FINAL 4/14/06 FLORIDA DEPARTMENT OF ENVIRONMENTAL PROTECTION Division of Water Resource Management, Bureau of Watershed Management CENTRAL DISTRICT • MIDDLE ST. JOHNS BASIN TMDL Report Nutrient and Unionized Ammonia TMDLs for Lake Jesup, WBIDs 2981 and 2981A Xueqing Gao April 14, 2006 Executive Summary This report presents the Total Maximum Daily Load (TMDL) for nutrients and unionized ammonia for Lake Jesup (including Lake Jesup outlet), in the Middle St. Johns Basin. The lake was verified as impaired for nutrients and unionized ammonia due to elevated annual average Trophic State Index (TSI) values and exceedances of the unionized ammonia criterion (0.02 milligrams per liter [mg/L]), and was included on the Verified List of impaired waters for the Middle St. Johns Basin that was adopted by Secretarial Order on May 27, 2004. 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. The purpose of the TMDL is to establish the allowable loadings of pollutants to Lake Jesup that would restore the waterbody so that it meets its applicable water quality criteria for nutrients and unionized ammonia. The nutrient TMDL for Lake Jesup was developed through four major steps: 1. Establish the TSI target 2. Model the existing nutrient load 3. Model the load that would achieve the TSI target (the TMDL) 4. Estimate the percent load reduction needed to meet the TMDL. To establish the TSI target, the Department first estimated the background TSI for the lake by comparing results from several methods, including a historic sedimentation rate method, literature published values, a TSI defined by the Florida Impaired Waters Rule, an Ecoregion approach, a hydrogeomorphologic method, and a model simulated background condition. Results from these different methods all converged on a TSI of 60. To allow some assimilative capacity above background, the Department added 5 TSI units to the estimated background TSI and defined 65 as the target TSI for Lake Jesup. Nutrient loads from the watershed were simulated using a watershed pollutant loading model developed by PBS&J. This model is based on the Soil Conservation Service curve number approach, which takes into consideration the landuse, soil, and antecedent moisture condition of the soil in simulating the watershed loads. Nutrient loads from other sources, including groundwater input through baseflow and Artesian flow, loading from septic tanks, atmospheric deposition directly on to the lake surface, and nitrogen fixation were also considered. Estimates of nutrient loads from all these sources were entered into the Bathtub model to estimate in-lake TN, TP, and chlorophyll a concentrations, and model calibration was conducted through fitting model simulated concentrations with measured results. The watershed nutrient loads that resulted in existing TN, TP, and chlorophyll a concentrations were considered the existing nutrient loads. To estimate the nutrient TMDL, nutrient loads from different sources were adjusted using the calibrated PBS&J-Bathtub model suite until the target TSI was achieved. The nutrient loads that resulted in the target TSI were considered the TMDL. The percent load reduction required to achieve the TMDL was then calculated by dividing the difference between the existing load and the TMDL by the existing load. The following table provides the TN and TP TMDLs and ii Florida Department of Environmental Protection required percent load reductions to achieve the TMDLs. As there are no major wastewater facilities discharging to surface waters in the Lake Jesup watershed, no wasteload allocation for conventional point source (WLANPDES wastewater ) was estimated. TMDL components for Lake Jesup TMDL WBID Parameter WLA LA MOS (kg/year)* NPDES Stormwater 2981 (including 2981A) TN 247,300 50% 50% Implicit 2981 (including 2981A) TP 19,000 34% 34% Implicit * = Kilograms per year Un-ionized ammonia TMDL was not directly addressed in this TMDL report. Based on the observed relationship between pH and chlorophyll a concentrations, and the relationship between pH and un-ionized ammonia concentrations, the lake un-ionized ammonia concentration should meet the water quality criterion of 0.02 mg/L, once the target TSI of the lake is achieved. iii Florida Department of Environmental Protection TMDL Report: Middle St. Johns Basin, Lake Jesup, WBIDs 2981/2981A, Nutrients/Unionized Ammonia Acknowledgments This analysis could not have been accomplished without substantial support and assistance from the Seminole County Public Works Department and PBS&J. The county has very actively assisted the Florida Department of Environmental Protection (Department) in obtaining the needed information for total maximum daily load (TMDL) development and in providing valuable comments and suggestions. PBS&J, an environmental consulting company hired by Seminole County, played an indispensable role in coordinating information collection and assembly for the Department, providing the watershed model, and actively updating the model. The Department recognizes and appreciates the help received from Kim Ornberg, Mark Flomerfel, Gloria Eby, and Donald E. McKenna from Seminole County; and Joe Walter and his staff from PBS&J. The Department acknowledges the significant input of the St. Johns River Water Management District, especially the contributions of Troy Keller and Yanbing Jia. Both provided valuable suggestions on the modeling approach and constantly exchanged information with the Department on their efforts in developing the pollutant load reduction goal (PLRG) for Lake Jesup. The studies conducted by Troy Keller on potential water quality targets for the PLRG provided an important basis for the Department to develop its water quality targets for the TMDL. The Department would like to thank the Orange County Public Works Department and the cities of Orlando, Winter Park, Maitland, Altamonte Springs, Casselberry, Winter Springs, Oviedo, and Lake Mary. All these agencies provided valuable information to help the Department better understand the Lake Jesup watershed, and also provided a significant amount of data to support the modeling efforts. Our appreciation goes to the Friends of Lake Jesup (Robert King and his colleagues). The concerns raised by this environmental group helped the Department to consider various issues related to TMDL development and the management of the overall watershed and lake. The Department also thanks Doug Dycus (PBS&J) and Steve Lienhart (URS Corporation) for their valuable input and suggestions. Finally, this TMDL could not have been completed without close cooperation among Department staff. Mary Paulic did a great job of organizing local stakeholder meetings. Barbara Donner provided assistance in basin delineation and estimated the forest/wetlands ratio for background condition. Rick Hicks and Haizhi Chen provided data for ground water quality. Douglas Gilbert, Wayne Magley, Jan Mandrup-Poulsen, Fred Calder, and Paul Lee all provided valuable suggestions and comments regarding water quality modeling, ground water simulation, water management policy and regulation, and public involvement in TMDL development and implementation. Editorial assistance provided by Daryll Joyner, Jan Mandrup-Poulsen, and Linda Lord For additional information on the watershed management approach and impaired waters in the Middle St. Johns Basin, contact Xueqing Gao Florida Department of Environmental Protection Bureau of Watershed Management iv TMDL Report: Middle St. Johns Basin, Lake Jesup, WBIDs 2981/2981A, Nutrients/Unionized Ammonia Watershed Planning and Coordination Section 2600 Blair Stone Road, Mail Station 3565 Tallahassee, FL 32399-2400 Email: [email protected] Phone: (850) 245-8464, SunCom: 205-8464 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 Planning and Coordination Section 2600 Blair Stone Road, Mail Station 3565 Tallahassee, FL 32399-2400 Email: [email protected] Phone: (850) 245-8464, SunCom: 205-8464 Fax: (850) 245-8434 v Florida Department of Environmental Protection TMDL Report: Middle St. Johns Basin, Lake Jesup, WBIDs 2981/2981A, Nutrients/Unionized Ammonia Contents Chapter 1: INTRODUCTION _____________________________________________ 1 1.1 Purpose of Report ________________________________________________ 1 1.2 Identification of Waterbody ________________________________________ 1 1.3 Background ______________________________________________________ 3 Chapter 2: DESCRIPTION OF WATER QUALITY PROBLEM __________________ 5 2.1 Statutory Requirements and Rulemaking History ______________________ 5 2.2 Information on Verified Impairment __________________________________ 5 Chapter 3. DESCRIPTION OF APPLICABLE WATER QUALITY STANDARDS AND TARGETS ______________________________________________ 7 3.1 Classification of the Waterbody and Criteria Applicable to the TMDL ______ 7 3.2 Applicable Water Quality Standards and Numeric Water Quality Target ___ 7 3.2.1 Unionized Ammonia Criterion _____________________________________ 7 3.2.2 Interpretation of Narrative Nutrient Criterion __________________________ 7 Chapter 4: ASSESSMENT OF SOURCES _________________________________ 15 4.1 Types of Sources ________________________________________________ 15 4.2 Potential Sources of Nutrients in the Lake Jesup