Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas (2014)

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N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP REPORT 767 Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas Michael Barrett Lynn Katz Department of Civil, arChiteCtural, anD environmental engineering University of texas at aUstin Austin, TX Scott Taylor rBf Consulting Carlsbad, CA John Sansalone Department of environmental engineering sCienCes University of florida Gainesville, FL Marty Stevenson KinnetiC laBoratories, inC. Lahaina, HI Subscriber Categories Highways • Environment • Hydraulics and Hydrology TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2014 www.TRB.org Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

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C O O P E R A T I V E R E S E A R C H P R O G R A M S AUTHOR ACKNOWLEDGMENTS This study was conducted with funding provided through the National Cooperative Highway Research Program (NCHRP) Project 25-32, Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. The NCHRP is supported by annual voluntary contributions from the state Depart- ments of Transportation. This project was prepared by Dr. Michael Barrett and Dr. Lynn Katz, University of Texas at Austin; Scott Taylor, RBF Consulting; Dr. John Sansalone, University of Florida; and Marty Stevenson, Kinnetic Laboratories, Inc. CRP STAFF FOR NCHRP REPORT 767 Christopher W. Jenks, Director, Cooperative Research Programs Christopher Hedges, Manager, National Cooperative Highway Research Program Danna Powell, Senior Program Assistant Eileen P. Delaney, Director of Publications Margaret B. Hagood, Editor NCHRP PROJECT 25-32 PANEL Field of Transportation Planning—Area of Impact Analysis William Fletcher, Oregon DOT, Salem, OR (Chair) Gregory E. Granato, U.S. Geological Survey, Northborough, MA G. Scott McGowen, California DOT, Sacramento, CA Le Chi Nguyen, Washington State DOT, Seattle, WA Judy A. Ruszkowski, Earl Engineering Services, Lyons, MI John C. Taylor, Mississippi DOT, Jackson, MS Christopher I. Thornton, Colorado State University, Fort Collins, CO Patricia A. Cazenas, FHWA Liaison Stephen F. Maher, TRB Liaison

F O R E W O R D By Christopher Hedges Staff Officer Transportation Research Board This NCHRP report presents prototype best management practices (BMPs) for the removal of dissolved metals in stormwater runoff. Three conceptual configurations are presented in detail: two vault system configurations for urban and rural settings, and an inlet scupper with media for bridge deck drainage systems. The report also includes standard protocols to accurately measure the levels of dissolved metals in stormwater. Practical guidance on the use of these protocols is provided in an appendix to the final report. The report is accompanied by an Excel spreadsheet on CD designed to assist in sizing the filter bed in the vaults and the bridge deck inlet scupper. The report is suitable for immediate application by transportation practitioners in plan- ning, design, and construction, particularly in areas where receiving waters are most sus- ceptible to the impacts of dissolved metals. Starting in the late 1980s, efforts to address polluted stormwater runoff have increased significantly, and the requirements for treating the runoff have gotten more stringent. Not long ago, most highway runoff could be treated using a few simple treatment methods such as bioswales, wet ponds, or vegetated filter strips. More recently however, the treatment requirements have been shifting to include the removal of dissolved metals. Dissolved met- als in stormwater are becoming more of a concern to regulatory agencies, particularly in highly urbanized areas where land values and lack of available space limit the treatment options. Furthermore, there are concerns about the current methods used to determine dissolved metal content. There is evidence that the measurements obtained can vary widely from the effects of a number of factors, including the measurement method and testing protocols, the testing equipment used, methods of cleaning the test equipment, and the scheduling of sampling times during storm events. Under NCHRP Project 25-32, a research team led by the University of Texas at Austin studied the environmental chemistry of metals in highway runoff, reviewed key proper- ties that control the chemical speciation of metals within water, and identified processes and parameters that affect the rate and extent of removal of metal ions from particulate matter. Based on the results, the team developed conceptual configurations for three design scenarios: highly urbanized areas, more rural locations with vegetated shoulders or embankments, and bridges. For each configuration, the design engineer is provided with guidance on integrat- ing them with both new and existing drainage systems. Each configuration involves pre- treatment of runoff, pH buffering, physical retention of the media, hydraulic design, and system maintenance.

