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TRANSPORTATION RESEARCH BOARD WASHINGTON, D.C. 2013 www.TRB.org NAT IONAL COOPERAT IVE H IGHWAY RESEARCH PROGRAM NCHRP SYNTHESIS 449 Research Sponsored by the American Association of State Highway and Transportation Officials in Cooperation with the Federal Highway Administration SubScriber categorieS Highways â¢ Environment â¢ Maintenance and Preservation Strategies to Mitigate the Impacts of Chloride Roadway Deicers on the Natural Environment A Synthesis of Highway Practice conSultantS Laura Fay Xianming Shi and Jiang Huang Western Transportation Institute Montana State University Bozeman, Montana
NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administra- tors and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in coop- eration with their state universities and others. However, the accelerat- ing growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Association and it receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board of the National Research Coun- cil was requested by the Association to administer the research pro- gram because of the Boardâs recognized objectivity and understanding of modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; it possesses avenues of communication and cooperation with federal, state, and local governmental agencies, universities, and industry; its relationship to the National Research Council is an insurance of objec- tivity; it maintains a full-time research correlation staff of specialists in highway transportation matters to bring the findings of research directly to those who are in a position to use them. The program is developed on the basis of research needs identified by chief administrators of the highway and transportation departments and by committees of AASHTO. Each year, specific areas of research needs to be included in the program are proposed to the National Research Council and the Board by the American Association of State Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Research Council and the Transportation Research Board. The needs for highway research are many, and the National Coop- erative Highway Research Program can make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or duplicate other highway research programs. NOTE: The Transportation Research Board of the National Acad- emies, the National Research Council, the Federal Highway Adminis- tration, the American Association of State Highway and Transporta- tion Officials, and the individual states participating in the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturersâ names appear herein solely because they are considered essential to the object of this report. NCHRP SYNTHESIS 449 Project 20-05 (Topic 43-12) ISSN 0547-5570 ISBN 978-0-309-27093-9 Library of Congress Control No. 2013936328 Â© 2013 National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their manuscripts and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. 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Such approval reflects the Governing Boardâs judgment that the program concerned is of national importance and appropriate with respect to both the purposes and resources of the National Research Council. The members of the technical committee selected to monitor this project and to review this report were chosen for recognized scholarly competence and with due consideration for the balance of disciplines appropriate to the project. The opinions and conclusions expressed or implied are those of the research agency that performed the research, and, while they have been accepted as appropriate by the technical com- mittee, they are not necessarily those of the Transportation Research Board, the National Research Council, the American Association of State Highway and Transportation Officials, or the Federal Highway Administration of the U.S. Department of Transportation. Each report is reviewed and accepted for publication by the technical committee according to procedures established and monitored by the Transportation Research Board Executive Committee and the Govern- ing Board of the National Research Council. Published reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from: Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet at: http://www.national-academies.org/trb/bookstore Printed in the United States of America
THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medicine The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished schol- ars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. On the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Acad-emy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Charles M. Vest is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the ser- vices of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, on its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academyâs purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Acad- emy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. Charles M. Vest are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is one of six major divisions of the National Research Council. The mission of the Transportation Research Board is to provide leadership in transportation innovation and prog- ress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multimodal. The Boardâs varied activities annually engage about 7,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. www.TRB.org www.national-academies.org
TOPIC PANEL 43-12 ANNETTE M. DUNN, Iowa Department of Transportation, Ames G. MICHAEL FITCH, Virginia Department of Transportation, Charlottesville FRANK N. LISLE, Transportation Research Board STEVEN M. LUND, Minnesota Department of Transportation, St. Paul MONTY MILLS, Washington State Department of Transportation, Olympia MAX S. PERCHANOK, Ontario Ministry of Transportation, St. Catherines LAURENE POLAND, Massachusetts Department of Transportation, Boston GABRIEL GUEVARA, Federal Highway Administration (Liaison) SUSAN JONES, Federal Highway Administration (Liaison) SYNTHESIS STUDIES STAFF STEPHEN R. GODWIN, Director for Studies and Special Programs JON M. WILLIAMS, Program Director, IDEA and Synthesis Studies JO ALLEN GAUSE, Senior Program Officer GAIL R. STABA, Senior Program Officer DONNA L. VLASAK, Senior Program Officer TANYA M. ZWAHLEN, Consultant DON TIPPMAN, Senior Editor CHERYL KEITH, Senior Program Assistant DEMISHA WILLIAMS, Senior Program Assistant DEBBIE IRVIN, Program Associate COOPERATIVE RESEARCH PROGRAMS STAFF CHRISTOPHER W. JENKS, Director, Cooperative Research Programs CRAWFORD F. JENCKS, Deputy Director, Cooperative Research Programs NANDA SRINIVASAN, Senior Program Officer EILEEN P. DELANEY, Director of Publications NCHRP COMMITTEE FOR PROJECT 20-05 CHAIR CATHERINE NELSON, Oregon DOT MEMBERS KATHLEEN S. AMES, Michael Baker, Jr., Inc. STUART D. ANDERSON, Texas A&M University BRIAN A. BLANCHARD, Florida DOT CYNTHIA J. BURBANK, PB Americas LISA FREESE, Scott County (MN) Community Services Division MALCOLM T. KERLEY, Virginia DOT RICHARD D. LAND, California DOT JOHN M. MASON, JR., Auburn University ROGER C. OLSON, Minnesota DOT ROBERT L. SACK, New York State DOT FRANCINE SHAW-WHITSON, Federal Highway Administration LARRY VELASQUEZ, JAVEL Engineering, Inc. FHWA LIAISONS JACK JERNIGAN MARY LYNN TISCHER TRB LIAISON STEPHEN F. MAHER Cover figure: An NJDOT truck spreads anti-icing material on a New Jersey road (Courtesy: New Jersey Department of Transportation).
Highway administrators, engineers, and researchers often face problems for which information already exists, either in documented form or as undocumented experience and practice. This information may be fragmented, scattered, and unevaluated. As a con- sequence, full knowledge of what has been learned about a problem may not be brought to bear on its solution. Costly research findings may go unused, valuable experience may be overlooked, and due consideration may not be given to recommended practices for solving or alleviating the problem. There is information on nearly every subject of concern to highway administrators and engineers. Much of it derives from research or from the work of practitioners faced with problems in their day-to-day work. To provide a systematic means for assembling and evaluating such useful information and to make it available to the entire highway commu- nity, the American Association of State Highway and Transportation Officialsâthrough the mechanism of the National Cooperative Highway Research Programâauthorized the Transportation Research Board to undertake a continuing study. This study, NCHRP Proj- ect 20-5, âSynthesis of Information Related to Highway Problems,â searches out and syn- thesizes useful knowledge from all available sources and prepares concise, documented reports on specific topics. Reports from this endeavor constitute an NCHRP report series, Synthesis of Highway Practice. This synthesis series reports on current knowledge and practice, in a compact format, without the detailed directions usually found in handbooks or design manuals. Each report in the series provides a compendium of the best knowledge available on those measures found to be the most successful in resolving specific problems. This synthesis documents the range of methods, tools, and techniques used by transpor- tation agencies to minimize the environmental impact of chloride-based roadway deicers. The report presents information on preventative measures designed to reduce the amount of chloride deicers entering the natural environment adjacent to roads, as well as strategies for reducing the impacts once the deicers are in the environment. Information used in this study was acquired through a review of the literature and a survey of state departments of transportation and Canadian provincial transportation agen- cies. Follow-up interviews with selected agencies provided additional information. Laura Fay, Xianming Shi, and Jiang Huang, Western Transportation Institute, Montana State University, Bozeman, collected and synthesized the information and wrote the report. The members of the topic panel are acknowledged on the preceding page. This synthesis is an immediately useful document that records the practices that were acceptable with the limitations of the knowledge available at the time of its preparation. As progress in research and practice continues, new knowledge will be added to that now at hand. FOREWORD PREFACE By Jo Allen Gause Senior Program Officer Transportation Research Board
CONTENTS 1 SUMMARY 3 CHAPTER ONE INTRODUCTION Methodology, 4 Report Structure, 4 6 CHAPTER TWO BACKGROUND Environments at Risk, 6 Mitigation Techniques, 9 12 CHAPTER THREE PROACTIVE MITIGATION STRATEGIES Salt Management Plans, 12 Staff Training, 13 Monitoring and Record Keeping, 15 Anti-icing, Deicing and Pre-wetting Practices, 16 Weather Forecasting and Road Weather Information Systems, 18 Snowplows, 20 Vehicle-Mounted Spreaders, 23 Roadway and Pavement Design, 24 Vegetation Management, 25 Innovative Snow Fences, 26 Design and Operations of Road Maintenance Yards, 29 31 CHAPTER FOUR REACTIVE MITIGATION STRATEGIES General Considerations, 31 Infiltration Trenches and Basins, 32 Detention, Retention, and Evaporation Ponds, 33 Wetlands and Shallow Marshes, 35 Vegetated Swales and Filter Strips, 37 Overview of Reactive Strategies, 38 40 CHAPTER FIVE NEW AND EMERGING TECHNOLOGIES Synchronizing Vehicle Location and Other Sensor Technologies, 40 Maintenance Decisions Support System, 42 Fixed Automated Spray Technology, 43 Thermal Deicing Methods, 44 47 CHAPTER SIX CONCLUSIONS Conclusions, 47 Suggestions for Future Research, 47 51 REFERENCES 66 GLOSSARY 67 APPENDIX A SURVEY AND RESPONSES Survey Questionnaire, 67 Summary of Survey Results, 70
87 APPENDIX B CASE EXAMPLES Closed Loop Controllers, 87 Vegetation Management, 88 Snow Disposal and Melting, 90 Making Salt Brine from Recycled Vehicle Wash Bay Water, 92 Case Example Questionnaire, 95 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.
SUMMARY STRATEGIES TO MITIGATE THE IMPACTS OF CHLORIDE ROADWAY DEICERS ON THE NATURAL ENVIRONMENT The past few decades have seen steady increase in the use of chloride roadway deicers for winter maintenance operations, along with the awareness of associated environmental risks. The United States currently spends approximately $2.3 billion annually to keep high- ways free of snow and ice, and the associated corrosion and environmental impacts add at least $5 billion. The environmental impacts of chloride roadway deicers depend on a wide range of factors unique to each deicer formulation and the location of application. Chloride-based deicers used in winter maintenance practices can impact the environ- ment adjacent to the road. The objective of this synthesis is to document strategies used by transportation agencies to mitigate the impacts of chloride roadway deicers on the natural environment, including the surrounding soil and vegetation, ground and surface water, aquatic biota, and wildlife. The scope of this synthesis covers solid and liquid chloride- based roadway deicersâsodium chloride, magnesium chloride, and calcium chloride. Information presented in this synthesis was obtained through a comprehensive litera- ture review utilizing information published domestically and internationally, including government reports, technical documents or webpages, journal publications, and confer- ence presentations and proceedings. Additional information was gathered through a survey that was sent to all state departments of transportation (DOTs) and to Canadian provin- cial transportation agencies. A total of 40 state DOTs responded with a response rate of 80%, and 12 Canadian provincial transportation agencies responded with a response rate of 100%. Follow-up interviews with six selected agencies were conducted. Information gained from the interviews was converted into four case examples. The synthesis presents information on identified proactive strategies used to mitigate the impacts of chloride road deicers on the natural environment. Proactive strategies entail preventative measures designed to reduce the amount of chloride deicers entering the envi- ronment, which can reduce the need for or dependence on reactive strategies. The effective practices identified from the survey and literature review and presented in this synthesis include salt management plans; staff training; monitoring and record-keeping; anti-icing, deicing, and pre-wetting practices; weather forecasting and Road Weather Information Systems; snowplows; vehicle-mounted spreaders; roadway and pavement design; vegeta- tion management; innovative snow fences; and design and operations of road maintenance yards. Most methods, techniques, and tools can be used alone, paired in a series, or inte- grated to form a proactive mitigation effort. Survey responses identified proactive mitiga- tion strategies as the most common methods currently used to mitigate the impacts of chloride road deicer on the natural environment. Reactive strategies used to mitigate the impacts of chloride road deicers on the natural environment were also identified. Reactive strategies aim to reduce the impacts of chloride deicers once they are in the environment. The following effective practices were identified from the literature review and confirmed by survey responses: infiltration trenches and
2 basins; detention, retention, and evaporation ponds; wetland and shallow marshes; vegetated swales; and filter strips. Many of the strategies presented in this synthesis were designed for and are frequently used in stormwater management and aid only in the retention or capture of chloride-laden water and do not actually treat or remove chloride from the water. All of the presented strategies contribute to the effective treatment of both the velocity and the quality of highway stormwater runoff. The majority of the reactive strategies identified were not originally installed for this purpose, and their cost-effectiveness for chloride deicer environmental management has yet to be examined and validated. For deicer environmental management, reactive strategies may vary, and need to be designed, sited, installed, and maintained properly. Reactive strategies may be used individually or synergistically and a combination of reactive strategies can help enhance overall performance, increase service life, and preserve downstream water bodies. This synthesis also presented information on new and emerging technologies identified through the survey and literature review including: synchronizing vehicle location and other sensor technology, maintenance decision support systems (MDSS), fixed automated spray technology, and thermal deicing methods. Many of the proactive and reactive measures and the emerging technologies discussed can be used as performance measures to monitor the effectiveness of chlorides (e.g., MDSS) and/or the environmental impacts (e.g., vegetation management), if appropriate data are collected, processed, and reported. This information can then be assimilated into usable result-based standards and incorporated into salt management plans and monitoring and training programs. Effective methods, techniques, and tools have been developed and are constantly evolv- ing to minimize the impacts of chloride roadway deicers on the environment. The synthesis concludes that a combination of both proactive and reactive strategies may lead to better mit- igation of environmental impacts. Strategies may vary, depending on the specific climate, site, and traffic conditions. The key is to select an appropriate suite of tools, techniques, or methods that can function most effectively for the given set of conditions. This synthesis work identified main gaps in the knowledge base where additional research is warranted. The recommended research includes addressing knowledge gaps in the follow- ing areas: â¢ Fundamentals (e.g., benefits and risks of using liquids for anti-icing and deicing, impacts and implications of removing impaired roadside vegetation, cost-effectiveness and environmental impacts of agro-based deicers, fate and transport of pollutants), â¢ Monitoring (e.g., mobile salinity sensor, salt-tolerant vegetation, correlating the chloride loading in adjacent soils with deicer usage, effectiveness of salt management plans), â¢ Strategies (e.g., appropriate application rates for anti-icing and deicing, effectiveness of incentive programs, effective use of hot water, innovative use of roadside vegetation, efficiency of reactive strategies in cold regions), and â¢ Technology (e.g., anti-icing pavement, better chemical products, improved thermal road mapping).
3 road maintenance. The environmental impacts of chloride salts have been a subject of research since their use for high- way maintenance became widespread during the 1960s (Hawkins 1971; Roth and Wall 1976; Paschka et al. 1999; Ramakrishna and Viraraghavan 2005). In a recent review, Fay and Shi (2012) presented a comprehensive survey of cur- rent knowledge and examined the environmental impacts of materials used for snow and ice control (e.g., abrasives, chlo- rides, acetates/formates, glycols, agro-based deicers, urea). Existing knowledge may be utilized to minimize the environmental impacts of chloride roadway deicers. For instance, deicers that contain significant amounts of calcium (Ca) and magnesium (Mg) should not be applied near soils significantly contaminated with metals or where any mobi- lized metals could easily be released to a sensitive receiving water body (Horner and Brenner 1992). To promote sound environmental stewardship, agencies may consider a holistic view of snow and ice control and consider accounting for the indirect costs of road salting, such as the costs to roadside vegetation (Trahan and Peterson 2008) and to motor vehicles and infrastructure (Shi 2005). Efforts will continue in the areas of managing the footprint of chloride roadway deicers and minimizing the associated risk and liability. When promoting environmentally responsible winter road service, public perception is an important aspect to con- sider. The general public often recognizes the need for and benefits of such operations, yet is concerned about the envi- ronmental risks associated with the use of chloride roadway deicers, traction sand, and other materials for snow and ice control. In the United States, water quality, air quality, and wildlife issues are regulated with the guidance of the Clean Water Act, Clean Air Act, and Federal Endangered Species Act. These laws also detail the identification and manage- ment of environmentally sensitive areas, such as those on the list of impaired streams for water quality and the list of PM-10 nonattainment communities for air quality. Despite their potential damaging effects, snow and ice control chem- icals can reduce the need to apply abrasives and pose less threat to the surrounding vegetation, water bodies, aquatic biota, air quality, and wildlife. Performance measures are tools used to assess progress toward achieving a defined goal (FHWA 2012). Environ- mental performance measures for winter maintenance oper- CHAPTER ONE INTRODUCTION This synthesis presents information on strategies used to mitigate the impacts of chloride roadway deicers on the natural environment. Many of the identified solutions also could apply to mitigating the impacts of abrasives and non- chloride-based roadway deicers. Specific items that will be discussed include strategies used to control the source of deicer contamination without jeopardizing the level of ser- vice (LOS) on winter roads [salt management plans; staff training; monitoring and keeping records; anti-icing, deic- ing, and pre-wetting practices; weather forecasting and Road Weather Information Systems (RWIS); snowplows; vehicle- mounted spreaders; roadway and pavement design; proac- tive vegetation management; innovative snow fences; and road maintenance yard design and operation], those used to reduce the impacts of chloride roadway deicers once they are in the environment (infiltration trenches and basins; deten- tion, retention, and evaporation ponds; wetland and shallow marshes; and vegetated swales and filter strips), and new and emerging technologies [synchronizing vehicle location and other sensor technologies, maintenance decision sup- port systems (MDSS), fixed automated spray technology (FAST), and thermal deicing methods]. These items have been identified through a comprehensive literature review and practitioner surveys, aimed to guide state departments of transportation (DOTs) and others in promoting sustain- able winter service and environmental stewardship best practices. The information will also help agencies meet reg- ulatory requirements within their cultural, political, fiscal, technological and other constraints. Environmental needs can vary by region (e.g., urban vs. rural, marshlands vs. mountains) and a âone-size-fits-allâ approach is unlikely to work effectively. The past few decades have seen steady increase in the use of chloride roadway deicers for winter maintenance opera- tions, along with the awareness of associated environmental risks. In the United States and Canada, more than US$2.3 billion and US$1 billion is spent annually on winter highway maintenance, respectively (TAC 2002; FHWA 2005). Chlo- ride salts, primarily sodium chloride (NaCl), magnesium chloride (MgCl2), and calcium chloride (CaCl2), are the main freezing point depressants in a wide variety of snow and ice control products, as they are relatively low cost, easy to use, and safe for the applicator and road user. Accord- ing to Salt Institute statistics, the United States in 2007 sold approximately 20.2 million tons of NaCl for use in winter
4 mitigate the impacts of chloride roadway deicers on the natural environment. Technical documents, government reports, journal publications, and conference presentations and proceedings were used initially to identify pertinent information, and from local, state, federal, and international governments and organizations as well as organizations that work to promote winter maintenance effective practices, on webpages, manuals, field guides and reports, and published specifications. The literature review information was used to shape the outline of the report and to create the survey and interview questions. Information presented in this synthesis was obtained through a comprehensive literature review utilizing infor- mation published domestically and internationally, includ- ing government reports, technical documents or webpages, journal publications, and conference presentations and proceedings. Additional information was gathered using a practitioner survey. The survey was sent to all state DOTs and to Canadian provincial transportation agencies. A total of 40 state DOTs responded with a response rate of 80%, and 12 Canadian provincial transportation agen- cies responded with a response rate of 100%. Information gained from the survey was used to provide resources and information utilized in the report. Appendix A presents the survey questions and responses. Follow-up interviews with six selected agencies were conducted. Information from the interviews was used to provide resources and information utilized in the report, and was converted into four case examples: closed loop control- lers, vegetation management, snow disposal and melting, and making salt brine from recycled vehicle wash bay water. Appendix B presents the case examples. REPORT STRUCTURE Information in this synthesis is presented as follows. Chap- ter one introduces the reader to the topic of the synthesis, defines its scope and objectives, and describes the methodol- ogy section and the report structure. Chapter two provides a review of background information to provide context for the topic, including environmental issues associated with the use of chloride roadway deicers and overview of mitigation techniques. Chapter three discusses preventative measures designed to reduce the amount of chloride roadway deicers entering the environment, which can reduce the need for or dependence on reactive strategies. Chapter four discusses mitigation measures that reduce the impacts of chloride road deicers once they have reached the environment adja- cent to the road. Chapter five presents information on recent advances identified by the survey respondents or identified in the literature review. Chapter six provides a summary of the key findings from each chapter and a discussion of knowledge gaps and areas for future research. The synthe- ations can focus on ecosystems, habitat and biodiversity, water quality, wetlands, and/or air quality [Environmental Plan 2008; Strategic Highway Research Project (SHRP) 2009]. Nonenvironmental performance measures for winter maintenance operations may focus on mobility, reliability, accessibility, safety, or vehicle speed (Qiu and Nixon 2009; SHRP 2009; Usman et al. 2010). Regardless of the perfor- mance measure being assessed, data need to be collected to allow for comparison of products, equipment, road surface condition, and the like, as well as for recommendations and planning. Many DOTs have implemented programs to assess environmental performance measures (CTC & Associates 2007), but limited information on each program has been published. Organizations such as FHWA and AASHTO, however, have developed web-based tools and resources such as the Center for Environmental Excellence (http:// environment.transportation.org/), Eco-Logical (http://www. environment.fhwa.dot.gov/ecological/eco_index.asp), and INVEST (https://www.sustainablehighways.org/). Informa- tion gathered from the assessment of performance measures can then be used to establish result-based standards in the field of winter maintenance. Results-Based Winter Mainte- nance Standards, a multiyear project currently underway through Aurora, aims to develop quantitative methods to understand the relationships between key aspects of winter maintenance (e.g., maintenance operations, road surface conditions, highway safety, mobility). The environmental cost associated with chloride roadway deicers is a factor to be balanced with the value they provide. This is evidenced in a growing number of new initiatives to manage and limit deicer usage, such as the Transportation Association of Canadaâs Road Salt Management Guide, the Minnesota Pollution Control Agencyâs Metro Area Chlo- ride Project, and the New Hampshire Road Salt Reduction Initiative. The recent NCHRP report Grand Challenges: A Research Plan for Winter Maintenance identified âbalancing social, environmental and economic factorsâ as one of the six critical issues in advancing winter highway maintenance (Wilfrid A. Nixon and Associates 2010). In light of the ever- increasing urbanization and customer demand for higher LOS, this issue is anticipated to be one of the greatest and most persistent challenges for the highway agencies in the coming years. In this context, there is a need to identify ways to maintain acceptable LOS while minimizing the environ- mental cost of winter road maintenance. METHODOLOGY A review of all available literature, surveys, and interviews were used to assemble the information presented in this syn- thesis. Details on each of these tasks are presented as follows. An extensive literature review was conducted to gather information on proactive and reactive strategies used to
5 sis is followed by Appendix AâSurvey and Responses, and Appendix BâCase Examples, which highlight effective practices on the following topics: closed loop controllers, vegetation management, snow disposal and melting, and making salt brine from recycled wash bay water. The report is designed to be used as an information guide and a reference document. Each topic has an additional resources section that provides further references.
