the Wekiva 

River and Rock Springs Run (Mattson et al., 2006). This study showed positive correlations for 

both periphyton biomass versus nitrate concentration and cell density versus nitrate 

concentration. The functional relationships of periphyton biomass (represented as ash free dry 

mass, or AFDM) versus nitrate concentration and cell density versus nitrate concentration are 

shown in Figures 3.1-A, and –B, respectively. Data presented in these figures represent longterm average biomass, cell densities, and nitrate concentrations measured at 13 stations across 

the Suwannee River system (including the Withlacoochee River and Santa Fe River). Figure 

3.2 shows locations of these stations. As shown in Figures 3.1-A and –B, both periphyton 

biomass and cell density per unit increase of nitrate concentration significantly increased when 

nitrate concentration reached a level between 200 – 300 μg/L. 

To narrow down the nitrate concentration that may significantly impact the periphyton biomass 

and cell density per unit increase of nitrate concentration, the Department contracted Professor 

Xufeng Niu of the Department of Statistics, Florida State University, to conduct a change-point 

analysis. The applied method fits a step function through observed data by examining the 

probability of each data point as the change-point. A nitrate concentration change point was 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

11

Figure 3.1-A Relationship between mean nitrate concentration and mean 

periphyton cell density from sampling sites on the Suwannee, 

Santa Fe, and Withlacoochee Rivers (Mattson et al. 2006). 

Figure 3.1-B Relationship between mean nitrate concentration and mean 

periphyton biomass from sampling sites on the Suwannee, 

Santa Fe, and Withlacoochee Rivers (Mattson, 2006). 

Mean NOx vs. Mean Biomass

1

2

3

4

5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Mean NOx (mg/L)

AFDW g / m2

Mean NOx vs. Mean Cell Density

0

100000

200000

300000

400000

500000

600000

700000

800000

900000

1000000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Mean NOx (mg/L)

Cells / cm2
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

12

 

Figure 3.2. Locations of water quality stations from which nitrate and 

periphyton abundance samples were collected and used for 

the change-point analysis 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

13

identified at a 5% significant level if the change of cell density or periphyton biomass caused by 

the nitrate concentration was 3.5 times higher (the T test critical value) than the standard error 

of the change of cell density or periphyton biomass The identified step function (the changepoint model) was also compared to linear regression and non-linear regression models for its 

goodness-of-fit and the extent of over-fitting based on the Bayesian Information Criterion (SBC). 

For both periphyton cell density and periphyton biomass, change-point step functions were 

shown to be the best model among the models tested. This supports the use of the changepoint model identified in the T test. Details of the change-point analyses are provided in 

Apendix B. 

For the functional relationship between cell density and nitrate concentration, the change-point 

step function identified two cell density levels (Table 3 in Apendix B). One level is about 

162,998 cells/cm2

 (P = 0.009), and the other is about 162,998 + 453,295 = 616,293 cells/cm2 (P 

= 0.0001). In this study, the 162,998 cells/cm2

 was considered as the baseline condition under 

which no significant nitrate impact was detected. The nitrate concentration that significantly 

changed the cell density level from 162,998 cells/cm2

 to 616,293 cells/cm2 was identified by the 

change-point step function as 0.401 mg/L (Table 2 in Apendix B), indicating that, to prevent the 

periphyton cell density from switching to the higher level, the nitrate concentration should not 

exceed 0.401 mg/L. In addition, based on Table 2 and Figure 4 of Appendix B, the cell 

density switch occurred when the nitrate concentration reached between 0.286 mg/L and 0.401 

mg/L. Although the nitrate concentration that started the cell density switch could be any nitrate 

concentration between 0.286 mg/L and 0.401 mg/L, 0.286 mg/L was chosen in this TMDL as 

the nitrate target to control periphyton cell density to make the nitrate target conservative. 

For the functional relationship between periphyton biomass and nitrate concentration, the 

change-point step function identified two biomass levels (Table 5 in Apendix B). One level is 

about 1.73 g/m2

 (P= 0.00), and the other level is about 1.73 + 2.42 = 4.15 g/m2 (P = 0.0001). In 

this study, the 1.73 g/m2

 was considered as the baseline condition under which no significant 

nitrate impact was detected. The nitrate concentration that significantly changed the biomass 

level from 1.73 g/m2

 to 4.15 g/m2 was identified by the change-point step function as 0.420 mg/L 

(Table 4 in Apendix B), indicating that, to prevent the periphyton biomass from switching to the 

higher level, the nitrate concentration should not exceed 0.420 mg/L. In addition, based on 

Table 4 and Figure 6 of Appendix B, the highest observed nitrate concentration that allowed 

the biomass baseline condition was between 0.401 mg/L and 0.0.420 mg/L. Although the 

nitrate concentration that started the biomass switch could be any nitrate concentration between 

0.401 mg/L and 0.420 mg/L, 0.401 mg/L was chosen in this TMDL as the nitrate target to control 

periphyton biomass to make the nitrate target conservative. 

 

Based on the above discussion, nitrate concentrations lower than 0.286 mg/L and 0.401 mg/L 

should be appropriate to maintain periphyton cell density and biomass at baseline conditions, 

respectively. Because 0.286 mg/L is lower than 0.401 mg/L, 0.286 mg/L was selected for the 

TMDL target to maintain both cell density and biomass at baseline conditions. Choosing the 

lower nitrate concentration between 0.286 and 0.401 mg/L also adds to the margin of safety of 

the nitrate TMDL. 

3) Relationship between ecological efficiency and nitrate concentration

 

Wetland Solutions, Inc (WSI, 2005) studied the effects of nutrient concentrations on the 

community metabolic rates in the Wekiva River, Rock Springs Run, and two reference creeks 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

14

(ASC and JC). The gross community primary production, community respiration, net primary 

production, and ecological efficiency were measured and examined. The community metabolic 

parameter shown to have a significant functional relationship with nutrient concentrations was 

ecological efficiency, which is defined as the quotient between the rate of gross primary 

productivity (GPP) and the incident photosynthetically active radiation (PAR) during a specified 

time interval. It is an ecosystem-level property that estimates the overall efficiency of an aquatic 

ecosystem to utilize incident solar radiation. 

To examine the effect of nitrate concentrations on the ecological efficiency, experimental sites 

were set up in streams with different nitrate concentrations. Figures 3.3 - 3.5 show locations of 

these segments. Two test stream segments were set up in both the Wekiva River and Rock 

Springs Run, and one test stream segment was set up for each of Alexander Springs Creek 

(ASC) and Juniper Creek (JC). As shown in Figure 3.3, the test segment RSR-SEG1 (one of 

the test segments for Rock Springs Run) is located close to the spring vent where high nitrate 

concentrations are typically observed. Segment RSR-SEG2 is a downstream site located close 

to the confluence of Rock Springs Run and the Wekiva River, and the average nitrate 

concentration at this site was lower than 300 μg/L at the time the study was conducted. 

For the Wekiva River, WR-SEG1 is the test segment located close to the Wekiva Spring, where 

high nitrate concentrations were observed. Segment WR-SEG2 is the downstream segment 

where nitrate concentration decreased to about 300 μg/L at the time the study was conducted. 

Table 3.1 lists ecological efficiency results and nitrate+nitrite concentrations from these test 

segments. 

Table 3.1. Ecological efficiencies and nitrate concentrations at test 

segments in WRMS, RSR, JC, and ASC. 

Test 

Segments 

Ecological 

Efficiency 

(g O2/mol) 

Nitrate+Nitrite 

(mg/L) 

Water Color 

(PCU) Period of Record 

WR-SEG1 0.11 1.09 8.75 4/29/2005 5/27/2005 

WR-SEG2 0.22 0.300 40.0 4/28/2005 5/26/2005 

RSR-SEG1 0.08 1.15 26.3 4/1/2005 4/20/2005 

RSR-SEG2 0.05 0.270 193 4/1/2005 4/21/2005 

ASC-SEG1* 0.36 0.009 58.8 4/29/2005 5/24/2005 

JC-SEG1** 0.47 0.015 38.8 3/31/2005 4/18/2005 

WR-SEG1 0.11 1.24 21.9 8/10/2005 8/31/2005 

WR-SEG2 0.14 0.365 96.3 8/9/2005 9/1/2005 

RSR-SEG1 0.05 1.03 77.5 7/12/2005 8/3/2005 

RSR-SEG2 0.07 0.045 350 7/12/2005 8/4/2005 

ASC-SEG1* 0.23 0.018 150 8/9/2005 8/29/2005 

JC-SEG1** 0.26 0.023 65.0 7/11/2005 8/1/2005 

*Test segment in Alexander Springs Creek. 

**Test segment in Juniper Creek. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

15

Figure 3.3. Wekiva River and Rock Springs Run stream segments for ecological 

evaluations. This figure was cited from Wetland Solution, Inc. (2005).
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

16

 

Figure 3.4. Juniper Creek stream segments for ecological evaluations. This figure 

was cited from Wetland Solution, Inc. (2005). 

Figure 3.5. Alexander Springs Run stream segments for ecological evaluations. This 

figure was cited from Wetland Solution, Inc. (2005). 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

17

Table 3.1 shows a general trend that the ecological efficiencies of the test segments with high 

nitrate concentration, e.g. WR-SEG1 and RSR-SEG1 were significantly lower than test 

segments of reference streams, e.g. ASC-SEG1 and JC-SEG1. For the Wekiva River, 

ecological efficiency significantly increased at the downstream test segment WR-SEG2 where 

nitrate concentrations significantly decreased. However, similar increases in ecological 

efficiency was not observed at the downstream segment (RSR-SEG2) located in Rock Springs 

Run even when the nitrate concentration at this segment also significantly decreased. One 

possible reason for the suppressed ecological efficiency at RSR-SEG2 is the high water color. 

As shown in Table 3.1, water color at RSR-SEG2 was dramatically higher for both test events 

than color levels observed for the other segments. High color at RSR-SEG2 suggested that the 

gross primary production (GPP) at this segment could be depressed due to the low light 

availability and the community could be dominated by heterotrophic organisms. Therefore, the 

amount of organic carbon that can be fixed by the unit photosynthetically active radiation (PAR) 

could become naturally lower even when the nitrate concentration was not high. 

Another explanation for the low observed ecological efficiency at RSR-SEG2 could be the type 

of aquatic flora dominating the community in this segment. Table 3.2 lists the percent stream 

bottom covered by different vegetation types in different test segments. These data were 

collected by Wetland Solutions, Inc (2005). The plant community data were aggregated into 

several different functional groups, including benthic algae (ALG), emergent aquatic plants 

(EMA), floating aquatic plants (FAP), submerged aquatic plants (SAV), shrubs (SHR), and vines 

(VINE). 

Table 3.2. Percent stream bottom covered by vegetation of different 

functional groups at different test segments. 

 

Functional Test Segments 

Vegetation 

Groups WR-SEG1 WR-SEG2 RSR-SEG1 RSR-SEG2 ASC-SEG1 JC-SEG1 

ALG 37.73 7.32 20.21 0.00 1.77 1.82 

EMA 5.03 9.13 10.00 37.11 19.16 1.22 

FAP 4.77 8.11 10.73 26.65 8.50 1.56 

SAV 1.45 27.87 4.49 0.00 48.58 4.21 

SHR 1.09 0.07 0.00 1.22 0.08 1.13 

VINE 0.00 0.22 0.08 0.00 0.02 0.00 

As shown in Table 3.2, unlike at any other sites, no benthic algae (ALG) or submerged aquatic 

vegetation (SAV) were observed at RSR-SEG2, the downstream site of the Rock Springs Run. 

This could be caused by the high water color observed at this segment. The dominant 

vegetation communities at RSR-SEG2 were emergent (EMA) and floating aquatic plants (FAP). 

As the measurement of ecological efficiency was based on measuring the water column 

dissolved oxygen concentration, and even if EMA and FAP can fix a significant amount of 

organic carbon using the PAR, less oxygen will be released into the water column than if the 

community is dominated by ALG and/or SAV. Therefore, it is not totally unexpected that low 

ecological efficiency was observed at RSR-SEG2. The low ecological efficiency observed at 

RSR-SEG2 might not be directly related to the nitrate concentration of this segment. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

18

Based on the above discussion, data measured at RSR-SEG2 were excluded when analyzing 

the relationship between ecological efficiency and nitrate concentration. Figure 3.6 shows the 

correlation between the ecological efficiency and nitrate concentration. 

The target ecological efficiency for this TMDL was chosen as the average of summer time 

ecological efficiency measurements taken from the reference sites [ASC-SEG1 (8/9/2005 – 

8/29/2005) and JC-SEG1 (7/11/2005 – 8/12/2005)] in the two sampling events (Table 3.1). As 

shown in Table 3.1, ecological efficiency varied greatly in the two reference creeks even when 

nitrate concentrations were low. Defining the target ecological efficiency based on summer data 

would address the influence of pollutant loadings from both springs and surface runoff (influence 

from nonpoint source loading is more significant in the summer rainy season than in the winter 

dry season). The target ecological efficiency defined using this method is 0.25 g O2/mol. Using 

the ecological efficiency – nitrate concentration equation defined in Figure 3.6, the target nitrate 

concentration is 0.293 mg/L or 293 μg/L. 

The target nitrate concentration based on ecological efficiency is very close to the target nitrate 

concentrations suggested by the results from the Rainbow River and Suwannee River studies, 

which are about 300 μg/L and 286 μg/L, respectively. Therefore, the Department established a 

final target concentration of 286 μg/L, which is the nitrate target derived from the change – point 

analysis based on periphyton data. This target is lower than both 293 μg/L and 300 μg/L and 

therefore is the most conservative target. It is protective of the structure and function of aquatic 

flora in the Wekiva River and Rock Springs Run and adds to the margin of safety (MOS) of this 

TMDL. 

Figure 3.6. Correlation between ecological efficiency and nitrate concentration in 

WR, RSR, ASC, and JC. 

The SJRWMD proposed a biologically effective nitrate concentration of 250 μg/L based on the 

Rainbow River Lyngbya wollei nutrient amendment experiment. Given the natural variation of 

y = -0.2034x + 0.3096

R2

 = 0.6692

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Nitrate concentration (mg/L)

Ecological efficiency (g O2/mol)

Target NOx = 0.293 mg/L 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

19

nitrate concentrations in ambient water, the SJRWMD, when proposed 250 μg/L as the nitrate 

effective concentration, conducted a statistical analysis to determine a nitrate target 

concentration that would ensure that the 250 ug/L target would be met the majority of the time. 

The SJRWMD concluded that the targets should ensure compliance with the 250 ug/L target at 

least 90% of the time and the statistical analysis indicated that the nitrate target should be 216 

μg/L for Wekiva River and 221 μg/L for Rock Springs Run. A detailed description of the 

statistical method used by the SJRWMD is provided by Mattson et al. (2006). 

After carefully reviewing all the above studies from which the SJRWMD’s nitrate target (250 

μg/L) was derived, the Department believes that it is not necessary to limit the percentage of 

time the 250 μg/L target can be exceeded and instead established the target as a monthly 

average concentration. This is mainly because the changes in aquatic vegetation biomass do 

not respond to the change of nutrient concentration in an instantaneous manner. Therefore, 

short-term exceedence of this target concentration may not produce negative biological or 

ecological effects. The 286 μg/L nitrate range obtained from the Suwannee River study was 

based on the correlation between the long-term average nitrate concentration and long-term 

average cell density and biomass. Therefore the 286 μg/L should be considered as a long-term 

average target instead of an instantaneous value. The nitrate range suggested by the Lyngbya

study was from a nutrient amendment experiment. The value can be considered as a threshold. 

However, the significant differences in growth rate and biomass between the above 600 μg/L 

treatment groups and below 300 μg/L treatment groups were not observed until 8 to 12 days 

after the nutrient amendment study started. This apparently suggested a time lag between the 

change of the nitrate concentration and the response from Lyngbya. In addition, the Lyngbya 

nutrient amendment study was conducted under the tightly controlled laboratory condition with 

no competition from other periphyton and plants, no grazing from aquatic animals, no removal 

effects from the shearing force of the stream flow, and no light attenuation from changing of 

water color. These factors are very common in natural stream systems such as the Wekiva 

River and RSR. All these natural processes could significantly slow down the response of 

Lyngbya to the change of nitrate concentration and further elongate the response time delay. 

