The National Academies

NCHRP 25-61 [Active]

Development of On-Bridge Stormwater Treatment Practices

  Project Data
Funds: 500,000
Staff Responsibility: David M. Jared
Research Agency: Geosyntec, Inc.
Principal Investigator: Brian Rowley
Effective Date: 9/14/2020
Completion Date: 9/14/2023

Stormwater treatment of bridge deck runoff continues to be a design challenge. Traditional methods of treating this runoff suggest treating an equivalent area of roadway offsite that discharges to the same receiving water body or piping the bridge deck stormwater to an offsite treatment location. NCHRP_Report_778: Bridge Stormwater Runoff Analysis and Treatment Options concludes that treatment of runoff from a comparable section of highway on land is preferable to treatment of runoff from the bridge deck. Where offsite mitigation is unacceptable due to (1) water quality restrictions placed on the receiving water body or (2) site-specific conditions making the piping of bridge runoff to bridge ends for offsite treatment infeasible or undesirable, stormwater designers have few options for effective on-bridge treatment of stormwater.
There is a growing need to develop more options for on-bridge treatment of stormwater. In addition to NCHRP_Report_778, the following reports provide relevant background on this topic and support the need for further research thereon:
  • NCHRP_Report_767: Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas
  • NCHRP Web-Only Document 265: Field Testing of BMPs Using Granulated Ferric Oxide Media to Remove Dissolved Metals in Roadway Stormwater Runoff (pending)
Research is needed to address on-bridge stormwater treatment challenges, including, but not limited to level of service; structural integrity; hydraulic function (including spread width); litter and sediment loads; freeze-thaw cycles; maintenance operations; and work zone safety.
The objectives of this research are to develop the following:
(1) On-bridge stormwater treatment applications with a focus on retrofitting existing bridges utilizing proven stormwater treatment practices; and
(2) Guidelines for selection (e.g., by media and materials), design, placement, and maintenance of the developed on-bridge stormwater treatment applications. The primary users of these guidelines will be bridge and hydraulic designers.
Accomplishment of the project objective(s) will require at least the following tasks.
Task descriptions are intended to provide a framework for conducting the research. The NCHRP is seeking the insights of proposers on how best to achieve the research objectives. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers’ current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meeting the research objectives.
Task 1. Literature review and proposal of on-bridge stormwater treatment practices for development. Work under this task should be divided into two concurrent subtasks:
Task 1a. Conduct literature review of relevant stormwater treatment practices. Identify treatment mechanisms, including filter media, filter media mixes, and other materials that have demonstrated effective removal of the major classes of highway runoff pollutants from stormwater, with focus on dissolved pollutants. Provide a comparison of long-term pollutant removal efficiency of materials or mixes to hydraulic capacity and cost.
Task 1b: Propose on-bridge stormwater treatment practices for development. With consideration of current treatment practices identified in Task 1a, propose at least three practical on-bridge stormwater treatment practices for development in this project, with at least one involving media filtration. The configurations should (a) be suitable for bridge retrofit scenarios without impacting the structural integrity and serviceability of the bridge; (b) have appropriate hydraulic characteristics for efficient drainage under all climatic conditions; (c) allow for easy access and typical (e.g., annual) maintenance; (d) continue to meet AASHTO spread width criteria if the practice should fail; and (e) use readily available materials approved under state or municipal agency specifications, unless justification for alternative materials can be provided.
Task 2. Submit Interim Report 1. This report shall summarize findings from Task 1, provide hydraulic and structural design assumptions, and provide recommendations on two or more bridge treatment applications for further development. Interim Report 1 shall propose strategies for laboratory testing of water quality and field demonstration of installation and removal. Following NCHRP review of the report, the applications to be developed will be discussed at an interim meeting. NCHRP approval of Interim Report 1 is required before proceeding with Task 3. The interim meeting will be held at TRB offices in Washington, D.C.
Task 3. Develop and test stormwater treatment practices. As a first step, develop a quality assurance project plan (QAPP) for the selected testing strategies from Task 2. The QAPP should include:
  • Use of state-certified water quality laboratories  
  • Description and schematic(s) of site or experiment design
  • Methods for litter and traction sand loading to simulate clogging of media filtration
Task 4. Submit Interim Report 2. This report shall summarize findings from Task 3, including discussion of variables affecting performance that could not be addressed by this project. Following NCHRP review of the report, Interim Report 2 will be discussed at an interim meeting, along with an outline for draft guidelines to be developed in Task 5. NCHRP approval of Interim Report 2 is required before proceeding with Task 5. 
Task 5. Develop guidelines for the chosen practices. The guidelines shall include recommendations and constraints for each of the following: appropriate bridge site selection, design specifications, constructability, and maintenance. These guidelines should be consistent with the findings of both Interim Reports and provide presentation materials that summarize the results of the research and could be used for multiple purposes and audiences.

To create a link to this page, use this URL: http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=4791