6 CHAPTER TWO BACKGROUND This synthesis provides information on proactive and reac- tive strategies that can be used to mitigate the impacts of chloride-based roadway deicers on the natural environment. To provide context for the information presented in this syn- thesis, this chapter briefly reviews the potential environmen- tal impacts of chloride roadway deicers on the environment and the mitigation strategies that have been implemented to reduce these impacts. ENVIRONMENTS AT RISK There are growing concerns over the impact of deicers on the transportation infrastructure, motor vehicles, and the environment (DâItri 1992; Menzies 1992; Buckler and Granato 1999; Levelton Consultants Ltd. 2007; Shi et al. 2009a, b, c). Chloride ions (Clâ) are conservative, which means once dissolved they do not degrade in the environ- ment and remain in solution (Ministry of Environment 2011). The environmental impacts of chloride roadway deicers depend on factors unique to each formulation and the location of application. According to Ramakrishna and Viraraghavan (2005, p. 60), the degree and distribu- tion of the impacts in the highway environment are defined by spatial and temporal factors, such as draining charac- teristics of road and adjacent soil, amount and timing of materials applied, âtopography, discharge of the receiving stream, degree of urbanization of the watershed, tempera- ture, precipitation, dilution,â and adsorption onto and bio- degradation in soil. A recent survey of winter maintenance practitioners found water quality to be of the greatest concern, with air quality, vegetation, endangered spe- cies, and subsurface well contamination also mentioned as highly relevant (Levelton Consultants Ltd. 2007). As early as 1971, a study by the U.S. Environmental Protection Agency (EPA) found highway chloride deicing salts able to âcause injury and damage across a wide environmental spectrumâ and uncovered salt storage sites to be âa serious source of ground and surface water contaminationâ (Field and OâShea 1992). More recent research confirm that repeated applications of chloride deicers and abrasives or âseepage from mismanaged salt storage facilities and snow disposal sitesâ may adversely affect the surrounding soil and vegetation, water bodies, aquatic biota, and wildlife (Buckler and Granato 1999; Venner Consulting and Par- sons Brinckerhoff 2004; Levelton Consultants Ltd. 2007). There is a need to better understand and assess the envi- ronmental impacts of chloride deicers, in an effort to con- duct sustainable winter operations in an environmentally and fiscally responsible manner. Figure 1 is an environmen- tal pathway model that illustrates how deicers can move in the environment and where the impacts can occur (Levelton Consultants 2007). Environments that can be impacted by deicers include soil, ground and surface water, and vegeta- tion; the figure presents the chloride deicer impacts to each of these environments. Roadway winter operations are only one source from which chlorides can enter the environment, as other industries (e.g., water softeners) and private-sector (e.g., malls and parking lots) winter operations also intro- duce significant amount of chlorides. Soil Deicer migration into soils adjacent to roadways can cause the swelling and compaction of soil, change its electrical con- ductivity, and lead to loss of soil stability by means of dry-wet cycling, osmotic stress, and mobilization of nutrients (Envi- ronment Canada 2010). Factors that affect the concentrations of deicer in the soil are the type and texture of soil, as well as its water concentration, cation exchange capacity, perme- ability, and infiltration capacity (DâItri 1992). Lundmark and Jansson (2008) used the dynamic modeling approach to suc- cessfully represent âthe spread of deicing salt from road to surroundings, deposition in the roadside environment and the subsequent infiltration into roadside soilâ (p. 215). With increasing distance from the road, the field observations con- firmed a general decrease in the chloride content of soil, with supporting evidence in soil physical properties, vegetation properties, and snow characteristics. Amrhein et al. (1992) studied the effect of deicers on the mobilization of metallic and organic matters in roadside soils and found the heavy metal concentrations to generally increase with increasing salt concentration. Buzio et al. (1977) studied the distribu- tion of salt near a deicing salt stockpile and its effects on soil, by sampling the soil from 17 sites on an adjacent slope, and found extensive lateral movement of chloride with subsequent leaching to a depth greater than 76 cm. Ground and Surface Waters The potential impact of chloride deicers on the groundwa- ter is of great concern, especially in the long run, as it may
7 undermine the quality of drinking water and increase the health and corrosion risks. One identified health risk related to deicers in the public water supplies is toxemia associ- ated with pregnancy (Sorensen et al. 1996). However, most water supplies do not test high enough on a regular basis to warrant concern. Health risks associated with water quality were also addressed in the Road Salt and Winter Mainte- nance for British Columbia Municipalities report; however, it was stated that âwater would become unpalatable to most people before these conditions would ariseâ (Warrington 1998, sect. 2.2). For humans, long-term exposure to sodium may lead to hypertension (EPA 2003). Groundwater con- tamination from deicers depends on the frequency of the precipitation, the texture and drainage characteristics of the roadside soil, the distance between the groundwater and the surface and the roadway, the permeability of the aquifer material, the direction and rate of groundwater flow, and the deicer application rate (DâItri 1992). For example, shallow and localized aquifers are at greater risk of contamination than deep and regional water sources. FIGURE 1 Environmental pathway model modified by Levelton Consultants (2007), showing the deicer footprint on the environment.
8 According to Eldridge et al. (2010), chloride criteria rec- ommended by the EPA for fish species for chronic condi- tions should not exceed a 4-day average of 230 mg/l and for acute conditions not to exceed a 1-hour average of 860 mg/l. Both chronic and acute criteria should not be exceeded more than once every 3 years on average. State limits on chlo- rides could be even more stringent. Anthropogenic sources of sodium that can significantly contribute to surface water include road salt, water treatment chemicals, domestic water softeners, and sewage effluent (EPA 2003). Pollut- ants, originating from salting, sanding, and other mainte- nance activities, pose threats to water resources (Hanes et al. 1970; Sorensen et al. 1996; Missoula CityâCounty Health Department 1997; Rosenberry et al. 1999; TurnerâFairbank Highway Research Center 1999; TAC 2003d; Corsi et al. 2010) and potentially impair the water quality or alter the aquatic habitat. However, the damaging impacts depend on site-specific conditions and concentrations of pollutants in the receiving environments. A case study found that about 55% of road salts are transported in surface runoff with the rest infiltrating through soils and into groundwater aquifers (Church and Friesz 1993). Work by Corsi et al. (2010) found road salt to cause detrimental impacts to surface water on local, regional, and national scales, with short- and long-term impacts to streamwater quality and aquatic life. The degree to which the surface water is contaminated from deicers is a function of the amount of time the deicer takes to reach the water body, the dilution factor, the residence time of the water body, and the frequency and rate of deicer applica- tion (DâItri 1992). The impact of deicers on receiving waters may be negligible in many cases, depending on the type and designated use of the receiving water, and on the drainage system used to discharge the runoff (TurnerâFairbank High- way Research Center 1999). In addition, groundwater and vulnerable aquifers can be affected by any material applied or spilled on the land, including deicers and abrasives. Vegetation Common deicer exposure mechanisms to plants include increased concentrations in the soil and water that can result in uptake by plant roots, or accumulation on foliage and branches owing to splash and spray (TRB Special Report 235 1991). Runoff from salt stockpiles was found to significantly damage nearby trees and to reduce the number of plant spe- cies available in soils. Salt concentrations higher than 15,000 ppm were found leaching from salt stockpiles (Buzio et al. 1977). (Appendix B provides details on the topic of needle browning.) Hanes et al. (1970) described the three major effects of salt on plant growth. First, salt can increase soil salinity and alter the osmotic pressure gradient, inhibiting the uptake of water by plant roots. Second, salt accumula- tions can occur in plant tissues. Third, salt can induce ionic imbalances, causing plant injury symptoms such as desic- cation and leaf burn. Deicing salt exposure resulting from spray within 33 to 65 ft (10 to 20 m) of the road was dem- onstrated to cause a greater severity of foliar damage than uptake through the soil alone (Hofstra and Hall 1971; Viskari and Karenlampi 2000; Bryson and Barker 2002). On pri- mary highways within 100 ft (30 m) of the road, highway agencies estimate that 5% to 10% of the plants in high-use sections are affected by deicers, and report that shrubs and grasses can tolerate increased concentrations better than trees. Plants with broader leaves are generally affected more than plants with narrow leaves (TRB Special Report 235 1991). Many studies have indicated that needle necro- sis (death), twig dieback, and bud kill are associated with areas of heavy deicing salt usage, with trees and foliage down wind and facing the roadside more heavily affected than trees further away (Hofstra and Hall 1971; Lumis et al. 1973; Sucoff et al. 1976; Pedersen et al. 2000). Studies have shown that the slope of the roadside adjacent to the treated roadway is an important variable in defining the extent of plant injury from deicer treatment, with vegetation showing effects up to 20 ft (6 m) away on flat surfaces, 40 to 55 ft (12 to 17 m) away for steep down slopes, and only 10 ft (3 m) up slope (TRB Special Report 235 1991). Aerial drift of deicers resulting from vehicular splash, plowing, and wind has also been observed to impact veg- etation adjacent to roadways. Nicholson and Branson (1990) showed that deicer particulates deposited on the road could be removed and re-suspended by vehicular traffic. Wet conditions, increased vehicle speed, wind currents, and updrafts generated by vehicular traffic can cause redistri- bution of deicers off the roadway into the adjacent envi- ronment (Kelsey and Hootman 1992). Generally traveling from 6 to 130 ft (2 to 40 m), deicing particles have been observed up to 330 ft (100 m) from the roadway (Lumis et al. 1973; Blomqvist and Johansson 1999; Trahan and Peterson 2007). Kelsey and Hootman (1992) observed sodium deposi- tion within 400 ft (122 m) of a toll way and sodium-related plant damage within 1,240 ft (378 m) of the toll way. Field tests have shown that 20% to 63% of the NaCl-based deic- ers applied to highways in Sweden were carried through the air, with 90% of them deposited within 65 ft (20 m) of the roadside (Blomqvist and Johansson 1999). Native plant succession or loss of native plant species as a result of deicer use has been observed in soils and in low flush-rate surface waters adjacent to roadways, as well as in wetland-type environments that receive water flow from treated roadways. In wetlands with elevated deicer concen- trations, a decrease in plant community richness, evenness, cover, and species abundances has been observed (Rich- burg et al. 2001). In wetlands specifically, reducing and/or halting deicer treatment can allow for native plant recovery after multiple water years, but this includes the reintroduc- tion of non-native species as well (TRB Special Report 235 1991; Moore et al. 1999). A study of a bog contaminated with salt from a leaching deicer pile showed a decline in native plant species and introduction of non-native plant
9 species (Wilcox 1986). Within 4 years of the contamina- tion event, native plants were returning to the bog. Other Environmental Risks A study from the Michigan DOT suggested that endangered and threatened species and the habitat on which they depend for survival could be adversely affected by the use of cer- tain deicers (Public Sector Consultants 1993). In extremely sensitive environments, small applications of deicers may be detrimental to the ecosystem. Salt may accumulate on the side of roadways following deicer applications and during spring as snow melts; in areas with few natural salt sources, this could attract deer and other wildlife to the road network (Bruinderink and Hazebroek 1996). The presence of wild- life on roadways to glean deicing salts has led to increased incidents of wildlife-vehicle collisions (Forman et al. 2003). Deicers are generally at most low to mild skin and eye irri- tants to humans as can be referenced in their Materials Safety Data Sheet. Issues arise when there is direct ingestion of product, generally in the case of wildlife. MITIGATION TECHNIQUES This section presents a brief summary of practices used to mitigate the impacts of chloride roadway deicers on the nat- ural environment, with a focus on those identified from the survey of winter maintenance practitioners (see Figure 2). FIGURE 2 Methods, techniques, or tools identified by survey respondents as being used to reduce chloride roadway deicer usage or the impacts of chlorides on the natural environment. Mitigation is the process of taking steps to avoid or min- imize negative environmental impacts. A wide variety of mitigation techniques and approaches used to reduce deicer environmental impacts have been explored. Strategies can be implemented in technology, management, or both. The practices can be divided into two groups, the first of which focuses on the preventative and proactive approach to reduce amount of salts used, lost, or wasted, and the sec- ond of which focuses on the reactive approach to capture or retain salts once applied so as to reduce their impacts on the adjacent environment. Figure 2 shows that the most frequently used proactive and reactive mitigation strategies used by DOT practitioners and Canadian provincial govern- ment practitioners include anti-icing and deicing practices, staff training, equipment and/or technology, monitoring and keeping usage records, maintenance yard design and opera- tion, salt management plans, detention or retention ponds, and vegetation management. The proactive practices aim to âutilize the minimum amount of material necessary to achieve the desired outcome (or LOS)â and to keep the chlorides on the road, following the 4-Râs (right material, right amount, right place, and right time) principle (TAC 2003i). Ninety-one percent of survey respon- dents stated that their agency had made efforts in the past 5 years to reduce the amount of chloride deicers applied during winter maintenance operations (n = 35 in United States, n = 12 in Canada). Survey respondents were asked if any official or unofficial policy changes have been made to encourage the use of less chloride deicing material. In general, the responses from Canada were in the affirmative, whereas the responses from the United States were in the negative and any changes that were encouraged were unofficial. Little information is available from the winter mainte- nance community on reactive strategies, such as removing the chlorides from the environment adjacent to the road fol- lowing winter maintenance activities. This is likely because chloride ions will not break down over time and they cannot be easily treated or removed from the environment. The vast majority of the reactive strategies identified were not origi- nally installed for this purpose. Survey respondents were asked if they had observed chloride deicer mitigation in the adjacent roadside environment from implementation of strat- egies for other purposes, and many respondents indicated that they had observed mitigation of chloride roadway deicers in the environment adjacent to the road following implementa- tion of strategies for other purposes [63% (United States n = 21, Canada n = 9) responded yes and 38% (United States n = 15, Canada n = 3) responded no]. Eighty percent of the survey respondents that indicated they had observed this stated that the original reason for implementation of the strategy was for cost-savings purposes as a result of budgetary constraints, which had the side benefit of reducing impacts of chlorides on the environment by reducing the overall amount of chlorides put in the environment. Other strategies that survey respon- dents had implemented for other purposes and observed the side benefit of chloride roadway deicer mitigation in the road- side environment include the following: â¢ Stormwater treatment techniques, â¢ Implementation of new technology [automatic vehi- cle location (AVL), AVL/Global Positioning System (GPS), RWIS, MDSS, pavement temperature sensors, and localized forecasting],
10 â¢ Management strategies [monitoring salt use, operator training (e.g., proper application rates), good house- keeping, and streamlining operations], and â¢ Pre-wetting. Because they were not designed specifically for miti- gating the impacts on chloride roadway deicers, the cost- effectiveness of these strategies for deicer environmental management has not yet been examined and validated. When survey respondents were asked if their state or agency has made any effort to mitigate or reduce the impacts of chloride deicers (either through reduced chloride deicer use or by reducing the impacts of chlorides to the natural environment), 88% responded yes (n = 35 United States). Defined application guidelines or performance specifica- tions were also available on the following practices: â¢ Use of chlorides for winter maintenance prac- ticesâ95% (U.S. responses only) said yes, â¢ Tools or methods to determine the effectiveness of chlorides used in winter maintenance practicesâ48% (U.S. responses only) said yes, and â¢ Tools or methods to quantify the environmental impacts of chlorides used in winter maintenance prac- ticesâonly 28% (U.S. responses only) said yes. In other words, although state DOTs are making an effort to mitigate or reduce the impacts of chloride deicers, the amount of information available to aid in this process is still limited. This confirms the need for this synthesis work and more in-depth research to address relevant knowledge gaps. Additional Resources for Chapter Two Brink, M., and M. Auen, âGo Light with the Salt, Please: Developing Information Systems for Winter Roadway Safety,â TR News, No. 230 (Jan.âFeb., 2004), 2004, pp. 4â9. Davis, R.S., Transportation Research Circular E-C063: Regulating Deicing Runoff from Highway Operations, Sixth International Symposium on Snow Removal and Ice Control Technology, Spokane, Wash., June 7â9, 2004, pp. 307â322 [Online]. Available: http://onlinepubs.trb.org/onlinepubs/ circulars/ec063.pdf. Eldrige, W.H., D.B. Arscott, and J.K. Jackson, Stroud Water Research Center Expert Report on the Proposed Rulemaking by the Pennsylvania Environmental Qualtiy Board [25 PA. CODE CH. 93] for Ambient Water Quality Criterion; Chloride (Ch) [40 Pa.B. 2264], Stroud Report # 2010004 [accessed May 1, 2010]. Environment Canada, Code of Practice for the Environ- mental Management of Road Salts, EPS 1/CC/5, Environment Canada, Gatineau, QC, Canada, Apr. 2004 [Online]. Avail- able: http://www.ec.gc.ca/nopp/roadsalt/cop/pdf/1774_ EngBook_00.pdf. Environment Canada, PSL2 Substances, Environment Can- ada, Gatineau, QC, Canada, [Online]. Available: http://www. ec.gc.ca/lcpe-cepa/default.asp?lang=En&n=C6C230D5- 1&wsdoc=E822E0D8-E349-D4C1-0899-AF7F35ADA0E8 [accessed July 08, 2012]. Environmental Protection Agency (EPA), Storm Water Management Fact Sheet, Minimizing Effects from Highway Deicing, EPA 832-F-99-016, EPA, Washington, D.C., Sep. 1999. Golub, E., R. Dresnack, W. Konon, J. Meegoda, and T. Marhaba, Salt Runoff Collection System, Final Report, FHWA-NJ-2003-026, 2008 [Online]. Available: http:// transportation.njit.edu/nctip/final_report/SaltRunoffCol- lectionSystems.pdf. Hogbin, L.E., Loss of Salt Due to Rainfall on Stockpiles Used for Winter Road Maintenance, RRL Report 30, Road Research Laboratory, Crowthorne, United Kingdom, 1966. Kaushal, S.S., et al., âIncreased Salinization of Fresh Water in the Northeastern United States,â Proceedings of the National Academy of Sciences, Vol. 102, No. 38, 2005, pp. 13517â13520 [Online]. Available: http://www.pnas.org/ content/102/38/13517.full.pdf+html. Levelton Consultants Limited, NCHRP Report 577: Guidelines for the Selection of Snow and Ice Control Mate- rials to Mitigate Environmental Impacts, Transportation Research Board of the National Academies, Washington, D.C., 2007 [Online]. Available: http://onlinepubs.trb.org/ onlinepubs/nchrp/nchrp_rpt_577.pdf. Massachusetts Highway Department, Snow & Ice Con- trol Generic Environmental Impact Report, Boston, May 2006 [Online]. Available: http://www.mhd.state.ma.us/ downloads/projDev/2009/Snow_Ice_GEIR.pdf. MassDOT, âSalt Remediation Program,â Boston [Online]. Available: http://www.mhd.state.ma.us/default. asp?pgid=content/environ/salt_rem&sid=about [accessed June 28, 2012]. Smithson, L.D., Transportation Research Circular E-C063: Implementing Snow and Ice Control Research, Sixth International Symposium on Snow Removal and Ice Control Technology (04-056), Spokane, Wash., June 7â9, 2004, pp. 208â218 [Online]. Available: http://onlinepubs. trb.org/onlinepubs/circulars/ec063.pdf Staples, J.M., L. Gamradt, O. Stein, and X. Shi, Recom- mendations for Winter Traction Materials Management
11 on Roadways Adjacent to Bodies of Water, MT FHWA/ MT-04-008/8117-19, Montana Department of Transporta- tion, Helena, Dec. 2004 [Online]. Available: http://www. mdt.mt.gov/other/research/external/docs/research_proj/ traction/final_report.pdf. Thunqvist, E.-L., âPollution of Groundwater and Surface Water by Roadsâwith Emphasis on the Use of Deicing Salts,â TRITA-AMI-LIC, No. 2054, Kungliga Tekniska Hoegskolan, Inst Foer Mark-Och Vattenteknik, 2000, 96 pp. [Online]. Available: http://trid.trb.org/view.aspx?id=728779. Transportation Research Board, Conference Proceedings 16: Snow Removal and Ice Control Technology, Selected Papers Presented at the Fourth International Symposium, Reno, Nev., Aug. 11â16, 1996, 170 pp. Transportation Research Circular E-C126: Surface Transportation Weather and Snow Removal and Ice Control Technology, Fourth National Conference on Surface Trans- portation Weather and Seventh International Symposium on Snow Removal and Ice Control Technology, Indianapolis, Ind., June 16â19, 2008. Transportation Research Circular E-C162: Winter Main- tenance and Surface Transportation Weather, International Conference on Winter Maintenance and Surface Transpor- tation Weather, Coralville, Iowa, Apr. 30âMay 3, 2012. Venner Consulting and Parsons Brinckerhoff for AAS- HTO, Environmental Stewardship Practices, Procedures, and Policies for Highway Construction and Maintenance, NCHRP Project 25-25, Task 4, Transportation Research Board of the National Academies, Washington, D.C., Sep. 2004, 850 pp. [Online]. Available: http://onlinepubs.trb.org/ onlinepubs/archive/notesdocs/25-25%284%29_fr.pdf. Yu, S.L. and T.E. Langan, Controlling Highway Runoff Pollu- tion in Drinking Water Supply Reservoir Watersheds, Report No. VTRC 00-R7, Virginia Transportation Research Council and FHWA, Charlottesville, Oct. 1999 [Online]. Available: http:// www.virginiadot.org/vtrc/main/online_reports/pdf/00-r7.pdf.