Therefore, treating the 300 μg/L nitrate concentration obtained from the Lyngbya study as an 

exact instantaneous value is not necessary. 

The same concept also applies to the target nitrate value obtained from the correlation between 

the ecological efficiency and the nitrate concentration. The ecological efficiency shown in Table 

3.1 and Figure 3.6 are average values for a period from three to four weeks (WSI, 2005). The 

nitrate target value derived from an equation, based on average ecological efficiency, should not 

be treated as an exact instantaneous value. It is more appropriate that the target number be 

treated as an average target, over a certain time period. 

Based on above discussions, the Department established the 286 μg/L threshold as a monthly 

average target concentration. To address the temporal variation of nitrate concentration in the 

Wekiva River, the Department analyzed the monthly variation of nitrate concentration in a 

Wekiva River WBID with high nitrate concentrations (WBID 2956) using the data collected 

during 1999 through 2005. The monthly variation of nitrate concentration in this WBID is shown 

in Figure 3.7. It appears that the high nitrate concentrations typically appear during the winter, 

early spring, and later fall, while concentrations are typically lower during the summer season. 

This observation is not a surprise because one of the major nitrate contributors to the Wekiva 

River is springs, and summer months typically have higher rainfall and dilution by the surface 

runoff could play an important role in reducing the in-stream nitrate concentration. Expressing 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

20

the target as a monthly average provides a margin of safety because restoration activities 

designed to address the higher winter nitrate concentrations should help ensure that summer 

nitrate concentrations are even lower. 

Toxicity effects of nitrate concentration in the Wekiva River and Rock Springs Run were also 

discussed by the SJRWMD in the nutrient PLRG. However, all the discussions were based on 

literature published nitrate toxicity studies conducted in other waterbodies. All these studies 

concentrated on the acute toxicity effects of nitrate, and chronic effects were only implied by 

multiplying the acute toxicity results by various safety factors. At the time this TMDL was 

developed, no information or measurements specific to the Wekiva River and Rock Springs Run 

indicated that the existing nitrate concentration has caused any toxic effects to aquatic fauna in 

these waterbodies. In contrast, results from 10 Stream Condition Index (SCI) conducted in the 

upper reach of Wekiva River (WBID 2956) from 1999 through 2004 showed that benthic 

macroinvertebrate communities were in good or excellent condition. Results from 2 BIORECON 

and 8 SCIs for the Rock Springs Run (WBID 2967) in 1997, 1999, and 2002 through 2004 also 

showed benthic macroinvertebrate communities were in good or excellent condition. 

Apparently, even under the existing high nitrate concentrations, no direct toxic impacts were 

observed with the benthic macroinvertebrates communities, which are typically considered 

sensitive index organisms to toxic materials. The 286 μg/L target nitrate concentration therefore 

should be sufficient to protect the aquatic fauna in the Wekiva system. 

Figure 3.7. Monthly variation of nitrate concentration in upstream WRMS 

In conclusion, based on the information currently available, the Department believes that a 

monthly average nitrate concentration of 286 μg/L should be sufficiently protective of the aquatic 

flora and fauna in the Wekiva system. This target concentration is higher than long-term 

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

1.000

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Month

Nitrate concentration (mg/L)
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

21

median nitrate concentrations of the two reference streams – ASC and JC, which are 50 and 80 

μg/L, respectively (Mattson et al. 2006). However, TMDL targets are designed to identify the 

threshold above which impairment is expected to occur, and natural aquatic systems have 

assimilative capacities for nutrients. An elevated pollutant concentration in the system alone 

does not necessarily constitute impairment as long as there is no negative response from the 

local aquatic flora or fauna. Based on information provided above, 286 μg/L nitrate is the target 

concentration that will not cause an imbalance in the aquatic flora and fauna in the Wekiva River 

and Rock Springs Run. 

3.2.2.2. Setting the total phosphorus target 

The total phosphorus target (TP) for the Wekiva River and Rock Springs Run was established 

based on the studies on the attached algal communities conducted by the GreenWater Labs 

(2005) and the ecosystem metabolism studies conducted by the Wetland Solution, Inc. (2005). 

The GreenWater Labs collected attached algal samples from 15 sampling sites along the 

Wekiwa Spring/Wekiva River and 9 sites along Rock Springs/Rock Springs Run. Each site was 

sampled in winter during December 2004-January 2005 and in summer in June of 2005. At 

each site, nutrient (include nitrogen and phosphorus) samples were collected at the same time 

that attached algal samples were collected and analyzed. Figure 3.8 shows the locations of 

these sampling sites in the Wekiva River and Rock Springs Run. 

 

The SJRWMD analyzed the relationship between Chl a concentration, algal biovolume, ash free 

dry mass of algal samples, and percent blue-green and green algal biovolume in the total algal 

biovolume and TP concentration. These analyses yield a threshold relationship between 

percent biovolume of blue-green and green algae and TP concentration (Figure 3.9). High 

percent biovolumes of blue-green and green algae were observed when the TP concentration 

increased above 90 μg/L. 

The Department also analyzed the relationship between the ecological efficiency and TP data 

collected by the Wetland Solutions, Inc. Table 3.3 lists the ecological efficiency and TP data 

used in this analysis and test stream segments from which these data were collected. Again, 

because of the high color and the vegetation communities dominated by emergent and floating 

aquatic vegetation at RSR-SEG2, data from this sampling site were excluded from the analysis. 

Figure 3.10 shows the correlation between the ecological coefficient and TP concentration at 

these test segments. Again, 0.25 g O2/mol was chosen as the target ecological efficiency. 

Based on this target and the correlation equation shown in Figure 3.10, the target TP 

concentration should be 65 μg/L. Because the 65 μg/L TP target is lower than the 90 μg/L 

concentration derived from GreenWater labs attached algal studies, it should addresse both the 

ecological efficiency and blue-green and green algae dominance issues. Therefore, 65 μg/L 

was chosen as the final TP target for this TMDL. 

There was no seasonal pattern for the percentage blue-green and green algae indicating a 

critical season or month. There were not enough data to determine when would be the critical 

season for the low ecological efficiency. Analysis on the monthly distribution of TP 

concentration in the Wekiva River indicated that high TP concentrations were typically observed 

during the summer months, which is the typical growth season. Therefore, there is not enough 

information to determine whether establishing the 65 μg/L as the annual average target would 

be sufficiently protective. As the 65 μg/L target was derived from the ecological efficiency 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

22

studies and these studies had a time scale of close to one month, theTP threshold of 65 μg/L 

was expressed as a monthly target for this TMDL. 

 

Figure 3.8. Sampling stations used by the GreenWater Labs for attached algal 

studies in the Wekiva River and Rock Springs Run (GreenWater Labs, 

2005) 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

23

 

 

Figure 3.9. Relationship between TP concentration and percent biovolume of bluegreen and green algae in the Wekiva River and Rrock Springs Run 

(Mattson et al. 2006) 

Table 3.3. Ecological efficiencies and TP concentrations at test segments in 

theWekiva River (WR), Rock Springs Run (RSR), Juniper Creek (JC), and 

Alexander Springs Creek (ASC) 

Test 

segments

Ecological 

efficiency 

(g O2/mol)

TP 

concentration 

(mg/L)

Water color 

(pcu) Period of Record

WR-SEG1 0.11 03125 8.75 4/29/2005 5/27/2005

WR-SEG2 0.22 0.118 40.0 4/28/2005 5/26/2005

RSR-SEG1 0.08 0.091 26.3 4/1/2005 4/20/2005

RSR-SEG2 0.05 0.096 193 4/1/2005 4/21/2005

ASC-SEG1* 0.36 0.045 58.8 4/29/2005 5/24/2005

JC-SEG1** 0.47 0.024 38.8 3/31/2005 4/18/2005

WR-SEG1 0.11 0.158 21.9 8/10/2005 8/31/2005

WR-SEG2 0.14 0.141 96.3 8/9/2005 9/1/2005

RSR-SEG1 0.05 0.097 77.5 7/12/2005 8/3/2005

RSR-SEG2 0.07 0.180 350 7/12/2005 8/4/2005

ASC-SEG1* 0.23 0.055 150 8/9/2005 8/29/2005

JC-SEG1** 0.26 0.025 65.0 7/11/2005 8/1/2005

*Test segment in Alexander Springs Creek. 

**Test segment in Juniper Creek. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

24

 

Figure 3.10. Correlation between ecological efficiency and TP concentration in the 

Wekiva River, Rock Springs Run, Alexander Springs Creek, and Juniper 

Creek. 

3.2.2.3. Summary on the water quality targets 

Based on above analyses, the nutrient targets for this TMDL are monthly averages of 286 μg/L 

for nitrate and 65 μg/L for TP. These water quality targets apply to both the Wekiva River and 

Rock Springs Run. These targets will protect the structure and functions of the aquatic 

vegetation communities and also protect the aquatic fauna based on historic SCI and 

BIORECON results for benthic macroinvertebrates. 

y = -2.0335x + 0.3817

R2

 = 0.5445

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

TP concentration (mg/L)

Ecological Efficiency (g O2/mol)

Target TP = 65 μg/L 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

25

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 target 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 NPDES Program. These 

nonpoint sources included certain urban stormwater discharges, including those from local 

government master drainage systems, construction sites over five 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 (see Section 6.1 on Expression and Allocation of the TMDL). 

However, the methodologies used to estimate nonpoint source loads do not distinguish between 

NPDES and non-NPDES stormwater discharges, and as such, this source assessment section 

does not make any distinction between the two types of stormwater. 

4.2 . Potential Sources of pollutants in Watersheds of the Wekiva River and RSR 

4.2.1 Point Sources 

4.2.1.1 Wastewater Point Sources 

There are eight wastewater facilities that are authorized to discharge to surface waters within 

the drainage basin of the Wekiva River. No NPDES permitted facilities were identified in the 

subbasin of Rock Springs Run. Table 4.1 lists the permit numbers, names, business types, and 

permit types of these facilities, and Figure 4.1 shows the locations of these facilities. Five of the 

facilities are concrete batch plants and operate under generic permits. These facilities may 

discharge wastewater with high pH, high dissolved and total suspended solids, but elevated 

nitrate and TP concentrations from these facilities are typically not expected. The other three 

are domestic wastewater facilities: the Wekiva Hunt Club WWTF (FL0036251), Altamonte 

Springs Regional Water Reclamation Facility (FL0033251), and SCES/Yankee Lake WRF 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

26

(FL0042625). These facilities have the potential to contribute nitrate and TP to Wekiva River 

and, as such, are described in more detail below, however they are not considered significant 

sources of nutrient loading to the Wekiva River 

Table 4.1. NPDES permitted facilities identified in the drainage basin discharge to 

Wekiva River. 

Permit Number Facility Name Wastewater Type Permittee

FL0042625 SCES/Yankee Lake 

WRF Domestic Wastewater 

Seminole County 

Environmental 

Services 

FL0033251 

Altamonte Springs 

Regional Water 

Reclamation Facility 

Domestic Wastewater City of Altamonte 

Springs 

FL0036251 Wekiva Hunt Club 

WWTF Domestic Wastewater Sanlando Utilities Corporation 

FLG110301 

Florida Rock 

Industries – Carder 

Road CBP 

Industrial Wastewater Florida Rock 

Industries 

FLG110557 

Rinker Materials – 

Lockhart Concrete 

Batch 

Industrial Wastewater Rinker Materials 

FLG110231 Action Ready Mix 

CBP Industrial Wastewater Action Ready Mix 

CBP 

FLG110672 CEMEX – Lockhart 

CBP Industrial Wastewater CEMEX – Lockhart 

CBP 

FLG110464 Inland Materials – 

Orlando CBP Industrial Wastewater Inland Materials 

SCES/Yankee Lake WRF is located in Sanford, close to the most downstream segment of 

Wekiva River (Figure 4.1). It has a 2.5 MGD annual average daily flow (AADF) permitted 

capacity, with advanced wastewater treatment facilities, including influent screening, grit 

removal, anoxic basin followed by aeration chamber, chemical feed, clarification, tertiary 

filtration, disinfection by chlorination, and aerobic digestion of residuals. Residuals of the facility 

are hauled to the SCES Greenwood Lakes WWTF for additional treatment. 

The majority of the treated wastewater from SCES/Yankee Lake WRF is reused. The facility 

has a slow rate land application system with an anticipated capacity of 3.707 MGD AADF, 

consisting of a reclaimed water transmission/distribution system for public access irrigation of 

recreational areas, residential lawns, golf course, urban landscapes, road medians, nurseries 

and citrus groves within its Reuse Service Area. Wet-weather or reject flows are sent to three 

backup systems including 1) a 0.35 MGD AADF permitted capacity slow-rate restricted public 

access system that consists of a 72.6 acre sprayfield, 2) a 0.36 MGD AADF permitted capacity 

rapid infiltration basin system that consists of five rapid infiltration basins (RIBs) with a total 

wetted area of 800,000 square feet, and 3) a 0.75 MGD AADF permitted capacity wet-weather 

back-up discharge to an upland/receiving wetland system.
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

27

 

Figure 4.1. NPDES permitted facilities located in the Wekiva River drainage 

area.
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

28

The upland/receiving wetland system is not anticipated to discharge to other surface waters 

except under extreme wet-weather conditions, which may create intermittent flow through Sulfur 

Creek, which discharges from Yankee Lake through the receiving wetlands. This infrequent 

discharge may eventually reach the lower reach of the Wekiva River close to its confluence with 

St. Johns River. The permit issued to the facility requires the permittee to monitor the water 

quality in Sulfur Creek monthly when there is flow through Sulfur Creek to ensure that the 

wetland operation does not adversely impact the water quality of the creek. Based on the 

information from the Department’s Central District Office, there have only been four months 

when there was flow in Sulfur Creek since July 2005, when the facility started to discharge to 

the upland/receiving wetland system. Table 4.2 shows monitoring results in Sulfur Creek 

upstream and downstream of the effluent point and at the effluent point during the four months 

period. 

Table 4.2. Results of water quality monitoring in Sulfur Creek upstream and 

downstream of the effluent point and at the effluent point when flow 

appeared in the creek. 

August 3, 2005 October 5, 2005 November 9, 2005 March 1, 2006 Parameter Upst Downst Efflu Upst Downst Efflut Upst Downst Efflu Upst Downst Efflu

ammonia, 

mg/L 0.055 0.052 0.026 0.037 0.036 0.024 0.027 0.023 0.043 0.026 0.043

TKN, mg/L 1.1 0.97 1.1 1.2 1 0.93 0.81 

TN, mg/L 1.1 0.97 0.840 1.1 1.2 1.2 1 0.93 1.400 0.81 2.5

nitrite+nitrate, 

mg/L

0.020 

U

0.020 

U

0.0075 

U

0.0075 

U

0.0075 

U

0.0075 

U

0.0075 

U

0.0075 

U

nitrate 0.200 0.056 0.048 0.46 0.560 1.636

TP, mg/L 0.050 

U

0.050 

U 0.320 0.22 0.09 0.071 0.180 0.017 0.012 U 0.15

Flow, day 

MGD 1.757 1.588 0.512 0.853

As shown in Table 4.2, in no cases for the four monitoring events were the nitrate and TP 

concentrations downstream of the effluent point significantly higher than those upstream of the 

effluent point, indicating that the discharge did not have any significant negative impact on 

Sulfur Creek water quality. This also indicates that the occasional backup discharge from the 

SCES/Yankee Lake WRF into the upland/receiving wetland system is not a significant source of 

nitrate or TP to the WR and RSR. 

