Mercury TMDL Development for the Willamette River Basin (Oregon) – Technical Support Document October 9, 2019 PREPARED FOR PREPARED BY Oregon Department of Environmental Tetra Tech Quality One Park Drive, Suite 200 and PO Box 14409 U.S. Environmental Protection Research Triangle Park, NC 27709 Tel 919-485-8278 Agency, Region 10 Fax 919-485-8280 tetratech.com The primary authors of this report are: Jonathan Butcher, Michelle Schmidt, and Mark Fernandez, Tetra Tech, Inc., Research Triangle, NC Willamette Mercury TMDL TSD October 2019 CONTENTS CONTENTS.................................................................................................................................................... I TABLES ....................................................................................................................................................... III FIGURES ..................................................................................................................................................... IV ACRONYMS AND ABBREVIATIONS ....................................................................................................... VII 1.0 INTRODUCTION ..................................................................................................................................... 1 1.1 Problem Definition ............................................................................................................................ 1 1.2 Technical Approach .......................................................................................................................... 8 1.2.1 2006 Technical Approach ....................................................................................................... 8 1.2.2 Revised Technical Approach ................................................................................................ 10 2.0 DATA SOURCES ................................................................................................................................. 11 2.1 Mercury Database Development .................................................................................................... 12 2.2 Mercury Data for TMDL Update ..................................................................................................... 13 3.0 FOOD WEB MODEL ............................................................................................................................ 17 3.1 Model Conversion ........................................................................................................................... 17 3.2 Updating the Distributions .............................................................................................................. 18 3.3 Initial Model Calibration .................................................................................................................. 21 3.4 FWM Modifications ......................................................................................................................... 22 3.5 Final Calibrated FWM ..................................................................................................................... 25 3.6 Discussion ...................................................................................................................................... 34 3.7 Food Web Model Results ............................................................................................................... 34 4.0 MERCURY TRANSLATOR MODEL .................................................................................................... 39 4.1 Challenges for the Mercury Translator ........................................................................................... 39 4.1.1 The Translator and Censored Data ...................................................................................... 39 4.1.2 Non-contemporaneity ............................................................................................................ 40 4.1.3 Addressing Censoring in Paired and Aggregated Data ........................................................ 41 4.2 Exploratory Data Analysis .............................................................................................................. 41 4.2.1 Spatial Variability................................................................................................................... 41 4.2.2 Paired versus Aggregated Approach .................................................................................... 43 4.2.3 Seasonal Variability............................................................................................................... 45 4.2.4 Weighted versus Unweighted Regression Analyses ............................................................ 47 4.2.5 Effect of Inclusion of Coast Fork Willamette Data ................................................................ 51 i Willamette Mercury TMDL TSD October 2019 4.2.6 Final Mercury Translator Approach ....................................................................................... 54 4.3 Translating MeHg Targets to THg Targets ..................................................................................... 55 5.0 MASS BALANCE MODEL ................................................................................................................... 57 5.1 Mass Balance Model Approach ...................................................................................................... 57 5.2 HSPF Watershed Model ................................................................................................................. 57 5.2.1 Updated Land Use in the Willamette River Basin ................................................................. 62 5.2.2 Representation of Impoundments ......................................................................................... 68 5.3 Source Characterization ................................................................................................................. 71 5.3.1 Atmospheric Deposition and Surface Runoff ........................................................................ 71 5.3.2 Soil Matrix Sources ............................................................................................................... 76 5.3.3 Groundwater Loading ........................................................................................................... 79 5.3.4 Mining Sources ..................................................................................................................... 80 5.3.5 POTW Sources ..................................................................................................................... 85 5.3.6 Industrial Discharges ............................................................................................................ 89 5.3.7 Urban Stormwater (MS4s) .................................................................................................... 98 5.4 Instream Delivery of THg .............................................................................................................. 109 5.4.1 Estimates of Riverine Loads ............................................................................................... 109 5.4.2 Losses during Transit .......................................................................................................... 111 5.4.3 Reservoir Processes ........................................................................................................... 112 5.5 Mass Balance Model Results ....................................................................................................... 114 REFERENCES .......................................................................................................................................... 145 ii Willamette Mercury TMDL TSD October 2019 TABLES Table 1-1. Waterbody Segments Assessed for Mercury in the Willamette River Basin in 2012 ................. 3 Table 2-1. Summary of Mercury Data Sources for the Phase II TMDL Analysis ....................................... 11 Table 3-1. Fish Species in the Food Web Model and Identification of Updated Distributions ................... 20 Table 3-2. List of Input Distribution Parameters for the 2006 FWM and the Updated FWM ..................... 29 Table 3-3. Updated FWM Biomagnification Factors (BMFs; L/kg) for Fish Tissue THg Concentrations (mg/kg wet weight) as a Function of Water Column dMeHg Concentration (mg/L) ...................... 35 Table 3-4. Estimated FWM Fish Tissue THg Concentrations (mg/kg wet weight) .................................... 35 Table 3-5. Comparison of [Cumulative] BMFs Calculated for the Willamette River Basin to USEPA’s (2001) Draft National BAFs (L/kg) .................................................................................. 37 Table 4-1. Frequency of Non-detects and Estimated Values in WRB Paired Mercury Translator Data ... 40 Table 4-2. Two-Sample t Tests on Summer vs. Winter dMeHg and THg Concentrations ........................ 45 Table 4-3. Statistics for Hg Translator Scenarios ...................................................................................... 46 Table 4-4. Species-specific Surface Water THg Target Levels (ng/L) to Meet a Fish Tissue YConcentration of 0.040 mg/kg MeHg ........................................................................................... 56 Table 5-1. 2011 NLCD Land Cover Summary for the Willamette River Basin .......................................... 65 Table 5-2. Percent