12 CHAPTER THREE PROACTIVE MITIGATION STRATEGIES concurrently: safety, environmental protection, continual improvement, fiscal responsibility, efficient transportation systems, accountability, measurable progress, communica- tion, and a knowledgeable and skilled workforce (TAC 2003a). Key components of an SMP may include the following: â¢ A statement of policy and objectives â¢ Situational analysisâon-road use, salt-vulnerable areas, sand and salt storage sites, snow disposal sites, training, etc. â¢ Documentation â¢ Proposed approaches â¢ Training and management review (TAC 2003a). The TAC recommends applying general and broad guide- lines developed at the federal level to the development of local guidelines, considering the amount of salts used; road- way systems; funding constraints; local weather conditions; and variability in conditions across a country, state, prov- ince, county, or municipality (TAC 2003a). A successful SMP may feature the following: â¢ It is based on policy with guiding principles from a high-level organization. â¢ It is activity based, with each activity assessed at the outset against clearly established standards or objec- tives showing minimized environmental impacts. â¢ Deficiencies in current operations are identified and corrective actions are established and implemented. â¢ Required actions are documented in policies and proce- dures and communicated throughout the organization. â¢ Activities are recorded, monitored, audited, and reported periodically to assess the progress and iden- tify areas for further improvement. â¢ Gaps between actions and desired outcomes are identi- fied and corrective actions are developed and imple- mented, with necessary modifications made to policies and procedures and appropriate training. â¢ The review cycle continues on an ongoing basis (TAC 2003a). The city of Windsor, Ontario, specified responsibilities of each personnel in an SMP as follows: â¢ Executive Director, OperationsâHas corporate respon- sibility for the SMP. This chapter presents information on strategies used to con- trol the source of chloride deicer contamination without jeop- ardizing the LOS on winter roads. These are preventative measures designed to reduce the amount of chloride deicers entering the environment, which can reduce the need for or dependence on reactive strategies discussed in chapter four. Proactive strategies used to mitigate the impacts of chlo- ride road deicers on the natural environment identified from the practitioner surveys and literature review and presented here include salt management plans; staff training; monitor- ing and keeping records; anti-icing, deicing, and pre-wetting practices; weather forecasting and RWIS; equipment technol- ogies; vehicle-mounted spreaders; roadway design; vegetation management; innovative snow fences; and road maintenance yard design and operation. This synthesis does not discuss other proactive strategies that could reduce chloride deicer usage, such as the use of non-chloride roadway deicers and the incorporation of environmental staff in maintenance practices (Staples et al. 2004). Most methods, techniques, and tools pre- sented in this chapter can be used alone, paired in a series, or integrated to form a proactive mitigation effort. Research in progress on this topic includes the updating of âChapter 8, Winter Operations and Salt, Sand and Chemical Managementâ of NCHRP Report 25-25(04) Environmental Stewardship Practices, Procedures and Policies for High- way Construction and Maintenance (2004); and the TAC Salt Management Guide. The Clear Roads Pooled Fund (www. ClearRoads.org) has recently sponsored research to establish effective deicing and anti-icing application rates (i.e., updating FHWA anti-icing guidelines), to understand the chemical and mechanical performance of road salts on specialized pavement types, and to improve snowplow design and the like. SALT MANAGEMENT PLANS Salt management plans (SMPs) provide the maintenance agency with a strategic tool through which its commitment to effective salt management practices can be fulfilled while maintaining its obligation to providing safe, efficient, and cost- effective road management. SMPs apply to all winter mainte- nance staff and personnel (including hired contractors), and protect the people and the environment (TAC 2003a). An SMP is generally agency-based and aims to follow these principles
13 from an amalgamation of earlier guides and the 2010â2011 best practices sheets (Peter Noehammer, personal communicationâ Case Study Interview, Toronto, Mar. 28, 2012). In this synthesis work, the survey respondents were asked (1) if their state or agency has made any effort to mitigate the impacts of chloride deicers, either through reducing chlo- ride deicer usage or by reducing the impacts of chlorides to the natural environment; and (2) if their state or agency has implemented any tools, techniques, practices, or strategies to reduce the impacts of chloride deicers. The following are the responses pertinent to SMPs: â¢ Developed an SMP based on the Environment Canada Code of Practice (city of Toronto, Ontario, and Manitoba Infrastructure & Transportation, Canada). â¢ Produced a statewide SMP that dictates the docu- mentation of salt usage data by (maintenance) shop, snow route, and truck in an effort to identify both champions and excessive salt users; intensified best practices training for shop managers and front-line forces; joined MDSS Pooled Fund Study; performed post-storm reviews; and increased anti-icing and pre- wetting (practices) (Maryland DOT). Additional Resources for Salt Management Plans City of Toronto, âSalt Management Plan Summary,â City of Toronto, Works & Emergency Services, Transportation Ser- vices Division, Sep. 2004 [Online]. Available: http://www. toronto.ca/transportation/snow/pdf/02smp.pdf. Environment Canada, Code of Practice for the Environ- mental Management of Road Salts, EPS 1/CC/5, Environment Canada, Gatineau, QC, Canada, Apr. 2004 [Online]. Avail- able: http://www.ec.gc.ca/nopp/roadsalt/cop/pdf/1774_ EngBook_00.pdf. Ostendorf, D.W., E.S. Hinlein, C. Rotaru, and D.J. DeGroot, âContamination of Groundwater by Outdoor Highway Deicing Agent Storage,â Journal of Hydrology, Vol. 326, 2006, pp. 109â121. Transportation Association of Canada (TAC), Synthesis of Best Practices, Road Salt Management, TAC, Ottawa, ON, Canada, Sep. 2003a [Online]. Available: http://www.tac-atc. ca/english/resourcecentre/readingroom/pdf/roadsalt-1.pdf. Transportation Association of Canada (TAC), Ottawa, ON, Canada, [Online]. Available: http://www.tac-atc.ca/. STAFF TRAINING Winter maintenance staff and personnel training is of partic- ular importance for the effective and efficient use of chloride â¢ Maintenance ManagerâEnsures that the SMP is developed, maintained, and implemented consistently across the organization. Oversees the maintenance and upgrading of the winter maintenance facilities in com- pliance with the SMP. â¢ Fleet ManagerâPurchases, maintains, and calibrates the winter maintenance fleet in compliance with the SMP. â¢ Coordinator/Supervisor/ForemanâEnsures that win- ter maintenance activities are carried out in compli- ance with the SMP. â¢ Winter Maintenance PersonnelâCarries out winter maintenance duties in accordance with the policies and procedures set out in the SMP as directed by their manager. â¢ Technical Support ManagerâAssists in the develop- ment of methods to compile performance measures in compliance with the SMP (City of Windsor 2005). An SMP set out by Renfrew County in Canada consisting of the following eight stages (Pinet 2006): 1. Salt management plan 2. Training 3. Winter roads condition model 4. Route optimization 5. RWIS 6. Pre-wetting 7. Updated salt management plan 8. Revised operational plan. In addition to implementing SMP on existing roads, neg- ative impacts of chloride roadway deicers need to be consid- ered during the new road design and construction stages. For a Highway 175 extension in Quebec, Canada, the develop- mental plan considered existing maintenance operations and developmental means and established objectives to reduce the impacts of road salts during design and construction (Tremblay and Guay 2006). With the basic SMP guidelines, agencies can further improve the SMP to accommodate their budget plans and cli- matic and road conditions. One such improvement by the city of Toronto, Canada, entails innovative salt management practices, such as implementing electronic salt dispensers to control the salt flow, mixing sand into the salt when conditions permit, and pre-wetting the road salt (Welsh 2005). The Road Salt Working Group in Canada and another working group with Environ- ment Canada released a best practices manual in 2004 that pro- vides guidance for municipalities to develop their own SMPs. The TAC is currently updating the salt management guide
14 roadway deicers. The success of winter maintenance opera- tions often hinges on changing the daily practices and per- ceptions about chloride deicer usage and updating the related value system and workplace culture. Such changes often require the personnel at different levels, including managers, supervisors, operators, and hired contractors, to learn new ideas, technology, and skills, and to accept and implement new approaches. Research has suggested that only 20% of the critical skills are obtained through training, whereas the remaining 80% is learned on the job (TAC 2003b). A comprehensive training program is recommended to demonstrate the purpose and value of new procedures, address resistance to change, and ensure competency of personnel carrying out their duties. The training can also focus on using less deicer without compromising public safety or mobility. The TAC (2003b) training components include the following: â¢ A needs assessment of the staff. â¢ Considering who to train and how best to convey the information to an audience and maximize the learn- ing (e.g., verbal/visual aids, group discussion, practical application). â¢ Designing the training program to identify the learn- ing goals, components, and logical progression, and develop a lesson plan. â¢ Determining the training methods (e.g., in class, in field, post-storm debriefing). â¢ Potentially having a current staff member trained to train other staff, so as to add credibility and provide opportunity for follow-up questions and feedback. â¢ Evaluation of the training program (including training material implementation). â¢ Assessing how much transfer of training occurred and the need for refresher courses. The first step of training is to identify the learning goals; for example, LOS guidelines, principles of ice formation, chemistry of road salts, and the environmental impacts of road salts. Annual training close to the onset of the snow and ice season is desirable in order to ensure current learning goals are taught, reinforced, and tested. The level of comprehension of the learning goals and compliance should be monitored throughout the snow and ice season. Refresher sessions are strongly recommended to reinforce the learning goals (TAC 2003b). The power of positive messaging has been proven effective in mitigating the adverse effects associated with adult training. For instance, using statistical data to provide regular feedback to operators, such as posting annual material or cost savings, can reinforce the importance of their efforts. Operators are encouraged to share information, experiment with new concepts, and challenge old ideas (TAC 2003b). The important role of technology in staff training has been validated by agencies. One powerful training tool is computer-based training, developed under the leadership of AASHTO and for the winter maintenance staff in state and local governments. The course consists of several lessons of about 40 units, covering several winter roadway management topics (http://sicop.transportation.org/Documents/CBT_ Flyer_v2b%5B1%5D.pdf). The computer-based training was updated with the latest research and operational techniques by 2010 and was converted to a web-based application in 2012 (Lee Smithson, personal communication, Sep. 14, 2012). Another advanced tool for training is the high-fidelity simu- lator, which has been utilized to enhance the performance of Utah DOT maintenance operators (snowplow drivers). In such a simulator, different scenarios have been developed to address the DOT user needs in managing incidents and to custom- ize the training program. Overall, the simulator training was found to decrease the accidents ratio and reduce cost and fuel usage when the performance of simulator trainees was com- pared against that of a control group (CTC & Associates 2008). In this synthesis work, the survey respondents identi- fied annual operator training and âsnow universitiesâ as an important tool to reduce the impacts of chloride deicers on the natural environment. Many survey respondents agreed that the training helped their state or agency to mitigate or reduce the impacts of chloride deicers. Some of the responses are given below as an example: â¢ We have reduced the amount of salt in traction mate- rial and increased our training to educate the operators (Pennsylvania DOT). â¢ Through ongoing operator training, equipment calibra- tion, and improved delivery systems focusing on place- ment and retention of product. Our goal is to apply only the amount of product necessary to meet our needs (Montana DOT). â¢ Reduction of salt in our sand, increased operators training, and utilization of MDSS (Colorado DOT). â¢ Operators are all given training in Salt Smart principles (Manitoba Infrastructure & Transportation, Canada). â¢ Efforts made in the past 5 years include intensified Best Practices training for shop managers and front-line forces, post-storm reviews, updated SMP and training sessions that reinforce benefits of salt management within the Snowfighters Training Program for operators (New Brunswick Department of Transportation, Canada). â¢ Training sessions were held and more will be held over the coming years so that users can use the devices to their full potential (Ministry of Transport of Quebec, Canada). Additional Resources for Staff Training Smithson, L.D., âAchieving Technology Transfer with Inter- active Computer-Based Training,â presented at SIRWEC 2006 XIII International Road Weather Conference, In the Proceedings SIRWEC 2006, Applied Research Lectures, Turin, Italy, Mar. 25â27, 2006, pp. 164â169.
15 A major component of deicer monitoring is the moni- toring of chloride levels in roadways and in water bodies. Although it is not practical for most road authorities to moni- tor the chloride level in all the stormwater runoff from road- ways, salt-vulnerable areas at least should be monitored. A good example comes from a municipality in Canada that worked with a local conservation authority to add chloride sensors to the stream monitoring network. Water monitoring can be complicated and the following issues may be exam- ined before initiating a monitoring program (TAC 2003d): â¢ At what frequency will samples be collected? â¢ Will sampling be continuous or periodical? â¢ Will the data be communicated back to a central loca- tion automatically? â¢ What power and telephone capabilities for data com- munication will be needed at the sampling location? â¢ Are any confounding data present, such as chlorides entering the environment from other sources (private use or private contractors, water softeners, landfills, etc.)? Data obtained from the deicer monitoring and record keeping can be used to determine whether and how a par- ticular measure (e.g., new winter maintenance technique) or event affects the natural environment (e.g., chloride levels in the aquatic environment). According to the TAC (2003g, p. 11), âspecific staff should be tasked with monitoring what is brought onto each site, what is being discharged from the site, any onsite or downstream contamination and environ- mental impacts.â Many survey respondents recognized the importance of good practices in deicer monitoring and record keeping. Some of the responses are given below as an example: â¢ Monitor more than 100 sites statewide for chloride loading every spring and fall (Washington DOT). â¢ Have a couple of projects starting to track chlorides in the water and mitigation opportunities (Ministry of Transport of Ontario, Canada). â¢ Monitor wells at each maintenance facility and an Environmental Management Plan for chlorides (Alberta, Canada). â¢ In an effort to monitor salt usage rates, installed AVL equipment on a sample of 20 trucks (Kentucky DOT). â¢ Efforts made in the past 5 years include capturing salt usage data by shop, snow route, and truck in an effort to identify both champions and excessive salt users, auditing of salt usage (Maryland DOT). â¢ Maintenance management accounting system to monitor materials usage and application rates (New York DOT). â¢ Monitor our salt storage sites. Our goal is to reduce rain and surface water contact with salt storage piles (Ohio DOT). Transportation Association of Canada (TAC), Synthesis of Best Practices, Training,â TAC, Ottawa, ON, Canada, Sep. 2003b [Online]. Available: http://www.tac-atc.ca/eng- lish/resourcecentre/readingroom/pdf/roadsalt-2.pdf. Transportation Association of Canada (TAC), TAC, Ottawa, ON, Canada [Online]. Available: http://www.tac-atc.ca/. MONITORING AND RECORD KEEPING To facilitate deicer environmental management, environ- mental parameters relevant to chloride deicers must be monitored, with good records kept on deicer applications. Such data will greatly assist the understanding of deicer migration from work sites (or roadways) to the surrounding fields and downstream. Good practices of equipment cali- bration, deicer monitoring, and record keeping will also aid in assessing the extent of deicer impacts and the effective- ness of mitigation measures. The maintenance agency may document the following data on a regular basis: â¢ Salt stored under cover â¢ Storage sites with collection and treatment of wash water and drainage â¢ Inspection and repair records â¢ Stockpiling records â¢ Brine production quality control (e.g., concentrations) â¢ Pavement temperature trends in daily logs, along with pavement conditions, weather conditions, and winter treatment strategy (TAC 2003d). To enable benchmarking, the maintenance agency may also consider obtaining a baseline condition of the work- ing sites and surrounding areas before the deicer applica- tion. This will provide a reference for future monitoring and comparisons. The amount of material used during the year should be monitored. Advanced sensing devices (e.g., weight-in-motion or scale sensors) for truckload tracking can be combined with the routine monitoring to provide more accurate information for operators and managers (TAC 2003g). The maintenance agency may report the fol- lowing activities or conditions: â¢ Total length of road on which salt is applied â¢ Winter severity rating â¢ Total number of events requiring road salt application during the winter season â¢ Materials usage (e.g., total quantity of road salts used) â¢ Description of non-chloride materials used for winter road maintenance â¢ State of calibration equipment â¢ Average chloride concentration and frequency of sam- pling at each sampling location, if available (Highway Deicing Task Force Report 2007).
16 In more recent years, there has been a transition from mostly deicing to anti-icing wherever possible (OâKeefe and Shi 2005). As illustrated in Figure 3, anti-icing is the proac- tive application of chemicals (freezing-point depressants) to prevent the bonding of ice to the pavement (or prevent black ice formation), whereas deicing is the reactive application of chemicals to break the ice-pavement bond. Relative to deic- ing and sanding, anti-icing leads to improved LOS; reduced need for chemicals, abrasives, or plowing; and associated cost savings and safety and mobility benefits (Hossain et al. 1997; Kroeger and Sinhaa 2004; Conger 2005; OâKeefe and Shi 2005). Russ et al. (2007) developed a decision tree for liquid anti-icing for the Ohio DOT, which aimed to help main- tenance supervisors consider a number of factors, including current road and weather conditions, the availability of main- tenance personnel, and the best treatment strategy. Russ et al. (2007, p. 114) concluded that âif there is forecast winter weather likely to affect driving conditionsâ¦ [and] there is no or very little salt residue on the road, pretreatment is recom- mended, except under the following conditions: (a) pretreat- ment would be rendered ineffective by weather conditions or (b) blowing snow may make pretreated roads dangerous.â FIGURE 3 Anti-icing (top) and deicing operations (bottom) (Courtesy: Wisconsin and Kansas DOTs, respectively). Additional Resources for Monitoring and Record Keeping Anderson, B., âMeasuring Winter MaintenanceâWhatâs Behind the Numbers?â prepared for the 2004 Annual Con- ference of the Transportation Association of Canada, Quebec City, Quebec, 2004 [Online]. Available: http://transporta- tionassociation.ca/english/resourcecentre/readingroom/ conference/conf2004/docs/s17/anderson.pdf. Environment Canada, Code of Practice for the Environ- mental Management of Road Salts, EPS 1/CC/5, Environment Canada, Gatineau, QC, Canada, Apr. 2004 [Online]. Available: http://www.ec.gc.ca/nopp/roadsalt/cop/pdf/1774_EngBook_ 00.pdf. Perera, N., B. Gharabaghi, and P. Noehammer, âStream Chloride Monitoring Program of City of Toronto: Implica- tions of Road Salt Applications,â Water Quality Research Journal of Canada, Vol. 44, No. 2, 2009, pp. 132â140. Transportation Association of Canada (TAC), Synthesis of Best Practices, Drainage and Stormwater Management, TAC, Ottawa, ON, Canada, Sep. 2003d [Online]. Available: http://www.tac-atc.ca/english/resourcecentre/readingroom/ pdf/roadsalt-4.pdf. Transportation Association of Canada (TAC), Synthesis of Best Practices, Pavement and Salt Management, TAC, Ottawa, ON, Canada, Sep. 2003e [Online]. Available: http:// www.tac-atc.ca/english/resourcecentre/readingroom/pdf/ roadsalt-5.pdf. ANTI-ICING, DEICING, AND PRE-WETTING PRACTICES A successful highway winter maintenance program requires appropriate selection of chemicals for snow and ice control, the right equipment, well-trained staff, informed decisions, and proper execution of strategies and tactics (e.g., anti-icing, deicing, pre-wetting). Over the past two decades, maintenance agencies in North America have gradually moved from the use of abrasives to the use of more chemicals (Staples et al. 2004). The detrimental environmental impacts of abrasives generally outweigh those of chlorides, and the use of abrasives requires at least seven times more material than salt to achieve a com- parable LOS (Nixon 2001). Abrasives, especially those not pre-wetted, have limited effectiveness on roads with higher vehicle speeds (CTC & Associates 2008). Rochelle (2010) evaluated various deicers in the laboratory and found that âthe presence of chemical, regardless of chemical type, increased the friction of the pavement surface and reduced the shearing temperature as compared to non-chemically treated substrates for all pavement types, all application rates and all storm sce- nariosâ (p. xiii). A combination of salting and snowplowing is considered the best practice for snow and ice control.
17 Furthermore, a recent study (Peterson et al. 2010) spon- sored by Clear Roads synthesized the current practices of during-storm direct liquid applications (DLA) and found DLA to be âa valuable asset for the winter maintenance toolbox.â The identified benefits of DLA include reduced application rates, reduced loss of materials, faster post- storm cleanup, quick effect, further prevention of bonding, expanded toolbox, accurate low application rates, reduced corrosion effects, and leveraging proven benefits of liquids. In a case study, the shift from using rock salt to brine for deicing led to roughly 50% materials savings, as the stan- dard application rate of rock salt and salt brine was 250 pounds and 50 gallons per lane mile, respectively, and 1 ton of rock salt makes about 1,000 gallons of brine (Dave Frame, CalTrans, personal communication, Apr. 5, 2012). Depending on the road weather scenarios, resources avail- able and local rules of practice, agencies use a combination of tools for winter road maintenance and engage in activities ranging from anti-icing, deicing (including direct liquid or slurry applications), and sanding (including pre-wetting), to mechanical removal (e.g., snowplowing) and snow fenc- ing. When the pavement temperature drops below â12.2ÂºC (10ÂºF), salt is no longer cost-effective, and agencies thus uti- lize other chemicals either alone or as pre-wetting agent to enhance the performance of salt (Ohio DOT 2011) or apply abrasives to provide a traction layer on pavement. Pre-wet- ting is defined as the approach of adding liquid chemicals to abrasives or solid salts to make them easier to manage, dis- tribute, and stay on roadways. Pre-wetting has been shown to increase the performance of solid chemicals or abrasives and their longevity on the roadway surface, thereby reduc- ing the amount of materials required (Hossain et al. 1997). Pre-wetting is preferable to the application of dry salt to roadways, which is susceptible to the effects of wind, traf- fic, and bounce before it can actively melt snow and ice. In a case study, the use of brine to pre-wet salt allowed for a 15% reduction in product usage, as the pre-wetted salt exhibited equivalent ice melting performance, better adherence to the road surface, and less loss and scatter (Peter Noehammer, Toronto, personal communication, Mar. 28, 2012). Dahlen and Vaa (2001, p. 34) found that âby using heated materials or adding warm water to the sand it is possible to maintain a friction level above the standard, even after the passage of 2,000 vehicles.â Owing to the diversity in chemical products, pavement surfaces, traffic, and other conditions, there is still a lack of consensus in the appropriate application rate for a spe- cific road weather scenario, which hinders the optimal use of chloride roadway deicers. NCHRP Report 577 provided guidelines for the selection of snow and ice control mate- rials, including anti-icers, deicers, and abrasives (Levelton Consultants 2007). Depending on the pavement tempera- ture, an anti-icer rate of 65 to 400 pounds per lane mile was recommended. For deicers, an application rate of 200 to 700 pounds per lane mile was recommended. For abrasives (pre- wet, dry, or mixed with road salt), an application rate of 500 to 600 pounds per lane mile was recommended. Such guid- ance was based on information provided by Blackburn et al. (2004) and Wisconsin Transportation Information Center (1996). FHWA provides guidance on the application rate of anti-icing materials, including liquid chemicals, solids, and pre-wetted solids, in its Manual of Practice for an Effective Anti-icing Program (Ketcham 1996). This guidance covers four types of storm events: light snow, light snow with peri- ods of moderate or heavy snow, moderate or heavy snow, and frost or black ice. The suggested application rates (e.g., 100 pounds per lane mile) varied as a function of chemical type, pavement temperature and its trend, and other factors. The Salt Institute (2007) provided guidelines for salt appli- cation in The Snowfighters Handbook: A Practical Guide for Snow and Ice Control. Depending on weather, road surface and temperature conditions, recommended application rates ranged between 100 and 400 pounds per lane mile. When salt-treated abrasives were employed, a range of 750 to 1,000 pounds per lane mile was recommended. For anti-icing, the application rate of chemical products may significantly affect the skid resistance on asphalt pave- ment. In some cases, too high an application rate can lead to a reduction in the coefficient of friction of pavement (Leggett and Sdoutz 2001). The following are the survey responses from this synthe- sis work pertinent to operational strategies: â¢ Increasing costs have resulted in new strategies that include (1) improved targeting of known roadway problem areas, (2) conversion to salt brine, and (3) more pre-wetting in sand applications (Alaska DOT). â¢ The Ministry of Transport of Ontario uses the TAC Best Management Practices including reduced salt applica- tion rates with pre-wet or pre-treated salt, direct liquid application (Ministry of Transport of Ontario, Canada). â¢ Currently, pre-wet is being used for all of our snowplow trucks to seek to reduce usage. The pre-wet brines help keep the material on the road especially with wind and traffic trying to carry it off the highway (Alberta, Canada). Additional Resources for Anti-icing, Deicing, and Pre- wetting Practices Burtwell, M., Transportation Research Circular Number E-C063: Deicing Trails on UK Roads: Performance of Prewet- ted Salt Spreading and Dry Salt Spreading, Sixth International Symposium on Snow Removal and Ice Control Technology (04-063), Spokane, Wash., June 7â9, 2004, pp. 564â584. CTC & Associates, LLC, Anti-icing in Winter Mainte- nance Operations: Examination of Research and Survey of State Practice, Transportation Research Synthesis 0902,
18 Minnesota Local Road Research Board, May 2009 [Online]. Available: http://www.lrrb.org/pdf/trs0902.pdf. Federal Highway Administration (FHWA), Manual of Practice for an Effective Anti-icing Program: A Guide for Highway Winter Maintenance Personnel, FHWA- RD_95-202, June 1996 [Online]. Available: http://www. fhwa.dot.gov/reports/mopeap/eapcov.htm. Hunt, C.L., G.F. Mitchell, and W. Richardson, Trans- portation Research Circular E-C063: Field Persistence of Anti-Icing Sodium Chloride Residuals, Sixth International Symposium on Snow Removal and Ice Control Technology (04-049), Spokane, Wash., June 7â9, 2004, pp. 609â624. Luker, C., B. Rokosh, and T. Leggett, Transportation Research Circular E-C063: Laboratory Melting Perfor- mance Comparison: Rock Salt With and Without Prewet- ting, Sixth International Symposium on Snow Removal and Ice Control Technology (04-032), Spokane, Wash., June 7â9, 2004, pp. 585â601. Nixon, W. and A.D. Williams, A Guide for Selecting Anti- icing Chemicals, Version 1.0.IIHR, Technical Report No. 420, 2001[Online]. Available: http://dot.alaska.gov/stwd- des/research/assets/pdf/anti_icing_guide.pdf. Nixon, W.A., G. Kochumman, J. Qiu, L. Qiu, and J. Xiong, Transportation Research Circular E-C063: Role of Performance Specifications in Developing a Quality Con- trol System for Winter Maintenance, Sixth International Symposium on Snow Removal and Ice Control Technology (04-046), Spokane, Wash., June 7â9, 2004, pp. 555â563. OâKeefe, K. and X. Shi, Synthesis of Information on Anti- icing and Pre-wetting for Winter Highway Maintenance Practices in North America, Final Report, prepared for the Pacific Northwest Snowfighters Association in Collabora- tion with the Washington State Department of Transporta- tion, Olympia, Aug. 2005. Smithson, L.D., Transportation Research Circular E-C063: Proactive Snow and Ice Control Toolbox, Sixth International Symposium on Snow Removal and Ice Con- trol Technology (04-061), Spokane, Wash., June 7â9, 2004, pp. 153â157 [Online]. Available: http://onlinepubs.trb.org/ onlinepubs/circulars/ec063.pdf. Strategic Highway Research Program (SHRP), 1999â2000 Technology and Usage Survey Results: Anti-icing Techniques and Road Weather Information System Technology, Anti-icing/ RWIS Lead States Team, Transportation Research Board of the National Academies, Washington, D.C., May 2000. Thompson, G.E., Transportation Research Circular E-C063: Anti-Icing and Material Distribution Performance Measures for Achieving Level of Service Through Mobile Data Collection, Sixth International Symposium on Snow Removal and Ice Control Technology (04-004), Spokane, Wash., June 7â9, 2004, pp. 503â515 [Online]. Available: http://onlinepubs.trb.org/onlinepubs/circulars/ec063.pdf. WEATHER FORECASTING AND ROAD WEATHER INFORMATION SYSTEMS Weather observations and forecasts are important inputs for developing more effective and efficient treatment strat- egies in winter maintenance operations such that the opti- mal amount of chloride roadway deicers are used and their environmental footprint is minimized. Accurate weather forecasts and data help to minimize the need for chlorides while allowing for the same, or better, level of service to be provided. Weather information may be gathered from a variety of sources such as free weather services, private-sec- tor weather forecast services, RWIS, public-sector weather services (or mesonets), and decision support systems, each providing distinctive levels of detail in weather information. Accurate weather information must be obtained and used to meet winter road maintenance challenges (Ohio DOT 2011). Near-real-time weather and road condition information and customized weather service are valuable to the success of proactive maintenance strategies (Shi et al. 2007a; Ye et al. 2009c). When considering the choice between spatially or temporally improved forecasts, Fu et al. (2009) found that improved spatial resolution of forecast data would provide greater expected benefit to service levels. Mesonets are regional networks of weather informa- tion that integrate observational data from multiple sources to provide a more comprehensive and accurate picture of current weather conditions (Shi 2010). Current mesonets include Washington Stateâs rWeather, University of Utahâs MesoWest, Iowaâs WeatherView, and Californiaâs Weather- Share. Working in partnership with federal, state, and local governments as well as with several Canadian provinces, the Clarus Initiative developed a road weather observation network that provides integrated and quality-checked atmo- spheric and pavement observations from mobile and fixed platforms; after running successfully for several years on a research and development platform, the system in now being transitioned to the National Weather Service where it will be integrated into the Meteorological Assimilation Data Ingest System, where its functionality will be stream- lined into an operations environment (Pisano et al. 2005a, b, 2008). These data management systems are expected to maximize availability and utility of road weather observa- tions and facilitate more accurate, route-specific forecasting of road weather conditions. Shi and colleagues (2007b) examined the labor and mate- rials costs in the 2004â05 season for 77 Utah DOT winter
19 maintenance sheds and established a neural network model to treat the shed winter maintenance cost as a function of weather service usage, evaluation of DOT weather service, level-of-maintenance, seasonal vehicle-miles traveled, anti- icing level, and winter severity index. The model estimated the value and additional saving potential of the DOT cus- tomized weather service to be 11%â25% and 4%â10% of the DOT labor and materials costs for winter maintenance, respectively. The risk of using the worst weather service providers was estimated to be 58%â131% of the DOT labor and materials costs for winter maintenance. The Utah DOT Weather Information Program was estimated to feature a benefitâcost ratio of 11:1. Ye et al. (2009b, 2009c) conducted case studies to ana- lyze the benefits and costs associated with the use of weather information for winter highway maintenance. The survey of winter maintenance personnel found that free weather infor- mation sources, private-sector weather providers, and RWIS were the most widely used weather information sources. Air temperature, wind, and the type and amount of precipitation were primary parameters of current and forecast weather conditions, whereas road weather elements (e.g., pavement temperature, bridge temperature, pavement conditions) were also widely used in winter maintenance. The case studies collectively showed that winter maintenance costs decreased as the use of weather information increased or its accuracy improved. Table 1 summarizes the benefits and costs associ- ated with weather information for winter maintenance. The study (Ye et al. 2009c) recommended the use of weather information to be more focused on the road environment, in order to develop better winter maintenance strategies. In addition, the maintenance agencies should continue to invest in road weather information with high accuracy (such as RWIS and customized weather service) and to ensure high usage of the existing road weather information services. RWIS has been well documented through studies such as NCHRP Synthesis 344: Winter Highway Operations and the FHWA Test and Evaluation Project 28: Anti-icing Technology, Field Evaluation Report. The Strategic Highway Research Pro- gram (SHRP)-sponsored research in the early 1990s examined the potential benefits of improved weather information (Boselly et al. 1993a, b). The study analyzed the potential cost-effec- tiveness of adopting improved weather information (including RWIS and tailored forecasting services), which used a simula- tion model based on data from three U.S. cities. It indicated that the use of RWIS technologies can improve the efficiency and effectiveness as well as reduce the costs of highway winter maintenance practices. Ballard et al. (2002) identified a number of benefits available from RWIS in California, including the increased ability to obtain meteorologically accurate data and the potential for data dissemination and exchange with other agencies. Strong and Fay (2007) found that Alaskaâs benefits from RWIS usage included reduced staff overtime, less misdi- rected staff time, fewer wasted materials and equipment, and improved roadway LOS. Figure 4 shows an RWIS installed in the Kansas roadway environment. FIGURE 4 RWIS (Courtesy: Kansas DOT). TABLE 1 CASE STUDIES OF WEATHER INFORMATION OF WINTER HIGHWAY MAINTENANCE Case Study State Winter Season Winter Maintenance Cost ($ 000s) Benefits ($ 000s) Weather Information Costs ($ 000s) Benefitâ Cost Ratio Benefits/ Mainte- nance Costs (%) Iowa 2006â07 14,634 814 448 1.8 5.6 Nevada 2006â07 8,924 576 181 3.2 6.5 Michigan 2006â07 31,530 272 7.4 36.7 0.9 Source: Ye et al. (2009c). Note: The analysis considered agency benefits but excluded benefits to motorists, society, and the environment.