The Altamonte Springs Regional Water Reclamation Facility is located in the southeastern part 

of the Wekiva Study Area. The facility currently has a 12.5 MGD AADF permitted discharge to 

Little Wekiva River (Figure 4.1). However, the majority of the treated wastewater from the 

facility has been directed to reuse by the City of Altamonte Springs for purposes of irrigation 

within the 5,900 acre Reuse Service Area consisting of city parks, street, and highway medians, 

city-owned nurseries, residential and commercial lawns. Reclaimed water is also used for street 

cleaning, dust control, fire protection, water-to-air heat pumps, chillers (cooling water towers), 

and at automatic car washes. The actual discharge from the facility to the Little Wekiva River is 

significantly lower than the permitted 12.5 MGD (Table 4.3), with a long-term annual average 

discharge of 1.2 MGD. In addition, the facility also has a planned project that would take the 

excess reclaimed water to the City of Apopka for reuse and recharge, which will further 

decrease the discharge to the surface water. Table 4.3 lists the long-term monthly average 

daily discharge rate from the facility to the Little Wekiva River, the monthly average TP 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

29

concentration of the discharge, and monthly TP loadings from the facility to surface waters. 

This summary was based on the discharge rate measured in 1999 through 2006, and TP 

concentrations in 2000 through 2002. No routine monitoring results of nitrate for the facility 

were available to the Department at the time this TMDL was developed. 

 

Table 4.3. Long-term monthly average daily discharge rate, TP monthly average 

concentrations, and long-term TP monthly average loading for Altamonte 

Springs Regional Water Reclamation Facility. 

Month

Monthly Average 

Daily Flow 

(MGD)

Monthly flow 

(million 

gallons/month)

TP (mg/L) TP loading 

(lbs/month)

January 0.80 24.88 1.39 287.9

February 0.87 24.40 1.24 252.3

March 1.54 47.82 1.46 583.4

April 1.08 32.25 1.53 412.4

May 1.15 35.61 1.71 508.8

June 1.04 31.07 1.70 440.6

July 1.08 33.44 1.51 422.0

August 1.41 43.67 1.44 524.3

September 2.03 60.86 1.35 686.6

October 1.45 45.08 1.67 630.4

November 0.89 26.57 1.52 337.5

December 1.40 43.53 1.52 554.2

Mean 1.23 38.07 1.50 470.0

Influence of the discharge on the TP concentration of the Little Wekiva River is shown in Figure 

4.2. TP concentrations measured at water quality stations upstream and downstream of the 

discharge point were analyzed. As shown in Figure 4.2, upstream of the WRF discharge point, 

the long-term average TP concentration of Lake Lotus, which is located within the Little Wekiva 

Canal basin and is close to the confluence of Little Wekiva Canal and the Little Wekiva River, is 

about 70 μg/L. This TP concentration is very close to the TP concentration measured from a 

water quality station (21FLORANLWD) located close to the inlet of the lake, which is about 60 

μg/L. On the Little Wekiva River side, the long-term average TP concentration of Spring Lake, 

which is also located upstream of the WRF discharge point, is about 40 μg/L. The TP 

concentrations from all the stations upstream of the discharge point are significantly lower than 

the TP concentrations of the WRF’s efflluent, which is about 1500 μg/L (Table 4.3). 

Immediately downstream of the discharge point, the long-term average TP concentrations of the 

Little Wekiva River increases to about 190 μg/L (based on data from 21FLSEM WET, Figure 

4.2), indicating a significant impact of the discharge on the river TP concentration. This high TP 

concentration, plus high TP concentrations in the discharges from several springs (Table 4.11 

of this report), including Starbuck Springs (a second magnitude spring, with a long-term average 

discharge 14.3 cfs, and TP concentration 160 μg/L), Sanlando Springs (a second magnitude 

spring, with a long-term average discharge 19.6 cfs, and TP concentration 180 μg/L), and Palm 

Springs (a third magnitude spring, with a long-term average discharge 6.88 cfs, and TP 

concentration 120 μg/L), result in a long-term average TP concentration of 170 μg/L measured 

from a station (21FLSJWMLW-WUR) located at the outlet of the Little Wekiva River into the 

main stem of the Wekiva River, indicating the influence of the WRF discharge on the TP 

concentration of the main stem of the Wekiva River. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

30

 

Figure 4.2. Influence of the Altamonte Springs Regional WRF on the spatial 

distribution of TP concentration in the Little Wekiva River. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

31

Subsequent removal of TP discharged from the WRF during stream transport may not be 

significant. As was shown in Figure 4.2, from the station immediately downstream of the 

effluent point (21FLSEM WET) to the outlet of the Little Wekiva River to the Wekiva River main 

stem, the TP concentration did not change significantly. It appears that, to achieve the TP 

target of the Wekiva River main stem, TP loading from the WRF needs to be reduced 

significantly. 

Wekiva Hunt Club WWTF is located about 1.3 miles east of the confluence of Rock Springs Run 

and the Wekiva River. The facility has a 2.9 mgd AADF permit to Sweetwater Creek, which in 

turn discharges to Cove Lake in the northwest, and then to the Wekiva River about 0.4 mile 

downstream of the Rock Springs Run and the Wekiva River confluence. The facility currently 

does not have effluent limits for either TN or nitrate. The TP effluent limits for the facility are 0.4 

mg/L monthly average and 0.5 mg/L for any single sample. 

Long-term monthly average nitrate and TP concentrations of the effluents from the facility were 

analyzed based on effluent data for the period of 1999 through 2006 retrieved from the Permit 

Compliance System (PCS) database and tabulated in Table 4.4. Compared to the annual 

average nitrate target and the monthly average TP target established for the Wekiva River and 

Rock Springs Run, discharge concentrations from the facility are considered very high. Table 

4.4 also lists the long-term monthly average nitrate and TP loadings from the facility. 

While the mean nutrient loads discharged are fairly significant, the discharge nitrate and TP 

concentrations can be significantly attenuated in the process of transport through the 

Sweetwater Creek – Cove Lake system before it reaches the Wekiva River. Based on 

information from the Department’s Central District Office (Chris Ferraro, personal 

communication), the SJRWMD has been working on restoration projects to clean up Cove Lake. 

The SJRWMD funded a project where a deep area south of Cove Lake and Wekiva Springs 

Road was dredged deeper to create a sedimentation basin to allow eroded materials from 

Sweetwater Creek to settle out before the flow reaches Cove Lake. The project may further 

attenuate the nitrate and TP concentrations of the discharge from Wekiva Hunt Club WWTF. 

Table 4.4. Long-term monthly average nitrate and TP concentrations and loadings 

for the effluent discharge from Wekiva Hunt Club WWTF in the period 

from 1999 through 2006. 

Month

Average 

monthly flow 

(million 

Gallon/month)

Nitrate 

concentration 

(mg/L)

TP 

concentration 

(mg/L)

Nitrate loading 

(lb/month)

TP loading 

(lb/month)

January 51 10.43 0.16 4445 68 

February 46 10.67 0.21 4102 81 

March 41 10.12 0.19 3467 65 

April 39 12.12 0.19 3950 62 

May 38 9.46 0.19 3004 60 

June 39 11.35 0.24 3699 78 

July 47 8.88 0.12 3488 47 

August 48 8.45 0.19 3390 76 

September 55 7.96 0.24 3659 110 

October 47 9.74 0.20 3826 79 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

32

November 42 9.85 0.18 3457 63 

December 52 9.12 0.17 3963 74 

Mean 45 9.85 0.19 3704 72 

To analyze the possible attenuation rates for nitrate and TP along the path from the facility 

discharge point to the WR, the Department examined the water quality data collected from 

several monitoring sites along the transport path. These sites include: 

Site #1: Background Sweetwater Creek, upstream of the outfall to Sweetwater Creek; 

Site #2: 2400 feet downstream of the outfall to Sweetwater Creek, and about 200 feet 

 upstream of the southernmost tributary that enters from the creek from the east; 

Site #3: 1000 feet upstream of the Wekiva Springs Road bridge; 

Site #4: Downstream side of the Wekiva Springs Road bridge, 200 feet downstream of 

 the northernmost tributary that enters from the west; 

Site #5: North end of Cove lake at the discharge culvert to Wekiva Marina; 

Site #6: Weir structure located at River Bend Road; 

Site #7: Miami Springs Road bridge, upstream of confluence with Sweetwater Creek; 

Site #8: Wekiva River, downstream of Sweetwater Creek discharge. 

Figure 4.3 shows the locations of these water quality sites. Tables 4.5 and 4.6 show measured 

nitrate and TP concentrations at each sampling site, respectively, during the period from 

January, 2005 through April, 2006. Nitrate and TP concentrations of the effluent discharge are 

also included in Tables 4.5 and 4.6. Figures 4.4-A and -B show the long-term average spatial 

trend of nitrate and TP concentrations at these sampling sites. 

Table 4.5. Nitrate concentrations at different sampling sites along the Sweetwater 

Creek – Cove Lake system 

Unit: mg/L 

Sites 1/05 2/05 3/05 5/05 6/05 7/05 8/05 9/05 10/05 11/05 1/06 2/06 4/06 mean

Site #1 1.53 0.358 0.247 0.329 0.291 1.13 0.432 0.245 0.199 0.424 0.254 0.361 0.289 0.468

Effluent 11.00 7.050 4.740 6.600 9.050 4.300 7.800 8.700 8.600 6.350 9.060 10.080 N/A 7.778

Site #2 1.19 0.687 0.51 0.577 0.401 1.64 0.349 0.338 0.23 0.28 4.13 0.424 0.345 0.854

Site #3 1.05 0.815 0.459 0.589 0.202 1.23 0.374 0.35 0.201 0.286 4.04 0.424 0.389 0.801

Site #4 1.04 0.816 0.476 0.563 0.227 1.23 0.373 0.367 0.155 0.26 3.89 0.407 0.119 0.763

Site #5 1.04 1.3 0.327 0.243 0.019 0.385 0.019 0.402 0.178 0.321 0.574 1.74 0.000 0.504

Site #6 0.229 0.606 0.045 0.042 0.019 0.554 0.022 0.22 0.28 0.335 0.742 1.05 0.000 0.319

Site #7 0.641 0.701 0.504 0.569 0.384 0.273 0.838 0.741 0.705 0.398 0.841 0.739 0.881 0.632

Site #8 0.711 0.696 0.509 0.586 0.457 0.273 0.773 0.714 0.686 0.521 0.834 0.76 0.866 0.645

Table 4.6. TP concentrations at different sampling sites along the Sweetwater Creek 

– Cove Lake system 

Unit: mg/L 

Sites 1/05 2/05 3/05 5/05 6/05 7/05 8/05 9/05 10/05 11/05 1/06 2/06 4/06 mean

Site #1 0.224 0.096 0.093 0.148 0.22 0.28 0.229 0.208 0.136 0.214 0.064 0.09 0.05 0.158

Effluent 0.097 0.240 0.127 0.220 0.840 0.190 0.380 0.670 0.390 0.210 0.110 0.112 N/A 0.299

Site #2 0.196 0.134 0.134 0.115 0.26 0.202 0.279 0.111 0.122 0.119 0.128 0.124 0.102 0.156

Site #3 0.311 0.117 0.107 0.114 0.147 0.25 0.237 0.155 0.095 0.0988 0.134 0.096 0.12 0.152

Site #4 0.192 0.103 0.11 0.108 0.157 0.94 N/A 0.157 0.0841 0.102 0.148 0.092 0.116 0.192

Site #5 0.192 0.034 0.126 0.087 0.103 0.222 0.156 0.188 0.0686 0.133 0.106 0.062 0.174 0.127
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

33

Site #6 0.308 0.069 0.105 0.109 0.115 0.864 0.0686 0.127 0.0719 0.119 0.084 0.136 0.174 0.181

Site #7 0.199 0.065 0.085 0.085 0.074 0.22 0.084 0.02 0.0586 0.108 0.09 0.116 0.112 0.101

Site #8 0.09 0.017 0.098 0.089 0.144 0.22 0.0706 0.02 0.0592 0.114 0.094 0.118 0.104 0.095

As shown in Table 4.5, with the exception of one sampling event in January of 2006, nitrate 

concentrations dramatically decrease by the time the effluent reaches Site #2, which is about 

2,400 feet downstream of the effluent point. A similar trend was also observed for TP (Table 

4.6). In most cases, when the effluent TP concentration was significantly higher than the 

background condition measured at Site #1, a significant decrease in TP concentration was 

observed when the discharge reached Site #2. Nitrate concentration in the stream decreased 

more rapidly than TP, suggesting that nitrate is quickly assimilated by the Sweetwater Creek 

system, instead of being merely diluted by the flow in the creek. 

These downstream trends are readily seen in Figures 4.4-A and –B. On the long-term average 

basis, nitrate concentrations decrease from 7.78 mg/L at the effluent point to about 0.319 mg/L 

at Site #5, while TP concentrations decrease from 0.299 mg/L to 0.127 mg/L at Site #5 (Site #5 

is located at the outlet of Cove Lake and close to the discharge point of Sweekwater Creek into 

WRMS). The decreases in concentration between the effluent point and the outlet of Cove Lake 

represent attenuation rates of 96% for nitrate and 39% for TP. These attenuation rates will be 

used in a later chapter to estimate the wasteload allocation for the facility. 

4.2.1.2 Municipal Separate Storm Sewer System Permittees 

Within the drainage basin of the Wekiva River System, Orange County has a Phase I MS4 

permit (FLS000011). The Florida Department of Transportation (FDOT) District 5 and City of 

Maitland are co-permittees for this permit. Seminole County also holds a Phase I MS4 permit 

(FLS000038) with FDOT District 5, City of Altamonte Springs, and City of Lake Mary being copermittees for this permit. In addition, the City of Orlando holds a Phase I MS4 permit 

(FLS000014). Lake County does not have MS4 permit within the boundary of the drainage 

basin. 

4.2.2 Nonpoint Sources 

Additional nitrate and TP loadings to the Wekiva River system are primarily generated from 

nonpoint sources in the drainage basin. Major nonpoint sources may include, but are not limited 

to, loadings from surface runoff and ground water input from the surficial aquifer as stream 

seepage, as well as spring flows from the Floridan aquifer. 

In this analysis, nitrate and TP loadings from the drainage basin to the Wekiva River system 

were estimated based on annual average rainfall, the area of different landuse categories 

summarized based on the SJRWMD’s year 2000 landuse GIS coverage (scale 1:40,000), and 

runoff coefficients and event mean concentrations (EMCs) of nitrate and TP for different 

landuses (Harper, 2003). The nitrate and TP loadings estimated using this method reflect the 

potential amount of each pollutant that can be generated from different landuses in the drainage 

basin. These loading estimates did not take into consideration the attenuation during the 

pollutant transport across the drainage basin. The loading estimates therefore can be higher 

than the pollutant loadings that eventually reach the Wekiva River systems. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

34

Figure 4.3. Locations of water quality stations along the Sweetwater Creek – Cove Lake 

systems for Wekiva Hunt Club WWTF.
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

35

 

Figure 4.4. Long-term spatial trend of nitrate and TP concentration at different 

sampling sites along the Sweetwater Creek – Cove Lake system. 

B

0.158

0.299

0.156 0.152

0.192

0.127

0.181

0.101 0.095

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

Site #1 Effluent Site #2 Site #3 Site #4 Site #5 Site #6 Site #7 Site #8

Site

TP concentration (mg/L)

A

0.468

0.854 0.801 0.763

0.504

0.319

0.632 0.645

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

4.000

Site #1 Effluent Site #2 Site #3 Site #4 Site #5 Site #6 Site #7 Site #8

Site

Nitrate Concentration (mg/L)

7.78 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

36

4.2.2.1 Land Uses 

Based on the drainage basin delineation provided by the SJRWMD, the Wekiva River system 

drains a basin area of about 240,948 acres. Figure 4.5 shows the boundary of the drainage 

basin and the landuse categories (SJRWMD year 2000 landuse GIS coverage) aggregated 

based on the Florida Landuse Classification Code System (FLUCCS) level one landuse 

classification. Table 4.7 summarizes the landuse area from different landuse areas. According 

to Table 4.7, urban and built-up area occupies about 69,374 acres, which accounts for about 

28.8% of the total drainage basin and ranks first among all the individual landuse categories for 

percent landuse acreage. About 32,464 acres of the basin land are used for various agricultural 

practices. Percent acreage for agricultural landuse is about 13.5%. Natural landuse, including 

rangeland, upland forest, water, and wetlands, when combined, occupy about 135,904 acres, 

which accounts for about 56.4% of the total area of the drainage basin. The remaining about 

1.0% of the basin landuse is comprised of transportation, communications, and utilities. 