C O N T E N T S 1 Chapter 1 Introduction 1 1.1 Background 1 1.2 Research Approach 1 1.2.1 Phase I 2 1.2.2 Phase II 3 1.3 Report Structure 4 Chapter 2 Characterization of Highway Runoff 4 2.1 Stormwater Composition 6 2.2 Particles in Highway Runoff 7 2.3 Metal Partitioning and Complexation in Highway Runoff 10 2.4 Summary 11 Chapter 3 Environmental Chemistry of Metals in Surface Waters 11 3.1 Introduction 11 3.1.1 Metal Speciation 11 3.1.2 Natural Water Composition 13 3.1.3 Characterization of Natural Organic Matter in Receiving Waters 17 3.1.4 Summary 18 3.2 Metal Ion Speciation in Solution: Complexation Reactions 18 3.2.1 Complexation with Inorganic Ligands 22 3.2.2 Complexation in the Presence of Chelating Agents 22 3.2.3 Complexation by Humic Substances 24 3.2.4 Modeling Metal Complexation 26 3.2.5 Summary 26 3.3 Oxidation/Reduction Processes 29 3.3.1 Summary 29 3.4 Precipitation Processes 31 3.4.1 Summary 31 3.5 Sorption Processes 31 3.5.1 Charge Development in Clays and Clay Minerals 33 3.5.2 Surface Complexation 36 3.5.3 Surface Complexation Models 40 3.5.4 Summary 40 3.6 Bioavailability and the Biotic Ligand Model 42 3.6.1 Summary 42 3.7 Conclusions 45 Chapter 4 Treatment of Metals in Highway Runoff 45 4.1 Infiltration 46 4.2 Adsorption 51 4.3 Recommendation for Media Selections

52 Chapter 5 Laboratory Testing and Modeling Methods 52 5.1 Introduction 52 5.2 Development of the Laboratory Testing Protocol 52 5.2.1 Important Factors Affecting Laboratory Evaluation of Metal Adsorption 56 5.3 Development of a Synthetic Runoff Cocktail 56 5.3.1 Collection and Preparation of Highway Runoff Organic Matter 59 5.3.2 Composition of the Inorganic Constituents in the Synthetic Runoff 60 5.3.3 Media Selection and Preparation 61 5.4 Batch Reactor Studies 62 5.5 Experimental Column System 65 5.6 Experimental Results 65 5.6.1 Batch Reactor Studies of Cu Adsorption Capacity and Equilibration Times 66 5.6.2 Column Protocol Verification 66 5.6.3 Contrasting Performance of Different Media and Different Metal Ions 69 5.6.4 Impact of Highway Organic Matter 71 5.6.5 Effects of pH and Ionic Strength on Cu(II) and Zn(II) Sorption 72 5.6.6 Evaluation of pH Stabilizing Media 74 5.6.7 Experiments Conducted at pH Representative of Stormwater 76 5.6.8 Experiments Conducted with Real Stormwater 78 5.6.9 Experiments Conducted at Alkalinity Representative of Stormwater 81 5.7 Application of Results for Field Scale Design 83 Chapter 6 Conceptual BMP Designs 83 6.1 Basis of BMP Design Concepts 84 6.1.1 Site-Specific Constraints and Design Considerations 87 6.1.2 Design Procedure 88 6.1.3 Description of Construction Details of Preferred Concept Alternatives 90 Chapter 7 Recommendations for Future Work 90 7.1 Introduction 90 7.2 Field Testing of GFO Conceptual BMPs 90 7.3 Additional Characterization of Highway Runoff 90 7.4 Incorporation of GFO in the PFC 91 7.5 Incorporation of GFO in Filtration Systems 92 Chapter 8 Summary and Conclusions 92 8.1 Introduction 92 8.2 Characterization of Highway Runoff 92 8.3 Environmental Chemistry of Metals in Natural Waters 93 8.4 Previous Studies of the Treatment of Dissolved Metals 94 8.5 Laboratory Evaluation of Dissolved Metals Removal 95 8.6 Stormwater Treatment Conceptual Designs 96 8.7 Recommendations for Future Research 97 Bibliography

A-1 Appendix A Practical Guidance for Measurement of Dissolved Metals in Stormwater Runoff B-1 Appendix B Detailed Cleaning Protocol for Equipment to be used for Collection of Stormwater Samples for Measurement of Dissolved Metals Note: Many of the photographs, figures, and tables in this report have been converted from color to grayscale for printing. The electronic version of the report (posted on the Web at www.trb.org) retains the color versions.