20 The following are the survey responses from this synthe- sis work pertinent to weather forecasting and RWIS: â¢ Currently have 18 RWIS sites with sensors that give the chemical factor and thus help us to avoid the over- application of salt when we do have a winter storm event (South Carolina DOT). â¢ Currently have 49 fixed road weather stations and more than 140 mobile road weather stations are made available to decision makers. Training sessions were held and more will be held over the coming years so that users can use the devices to their full potential (Quebec, Canada). â¢ Have reduced chloride use by storm intensity/duration forecasting (Utah DOT). â¢ Road weather stations were implemented first as tools to help decision makers better plan operations. If the operations are better planned, it is possible to reduce the amount of road salts spread by using other tech- nologies or other materials or simply to spread the right amount at the proper time (Quebec, Canada). Additional Resources on Weather Forecasting and RWIS Ballard, L., Transportation Research Circular E-C063: Analysis of Road Weather Information System Use in Cali- fornia and Montana, Sixth International Symposium on Snow Removal and Ice Control Technology (04-060), Spo- kane, Wash., June 7â9, 2004, pp. 190â207. Conger, S.M., NCHRP Synthesis 344: Winter Highway Operations, Transportation Research Board of the National Academies, Washington, D.C., 2005, 74 pp. [Online]. Avail- able: http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_ syn_344.pdf. Ericksson, D., Transportation Research Circular E-C063: Reducing Salt Consumption by Using Road Weather Infor- mation System and Mesan Data, Sixth International Sym- posium on Snow Removal and Ice Control Technology (04-058), Spokane, Wash., June 7-9, 2004, pp. 278â281. Ketcham, S.A., et al., Test and Evaluation Project 28: Anti-icing Technology, Field Evaluation Report, FHWA Report RD-97-132, Federal Highway Administration, Wash- ington, D.C., Mar. 1998. Mitchell, G.F., W. Richardson, and A. Russ, Evaluation of ODOT Roadway/Weather Sensor Systems for Snow & Ice Removal Operations/RWIS Part IV: Optimization of Pre- treatment or Anti-icing Protocols, Final Report, prepared for Ohio Department of Transportation and FHWA, Nov. 2006. Strategic Highway Research Program (SHRP), 1999â 2000 Technology and Usage Survey Results: Anti-icing Techniques and Road Weather Information System Technol- ogy, Anti-icing/RWIS Lead States Team, Transportation Research Board of the National Academies, Washington, D.C., May 2000. Strong, C. and L. Fay, RWIS Usage Report, Final Report prepared for the Alaska Department of Transportation and Public Facilities Division of Program Development, Juneau, Sep. 2007 [Online]. Available: http://www.westerntrans- portationinstitute.org/documents/reports/4W1526_Final_ Report.pdf. Zwahlen, H.T., A. Russ, and S. Vatan, Evaluation of ODOT Roadway/Weather Sensor Systems for Snow and Ice Removal Operations Part I: RWIS, Russ College of Engi- neering and Technology, Ohio University, Athens, 2003. SNOWPLOWS This section presents information on snow and ice control equipment but with a focus on snowplows, whereas dispens- ing technologies (or road salt/sand equipment) such as vehi- cle-mounted spreaders are discussed in the next section and integrated technologies are discussed in chapter five. Main- tenance agencies have identified and validated advances in equipment and technology that are considered effective practices of winter road maintenance. Advanced equipment technologies can make maintaining winter roadways more efficient, safer, less costly, and environmentally friendly. Additionally, advanced equipment technologies help to min- imize the need for chlorides while allowing for the same, or better, LOS to be provided. The use of advanced winter maintenance equipment and technologies has increased throughout the United States and Canada since the time the SHRP began funding research in new areas of winter maintenance technology (SHRP Project H-207 and SHRP Project H-208) and the International Win- ter Maintenance Technology Scanning Review was com- pleted in 1998. Highway agencies have been under increasing pressure to conduct timely and environmentally responsible snow removal operations, generally without a corresponding increase in staffing or fiscal resources. Consequently, when a new piece of equipment becomes available, highway agen- cies should determine whether it can improve their opera- tions, reduce their material usage, or lower their ongoing expenditures. For instance, Figure 5 shows the Ohio DOT trucks equipped with onboard wetting systems to apply brine or other liquids to dry rock salt as it leaves the vehicle (Ohio DOT 2011). The pre-wetting at approximately 7 to 10 gallons of brine per each ton of salt has been successful. According to the TAC (2003i, p. 2), âwinter mainte- nance equipment, once optimized, can help an organiza- tion meet the 4-Râs of salt management: the Right Material;
21 the Right Amount; the Right Place and the Right Time.â Winter maintenance equipment and technology can be categorized into three groups: equipment for mechani- cal snow/ice control (snowplows, snow removal/disposal equipment); equipment for applying road salts or abrasives (spreaders, electronic spreader control, calibration equip- ment); and operational support equipment (material usage monitor, materials loading/handling equipment, brine sup- ply equipment). The snow removal/disposal equipment is used to remove the piled snow containing salt or other road pollutants in an appropriate manner. The Synthesis of Best Practices in Snow Storage and Disposal (TAC 2003h) pro- vides more information. Mechanical snow/ice control equipment mainly includes: snowplowing vehicles (trucks, motor graders, loaders, and snowplows with cutting edge), and snow removal/disposal equipment (loading, hauling and dumpling equipment and snow blowers). There are various types of snowplows: front- mounted one-way plows that move the snow to the right only, front mounted reversible plows and âvâ shaped plows, wing- plows, underbody plows, and vertical plows, to name a few. Figure 6 shows (a) standard plow truck with front-mount Gull-Wing plow and right-hand mid-body mount wing plow; (b) reversible straight blade snowplow with right- and left- hand wing plows; (c) tandem axle plow truck with front reversible straight blade snowplow and mid-body mount right-hand wing plow; and (d) triple-axle plow truck with 10-cubic-yard spreader and 350-gallon pre-wetting tanks and tow plow in action. The technologies for snowplows are constantly evolv- ing, ranging from low-tech calibrated spreaders, to multi- purpose trailers (Kroeger and Sinhaa 2004), to high-tech vehicle guidance systems. Lannert (2008) discussed the use of wider front plows to clear one 12-ft lane in one pass in Missouri using a 14-ft-wide plow. The cost of this con- version was less than $400 per foot of plow. The benefits obtained from this practice included a reduction in the num- ber of passes needed, saved fuel, and reduced labor. The use of trailer plows was also discussed, which produced the benefits of one snowplow truck and operator clearing more than 24 feet of lane at high speeds while reducing fuel usage through the elimination of multiple plows. The author noted that tow plows also can reduce an agencyâs capital investment needs by 20% to 30% and still achieve the same amount of work. Macfarlane (2001) discussed the use of a plow truck equipped with a reversible plow FIGURE 5 Ohio DOT pre-wetting equipment.
22 When survey respondents were asked if their state or agency has implemented any tool, techniques, practices, or strategies to reduce the impacts of chloride deicers, many respondents stated that they were working on annual or better calibration of equipment (e.g., adding ground speed controllers to salt trucks), or training on how to calibrate the equipment. Additional Resources for Snowplows Transportation Association of Canada (TAC), Synthe- sis of Best Practices, Winter Maintenance Equipment and Technologies, TAC, Ottawa, Ontario, Sep. 2003i [Online]. Available: http://www.tac-atc.ca/english/resourcecentre/ readingroom/pdf/roadsalt-9.pdf. Veneziano, D., L. Fay, Z. Ye, D. Williams, and X. Shi, Development of a Toolkit for Cost-Benefit Analysis of Spe- cific Winter Maintenance Practices, Equipment and Opera- tions, Final Report, prepared for the Wisconsin Department of Transportation and the Clear Roads Program, Madison, Sep. 2010a. and wing. Dedicated left-hand cast plows and wings lack flexibility because they are only used on multilane, wide- median highways. A better solution is the use of a reversible plow and switchable wing mounting. The New Brunswick DOT tried this in 1995 and found several benefits, includ- ing improved plowing efficiency and equipment versatility, reduced run-up collisions, and operators of plows having improved visibility. Recent work has also quantified vis- ibility improvements from deflectors placed over snowplow blades (Thompson and Nakhla 2002). Additionally, previ- ous work investigating the development of moldboards indi- cated that energy consumption could be reduced through the effective use of such attachments (Pell 1994). Vehicle guidance and collision avoidance systems have been used to assist snowplow drivers in low visibility conditions. This technology appears to be most beneficial on high-volume roads that experience frequent road closures from winter weather (Cuelho and Kack 2002). It also is possible to cou- ple plowing and spreading such that there is less need to spread chemicals for snow and ice control, thus reducing the salt footprint. FIGURE 6 Various plow trucks (Courtesy: Utah DOT). (a) (b) (c) (d)
23 VEHICLE-MOUNTED SPREADERS Advances in dispensing technologies (e.g., vehicle- mounted spreaders) may greatly reduce the amount of chloride deicers used for winter maintenance without sac- rificing the LOS. To meet diverse user requirements, man- ufacturers provide different spreader types, which include hopper spreaders (see Figure 7), tailgate spreaders, reverse dumping spreaders, and other new types of spreaders. In the winter road maintenance context, âspreading opera- tions are directed at achieving three specific goalsâ¦: anti- icing, deicing, and traction enhancement...the selection of the appropriate spreading operation is based on economics, environmental constraints, climate, level of service, mate- rial availability, and application equipment availabilityâ (TAC 2003i). FIGURE 7 Snowplows with hopper-type spreaders (right lanes) and âall-liquidâ truck (center lane) (Courtesy: Utah DOT). According to a recently completed Clear Roads study (Blackburn 2008), âautomatic control of material applica- tion rates is achieved with ground-speed-oriented control- lersâ¦ [in this study], actual salt, abrasive, and pre-wetting liquid chemical dispensing rates from spreader trucks with various types of manual and ground-speed-controller units were investigated and documented from both a yard study and in simulated field settings that would be used during winter storm events.â Figure 8 shows a spreader controller, which âreceives data from sensors, records this informa- tion in non-volatile memory, and transmits these data when the vehicle is in range of the base stationâ (Gattuso et al. 2005, p. 4). Currently, the vast majority of road agencies use spreader systems that are adjustable as to amount of material applied per lane mile. Spread rates can be manually reset by in-cab controls. The Minnesota DOT developed a spreader control that used on-vehicle friction sensors to automatically adjust a zero-velocity spreader (Erdogan et al. 2010). The controller that was developed was found to adequately apply granular materials up to speeds of 25 mph. FIGURE 8 A spreader controller. In the third phase of the Highway Maintenance Concept Vehicle (HMCV) project, a decision matrix was developed to automatically control the spreading of chemicals based on the information available (air temperature, pavement tem- perature, road friction, type and application rate of salt or sand) (McCall and Kroeger 2001). This prompted the fourth phase of the HMCV project that investigated the feasibility of integrating geo-location data, on-board sensor devices, and friction measurements with an automatic material spreader system. It was also mentioned that a rule-based algorithm using the FHWA Manual of Practice for Snow and Ice Control guidelines will be coded into an application capable of con- trolling the material distribution (McCall and Kroeger 2001). In addition, hoppers configured to allow the snowplow to carry and spread both liquid and granular materials in dif- ferent amounts are becoming more common, especially in areas sensitive to certain chemicals and materials. As shown in Figure 9, a more advanced version of such systems has been patented, which claims to enable âcoordinated applica- tion of a plurality of materials to a surface simultaneously and in desired proportions and/or widths automatically and/ or selectivelyâ (Doherty 2005). Another patented technology is a surface condition sens- ing and treatment system, which includes an electromag- netic radiation transmitter used to determine one or more characteristics of a road surface such as friction, ice or snow, and freezing point temperature as well as depth, density, and composition of the road surface material. The system also comprises a geographic information system (GIS), material spreader control system, and a temperature sensor. The system features manual or automatic material spreader control by using the information obtained from the sensing devices and weather forecasts. The system may be controlled both remotely and locally, and the data may be transmitted, received, and processed. The researcher indicated that the entire system may also have a vehicle-mounted application (Andrle et al. 2002).
24 FIGURE 9 A system for synchronized application of a plurality of materials (solid or liquid) (McCall and Kroeger 2001). In this synthesis work, when survey respondents were asked if their state or agency has made any effort to mitigate or reduce the impacts of chloride deicers, some of the follow- ing responses were provided: â¢ Thru ongoing operator training, equipment calibra- tion, and improved delivery systems focusing on place- ment and retention of product. Our goal is to apply only the amount of product necessary to meet our needs (Montana DOT). â¢ Increasing the number of closed loop spreader control systems on our fleet with AVL/GPS. Offering a âGreen Incentiveâ for our winter plow vendors to install similar AVL closed loop spreader controls (Massachusetts DOT). Additional Resource for Vehicle-Mounted Spreaders Transportation Association of Canada (TAC), Synthesis of Best Practices, Winter Maintenance Equipment and Tech- nologies, TAC, Ottawa, ON, Sep. 2003i [Online]. Available: http://www.tac-atc.ca/english/resourcecentre/readingroom/ pdf/roadsalt-9.pdf. ROADWAY AND PAVEMENT DESIGN Good roadway design can help reduce the amount of snow and ice accumulated on the pavement, improve the per- formance of snow and ice control chemical, minimize the chemical usage for the same or better LOS, and thus reduce environmental impacts. Elevated road surfaces are com- mon not only for drainage and visibility but for reducing snow drift. Road cuts are notorious for accumulating blow- ing snow. Roadway design and snow fences are important tools to consider especially in open and windy areas (Dan Williams, Montana DOT, personal communication, Sep. 6, 2011). According to the TAC (2003e, p. 8), âa good cross- fall on any pavement willâ¦keep the chemicals on the road longerâ¦Higher slope percentages tend to shed snow and ice control liquids more quickly, such that a 2% crossfall is pre- ferred to a 3% crossfall. Poor road design and poor cross- fall as a result of deterioration of the pavement necessitates broadcast spreading, leading to greater loss of chemicals to the adjacent environment.â TAC (2003c) has discussed basic principles to consider in planning and designing of roadway and bridge facilities for minimizing snow and ice buildup. A desirable alternative to chemical usage for snow and ice control is pavement layers designed to reduce the bond of ice to pavement or to prevent or treat winter precipitation. These range from antifreezing pavements that rely on physical action, to high-friction in situ anti-icing polymer overlays, to asphalt pavements containing anti-icing additives, to heated pavements. Pavement treatments may be used alone or in combination with other strategies for winter highway main- tenance operations. In light of cost considerations, they are most suitable for critical highway locations such as bridge decks, mountain passes, sections prone to frost and/or sensi- tive to chemicals, and locations featuring drastic changes in road conditions. Relative to the fixed anti-icing spray tech- nology discussed in chapter five, pavement treatments may exhibit higher reliability and incur less capital and mainte- nance costs. Takeichi et al. (2001) evaluated three types of pavement that provide antifreezing effect through rough sur- face texture and another eight types through pavement bend- ing. The study found that âthe pavement in which grooves were cut and filled with urethane resinâ¦and the pavement with cylindrical or doughnut-shaped rubber embedded at regular intervals in the surfaceâ¦had particularly high anti- freezing effectivenessâ (p. 114). These two types of pave- ment were installed at intersections and exhibited positive performance for pedestrians and automobiles. Textured seal coats for pavements or bridge decks have the potential to prevent dangerous icy or slippery conditions (Adams et al. 1992; Alger 2007; Nixon 2006, 2007). An example of an additive to hot-mix asphalt pavements that is intended to provide anti-icing benefits throughout the life of the pave- ment is composed of anti-icing chemicals (mostly CaCl2) encapsulated in linseed oil, which is then incorporated in the top course. Several reports are available on the field perfor- mance of this product on pavements and, in general, the per- formance is still inconclusive (Burnett 1985; Maupin 1986; Kiljan 1989; Turgeon 1989). Other anti-icing additives exist that need to be considered (Lu et al. 2009), all of which aim to reduce the usage of deicers and improve the efficiency of mechanical removal. The heating and cooling rates of pavement vary depend- ing on the pavement type, the time of year, and air and ground temperatures. Concrete pavements, because of the light color and higher thermal mass, generally heat up and cool down more slowly than do asphalt pavements. However, concrete pavement surfaces tend to be less permeable than
25 aged asphalt ones, and âtend to shed brine more quicklyâ¦ and may require more frequent application of snow and ice control chemicals or a great quantity based on the pavement temperature trendsâ (TAC 2003e). Open friction course (OFC) asphalt pavements can be used to reduce noise, improve drainage, and reduce spray, âwhich can be benefi- cial in areas that are vulnerable to salt sprayâ (TAC 2003e). The TAC (2003d) advises to plan and design proper the road drainage system so as to isolate salt-laden drainage from vulnerable areas, and prevent sudden chloride pulses during spring runoff on the aquatic habitat. Site character- istics must be assessed to minimize the potential impact on âpotable water taken from groundwater sources, sensitive aquatic habitats, agricultural lands, wetlands and wildlifeâ (TAC 2003d, p. 2) and mitigation measures must be imple- mented as deemed necessary. These may include sheet flow, V-ditch, storm sewer, flat bottom (trapezoidal) ditch, flat bottom (trapezoidal) ditch with storage, dry basin (pond), wet basin (pond), and buffer strip and containment berm, used individually or synergistically. Pervious concrete has been increasingly used as a powerful tool to mitigate watershed impacts owing to stormwater runoff. It can also help mitigate the urban heat island. Pervious concrete pavements have an open network of pores to allow infiltration through the pavement with a subsequent reduction in the quantity of stormwater runoff and an improvement in water quality (McCain et al. 2010; Brown 2012). A demonstration project in Yakima, Wash- ington (Yakima County 2012) has shown that compared with those from impervious (traditional) asphalt pave- ment, water samples collected from vaults in pervious concrete pavement had significantly lower biochemical oxygen demand, total suspended solids, copper, lead, zinc, #2 Diesel, and motor oil, respectively. A typical pervious concrete mix design used in the United States consists of cement, single-sized coarse aggregate (between 1â³ and the No. 4 sieve), and a water/cement ratio between 0.27 and 0.43. The various mixes can feature a wide range of properties; for example, effective air voids of 14% to 31%, permeability of 35â800 in./h, and compressive strength of 800â3,000 psi (Schaefer et al. 2006). Clogging can reduce the effectiveness of pervious concrete and special main- tenance techniques are generally needed to restore per- formance, such as sweeping and/or vacuuming (McCain et al. 2010). According to the EPA (2012), traction sand should not be applied to pervious concrete pavements, and while pervious concrete does not treat chloride or other deicers, reduced application rates are needed. Several pervious concrete sections were constructed at MnROAD (a Minnesota DOT pavement research facility) between 2006 and 2008 and have not been impacted by any sand- ing, salting, or plowing operations (Eller and Izevbekhai 2007; Bernard Izevbekhai, MnDOT, personal communi- cation, Mar. 10, 2012). Additional Resources for Roadway and Pavement Design Transportation Association of Canada (TAC), Synthesis of Best Practices, Road and Bridge Design, TAC, Ottawa, ON, Sep.2003c [Online]. Available: http://www.tac-atc.ca/ english/resourcecentre/readingroom/pdf/roadsalt-3.pdf. Transportation Association of Canada (TAC), Synthesis of Best Practices, Pavement and Salt Management, TAC, Ottawa, ON, Sep. 2003e [Online]. Available: http://www. tac-atc.ca /english /resourcecentre /readingroom/pdf/ roadsalt-5.pdf. VEGETATION MANAGEMENT A healthy and mature vegetation zone along the roadway can play an essential role in preserving the soil base adjacent to the pavement and thus slow down the pavement dam- age. The vegetation near the roadway can inhibit or prevent the soil erosion and loss by wind and rain (Johnson 2000a). However, roadside vegetation, especially salt-vulnerable species, is also subject to the potential negative impacts of the snow and ice control chemicals and abrasives (Fay and Shi 2012). These impacts are most severe within 50 ft of the pavement, and can extend to hundreds of feet away from the roadway depending on the traffic volume and traffic speed, wind direction, and water precipitation near a particular road (Johnson 2000b). Effective salt management will significantly benefit the vegetation management. Road salts enter the environment mainly through either salt spray or salt-laden runoff. Salt usage monitoring, record keeping, operator training, and wrapping of salt-vulnerable species before the winter are among the most effective methods. Several precautionary measures were proposed in the TAC report (2003f) to miti- gate the negative impacts associated with roadway deicers. For example, four approaches were identified to minimize the negative impact when deicers were deployed in the form of the salt spray: optimizing the salt usage, select- ing the right plant species, applying deicers at the right locations, and ensuring long-term survival of the vegeta- tion. Four approaches were suggested for mitigating the salt-laden runoff: selecting plant species that are able to tolerate salt-laden runoff, avoiding heavy runoff collection areas, ensuring that the salt-laden roadway runoff is not directed to the plants, and adapting appropriate drainage designs. (More details for drainage design practices can be found in TAC 2003c.) For effective management of roadside vegetation for local agencies, Johnson (2000a) highlighted seven effective prac- tices identified through research, surveys, and discussion with industry experts.
