GILBERT SWAMP WATERSHED ASSESSMENT MAY | 2018 PREPARED FOR Charles County Department of Planning and Growth Management Watershed Protection and Restoration Program 200 Baltimore St., La Plata, MD 20646 PREPARED BY KCI TECHNOLOGIES, INC. 936 RIDGEBROOK ROAD SPARKS, MD 21152 ACKNOWLEDGEMENTS The Gilbert Swamp Watershed Assessment was a collaborative effort between Coastal Resources, Inc., KCI Technologies, Inc. and Charles County Department of Planning and Growth Management (PGM). The resulting report was authored by the following individuals from KCI Technologies, Inc. and Charles County. Susanna Brellis | KCI Technologies, Inc. Yinting Hou | KCI Technologies, Inc. Robert Owen | KCI Technologies, Inc. Michael Pieper | KCI Technologies, Inc. James Tomlinson | KCI Technologies, Inc. Erica Hahn | Charles County Dept. of PGM Charles Rice | Charles County Dept. of PGM Karen Wiggen | Charles County Dept. of PGM For more information pertaining to the Restoration Plan, please contact: Karen Wiggen, Planner Charles County Government Department of Planning and Growth Management 200 Baltimore St. La Plata, MD 20646 301-645-0683 [email protected] And visit us on the web: www.charlescountymd.gov/watershed Gilbert Swamp Watershed Assessment TABLE OF CONTENTS 1 Introduction ------------------------------------------------------------------------------------------------- 7 1.1 Background ------------------------------------------------------------------------------------------------------ 7 1.2 Watershed description --------------------------------------------------------------------------------------- 7 1.3 Previous Watershed Studies and Assessments ------------------------------------------------------- 10 1.4 Goals -------------------------------------------------------------------------------------------------------------- 10 1.4.1 Watershed Assessments ----------------------------------------------------------------------------------------------10 1.4.2 Impervious Restoration -----------------------------------------------------------------------------------------------11 1.4.3 TMDLs ---------------------------------------------------------------------------------------------------------------------11 2 Watershed Assessment Methods --------------------------------------------------------------------- 12 2.1 Upland Assessment ------------------------------------------------------------------------------------------- 13 2.1.1 Neighborhood Source Assessment---------------------------------------------------------------------------------13 2.1.2 Hotspot Site Investigations ------------------------------------------------------------------------------------------13 2.2 Nutrient Synoptic Survey ----------------------------------------------------------------------------------- 14 2.2.1 Water Quality Sampling ----------------------------------------------------------------------------------------------14 2.2.2 Stream Discharge Measurement -----------------------------------------------------------------------------------15 2.3 Stream Corridor Assessment ------------------------------------------------------------------------------- 15 3 Watershed Assessment Results ----------------------------------------------------------------------- 18 3.1 Upland Assessment ------------------------------------------------------------------------------------------- 18 3.1.1 Neighborhood Source Assessment---------------------------------------------------------------------------------18 3.1.2 Hotspot Site Investigations ------------------------------------------------------------------------------------------20 3.2 Synoptic Water Quality Survey ---------------------------------------------------------------------------- 23 3.2.1 Stream Discharge -------------------------------------------------------------------------------------------------------23 3.2.2 Water Quality -----------------------------------------------------------------------------------------------------------23 3.3 Stream Corridor Assessment ------------------------------------------------------------------------------- 33 4 Potential Water Quality Improvement Projects -------------------------------------------------- 44 4.1 Stream Restoration ------------------------------------------------------------------------------------------- 46 4.2 Shoreline Erosion Control ----------------------------------------------------------------------------------- 48 4.3 Stormwater BMPs -------------------------------------------------------------------------------------------- 48 4.3.1 Watershed Assessment Stormwater BMP Analysis ------------------------------------------------------------48 4.4 Reforestation --------------------------------------------------------------------------------------------------- 