Table 4.7. Acreages and percent acreages of different landuse categories for the 

Wekiva River system draingage basin 

Landuse FLUCCS Code Landuse Description Acreages Percent Acreages

1000 Urban and Built-Up 69,374 28.8%

2000 Agriculture 32,464 13.5%

3000 Rangeland 17,362 7.2%

4000 Upland Forest 55,867 23.2%

5000 Water 10,355 4.3%

6000 Wetlands 52,320 21.7%

7000 Barren Land 901 0.4%

8000 Transportation, 

Communications, Utilities. 2,305 1.0%

Total 240,948 100.0%

For loading estimation purposes, level 1 landuse categories were further divided into the subcategories listed in Table 4.8. In addition, Table 4.8 listed the acreage, runoff coefficients, 

nitrate and TP EMCs, and nitrate and TP loadings from these different landuses. A long-term 

annual average rainfall of 51 inches was used for estimating the long-term annual average 

pollutant loading. This number was calculated based on the rainfall data collected from a 

weather station located in Sanford. The period of record is from 1957 through 2002. Table 4.9

lists the percent nitrate and TP loadings from different landuse categories. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

37

Figure 4.5. Principal land uses in the drainage basin of Wekiva River. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

38

 

Table 4.8. Classification of land use categories in the Wekiva River 

watershed 

Event mean 

concentration 

(mg/L) 

Nitrate loading TP loading 

Laduse Acreage 

Runoff 

Coefficie. 

Annual 

Runoff 

(ac-ft/y.) 

Monthly 

Runoff 

(ac-ft/m) 

nitrate TP Annual 

(lb/yr.) 

Month 

(lbs/m.) 

Annual 

(lb/yr.) 

Monthly 

(lbs/m.) 

Agriculture/ 

Golf Course 34615 0.3 44134 3678 0.58 0.34 69622 5802 41293 3441 

Forest and Rural 

Open 55867 0.08 18995 1583 0.31 0.05 16015 1335 2583 215 

Rangeland 17362 0.12 8855 738 0.4 0.34 9633 803 8188 682 

Low-Density 

Residential 17668 0.27 20274 1690 0.63 0.3 34739 2895 16543 1379 

Medium-Density 

Residential 29098 0.37 45757 3813 0.65 0.4 80893 6741 49780 4148 

High-Density 

Residential 6551 0.68 18932 1578 0.67 0.49 34500 2875 25231 2103 

Commercial 5376 0.85 19421 1618 0.67 0.29 35390 2949 15318 1277 

Institutional 1532 0.84 5469 456 1.05 0.15 15619 1302 2231 186 

Industrial/Utility 2499 0.79 8390 699 0.4 0.31 9128 761 7074 590 

Transportation 

Facilities 2305 0.78 7641 637 0.4 0.34 8313 693 7066 589 

Openland 5399 0.16 3671 306 0.31 0.05 3095 258 499 42 

Water 10355 0.5 22004 1834 0.19 0.11 11371 948 6583 549 

Wetlands 52320 0.23 51143 4262 0.4 0.19 55640 4637 26429 2202 

Total 240948 274686 22891 383959 31997 208819 17402 

*: Runoff coefficients were cited from Harper (2003). 

**: EMCs were provided by the CDM. 

Table 4.9. Percent pollutant contribution from different landuse categories 

Landuse Nitrate TP

Agriculture/Golf Course 18.1% 19.8%

Forest and Rural Open 4.2% 1.2%

Rangeland 2.5% 3.9%

Low-Density Residential 9.0% 7.9%

Medium-Density Residential 21.1% 23.8%

High-Density Residential 9.0% 12.1%

Commercial 9.2% 7.3%

Institutional 4.1% 1.1%

Industrial/Utility 2.4% 3.4%

Transportation Facilities 2.2% 3.4%

Openland 0.8% 0.2%

Water 3.0% 3.2%

Wetlands 14.5% 12.7%

Total 100.0% 100.0%

As shown in Table 4.9, the most important nitrate and TP contributors in the drainage basin are 

urban landuses, which include low, medium, and high density residential, commercial, 

institutional, industrial/utility, transportation facilities, and other urban open lands. These 

landuses contribute about 218,583 lbs/year (18,215 lbs/month) and 123,244 lb/year (10270 

lbs/month) of nitrate and TP, which account for about 57% and 59% of the total nitrate and TP 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

39

from the entire drainage basin, respectively. In addition, agricultural landuses contribute about 

18% of nitrate and 20% of TP, and wetlands contribute about 15% of the nitrate and 13% of the 

TP. Total human landuses contribute about 78% nitrate and 83% of TP, while natural 

landuses, including forest, waters, and wetlands, contribute about 22% of the nitrate and 17% of 

the TP through surface runoff. 

Another possible nonpoint source of nitrate and TP to receiving waters is septic tank discharge. 

While properly installed and maintained septic tanks can remove phosphorus relatively 

effectively, significant amounts of nitrate can still be released into the ground water or surface 

runoff due to the low adsorption rate of nitrate by soil particles. 

A GIS shapefile showing locations of septic tank-using land parcels within the boundary of the 

Wekiva River drainage basin was provided by the CDM (Figure 4.6). However, no data on the 

number of septic tanks located in the drainage basin were available to the Department at the 

time this TMDL was developed. To estimate the pollutant loading from septic tanks, the number 

of septic tanks in the basin is required. This number was estimated based on the following 

information: 

(1) The total number of septic tanks located in the Lake County part of the Wekiva study 

Area was provided by the CDM, Inc., which is 9,286 septic tanks. 

(2) The total acreage of the septic tank-using land parcels in Lake County part of the 

Wekiva Study Area was provided by the CDM, Inc. The total acreage is 20,599 acres. 

(3) The number of septic tanks per acre of septic tank-using parcel were estimated as the 

quotient between the total number of septic tanks in (1) and the total acreage in (2), and 

is 0.45 septic tanks/per acre 

(4) Assuming that septic tanks that contribute significant quantities of nutrients to receiving 

waters through surface runoff are typically located within 200 meters of receiving waters 

(Reckhow, 1980), the total acreage of septic tank-using land parcels in the Wekiva River 

drainage basin that could contribute significant quantities of nutrients to receiving waters 

through surface runoff is 458 acres. 

(5) Multiplying 458 acres in (4) by the 0.45 septic tank/per acre in (3), the total number of 

septic tanks in the Wekiva River drainage basin that can contribute significant quantities 

of nutrients to receiving waters through surface runoff is 206 septic tanks. 

The nitrate and TP loadings from septic tanks to the Wekiva River system were estimated using 

the following equation: 

 W = F * N * C * (1-R) 

Where: 

 W is the total loading from septic tanks. 

 F is the number of people per household. 

N is the number of septic tank-using households. 

C is the per capita pollutant loading. 

R is the pollutant removal efficiency. 

Based on Summary Population and Housing Characteristics in Florida published by the United 

States Census Bureau in 2000 (http://www.census.gov/prod/cen2000/phc-1-11.pdf), the number 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

40

Figure 4.6. Location of septic tank-using land parcels in the Wekiva Study 

Area. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

41

of people per household in Lake, Orange, and Seminole Counties are 2.34, 2.61, and 2.59, 

respectively. The average household size (F) for these three counties is 2.51. 

The number of septic tank-using households within 200 meters to receiving waters could be 

considered the same as the number of septic tanks in the same area, assuming that each 

household uses one septic tank. 

Per capita TP loading (Table 4.10) for raw sewage was cited from Reckhow (1980). It was a 

typical value calculated as the mean TP loading from various studies. Nitrate concentration in 

raw sewage is typically very low. Most of the nitrate appears in the drainage field of 

conventional septic tanks when organic nitrogen is mineralized through ammonification and 

ammonia is oxidized through nitrification. Typically, the physical and biochemical processes 

happening in septic tanks and drainage fields, including precipitation in the septic tank and 

denitrification in the drainage filed, can remove about 40 to 45% of the total nitrogen (Burton, 

1991), and the remaining part of TN was assumed to be in the form of nitrate in this TMDL. 

Pollutant removal efficiency (R) is the percent at which TP and nitrate is removed by the septic 

tank system (including the tank and the soil). In this case, it is assumed that within 200 meters, 

70% of TP and 45% of the TN will be removed. The remaining 55% of TN will become nitrate 

and, together with the remaining 30% of TP, enter surface runoff or ground water. 

Based on above information, the TP and nitrate loadings from septic tanks in the Wekvia River 

drainage basin that are within 200 meters to receiving water are about 499 lbs/year and 2,890 

lbs/year, respectively. Compared to nitrate and TP loadings from various landuse categories, 

loadings from septic tank through surface runoff are relatively small. 

Table 4.10. Nutrient load for household wastewater discharged into septic tanks 

(kilograms/capita/year) (cited from Reckhow, 1980) 

TP TN Reference 

1.49 6.45 Ligman et al., 1974 

1.43 5.99 Laak, 1975 

N/A 2.65 Bennet and Linstedt, 1975 

0.74 4.61 Chan, 1978 

1.59 N/A Ellis and Childs, 1973 

1.49 2.15 Siegrist et al., 1976 

3 N/A Bernhard, 1975 

0.8 N/A Otis et al., 1975 

N/A 8.2 Walker et al., 1973 

1.28 3.2 EPA, 1974 

1.46 4.61 Median 

N/A = Not available 

The low nitrate and TP loadings from septic tanks estimated using the above method are mainly 

loadings through surface runoff, which is why a 200 meter distance limit was applied. However, 

septic tank pollutant loadings can also contribute to the surface water pollution via a ground 

water pathway, even for those septic tanks located beyond 200 meter distance limit. This is 

especially true for the Wekiva River drainage basin because this area is underlaid by a Karst 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

42

geology characterized by limestone or dolostone bedrock with caves and springs. A study 

conducted by the Florida Department of Health indicated that using the conventional onsite 

sewage treatment and disposal system in Karst areas could produce nitrate concentrations as 

high as 60 mg/L in the groundwater adjacent to the drainage field (DOH 2004). The nitrate can 

be carried into surface waters through either baseflow, or more importantly in the Wekiva River 

system, through springs discharge. 

At the time this TMDL was developed, not enough information was available for the Department 

to determinethe septic tank pollutant loading through ground water. Therefore, nitrate and TP 

loadings through spring discharges were estimated. Nitrate and TP loadings through spring 

discharges can include contribution form septic tanks, other human activities such as 

agricultural practices, and natural background. 

There are about 30 springs located in the Wekiva River drainage area. These springs either 

discharge directly to the main stem of the Wekiva River or discharge to major tributaries, 

including RSR, Blackwater Creek (BWC), and Little Wekiva River (LWR), which in turn 

discharge into the WR. Figure 4.6 shows the locations of these springs. Table 4.11 shows the 

magnitude, discharge rate, and nitrate and TP concentrations of these springs. Table 4.12

shows the nitrate and TP loadings and percent nitrate and TP loadings from these springs. 

Among the 30 springs located in the Wekvia River drainage basin, Rock Springs and Wekiva 

Springs are the two largest springs. Both of them discharge at more than 50 cfs, while the 

majority of the other springs discharge at less than 10 cfs. Seminole Springs discharges at a 

rate of 35.2 cfs, ranking the third in discharge rate. This spring is located in Lake County and 

discharges into Blackwater Creek. Several other springs, including Messant Spring in Lake 

County (discharging to Blackwater Creek), Starbuck Springs located in Seminole County 

(discharging to Blackwater Creek), and Sanlando Springs located in Seminole County 

(discharging to Little Wekiva River) discharge at a long-term average rate of more than 10 cfs. 

According to Table 4.12, the total nitrate and TP loading from all the 30 springs are about 

511,433 lbs/year and 78,952 lbs/year, respectively. The total nitrate loading from springs is 

higher than the nitrate loading from surface runoff, which is about 383,959 lbs/year (Table 4.8). 

TP loading from springs are also significant compared to the TP loading from surface runoff, 

which is about 197,506 lbs/year. These numbers indicate that springs are a very important 

source of nitrate and TP in the Wekiva River system. 

Among all the springs, Rock Springs and Wekiva Springs are the largest nitrate contributors. 

Combined nitrate loadings from these two springs account for about 70% of the spring nitrate. 

In addition, these two springs contribute about 59% of the spring TP, indicating that efforts to 

control nitrate and TP should be put on the recharge areas of these two springs. Other than 

these two springs, Seminole Spring contributes about 19% of the spring nitrate and 7% of spring 

TP. Sanlando Spring and Starbuck Springs contribute about 4.5% and 2.1 % of the spring 

nitrate and 8.8% and 5.7% of the spring TP, respectively. Considering the high nitrate and high 

TP concentrations observed in these springs, studies on the nitrate and TP loadings in recharge 

areas of these springs should also be stressed. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

43

Figure 4.7. Locations of springs in the Wekiva River drainage area.
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

44

Table 4.11. Characteristics of springs located in the Wekiva River drainage basin. 

Spring Name Spring Magnitude Discharge 

(cfs)

NO3/NO2 

(mg/L)

TP 

(mg/L)

Lake County

Blackwater Spring 3rd 1.4 0.92 N/A

Blue Algae Boil 5th 0.14 0.03 0.05

Blueberry Spring 5th 0.07 0.03 N/A

Boulder Spring 5th 0.19 0.08 0.18

Camp La-No-Che 

Spring 4th 0.7 N/A 0.06

Cedar Spring 5th 0.03 0.03 0.05

Droty Spring 4th 0.62 0.03 0.08

Green Algae Boil 5th 0.14 N/A 0.06

Markee Spring 4th 0.25 0.02 0.06

Messant Spring 2nd 14.7 0.01 0.04

Mocassin Spring 4th 0.29 0.01 N/A

Palm Spring 4th 0.63 0.01 0.02

Seminole Spring 2nd 35.2 1.37 0.08

Sharks Tooth 

Spring 5th 0.15 0.09 0.05

Snail Springs 5th 0.09 0.02 0.15

Tricle Spring N/A N/A N/A N/A

Orange County

Barrel Spring 4th 0.25 0.05 N/A

Rock Springs 2nd 57.9 1.5 0.08

Sulphur Spring 4th 0.74 0.02 0.03

Tram Springs N/A N/A N/A N/A

Wekiva Springs 2nd 67.1 1.43 0.28

Witherington 

Spring 3rd 4.7 0.38 N/A

Seminole County

Gingar Ale Springs 5th 0.11 N/A 0.04

Island Spring 3rd 7.83 0.01 0.51

Miami Springs 3rd 5.05 0.17 0.12

Nova Spring 3rd 8.52 0.12 0.14

Palm Spring 3rd 6.88 0.69 0.12

Pegasus Spring 3rd 2.8 0.54 0.22

Sanlando Spring 2nd 19.6 0.59 0.18

Starbuck Springs 2nd 14.3 0.39 0.16

Data cited from SJRWMD’s Springs website 

(http://sjrwmd.com/programs/plan_monitor/gw_assess/springs/). 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

45

Table 4.12. Nitrate and TP loadings from springs located in the Wekiva 

River drainage basin and percent loadings from these springs 

Loading Percent loading 

Spring Name NO3/NO 

(lbs/year)

TP 

(lbs/year) NO3/NO TP 

Lake County

Blackwater Spring 2536 0.5%

Blue Algae Boil 8 14 0.0% 0.0%

Blueburry Spring 4 0.0%

Boulder Spring 30 67 0.0% 0.1%

Camp La-No-Che 

Spring 83 0.1%

Cedar Spring 2 3 0.0% 0.0%

Droty Spring 37 98 0.0% 0.1%

Green Algae Boil 17 0.0%

Markee Spring 10 30 0.0% 0.0%

Messant Spring 289 1158 0.1% 1.5%

Mocassin Spring 6 0.0%

Palm Spring 12 25 0.0% 0.0%

Seminole Spring 94967 5546 18.6% 7.0%

Sharks Tooth 

Spring 27 15 0.0% 0.0%

Snail Springs 4 27 0.0% 0.0%

Tricle Spring 

Orange County

Barrel Spring 25 0.0%

Rock Springs 171032 9122 33.4% 11.6%

Sulphur Spring 29 44 0.0% 0.1%

Tram Springs 

Wekiva Springs 188959 36999 36.9% 46.9%

Witherington 

Spring 3517 0.7%

Seminole County

Gingar Ale Springs 9 0.0%

Island Spring 154 7864 0.0% 10.0%

Miami Springs 1691 1193 0.3% 1.5%

Nova Spring 2013 2349 0.4% 3.0%

Palm Spring 9349 1626 1.8% 2.1%

Pegasus Spring 2978 1213 0.6% 1.5%

Sanlando Spring 22773 6948 4.5% 8.8%

Starbuck Springs 10983 4506 2.1% 5.7%

Total 511433 78952 100.0% 100.0%
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

46

Table 4.13 summarizes the possible nonpoint source contributors of nitrate and TP loadings in 

the Wekiva River drainage system considered in this TMDL. The contribution of nitrate and TP 

loads from septic tanks located with 200 meters to receiving water through surface runoff is not 

a major source. Nitrate loadings from different landuses through surface runoff and springs are 

comparable, and springs contribute slightly more nitrate than the surface runoff. The major 

contributor of TP apparently is the surface runoff from the drainage area. Spring TP contribution 

appears to be less important than the surface runoff. 