26 1. Developing an integrated roadside vegetation man- agement plan 2. Developing a public relations plan 3. Developing a mowing policy and improved procedures 4. Establishing sustainable vegetation 5. Controlling noxious weeds 6. Managing living snow fences 7. Adapting integrated construction and maintenance practices. The proactive approaches include selecting the right vege- tation for specific environmental and road conditions, select- ing the right salt-tolerant grasses and sods/ native grasses and wildflowers, establishing effective turf establishment practices and protecting existing vegetation, optimizing deicer usage, and using eco-friendly vegetation products (Johnson 2000b). A study by the University of Minnesota (Johnson 2000a) has identified a list of critical factors in determining the degree of roadside vegetation damage: temperature, light, humidity, wind, soil water, soil texture and drainage, and precipitation. Other critical factors include the type and con- dition of the roadside vegetation. Strategies to reduce salt damage should consider such factors; the cost of establish- ing the soil foundation and the covering turf, and the cost of maintenance and reparation, tend to define the cost-effec- tiveness of roadside vegetation management. Another study (Dudley 2011) was focused on the impact of a MgCl2-based deicer, a NaCl-based deicer, and the major salts contained in these deicers on seed germination and seedling growth and the development of 15 species of grasses and forbs native to Colorado. The results suggested that the salt concentration exerted a great impact on the pro- portions of normal and abnormal seeds and seedlings. Using species with the highest germination rate would provide the best opportunity for establishing plants along highways treated with deicing products. Planting should be done in the fall, and soil should be amended. Reactive approaches to vegetation management that are usually practiced during or after deicer deployment include irrigation to flush salt from soil, soil treatments, vacuuming and sweeping, rejuvenation of damaged areas, and design and construction strategies. One reactive approach entails treating the soil with gypsum to reverse the effects of salt accumulation. Planting salt-resistant or alkali grass can alle- viate the effects of chloride roadway deicer on adjacent soil and vegetation (Johnson 2000b). Additional Resources for Vegetation Management Baltrenas, P., A. Kazlauskiene, and J. Zaveckyte. âExperi- mental Investigation into Toxic Impacts of Road Mainte- nance Salt on Grass Vegetation,â Journal of Environmental Engineering and Landscape, Vol. 14, No. 2, 2006. Berger, R.L., NCHRP Synthesis 341: Integrated Roadside Vegetation Management, Transportation Research Board of the National Academies, Washington, D.C., 2005 [Online]. Available: http://onlinepubs.trb.org/onlinepubs/nchrp/ nchrp_syn_341.pdf. Brinckerhoff, P., Compendium of Best Management Practices for Environmental Compliance and Steward- ship at Highway Transportation Maintenance Facilities, prepared by EA Engineering, Science and Technology Inc. and Applied Research Associates, Inc. for AASHTO Stand- ing Committee on the Environment, Washington, D.C., Nov. 2009. [Online]. Available: http://onlinepubs.trb.org/ onlinepubs/nchrp/docs/nchrp25-25%2846%29_FR.pdf. Eck, R.W. and H.W. McGee, Vegetation Control for Safety, A Guide for Local Highway and Street Maintenance Personnel, FHWA-SA-07-018, Federal Highway Adminis- tration, Washington, D.C., 2007. Johnson, A.M., Best Practices Handbook on Roadside Vegetation Management, Mn/DOT 2000-19, Minnesota Department of Transportation, St. Paul, Sep. 2000 [Online]. Available: http://www.lrrb.org/pdf/200019.pdf. Ministry of Transportation and Infrastructure, Brit- ish Columbia, Environmental Best Practices for Highway Maintenance Activities, Oct. 2010 [Online]. Available: http://www.th.gov.bc.ca/publications/eng_publications/ environment/references/Best_Practices/Envir_Best_Prac- tices_Manual_Complete.pdf. Transportation Association of Canada (TAC), Syn- thesis of Best Practices, Vegetation Management, Sep. 2003f [Online]. Available: http://www.tac-atc.ca/english/ resourcecentre/readingroom/pdf/roadsalt-6.pdf. [end] INNOVATIVE SNOW FENCES A properly designed and placed snow fence can be a cost- effective tool for snow and ice control for highway segments where the abundance of wind leads to blowing and drift- ing snow on the winter roadways. For such locations, there is a considerable risk of closing the roadways or requiring excessive plowing and chemical usage. The use of primary drift control technique (snow fence) to minimize the amount of snow blowing onto the roadway will provide a number of benefits to the public and landowners. Some of the ben-
27 efits include reducing blowing/drifting snow on roadways, storing snow at low cost, creating safer travel condition, and reducing the need for snow and ice control chemicals (TAC 2003f). According to Tabler (2005), âtotal cost for snow fence [is around] $1.39 per square feet of fence frontal area.â Data from a Wyoming study shows that âstoring snow with snow fences costs three cents a ton over the 25-year life of the fence, [relative] to three dollars a ton for moving itâ (Tabler 1991). In the 1970s, the Wyoming DOT reduced snow and ice removal costs by more than one-third on a 45-mile stretch of I-80 where fences were installed. The fences had been effective in preventing drift formation over the 20 years since installation (Tabler 1991). In 1991, the SHRP developed a Snow Fence Guide to cover essential information for maintenance personnel to design and locate snow fences correctly. This guide provides some helpful tips for snow fence technology. For instance, âa single row of taller fence is always preferable to multiple rows of shorter fence. The taller fence not only traps more snow, but also much more effectively improves driver visibility, costs less, and requires less land. A rule of thumb is that fences are to be at least 8 ft. (2.4 m) tallâ (Tabler 1991, p. 41). For temporary fencing, âfield installation of prefabricated panels requires approximately three person-hours per 100 ft. (30 m) of fence. It takes less time to install the 8-ft. (2.4-m) fence than to build a series of conventional 4-ft. (1.2-m) fences of the same storage capacity. Material and fabrication costs are comparable to costs for permanent fences.â At the state level, the Wyoming DOT has conducted extensive research on snow fence technology for more than 40 years and specifications have been published (Wyoming DOT 2003). Snow fence technology is being widely used by the state DOTs to effectively trap and control blowing and drifting snow at critical locations. Snow fencing has been proven to be a low-cost mitigation method to prevent blowing snow related accidents. It also helps by reducing maintenance costs and wear-and-tear on the winter maintenance equip- ment (Wyoming DOT 2009). The Iowa DOT maintains approximately 120 miles of snow fence on Iowa highways (Iowa DOT 2012a). The types of snow fences used by Iowa DOT include temporary fences (4 ft tall and made of wood or plastic), permanent fences (6 ft tall and made of wood or plastic), living snow fences (made of trees, bushes or native grasses), or standing corn snow fences (8â12 rows of corn left standing after harvest). A comparison of all available snow fence types was also given in Table 2 along with their benefits (Iowa DOT 2012b). Engineered mitigation of blowing and drifting snow through road design and snow fences has been integrated into a software tool, which can reduce maintenance costs and closure times and enhance overall LOS by âimproving visibility, preventing drifting on the road, and reducing road icingâ (Chen et al. 2009). TABLE 2 TYPE OF SNOW CONTROL Type Description Advantages Agreement Length Structure, Permanent Six- to eight-foot- tall fence consisting of two wooden posts, lightweight plastic fence, and 2â x 4â supports Very low mainte- nance Takes up as little as 1-foot width of land 10-year minimum Structural, Temporary Four-foot tall porta- ble plastic fence or wooden fence Installed after har- vest and removed before planting Fall to Spring Standing Corn One section of eight to 16 rows of corn Can reduce soil erosion Serve as wildlife habitat Public service orga- nizations benefit from picking by hand Fall to Spring Living Trees, Shrubs, or Native Grasses Two or more rows of trees or shrubs, or a combination of both Wildlife habitat Reduces soil ero- sion Hunting ground 10-year minimum CRP Living Snow Fence Two or more rows of trees or shrubs, or a combination of both with 75- to 100-foot native grass buffer Wildlife habitat Reduces soil ero- sion Hunting ground 10â15 years per CRP program guidelines Source: Iowa DOT (2012b). An alternative to traditional snow fences can be âliving snow fences,â which are trees, shrubs, and/or native grasses planted at critical locations along public travel roads or around communities and farmsteads. They are economi- cally feasible and offer an environmentally sound solution for snow management. With living snow fences established, less salt and fewer plow and truck trips are used to keep road- ways clear. Such fences can also provide wildlife habitat, control soil erosion, and help improve water quality (Min- nesota DOT 2012). A diagram of the living snow fence is provided as Figure 10 to illustrate the structure of a typical living snow fence used by the Iowa DOT Conservation Research Program (Iowa DOT 2012c). Height, density, length, and plant protec- tion are listed as the key design elements to establish a cost- effective living snow fence. Doubling the height is believed to increase snow storage by four times and should be consid- ered as an important economic factor in species selection. Vegetation with about 50% density will capture and store the greatest amount of snow. Conifers are preferred to plants in light of their appropriate height and year-around foliage and they can be used in combination with many deciduous trees and shrubs (USDA Forest Service 1999). The Minnesota DOT has produced a manual for design, installation, and maintenance of living snow fences, Catching the Snow with
28 Living Snow Fences (Gullickson et al. 1999). Minnesota also purchases crops such as standing corn to act as temporary living snow fences. The costs and benefits of living snow fences have been compared with traditional structural snow fences. The U.S. Department of Agriculture (USDA) Forest Service (1999) listed the major advantages of living snow fence over the traditional ones as follows. Service life can be 50 to 75 years for living snow fences versus 5 to 7 years for a slat snow fence (made of wood, metal, or plastic). Slat snow fence installation and maintenance costs are 4 times greater than those for a living snow fence over a 50-year span. For living snow fences, the average cost is $3 per mile per year for each unit of snow trapped, vs. $185 per mile per year for a 4-ft slat fence. Living snow fences provide habitat for wildlife and can be designated to conserve energy for farmsteads, feedlots, and community facilities; however, they have some limitations. It takes 5 to 7 years for living snow fences to provide effective snow control and 20 years to fully mature, and new plantings should be protected from grazing. Living snow fences require more space than slat, and plant estab- lishment is subject to site conditions (USDA Forest Service 1999). Tabler (1991) discussed one more disadvantage of liv- ing snow fences: their height and porosity and the resultant drift length and storage capacity could change with time. In a 2012 report (Wyatt et al. 2012), researchers developed a tool to help transportation managers determine the feasibil- ity of installing a living snow fence at snow problem areas in Minnesota. The tool factors in the cost of snow and ice con- trol, the safety benefits from reduced crashes and improved mobility, and the farmer or landowner cost of installing and maintaining a snow fence on private property. A dollar fig- ure for each cost and benefit item is generated to aid in deter- mining the most cost-effective sites for future installation. Additional Resources for Innovative Snow Fences Iowa Department of Transportation (IDOT), âLiving Snow Fence. Conservation Research Program,â State Farm Ser- vice Agency, IDOT, Ames, 2012c [Online]. Available: http:// www.iowadot.gov/maintenance/pdf/crplivingsnowfence.pdf. Johnson, A.M., Best Practices Handbook on Roadside Vegetation Management, Minnesota Department of Trans- portation, 2000-19. Sep. 2000 [Online]. Available: http:// www.lrrb.org/pdf/200019.pdf. Matsuzawa, M., Y. Ito, and Y. Kajiya, Transportation Research Circular E-C063: Development of Advanced Snowbreak Fences, Sixth International Symposium on Snow Removal and Ice Control Technology (04-020), Spokane, Wash., June 7â9, 2004, pp. 636â644 [Online].Available: http://onlinepubs.trb.org/onlinepubs/circulars/ec063.pdf. Natrona County Conservation District, Wyoming Web- site, âWhat Are Living Snow Fences?â [Online].Avail- able: http://www.natronacountyconservationdistrict.com/ images/Living_Snow_Fences.pdf [accessed July 8, 2012]. Nixon, W.A., M. Davidson, and G. Kochumman, âLiving Snow Fences,â 2006 [Online]. Available: http://trid.trb.org/ view.aspx?id=804894. Powell, K., et al., The Use of Trees and Shrubs for Con- trol of Blowing Snow in Select Locations Along Wyoming Highways, Wyoming Highway Department, 1991 [Online]. Available: http://www.ops.fhwa.dot.gov/weather/best_ practices/1024x768/transform_param2.asp?xslname=pub. xsl&xmlname=publications.xml&keyname=848. Staples, J.M., L. Gamradt, O. Stein, and X. Shi, Recom- mendations for Winter Traction Materials Management on Roadways Adjacent to Bodies of Water, FHWA/MT-04- 008/8117-19, Montana Department of Transportation. Hel- ena, Dec. 2004 [Online]. Available: http://www.mdt.mt.gov/ other/research/external/docs/research_proj/traction/final_ report.pdf. Tabler, R.D., Design Guidelines for the Control of Blow- ing and Drifting Snow, Strategic Highway Research Pro- gram, Report SHRP-H-381, Transportation Research Board of the National Academies, Washington, D.C., Feb. 1994 [Online]. Available: http://onlinepubs.trb.org/onlinepubs/ shrp/SHRP-H-381.pdf. Tabler, R.D., Controlling Blowing and Drifting Snow with Snow Fences and Road Design, Final Report, Trans- portation Research Board of the National Academies, Wash- ington, D.C., Aug. 2003 [Online]. Available: http://www. transportation.org/sites/sicop/docs/Tabler.pdf. Tabler, R.D., Transportation Research Circular E-C063: Effect of Blowing Snow and Snow Fence on Pavement Tem- perature and Ice Formation, Sixth International Symposium on Snow Removal and Ice Control Technology (04-030), Spokane, Wash., June 7â9, 2004, pp. 401â403 [Online]. Available: http://onlinepubs.trb.org/onlinepubs/circulars/ ec063.pdf. Transportation Association of Canada (TAC), Synthesis of Best Practices, Vegetation Management, TAC, Ottawa, ON, Sep. 2003f [Online]. Available: http://www.tac-atc.ca/ english/resourcecentre/readingroom/pdf/roadsalt-6.pdf. FIGURE 10 Diagram of a living snow fence used by the Iowa DOT Conservation Reserve Program (CRP) (Iowa DOT 2012c).
29 tank (TAC 2003g). For brine production facilities, particular caution must be paid to the water supply line, which needs to be insulated to prevent them from freezing damage. Periodic inspection of tanks, pumps, and pipes/hoses needs to be car- ried out and any leaks repaired immediately (TAC 2003g). Maintenance yard sites should be chosen such that the drainage can be directed away from the storage areas, any down-gradient groundwater well location, and salt-vulnerable areas. The snow plowed from the site needs to be dealt with similarly to avoid the contamination by the melt water. The salt-laden water should be properly managed, either recycled for brine production or disposed at a sewage treatment facility where permitted (TAC 2003g). The reduction of site drainage can benefit from special regulations designated for the man- agement of road maintenance yards. The recent revision of standards in Alberta, Canada, on the management of highway maintenance yards features two relevant provisions: (1) provi- sion of covered storage for salt and freezeproofed sand and (2) provision of the management of runoff water in contact with chlorides. When designing and developing the yards, consider using an Environmental Management Plan. The yards are subjected to annual monitoring to ensure that the salt is being managed in ways that decrease the environmen- tal impacts from the yard (Hood 2006). The guidance for the design and operations of road main- tenance yards as discussed in this section has been adapted by some road authorities. In this synthesis work, the respon- dents provided the following feedback: â¢ New patrol yards and upgrades are designed and built with enhanced environmental protection (City of Ontario, Canada). â¢ Improved storage of deicers, improved housekeep- ing at sites. Including controlling runoff from storage sites using paved aprons; loading indoors where pos- sible (Nova Scotia Department of Transportation and Infrastructure Renewal, Canada). â¢ Storage facilities are designed to divert surface and rain water from entering our salt storage and cleaning up any spilled salt in our facilities (Ohio DOT). â¢ All of the salt and other chlorides are stored in shel- ters or tanks and not exposed to the weather (Alberta, Canada). â¢ Our salt pollution controls are in the storage of salt. We try to cover all stored salt and prevent runoff (Kansas DOT). Additional Resources for Design and Operations of Road Maintenance Yards Brinckerhoff, P., Compendium of Best Management Prac- tices for Environmental Compliance and Stewardship at Highway Transportation Maintenance Facilities, prepared by EA Engineering, Science and Technology Inc. and Transportation Association of Canada (TAC), Ottawa, ON [Online]. Available: http://www.tac-atc.ca/. Wyoming Department of Transportation, âWYDOTâs Winter Research Services,â 2009 [Online].Available: http://www.dot.state.wy.us/wydot/engineering_technical_ programs/field_operations/state_maintenance_office/ winter_research_services. DESIGN AND OPERATIONS OF ROAD MAINTENANCE YARDS Salt spillage or seepage in the maintenance yard has been a main pathway for chloride deicers entering the groundwater. According to the TAC (2003g), âgood (maintenance) yard design and salt handling practices are essential to prevent- ing unnecessary salt loss and the resultant environmental impacts.â These include planning, site selection, designing a functional facility, salt storage, site drainage, site operation and maintenance, monitoring, record keeping, and training. Practical considerations include noting the prevailing winter wind direction, positioning building and doors with regard to sheltering loading operations, minimizing snow drifting around doorways, keeping precipitation out of the storage areas, using low permeable surfaces, and avoiding spillage during stockpiling and truck loading (TAC 2003g). Solid snow and ice control product stockpiles must not be exposed to the rain or snow, and proper storage may entail the use of temporary or permanent sheds, domes, barns, or silos with the roof and exterior made of waterproof mate- rial. Solid stockpiles can be stored outside on a low perme- able asphalt or concrete pad and covered with a tarp, but this is not recommended and is a short-term, temporary option. Both asphalt and concrete are somewhat permeable and need to be sealed to minimize infiltration, and floors should be inspected periodically for cracks and repaired or resealed as necessary. Containment under and around the sides of the solid stockpiles (e.g., plastic liner) is an effective way to miti- gate the long term-loss of solid deicer salts. Where practical, trucks are to be loaded inside storage structures and all spills cleaned up daily (TAC 2003g). Liquid deicer management involves both storage of liquid products and management of the brine production facility. Many local environmental regulators have specified regula- tions regarding placement and containment of liquid snow and ice control products, which should be carefully followed. Regardless the ownership of liquid product storage contain- ers by the snow/ice control agency or product suppliers, ade- quate protection needs to be provided to prevent damages from vehicle impacts and deicer spillage. A secondary con- tainment should be considered, either with double-walled tanks or containment dykes, with containment capacity approximately 110% to 125% of the capacity of the largest
30 Applied Research Associates, Inc. for AASHTO Standing Committee on the Environment, Nov. 2009 [Online]. Avail- able: http://onlinepubs.trb.org/onlinepubs/nchrp/docs/ nchrp25-25%2846%29_FR.pdf. Fitch, G.M., S. Bartelt-Hunt, and J.A. Smith, âChar- acterization and Environmental Management of Storm Water Runoff from Road Salt Storage Facilities,â Trans- portation Research Record: Journal of the Transportation Research Board No. 1911, Transportation Research Board of the National Academies, Washington, D.C., 2005, pp. 125â132. Hood, T., âSalt Management in Alberta Highway Main- tenance Yards,â Annual Conference & Exhibition of the Transportation Association of Canada, Transportation Association of Canada, Ottawa, ON, 2006. Meegoda, J.N., T.F. Marhaba, and P. Ratnaweera, âStrat- egies to Mitigate Salt Run off from Salt Storage and Salt Truck Maintenance Facilities,â Practice Periodical of Haz- ardous, Toxic, and Radioactive Waste Management, Vol. 8, 2004, pp. 247â252. Michigan Department of Environmental Quality, Salt and Brine Storage Guidance for Road Agency Maintenance and Other Facilities, revised Aug. 2007, Lansing [Online]. Available: http://www.michigan.gov/documents/deq/deq- ess-p2tas-bulksaltbrineguidance_267024_7.pdf. Ostendorf, D.W., E.S. Hinlein, and S.K. Choi, âReduced Road Salt Spillage Due to Indoor Delivery and Loading,â Journal of Environmental Engineering, Vol. 138, No. 2, pp. 23â228, 2012. Transportation Association of Canada (TAC), Synthesis of Best Practices, Design and Operation of Road Main- tenance Yards, TAC, Ottawa, ON, Sep. 2003g [Online]. Available: http://www.tac-atc.ca/english/resourcecentre/ readingroom/pdf/roadsalt-7.pdf.
