CHARLES COUNTY MUNICIPAL STORMWATER RESTORATION PLAN PLAN TO ACHIEVE STORMWATER WASTE LOAD ALLOCATIONS AND IMPERVIOUS SURFACE RESTORATION CHARLES COUNTY, MARYLAND DECEMBER 2017 CHARLES COUNTY MUNICIPAL STORMWATER RESTORATION PLAN P L A N T O A C HI E V E S T O R M W AT E R W A ST E LO AD A LLOCATIONS AND IM P E R V IO U S S U R F AC E R ESTORATION Compliance document for Part IV.E.2.a. and b. of MS4 Discharge Permit #11-DP-3322. DECEMBER 2017 PREPARED FOR CHARLES COUNTY, MARYLAND DEPARTMENT OF PLANNING AND GROWTH MANAGEMENT 200 BALTIMORE ST. LA PLATA, MD 20646 PREPARED BY KCI TECHNOLOGIES, INC. 936 RIDGEBROOK ROAD SPARKS, MD 21152 Restoration Plan Acknowledgements This watershed restoration plan was completed as a collaborative effort between the following partners: Charles County Department of Planning and Growth Management KCI Technologies, Inc. The report was authored by the following individuals from KCI Technologies, Inc.: Susanna Brellis Mike Pieper Bill Frost, P.E. Megan Crunkleton County staff providing expertise, oversight, and review include: Karen Wiggen Charles Rice Erica Hahn Appropriate citation for the Restoration Plan is as follow: KCI Technologies, Inc. 2016. Charles County Municipal Stormwater Restoration Plan. Prepared by KCI Technologies, Inc., Sparks, Maryland for Charles County Department of Planning and Growth Management, La Plata, Maryland. Dated June 2016. For more information pertaining to the Restoration Plan, please contact: Karen Wiggen, Planner Charles County Government Department of Planning and Growth Management P.O. Box 2150 La Plata, MD 20646 301-645-0683 [email protected] And visit us on the web: www.charlescountymd.gov/watershed ii Charles County, Maryland Restoration Plan Table of Contents 1 Introduction and Background ......................................................................................... 8 1.1 Purpose ......................................................................................................................................... 8 1.2 Plan Development ......................................................................................................................... 8 1.3 Charles County MS4 Permit .......................................................................................................... 9 1.4 MS4 Permit Coverage ................................................................................................................. 11 1.5 Anticipated Growth ..................................................................................................................... 13 1.5.1 Offsetting Loads from Future Growth ................................................................................ 13 1.5.2 Estimates of Future Growth ................................................................................................ 13 1.6 Impairments, Water Quality, and Land Use/Land Cover ............................................................ 17 1.6.1 Impairments ........................................................................................................................ 17 1.6.2 Water Quality ...................................................................................................................... 17 1.6.3 Biological Condition ............................................................................................................ 19 1.6.4 Land Use/Land Cover .......................................................................................................... 20 1.7 Watershed Planning Approach ................................................................................................... 24 1.7.1 Watershed Assessments ..................................................................................................... 24 1.7.2 Impervious Surface Restoration Assessment ...................................................................... 26 1.8 Best Management Practices ....................................................................................................... 26 1.8.1 Structural Practices ............................................................................................................. 27 1.8.2 Operation and Programmatic Practices .............................................................................. 29 1.8.3 Implementation Levels ........................................................................................................ 32 1.8.4 Pollutant Reductions and Impervious Credits .................................................................... 32 2 Local TMDLs ................................................................................................................. 34 2.1 Mattawoman Creek TMDL for Nitrogen and Phosphorus .......................................................... 39 2.1.1 Sources ................................................................................................................................ 40 2.1.2 Modeling Approach ............................................................................................................. 40 2.1.3 Reduction Target Derivation ............................................................................................... 41 2.1.4 Summary of Findings from 2015 Watershed Assessment .................................................. 44 2.1.5 2015 Progress ...................................................................................................................... 44 2.1.6 Restoration Plan .................................................................................................................. 46 2.1.7 Load Reductions Expected .................................................................................................. 50 2.1.8 Cost and End Date of Mattawoman TMDL Restoration ..................................................... 52 2.2 Lower Patuxent Bacteria TMDL (Indian Creek, Charles County, MD) ......................................... 54 2.2.1 Sources ................................................................................................................................ 54 2.2.2 Summary of Findings from Lower Patuxent Assessment ................................................... 56 2.2.3 Modeling Approach ............................................................................................................. 56 2.2.4 Reduction Target Derivation ............................................................................................... 60 2.2.5 2015 Progress ...................................................................................................................... 63 iii Charles County, Maryland Restoration Plan 2.2.6 Restoration Plan .................................................................................................................. 63 2.2.7 Load Reductions Expected .................................................................................................. 64 2.2.8 Cost and End Date of Indian Creek TMDL Restoration ....................................................... 64 2.3 Potomac River PCB TMDL ........................................................................................................... 65 2.3.1 Potomac River PCB Disaggregation ..................................................................................... 65 2.3.2 Sources ................................................................................................................................ 65 3 Chesapeake Bay TMDL and Impervious Surface Reduction ............................................ 68 3.1 Impervious Restoration ............................................................................................................... 68 3.1.1 Impervious Surface Analysis ............................................................................................... 68 3.1.2 20% Impervious Restoration Goal ...................................................................................... 71 3.1.3 Impervious Restoration Progress ........................................................................................ 72 3.1.4 Planned Impervious Restoration (Scenario 1) .................................................................... 75 3.1.5 Planned Impervious Restoration (Scenario 2) .................................................................... 77 3.1.6 Cost of Impervious Restoration .......................................................................................... 80 3.2 Chesapeake Bay TMDL for Nitrogen and Phosphorus ................................................................ 85 3.2.1 Sources ................................................................................................................................ 85 3.2.2 Modeling Approach ............................................................................................................. 85 3.2.3 Baseline and Target Loads .................................................................................................. 86 3.2.4 Chesapeake Bay TMDL Progress ......................................................................................... 87 3.2.5 Bay TMDL Restoration ........................................................................................................ 88 3.2.6 Load Reductions Expected .................................................................................................. 91 3.2.7 Additional Reductions ........................................................................................................