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8C H a P T E r 1 1.1 Statement of Project Need and Objectives 1.1.1 Statement of Need Departments of transportation (DOTs) are faced with increasing regulatory standards and environmental chal- lenges that mandate better stormwater quality management outcomes, often with limited funding. Best management practices (BMPs), both nonstructural practices and struc- tural treatment systems, play a key role in the DOTâs ability to comply with the Clean Water Act (CWA) and protect water resources in the environment. Structural BMPs remove pollutants from stormwater run- off, and they are always something less than 100% effective. Nonstructural BMPs prevent the contact of pollutants with stormwater, so they can be more effective for the source they are implemented for. Nonstructural BMPs have the potential to provide the best opportunity to prevent and reduce pollution in highway runoff for many pollutants of concern. However, there is little documentation quantifying the effectiveness of nonstructural BMPs or discussing implementation and the operational challenges of their implementation. It is also important to understand basic implementation variables of nonstructural practices so the practitioner can ensure that maximum benefit is being achieved from the BMP. Treatment BMP selection involves a variety of assessments by the practitioner, including the pollutant of concern, physical site constraints, site access, climate, and operation and maintenance (O&M) requirements. Long-term data from the International Stormwater BMP Database and other resources can provide insight on BMP performance, but there is less information on how BMP effectiveness is affected by physical, chemical, biological, and thermal influences; maintenance; and opera- tional practices. Further, the life-cycle cost and service life of most treatment controls are unknown and variable, making it difficult for a DOT to budget for long-term O&M of installed devices. Some DOTs have learned valuable lessons regarding real-world challenges to BMP implementation and opera- tion. This information was gathered as a part of the literature review and DOT survey for this project. DOTs are developing better means for data analysis and reporting that can be used to leverage limited resources in the face of increasing National Pollutant Discharge Elimina- tion System (NPDES) permit requirements. Regulatory rules and programs such as total maximum daily loads (TMDLs), 401 certifications, and other requirements, including the Endangered Species Act and Comprehensive Environmen- tal Response, Compensation, and Liability Act (CERCLA) projects, especially those associated with cleanups of legacy- contaminated sediments, require significant record keeping and documentation of performance. There are fundamental needs for guidance to assist agencies with these challenges, including describing conditions where nonstructural BMPs can achieve maximum benefit in a highway environment for program-level measures and providing information to assist the practitioner in evaluating treatment BMPs on a project- specific basis using performance and cost information. The stormwater management field is rapidly evolving, and new and better data are being developed. The information pro- vided in this report is current as of the date of publication, but the practitioner is encouraged to review new sources of data as they become available. The performance and cost information provided herein should be continuously refined by the user to maintain a contemporary stormwater assessment tool. 1.1.2 Objectives The objective of this report is to provide information that will allow the practitioner to optimize the BMP elements (non- structural and treatment) of a DOT stormwater program. This objective is achieved for nonstructural measures by describing the BMP, its applicability, targeted pollutants, variables that are important for implementation, implementation barriers, and effectiveness. A general discussion of costs is also provided. Introduction
9 For treatment BMPs, this guidance provides an evaluation tool for assisting in their selection and determining whole life costs of treatment, including the following information: ⢠BMP performance metrics; ⢠Comparative service life and long-term BMP effectiveness for enhancing water quality for typical highway runoff constituents; ⢠Life-cycle costs based on capital investment, maintenance, and operational expense data; and ⢠Constituent removal performance. The companion tool to this document is provided on the accompanying CD-ROM in a spreadsheet format that facili- tates the comparison of treatment BMPs by the practitioner. The tool may be customized by the practitioner to include local performance and cost data, or the tool default values may be used. 1.2 Scope of Report Research for the project consisted of a literature review as well as surveys and interviews with DOT staff in all 50 states to determine DOT practices for BMPs and identify applica- ble grey literature that would support the objectives of the study. A precursor survey of DOTs found that they had very little actual data on