31 CHAPTER FOUR REACTIVE MITIGATION STRATEGIES for a given site (Oberts 2003). Early in the spring thaw, when flow rates are lower, dissolved pollutants may be transported by lower volumes and lower velocities. At this stage, receiv- ing waters may be more vulnerable to the impacts of these soluble pollutants. Later, suspended pollutants such as sand and chlorides may be carried by runoff with higher veloci- ties and higher volumes that may reduce the efficiency of the reactive mitigation strategy. For deicer environmental management, the reactive strate- gies reviewed in this synthesis may vary depending on the specific climate, site, and traffic conditions. The reactive strat- egies may be used individually or synergistically and consider the potential for contaminated water to recharge into aquifers. Field monitoring of deicer use has allowed for lessons to be learned and for the implementation of site-specific reactive mitigation strategies to be employed. According to Golub et al. (2008), âto select the appropriate structure to install, collaboration of engineering design, installation, field moni- toring, analysis of monitored data and assessment of perfor- mance and effectiveness are important.â Continued research is needed in understanding the fate and transport of pollutants related to snow and ice control activities and in evaluating and improving the efficiency of reactive mitigation strategies used for stormwater management, particularly those in cold regions (Denich and Bradford 2009). Section 5.3 of the High- way Runoff Manual provides guidance on how to select the appropriate reactive strategy for your site (WSDOT 2011). Note that vegetation along roadsides can play a crucial role in the treatment of runoff through chemical and bio- logical processes. Eppard et al. (1992) suggested revegeta- tion with salt-tolerant species. Biotechnical methods suggest using a 70:30 mix of perennial rye-grass, because it shows high resistance to the toxic effects of salt, and fescue-grass when building new roads or reconstructing existing road (Baltrenas and Kazlauskiene 2009). Additional Resources for General Considerations Arika, C., D.J. Canelon, and J.L. Neiber, Impact of Alter- native Storm Water Management Approaches on Highway Infrastrcture: Guide for Selection of Best Management PracticesâVolume 1, Final Report prepared for Minnesota Department of Transportation, St. Paul, Feb. 2006 [Online]. Available: http://www.lrrb.org/pdf/200549A.pdf. This chapter presents information on strategies used to reduce the impacts of chloride deicers once they are in the environment. These are typically defined as structural effec- tive practices; that is, reactive measures implemented along the roadside to physically trap salt-laden stormwater runoff and to allow pollutants to settle out, evaporate, infiltrate, or be absorbed. They are designed to treat both the velocity and the quality of highway stormwater runoff. The basic mecha- nisms for pollutant removal are gravity settling, infiltration of soluble nutrients through soil or filters, or biological and chemical processes (TurnerâFairbank Highway Research Center 1999). Reactive strategies used to mitigate the impacts of chlo- ride road deicers on the natural environment identified from the practitioner surveys and literature review and presented here include infiltration trenches and basins, detection/ retention/evaporation ponds, wetland and shallow marshes, vegetated swales, and filter strips. Other reactive strategies that could mitigate environmental impacts of chloride road- way deicers, but are not discussed in this synthesis, include strategic use of salt-tolerant plants to buffer roadways and controlled release of highway runoff to mitigate spikes in deicer concentrations. The vast majority of the reactive strat- egies identified by survey respondents were not originally installed for this purpose; as such, their cost-effectiveness for deicer environmental management is yet to be examined and validated. Golub et al. (2008) discussed other effective practices that can remove salt from collected runoff, including ther- mal distillation processes, multistage flash distillation, multiple effect distillation, vapor compression distillation, reverse osmosis, and electro dialysis. However, these will not be covered in this synthesis, as they were not identified as current practices used by the agencies surveyed and their high capital and maintenance costs hinder the implementa- tion by highway agencies. GENERAL CONSIDERATIONS Knowledge of the interactions of the precipitation and the pollutants aids in selection of appropriate practices. Under- standing the temporal evolution of such interactions can aid in choosing appropriate best management practices (BMPs)
32 Environmental Protection Agency (EPA), Erosion, Sedi- ment and Runoff Control for Roads and Highways, US EPA- 841-F-95-009d, EPA, Washington, D.C., Dec. 1995 [Online]. Available: http://water.epa.gov/polwaste/nps/runoff.cfm. Environmental Protection Agency (EPA), Preliminary Data Summary of Urban Storm Water Best Management Practices, EPA-821-R-99-012, EPA, Washington, D.C., Aug. 1999 [Online]. Available: http://water.epa.gov/scitech/ wastetech/guide/stormwater/. Golub, E., R. Dresnack, W. Konon, J. Meegoda, and T. Marhaba, Salt Runoff Collection System, Final Report, FHWA- NJ-2003-026, New Jersey Institute of Technology, Newark, 2008, 138 pp. [Online]. Available: http://transportation.njit. edu/nctip/final_report/SaltRunoffCollectionSystems.pdf. Michigan Department of Environmental Quality, Salt and Brine Storage Guidance for Road Agency Maintenance and Other Facilities, revised Aug. 2007, Lansing [Online]. Available: http://www.michigan.gov/documents/deq/deq- ess-p2tas-bulksaltbrineguidance_267024_7.pdf. Perkins, R. and Y.D. Hazirbaba. Bridge Deck Runoff: Water Quality Analysis and BMP Effectiveness, Final Report #RR08.13, prepared for Alaska University Transportation Center, Fairbanks, Dec. 2010 [Online]. Available: http://ine. uaf.edu/autc/files/2011/03/RR08.13.Final-Bridge-Runoff- Report-Dec-2010-sb.pdf. Roseen, R.M., et al., âSeasonal Performance Variations for Strom-Water Management Systems in Cold Climate Conditions,â Journal of Environmental Engineering, Vol. 135, No. 3, 2009, p. 128. Shi, X., et al., Evaluation of Alternative Anti-icing and Deicing Compounds using Sodium Chloride and Magne- sium Chloride as Baseline DeicersâPhase I, Final Report No. CDOT-2009-1, Colorado Department of Transportation, Denver, Feb. 2009. Staples, J.M., L. Gamradt, O. Stein, and X. Shi, Recom- mendations for Winter Traction Materials Management on Roadways Adjacent to Bodies of Water, MT FHWA/MT-04- 008/8117-19, Montana Department of Transportation, Hel- ena, Dec. 2004 [Online]. Available: http://www.mdt.mt.gov/ other/research/external/docs/research_proj/traction/final_ report.pdf Transportation Association of Canada (TAC), Synthesis of Best Practices, Drainage and Stormwater Management, Sep.2003d [Online]. Available: http://www.tac-atc.ca/ english/resourcecentre/readingroom/pdf/roadsalt-4.pdf. Urban Storm Drainage, Criteria Manual Volume 3âBest Management Practices, Urban Drainage and Flood Con- trol Districts, Denver, Colo., Nov. 2010 [Online]. Avail- able: http://www.udfcd.org/downloads/pdf/critmanual/ Volume%203%20PDFs/. Washington State Department of Transportation (WSDOT), Highway Runoff Manual, M31-16.03, Design Office, Environmental and Engineering Program, WSDOT, Olympia, Nov. 2011 [Online]. Available: http://www. wsdot.wa.gov/publications /manuals /fulltext /M31-16/ HighwayRunoff.pdf. Washington State Department of Ecology (WSDE), Stormwater Management in Western Washington, Volume III Hydrologic Analysis and Flow Control Design/BMPs, Pub. No. 05-10-31, Water Quality Program, WSDE, Olym- pia, Feb. 2005a [Online]. Available: https://fortress.wa.gov/ ecy/publications/publications/0510031.pdf. Washington State Department of Ecology (WSDE), Stormwater Management in Western Washington, Volume IV Source Control BMPs, Pub. No. 05-10-32, Water Quality Program, WSDE, Olympia, Feb. 2005b [Online]. Available: https://fortress.wa.gov/ecy/publications/publications/ 0510032.pdf. Wyoming Department of Environmental Quality (WYDEQ), Urban Best Management Practices for Non- point Source Pollution, Point and Nonpoint Source Pro- grams, Water Quality Division, WYDEQ, Sep. 1999 [Online]. Available: http://deq.state.wy.us/wqd/watershed/ Downloads/NPS%20Program/92171.pdf. INFILTRATION TRENCHES AND BASINS Infiltration trenches and basins treat runoff and reduce water volume by allowing for water to infiltrate into the surround- ing soil (Staples et al. 2004). Infiltration technologies require a pre-settling or pre-treatment to remove suspended solids that otherwise would clog the system and reduce the infiltra- tion capacity. Infiltration systems may have limited potential to treat chlorides in runoff, but have been found to effec- tively remove fine silts, clays, and phosphorus in the Lake Tahoe region (TIRRS 2001). In Washington State, infiltra- tion technologies including bioinfiltration ponds, ponds, trenches, vaults, and drywells are the preferred methods for flow control and runoff treatment, offering the highest level of pollutant removal (WSDOT 2011). They are preferred partially because of their ability to recharge groundwater and help maintain base stream flow, although it is difficult to successfully utilize this technology if chloride contamina- tion is significant. Infiltration trenches are excavated trenches filled with stone and lined with filter fabric where runoff is collected and allowed time to percolate into the soil (Staples et al.
33 2004). Infiltration trenches reduce runoff volume and have moderate to high ability to remove soluble pollutants in the runoff; they are suitable for salt storage facilities. They are also often sited âadjacent to roads where space is limitedâ (Golub et al. 2003). Figure 11 (left) shows a photo of a well- established infiltration trench along a roadside. According to Golub et al. (2003), âthe depth of groundwater and soil type limits the use of this option. The maximum drainage area for the system cannot exceed 5 acres and not be used in an area that experiences long and cold winters because freezing of the soil prevents pollution removal.â The trenches require regular maintenance (including inspection of the inlet struc- tures), because suspended solids in runoff can clog them and cause them to fail or to require more costly maintenance such as excavation (Hayes et al. 1996). Infiltration basins function similarly to infiltration trenches, but more closely resemble a dry pond (Staples et al. 2004). Figure 11 (right) shows a photo of a typical vegetated infiltration basin. Infiltration basins hold runoff, allowing for longer infiltration times; but unlike dry or wet ponds, they release runoff from storm events. Design consider- ations (e.g., infiltration rates and site selection) play a crucial role in the effectiveness of an infiltration basin, as regular maintenance may be required. Infiltration basins are not rec- ommended in areas with compacted soil, high groundwater levels, or high levels of sediment in stormwater; dense veg- etation, consisting of deep rooted plants at the bottom of the basin, can enhance infiltration capacity and reduce soil ero- sion. Infiltration basins effectively decrease the runoff vol- ume and reduce downstream flooding, and also can remove sediment, metals, bacteria, and organics. Additional Resources for Infiltration Trenches and Basins Barr Engineering Company, Minnesota Urban Small Sites BMP Manual, Stormwater Best Management Practices for Cold Climates, prepared for the Metropolitan Council, July 2001 [Online]. Available: http://www.metrocouncil.org/ environment/water/BMP/manual.htm. Hayes, B.D., T.F. Marhaba, N.W. Angnoli, and D.M. Lackey, Evaluation of Highway Runoff Pollution Control Devices, Final Report, NJDOT Task Order #43, Project 7620, 1996. Ostendorf, D.W., R.N. Palmer, and E.S. Hinlein, âSeason- ally Varying Highway Deicing Agent Contamination in a Groundwater Plume from an Infiltration Basin,â Hydrology Research, 2009. Staples, J.M., L. Gamradt, O. Stein, and X. Shi, Recom- mendations for Winter Traction Materials Management on Roadways Adjacent to Bodies of Water, FHWA/MT-04- 008/8117-19, Montana Department of Transportation, Hel- ena, Dec. 2004 [Online]. Available: http://www.mdt.mt.gov/ other/research/external/docs/research_proj/traction/final_ report.pdf. Washington State Department of Transportation (WSDOT), Highway Runoff Manual, M31-16.03, Design Office, Environmental and Engineering Program, WSDOT, Olympia, Nov. 2011 [Online]. Available: http://www. wsdot.wa.gov/publications /manuals /fulltext /M31-16/ HighwayRunoff.pdf. DETENTION, RETENTION, AND EVAPORATION PONDS Dry ponds remove pollutants through sedimentation or settling and can be used to remove suspended solids such as traction sand from the roadway. Dry ponds use a small amount of space and do not increase water temperature, so they can be used in areas where stream temperature will impact aquatic species such as fish (Staples et al. 2004). They FIGURE 11 An infiltration trench (left) and an infiltration basin (right) (Photos: www.lowimpactdevelopment.org/greenstreets/ practices.htm [left] and www.sudswales.com/types/source-control/infiltration-basins [right]).
34 are one of the least expensive runoff treatment practices per unit area, and can perform well in cold climates and remain effective during the winter. Heavy spring runoff storm events can increase the potential for scour and resuspension of accumulated sediment if this possibility is not accounted for with an appropriate forebay (Staples et al. 2004). Dry settling ponds hold runoff for a given period of time and release it at a controlled rate so that the pond remains dry between storm events (Staples et al. 2004). They provide more volume control than water quality control. For the detention time in the pond, consider the size of the suspended solids to be removed. Dry extended detention ponds provide a higher level of water treatment than dry settling ponds, because they are designed to hold runoff for longer periods, which allows more particles to settle out (Staples et al. 2004). Shallower ponds with longer flow lengths tend to show greater sediment removal. Sediment removal rates of up to 60% have been observed for dry pond detention times of up to 24 hours. An additional 28% sediment removal was observed when baffles were added (Shammaa and Zhu 2001). Wet ponds have high community acceptance, and fea- ture low maintenance and cost requirements (FHWA 2003). They can increase water temperature, which can be detri- mental to the ecosystem, but large plants or trees can be used to mitigate this impact (Staples et al. 2004). Figure 12 shows a photo of a typical wet retention pond. Wet ponds can be designed for the treatment of conventional pollutants, or be modified to enhance removal of nutrients or dissolved met- als (WSDOT 2011). They generally have higher sediment removal rates than dry ponds and offer effective pollut- ant removal through mechanisms such as settling, nutrient uptake by plants, and biochemical processes. The effective- ness of wet ponds can be reduced in cold climates, particu- larly if a surface ice layer forms. FIGURE 12 Wet retention pond. (Photo: http:// rwmwd.org/). Although only basic maintenance may be needed for a wet pond, regular inspections, particularly during the first few months of the service life, can help ensure proper perfor- mance, vegetation growth, and bank stability. Also, incor- porating multiple pools of varying depths can help ensure sufficient performance during winter and spring conditions. A sediment forebay also may need to be added. Wet settling ponds contain water even between storm events and require more area than wet or dry ponds. The permanent pool provides additional treatment of runoff, and is designed to allow runoff from a storm event to dis- place the volume of water held in the pond from the pre- vious storm (Staples et al. 2004). Hydraulic residence time greatly affects the pollutant removal efficiencies, and studies have demonstrated that approximately 90% of the pollutant removal occurs between rain events. It has been determined that sedimentation removes an estimated two-thirds of trace metals and sediment within 24 hours of a rainfall event (Barr Engineering Company 2001). Wet ponds may require a large contributing watershed of at least 10 acres (Barr Engineering Company 2001). Additionally, depth to groundwater may be considered if groundwater contamination is a concern. Dry and wet settling ponds are among the most cost-effective and commonly used runoff treatment measures (Staples et al. 2004). Wet extended detention ponds combine the qualities of both wet and dry ponds to treat runoff (Staples et al. 2004). These ponds contain a permanent pool with additional vol- ume to hold and treat additional runoff and provide a higher level of treatment and reduce the velocity of runoff. Removal efficiencies of 60%â80% total suspended solids have been reported for various wet extended detention ponds. (Barr Engineering Company 2001). Wet extended detention ponds generally may need more area than wet or dry ponds. Wet ponds and wet extended detention ponds are not ideally suited for arid climates since greater maintenance may be needed. According to Golub et al. (2008), âevaporation ponds can be an inexpensive method to separate the dissolved salt. The brine, collected at the maintenance facility, can be directed to an evaporation pond during active periods in the winterâ¦ The collected brine can then be evaporated in the summer period or reused on site for brine making.â To facilitate the evaporation of brine in the non-winter months, a best prac- tice is to take advantage of site topography and use a cover for the evaporation pond (Hayes et al. 1996). Meegoda et al. (2004) studied the effective practices to mitigate salt water runoff from winter maintenance yards in New Jersey and proposed the use as brine in pre-wetting. Alleman et al. (2004) investigated the reuse of wash water at Indiana DOT locations for brine generation and found that salt truck wash water offers a cost-effective and environmentally friendly option for manufacturing a recycled salt brine solution. Fitch et al. (2004) conducted a study for the Virginia DOT which collected stormwater runoff from loading pads to onsite ponds or collection basins and examined the chloride con-
35 centrations in the basins. High chloride levels were found in the collection basins, exceeding both state and federal stan- dards. It was found that the DOT would realize significant cost saving by reducing runoff to the collection basins, and the method suggested was to use the runoff water to generate brine that would require no pretreatment. The cost-benefit analysis indicated capital investment associated with the brine production using runoff water at the DOT maintenance locations would be recovered within 2 years for anti-icers produced and 4 years for pre-wetting brine produced. In addition, they reported that low hydraulic retention time and warmer temperatures favored successful brine generation. Another method used by the DOT to reduce the amount of water in stormwater ponds was the practice of applying the brine to gravel roads for dust suppression (Fitch et al. 2004). According to Golub et al. (2008), âwhen constructing detention or retention ponds, (one needs to) consider the runoff area (loading pad size), annual average precipitation, and evaporation rates for determining pond area and volume necessary for each site.â When survey respondents were asked if their state or agency has implemented any tools, techniques, practices, or strategies to reduce the impacts of chloride deicers, the fol- lowing response was provided: â¢ At storage facilities, we have constructed retention ponds to prevent chloride off site migration (Montana DOT). Additional Resources for Detention, Retention, and Evaporation Ponds Alleman, J.E., B.K. Partridge, and L. Yeung, Innova- tive Environmental Management of Winter Salt Run-Off Problems at INDOT Yards, Final Report FHWA/IN/ JTRO-2001/27, Indiana Department of Transportation, Indi- anapolis, 2004 [Online]. Available: http://trid.trb.org/view. aspx?id=787489. Hayes, B.D., T.F. Marhaba, N.W. Angnoli, and D.M. Lackey, Evaluation of Highway Runoff Pollution Control Devices, Final Report, NJDOT Task Order #43, Project 7620, 1996. Meegoda, J.N., T.F. Marhaba, and P. Ratnaweera, âStrat- egies to Mitigate Salt Run Off from Salt Storage and Salt Truck Maintenance Facilities,â Practice Periodical of Haz- ardous, Toxic, and Radioactive Waste Management, Vol. 8, 2004, pp. 247â252. Staples, J.M., L. Gamradt, O. Stein, and X. Shi, Recom- mendations for Winter Traction Materials Management on Roadways Adjacent to Bodies of Water, FHWA/MT-04- 008/8117-19, Montana Department of Transportation, Hel- ena, Dec. 2004 [Online]. Available: http://www.mdt.mt.gov/ other/research/external/docs/research_proj/traction/final_ report.pdf. Washington State Department of Transportation WSDOT, Highway Runoff Manual, M31-16.03, Design Office, Envi- ronmental and Engineering Program, WSDOT, Olympia, Nov. 2011 [Online]. Available: http://www.wsdot.wa.gov/ publications/manuals/fulltext/M31-16/HighwayRunoff.pdf. WETLANDS AND SHALLOW MARSHES Wetlands use the natural processes of adsorption, filtration, sedimentation, and related processes to remove pollutants (Earles 1999). Through the combination of these processes, constructed wetlands can be effective in removing both sus- pended and dissolved pollutants. Natural wetlands cannot be used for stormwater treatment purposes owing to current wetland protection guidelines. The use of wetlands can be limited in arid regions as a result of evaporation and may be limited in cold regions in light of limited plant growth. Constructed wetlands use physical and chemical pro- cesses of natural wetlands (e.g., adsorption, plant uptake, set- tling, decomposition) to treat water from runoff and reduce its velocity (Staples et al. 2004). They can provide treatment for dissolved metals through sedimentation and geochemi- cal processes (WSDOT 2011). Similar to wet ponds, they are effective at removing high levels of suspended solids with minimal maintenance (Staples et al. 2004). Stormwa- ter wetlands are designed to store runoff, sustain plant life, and promote microbial growth, which contributes to pollut- ant removal. They require minimal maintenance and can decrease peak discharges. Design considerations need to be assessed carefully, along with site characteristics. Typical design criteria consist of particle size removal efficiencies and treatment volume (Barr Engineering Company 2001). Limited data are available regarding the use of constructed wetlands for runoff mitigation, and optimal design criteria have not been identified for their use in temperate regions (Earles 1999). Although little information is available for their use in cold regions, constructed wetlands are in use in latitudes as far north as the Arctic Circle. Figure 13 shows a constructed wetland just after completion and after one season, respectively. According to Golub et al. (2008), âconstructed wetlands can be used as an effective technique for salt runoff treatment from salt storage facilities and roadsâ¦potential problems involved with the system include increased mosquito population, low pollutant remove in winter months, and regulatory problems.â When selecting a site for a wetland, the distance from the runoff source, available land, topography, soil type and permeability, and groundwater and base flow should be con- sidered (Staples et al. 2004). Although wetlands have been estimated to cost 25% more than runoff ponds of equivalent
36 volume (CWP 2003), wetlands and marshes are generally more aesthetically appealing than ponds and offer second- ary benefits of creating habitat for wildlife, providing visual screening, and reducing obtrusiveness of drainage facilities (WSDOT 2011). Maintenance can vary depending on the location of the wetland with respect to residential areas. A properly designed forebay, detention pond, or grease/sedi- ment trap that removes sediment and other pollutants can enhance the treatment and limit maintenance to cleaning of the forebay instead of the entire wetland (Golub et al. 2008). Maintenance access for vehicles should be included in the design, and as recommended in several surveys, the forebay or inlet pool could be lined with a hard surface to facilitate cleaning (NYSSMDM 2010). Vegetation is also an important aspect of a treatment wet- land, for example, using plants that can withstand high salt concentrations. Consider monitoring constructed wetland vegetation and hydrologic conditions, especially during the establishment period. Grass infiltration areas also can be utilized to reduce the initial chloride concentration in the runoff before it reaches the wetland, so as to decrease harm- ful impacts to the wetland vegetation (NYSSMDM 2010). There are four different configurations: shallow marsh system, pond/wetland system, extended detention wetland system, and pocket wetland system (Barr Engineering Com- pany 2001). Each configuration includes a pool or forebay at the inlet and a pool at the outlet for increased sedimenta- tion of large particles and for enhanced reduction in incom- ing and outgoing flow velocities. These pools should reduce resuspension of accumulated sediment. A shallow marsh is a type of constructed wetland that is characterized by heavy vegetation and shallow water levels. Although there is stand- ing water within shallow marshes, limited storage volume can create potential complications after larger storms (Sta- ples et al. 2004). Small or perched wetlands that intercept the shallow water table or that are primarily surface water dependent may be most susceptible to chloride-laden runoff, as a result of their small size and reduced dilution potential. With high and prolonged chloride loadings, changes in local plant composition may occur, potentially reducing the over- all value and diversity of the wetland (TAC 2003h). Additional Resources for Wetlands and Shallow Marshes Federal Highway Administration (FHWA), New Hamp- shire Department of Transportationâs Route 101 Ecological Protection and Enhancement Features, Last modified Apr. 22, 2004 [Online]. Available: http://www.fhwa.dot.gov/ environment/ecosystems/nh.htm. Hayes, B.D., T.F. Marhaba, N.W. Angnoli, and D.M. Lackey, Evaluation of Highway Runoff Pollution Control Devices, Final Report, NJDOT Task Order #43, Project 7620, 1996. Metropolitan Council, Stormwater Wetlands Urban Small Sites Best Management Practice Manual [Online]. Available: http://www.metrocouncil.org/environment/ Watershed/BMP/manual.htm [accessed July 7, 2012]. NYSSMDM, New York State Stormwater Management Design Manual, prepared by the Center for Watershed Pro- tection for New York State Department of Environmental Conservation, Aug. 2010 [Online]. Available: http://www. dec.ny.gov/chemical/29072.html. Roseen, R.M., et al., âWater Quality and Flow Perfor- mance-Based Assessments of Stormwater Control Strate- gies During Cold Weather Months,â Proceedings of the Water Environment Federation, Sustainability 2008, 2008, pp. 562â564(3). Staples, J.M., L. Gamradt, O. Stein, and X. Shi, Recom- mendations for Winter Traction Materials Management on FIGURE 13 A constructed wetland just after completion (left) and after one season of plant installation (right) (Photos: http://avery. ces.ncsu.edu/content/BannerElkConstructedStormwaterWetland).