54 5 Programmatic Practices --------------------------------------------------------------------------------- 55 5.1 Trash Clean-Ups ----------------------------------------------------------------------------------------------- 55 3 Gilbert Swamp Watershed Assessment 5.2 Homeowner Practices --------------------------------------------------------------------------------------- 56 5.3 Septic Practices ----------------------------------------------------------------------------------------------- 60 6 Treatment Summary ------------------------------------------------------------------------------------- 62 6.1 Existing BMPs – Actual Implementation --------------------------------------------------------------- 62 6.2 Planned Implementation ----------------------------------------------------------------------------------- 63 6.3 Impervious Credit -------------------------------------------------------------------------------------------- 64 6.4 Local TMDL and Bay TMDL Baseline and Target Loads --------------------------------------------- 65 6.4.1 Local TMDLs ------------------------------------------------------------------------------------------------------------- 65 6.4.2 Chesapeake Bay TMDL ------------------------------------------------------------------------------------------------ 65 6.5 Bay TMDL Expected Load Reductions ------------------------------------------------------------------- 65 6.6 Cost Summary ------------------------------------------------------------------------------------------------- 68 7 Prioritization ----------------------------------------------------------------------------------------------- 69 References -------------------------------------------------------------------------------------------------------- 71 LIST OF TABLES TABLE 1: CHARLES COUNTY BAY TMDL STORMWATER GOALS -------------------------------------------------------------------------- 12 TABLE 2: WATER CHEMISTRY ANALYTICAL METHODS ------------------------------------------------------------------------------------- 14 TABLE 3: SCA REACH SELECTION AND EXCLUSION FACTORS ------------------------------------------------------------------------------ 16 TABLE 4: GENERAL CHARACTERISTICS OF NEIGHBORHOODS ASSESSED------------------------------------------------------------------- 18 TABLE 5: NEIGHBORHOOD POLLUTION SEVERITY AND RESTORATION POTENTIAL -------------------------------------------------------- 20 TABLE 6: HOT SPOT INVESTIGATION LOCATIONS AND OPERATIONS ---------------------------------------------------------------------- 22 TABLE 7: NUTRIENT RANGES AND RATINGS FROM FRINK (1991) ------------------------------------------------------------------------ 23 TABLE 8: TOTAL NUTRIENT RANGES AND RATINGS FROM SOUTHERLAND ET AL.,(2005) ----------------------------------------------- 23 TABLE 9: STREAM DISCHARGE MEASUREMENT AND IN SITU WATER QUALITY MEASUREMENT RESULTS -------------------------------- 30 TABLE 10: WATER QUALITY GRAB SAMPLING RESULTS- NUTRIENT AND BACTERIA CONCENTRATIONS AND INSTANTANCEOUS LOADS. 32 TABLE 11: WATERSHED DATA POINTS BY SEVERITY --------------------------------------------------------------------------------------- 34 TABLE 12: STREAM RESTORATION AND PIPE OUTFALL SITE RANKING CRITERIA --------------------------------------------------------- 46 TABLE 13: STREAM RESTORATION PROJECT DESCRIPTIONS ------------------------------------------------------------------------------- 47 TABLE 14: STREAM RESTORATION REMOVAL EFFICIENCY AND IMPERVIOUS ACRE EQUIVALENT ---------------------------------------- 47 TABLE 15: STREAM RESTORATION COST, IMPERVIOUS CREDIT, AND LOAD REDUCTION ------------------------------------------------ 47 TABLE 16: PROPOSED SWM BMP PROJECTS --------------------------------------------------------------------------------------------- 49 TABLE 17: AREA TREATED BY SWM BMP PROJECTS PER TYPE -------------------------------------------------------------------------- 50 TABLE 18: STORMWATER BMP RUNOFF DEPTH TREATED, IMPERVIOUS TREATED, LOAD REDUCTION, AND COST ------------------- 53 TABLE 19: REFORESTATION BMPS EFFICIENCY AND IMPERVIOUS ACRE EQUIVALENT --------------------------------------------------- 54 TABLE 20. REFORESTATION SITE COST, IMPERVIOUS CREDIT, AND LOAD REDUCTION ---------------------------------- 55 TABLE 21: TRASH CLEAN-UP SITES --------------------------------------------------------------------------------------------------------- 56 TABLE 22: REMOVAL EFFICIENCIES FOR HOMEOWNER PRACTICES ----------------------------------------------------------------------- 57 TABLE 23: PROJECTED NUTRIENT REMOVAL AND IMPERVIOUS CREDIT FROM PLANNED RAIN BARRELS ------------------------------- 59 TABLE 24. PROJECTED NUTRIENT REMOVAL AND IMPERVIOUS CREDIT FROM