GEORGIA DEPARTMENT OF NATURAL RESOURCES Lakes Oconee and Sinclair Proposed Criteria Technical Support Document Elizabeth A. Booth, Ph.D., P.E. and Victoria A. Adams 8/10/2018 TABLE OF CONTENTS 1.0 INTRODUCTION ................................................................................................................. 6 2.0 PROPOSED LAKE CRITERIA ............................................................................................ 8 3.0 WATER QUALITY DATA .................................................................................................... 9 4.0 MODEL DEVELOPMENT ..................................................................................................12 4.1 Watershed Modeling (LSPC) ......................................................................................... 12 4.1.1 Meteorological Data ..............................................................................................14 4.1.2 Land Cover ...........................................................................................................16 4.1.3 Soils .....................................................................................................................19 4.1.4 Stream Characteristics .........................................................................................19 4.1.5 Watershed Point Source Discharges ....................................................................22 4.1.6 Land Application Systems.....................................................................................24 4.1.7 Septic Tanks .........................................................................................................26 4.1.8 Water Withdrawals ...............................................................................................27 4.1.9 Agricultural Water Withdrawals .............................................................................27 4.1.10 LSPC Modeling Parameters ...............................................................................30 4.2 LSPC Model Calibration ................................................................................................. 34 4.3 Lake Hydrodynamic Modeling (EFDC) ............................................................................ 42 4.3.1 Tributary Inputs .....................................................................................................44 4.3.2 Point Sources Discharges.....................................................................................47 4.3.3 Water Withdrawals ...............................................................................................47 4.3.4 Meteorological Data ..............................................................................................47 4.4 Water Quality Lake Modeling (EFDC) ............................................................................. 48 4.4.1 Point Sources Discharge ......................................................................................53 4.4.2 Sediment Oxygen Demand ...................................................................................53 4.4.3 Nutrient Fluxes .....................................................................................................53 4.4.4 Modeling Parameters ............................................................................................54 4.5 EFDC Model Calibration and Verification ........................................................................ 56 5.0 MODEL SCENARIOS ........................................................................................................63 5.1 Description of Scenarios ................................................................................................ 63 5.1.1 Scenario 1A (Calibration) ......................................................................................63 5.1.2 Scenario 1B (All Forest) ........................................................................................64 5.1.3 Scenario 1C (No Point Sources – Current Landuse) .............................................64 5.1.4 Scenario 1D (Current Permit) ...............................................................................64 5.1.5 Scenario 1E (2050 Permitted Flows and Current Landuse) ..................................64 5.1.6 Scenario 1F (50% of P Strategy) ..........................................................................64 5.1.7 Scenario 1G (2050 Permitted Flows Maintaining Loads and Current Landuse) ....65 5.2 Model Calibration............................................................................................................ 65 5.2.1 Lake Oconee ........................................................................................................65 5.2.2 Lake Sinclair .........................................................................................................67 Georgia Environmental Protection Division 1 Atlanta, Georgia 5.3 Effects of Land Use Change and Point Sources ............................................................. 68 5.3.1 Lake Oconee ........................................................................................................68 5.3.2 Lake Sinclair .........................................................................................................70 5.4 Effects of Future Permitted Flows ................................................................................... 72 5.4.1 Lake Oconee ........................................................................................................72 5.4.2 Lake Sinclair .........................................................................................................74 5.5 Effects of Point Source Nutrient Management ................................................................ 76 5.5.1 Lake Oconee ........................................................................................................76 5.5.2 Lake Sinclair .........................................................................................................78 5.6 Scenario Summaries ...................................................................................................... 80 5.6.1 Chlorophyll a Results ............................................................................................80 5.6.2 Nitrogen Results ...................................................................................................81 5.6.3 Phosphorus Results..............................................................................................82 5.6.4 pH .........................................................................................................................83 6.0 DESIGNATED USE SUPPORT .........................................................................................85 6.1 Recreational Use Support .............................................................................................. 85 6.1.1 Lake Oconee ........................................................................................................85 6.1.2 Lake Sinclair .........................................................................................................88 6.2 Fisheries Use Support ................................................................................................... 90 6.2.1 Lake Oconee Fisheries .........................................................................................90 6.2.2 Lake Sinclair Fisheries ..........................................................................................92 6.2.3 Appropriate Phosphorus Criteria ...........................................................................96 6.3 Drinking Water Source Use Support .............................................................................. 97 6.3.1 Lake Oconee Intakes ............................................................................................97 6.3.2 Lake Sinclair Intakes .............................................................................................98 ACKNOWLEDGEMENTS .......................................................................................................101 REFERENCES .......................................................................................................................102 Appendix A Water Quality Data ...............................................................................................103 Appendix B Proposed Water Quality Standards for West Point Lake Memo ........................... 117 Georgia Environmental Protection Division 2 Atlanta, Georgia List of Figures 1-1. Location of Lakes Oconee and Sinclair ......................................................................... 7 3-1. Lake Oconee Monitoring Sites ...................................................................................... 10 3-2. Lake Sinclair Monitoring Sites ...................................................................................... 11 4-1. Linkage between LSPC and EFDC .............................................................................. 12 4-2. Sub-delineated 12-Digit HUC Coverage for the Lakes Oconee and Sinclair Watersheds ................................................................................................................. 13 4-3. Meteorological Stations Used in the Lakes Oconee and Sinclair LSPC Models ............ 15 4-4. Lakes Oconee and Sinclair Watersheds Land Cover from 2008 GLUT ........................ 17 4-5. Lakes Oconee and Sinclair Watersheds Impervious Coverage from 2005 GLUT ......... 18 4-6. Lakes Oconee