37 Roadways Adjacent to Bodies of Water, FHWA/MT-04- 008/8117-19, Montana Department of Transportation. Hel- ena, Dec. 2004 [Online]. Available: http://www.mdt.mt.gov/ other/research/external/docs/research_proj/traction/final_ report.pdf. Washington State Department of Transportation (WSDOT), Highway Runoff Manual, M31-16.03, Design Office, Environmental and Engineering Program, WSDOT, Olympia, Nov. 2011 [Online]. Available: http://www. wsdot.wa.gov/publications /manuals /fulltext /M31-16/ HighwayRunoff.pdf. Yu, S.L., A. Earles, and G.M. Fitch, âAspects of Func- tional Analysis of Mitigated Wetlands Recieving High- way Runoff,â Transportation Research Record: Journal of Transportation Research Board, No. 1626, Transportation Research Board of the National Academies, Washington, D.C., 1998 [Online]. Available: http://trb.metapress.com/ content/86q14308431580g8/. VEGETATED SWALES AND FILTER STRIPS Biofiltration is the use of closely grown vegetation to filter runoff. This is achieved by allowing water to flow through the vegetation, which decreases the runoff velocity and allows particles to settle (Staples et al. 2004). Biofiltration systems are generally open channel and are referred to as swales, filter strips, or natural and engineered dispersion. They provide effective removal of pollutants through mech- anisms such as adsorption, decomposition, ion exchange, fil- tration, and volatilization. The effectiveness of biofiltration in colder climates can be limited by the short growing season and cold temperatures as well as by the potential damage of deicers and abrasives to the vegetation. Biofiltration is most effective when combined with other treatment options such as ponds, infiltration trenches, or wetlands (Watson 1994). Bioinfiltration swales can be dry, grassy, or vegetated channels (Staples et al. 2004; WSDOT 2011). Swales are generally located in naturally low topographic areas of uni- form grade such as road ditches (Staples et al. 2004). They treat runoff by reducing its velocity and allowing particles to settle out. Swales are useful for runoff control on high- way medians and a main design consideration is the volume of runoff to be treated (Barr Engineering Company 2001). The recommended minimum swale length is 100 ft with the width over designed as opposed to the length, to promote shallow flow, which enhances pollutant removal (Colwell et al. 2000). Where possible, use of salt-tolerant vegeta- tion needs to be considered. The addition of check dams can significantly increase the detention time and therefore sediment removal rate of swales (Yu et al. 2001). Dry swales may have check dams to temporarily pond runoff to both increase the removal of suspended solids and reduce the run- off velocity. Wet swales vary from dry swales only by having impermeable soils and being located close to the water table (Staples et al. 2004). They frequently have standing water and function similar to a wet pond, where new stormwater runoff replaces the existing volume of water. In addition, wet swales improve water quality through mechanisms such as adsorption, sedimentation, and microbially assisted decom- position of pollutants (Barr Engineering Company 2001). Vegetated swales require low maintenance other than mowing, clearing, and cleaning out if plugged (Staples et al. 2004). They are generally inexpensive, with costs increas- ing with maintenance and watering. An initial watering or inclusion of irrigation in dry climates may help ensure the success of the vegetation. In winter months when plants are dormant or covered by snow, this treatment may be less effective (Yu et al. 2001). Similar to swales, vegetated filter strips are densely veg- etated areas bordering impervious surfaces that treat runoff by reducing its velocity and allowing particles to settle out. The difference is that the runoff flows perpendicularly across the length of the vegetation, known as sheet flow (Staples et al. 2004). Vegetated filter strips are best located in naturally low- topographic areas of uniform grade, such as roadside ditches or along roadsides. They have shown a wide range of sediment removal rates based on the length (Yu et al. 1995). Vegetated filter strips have been primarily used in an agricultural setting and studies have demonstrated a 50% removal rate of phos- phorus, nitrogen, and sediment with a 15-ft grass buffer and a 70% removal rate with a 100-ft grass buffer (Barr Engineering Company 2001). To be effective, vegetated filter strips are to be 15 ft wide and at least 25 ft long for slopes ranging from 2% to 6% and they are not recommended for slopes greater than 10% (Watson 1994; Caraco and Claytor 1997). The strips should be wider for locations with steeper slopes. An accumu- lation of sediment in the first 30 cm of vegetation should be designed for to avoid blocking of water flow or ponding onto the roadway (Staples et al. 2004). Incorporating native vegeta- tion along with trees and shrubs into filter strips may enhance pollutant removal (Barr Engineering Company 2001). Vegetated swales and filter strips are low-cost solutions and generally have a life expectancy of 20 to 50 years (Schueler 1987). They can be used for snow storage and allow the melt- water to infiltrate. Vegetated swales and filter strips require minimal maintenance (mainly mowing and sediment/debris removal), which helps to keep their life-cycle cost low. During the winter months, cold weather can impact the vegetation and buildup of sediment and deicers should be monitored. Native grass sod has been shown to effectively work as the vegeta- tion for vegetated swales and filter strips in studies conducted in Montana and California (Dollhopf et al. 2008; Ament et al. 2011). Initial costs may be higher than if seeds were used, but sod has been shown to remove up to 99% of total suspended sol- ids in runoff, much higher than seeding methods (EPA 2002).
38 Natural and engineered dispersions are similar to filter strips, but have a conveyance system that concentrates run- off to the dispersion area, through storm sewer pipe, ditch, or similar (WSDOT 2011). The concentrated flow is then dispersed at the end of the conveyance system to mimic sheet flow. Natural dispersions can be selected based on site topography and soil and vegetation characteristics. Engi- neered dispersions are enhanced sites by inclusion of com- post-amended soils and additional vegetation. Additional Resources for Vegetated Swales and Filter Strips Ament, R., S. Jennings and P. Blicker, Steep Cut Slope Composting: Field Trials and Evaluation, Final Report, FHWA/MT-10-008/8196, prepared for Montana Department of Transportation, Helena, Apr. 2011 [Online]. Available: ht tp://www.ewu.edu /Documents /CBPA/NWTTAP/ Newsletter/Publications/FHWA_MT_10_008_8196.pdf. Anchorage (Alaska), Guidance for Design of Biofiltra- tion Facilities for Stream Water Quality Control, Watershed Management Program, Montgomery Watson (Firm), 1994. Dollhopf, D., et al., Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control, Califor- nia Department of Transportation, Sacramento, Dec. 2008 [Online]. Available: http://www.dot.ca.gov/hq/LandArch/ research/docs/Montana_State_Native_Grass_Sod_For_ Biostrips_Bioswales_Sediment_Control.pdf. Staples, J.M., L. Gamradt, O. Stein, and X. Shi, Recommen- dations for Winter Traction Materials Management on Road- ways Adjacent to Bodies of Water, FHWA/MT-04-008/8117-19, Montana Department of Transportation. Helena, Dec. 2004 [Online]. Available: http://www.mdt.mt.gov/other/research/ external/docs/research_proj/traction/final_report.pdf. Washington State Department of Transportation (WSDOT), Highway Runoff Manual, M31-16.03, Design Office, Envi- ronmental and Engineering Program, WSDOT, Olympia, Nov. 2011 [Online]. Available: http://www.wsdot.wa.gov/ publications/manuals/fulltext/M31-16/HighwayRunoff.pdf. Watson, M., Guidance for Design of Biofiltration Facili- ties for Stream Water Quality Control, Municipality of Anchorage Watershed Management Program Document No. CPg96002, 1994. OVERVIEW OF REACTIVE STRATEGIES A combination of reactive strategies is recommended to enhance overall performance, increase service life, and pre- serve downstream water bodies. This is achieved by utiliz- ing a series of treatment methods that each focus on one aspect of water treatment. An integrated treatment method may incorporate a vegetated filter strip with swales, an infiltration basin and finally a pond system. Specific design criteria in each system should be considered to ensure that suitable design requirements are attained (Barr Engineering Company 2001). Table 3 presents the average removal efficiencies (Â± the 67% confidence interval) of various best practices reported by Weiss et al. (2007). Removal efficiencies for total suspended solids and phosphorus were analyzed over a 20-year period as a function of the pollutant load and water quality volume, which is defined as the volume of runoff that the effective practice is designed to store or treat. It was determined that infiltration trenches and bio- retention filters are the most effective treatment techniques for removing total suspended solids. The results suggest that constructed wetlands are a cost-effective stormwater treatment method if sufficient land area is available (Weiss et. al. 2007). The most efficient BMP must be identified during the design stage, in light of the target water quality volume, cost, and other constraints. Note that âremovalâ in this context is truly removal from surface water by means of diversion and dilution. TABLE 3 AVERAGE REMOVAL EFFICIENCIES OF VARIOUS BEST PRACTICES Source: Weiss et al. (2007). Great care must be exercised to ensure that the imple- mented practices function effectively in cold regions, espe- cially during the winter and spring months. Roseen et al. (2008) evaluated bioretention systems, a wetlands system, and a sand filtration system throughout winter seasons, and concluded that the winter months had no effect on overall performance of these systems. Nonetheless, they acknowl- edge the potential risk posed by the winter in cold regions. Traditional design guidelines developed in temperate regions may need adjustment. If necessary, modifications to design features could be made to accommodate site-specific needs. Such modifications can be explored in six categories: fea- sibility, conveyance, pretreatment, treatment, maintenance, and landscaping (Caraco and Claytor 1997).
39 Staples et al. (2004) summarized the reactive strategies for mitigating highway runoff, with a focus on cold regions and rural transportation, and discussed their applicabil- ity, site criteria, engineering characteristics, maintenance issues, cost, effectiveness, efficiency, and the like. Despite the challenges of winter conditions, reactive strategies such as ponds, wetlands, and vegetated swales and filter strips can still remove high levels of sediment from runoff if they are designed, sited, installed, and maintained properly. In contrast, dissolved pollutants from chloride roadway deicers are difficult to remove. Table 4 provides a summary of selec- tion criteria for reactive mitigation strategies, with a focus on the removal of suspended solids or dissolved pollutants, the characteristics of the strategy, and their applicability in cold regions. The importance of proper maintenance of reactive miti- gation strategies cannot be overestimated. Time and budget commitments for maintenance for all these reactive strate- gies will aid in their continued function and success. Many of them fail because of the lack of continued support for maintaining the installed facilities. TABLE 4 SUMMARY OF SELECTION CRITERIA FOR REACTIVE STRATEGIES
40 CHAPTER FIVE NEW AND EMERGING TECHNOLOGIES This chapter presents information on new and emerging technologies utilized to mitigate the impacts of chloride roadway deicers on the natural environment. New and emerging technologies presented in this chapter, identified from the practitioner survey and literature review, includes synchronizing vehicle location and other sensor technolo- gies, MDSS, FAST, and thermal deicing methods. Other emerging technologies that could reduce chloride deicer usage, such as advances in the research and development of non-chloride roadway deicers, are not discussed in this synthesis. Note that a guide for implementation of emerg- ing technologies can found in the Highway Runoff Manual 22.214.171.124 (WSDOT 2011). The majority of mitigation strategies identified by the practitioner surveys were proactive prac- tices (see chapter four); this chapter also focuses on recent advances in pro-active deicer environmental management. Although there are recent advances in reactive strategies (see chapter five) as well, they generally are not aimed at enhancing the removal of pollutants associated with chloride roadway deicers. In this work, survey respondents were asked to provide an example of a new technology, tool, or methods they are using to reduce the impacts of chlorides on the natural environ- ment. Figure 14 reveals that the top three technologies being implemented for deicer environmental management include (1) advanced material controllers or ground speed control- lers, (2) liquid anti-icing or pre-wetting, and (3) automatic vehicle location (AVL)/global positioning system (GPS). They are followed by environmentally friendly deicers/ anti-icers/additives, MDSS, FAST, salt brine making, living snow fences, clearing vegetation from right-of-way, train- ing, environmental monitoring, plowing techniques, slurry technology, and 14-ft tow plows. The vast majority of these technologies (except the final two) have been available and in practice for more than a decade. Many of them (especially the top three, MDSS, and FAST) also have been extensively researched and show desirable benefitâcost ratios. Five new and emerging technologies identified through the literature review and the practitioner surveys are syn- chronizing vehicle location and other sensor technologies, MDSS, FAST, thermal deicing methods, and innovative snow fences. Other emerging technologies could reduce chloride deicer usage, such as advances in the research and development of non-chloride roadway deicers. An emerging technology implementation guide can be found in the High- way Runoff Manual 126.96.36.199 (WSDOT 2011). FIGURE 14 New and emerging technologies implemented by survey respondents to mitigate the impacts of chlorides on the natural environment. SYNCHRONIZING VEHICLE LOCATION AND OTHER SENSOR TECHNOLOGIES Numerous equipment technologies support winter road maintenance by helping manage the operations with timely, useful data or by supporting the service delivery itself. Advanced vehicle-based sensor technologies, including AVL, mobile RWIS technologies (surface temperature sen- sors, on-board freezing point and ice-presence sensors, and salinity sensors), visual and multispectral sensors, and mil- limeter wavelength radar sensors, have been developed in the past decade or so to achieve improvements in winter maintenance efficiency and safety. Among them, Shi and colleagues (2007) found AVL systems and road surface tem- perature sensors to be the only ones that had matured and became fully operational, whereas the remainders were still in the development and testing phases. AVL is a technology that integrates vehicle location infor- mation with other information from the vehicle to provide temporally and spatially referenced information on a main- tenance vehicleâs activities, as illustrated in Figure 15 (Allen 2006). Other than GPS information, real-time information may include type of applied material, application rate, posi- tion of plow blade, and pavement temperature (Vonderohe
41 2004). AVL can assist in storm response, guide storm event planning by providing previous storm event histories, and help agencies simplify tracking and reporting requirements, thus decreasing the paperwork and time required to manage winter maintenance activities (Ye et al. 2012). FIGURE 15 Schematic diagram of AVL system (Allen 2006). The enhanced vehicle tracking and dispatching capa- bilities through AVL have been proven to reduce response time, improve resource management, coordination, and information-sharing, reduce staff fatigue during peak opera- tions, improve the efficiency of overall winter maintenance operations, and reduce chemical consumption while achiev- ing comparable or higher LOS (Meyer and Ahmed 2003; Anthony 2004; Ye et al. 2012). The incorporation of other mobile data collection (e.g., pavement temperature) with AVL is anticipated to further optimize the usage of roadway deicers for snow and ice control. In 1999, the Missouri DOT (2009) conducted a research project to evaluate the benefits of a temperature detection system. The project included a laboratory test as well as a field evaluation of 50 such mirror-mounted pavement temperature sensors distributed throughout the state. The laboratory test shows good sensor accuracy. A material savings of $185,119 during the winter of 1998â99 was estimated excluding the savings from per- sonnel and equipment. Assuming 1 year as the life of the sensors, the project team calculated the benefitâcost ratio to be 9.49. There is a rich repository of documented experience on lessons learned and best practices for use of AVL in winter maintenance operations. Some of the major themes include the need for thoughtful integration of AVL into an existing vehicle fleet in light of the variety of expected users and sen- sor packages, and the need to consider the communications requirements of the various technologies. Through several years of demonstration and evaluation, many problems that plagued earlier AVL deployments, such as sensor protection, communications availability, and GPS accuracy, have been addressed. The level of support from the vendor commu- nity has improved as AVL vendors have become flexible, adapting and customizing systems to meet specific customer requirements. Vendors also provide customized maps, sta- tistical analysis, and reports as requested by the customer. There are a few overall trends regarding the future use of vehicle-based technologies for snow and ice control. First of all, integration was an underlying goal in several U.S. winter main- tenance vehicle-based technology projects. The HMCV under the sponsorship of several state DOTs have incorporated some of the latest technologies, including temperature sensors, fric- tion sensors, freezing-point sensors, high intensity lights, GPS/ AVL, ground speed spreaders, pre-wetting equipment, liquid spreaders, power boosters, and underbody plows (Kroeger and Sinhaa 2004). Agency snowplow specifications are increas- ingly requiring vendors to allow greater levels of technology integration with road condition sensors, spreader controllers, and other vehicle equipment. Second, there is a trend toward increased automation of snowplow operations. This trend rec- ognizes the complexity associated with executing winter main- tenance tasks during storm events, when such tasks are most critical. In the future, two-way AVL could allow a maintenance manager to select application rates without needing to involve the vehicle operator. Finally, while many of the vehicle-based sensor technologies hold great promise in assisting in the win- ter maintenance process, technological and other barriers cur- rently impede their greater implementation. In this synthesis work, when survey respondents were asked if their state or agency has made any effort to miti- gate or reduce the impacts of chloride deicers, the following response was provided: â¢ Increasing the number of closed loop spreader con- trol systems on our fleet with AVL/GPRS. Offering a âGreen Incentiveâ for our winter plow vendors to install similar AVL closed loop spreader controls (Rhode Island DOT). Additional Resources for Synchronizing Vehicle Location and Other Sensor Technologies Andrey, J., J. Li and B. Mills, âA Winter Index for Bench- marking Winter Road Maintenance Operations on Ontario Highways,â presented at the 80th Annual Meeting of the Transportation Research Board, Washington, D.C., Jan. 2001. Meyer, E., âBenefit-cost Assessment of Automatic Vehi- cle Location (AVL) in Highway Maintenance,â presented at the 2003 Mid-Continent Transportation Research Sympo- sium. Ames, Iowa, 2003. Shi, X., et al., Vehicle-Based Technologies for Winter Maintenance: The State of the Practice, Final Report, NCHRP 20-02/200, Transportation Research Board of the National Academies, Washington, D.C., 2006 [Online]. Avail- able: http://maintenance.transportation.org/Documents/ Final%20Report%202007%20Task%20200.pdf.
42 Strong, C., N. El Ferradi, and X. Shi, âState-of-the-Prac- tice of Automatic Vehicle Location for Winter Maintenance Operations,â presented at the 86th Annual Meeting of the Transportation Research Board, Washington, D.C., Jan. 21â25, 2007. Veneziano, D. and C. Strong, âPilot Test of Automatic Vehicle Location on Snow Plows Technical Memorandum 2: Pre-Pilot Test Results,â Western Transportation Institute. Helena, Mont., July 2007. Veneziano, D., L. Fay, Z. Ye, D. Williams, X. Shi, and L. Ballard, Development of a Toolkit for Cost-Benefit Analysis of Specific Water Maintenance Practices, Equipment and Operations: Final Report, WisDOT 0092-09-08, Western Transportation Institute, Bozeman, Mont., Nov. 2010b. Washington State Department of Transportation (WSDOT), Highway Runoff Manual, M31-16.03, Design Office, Environmental and Engineering Program, WSDOT, Nov. 2011 [Online] Available: http://www.wsdot.wa.gov/ publications/manuals/fulltext/M31-16/HighwayRunoff.pdf. MAINTENANCE DECISIONS SUPPORT SYSTEM An MDSS is a software application that integrates informa- tion from a variety of sources, such as fixed RWIS, weather service forecasts and others observations, to assist managers in making appropriate winter maintenance decisions. The goal is to best utilize resources for effective snow and ice control. It has been proven to be a powerful management tool that facilitates proactive (vs. reactive) winter road mainte- nance operations. The global essential function of the MDSS is fulfilled as two interrelated applications: â¢ Application 1: Predict and portray how road condi- tions will change owing to the forecast weather and the application of several candidate road maintenance treatments, based on an assessment of current road and weather conditions and time- and location-specific weather forecasts along transportation routes. This may be termed a âreal-time assessment of current and future conditions.â â¢ Application 2: Suggest optimal maintenance treat- ments that can be achieved within available staffing, equipment, and materials resources. This may be termed âreal-time maintenance recommendations.â Application 1 involves the integration of information on recent and current road and weather conditions, along with reports of winter maintenance actions, from a variety of sources. Application 2 interprets that information and pro- duces recommendations for future action (Ye et al. 2009a). A transportation agency may choose to implement the MDSS in various ways, with diversity in forecasting services, feed- back mechanism, treatment recommendations module, and In-vehicle Graphical User Interface (Ye et al. 2009a). MDSS was proven to be an effective system when it was implemented statewide by the Indiana DOT. For the fiscal year 2009 ice and snow season, MDSS helped INDOT to save $12,108,910 (228,470 tons) in salt usage. When nor- malized for varying winter conditions, INDOT still real- ized savings of $9,978,536 (188,274 tons) in salt usage (McClellan et al. 2009). A case study in Maine (Cluett and Jenq 2007) tracked 12 winter storm events that required response in order to characterize the use of the MDSS as a maintenance tool, versus not using a MDSS. The results of the MDSS system were positive and strongly support the future implementation of a MDSS for winter maintenance operations. It was also cautioned that receiving too many alerts may be distracting at times and can be misleading during important warnings. Overall, MDSS was considered beneficial for the environment, safety, and cost reduction. Ye et al. (2009a) established a methodology for analyzing the tangible benefits of the Pooled-Fund version MDSS. The methodology entails the use of a baseline data module and a simulation module and benefits considered included reduced material usage (agency benefit), improved traffic safety (user benefit), and reduced traffic delay (user bene- fit). The methodology was applied to three case study states with diversity in climatological conditions. The analysis results indicated that the use of MDSS could bring much more benefits than costs. Integration is also a key consideration with the MDSS, which will make more appropriate roadway treatment recom- mendations as the quality of information (inputs) improves. The AVL/MDSS system was developed and implemented by Minnesota DOT to provide better information to opera- tors to optimize chemical use and service level, and provide better information for supervisors and managers to enhance scheduling, dispatch, and safety (Hille and Starr 2008). In Japan, Makino and colleagues (2012) reported the devel- opment of a system similar to MDSS coupled with AVL, which âenables flexible shifting of snow removal sections.â Such flexibility can be valuable in fighting extremely severe winter storms and optimizing the use of resources including roadway deicers. When survey respondents were asked if their state or agency has made any effort to mitigate or reduce the impacts of chloride deicers, some of the following responses were provided: â¢ Using MDSS to suggest the most effective treatment types, application rates and timing (South Dakota DOT). â¢ Implemented MDSS statewide in 2009 with the hopes that it would reduce application rates (Wisconsin DOT).