Table 4.13. Summary of nitrate and TP loadings from possible nonpoint sources in 

the Wekiva River drainage areas. 

Loading Percent Loading 

Sources NO3/NO2 

(lbs/year) 

TP 

(lbs/year) NO3/NO2 TP 

Surface runoff 

from landuses 383,959 208,819 43% 73% 

 Spring 

contribution 511,433 78,952 57% 27% 

Surface runoff 

from septic tanks 2,890 499 0% 0% 

Total 898,282 288,270 100% 100% 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

47

Chapter 5: DETERMINATION OF ASSIMILATIVE 

CAPACITY 

Ideally, existing loading and target loading reaching a given waterbody should be simulated 

using hydrologic and water quality models. However, there was not adequate time available to 

develop this TMDL using a modeling approach, and an alternative approach was used to 

estimate the existing and target loadings. 

Existing stream loading can be estimated by multiplying the measured stream flow by the 

measured pollutant concentrations in the stream. To estimate the pollutant loading this way, 

flow measured at the outlet of each stream segment under question is required. Several USGS 

gauging stations were identified in the Wekiva River main stem and its major tributaries. 

However, none of these stations were located at outlets of the stream segments under question. 

The Department considered the feasibility of using the available flow measurements to estimate 

the flow at each segment outlet based on the drainage area ratio among these stream 

segments. This method would normally provide an approximation of flow estimates at the 

stream segment outlets. However, because of the ubiquitous existence of springs in the Wekiva 

River drainage area, flow estimation based on drainage area ratio will not give an accurate 

result. Therefore, the loads of nitrate and TP were not explicitly calculated. Instead, the percent 

load reduction required to achieve the nitrate and TP concentration targets were calculated 

assuming the percent loading reduction would be the same as the percent concentration 

reduction. 

The percent reduction required to achieve the water quality target was calculated using the 

following formula: 

[(existing mean concentration – target concentration) / existing mean concentration] x 100 

As discussed in Chapter 3, both the nitrate target and the TP target were established as 

monthly averages in this TMDL. Therefore, long-term monthly average concentrations were 

calculated for each month for each parameter based on measured concentrations for the period 

of record. To make sure that the monthly average concentrations will meet the concentration 

target even under the worse case scenario, the highest monthly average nitrate and TP 

concentrations were used as existing monthly mean concentrations to calculate the percent 

reduction required to achieve the nitrate and TP targets. This approach adds to the margin of 

safety of the TMDL. 

To make sure that the estimated existing mean concentrations represent the existing conditions 

of the stream, only recent data were used to estimate the existing mean concentration. 

Because the Verified Period for the Wekiva River basin water quality assessment started at 

1996, no data earlier than 1996 were used in this analysis. 

Because different nitrate and TP concentrations were observed in different stream segments, 

percent reduction requirements were calculated separately for each segment. The Wekiva 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

48

River was divided into three segments, including Wekiva Spring (WS, WBID 2956C), upstream 

Wekiva River (UWRMS, WBID 2956), and downstream Wekiva River (DWRMS, 2956A). 

Rock Springs (RS) and Rock Springs Run (RSR) are currently combined in the same WBID 

(2967). To estimate the existing concentrations of RS, nitrate and TP concentration 

measurements collected from a water quality station located at the spring boil – station 21FLGW 

11395, were excluded from the Rock Springs Run WBID and used specifically for existing 

nitrate and TP concentrations calculation for the spring. 

Because nitrate and TP concentrations for Wekiva Spring (WBID 2956C) were only measured in 

2002, 2003, and 2004 during very limited sampling events, monthly averages were not 

calculated for nitrate or TP for the spring and the highest observed concentrations were used as 

the existing condition. Tables 5.1 and 5.2 show the existing mean concentrations, target 

concentration and percent reductions required for the stream segments (springs) mentioned 

above. 

In addition to calculating required reductions in Rock Springs Run (WBID 2967), Wekiva Spring 

(WBID 2956C), and the Wekiva River (WBIDs 2956 and 2956A), the Department also 

calculated required reductions in nitrate and TP concentrations for the Little Wekiva River (LWR, 

WBID 2987), and Black Water Creek (BWC, WBID 2929A). 

Table 5.1. Existing and target nitrate concentrations for related stream segments 

and percent concentration reduction required to achieve the nitrate 

target. 

Unit: (mg/L) 

Year RS RSR 

(2967) 

WS 

(2956C) 

UWRMS 

(2956) 

DWRMS 

(2956A) 

LWR 

(2987) 

BWC 

(2929A) 

January 1.50 0.62 1.30 0.88 0.54 0.70 0.29 

February N/A 0.65 N/A 0.88 0.38 0.59 0.21 

March N/A 0.52 N/A 0.52 0.41 0.26 0.29 

April 1.50 0.58 1.25 0.63 0.39 0.36 0.35 

May 1.30 0.77 N/A 0.70 0.33 0.39 0.46 

June N/A 0.77 N/A 0.40 0.35 0.44 0.32 

July 1.40 0.57 1.34 0.52 0.30 0.25 0.59 

August N/A 0.08 N/A 0.44 0.24 0.26 0.12 

September N/A 0.57 N/A 0.61 0.29 0.36 0.24 

October 1.50 0.53 0.94 0.42 0.27 0.17 0.29 

November N/A 0.43 N/A 0.60 0.47 0.28 0.27 

December N/A 0.73 N/A 0.86 0.30 0.49 0.14 

Existing Mean 

(highest monthly 

mean) 

1.50 0.77 1.34 0.88 0.54 0.70 0.59 

Target 

Concentration 0.286 0.286 0.286 0.286 0.286 0.286 0.286 

Percent 

Reduction 81% 63% 79% 68% 47% 59% 52%
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

49

Table 5.2. Existing and target TP concentrations for related stream segments and 

percent concentration reduction required to achieve the TP target. 

Unit: mg/L 

Month RS RSR 

(2967) 

WS 

(2956C) 

UWRMS 

(2956) 

DWRMS 

(2956A) 

LWR 

(2987) 

BWC 

(2929A) 

January 0.081 0.078 0.181 0.094 0.102 0.163 0.034

February N/A 0.084 0.106 0.087 0.088 0.292 0.049

March N/A 0.086 0.065 0.110 0.125 0.179 0.062

April 0.084 0.095 0.117 0.110 0.102 0.117 0.045

May 0.082 0.104 0.160 0.144 0.116 0.254 0.060

June N/A 0.109 0.029 0.145 0.130 0.161 0.101

July 0.078 0.140 0.118 0.114 0.121 0.151 0.061

August N/A 0.112 0.048 0.124 0.117 0.135 0.052

September N/A 0.153 0.081 0.168 0.150 0.141 0.073

October 0.084 0.133 0.107 0.156 0.125 0.127 0.096

November N/A 0.108 0.014 0.126 0.107 0.178 0.050

December N/A 0.086 N/A 0.093 0.095 0.238 0.087 

Existing 

Mean 

(highest 

monthly 

mean) 

0.084 0.153 0.181 0.168 0.150 0.292 0.101 

Target 0.065 0.065 0.065 0.065 0.065 0.065 0.065 

Percent 

reduction 23% 58% 64% 61% 57% 78% 36%

Based on Table 5.1, the percent reduction required to achieve the nitrate target of 286 μg/L 

ranges from 47% for the downstream segment of the Wekiva River (WBID 2956A) to 81% for 

the spring vent of Rock Spring. The downstream segments of the river typically have relatively 

low nitrate concentrations, and therefore low percent required reduction. Upstream segments 

typically have higher nitrate concentrations than the downstream segments, and spring vents 

have the highest nitrate concentrations. Therefore, high percent reductions are usually required 

for the upstream segment and spring boil. This spatial trend indicates the importance of springs 

as the nitrate contributor. In addition to the Wekiva River and Rock Springs Run, 59% and 52% 

reductions are required Little Wekiva River and Blackwater Creek, respectively, to achieve the 

nitrate target for the main stem of the Wekiva River. 

The required percent reduction for TP ranged from 23% for Rock Spring and 78% for the Little 

Wekiva River tributary. The spatial trend of the required percent reduction is not as consistent 

as that of nitrate. While required TP percent reductions differ significantly between Rock Spring 

and Rock Springs Run, the required TP percent reductions are not dramatically different among 

Wekiva Spring, the upstream segment of the Wekiva River, and the downstream segment of the 

Wekiva River. To achieve the TP target for the main stem of the Wekiva River, a 78% reduction 

is required for the Little Wekiva River tributary, indicating the relative importance of the Little 

Wekiva River tributary as the phosphorus contributor. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

50

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 (wasteload 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 (1) 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 (2) 

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

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

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

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

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

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

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

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

appropriate measure. TMDLs for the Wekiva River, RSR and other related WBIDs in the 

drainage basin of the Wekiva River system are expressed in terms of pounds per month, 

pounds per day, and percent reduction of nitrate and TP, and represent the maximum long-term 

nitrate and TP loadings the WR and RSR can assimilate and maintain a balanced aquatic flora 

and fauna (Table 6.1). It should be noted that the expression of the TMDL on a mass per day 

basis is for information purposes only
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

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Table 6.1. TMDL components for RSR, WRMS, and related WBIDs 

WBID Parameter 

TMDL

(percent 

reduction) 

WLANPDES wastewater WLANPDES Stormwater LA MOS

RS Nitrate 81% N/A 81% 81% Implicit 

RS TP 23% N/A 23% 23% Implicit 

RSR 

(2967) Nitrate 63% N/A 63% 63% Implicit 

RSR 

(2967) TP 58% N/A 58% 58% Implicit 

WS 

(2956C) Nitrate 79% N/A 79% 79% Implicit 

WS 

(2956C) TP 64% N/A 64% 64% Implicit 

UWRMS 

(2956) Nitrate 68% 2,805 lbs/month 68% 68% Implicit 

UWRMS 

(2956) TP 61% 40 lbs/month 61% 61% Implicit 

DWRMS 

(2956A) Nitrate 47% N/A* 47% 47% Implicit 

DWRMS 

(2956A) TP 57% 191 lbs/month 57% 57% Implicit 

*While there is no WLA for nitrate for DWRMS, it should be noted that a WLA of 572 lbs/month has been established for Total 

Nitrogen for the SCES/Yankee Lake WRF (see Section 6.3.1). N/A in this table means not applicable. 

Altamonte Springs Regional Water Reclamation Facility does not discharge directly into any of the above segments. However, the

loading from the facility influences the main stem water quality through discharging into the Little Wekiva River. Therefore, WLA for 

TP was allocated to the facility as 26 lbs/month. A discharge limit of 286 μg/L was assigned to the facility for nitrate. 

In addition to the percent load reductions described in Table 6.1 that are needed to achieve the 

water quality in the main stem of the Wekiva River, nitrate loads from the Little Wekiva River 

and Blackwater Creek tributaries also need to be reduced by 59% and 52%, respectively. 

Similarly, TP loadings from the Little Wekiva River and Blackwater Creek should be reduced by 

78% and 36%, respectively. 

The percent load reductions listed on Table 6.1 were established to achieve the monthly 

average nitrate concentration of 286 μg/L and the monthly average TP concentration of 65 μg/L. 

While these percent reductions are the expression of the TMDL that will be implemented, EPA3

recommends that all TMDLs and associated load allocations and wasteload allocations include 

a daily time increment in conjunction with other appropriate temporal expressions that may be 

necessary to implement the relevant water quality standard. Daily maximum concentrations 

targets for nitrate and TP were established using the following equation4

, which assumes that 

the nitrate and TP data distributions are lognormal in Wekiva and Rock Springs Run: 

 MDL = LTA * exp(Zpσy – 0.5σy

2

) 

σy = sqrt(ln(CV2

 + 1)) 

 3

 November 2006 U. S. Environmental Protection Agency (USEPA 2006) Memorandum “Establishing TMDL “Daily” 

Loads in Light of the Decision by the U.S. Court of Appeals for the D.C. Circuit in Friends of the Earth, Inc. v. EPA et. 

al., No.05-5015 (D.C. Cir. 2006) and Implications for NPDES permits.” 

4

 EPA, “Options for Expressing Daily Load in TMDL (The Option),” June, 2007. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

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Where 

 LTA = long-term average 

 Zp = pth percentage point of the standard normal distribution, which can be obtained 

 from any statistics textbook. 

σ = standard deviation 

 CV = coefficient of variance 

For the daily maximum nitrate concentration, it was assumed that the average monthly target 

concentration should be the same as the average daily concentration. Also, assuming the 

target data set will have the same CV as the existing measured data set and allowing 10% 

exceedance, the daily maximum nitrate concentrations for Wekiva Upstream, Wekiva 

Downstream, and Rock Springs Run would be 0.47, 0.48, and 0.52 mg/L, respectively. The 

most conservative nitrate daily maximum target was chosen as the final daily maximum nitrate 

target for the Wekiva River – Rock Springs Run system, which is 0.47 mg/L (470 μg/L). The 

means, STDEVs, and CVs of nitrate concentrations of different water segments are listed in 

Table 6.2. 

Table 6.2. Daily maximum for target nitrate concentration (mg/L) 

Statistics Wekiva 

Upstream

Wekiva 

Downstream

Rock 

Springs 

Run 

Mean 0.65 0.38 0.59 

STDEV 0.33 0.2 0.4 

CV 0.51 0.53 0.68 

Daily Maximum 0.47 0.48 0.52 

This same approach was used to calculate the TP daily maximum concentrations for Wekiva 

Upstream, Wekiva Downstream, and Rock Springs Run, which are 0.09, 0.09, and 0.11 mg/L, 

respectively. The most conservative TP daily maximum target was chosen as the final daily 

maximum TP target for the Wekiva River – Rock Springs Run system, which is 0.09 mg/L (90 

μg/L). The means, STDEVs, and CVs of TP concentrations of different water segments are 

listed in Table 6.3. 

Table 6.3. Daily maximum for target TP concentration (mg/L) 

Statistics Wekiva 

Upstream

Wekiva 

Downstream

Rock 

Springs 

Run 

Mean 0.12 0.116 0.107 

STDEV 0.039 0.033 0.059 

CV 0.33 0.28 0.55 

Daily Maximum 0.09 0.09 0.11 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

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It should be emphasized that these daily maximum targets were developed for illustrative 

purposes. Implementation of the TMDL will be based on the monthly average concentration 

targets. 