life-cycle or maintenance costs of BMPs to guide BMP selection or budgeting, so individual outreach and discussions on the topic were deemed critical. Therefore, greater time was focused on discussions with DOTs com- pared to the literature review. The research team developed survey questions to address the project objectives. Questions were tested and refined with various state DOT maintenance managers, NPDES program managers, and hydraulics program leads to help focus the questions and maximize their pertinence and applicability to DOTs. The literature review was multifaceted and involved consul- tation with the team members as well as colleagues at research organizations and universities in the United States and abroad. Information was sought through inquiries to DOTs, via web literature searches, on the DOT Google search engine, through the University of Texas library system, and in consultations with contacts at universities, other research institutions, and TRB committees, especially the TRB Committee on Hydrology, Hydraulics and Water Quality (AFB60). Information for nonstructural BMPs was developed from published studies, grey literature, and consultation with DOTs. The definition of nonstructural BMPs for a DOT stormwater program for this study differs somewhat from that associated with traditional development and municipal separate storm sewer system (MS4) stormwater programs. In the development context, nonstructural BMPs are commonly defined as the use of natural area conservation and buffer areas, disconnection of impervious surfaces, limited clearing of native vegetation, and minimizing the use of impervious surfaces. Highway standards dictate the extent to which these design practices can be implemented in roadway projects. Accordingly, this study focuses on operational nonstructural BMPs, reflecting the primary DOT need to manage existing infrastructure. The information was formatted in the general categories noted previously for comparability between the practices. The following nonstructural practices were evalu- ated as a part of this study: ⢠Storm drain cleaning, ⢠Street sweeping, ⢠Smart landscaping practices, ⢠Trash management practices, ⢠Elimination of groundwater infiltration, ⢠Slope and channel restoration, ⢠Winter maintenance BMPs, and ⢠Irrigation runoff reduction practices. The BMPs listed are common nonstructural BMPs for a DOT stormwater program. Information for treatment BMPs was derived from DOT studies and the International Stormwater BMP Database. The International Stormwater BMP Database contains perfor- mance records for treatment BMP evaluations throughout the United States. The BMP database is an important resource allowing the development of relationships between storm- water influent and effluent quality for a specific BMP type. The information in the database was reviewed for basic data quality, and BMP evaluation studies that were incomplete or did not meet basic quality objectives were not included in the analysis. Although many of the records in the database are for studies completed outside of the highway environment, the information is applicable to highway BMPs for the range of influent qualities that are consistent with highway data. An important component of BMP performance is pollut- ant load reduction due to infiltration. Very few studies (in the database or completed by DOTs) document infiltration losses or provide information on pollutant load reduction through this mechanism. Further, measuring load reductions asso- ciated with infiltration is difficult. Identifying volume loss through a BMP requires careful measurement of influent and effluent volumes. Flow measurement for the wide range of discharge inflows that a BMP can experience during a storm event is technically daunting, and data quality is variable. To overcome the lack of high-quality load reduction data available for treatment BMPs, the hydrologic/hydraulic pro- cesses contributing to average annual BMP performance were accounted for using long-term continuous simulation via
10 the U.S. Environmental Protection Agency (U.S. EPA) Storm Water Management Model (SWMM). SWMM simulation results were coupled with BMP performance data to provide a consistent estimate of potential BMP load reduction per- formance in the BMP Evaluation Tool. The BMP Evaluation Tool consists of seven individual spreadsheets for the follow- ing BMPs: ⢠Vegetated strips, ⢠Vegetated swales, ⢠Dry detention basins, ⢠Bioretention, ⢠Retention/wet ponds, ⢠Sand filters, and ⢠Permeable friction course (PFC). The performance of BMPs will vary somewhat with geo- graphic location. This is due to variability in rainfall patterns, the pH of rainfall, soil chemistry, and forms of chemicals from local pollution sources. However, the primary variables in BMP performance are rainfall-runoff characteristics, influent quality, the size and dimensions of the BMP, and the unit treat- ment processes (i.e., sedimentation) provided by the BMP. Accordingly, the BMP Evaluation Tool allows the users to input local values for the primary site-specific variables and accept or override various defaults developed from national data and common BMP design guidance. The