Background: There are numerous guidance documents that provide information on the design and effectiveness of stormwater runoff-management controls to minimize negative effects on water quality. These documents can provide useful information on what management practices are available, but are usually lacking information on when and where to use them and on their expected performance. Only limited information has been compiled on the economics and effective implementation of best management practices (BMPs) for treating runoff, especially, in the highway environment.

The range of treatment options includes the commonly used site-specific practices, but a changing regulatory environment and new management priorities may also require planning at the watershed and sub-basin scales. BMP selection is no longer driven only by water quality criteria. Issues such as life cycle requirements of endangered species and the cumulative impacts of road density are now influencing the permitting process.

To maximize the use of limited resources in transportation agencies and to help agencies comply with regulatory requirements, an improved decision-making process was needed to guide state DOT practitioners on the most economical and effective use of runoff control measures. The focus of this project was on improving the scientific and technical knowledge base for the selection of BMPs and on the improvement of the decision-making process through a better understanding of BMP performance and application.

Objective: The objective of this project was to provide highway practitioners with the scientific and economic information needed for selection and design of best management practices (BMPs) to control highway runoff.

Tasks: Accomplishment of the project objective involved the following tasks.

The scope of this study includes BMPs intended to treat water quality parameters such as (but not limited to) the following:

• nutrients,
• petroleum hydrocarbons and gasoline additives,
• polynuclear Aromatic Hydrocarbons (PAHs),
• metals,
• pathogens,
• pesticides,
• temperature,
• suspended solids, and
• trash and debris.

(1.) Provide a comprehensive list of BMPs (single practice or treatment train) that are suitable for treatment of individual parameters and for combinations of parameters. The information should be presented in tabular format, showing the parameter(s) addressed, principal mechanisms of pollutant constituent removal or reduction, key design elements, significant variables that affect the range of effectiveness, and appropriate application settings. Parameters in combination should be organized into groups that can be treated with similar or common BMPs. Provide references for the source of information on each BMP. Document the results of Task 1 in a technical memorandum to NCHRP. (2.) Based on the best available current information, develop a methodology to evaluate BMPs that would employ criteria such as the following:

• Performance in treating parameters or groups of parameters;
• Design conflicts for parameters (e.g., extended retention of water removes suspended solids yet elevates temperature);
• Level of confidence in the fundamental scientific principles that relate to the design of the BMP;
• Assessment of factors resulting in a variation in performance over time or across different applications of the BMP;
• Range of parameter loadings that can be effectively treated by the BMP;
• Effect of loading timing or sequence, and seasonal variations, over the expected life of the BMP;
• Ongoing maintenance requirements and costs;
• Impacts of conflicts in regulatory requirements (e.g., Endangered Species Act vs. Clean Water Act);
• Installation and life-cycle costs in relation to anticipated benefits; and
• Practicability analysis (influence of other site-specific factors, such as safety and land cost and use, that affect the selection of BMPs).

(3.) Submit an interim report to document the results of Tasks 1 and 2 for review by the NCHRP. The contractor will be expected to meet with the NCHRP panel approximately 1 month later. A methodology for evaluation of BMPs will be approved at this meeting. (4.) After review and approval of the Task 3 report, use the approved methodology to evaluate the BMPs identified in Task 1. (5.) Based on existing information, provide a brief discussion on how the range of typical loadings in specific regions or settings will affect the selection and design of BMPs. (6.) Identify other external drivers at the watershed scale and the sub-basin scale levels (such as endangered species requirements, growth management strategies, and new regulatory requirements) and discuss how they affect the selection of BMPs. (7.) Based on the analysis of best available information collected in Tasks 1 through 6, present recommendations for transportation practitioners on the selection of BMPs for the control of highway runoff. (8.) Identify gaps in information that inhibit the ability to select or design BMPs. Present a recommended future research plan that would address the identified information gaps and enable the development of a practical and user-friendly decision tool for the selection of BMPs. (9.) Submit a final report that documents the entire research effort and provide a companion executive summary that outlines the research results.

In April 2003, the scope of this project was expanded to incorporate issues related to Low Impact Development (LID). The LID component will be combined with the approved working plan on Best Management Practices to form an overall set of guidelines for controlling highway runoff. In doing so, LID treatments designed to control water quantity will complement the water quality issues addressed by most BMPs. The additional work has the following main objectives:

1. Assess the potential effectiveness and suitability of emerging LID design strategies for addressing stormwater impacts from highways. This phase will involve a review and evaluation of the extensive literature on the subject and the facilitation of an LID workshop that will bring together highway and LID professionals to identify proven and potentially successful technologies.
2. Develop a manual of practical LID design guidelines and practices that meet identified regulatory requirements and resource protection goals. Concepts of environmental engineering unit processes and highway design issues will be incorporated into these guidelines in a manner consistent with the BMP evaluations that are associated with the remainder of the 25-20 project.
3. Develop and provide specifications for pilot projects and monitoring in order to evaluate design and construction issues, determine the cost and environmental benefits, and optimize LID techniques for transportation. This effort will be strongly linked to and coordinated with state departments of transportation (DOTs), which we anticipate would actually conduct the monitoring.



Status: Completed

Product Availability: The research results of this study are published as NCHRP Report 565: Evaluation of Best Management Practices for Highway Runoff Control.