FLORIDA DEPARTMENT OF ENVIRONMENTAL PROTECTION Division of Environmental Assessment and Restoration, Bureau of Watershed Restoration CENTRAL DISTRICT • MIDDLE ST. JOHNS BASIN FINAL TMDL Report Nutrient and Dissolved Oxygen TMDLs for the Six Middle St. Johns River Segments between the Inlet of Lake Harney (WBID 2964A) and St. Johns River above Wekiva River (WBID 2893C) Xueqing Gao December 7, 2009 Executive Summary This report estimates the total maximum daily loads (TMDLs) for nutrients, including total nitrogen (TN) and total phosphorus (TP), that can be discharged into the portion of the Middle St. Johns River from Lake Harney to the confluence of the St. Johns River with the Wekiva River, without causing nutrient and dissolved oxygen (DO) impairments. This portion of the Middle St. Johns River contains six waterbody segments uniquely identified with waterbody identification numbers (WBIDs): Lake Harney (WBID 2964A), St. Johns River Downstream of Lake Harney (WBID 2964), St. Johns River above Lake Jesup (WBID 2893F), St. Johns River above Lake Monroe (WBID 2893E), Lake Monroe (WBID 2893D), and St. Johns River above Wekiva River (WBID 2893C). Using the methodology in the Impaired Surface Waters Rule (IWR) (Rule 62-303, Florida Administrative Code [F.A.C.]), the Florida Department of Environmental Protection (Department) verified that these WBIDs were impaired for nutrients and DO. The impairments were caused by excessive nutrients discharged into these river segments. Based on Section 403.067, Florida Statues (F.S.), nutrient and DO TMDLs must be developed for these segments. Establishing target nutrient concentrations is an important step in developing TMDLs. In this report, the target nutrient concentrations established for the two lakes (Lake Harney and Lake Monroe) were applied to all the impaired river segments based on the assumption that, as river channels have lower water residence time than lakes, nutrient concentrations that are sufficient to protect lake water quality should be sufficiently protective for the river segments. The nutrient targets were established using three different methods, as follows: (1) determining the nutrient concentrations that will result in Trophic State Index (TSI) values of less than 60 in Lake Harney and Lake Monroe; (2) determining the nutrient concentrations that will restore the sediment nutrient deposition rates previously determined as the level under low anthropogenic impacts, based on paleolimnological studies; and (3) determining the recommended TN and TP concentrations in published literature for reference lakes. The final target nutrient concentrations, which are 0.07 milligrams per liter (mg/L) for TP and 1.18 mg/L for TN, are medians of the recommended nutrient values obtained from these three methods (0.060 to 0.073 mg/L for TP and 1.11 to 1.22 mg/L for TN). The target TN and TP loadings were estimated using the Hydrologic Simulation Program–Fortran (HSPF) Model set up and calibrated by the St. Johns River Water Management District (SJRWMD). This model simulates pollutant loadings from pervious and impervious areas of the watershed through surface runoff, interflow, and baseflow and includes the physical, chemical, and biological processes in receiving waters that influence nutrient dynamics. The HSPF Model divides the watershed areas immediately adjacent to the impaired waters into two watersheds (Lake Harney and Lake Monroe), which were further divided into 19 sub-basins. Nutrient inputs from the Upper St. Johns River, Econlockhatchee River, and Lake Jesup were included in the model as boundary conditions. The model also considers point source loadings from the Sanford/North Wastewater Treatment Plant (WWTP) through direct discharge and reuse, loadings from failed septic tanks, loadings from atmospheric deposition directly onto the impaired river segments, and loading attenuation from existing structural best management practices (BMPs). In simulating the target nutrient loadings, the needed nutrient percent reduction established for the Lake Jesup TMDLs was applied to the discharge from the lake into the St. Johns River. Loadings from the Upper St. Johns River and the Econlockhatchee River and point and nonpoint sources (anthropogenic land uses) from the watersheds immediately adjacent to the impaired waters were adjusted until the nutrient concentrations in these impaired segments met the target nutrient concentrations. The