Unnamed Tributary to Cocolamus Creek Watershed Sediment TMDL Perry County, Pennsylvania
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Unnamed Tributary to Cocolamus Creek Watershed Sediment TMDL Perry County, Pennsylvania Prepared by: Final Draft Submitted for EPA Approval, May 2021 TABLE OF CONTENTS EXECUTIVE SUMMARY......................................................................................................................................................................................... 1 Table 1. Summary of Annual Average TMDL (TMDLAvg) Variables for the UNT Cocolamus Watershed .................. 1 th Table 2. Summary of 99 Percentile Daily Loading TMDL (TMDLMax) Variables for the UNT Cocolamus Creek Watershed ................................................................................................................................................................. 1 INTRODUCTION ...................................................................................................................................................................................................... 2 Table 3. Aquatic-Life Impaired Stream Segments in the UNT Cocolamus Creek Watershed per the 2018 Final Pennsylvania Integrated Report ................................................................................................................................ 2 Figure 1. UNT Cocolamus Creek Watershed. ............................................................................................................ 3 Table 4. Existing NPDES-Permitted Discharges in the UNT Cocolamus Creek Watershed and their Potential Contribution to Sediment Loading. ........................................................................................................................... 4 TMDL APPROACH ................................................................................................................................................................................................... 4 SELECTION OF THE REFERENCE WATERSHED ....................................................................................................................................... 4 Table 5. Comparison of the Impaired UNT Cocolamus Creek Watershed and Reference Stony Run Subwatershed. 5 Table 6. Existing NPDES-Permitted Discharges in the Stony Run Subwatershed and their Potential Contribution to Sediment Loading. ..................................................................................................................................................... 7 Figure 2. UNT Cocolamus and Stony Run Watersheds .............................................................................................. 9 Figure 3. Stony Run Subwatershed.......................................................................................................................... 10 Figure 4. Example stream substrate and turbidity conditions within the UNT Cocolamus Watershed. ................. 11 Figure 5. Photograph showing the agricultural dominated ridge and valley landscape of the UNT Cocolamus Watershed. .............................................................................................................................................................. 12 Figure 6. Stream segments and drainageways flowing through areas with conditions that may exacerbate sediment loading in the UNT Cocolamus Watershed. ............................................................................................. 13 Figure 7. Example conditions and agricultural practices in the UNT Cocolamus Creek Watershed that may help prevent sediment loading. ...................................................................................................................................... 14 Figure 8. Example stream segments in the Stony Run Subwatershed.................................................................... 15 Figure 9. Example landscapes within the Stony Run Subwatershed ....................................................................... 16 Figure 10. Practices that may be protective against sediment loading in the Stony Run Subwatershed. .............. 17 Figure 11. Practices that may exacerbate pollutant loading in the Stony Run Subwatershed. .............................. 18 HYDROLOGIC / WATER QUALITY MODELING ....................................................................................................................................... 19 Figure 12. Riparian buffer analysis in the UNT Cocolamus Watershed ................................................................... 22 Figure 13. Riparian buffer analysis in the Stony Run Subwatershed ....................................................................... 23 CALCULATION OF THE TMDLAVG .................................................................................................................................................................. 24 ii Table 7. Existing Annual Average Loading Values for the Stony Run Subwatershed, Reference ........................... 24 Table 8. Existing Annual Average Loading Values for the UNT Cocolamus Creek Watershed, Impaired ............... 25 Table 9. Calculation of an Annual Average TMDL Value for the UNT Cocolamus Creek Watershed ..................... 26 CALCULATION OF LOAD ALLOCATIONS ................................................................................................................................................... 26 MARGIN OF SAFETY .......................................................................................................................................................... 26 WASTELOAD ALLOCATION .................................................................................................................................................. 26 LOAD ALLOCATION ............................................................................................................................................................ 27 LOADS NOT REDUCED AND ADJUSTED LOAD ALLOCATION ........................................................................................................ 27 Table 10. Average Annual Load Allocation, Loads Not Reduced and Adjusted Load Allocation ............................ 27 CALCULATION OF SEDIMENT LOAD REDUCTIONS ............................................................................................................................. 28 Table 11. Average Annual Sediment Load Allocations for Source Sectors in the UNT Cocolamus Creek Watershed ................................................................................................................................................................................ 28 CALCULATION OF A DAILY MAXIMUM “TMDLMAX” VALUE .............................................................................................................. 28 Table 12. Calculation of TMDLMax for the UNT Cocolamus Creek Watershed ......................................................... 29 th Table 13. 99 Percentile of Daily Loading TMDL (TMDLMax) Variables for the UNT Cocolamus Creek Watershed 30 th Table 14. Allocation of the 99 Percentile Daily Load Allocation (LAMax) for the UNT Cocolamus Creek Watershed ................................................................................................................................................................................ 30 CONSIDERATION OF CRITICAL CONDITIONS AND SEASONAL VARIATIONS ......................................................................... 31 RECOMMENDATIONS ........................................................................................................................................................................................ 31 PUBLIC PARTICIPATION .................................................................................................................................................................................. 32 CITATIONS .............................................................................................................................................................................................................. 32 APPENDIX A: BACKGROUND ON STREAM ASSESSMENT METHODOLOGY ................................................................. 34 Table A1. Impairment Documentation and Assessment Chronology ...................................................................... 36 APPENDIX B: MODEL MY WATERSHED GENERATED DATA TABLES ........................................................................................ 39 Table B1. Land Cover based on NLCD 2016 for the UNT Cocolamus Creek Watershed. “Open Water” pixels were excluded from the analysis. ..................................................................................................................................... 40 Table B2. Land Cover based on NLCD 2016 for the for the Stony Run Subwatershed. “Open Water” pixels were excluded from the analysis. ..................................................................................................................................... 40 Table B3. “Model My Watershed” Hydrology Outputs for the UNT Cocolamus Creek Watershed. ....................... 41 Table B4. “Model My Watershed” Hydrology Outputs for the Stony Run reference subwatershed ...................... 41 Table B5. Model My Watershed outputs for sediment in the UNT Cocolamus Creek Watershed. ........................ 42 Table B6. Model My Watershed Outputs for Sediment in the Stony Run reference subwatershed. ...................... 42 APPENDIX C: STREAM SEGMENTS IN THE UNT COCOLAMUS CREEK WATERSHED WITH SILTATION IMPAIRMENTS FOR AQUATIC LIFE USE ..................................................................................................................................................