6.2 Load Allocation 

Because no target load was explicitly calculated in this TMDL report due to the lack of flow data 

at the outlet of each stream segment, TMDLs are represented as the percent reduction required 

to achieve the nitrate and TP targets. The percent reduction assigned to all the nonpoint 

sources areas (LA) are the same as those defined for the TMDL percent reduction. To achieve 

the annual average nitrate target of 250 μg/L in Rock Springs Run and the Wekiva River, the 

nitrate loads from the nonpoint source related to RS, RSR (2967), WS (2956C), UWRMS 

(2956), and DWRMS (2956A) need to be reduced by 81%, 63%, 79%, 68%, and 47%, 

respectively. In addition, nitrate contributions from nonpoint sources related to the LWR (2987) 

and BWC (2929A) should also be reduced by 59% and 52%, respectively, to ensure that the 

nitrate target of the Wekiva River will be met. 

The required TP percent reductions to achieve the TP target of 65 μg/L are 23%, 58%, 64%, 

61%, and 57% for RS, RSR, WS, UWRMS, and DWRMS, respectively. About 78% and 36% of 

the TP loadings from the LWR and BWC tributaries, respectively, should also be reduced to 

achieve the TP target of the main stem. The nonpoint sources covered in this allocation include 

runoff, septic discharge through surface runoff, and the anthropogenic load contained in the 

spring discharge. All the nonpoint sources covered in LA are restricted to those sources in 

non-MS4 areas. 

6.3 Wasteload Allocation 

6.3.1 National Pollutant Discharge Elimination System Wastewater Discharges 

Three NPDES permitted facilities were identified in the Wekiva River system that may 

potentially contribute significant quantities of nitrate and TP to the Wekiva River. These facilities 

include SCES/Yankee Lake WRF (FL0042625), Wekiva Hunt Club WWTF (FL0036251), and 

Altamonte Springs Regional Water Reclamation Facility (FL0033251). 

The SCES/Yankee Lake WRF discharges very little nutrient load to the WR via a backup 

upland/receiving wetlands surface water system, with the majority of their AWT treated 

wastewater going to reuse. As described in Chapter 4, the upland/receiving wetlands system 

typically does not discharge to any receiving surface water except to Sulfur Creek under wet 

weather conditions. Although Sulfur Creek discharges to the downstream section of the WR 

intermittently under wet weather, water quality monitoring results in Sulfur Creek upstream and 

downstream of the effluent point from SCES/Yankee Lake WRF did not show any significant 

impact from the facility. Therefore, the Department concluded that the existing permit limits for 

the wetlands discharge (0.75 mgd discharge, and TP and TN limits of 1.0 mg/l, and 3.0 mg/l) 

are adequately protective of the Wekiva River. 

It should be noted that the facility currently does not have a nitrate effluent limit. The nitrate 

concentration of the effluent from this facility typically accounts for about 24 to 65% of the TN 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

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concentration, with an average percent nitrate concentration of 42% (Table 4.2). Because no 

negative impacts have been observed at the monitoring site downstream of the effluent point, 

the Department concluded that the a nitrate effluent limit was not needed. However, if the 

percent nitrate concentration from the effluent significantly increases in the future or negative 

impacts are detected in Sulfur Creek, the Department may require a permit limit for nitrate. 

The wasteload allocation for TN was calculated in place of nitrate as follows: 

TN allocation (lbs/month) = 8.36* monthly average TN limit * surface AADF limit *365/12 

Where, 

 8.36 is the conversion factor; 

 The facility’s monthly average TN limit is 3.0 mg/L; 

 The facility’s surface discharge AADF limit is 0.75 mgd; 

 Three Hundred and sixty five days are assumed for each year; and 

 The monthly load was calculated by dividing the annual load by 12. 

The monthly TN wasteload allocation is 572 lbs/month. This allocation, when represented as 

daily loading, would be 18.8 lbs/day, dividing the annual load by 365 days. 

The TP wasteload allocation was calculated as follows: 

TP allocation (lbs/month) = 8.36 * Annual average TP limit * surface AADF limit *365/12 

 8.35 is the conversion factor; 

 The facility’s monthly average TP limit is 1.0 mg/L; 

 The facility’s surface discharge AADF limit is 0.75 mgd; 

 Three hundred and sixty five days are assumed for all years; and 

 The monthly load was calculated by dividing the annual load by 12. 

The monthly TP allocation is 191 lbs/month. This allocation, when represented as daily 

loading, would be 6.3 lbs/day, dividing the annual load by 365 days. 

The Wekiva Hunt Club WWTF discharges into Sweetwater Creek, which in turn discharges to 

Cove Lake, and then the Wekiva River. The facility has a surface water discharge AADF of 2.9 

mgd and a monthly average TP discharge limit of 0.4 mg/L. The facility does not have any 

nitrate or TN discharge limit. Based on PCS data, the facility is currently discharging at a longterm annual average discharge rate of 539 million gallon/year, with long-term annual averages 

of 0.19 mg/L TP and 9.94 mg/L nitrate. The long-term annual average nitrate and TP loadings 

from the facility are 46,751 lbs/year and 869 lbs/year, respectively. However, based on the 

surface water monitoring data collected during January of 2005 through April of 2006, the 

discharge nitrate and TP concentrations have attenuation rates of 96% and 39%, respectively, 

by the time the effluent reaches the sampling site closest to the Wekiva River (Site #5). Based 

on these attenuation rates, the long-term annual average nitrate and TP concentrations at Site 

#5 are: 

 Nitrate concentration = 9.94 mg/L * (1 – 96%) = 0.398 mg/L 
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 TP concentration = 0.19 mg/L * (1 – 39) = 0.116 mg/L. 

To achieve the nitrate and TP targets of 0.286 mg/L and 0.065 mg/L, respectively, at the 

discharge point of Sweetwater Creek to the Wekiva River, percent reductions required are: 

 Nitrate percent reduction = (0.398 – 0.286)/0.398 * 100% = 28% 

 TP percent reduction = (0.116 – 0.065)/0.116 * 100% = 44%. 

Applying the nitrate and TP percent reductions to the long-term annual average nitrate and TP 

loadings discharged from the facility, the final wasteload allocations to the facility are: 

Nitrate wasteload allocation = 46, 751 lbs/year * (1 – 0.28) = 33,661 lbs/year = 2,805 lbs/month; 

TP wasteload allocation = 860 lbs/year * (1 – 0.44) = 482 lbs/year = 40 lbs/month; 

When represented as daily loads, the nitrate and TP wasteload allocations are 80.5 lbs/day and 

1.3 lbs/day, respectively. 

The Altamonte Springs Regional Water Reclamation Facility discharges directly into the 

Little Wekiva River, which in turn discharges into the main stem of the Wekiva River. To 

achieve the 65 μg/L TP target for the Wekiva River main stem, this TMDL recommends that the 

discharge from the Little Wekiva River into the main stem meets the 65 μg/L target at the outlet 

of the Little Wekiva River (roughly at station 21FLSJWMLW-UWR, Figure 4.2). The TP 

concentration at this location is calculated using the following equation: 

Qusgs Qwrf Qwrf Qsanlan Qpalm Qstar

Qusgs Qwrf Clakelotus Qwrf Cwrf Qsanlan Csanlan Qpalm Cpalm Qstar Cstar Cout

++++−

− + + + + = ( )( *) * * * *

Where, 

Cout is the TP concentration at the outlet of the Little Wekvia River, 

Qusgs is the flow measured at USGS gauge 02234990. The long-term average is 28.8 cfs. 

Clakelotus is the TP concentration of Lake Lotus, which is about 70 μg/L and reflects the stream 

TP concentration from combined contribution of nonpoint sources. 

Qwrf is the discharge from the Altamonte Springs WRF. The long-term average is 1.9 cfs. 

Cwrf is the long-term average TP concentration of WRF’s discharge, which is 1500 μg/L. 

Qusgs – Qwrf is the total stream flow minus the flow from the WRF. The difference primarily 

represents the flow created by nonpoint sources. 

Qsanlan is the long-term average discharge rate from Sanlando Springs, which is 19.6 cfs. 

Csanlan is the long-term average TP concentration in the discharge of Sanlando Springs, which is 

180 μg/L. 

Qpalm is the long-term average discharge rate from Palm Springs, which is 6.9 cfs. 

Cpalm is the long-term average TP concentration in the discharge of Palm Springs, which is 120 

μg/L. 

Qstar is the long-term average discharge rate from Starbuck Springs, which is 14.3 cfs. 

Cstar is the long-term average TP concentration in the discharge of Starbuck Springs, which is 

160 μg/L. 

Substituting the number for each of the items listed above into the equation, the final result of 

the Cout is 163 μg/L, which is close to the long-term average TP concentration of 173 μg/L 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

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measured at the outlet of the Little Wekiva River, suggesting that above equation, which 

represents only the mixing in the Little Wekiva River, reflects accurately the fate of TP in the 

stream. Loss of TP from the water column to the sediment through net deposition may not be a 

major factor in controlling the TP dynamics in the system. 

Possible reasons for high TP concentrations in the discharge of the three springs listed above 

was also explored. Table 4.11 listed nitrate and TP concentrations of all the springs located in 

the Wekiva Study Area. Nitrate and TP concentrations for the majority of these springs are 

relatively low. However, most of the springs located in the Seminole County, including the three 

springs listed above, have relatively high TP concentrations as well as high nitrate 

concentrations. These observations suggested that a significant portion of the high TP 

concentrations may have resulted from human activities instead of geological background. 

Therefore, to achieve the main stem TP target of 65 μg/L, TP concentrations from these springs 

also need to be reduced. 

Assuming that we will reduce the TP concentrations from all the nonpoint sources to 65 μg/L 

(including the concentration at the outlet of Little Wekiva Canal, which is represented by the TP 

concentration of Lake Lotus, and TP concentrations of the spring discharges), the TP 

concentration allowable for the WRF discharge, based on above equation, would be 83 μg/L. If 

the existing discharge rate of the WRF is retained, the allowable monthly loading of TP from the 

WRF would be 26 lbs/month. This represents about 94% reduction from its existing long-term 

average monthly loading of 470 lbs/month (Table 4.3). The daily allowable loading for the WRF 

would be 0.84 lbs/day. 

To estimate the target nitrate loading from the facility, the Department assumed that in-stream 

nitrate assimilation in the Little Wekiva River is insignificant comparing to the total watershed 

and point source loads, which adds to the margin of safety of this TMDL. Therefore, to achieve 

the nitrate target for the main stem of the Wekiva River, the Department recommend, at this 

point, to reduce the nitrate concentrations from all the nonpoint and point sources to 286 μg/L. 

This nitrate target also applies to the effluent of the WRF. Assuming that the facility’s existing 

discharge rate is allowed to be kept, the target nitrate loading is 91 lbs/month for monthly 

loading, and 2.9 lbs/day for daily loading. The facility does not have a routine monitoring 

requirement for nitrate. Based on two Reclaimed Water Effluent Analyses conducted in 2006, 

the effluent nitrate concentrations from the facility were 4.66 mg/L and 3.96 mg/L. Assuming 

that the average of these two numbers (4.31 mg/L or 4310 μg/L) reflects the long-term average 

concentration of the discharge, under the existing discharge rate (1.23 MGD), the existing 

nitrate load from the facility is 1371 lbs/month. The target load of 91 lbs/month represents about 

93% reduction of nitrate load from the existing condition. 

 

6.3.2 National Pollutant Discharge Elimination System Stormwater Discharges 

Because no information was available to the Department at the time this analysis was 

conducted regarding the boundaries and locations of all the NPDES stormwater dischargers, 

the exact stormwater nitrate and TP loadings from MS4 areas were not explicitly estimated. 

Within the Wekiva River drainage basin, Orange County has a Phase I MS4 permit 

(FLS000011), with the Florida Department of Transportation (FDOT) District 5 and City of 

Maitland as co-permittees. Seminole County also holds a Phase I MS4 permit (FLS000038) 

with FDOT District 5, City of Altamonte Springs, and City of Lake Mary being co-permittees for 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

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this permit. In addition, the City of Orlando holds a Phase I MS4 permit (FLS000014). Lake 

County does not have MS4 permit within the boundary of the drainage basin. The wasteload 

allocations for each of the MS4s are the same percent nitrate and TP reductions required for the 

LA assigned to the nonpoint sources in the river segments that belong to each county and 

municipality. 

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 is not 

responsible for reducing other nonpoint source loads within its jurisdiction. 

6.4 Margin of Safety 

Consistent with the recommendations of the Allocation Technical Advisory Committee 

(Department, February 2001), an implicit MOS was used in the development of this TMDL. An 

implicit MOS was provided by the conservative decisions associated with a number of modeling 

assumptions, the development of site-specific alternative water quality targets, and the 

development of assimilative capacity. 

The MOS was created in several aspects of the analyses. For example, the nitrate target was 

established based on the most conservative concentration from the three lines of evidence 

(Suwannee River periphtyon result, Rainbow Creek Lyngbya result, and Rock Springs Run and 

the Wekiva River ecological efficiency experiment). Requiring that the 286 μg/L target be met 

every month should result in the nitrate concentration to be even lower than the target 

concentration during the summer algal growth season based on seasonal analysis on the nitrate 

concentration, and therefore adds to the margin of safety. In addition, when estimating the 

required percent load reduction to achieve the water quality target, the highest long-term 

monthly averages of measured nitrate concentrations, instead of average long-term monthly 

averages, were chosen to represent the existing condition. This will make estimating the 

required percent load reduction more conservative and therefore add to the margin of safety. 

Similarly, the TP target concentration was established as a monthly average because no 

seasonal pattern could be identified for community structure and functions of aquatic flora in the 

system under question. Typically, if no seasonal pattern can be identified for biological 

responses to nutrient concentrations of the system, the time scale for the water quality target 

would be set as an annual average. For this TMDL, the Department found that TP 

concentrations in the system tend to be higher during the summer growth season and therefore 

established the TP target as a monthly average. This will not only address the growth season 

TP concentration properly, but also makes the in-stream TP concentration lower than the target 

TP concentration in other months of the year, which is more conservative and adds to the MOS. 

In addition, using the highest long-term monthly average instead of the average of long-term 

monthly average in calculating the required percent load reduction makes estimating the 

required percent load reduction more conservative and therefore adds to the margin of safety. 

6.5 Recommendations for Further Studies 

This TMDL is developed primarily based on the nitrate and TP PLRGs developed by the 

SJRWMD. Because of time limitations, the identification of impairments and development of 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

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water quality targets were based on data collected within one year. However, due to the varying 

nature of the local weather and hydrology, and the variation in responses from local flora and 

fauna to the change of nitrate and TP concentrations under different weather, hydrological, and 

hydraulic conditions, similar studies that could support the further identification of impairment 

and development of water quality targets should be conducted in the future for a longer time 

period to verify the conclusions and hypotheses used in this TMDL. 

The SJRWMD also proposed future studies to further examine the dynamics of aquatic flora and 

fauna to environments with changing nitrate and TP concentrations. Proposed studies include 

studies on the effects of nutrient variation on the spring aquatic communities, the relationship 

between nutrient concentration and periphytic algal growth under varying conditions of current 

velocity and light availability, the inhibitory effects of periphyton on SAV growth, and the effects 

of filamentous algal growth on macroinvertebrate and fish habitat. In addition, the Department 

recommends that the hydrology, hydraulic, and water quality of the Wekiva River system be 

simulated using calibrated models to better understand the effects of nitrate and TP pollutants 

on the in-river nitrate and TP concentrations and influences on the structure and functions of 

aquatic communities. Because springs are major nitrate contributors for both the Wekiva River 

and RSR, it would be very important to identify and address the potential pollutant sources of 

nitrate in the ground water recharge area. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

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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, referred to as the BMAP. This document will be developed 

over the next two years in cooperation with local stakeholders, who will attempt to reach 

consensus on detailed allocations and on how load reductions will be accomplished. The 

BMAP will include, among other things: 

• Appropriate load reduction allocations among the affected parties, 

• 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, 

• Confirmed and potential funding mechanisms, 

• Any applicable signed agreement(s), 

• Local ordinances defining actions to be taken or prohibited, 

• Any applicable local water quality standards, permits, or load limitation agreements, 

• Milestones for implementation and water quality improvement, and 

• Implementation tracking, water quality monitoring, and follow-up measures. 

