Restoration Plan for the Western Branch Watershed in Prince George’s County December 21, 2018 RUSHERN L. BAKER, III COUNTPreparedY EXECUTIV for:E Prince George’s County, Maryland Department of the Environment Stormwater Management Division Prepared by: 10306 Eaton Place, Suite 340 Fairfax, VA 22030 COVER PHOTO CREDITS: 1. M-NCPPC _Cassi Hayden 7. USEPA 2. PGC DoE 8. PGC DoE 3. Prince George’s County 9. PGC DoE 4. Prince George’s County 10. PGC DoE 5. Clean Water Partnership 11. Clean Water Partnership 6. Clean Water Partnership 12. Tetra Tech, Inc. 13. PGC DoE Western Branch Restoration Plan Contents Acronym List ............................................................................................................................. v 1 Introduction ......................................................................................................................... 1 1.1 What is a Restoration Plan? ......................................................................................................... 1 1.2 Watershed Restoration Goals and Objectives .............................................................................. 2 1.3 Structure of the Plan ..................................................................................................................... 3 2 Watershed Characterization ............................................................................................... 4 2.1 Physical and Natural Features ...................................................................................................... 4 2.1.1 Hydrology ............................................................................................................................ 4 2.1.2 Climate/Precipitation ........................................................................................................... 8 2.1.3 Topography/Elevation ......................................................................................................... 9 2.1.4 Soils .................................................................................................................................... 9 2.2 Land Use and Land Cover .......................................................................................................... 10 2.2.1 Land Use Distribution ........................................................................................................ 10 2.2.2 Imperviousness ................................................................................................................. 13 3 Water Quality Conditions .................................................................................................. 15 3.1 Water Quality Impairments ......................................................................................................... 15 3.2 Water Quality Trends .................................................................................................................. 15 3.2.1 Nutrients: Nitrogen and Phosphorus ................................................................................. 17 3.2.2 Total Suspended Solids .................................................................................................... 21 3.2.3 Biochemical Oxygen Demand and Dissolved Oxygen ..................................................... 24 3.2.4 Fecal Coliform Bacteria ..................................................................................................... 27 3.2.5 Analysis of Water Quality Data Gaps ................................................................................ 27 3.3 Biological Assessment ................................................................................................................ 29 3.1.1. Assessment Methodology ................................................................................................. 29 3.1.2. Biological Assessment Results ......................................................................................... 30 3.4 Trash Assessment ...................................................................................................................... 31 3.4.1 Trash Rating Protocol ....................................................................................................... 31 3.4.2 Results of Trash Assessment ........................................................................................... 33 4 Watershed Conditions ...................................................................................................... 34 4.1 Pollutant Sources ........................................................................................................................ 34 4.1.1 NPDES-Permitted Point Sources ...................................................................................... 34 4.1.2 Nonpoint and Other Sources ............................................................................................ 36 4.1.3 Illicit Discharge Detection and Elimination ........................................................................ 39 4.2 Existing Stormwater BMPs ......................................................................................................... 41 4.3 Existing Conditions ..................................................................................................................... 44 4.3.1 Stream Biology and Impervious Cover ............................................................................. 44 4.3.2 Storm Drain Network ......................................................................................................... 44 5 Restoration Methodology Development .......................................................................... 48 5.1 Strategy for Developing the Restoration Plan ............................................................................ 48 5.2 Load Reduction Targets and Existing Gap ................................................................................. 50 5.3 Strategy Management Options and Their Load Reductions ...................................................... 52 5.3.1 Programmatic Initiatives .................................................................................................... 53 5.3.2 Structural BMPs ................................................................................................................ 53 5.3.3 BMP Siting Procedures ..................................................................................................... 60 6 Restoration Activity Identification ................................................................................... 63 6.1 Load Reductions from Structural BMPs...................................................................................... 63 6.1.1 Retrofit Existing BMPs ...................................................................................................... 63 6.1.2 Stream Restoration and Outfall Stabilization Projects ...................................................... 64 6.1.3 Environmental Site Design Practices ................................................................................ 68 i Western Branch Restoration Plan 6.1.4 Load Reduction Scenarios ................................................................................................ 69 6.2 Restoration Strategy Costing ...................................................................................................... 70 6.2.1 Unit Cost Determination .................................................................................................... 70 6.2.2 Cost Analysis for Stream Restoration and Outfall Stabilization ........................................ 71 6.2.3 Cost Analysis for ESD BMPs ............................................................................................ 73 6.3 BMP Siting .................................................................................................................................. 76 6.3.1 Stream Restoration ........................................................................................................... 76 6.3.2 Outfall Repairs/Stabilization .............................................................................................. 76 6.3.3 BMP Siting Analysis .......................................................................................................... 78 6.3.4 Prioritizing BMP Locations ................................................................................................ 82 6.4 Additional Load Reduction Activities........................................................................................... 83 6.4.1 Programmatic Strategies .................................................................................................. 83 6.4.2 Additional County Programs ............................................................................................. 89 6.4.3 Wastewater Programs....................................................................................................... 90 6.4.4 Atmospheric Deposition Reductions ................................................................................. 91 7 Tracking and Adaptive Management ............................................................................... 92 7.1 Implementation Tracking ............................................................................................................ 92 7.2 Biological and Water Quality Monitoring ..................................................................................... 92 7.2.1 Biological Monitoring 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