Susquehecka Creek Watershed Sediment TMDL Snyder County, Pennsylvania
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Susquehecka Creek Watershed Sediment TMDL Snyder County, Pennsylvania Prepared by: Final Copy, June 2020 TABLE OF CONTENTS EXECUTIVE SUMMARY......................................................................................................................................................................................... 1 Table 1. Summary of Annual Average TMDL (TMDLAvg) Variables for the Susquehecka Creek Watershed ............. 1 th Table 2. Summary of 99 Percentile Daily Loading TMDL (TMDLMax) Variables for the Susquehecka Creek Watershed ................................................................................................................................................................. 1 INTRODUCTION ...................................................................................................................................................................................................... 2 Table 3. Aquatic-Life Impaired Stream Segments in the Susquehecka Creek Watershed per the 2018 Final Pennsylvania Integrated Report ................................................................................................................................ 2 Figure 1. Susquehecka Creek Watershed. ................................................................................................................. 3 Table 4. Existing NPDES-Permitted Discharges in the Susquehecka Creek Watershed and their Potential Contribution to Sediment Loading. ........................................................................................................................... 4 TMDL APPROACH ................................................................................................................................................................................................... 4 SELECTION OF THE REFERENCE WATERSHED ....................................................................................................................................... 5 Table 5. Comparison of the Impaired Susquehecka Creek Watershed and Reference Mahoning Creek Subwatershed. .......................................................................................................................................................... 5 Table 6. Existing NPDES-Permitted Discharges in the Mahoning Creek Subwatershed and their Potential Contribution to Sediment Loading. ........................................................................................................................... 7 Figure 2. Mahoning Creek Subwatershed. .............................................................................................................. 10 Figure 3. Example stream substrate conditions within the Susquehecka Creek Valley. .......................................... 13 Figure 4. Photograph showing the high amount of agricultural landcover within the Susquehecka Creek Valley . 15 Figure 5. Stream segments flowing through areas with conditions that may exacerbate sediment loading in the Susquehecka Creek Watershed. .............................................................................................................................. 16 Figure 6. Example agricultural practices in the Susquehecka Creek Watershed that may help prevent sediment loading. ................................................................................................................................................................... 17 Figure 7. Example stream segments in the Mahoning Creek Subwatershed. ........................................................ 18 Figure 8. Stream segments flowing through areas with conditions that may exacerbate sediment loading in the Mahoning Creek Subwatershed. ............................................................................................................................. 19 HYDROLOGIC / WATER QUALITY MODELING ....................................................................................................................................... 20 Figure 9. Riparian buffer analysis in the Susquehecka Creek Watershed ............................................................... 23 Figure 10. Riparian buffer analysis in the Mahoning Creek Subwatershed ............................................................ 24 CALCULATION OF THE TMDLAVG .................................................................................................................................................................. 25 Table 7. Existing Annual Average Loading Values for the Mahoning Creek Subwatershed, Reference ................. 25 Table 8. Existing Annual Average Loading Values for the Susquehecka Creek Watershed, Impaired ................... 26 Table 9. Calculation of an Annual Average TMDL Value for the Susquehecka Creek Watershed .......................... 27 ii CALCULATION OF LOAD ALLOCATIONS ................................................................................................................................................... 27 MARGIN OF SAFETY .......................................................................................................................................................... 27 WASTELOAD ALLOCATION .................................................................................................................................................. 27 LOAD ALLOCATION ............................................................................................................................................................ 28 LOADS NOT REDUCED AND ADJUSTED LOAD ALLOCATION ........................................................................................................ 28 Table 10. Average Annual Load Allocation, Loads Not Reduced and Adjusted Load Allocation ............................ 28 CALCULATION OF SEDIMENT LOAD REDUCTIONS ............................................................................................................................. 29 Table 11. Average Annual Sediment Load Allocations for Source Sectors in the Susquehecka Creek Watershed . 29 CALCULATION OF A DAILY MAXIMUM “TMDLMAX” VALUE .............................................................................................................. 29 Table 12. Calculation of TMDLMax for the Susquehecka Creek Watershed .............................................................. 30 th Table 13. 99 Percentile of Daily Loading TMDL (TMDLMax) Variables for the Susquehecka Creek Watershed .... 31 th Table 14. Allocation of the 99 Percentile Daily Load Allocation (LAMax) for the Susquehecka Watershed ............ 31 CONSIDERATION OF CRITICAL CONDITIONS AND SEASONAL VARIATIONS ......................................................................... 32 RECOMMENDATIONS ........................................................................................................................................................................................ 32 PUBLIC PARTICIPATION .................................................................................................................................................................................. 33 CITATIONS .............................................................................................................................................................................................................. 33 APPENDIX A: BACKGROUND ON STREAM ASSESSMENT METHODOLOGY ................................................................. 35 Table A1. Impairment Documentation and Assessment Chronology ...................................................................... 37 APPENDIX B: MODEL MY WATERSHED GENERATED DATA TABLES ........................................................................................ 40 Table B1. “Model My Watershed” Land Cover Outputs for the Susquehecka Creek Watershed ........................... 41 Table B2. “Model My Watershed” Land Cover Outputs for the Mahoning Creek Reference Subwatershed ......... 41 Table B3. “Model My Watershed” Hydrology Outputs for the Susquehecka Creek Watershed. ........................... 42 Table B4. “Model My Watershed” Hydrology Outputs for the Mahoning Creek reference subwatershed ............ 42 Table B5. Model My Watershed outputs for sediment in the Susquehecka Creek Watershed. ............................. 43 Table B6. Model My Watershed Outputs for Sediment in the Mahoning Creek Reference Subwatershed. .......... 43 APPENDIX C: STREAM SEGMENTS IN THE SUSQUEHECKA CREEK SUBWATERSHED WITH SILTATION IMPAIRMENTS FOR AQUATIC LIFE USE ................................................................................................................................................... 44 APPENDIX D: EQUAL MARGINAL PERCENT REDUCTION METHOD ............................................................................................ 46 Table D1. Equal Marginal Percent Reduction calculations for the Susquehecka Creek Watershed. ...................... 48 APPENDIX E: LEGAL BASIS FOR THE TMDL AND WATER QUALITY REGULATIONS FOR AGRICULTURAL OPERATIONS ......................................................................................................................................................................................................... 49 CLEAN WATER ACT REQUIREMENTS ..................................................................................................................................... 50 PENNSYLVANIA CLEAN STREAMS LAW REQUIREMENTS, AGRICULTURAL OPERATIONS....................................................................