FINAL Total Maximum Daily Loads of Sediment/Total Suspended Solids for the Anacostia River Basin, Montgomery and Prince George’s Counties, Maryland and The District of Columbia FINAL DEPARTMENT OF THE ENVIRONMENT 1800 Washington Boulevard, Suite 540 Baltimore, MD 21230-1718 and District of Columbia Department of the Environment - Natural Resources Administration Submitted to: U.S. Environmental Protection Division, Region III Watershed Protection Division 1650 Arch Street Philadelphia, PA 19103-2029 June 2007 EPA Submittal Date: June 22, 2007 EPA Approval Date: July 24, 2007 Anacostia River Sediment TMDL Document version: June 14, 2007 THIS PAGE DELIBERATELY LEFT BLANK Anacostia River Sediment TMDL Document version: June 14, 2007 FINAL Table of Contents List of Figures.................................................................................................................... ii List of Tables ..................................................................................................................... ii List of Abbreviations ....................................................................................................... iii EXECUTIVE SUMMARY .............................................................................................. v 1.0 INTRODUCTION ................................................................................................ 1 2.0 SETTING AND WATER QUALITY DESCRIPTION .................................... 3 2.1 Background and General Setting ............................................................ 3 2.1.1 Geology and soils ........................................................................... 3 2.1.2 Land use ......................................................................................... 6 2.2 Source Assessment.................................................................................... 8 2.2.1 Historical Causes of Sedimentation in the Anacostia Watershed 9 2.2.2 Current Nonpoint Sources of Sediment in the Anacostia .......... 10 2.2.3 Current Point Sources of Sediment in the Anacostia................. 11 2.2.4 Re-suspension of bed sediment in the tidal river ........................ 13 2.2.5 Summary of Baseline Loads........................................................ 13 2.3 Water Quality Characterization............................................................ 13 2.3.1 Tidal waters ................................................................................... 14 2.3.2 Non-tidal waters ........................................................................... 18 2.4 Water Quality Impairment .................................................................... 21 2.4.1 Designated Uses and Water Quality Standards .......................... 21 2.4.2 Assessment of tidal waters ........................................................... 24 2.4.3 Assessment of non-tidal waters.................................................... 24 3.0 TARGETED WATER QUALITY GOAL ....................................................... 25 4.0 TOTAL MAXIMUM DAILY LOADS AND ALLOCATIONS..................... 26 4.1 Overview .................................................................................................. 26 4.2 Analysis Framework............................................................................... 27 4.2.1 Tidal analysis................................................................................ 28 4.2.2 Non-tidal analysis ....................................................................... 32 4.3 Scenario Descriptions and Results ........................................................ 33 4.3.1 Baseline Conditions Scenario for Tidal Anacostia..................... 33 4.3.2 TMDL Conditions Scenario for Tidal Anacostia ....................... 35 4.3.3 TMDL Conditions Scenario for Non-tidal Anacostia ................ 35 4.4 Critical Condition and Seasonality ....................................................... 36 4.5 TMDL Loading Caps and Allocations .................................................. 36 4.6 Margin of Safety...................................................................................... 38 4.7 Summary of Sediment/TSS TMDLs for the Anacostia Watershed.... 39 5.0 ASSURANCE OF IMPLEMENTATION ........................................................ 46 REFERENCES................................................................................................................ 51 Appendix A – ESTIMATOR Model Results for Northwest Branch and Northeast Branch Sediment Loads ................................................................................................ A1 Appendix B – Flow Duration Curve/Quantile Regression Analysis of Effects of Urban Hydrology ............................................................................................................B1 Appendix C – Application of the Reference Watershed Approach in the Anacostia River Watershed ............................................................................................................ C1 Appendix D – Technical Approach Used to Generate Maximum Daily Loads ........D1 Anacostia River Sediment TMDL Document version: June 14, 2007 i FINAL List of Figures Figure 1. Location map of the Anacostia River watershed................................................ 4 Figure 2. Anacostia River subwatersheds.......................................................................... 5 Figure 3. Land use in the Anacostia watershed (LDR, MDR, and HDR denote low-, medium-, and high-density residential) ...................................................................... 7 Figure 4. Tidal Anacostia River, with Monitoring Locations, and TAM/WASP Model Segmentation............................................................................................................. 15 Figure 5. Long-term Growing Season Medians of Water Quality Parameters in the Tidal Anacostia River......................................................................................................... 17 Figure 6. Long-term Growing Season Medians of Secchi Depth in the Tidal Anacostia River.......................................................................................................................... 17 Figure 7. Submerged Aquatic Vegetation in the Tidal River .......................................... 18 Figure 8. Suspended Solids Data for NEB, 1995-2004, versus Flow Percentile............. 20 Figure 9. Suspended Solids Data for NWB, 1995-2004, versus Flow Percentile ........... 21 Figure 10. Annual precipitation at Reagan National Airport........................................... 26 Figure 11. Annual combined mean flow for Northeast and Northwest Branch tributaries ................................................................................................................................... 27 Figure 12. Schematic diagram of TAM/WASP modeling framework ............................ 30 Figure 13. 1995-1997 median growing season Secchi depth in tidal Anacostia River: predicted by calibrated model vs. observed.............................................................. 34 List of Tables Table 1. Summary of Anacostia Watershed land use (acres) ............................................ 6 Table 2. Summary of sediment loads by source ................................................................ 9 Table 3. Municipal and Industrial NPDES Permit Holders in the Anacostia Watershed with sediment/solids discharge limits ....................................................................... 12 Table 4. Water Quality Data Sets Used in TMDL Development .................................... 14 Table 5. Designated Uses and Sediment-Related Water Quality Standards for the Anacostia Watershed ................................................................................................ 23 Table 6. Growing season Secchi depth medians, computed from routine monitoring data ................................................................................................................................... 24 Table 7. Sediment/TSS TMDL Loading Caps and Allocations for the Anacostia Watershed ................................................................................................................. 37 Table 8. Summary of Annual Sediment/TSS TMDLs for the Anacostia Watershed (tons/year) ................................................................................................................. 40 Table 9. Summary of Growing Season Sediment/TSS TMDLs for the Anacostia Watershed (tons/growing season)............................................................................. 41 Table 10. Summary of Annually-Based Maximum Daily Loads of Sediment/TSS for the Anacostia River Watershed (tons/day) .................................................................... 42 Table 11. Summary of Seasonally-Based Maximum Daily Loads of Sediment/TSS for the Anacostia River Watershed (tons/day during growing season)......................... 44 Table 12. Anacostia River restoration activities by Signatories of the Anacostia Watershed Restoration Agreement, and other assisting organizations..................... 49 Anacostia River Sediment TMDL Document version: June 14, 2007 ii FINAL List of Abbreviations ANS-PCER Academy of Natural Sciences - Patrick Center for Environmental Research ARCWP Anacostia River and Tributaries Comprehensive Watershed Plan AWRC Anacostia Watershed Restoration Committee BARC Beltsville Agricultural Research Center BMPs Best Management Practices BOD Biochemical Oxygen