Prince George’s County Countywide Watershed Assessment for MS4 Permit (2014-2019) December 21, 2018 Prepared For Prince George’s County, Maryland Department of the Environment Stormwater Management Division Prepared By Tetra Tech 10306 Eaton Place, Suite 340 Fairfax, VA 22030 Cover Photo Credits 1. Prince George’s County DoE 2. Prince George’s County DoE 3. Clean Water Partnership 4. M-NCPPC_Cassi Hayden Prince George’s County Countywide Watershed Assessment for MS4 Permit (2014–2019) Contents Abbreviations and Acronyms ................................................................................................. iv 1 Introduction ......................................................................................................................... 1 1.1 Prince George’s County Impaired Waters .................................................................................... 4 1.1.1 Impaired Water Bodies ....................................................................................................... 4 1.1.2 Causes of Water Body Impairment ..................................................................................... 6 1.2 Prince George’s County Restoration Plans .................................................................................. 8 2 Current Water Quality Conditions .................................................................................... 10 2.1 Biological Assessment ................................................................................................................ 10 2.1.1 Assessment Methodology ................................................................................................. 10 2.1.2 Biological Assessment Results ......................................................................................... 11 2.2 Water Quality Monitoring Data .................................................................................................... 14 2.2.1 Trend Analysis .................................................................................................................. 14 2.2.2 Data Gaps ......................................................................................................................... 19 3 Visual Watershed Inspection ............................................................................................ 22 3.1 Stream Corridor Assessments .................................................................................................... 22 3.2 Photographic Trash Assessment ................................................................................................ 24 3.2.1 Trash Rating Protocol ....................................................................................................... 24 3.2.2 Results of Trash Assessment ........................................................................................... 25 3.3 IDDE Program Results ............................................................................................................... 29 4 Identifying and Ranking Water Quality Issues ................................................................ 34 4.1 Identifying Water Quality Issues (or Problems) .......................................................................... 34 4.2 Ranking Priorities ........................................................................................................................ 36 5 Water Quality Improvement Projects ............................................................................... 39 5.1 Watershed Restoration Practices ............................................................................................... 39 5.2 BMP Impacts on Water Quality Issues ....................................................................................... 40 5.3 BMP Site, Placement, and Design Constraints .......................................................................... 43 5.4 Identifying/Prioritizing BMPs for Each County Watershed ......................................................... 46 5.5 Prioritizing BMP Locations .......................................................................................................... 47 5.5.1 Land Ownership and Site Access ..................................................................................... 47 5.5.2 Location in the Watershed ................................................................................................ 48 5.5.3 Locations of Known Issues and Existing Treatment ......................................................... 49 6 Load Reduction Benchmarks and Deadlines .................................................................. 50 6.1 Load Reduction Benchmarks ...................................................................................................... 50 6.1.1 Chesapeake Bay TMDL .................................................................................................... 50 6.1.2 2014 Local TMDL Restoration Plans ................................................................................ 50 6.2 Current Implementation Rates and Benchmark Projections ...................................................... 51 6.3 Biological and Water Quality Responses to BMP Implementation ............................................. 53 6.3.1 Biological Results .............................................................................................................. 53 6.3.2 Water Quality Results ....................................................................................................... 56 6.4 Difficulties in Meeting Benchmarks ............................................................................................. 57 6.4.1 Required Load Reductions and Implementation ............................................................... 57 6.4.2 MDE TMDL Analysis ......................................................................................................... 58 6.4.3 Chesapeake Bay Program Evaluations ............................................................................ 59 6.4.4 2030 End Date .................................................................................................................. 59 6.4.5 Local Restoration Plan Revisions and Updates ................................................................ 60 6.5 Nonstormwater Programs to Reduce Loads .............................................................................. 60 6.5.1 County MS4 Programmatic Activities with Undetermined Load Reduction Potential ....... 60 6.5.2 Non-MS4 Technical Activities with Unknown Load Reduction Potential .......................... 62 7 Conclusion ........................................................................................................................ 64 i Prince George’s County Countywide Watershed Assessment for MS4 Permit (2014–2019) 7.1 Key Water Assessment Findings ................................................................................................ 64 7.2 Existing Water Quality Improvement Efforts ............................................................................... 64 7.3 Future Activities .......................................................................................................................... 65 8 Literature Cited .................................................................................................................. 66 Appendix A: Stream Concepts Considered in the Assessment ........................................ A-1 Appendix B: Water Quality Plots and Tables ...................................................................... B-1 Appendix C: Visual Inspection Photograph Comparisons ................................................ C-1 Appendix D: Watershed Maps for the Prioritized BMP Locations ..................................... D-1 Appendix E: Biological Degradation and BMP Implementation ........................................ E-1 Figures Figure 1-1. Locations of 8-digit watersheds in Prince George's County. ...................................................... 2 Figure 1-2. Watershed area in Prince George's County. .............................................................................. 3 Figure 2-1. Number of stream sites sampled by biological assessment round. ......................................... 11 Figure 2-2. Percent degradation per watershed by biological assessment round. ..................................... 12 Figure 2-3. Biological assessment ratings by monitoring location. ............................................................. 13 Figure 2-4. Biological assessment results (percent degraded) by major watershed. ................................. 13 Figure 2-5. Locations of water quality monitoring stations. ......................................................................... 15 Figure 2-6. Plot of TP over time in the Western Branch watershed............................................................ 16 Figure 2-7. Plot of TN over time in the Potomac River watershed.............................................................. 16 Figure 2-8. Locations without water quality monitoring stations. ................................................................ 21 Figure 3-1. Locations of SCA erosion points (with severity) and head cuts. .............................................. 23 Figure 3-2. Streams illustrating different amounts of trash and corresponding trash scores. .................... 25 Figure 3-3. Trash score distribution throughout the County. .....................................................................