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.) .......................................................................................... A6 Figure A-6: Comparison of the Modeled and Observed Bacteria Concentrations in the Unnamed Tributary of Beaverdam Creek ................................................................................................................................... A7 ii Figure A-7: Comparison of the Modeled and Observed Bacteria Concentrations in Mill Creek ............... A7 Figure A-8: Comparison of the Modeled and Observed Bacteria Concentrations in Barrows Creek ........ A8 Figure A-9: Comparison of the Predicted and Observed Surface Elevation at Station CHK015.12 .......... A8 Figure A-10: Comparison of Modeled and Observed Salinity at Stations Chickahominy Haven (Left) and Route 5 Bridge (Right) ................................................................................................................................ A9 Figure A-11: Model Calibration of Enterococci