An assessment of progress toward the BMAP milestones will be conducted every five years, 

and revisions to the plan will be made as appropriate, in cooperation with basin stakeholders. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

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60

References 

Bronmark, C and L. A. Hansson. 1998. The biology of lakes and ponds. Oxford University 

Press, New York, NY. 216 pp. 

Burton, F. L. 1991. Wastewater Engineering, treatment, disposal, and resuse. 3rd Edition. 

Metcalf & Eddy, Inc. McGraw-Hill Publishing Company, New York. 1040 pp. 

Cowell, B. C. and C. J. Dawes. 2004. Growth and nitrate-nitrogen uptake by the 

cyanobacterium Lyngbya wollei. J. Aquatic Plant Management 42: 69-71. 

D.C. Cir. (United States Court of Appeals for the District of Columbia). 2006. Friends of the Earth, 

Inc.v. EPA, et al. No. 05-5015. 

DOH. 2004. Wekiva basin onsite sewage treatment and disposal system study. Florida 

Department of Health. 

Florida Administrative Code. Chapter 62-302, Surface water quality standards. 

Florida Administrative Code. Chapter 62-303, Identification of impaired surface waters. 

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

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and the legislature on the allocation of total maximum daily loads in Florida. Tallahassee, 

Florida: Bureau of Watershed Management, Division of Water Resource Management. 

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

Harper, H. H. and D. B. Baker. 2003. Evaluation of alternative stormwater regulations for 

southwest Florida. Submitted to: Water Enhancement & Restoration Coalition, Inc. 

Prepared by Environmental Research & Design, Inc. 

Hornsby, D., R. A. Mattson, and T. Mirti. 2000. Surfacewater quality and biological monitoring. 

Annual Report. 1999. Suwannee River Water Management District Technical Report WR00-04. iv, 148 pp. 

Hupalo, R. B., C. P. Neubauer, L. W. Keenan, D. A. Clapp, and E. F. Lowe. 1994. 

Establishment of minimum flows and levels for the Wekiva River system. St. Johns River 

Water Management District Technical Publication SJ94-1. 86 pp. 

Komarek, J. 2003. Coccoid and colonial cyanobacteria. Pp. 59-116 IN: J. D. Wehr and R. G. 

Sheath (eds.), Freshwater Algae of North America. Ecology and Classification. Academic 

Press, New York, NY. 

Mattson, R. A., E. F. Lowe, C. L. Lippincott, and L. Battoe. 2006. Wekiva River and Rock 

Springs Run pollutant load reduction goals. Report to the Florida Department of 

Environmental Protectcion. St. Johns River Water Management District, Palatka, FL. 
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Florida Department of Environmental Protection 

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Osburn, W., D. Toth, and D. Boniol. 2002. Springs of the St. Johns River Water Management 

District. SJRWMD Technical Report SJ2002-5. 

Potapova, M. and D. F. Charles. 2005. Choice of substrate in algae-based water quality 

assessment. J. North American Benthological Soc. 24(2): 415-427. 

Reckhow, K. H., Beaulac, M. N., and Simpson, J. T. 1980. Modeling phosphorus loading and 

lake response under uncertainty: A manual and compilation of export coefficients. United 

States Environmental Protection Agency. EPA 440/5-80-011. 

Schmidt, W. 1997. Geomorphology and physiography of Florida. Pp. 1-12 IN: A. F. Randazzo 

and D. S. Jones(eds.), The Geology of Florida. University Press of Florida, Gainesville, FL. 

Stevenson, R. J., A. Pinowska, and Y-K Wang. 2004. Ecological condition of algae and 

nutrients in Florida Springs. Final Report to the Florida Department of Environmental 

Protection, Tallahassee, FL. 101pp. 

Toth, D. J. and C. Fortich. 2002. Nitrate Concentrations in the Wekiva Groundwater Basin, With 

Emphasis on Wekiva Springs. St. Johns River Water Management District Technical 

Publication SJ2002-2. 84 pp. 

United States Environmental Protection Agency. 2006a. Establishing TMDL “Daily” Loads in 

Light of the Decision by the U.S. Court of Appeals for the D.C. Circuit in Friends of the 

Earth, Inc. v. EPA, et al., No.05-5015, (April 25, 2006) and Implications for NPDES permits. 

Memorandum from Benjamin Grumbles, assistant administrator, Office of Water. U.S. 

Environmental Protection Agency, Washington, DC. 

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TMDL (draft). Office of Wetlands, Oceans, and Watersheds. 

WSI Inc. 2004. Work Plan. Pollutant load reduction goal (PLRG) analysis for the Wekiva River 

and Rock Springs Run, Florida. Report prepared for the St. Johns river Water management 

District, Palatka, FL. Pp. variously numbered. 

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TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

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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. In 1994, the Department’s 

stormwater treatment requirements were integrated with the stormwater flood control 

requirements of the state’s water management districts, along with wetland protection 

requirements, into the Environmental Resource Permit regulations. 

Chapter 62-40, F.A.C., also requires the water management districts 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 had been developed for Newnans Lake when this report was published. 

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 permitting 

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

promulgated regulations and began implementing the Phase I NPDES stormwater program in 

1990. These stormwater discharges include certain discharges that are associated with 

industrial activities designated by specific standard industrial classification (SIC) codes, 

construction sites disturbing 5 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 implemented Phase I of the MS4 permitting 

program on a countywide basis, which brought in all cities (incorporated areas), Chapter 298 

urban water control districts, and the Florida Department of Transportation throughout the 15 

counties meeting the population criteria. The Department received authorization to implement 

the NPDES stormwater program in 2000. 

An important difference between the federal NPDES and the state’s stormwater/environmental 

resource permitting programs is that the NPDES Program covers both new and existing discharges, 

while the state’s program focuses on new discharges only. Additionally, Phase II of the NPDES 

Program, implemented in 2003, expands the need for these permits to construction sites between 1 

and 5 acres, and to local governments with as few as 1,000 people. 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, as 

are other point sources of pollution such as domestic and industrial wastewater discharges. It should be 

noted that all MS4 permits issued in Florida include a re-opener clause that allows permit revisions to 

implement TMDLs when the implementation plan is formally adopted. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

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Appendix B. Change Point Analysis of the Suwannee 

River Algal Data 

Xu-Feng Niu 

 Department of Statistics 

Florida State University 

Tallahassee, FL 32306 

January-February 2007 

Technical Report Submitted to 

the Florida Department of Environmental Protection 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

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I. Background 

Per the request of the Wekiva Parkway and Protection Act (WPPA) passed by the Florida 

Legislature in 2004 (Chapter 369, Part III, FS), the Florida Department Environmental Protection 

(the Department) is developing a nitrate Total Maximum Daily Load (TMDL) for the Wekiva 

River and Rock Springs Run in the central Florida area. Based on information provided by the 

St. Johns River Water Management District (SJRWMD), these two waterbodies showed 

elevated periphyton abundance compared to two reference creeks (Juniper Creek and 

Alexander Springs Run) located in the same region and were therefore considered impaired. 

After examining the distribution of various physical, chemical, and biological parameters in the 

Wekiva River and Rock Springs Run and in reference waterbodies, it was decided that elevated 

nitrate concentrations in the Wekiva River and Rock Springs Run is one of the major pollutants 

that caused this impairment. According to the 1999 Florida Watershed Restoration Act (FWRA), 

Chapter 99-223, Laws of Florida, once a waterbody is verified for impairment, a TMDL must be 

developed. 

Establishing a nitrate target for the Wekiva River and Rock Springs Run is a critical part of the 

TMDL development. To define this target, a functional relationship between the periphyton 

abundance and nitrate concentration needs to be characterized. Ideally, the functional 

relationship would be built upon data collected from the Wekiva River and Rock Springs Run. 

Unfortunately, because of the limit amount of time available to this project, not enough data 

were available to establish the relationship in these two waterbodies. Therefore, this study uses 

nitrate and periphyton data collected from a monitoring network on the Suwannee River, which 

was established for the Surface Water Improvement and Management (SWIM) program by the 

Suwannee River Water Management District (Hornsby, et al. 2000). Much of the length of the 

Suwannee River is heavily influenced by spring inflow, and the algal communities appear to be 

generally similar in composition to those in the Wekvia River and Rock Springs Run. 

Therefore, results from the Suwannee River are considered applicable to the Wekiva River and 

Rock Springs Run (Mattson et al., 2006). 

Nitrate and periphyton data were collected concurrently from 13 stations across the Suwannee 

River and two tributaries (Withlacoochee River and Santa Fe River) during the period from 1990 

through 1998. Figure 1 shows locations of these water quality stations. Table 1 lists the period 

of records and number of samples for each station. Periphyton abundance was measured as 

both the cell density (cells/cm2

) and biomass density (ash free dry mass – AFDM/cm2). Longterm average nitrate concentrations and periphyton measurements were calculated for each 

sampling station. Functional relationships between nitrate and periphyton abundance were 

established by plotting either long-term average cell densities or biomass density to long-term 

average nitrate concentrations from all water quality stations. 

Significant relationships were found between nitrate concentration and algal abundance. 

Figure 2 shows the correlation of mean nitrate concentrations versus mean periphyton biomass 

(r = 0.84; P<0.001). There is also a significant positive correlation between mean algal density 

and mean nitrate concentration (Figure 3: r = 0.77; P<0.01), indicating that increasing nitrate 

concentration in nature streams could result in elevated periphyton biomass (Mattson, 2006). In 

addition, both Figures 2 and 3 suggest that there is a threshold nitrate concentration in the 

range between 0.2 and 0.4 mg/L, above which the increase of periphyton abundance per unit 

increase of nitrate concentration becomes significantly higher than below this threshold point.
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Figure 1. Locations of water quality stations from which measured 

nitrate and periphyton abundance were used for this 

analysis. 
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Table 1. Period of records and number of paired nitrate and periphyton 

samples from each station 

Stations Period of records Number of samples

SUW010 06/1990 – 12/1998 24 

SUW100 06/1990 – 12/1998 30 

SUW130 06/1990 – 12/1998 33 

SUW140 06/1996 – 12/1998 8 

SUW150 06/1990 – 12/1998 30 

SUW240 12/1992 – 12/1998 23 

SUW275 03/1990 – 06/1992 10 

SFR020 03/1990 – 12/1998 32 

SFR040 03/1990 – 12/1998 34 

SFR070 03/1990 – 12/1998 33 

WIT010 03/1990 – 09/1991 6 

WIT020 03/1990 – 09/1991 6 

WIT030 03/1990 – 06/1991 5 

The purpose of this study is to use change-point statistical analysis to identify the threshold 

nitrate concentration. This nitrate threshold, once being identified, can be used as the target 

nitrate concentration for the nitrate TMDL of the Wekiva River and Rock Springs Run. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

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Figure 2. Relationship between mean nitrate concentration and mean periphyton 

biomass from sampling sites on the Suwannee, Santa Fe, and 

Withlacoochee Rivers. 

 

Figure 3. Relationship between mean nitrate concentration and mean periphyton 

cell density from sampling sites on the Suwannee, Santa Fe, and 

Withlacoochee Rivers. 

Mean NOx vs. Mean Biomass

1

2

3

4

5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Mean NOx (mg/L)

AFDW g / m2

Mean NOx vs. Mean Cell Density

0

100000

200000

300000

400000

500000

600000

700000

800000

900000

1000000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Mean NOx (mg/L)

Cells / cm2
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The Detection Procedure 

Niu et al. (2000) introduced an iterative procedure for detecting and modeling level-shift change 

points. Niu and Miller (2007) reported the change point analysis and a model comparison 

procedure for the Stream Condition Index (SCI) and Biological Condition Gradient (BCG) data. 

The change-point detection procedure in Niuet al. (2000) is similar to that suggested by Chang 

(1982) and further developed by Chang et al. (1988) for detecting outliers and level shifts in 

time series analysis. Statistical details of this procedure can also be found in Pankratz (1991, 

Chapter 8). 

For simplicity, let us consider a response variable Y, after an appropriate transformation. 

Suppose that observations {( ,) Xi i Y , i n = 1, 2, , L } are available where n is the sample size 

and X is an independent variable. Moreover, we assume that the observations are arranged in 

the following manner: 

• The values { , Xi i n = 1, 2, , L } are distinct. If several ' Y s i are corresponding to a 

single X value, the median of the ' Y s i is taken to be the response value for the X value. 

• {( ,) Xi i Y , i n = 1, 2, , L } are sorted according to the values of X from least to greatest. 

For each integer l > 1, define the step variable () 0 i S l = for i l < and () 1 i S l = for i l ≥ . 

Step 1. Fit the linear regression model: 

0 1 () () () () Y l lSl l i i =+ + β β ε i , i n = 1, 2, , L , (1) 

where for a fixed l, the ( )' i ε l s are assumed to be independent and identically distributed normal 

random variables with mean zero and variance 2 σ ( )l . 

Step 2. Calculate the values { 1 1 L l l se l ( ) ( ) / ( ( )) = β β

) ) , l n = 2, 3, , ( 1) L − } where 1 se l ( ( )) β) is the 

estimated standard error of 1 β ( )l ) . 

Step 3. Let 1 Ll L L Ln ( ) max{ (2), (3), , ( 1)} = − L and compare 1 L l( ) with the critical value 

C=3.0 (or C=3.5). The critical value C=3.0 (or C=3.5) corresponds roughly to α = 0.10

(orα = 0.05), or the 10% (or the 5%) significance level, based on the simulation results of 

Chang et al. (1988). If 1 L l( ) is significant, we conclude that the response Y has a change point 

at 1 Xl with a level-shift 1 β ( )l ) . 

Step 4. Let *

11 1 () () Y Y lSl ii i = − β . Repeat Steps 1-3 on the new response variable * Yi for 

detecting a possible second change point. Continue the process until no further change point 

can be identified. 
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Step 5. Suppose that k change points are detected in the response variable Y and the 

corresponding X values are 1 2 {, ,, }k Xll l X X L . Fit the model 

0 11 2 2 () () () Y Sl Sl Sl i ii k = + + ++ + β ββ β ε L i k i , i n = 1, 2, , L . (2) 

Then the estimated coefficients 1 2 {, , , } β β β k

) ) ) L will be the k estimated level-shift values. 

II. Model Comparison 

Model (2) fits a step function 0 11 2 2 () () () ii k i k β + + ++ ββ β Sl Sl Sl L to estimate the mean (or 

median) value of the response variable Y and the predictor variable X. In practice, many other 

models may be considered to describe the relationship between Y and X. In particular, if the 

scatter plot of observations {( ,) Xi i Y , i n = 1, 2, , L } shows a straight line or a smooth curve 

pattern, a linear regression model or a nonlinear smooth-curve model should be fitted to the 

data instead of the step-function change point model in (2). 

For the response variable Y and the predictor variable X, the linear regression model has the 

form: 

 Y X i i =+ + β0 1 β ε i , i n = 1, 2, , L . (3) 

If the relationship between Y and X is nonlinear, many smooth-curve models may be 

considered. One of the choices is transforming the predictor variable X and fitting a regression 

model. For example, we may use the natural logarithm transformation log(X) instead of X as the 

predictor variable and fit the regression model: 

 0 1 log( ) Y X i i =+ + β β ε i , i n = 1, 2, , L . (4) 

When different models are fitted to the observations {( ,) Xi i Y , i n = 1, 2, , L }, model selection 

techniques need to be used to decide which model fits the data better. Statistical inferences 

such as estimation and prediction will then be based on the best model selected. The Bayesian 

Information Criterion (SBC) suggested by Schwartz (1978) is one of the popular criteria for 

model comparison. For a fitted model (linear or nonlinear) with p parameters, the SBC is defined 

as 

SBC(p) = − 2 log(maximum likelihood function) + p × log(n), 

where the likelihood function is based on the distribution assumption of the model such as 

normal or log-normal or other distribution families, and n is the sample size. When the random 

errors i ε ’s have a normal distribution, the SBC(p) has the simplified form: 
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SBC(p) = ( ) 2

1

ˆ log ( ) /( 1) n

i i i n YY np = × − −− ∑ + p × log(n), (5) 

where ˆY i is the fitted value based on one of the candidate models and 2

1

ˆ ( ) n

i i i

Y Y = ∑ − is the 

Residual Sum of Squares (RSS) based on the fitted candidate model. 