performance of BMPs may also vary by season, though sufficient infor- mation does not exist to quantify this difference. The tool reports average BMP performance over the time span of the prototype studies. The user is cautioned that the tool is not intended to be a BMP sizing tool. Instead, it is intended to allow a user to evalu- ate the average annual performance of a BMP that is sized according to local stormwater management requirements. Hence, the tool could be used to inform the potential revision of BMP sizing criteria. Capital cost information for the BMPs was developed using a unit price approach. Construction items were quantified on a per-unit basis, with unit prices referenced to those provided by RS Means publications. The default cost information can be adjusted using local data or regional cost information. O&M costs were estimated based on DOT studies that reported hours spent maintaining the BMPs, which were applied to maintenance crew costs and equipment required as a part of the maintenance task. Maintenance tasks have been defined for each BMP, and the frequency of the mainte- nance placed in three general categories to reflect the main- tenance level at various locations throughout the United States. Areas with higher rainfall rates could generally expect to have more frequent BMP maintenance requirements due to the increased runoff volume treated and higher vegetation growth rate. However, the frequency of maintenance will be partially affected by site-specific requirements, and the practitioner can compare the description of the three main- tenance levels to determine the one that is most consistent with the DOT standard. The whole life cost estimates assume a life span for each BMP. The BMP life span was estimated by determining the useful life of the major components. When major compo- nents need to be replaced, it is appropriate to assume that the entire BMP must be reconstructed. The life span of each BMP varies, and it was used to recapitalize the facility as an input to the whole life cost calculation. The cost information and guidance provided herein applies specifically to BMPs that are retrofit into existing DOT infra- structure as part of a highway improvement project. This is because the Interstate highway system is largely already con- structed, and DOTs are faced with NPDES permit compliance in part through water quality retrofit. Costs for stand-alone retrofit projects would be higher than indicated in the tool due to fixed costs such as traffic control that cannot be spread over other work items. Performance of BMPs of the same type and size is independent of whether a BMP has been installed as a part of new construction or as a stand-alone retrofit. The costs provided in this report and the BMP Evaluation Tool represent retrofit costs as part of a larger project; the prac- titioner is free to replace the default cost data with data that best reflect the condition of construction of the BMP. Retrofit of treatment BMPs, as well as enhanced installation of nonstructural and source control BMPs, will be important as DOTs continue to meet NPDES permit requirements and TMDL obligations and implement programs to ensure the protection of beneficial uses of receiving waters consistent with the goals of the CWA. 1.3 Intended Users and Uses The results of this project are intended for use by DOT prac- titioners at both the programmatic and project level. Results derived from the BMP Evaluation Tool and information in the report can be used to develop BMP plans at a watershed as well as project-specific scale. They can also be used to guide inspection and maintenance practices, asset manage- ment decisions, data gathering, and reporting practices. The average annual O&M cost information will be important to assist DOTs in programming resources to ensure that they are adequate to maintain the treatment systems. The capital cost information can be used to forecast the BMP portion of capi- tal cost budgets. The information provided for nonstructural BMPs can be used to assist DOTs in refining the implementation of non- structural measures in their stormwater programs. Success- ful implementation of nonstructural BMPs depends in part
11 on variables that the user controls, such as the speed of the sweeper for roadway sweeping activities. The information in this report will assist the practitioner in improving the performance of nonstructural BMPs through more targeted implementation. The use of nonstructural BMPs is intended as a complement to treatment BMPs. The practitioner must determine the level of resources that are to be shared between the two that will result in a stormwater program with the high- est performance for the lowest cost. The information pro- vided in this report on nonstructural (source control) BMPs will assist the practitioner in making this determination. 