43 When survey respondents were asked if their state or agency has implemented any tools, techniques, practices, or strategies to reduce the impacts of chloride deicers, the fol- lowing response was provided: â¢ We are using a program MDSS as a tool to give our employees a scientific approach to removing snow and ice in an effort to prevent over-applications (Indiana DOT). Additional Resources for MDSS Cluett, C. and J. Jenq, A Cast Study of the Maintenance Decision Support System (MDSS) in Maine, Best Prac- tices for Road Weather Management Version 2.0, FHWA- JPO-08-001, 2007 [Online]. Available: http://ntl.bts.gov/ lib/30000/30200/30234/14387.htm. Ye, Z.R., C. Strong, X. Shi, and S. Conger, Analysis of Maintenance Decision Support System (MDSS) Benefits and Costs, Study SD2006-10, 2009a [Online]. Available: http:// www.meridian-enviro.com/mdss/pfs/files/WTI-4W1408_ Final_Report.pdf. FIXED AUTOMATED SPRAY TECHNOLOGY Sensitive structures and critical segments of roadway net- work need to be freed of snow and ice in a timely manner, before maintenance vehicles can even travel to the site and treat them. For instance, bridge decks or shaded areas may feature hazardous driving conditions in wintery weather, such as frequent frost and black ice. In high-risk areas far from maintenance sheds or areas that experience a high traf- fic volume, anti-icing chemicals should be applied just prior to the frosting or icing event. Fixed Automated Spray Technology (FAST) systems aim to deliver anti-icing chemicals to key locations in a con- trolled manner, using pumps, piping, valves, and nozzles or discs (Zhang et al. 2009). They can reduce usage of chlo- ride roadway deicers through effective and uniform appli- cation and through better management of problem areas in the roadway network. As an anti-icing strategy, it reduces the chemical usage by applying the chemical âjust in timeâ (Pinet et al. 2001). Ideally, the application should be fully automated, using pre-programmed logic and real-time input from a number of atmospheric and pavement sensors on- site. Once the sensors detect ice presence or an imminent frost or icing event, the nozzles will be automatically trig- gered to spray the liquid chemical at predetermined rate and pattern, as shown in Figure 16. FAST has emerged as an important tool to enable proactive winter maintenance and to supplement mobile operations by providing effec- tive service delivery to high-risk locations. It aims to reduce crashes resulting from icy pavement and reduce the amount of labor and materials needed through timely prevention of ice formation/bonding or snow packing, with indirect ben- efits such as reduced corrosion and environmental impacts and reduced traveler delay and stress. The anticipated ben- efits from FAST systems are site-specific, as a function of winter weather severity, traffic density, accident history, and distance from maintenance yards, among other factors (Ye et al. 2013). FIGURE 16 A FAST system on a bridge in action (Pinet et al. 2001). In principle, FAST systems are to be deployed at locations that are remote, feature high traffic density and significant congestion, or are a considerable safety risk during wintery weather (Ye et al. 2013). FAST is not a solution for the entire road network, but rather for the following key locations where it can derive the maximum benefits (Pinet et al. 2001): â¢ A new structure with a history of accidents. â¢ High vehicle volume and/or key route. â¢ High speed ramp of rural freeway. â¢ Prevailing winds at most time ran across structure. â¢ Remote location of structure relative to dispatch loca- tion, not in same micro-climate. â¢ Structure prone to icing earlier and more often than interconnecting segments. Experience with FAST systems in North America and Europe has revealed a mixed picture. Since the mid-1980s, hundreds of automated anti-icing systems have been used throughout Europe as an established tool to battle snow and ice conditions on highways, bridges, and airports. In North America, FAST is a relatively new technology that has gained popularity since the late 1990s (SICOP 2004). Several stud- ies have indicated reductions in mobile operations costs and significant reductions in crash frequency, resulting in favor- able benefitâcost ratios. Yet activation frequency, system maintenance and training problems have been reported. On balance, North American transportation agencies consider FAST to be an evolving technology (Ye et al. 2013). The success of the FAST systems has to do with the appropriate choice of location, having a knowledgeable and dedicated staff, monitoring, and conducting maintenance. As of 2003,
44 23 states either had FAST systems or were planning to install them (Zwahlen et al. 2003). A survey conducted by Shi and colleagues, however, revealed that transportation agencies in North America were not planning to expand their number of FAST installations (2007a). Research conducted by Birst and Smadi (2009) for the North Dakota DOT documented how its two installed FAST systems performed relative to other bridge deck treatments and analyzed the benefits and costs of the sys- tems. Both FAST systems were installed in the Fargo Dis- trict and it was found that they required a steep learning curve. For this reason, vendor support was critical during the first winter season. The users favored the FAST sys- tem, especially under frost conditions (which often occur outside of normal operating hours), and are satisfied with the systemsâ ability to treat freezing conditions. The FAST systems were estimated be 95% reliable for spraying at the appropriate time with the proper application rate and system pressure. The averaged crash reduction for the two FAST sites was 50%, and the FAST implementation allowed one site to be removed from a high-crash location list (with site crash reduction rate of 66%). The benefit-cost analysis for both FAST sites were favorable with ratios of 4.3 ($1,257,869 net benefit) and 1.3 ($675,184 net benefit), respectively. A FAST system installed by the Maryland DOT in the 1998â99 winter season, which sprayed a mix- ture of calcium magnesium acetate and potassium acetate, was considered a major success, as it reduced accidents on the bridge by approximately 40% and led to cost savings of $16,000 resulting from avoided mobile operations (Lipnick 2001). For three remotely activated FAST systems installed at various sites in the Minnesota DOT roadway network, the number of winter weather-related accidents dropped 82% from the 18 to 24 months before the FAST installa- tions to a similar period after (Keranen 2000). FAST is not an âoff-the-shelfâ system that can be pur- chased and installed right away at any given site. Custom- ized design of the installation (e.g., spray logic) at each site after studying the site specifics and conditions is suggested (CERF 2005). The FAST systems have been found to not spray when wind speed is greater than 15 mph and when pavement temperature drops below 12Â°F (Birst and Smadi 2009). Previous studies have documented preventive main- tenance requirements for FAST, and these cover before-sea- son, during-season, and after-season inspection and services needed for the FAST system to work properly (Barrett and Pigman 2001; Roosevelt 2004). Additional Resources for FAST Barrett, M.L. and J.G. Pigman, Evaluation of Automated Bridge Deck Anti-icing System, Kentucky Transportation Cabinet Research Report #KTC-01-26/KH36-97-1F, Frank- fort, 2001. Bell, G.T., W.A. Nixon, and R.D. Stowe, A Synthesis to Improve the Design and Construction of Coloradoâs Bridge Anti-Icing Systems, Final Report No. CDOT- DTD-R-2005-19, Colorado Department of Transportation, Denver. 2006 [Online]. Available: http://www.coloradodot. info/programs/research/pdfs/2005/fast.pdf/view. Birst, S., and M. Smadi, Evlauation of North Dakotaâs Fixed Automated Spray Technology Systems, Upper Great Plains Transportation Institute, North Dakota State Univer- sity, Fargo, Oct. 2009 [Online]. Available: http://www.ugpti. org/pubs/pdf/DP219.pdf. Decker, R., Automated Bridge Deck Anti- and Deicing System, NCHRP IDEA Project 27 Final Report, Transporta- tion Research Board, National Research Council, Washing- ton, D.C., 1998 [Online]. Available: http://onlinepubs.trb. org/onlinepubs/archive/studies/idea/finalreports/highway/ NCHRP027_Final_Report.pdf. Friar, S. and R. Decker, âEvaluation of a Fixed Anti- icing Spray System,â Transportation Research Record 1672, Transportation Research Board, National Research Council, Washington, D.C., 1999, pp. 34â41. Johnson, C., I-35W and Mississippi River Bridge Anti- icing Project: Operational Evaluation Report, Report # 2001-22, Office of Metro Maintenance Operations, Minne- sota Department of Transportation, St. Paul, 2001. Snow and Ice Pooled Fund Cooperative Program (SICOP), Fixed, Automated Anti-icing Spraying Systems, SICOP, AASHTO, Washington, D.C., 2004. Waldman, J.R., Transportation Research Circular E-C063: State-of-the-Art Fixed Automated Spray Technol- ogy, Sixth International Symposium on Snow Removal and Ice Control Technology (04-001), Spokane, Wash., June 7â9, 2004, pp. 379â390 [Online]. Available: http://onlinepubs. trb.org/onlinepubs/circulars/ec063.pdf. Ye, Z., J. Wu, N. El Ferradi, and X. Shi, âAnti-icing for Key Highway Locations: Fixed Automated Spray Technol- ogy,â Canadian Journal of Civil Engineering, Vol. 40, No. 1, 2013, pp. 11â18. THERMAL DEICING METHODS Thermal deicing methods, also known as heated pavement technologies, aim to prevent ice formation or to facilitate snow and ice removal. They can reduce usage of chloride roadway deicers and contribute to better management of problem areas in the roadway network. Depending on the relative location of heating source to the pavement, they can be classified as internal heating [e.g., geothermal heat pumps (Seo et al. 2011),
45 electrical resistive heating (Yehia and Tuan 1998; Yehia et al. 2000; Chang et al. 2009; Yang et al. 2011)] and external heating (e.g., microwave and infrared heating). Infrared heat lamps and insulating bridge deck with urethane foam were attempted but found to be ineffective (Axon and Couch 1963; Zenewitz 1977). Geothermal Heating Geothermal energy has been used to melt ice and snow on roads, sidewalks, bridges, and other paved surfaces for years in locations around the world. Either heat pipe technolo- gies or direct geothermal hot water can be used to heat the pavement. Because of the limited number of geographical locations with geothermal fluids above 100Â°F, the heat pipe technology is used more commonly in the United States. The costs of different geothermal heating technologies are in ascending order as follows: geothermal snow melting without heat pump (around $20/ft2), ground source heat pumps ($35/ft2 for typical highway bridge deck systems), and âhydronicâ geothermal heating system. Total costs for the deck and heating system generally range from $100 to $150/ft2. This high cost has limited its usage to only critical areas such as bridge decks and airports (Lund 2000). A system that combines the geothermal energy and sum- mertime solar energy, known as the Gaia Snow-melting Sys- tem, was introduced and evaluated in Japan for melting snow (Morita and Tago 2000). The system utilizes the geothermal energy from the shallow ground and its auxiliary solar energy in the summer; when it was first installed in Ninohe, Iwate Prefecture in 1996, it was found to be effective in snow/ice melting and environmentally benign even under low tempera- tures for the month of January [averaging â8.3Â°C (17Â°F)]. Yas- ukawa (Institute for Geo-Resources and Environment 2007) summarized the advantages of geothermal heat pump appli- cation of Gaia System: reduced consumption of fossil fuels (and thus less CO2 emission), reduced consumption of elec- tricity with higher coefficient of performance, and reduced urban heat island effect with heat exhaust into underground. Hiroshi (1998) reported the implementation of a snow melt- ing technology utilizing tunnel spring water and hot spring water on a highway through the Abo Pass, where the average minimum temperature is around â18Â°C (â0.4Â°F) during the previous 5 years with average annual accumulated snowfall depth of 500 cm (16.5 ft).They concluded that such systems present a practical method to melt snow where sufficient ther- mal energy and a large site are available. This is based on their higher construction costs (1.15 to 1.24 times the cost of con- ventional, electric-powered road heating) and lower operating costs (22% to 46% of the conventional systems). Electrical Conductive Concrete As detailed in Table 5, a comparison of conductive concrete technology against other deicing technologies in the litera- ture revealed its potential to become the most cost-effective approach in the future (Kiljan 1989). Electrically conductive concrete is made by adding electrically conductive compo- nents to a regular concrete mix to attain stable electrical con- ductivity of the concrete. A thin layer of conductive concrete can generate enough heat because of its electrical resistance, and can be utilized to prevent ice formation on the pavement surface when connected to a power source. The conductive concrete includes two types: (1) conductive fiber-reinforced concrete and (2) concrete containing conductive aggregates. Each type has its own advantages and limitations. Recent advances in this field include electric roadway deicing sys- tems featuring the use of carbon nanofiber paper (Zhou et al. 2012) or carbon/glass fiber hybrid textile (Song 2012). These new materials have yet to be field evaluated but claim to offer enhanced electrical conductivity, improved heating capacity at low voltage, uniform and rapid heating, reliable performance, low cost, and/or improved service life. TABLE 5 COMPARISON OF DIFFERENT DEICING SYSTEMS Deicing System Initial Cost* Annual Operating Cost* Power Consumption Automated Spray System, 2004 $600,000 $12,000 Not applicable Electric heat- ing cable, 1961 $54/m2 $4.8/m2 323â430 W/m2 Hot water, 1993 $161/m2 $250/storm [76 mm snow] 473 W/m2 Heated gas, 1996 $378/m2 $2.1/m2 Not available Conductive concrete, 2003 $635/m2 $0.80/m2/storm 350 W/m2 Source: Kiljian (1989). *Cost figures were quoted directly from literature, and conversion to present worth was not attempted. A bridge deicing system implemented with conductive concrete deck was under evaluation from 2003 to 2008. Car- bon and graphite products (instead of steel shavings) were used in the conductive concrete mix design. In the storm events, an average of 500 W/m2 (46 W/ft2) was used to raise the slab temperature 16Â°F above the ambient temperature by the conductive concrete. The total construction cost of the bridge deicing system was $193,175. The cost per unit surface area of the conductive concrete inlay was $59/ft2. The operating cost of the deicing system was about $250 per major snow storm (Tuan 2008). The author stated that âthe most challenging task in the mix design was to achieve the long-term stability of the electrical conductivityâ¦ The use of high voltage and high current causes a safety concern.â The conductive concrete pavement technology has also found its application to airport runways. One such system was installed and operated at OâHare International Airport (Der-
46 win et al. 2003). The electrically conductive asphalt pavement used a unique blend of graphite, asphalt, and electricity to heat the runway surface and break the ice bond to pavement. It was installed and operated at the airport for 4 years since Novem- ber 1994. The installation costs were at $15/ft2. The conductive asphalt showed similar durability as regular asphalt concrete and âconsistently melted snow in all but the most severe condi- tions.â It was able to increase the pavement temperature 3Â°F to 5Â°F per hour as designed. The system was effective even when temperatures went down to â10Â°F in one of the winter seasons. Its ability to increase the pavement temperature 22Â°F confirmed its effectiveness in the extremely cold weather. Alternative Heating (Solar, Wind, Microwave, and Infrared) To further reduce the energy consumption by snow removal equipment and to overcome the problems associate with other methods, snow melting systems using natural energy have been under development in Japan. Many renewable heat sources can be used to heat the pavement such as solar energy and wind energy. Hiroshi (1998) outlined a number of snow melting systems using natural heat sources in Japan. The approaches include utilizing underground water sources or steam, storing heat underground and circulating it under pavements, and using electricity produced by wind power. Relative to electrical resis- tive heating systems, such systems entail relatively high capital cost, the savings are expected from reduced maintenance cost (energy savings) as well as environmental conservation. For microwave and infrared heating, limited technical information is available in the published domain and the knowledge is still lacking on their performance and cost- effectiveness (Long 1995; Hopstock and Zanko 2005). The infrared heaters can be mounted on a truck or on the bridge- side structures to provide heat from the lamps to melt the snow and ice on the pavement or bridge deck. Switzenbaum et al. (2001) described its application on aircraft. Microwave heating shares the similarities in the installation of infrared heaters and can be mounted on a truck or on the bridge-side structures (Johnson 2006). Additional Resources for Thermal Deicing Methods Federal Highway Administration (FHWA), Heated Bridge Technology, Report on ISTEA Sec. 6005 Program, FHWA- RD-99-158, FHWA, Washington, D.C., July 1999 [Online]. Available: http://www.fhwa.dot.gov/bridge/hbrdeck.pdf. Joerger, M.D. and F.C. Martinez, Electric Heating of I-84 in Ladd Canyon, Oregon, Final Report, SPR 304- 461, prepared for Oregon Department of Transportation and FHWA, June 2006 [Online]. Available: http:// www.oregon.gov/ODOT/TD/TP_RES/docs /Reports / LaddCanyonHeatingProject.pdf?ga=t. Joerger, M.D. and F.C. Martinez, Oregon Depart- ment of Transportation Region 5 Ladd Canyon Heating Project. Electric Heating of I-84 in Ladd Canyon, 2007 [Online]. Available: http://www.oregon.gov/ODOT/HWY/ REGION5/ladd_canyon.heating.shtml. Johnson, G., âSmart Roads Can De-ice Itself: Pavement Overlay Releases Chemical in Bad Weather,â Calgary Herald, 2006. NCHRP Research Results Digest 204: Winter Mainte- nance Technology and PracticesâLearning from Abroad, Transportation Research Board, National Research Council, Washington, D.C., 1995, 15 pp. Spitler, J.D. and M. Ramamoothy, âBridge Deck Deic- ing Using Geothermal Heat Pumps,â In Proceedings of the Fourth International Heat Pumps in Cold Climates Confer- ence, Alymer, Quebec, 2000. Switzenbaum, M., et al., âBest Management Practices for Airport Deicing Stormwater,â Chemosphere, Vol. 43, 2001, pp. 1051â1062. Tuan, C.Y. and S.A. Yehia, Transportation Research Circular E-C063: Implementation of Conductive Concrete Overlay for Bridge Deck Deicing at Roca, Nebraska, Sixth International Symposium on Snow Removal and Ice Con- trol Technology (04-002), Spokane, Wash. June 7â9, 2004, pp. 363â378 [Online] Available: http://onlinepubs.trb.org/ onlinepubs/circulars/ec063.pdf. Yehia, S. and C.Y. Tuan, âBridge Deck Deicing,â Trans- portation Conference Proceedings, 1998.
47 CHAPTER SIX CONCLUSIONS rate, infiltrate, or be absorbed. Table 7 summarizes the infor- mation on the reactive strategies presented and major pros and cons for each. The following effective practices were iden- tified in the literature review and confirmed by practitioner surveys: infiltration trenches and basins, detection/retention/ evaporation ponds, wetland and shallow marshes, vegetated swales, and filter strips. All were designed to reduce velocity and improve the quality of the highway stormwater runoff. The vast majority of the reactive strategies identified were not originally installed for this purpose, and their cost-effective- ness for deicer environmental management is yet to be exam- ined and validated. For deicer environmental management, reactive strategies may vary, and they need to be designed, sited, installed, and maintained properly. The reactive strate- gies may be used individually or synergistically, and a com- bination of reactive strategies is suggested to enhance overall performance, increase service life, and preserve downstream water bodies. Great care must be exercised to ensure their effective function in cold regions, especially during the win- ter and spring months. If necessary, the design could be modi- fied to accommodate site-specific needs. This synthesis also presented information on recent advances in methods, techniques, or tools used to mitigate the impacts of chloride roadway deicers on the natural envi- ronment, with a focus on proactive strategies. Five new and emerging technologies were identified through the literature review and the practitioner surveys: synchronizing vehicle location and other sensor technologies, maintenance decision support systems (MDSS), fixed automated spray technol- ogy, thermal deicing methods, and innovative snow fences. Most technologies presented here are not ânewâ to winter maintenance but instead have been recently implemented. Interviews with selected survey respondents provided information on identified effective practices. These were made into case examples on the following topics: closed loop controllers, needle browning, snow disposal and melt- ing, and making salt brine from recycled vehicle wash bay water. Case examples can be found in Appendix B. SUGGESTIONS FOR FUTURE RESEARCH A significant body of information about proactive and reactive tools, techniques, and methods used to mitigate the impacts of CONCLUSIONS This synthesis presented information on environments at risk of impacts from chloride roadway deicers, and mitigation techniques used to reduce the impacts of chloride roadway deicers on the natural environment including the surrounding soil and vegetation, water bodies, aquatic biota, and wildlife. Many of the identified techniques could also apply to mitigat- ing the impacts of abrasives and non-chloride-based roadway deicers. Information was presented on proactive strategies, reactive strategies, and new and emerging technologies. The survey responses and the literature identified reactive miti- gation strategies used to reduce the effects of chloride once it reaches the environment. Many of these strategies were designed for and are frequently used in stormwater manage- ment and to transport chlorides from sensitive areas to non- sensitive areas for treatment, as it is difficult to truly treat chlorides or remove chlorides from the environment. Proactive mitigation strategies are currently the most commonly used methods for reducing the footprint of chlo- ride roadway deicers. Proactive strategies entail preventative measures designed to reduce the amount of chloride deic- ers entering the environment, which can reduce the need for or dependence on reactive strategies. Table 6 summarizes the information on the proactive strategies presented and major pros and cons for each, based on information gathered from the literature review and survey. The following effec- tive practices were identified in the practitioner surveys: salt management plans, staff training, monitoring and record keeping, anti-icing/deicing/pre-wetting practices, weather forecasting and Road Weather Information Systems, equip- ment technologies, vehicle-mounted spreaders, roadway design, vegetation management, and road maintenance yard design and operations. These practices contribute to the ulti- mate goal of facilitating or enabling effective and efficient use of resources so as to apply the right type and amount of materials in the right place at the right time for snow and ice control. Most methods, techniques, and tools can be used alone, paired in a series, or integrated to form a proactive mitigation effort. Reactive strategies aim to reduce the impacts of chloride deicers once they are in the environment. They are typically implemented along the roadside to physically trap salt-laden stormwater runoff and to allow pollutants to settle out, evapo-
48 chloride roadway deicers on the natural environment is avail- able in the literature and in practitioner experience. There are still significant knowledge gaps where additional research or development is needed. For instance, there is an apparent need for further research in the design options, performance, and cost-effectiveness of reactive strategies for managing the footprint of chloride roadway deicers. There is also a lack of knowledge regarding the fate and transport of relevant pollutants (e.g., deicers, anti-icers, additives) in soil, vegetation, or water bodies, whereas such knowledge is much needed to guide the design, monitoring, and evaluation of reactive strategies in treating chloride- laden roadway runoff and minimizing potential damage to the receiving environment. Existing studies focused on dynamics in either a laboratory setting or an actual field setting; however, the former lack the field variables and the latter produce only site-specific results with limited transfer- ability. Such research should be conducted in a controlled field environment where a comprehensive test program can be formulated to examine selected processes or to test sig- nificant hypotheses. TABLE 6 SUMMARY TABLE OF IDENTIFIED PROACTIVE STRATEGIES WITH PROS AND CONS
49 The synthesis identified some knowledge gaps. Research recommended to fill those knowledge gaps includes the following: Fundamentals â¢ Investigate the negative impacts of abrasives on air quality, waterways, and the need for chlorides, etc. â¢ Investigate the benefits and risks of using liquids for anti-icing and deicing. â¢ Investigate how the presence of natural sunlight (vs. shaded areas) on a roadway affects needed salt applica- tions, and how removing trees along a road may let in more sunlight and reduce the need for deicers. â¢ Investigate the cost-effectiveness of various chemicals used for pre-wetting. â¢ Investigate the cost-effectiveness of products based on agricultural derivatives and whether they can reduce environmental impacts. Monitoring â¢ Develop a mobile salinity meter to assess residual chlo- ride left on the pavement (from previous applications) to mitigate the need to place more material down dur- ing a storm. â¢ Determine how salt-tolerant vegetative species estab- lish in areas of high salt use and monitor plant species and salt concentrations over time. â¢ Investigate chloride loading in roadside soils by prox- imity to the paved surface and how far the impact of chloride loading extends in roadside soils as a function of average annual usage of deicers. â¢ Monitor salt levels in soils around patrol yards. â¢ Monitor the effectiveness of salt management plans in protecting and preserving the natural environment (watercourses, groundwater, vegetation, etc.). Strategies â¢ Update the FHWA guidelines for anti-icing and deic- ing so as to establish appropriate application rates to achieve an acceptable level of service (LOS) (e.g., mea- sured by friction coefficients). â¢ Investigate the concept, feasibility, and implementation of incentive programs for more efficient winter main- tenance practices or technologies that reduce chloride deicer usage. An example involved the Massachusetts Department of Transportation (DOT) rewriting speci- fications on equipment and providing a financial incen- tive to private contractors that complied with the new specification before it became mandatory. â¢ Determine the minimum amount of chloride needed to maintain critical interstate highways at an extremely high LOS, including at a âwetâ condition throughout light to moderate snowfall. This would be based on current and future weather and pavement conditions, the data of which can be available in a MDSS-type application. â¢ Develop a written guide to the efficient use of road salt and chloride brines. â¢ Research the use of plants that can absorb salt from the roadside and be used as wildlife cover or harvested for use as a biofuel, and balance that with the potential risk of attracting wildlife to roadways. â¢ Identify performance measures for environmental and nonenvironmental winter maintenance operations that are feasible to measure and quantify. Technology â¢ Develop an affordable pavement friction course that prevents bonding of snow and ice without the use of chemicals. â¢ Develop an MDSS-type weather service that monitors pavement conditions and recommends accurate mate- rial rates based on those conditions. â¢ Research better chemical products, as new technolo- gies of modified salts would reduce the amount needed for performance and may be made of less corrosive chemicals. TABLE 7 SUMMARY TABLE OF IDENTIFIED REACTIVE STRATEGIES WITH PROS AND CONS
50 â¢ Develop improved sensors that measure parameters relevant to winter maintenance (e.g., pavement tem- perature, relative humidity, dew point, salinity). â¢ Develop a performance standard and winter severity index for MDSS. â¢ Investigate the effectiveness of spreading technologies. â¢ Improve thermal road mapping to simulate road tem- perature characteristics and assist highway supervisors in coordinating deployment of staff and materials. In light of the literature review, continued research and monitoring are necessary before the short- and long- term environmental impacts of many deicers can be bet- ter understood and mitigated. Performance parameters for both proactive and reactive strategies can be easily defined, but are more difficult to measure. Further investigation into measurement methods for performance parameters is warranted. Currently, results-based standards are common practice for many DOTs and highlight the success of many programs. To develop results-based standards, reliable data are needed from record-keeping and other sources. Many DOTs would benefit from the development of a stream- lined data collection and record-keeping system, which would enable the winter maintenance managers to assess the effectiveness of given strategies or practices in deicer environmental management and to help implement results- based standards. Accountability of salt use is an issue that some DOTs have taken on indirectly, as a result of tighten- ing budgets. Another way in which DOTs have incorpo- rated accountability into their programs is through the use of truck sensors and automatic vehicle location technology to track salt usage. This is an example of utilizing results- based standards to modify the approach to winter road maintenance practices.
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