W&M ScholarWorks Reports 2-24-2017 Bacteria TMDL Development for Lower Chickahominy River Watershed Located in Charles City, James City, and New Kent Counties, VA Virginia Institute of Marine Science Follow this and additional works at: https://scholarworks.wm.edu/reports Part of the Environmental Indicators and Impact Assessment Commons, and the Environmental Monitoring Commons Recommended Citation Virginia Institute of Marine Science. (2017) Bacteria TMDL Development for Lower Chickahominy River Watershed Located in Charles City, James City, and New Kent Counties, VA. Virginia Institute of Marine Science, College of William and Mary. https://doi.org/10.25773/v5-wasd-ts57 This Report is brought to you for free and open access by W&M ScholarWorks. It has been accepted for inclusion in Reports by an authorized administrator of W&M ScholarWorks. For more information, please contact [email protected]. Bacteria TMDL Development for Lower Chickahominy River Watershed Located in Charles City, James City, and New Kent Counties, VA Prepared for: Virginia Department of Environmental Quality Submitted by: Virginia Institute of Marine Science Submitted: February 24, 2017 TABLE OF CONTENTS TABLE OF CONTENTS ............................................................................................................................... i LIST OF FIGURES ...................................................................................................................................... ii LIST OF TABLES ....................................................................................................................................... iii LIST OF ABBREVIATIONS ....................................................................................................................... v EXECUTIVE SUMMARY ......................................................................................................................... vi 1.INTRODUCTION ..................................................................................................................................... 1 1.1 Regulations Background ............................................................................................................ 1 1.2 Watershed Characteristics ......................................................................................................... 1 1.3 Recreation Use Impairments ...................................................................................................... 5 2.TMDL ENDPOINT AND WATER QUALITY ASSESSMENT ........................................................................... 88 2.1 Applicable Water Quality Standards ............................................................................................. 8 2.2 Selection of a TMDL Endpoint .................................................................................................. 9 2.3 Discussion of In-stream Water Quality ......................................................................................... 9 3.BACTERIA SOURCE ASSESSMENT .................................................................................................. 13 3.1 Point Sources ............................................................................................................................. 15 3.2 Nonpoint Sources ...................................................................................................................... 18 4 TMDL DEVELOPMENT ........................................................................................................................ 32 4.1 Overview .................................................................................................................................... 32 4.2 Selection of A TMDL Endpoint ............................................................................................... 32 4.3 Model Development for Computing TMDL ................................................................................ 32 4.4 Consideration of Critical Conditions and Seasonal Variation ..................................................... 36 4.5 Margin of Safety ........................................................................................................................ 36 4.6 TMDL Computation ................................................................................................................. 36 4.7 Summary of TMDL and Load Allocation ...................................................................................... 39 5 IMPLEMENTATION AND PUBLIC PARTICIPATION .................................................................................... 42 5.1 General ....................................................................................................................................... 42 5.2 Staged Implementation ............................................................................................................. 42 5.3 Reasonable Assurance for Implementation ................................................................................ 43 5.4 Public Participation .................................................................................................................. 46 REFERENCES ........................................................................................................................................... 46 i APPENDIX A. MODEL DEVELOPMENT .............................................................................................. A1 A.1 Model Development .................................................................................................................. A1 A.2 Allowable Load Calculation ................................................................................................... A10 A.3 Sensitivity Test on Single Maximum Criteria by Reducing 50% of the Anthropogenic Source …………………………………………………………………………………………………………………………………………….A14 A.4 Total Maximum Daily Load ................................................................................................... A14 LIST OF FIGURES Figure ES.1: The Impaired Waters in the Lower Chickahominy River Watershed ................................... viii Figure 1.1: Location of the Lower Chickahominy River Watershed ............................................................ 2 Figure 1.2: Landuse of the Lower Chickahominy River Watershed............................................................. 4 Figure 1.3: Landuse Distribution in the Lower Chickahominy River Watershed ........................................ 5 Figure 1.4: Segments in the Lower Chickahominy River Watershed Impaired for Bacteria ....................... 6 Figure 2.1: VA-DEQ Monitoring Stations in the Enterococci Impaired Waters ........................................ 10 Figure 2.2: VA-DEQ Monitoring Stations in the E. coli Impaired Waters ................................................. 11 Figure 3.1: Subwatershed Delineation in the Lower Chickahominy River Watershed .............................. 14 Figure 3.2: Locations of the Individual Permits with WLAs, and the James City County VDOT and MS4 Areas ........................................................................................................................................................... 17 Figure 3.3: Cumulative Frequency Distributions of SSOs in the Lower Chickahominy River Watershed 22 Figure 4.1: Modeling Process for TMDL Development ............................................................................. 33 Figure 4.2: Time Series Comparison of Daily Stream Flow between Model Simulation and Observations from USGS Stream Gage 2042500 in 2010 ................................................................................................ 34 Figure 4.3: Time Series Comparison of E. coli between Model Simulation and Observations in Mill Creek .................................................................................................................................................................... 35 Figure 4.4: Time Series Comparison of Enterococci between Model Simulation and Observations at Two Stations in the Lower Chickahominy River. The Red Line Denotes the Single Sample Maximum of 104 cfu/100ml. ................................................................................................................................................... 35 Figure A-1: Receiving Water Model Grid .................................................................................................. A3 Figure A-2: Time Series Comparison of the Daily Stream Flow between Model Simulation and Observed Data from USGS Gage 01484800 from 2010 to 2013. The X-axis is Days of the Year, and the Y-Axis is Flow in cfs................................................................................................................................................... A5 Figure A-3: 4-year Accumulated Daily Stream Flow Comparison between Model Simulation and USGS Observations ............................................................................................................................................... A5 Figure A-4: Comparison of the Modeled and Observed Bacteria Concentrations in Non-tidal Diascund Creek ........................................................................................................................................................... A6 Figure A-5: Comparison of the Modeled and Observed Bacteria Concentrations in Beaverdam Creek. (Data from All Stations are Merged Together.) .........................................................................................