 Intuitively, there are two parts in (5), the first part is 

( ) 2

1

ˆ log ( ) /( 1) n

i i i n YY np = × − −− ∑ = 2

n ×logσˆ , 

which is a measure of the goodness-of-fit of the candidate model. In general, increasing the 

number of parameters in a model will improve the goodness-of-fit of the model to the data 

regardless how many parameters are in the true model that generated the data. When a model 

with too many predicators (significant or not significant ones) is fitted to a data set, we may get a 

perfect fit but the model will be useless for inference such as prediction. In statistics, fitting a 

model with too many unnecessary parameters is called over-fitting. The second part in SBC, p

× log(n), puts a penalty term on the complexity of a candidate model, which will increase when 

the number of parameters in a candidate model increases. Thus the criterion SBC requires a 

candidate model fitting the data well and penalizing the complexity of the model. For a group of 

candidate models, the SBC value can be calculated for each of the models and the 

preferred model is the one with the lowest SBC value. 

III. Change Point Analysis of Suwannee River Algal Data 

1. Mean Abundance (Cell Density) vs Mean NOx 

a). Change Point Analysis 

Table 2 presents the mean NOx and mean abundance data at stations along the Suwannee 

river and its two major tributaries (Withlacoochee and Santa Fe). The data were collected by the 

Suwannee River Water Management District (SRWMD). The first column of the table gives the 

station name. Columns 3 and 4 list the mean NOx and mean abundance at the 13 stations. 

Among stations with mean NOx above 0.4, it was noticed that station SUW275 reported much 

lower mean abundance (163243.90). The authors of this report consulted with Mr. Robert 

Mattson of SRWMD and learned that “the site SUW275 is ‘Suwannee River at Gopher River’ 

that is located way, way down on the river.” Mr. Mattson considers that SUW275 is the upper, 

tidal freshwater region of the Suwannee estuary. Current velocities there can be quite strong, 

and it also may be that the area got a short "shock" of salinity during the drought of 1990-91, 

even though it is usually a totally freshwater site. Furthermore, Mr. Mattson commented that 

“the site is a bit different and may not be entirely comparable to upstream, riverine sites such as 

SUW100 (Suwannee River at Ellaville - at the confluence with the Withlacoochee) and SUW130 

(Suwannee River near Luraville, between Ellaville and Branford).” 

 Based on discussion between the authors of this report and Mr Mattson, we think that the data 

at station SUW275 is not comparable with those at other stations. Thus the data at SUW275 

will be removed from the change point analysis in this report. After removing the data at Station 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

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SUW275, the mean NOx and mean abundance data at the remaining 12 stations of the 

Suwannee River system are listed in the last two columns in Table 2. 

Change point analysis was performed for mean abundance vs mean NOx. One change points 

was detected at the mean NOx values of 0.401, which was from the station SUW100. The 

change point has the statistic 1 L l( ) 6.39 = and is significant at the 5% level (95% confidence). 

Figure 4 presents the fitted step-function regression model to the mean abundance values. The 

R-square of the regression is 0.803, indicating that the step-function regression model fits the 

mean abundance values very well. 

Table 2. Mean NOx and Mean Abundance Data at the Suwannee River Stations 

Original Data Data Used in The Change Point Analysis 

Station Mean NOx Mean 

abundance Mean NOx Mean abundance 

SUW010 0.035 109810.67 0.035 109810.67 

SFR020 0.064 69202.03 0.064 69202.03 

SFR040 0.186 189050.82 0.186 189050.82 

WIT020 0.223 191812.50 0.223 191812.50 

WIT010 0.256 176643.67 0.256 176643.67 

WIT030 0.286 241469.20 0.286 241469.20 

SUW100 0.401 479615.50 0.401 479615.50 

SUW130 0.420 520475.42 0.420 520475.42 

SUW275 0.466 163243.90 

SFR070 0.565 663744.24 0.565 663744.24 

SUW150 0.589 920012.14 0.589 920012.14 

SUW240 0.671 588875.04 0.671 588875.04 

SUW140 0.900 525038.75 0.900 525038.75 

Change Points: 1) Mean NOx = 0.401 with the test statistic of 6.39 and confidence level 

 over 95%; 

 2) Highlighted numbers are the mean NOx-Abundance values at the 

 change point. 

 3) Notice that the mean NOx value just before the change point is 0.286. 

 Critical changes in mean abundance actually happened as the mean 

 NOx changed from 0.286 to 0.401.
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Mean NOx (Mg/L)

Mean Cell Density (/Square-CM)

0.2 0.4 0.6 0.8

0 2*10^5 4*10^5 6*10^5 8*10^5 10^6

Figure 4. Mean Cell Density vs Mean NOx Change-Point Model 

(Step Function) 

Change Points: Mean NOx=0.401 with the test statistic of 6.39 and confidence level 

over 95%; 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

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b). Model Comparison 

For the purpose of model comparison, two other models, the linear regression model in (3) and 

the non-linear regression model in (4), were also fitted to the data. Figure 5 presents the two 

fitted models. 

Mean NOx (Mg/L)

Mean Cell Density (/Square-CM)

0.2 0.4 0.6 0.8

0 2*10^5 4*10^5 6*10^5 8*10^5 10^6

Figure 5. Linear Model (Solid Black), and Non-Linear Model (Mean 

Cell Density on log(Mean NO), Red) 

The three fitted regression models are presented in Table 3. The SBC values for the 

change-point model, the linear regression model, and the non-linear regression model 

are 286.22, 293.32, and 294.13, respectively. Thus, the change-point model was the 

best model among the three models. Based on the fitted change-point model, the 

change point at Mean NOx of 0.401 is extremely significant (with p-values =0.0001). 

The mean abundance value at the change point increased 453295.37. 
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Table 3. Fitted Regression Models 

 

Model 1. Step-Function Regression (Change Point Model) : 

Coefficients: 

 Value Std. Error t value Pr(>|t|) 

(Intercept) 162998.1482 50152.6502 3.2500 0.0087 

 NOx_0.401 453295.3680 70926.5581 6.3911 0.0001 

Residual standard error: 122800 on 10 degrees of freedom 

Multiple R-Squared: 0.8033 

F-statistic: 40.85 on 1 and 10 degrees of freedom, the p-value is 

0.00007923 

 

 

SBC Value: 286.22 

Model 2. Linear Regression Model: 

Coefficients: 

 Value Std. Error t value Pr(>|t|) 

(Intercept) 76552.0120 87601.4494 0.8739 0.4027 

 MN 817477.3373 191903.4375 4.2598 0.0017 

Residual standard error: 165100 on 10 degrees of freedom 

Multiple R-Squared: 0.6447 

F-statistic: 18.15 on 1 and 10 degrees of freedom, the p-value is 

0.001663 

 

SBC Value: 293.32 

Model 3. Non-Linear Regression Model: 

Coefficients: 

 Value Std. Error t value Pr(>|t|) 

(Intercept) 664741.5001 84092.3831 7.9049 0.0000 

 MN1 215985.5866 53485.6084 4.0382 0.0024 

Residual standard error: 170800 on 10 degrees of freedom 

Multiple R-Squared: 0.6199 

F-statistic: 16.31 on 1 and 10 degrees of freedom, the p-value is 

0.002368 

SBC Value: 294.13 
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Florida Department of Environmental Protection 

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2. Mean Biomass vs Mean NOx 

a). Change Point Analysis 

Table 4 presents the mean NOx and mean biomass data at stations along the Suwannee river 

and its two major tributaries (Withlacoochee and Santa Fe). The first column of the table gives 

the station name. Columns 3 and 4 list the mean NOx and mean biomass at the 13 stations. 

Based on the discussion between the authors of this report and Mr Mattson, we decided to 

remove the data at the site SUW275 from the change point analysis in this report. After 

removing the data at Station SUW275, the mean NOx and mean Biomass data at the remaining 

12 stations of the Suwannee River system are listed in the last two columns in Table 4. 

Change point analysis was performed for mean biomass vs mean NOx. One change points was 

detected at the mean NOx values of 0.420, which was from the station SUW100. The change 

point has the statistic 1 L l( ) 6.10 = and is significant at the 5% level (95% confidence). Figure 6 

presents the fitted step-function regression model to the mean abundance values. The Rsquare of the regression is 0.788, indicating that the step-function regression model fits the 

mean abundance values very well. 

Table 4. Mean NOx and Mean Biomass Data at the Suwannee River Stations 

Original Data Data Used in The Change Point Analysis 

Station Mean 

NOx 

Mean 

abundance Mean NOx Mean Biomass 

SUW010 0.035 1.341 0.035 1.341 

SFR020 0.064 1.348 0.064 1.348 

SFR040 0.186 1.356 0.186 1.356 

WIT020 0.223 1.867 0.223 1.867 

WIT010 0.256 1.456 0.256 1.456 

WIT030 0.286 2.187 0.286 2.187 

SUW100 0.401 2.590 0.401 2.590 

SUW130 0.420 4.205 0.420 4.205 

SUW275 0.466 2.173 

SFR070 0.565 4.693 0.565 4.693 

SUW150 0.589 4.636 0.589 4.636 

SUW240 0.671 2.617 0.671 2.617 

SUW140 0.900 4.644 0.900 4.644 

Change Points: 1) Mean NOx=0.420 with the test statistic of 6.10 and confidence 

level over 95%; 
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 2) Highlighted numbers are the mean NOx-Abundance values at 

the change point. 

 3) Notice that the mean NOx value just before the change point 

is 0.401. Critical changes in mean abundance actually 

happened as the mean NOx changed from 0.401 to 0.420.

Mean NOx (Mg/L)

AFDW (g/Square-Meter)

0.2 0.4 0.6 0.8

12345

Figure 6. Mean Biomass vs Mean NOx Change-Point Model (Step 

Function) 

Change Points: Mean NOx=0.420 with the test statistic of 6.10 and confidence 

level over 95%; 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

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b). Model Comparison 

For the purpose of model comparison, two other models, the linear regression model in 

(3) and the non-linear regression model in (4), were also fitted to the data. Figure 7 

presents the two fitted models.

Mean NOx (Mg/L)

AFDW (g/Square-Meter)

0.2 0.4 0.6 0.8

1

2

3

4

5

Figure 7. Linear Model (Solid Black) and Non-Linear Model (Mean 

Biomass on log(Mean NO), Red) 

The three fitted regression models are presented in Table 5. The SBC values for the 

change-point model, the linear regression model, and the non-linear regression model 

are -4.33, 0.651, and 4.09, respectively. Thus, the change-point model was the best 

model among the three models. Based on the fitted change-point model, the change 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

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point at Mean NOx of 0.420 is extremely significant (with p-values =0.0001). The mean 

abundance value at the change point increased 2.424. 
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Florida Department of Environmental Protection 

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Table 5. Fitted Regression Models 

 

Model 1. Step-Function Regression (Change Point Model) : 

Coefficients: 

 Value Std. Error t value Pr(>|t|) 

(Intercept) 1.7350 0.2565 6.7630 0.0000 

 x1 2.4240 0.3974 6.0991 0.0001 

Residual standard error: 0.6788 on 10 degrees of freedom 

Multiple R-Squared: 0.7881 

F-statistic: 37.2 on 1 and 10 degrees of freedom, the p-value is 

0.0001158 

 

SBC Value: -4.33 

Model 2. Linear Regression Model: 

Coefficients: 

 Value Std. Error t value Pr(>|t|) 

(Intercept) 1.0344 0.4432 2.3341 0.0418 

 MN 4.4663 0.9708 4.6006 0.0010 

Residual standard error: 0.8353 on 10 degrees of freedom 

Multiple R-Squared: 0.6791 

F-statistic: 21.17 on 1 and 10 degrees of freedom, the p-value is 

0.0009793 

SBC Value: 0.651 

Model 3. Non-Linear Regression Model: 

Coefficients: 

 Value Std. Error t value Pr(>|t|) 

(Intercept) 4.1526 0.4746 8.7496 0.0000 

 MN1 1.1052 0.3019 3.6611 0.0044 

Residual standard error: 0.9639 on 10 degrees of freedom 

Multiple R-Squared: 0.5727 

F-statistic: 13.4 on 1 and 10 degrees of freedom, the p-value is 

0.004381 

SBC Value: 4.09 
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3. Summary and Conclusions 

In this report, change point analysis was preformed for the algal data at stations along 

the Suwannee river and its two major tributaries (Withlacoochee and Santa Fe). The 

main findings in this report are the followings: 

1) For the change point analysis of mean abundance vs mean NOx, one 

change point was detected at NOx=0.401 that is corresponding to the data 

at the site SUW100. The change point is significant at the confidence level 

95%. Model comparison shows that the change point model fit the data 

better than the linear regression model and a nonlinear regression model. 

The mean NOx value just before the change point is 0.286, indicating that 

critical changes in mean abundance actually happened as the mean NOx 

changed from 0.286 to 0.401.

2) For the change point analysis of mean biomass vs mean NOx, one change 

point was detected at NOx=0.420 that is corresponding to the data at the 

site SUW130. The change point is significant at the confidence level 95%. 

Model comparison shows that the change point model fit the data better 

than the linear regression model and a nonlinear regression model. The 

mean NOx value just before the change point is 0.401, indicating that 

critical changes in mean abundance actually happened as the mean NOx 

changed from 0.401 to 0.420.

Based on this analysis, we conclude that the major changes in mean abundance 

and mean biomass happened at mean NOx around 0.4. Further studies may be 

needed to confirm this finding.
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

81

References: 

Chang, I. 1982. “Outliers in Time Series," Unpublished Ph.D. Dissertation, Department of 

Statistics, University of Wisconsin, Madison. 

Chang, I., G.C. Tiao, and C. Chen. 1988. “Estimation of Time Series Parameters in the 

Presence of Outliers," Technometrics, 30: 193-204. 

Hornsby, D., R. A. Mattson, and T. Mirti. 2000. Surface water quality and biological 

 monitoring. Annual Report. 1999. Suwannee River Water Management District 

Technical 

 Report WR-00-04. iv, 148 pp 

Mattson, R. A., E. F. Lowe, C. L. Lippincott, J. Di, and L. Battoe. 2006. Wekiva River 

and 

 Rock Springs Run pollutant load reduction goals. Report to the Florida 

Department of 

 Environmental Protection. St. Johns River Water Management District. 

. 

Niu, X., P. Lin, and D. Meeter. 2000. “Detecting Change Points in the Species 

Composition and 

 Water Quality Data of WCA2A”. Department of Statistics, Florida State University, 

 Tallahassee. Technical Report Submitted to the Florida Department of 

Environmental 

 Protection. 

Niu, X., and D. Miller 2007. “Change Point Analysis and Model Comparison of Stream 

 Condition Index and Biological Condition Gradient Data.”

 Technical Report Submitted to the Florida Department of Environmental Protection. 

 Pankratz, A. 1991. Forecasting with Dynamic Regression Models. John Wiley & Sons Inc. New 

York. 

 Schwartz, G. 1978. Estimating the Dimension of a Model. The Annals of Statistics, 6: 461-464. 
TMDL Report: Middle St. Johns Basin, Wekiva River Main Stem and Rock Springs Run, Nitrate and TP 

Florida Department of Environmental Protection 

82

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 

www2.dep.state.fl.us/water/