1.4 Relationship with Other NCHRP Publications This project was intended to build on the information provided within NCHRP publications from other projects. Depending on the readerâs needs, those resources should be consulted in conjunction with the information provided here. Other NCHRP publications that relate to the selection of highway BMPs are: 1. NCHRP Report 565: Evaluation of Best Management Prac- tices for Highway Runoff Control provides the practitioner with information regarding BMP types, treatment unit processes, highway stormwater runoff characteristics, and guidance on treatment control selection based on per- formance data, hydrologic factors, and site constraints. Recommendations are provided for BMP design and implementation, monitoring, and water quality modeling (Oregon State University et al., 2006). 2. NCHRP Report 728: Guidelines for Evaluating and Selecting Modifications to Existing Roadway Drainage Infrastructure to Improve Water Quality in Ultra-Urban Areas presents focused research on the physical characteristics and asso- ciated water quality conditions of highways within the ultra-urban environment. This report offers the reader guidance on BMP selection based on cost, performance, and maintenance considerations along with information related specifically to retrofit practices. Case studies and lessons learned that illustrate the subject matter are pro- vided (Geosyntec Consultants et al., 2012). Other NCHRP reports, although not directly related to the selection of water quality BMPs, offer potentially relevant information pertaining to highway water quality impacts, mitigation strategies, or general issues relating to highway costs, maintenance, asset management, or research implementation: 1. NCHRP Report 688: Determining Highway Maintenance Costs (Cambridge Systematics, Inc., et al., 2011). 2. NCHRP Report 640: Construction and Maintenance Practices for Permeable Friction Courses (Cooley, Jr., et al., 2009). 3. NCHRP Report 632: An Asset Management Framework for the Interstate Highway System (Cambridge Systematics, Inc., 2009). 4. NCHRP Report 574: Guidance for Cost Estimation and Management for Highway Projects During Planning, Pro- gramming, and Pre Construction (Anderson et al., 2007). 5. NCHRP Report 474: Assessing the Impacts of Bridge Deck Runoff Contaminants in Receiving Waters (Dupuis, 2002). 6. NCHRP Synthesis 444: Pollutant Load Reductions for Total Maximum Daily Loads for Highways (Abbasi and Koskelo, 2013). 7. NCHRP Report 382: Facilitating the Implementation of Research Findings: A Summary Report (Bikson et al., 1996). 8. NCHRP Report 767: Measuring and Removing Dissolved Metals from Storm Water in Highly Urbanized Areas (Barrett et al., 2013). There are other NCHRP projects recently completed or currently in progress that are similar to this project that may be of value to the reader: 1. NCHRP Project 25-25/83, âCurrent Practice of Post- Construction Structural Stormwater Control Implemen- tation for Highways,â provides a synthesis of practices for post-construction structural stormwater control implemen- tation measures used by state transportation agencies with information regarding selection, design criteria, operation, and maintenance for BMPs. The project includes informa- tion on recent federal or state-level research programs and projects on post-construction stormwater discharge control. 2. NCHRP Project 25-41, âGuidelines for Achieving Vol- ume Reduction for Highway Runoff in Urban Areas,â has the research objective of developing guidelines to reduce the runoff volume from highway facilities in urban areas. The guidelines are divided into two subcatego- ries: (1) methods appropriate for new construction and (2) methods appropriate for retrofit construction. A spread- sheet tool was developed as a part of this project to assist in computing volume loss by treatment practice. The research considers alternative pavement systems, infiltration, and evapotranspiration methods as well as stor- age alternatives. Methods that are deemed to be technically and fiscally viable are refined with detailed design guidance for use by DOTs. Cost analysis methods are developed so DOTs can determine the relative costs between accomplish- ing volume reduction within the right-of-way or partner- ing with other entities to add volume reduction capacity to the developments that highways serve (e.g., commercial/ residential areas, airports, and industrial parks).
12 3. NCHRP Project 25-42, âBridge Stormwater Runoff Analy- sis and Treatment Options,â is an applied research project that provides guidance for assessing potential water quality impacts and selecting BMPs for stormwater runoff from bridge decks and associated vehicle approaches. There is a growing concern that untreated runoff from bridges may be affecting receiving waters even though the bridge deck represents only a small fraction of the impervious area of the highway system, and there is not strong evidence to sup- port the proposition that the quality of bridge deck runoff differs significantly from that of other highway runoff. The cost and environmental benefits of implementing storm- water controls for bridge deck runoff are reviewed, and a procedure is provided for the practitioner to determine the appropriate stormwater management practices for new and retrofit bridge projects. This project provides spreadsheet tools for use in BMP evaluation that are identical to those developed as a part of NCHRP Project 25-40.