final percent reductions needed to achieve the target nutrient concentration in all 6 impaired river segments range from 31 to 33 percent for TP and 37 to 39 percent for TN. ii Florida Department of Environmental Protection FINAL TMDL Report: Middle St. Johns Basin, Six Segments between the Inlet of Lake Harney (WBID 2964A) and St. Johns River above Wekiva River (WBID 2893C), Nutrients and DO, December 2009 Acknowledgments This TMDL report was developed based on the Hydrologic Simulation Program–Fortran (HSPF) Model created by the St. Johns River Water Management District (SJRWMD). We deeply appreciate the help and efforts of Dr. Yanbing Jia (SJRWMD Engineering Division) in explaining the model structure and assumptions. We also sincerely thank Dr. Jia and Dr. Xiaoqing Huang for providing the background information and data necessary to develop this report. Our special thanks also go to Dr. Sherry Brandt-Williams (SJRWMD’s Environmental Science Division) for all the stimulating discussions and suggestions on water quality target development. We sincerely appreciate the kind help of May Lehmensiek, who provided a tour through the Middle St. Johns River segments to help us better understand the structure and function of the system. We also want to thank Jennifer Gihring (Watershed Planning and Coordination Section of the Florida Department of Environmental Protection [Department]). Her effective contract management with BCI (also thanks to the efforts of Dr. Chandy John, Gerold Morrison, and other BCI staff) created large amounts of useful information on the system that were used to develop the TMDL. We also thank Chris Ferraro from the Department’s Central District Office and Michael Hatcher and Marc Harris from the Department’s Industrial Wastewater Section. They provided valuable information and suggestions on the point source dischargers in the basin. Last, but not least, we extend our appreciation to Christy Newsome and Janis Paulsen, who prepared the maps for this report. This TMDL report could not have be completed without the generous help of all these individuals. We sincerely thank them and hope to continue working with them in our future TMDL development efforts. Editorial assistance provided by: Jan Mandrup-Poulsen and Linda Lord For additional information on the watershed management approach and impaired waters in the Middle St. Johns Basin, contact: Samantha Budd 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: [email protected] Phone: (850) 245-8418 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 3555 Tallahassee, FL 32399-2400 Email: [email protected] Phone: (850) 245–8464 Fax: (850) 245–8434 iii Florida Department of Environmental Protection FINAL TMDL Report: Middle St. Johns Basin, Six Segments between the Inlet of Lake Harney (WBID 2964A) and St. Johns River above Wekiva River (WBID 2893C), Nutrients and DO, December 2009 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 __________________ 5 2.1 Statutory Requirements and Rulemaking History ___________________ 5 2.2 Information on Verified Impairment ______________________________ 5 2.2.1 Nutrients _______________________________________________ 6 2.2.2 Dissolved Oxygen _______________________________________ 8 2.3 Seasonal and Spatial Variation of Nutrients and DO in the Impaired Waterbodies ________________________________________________ 11 Chapter 3. DESCRIPTION OF APPLICABLE WATER QUALITY STANDARDS AND TARGETS ____________________________________________ 35 3.1 Classification of the Waterbody and Criteria Applicable to the TMDL _____________________________________________________ 35 3.2 Applicable Water Quality Standards and Numeric Water Quality Target _____________________________________________________ 35 3.2.1 Interpretation of Narrative Nutrient Criterion ________________ 35 3.2.2 Dissolved Oxygen ______________________________________ 49 Chapter 4: ASSESSMENT OF SOURCES ________________________________ 56 4.1 Types of Sources ____________________________________________ 56 4.2 Potential Sources of Pollutants in the Middle St. Johns River Basin __ 56 4.2.1 Point Sources __________________________________________ 56 4.2.1.1 Wastewater Point Sources ______________________________ 56 4.2.1.2 Municipal Separate Storm Sewer System Permittees ________ 59 4.2.2 Nonpoint Sources ______________________________________ 61 4.2.2.1 Basin Delineation and Boundary Condition ________________ 63 4.2.2.2 Land