Data and analytical methods are available to predict the runoff constituents and concentrations for highway and waterway scenarios; however, there are no guidelines on how to use these data and methods to make comprehensive assessments of the impacts of bridge runoff on receiving waters. As a result, to comply with permits and regulations, some projects have been required to include installation of costly enclosed drainage systems on bridges.
There is a need for a process to assist practitioners in making decisions on the need for, and the extent of, control of bridge deck runoff in both new and retrofit applications. It is envisioned that this process will encompass consideration of runoff constituents (e.g., metals, sediments, and nutrients), types of bridge runoff-management designs, impacts on receiving waters and aquatic biota, and other potential runoff impacts. The process should also include risk assessment for special potential problems, benefit/cost-effectiveness assessments, and other elements of a strong management process that streamlines and normalizes consideration of runoff concerns within the project development process.
This research was intended to integrate known technology applicable to the quality of runoff water, the background quality of the receiving water, and the water quality criteria applicable to the receiving water. The research was intended to determine the best application procedures and quality criteria for data associated with runoff and receiving water interaction. It also addressed reasonable treatments and proper disposal systems if and when warranted.
The objective of this research was to develop a rational process to identify, assess, and manage bridge deck runoff that may adversely impact the beneficial uses of receiving waters. Where warranted, the process addressed a range of mitigation alternatives that may include on-site control of bridge deck runoff, off-site watershed-based mitigation, or pollution trade-off opportunities. Where on-site control is proposed, appropriate new bridge design parameters for runoff and opportunities for existing bridge retrofits are considered along with non-structural best management practices.
Phase I consisted of the following tasks: (1) Critically review U.S. and international published and unpublished literature and completed and ongoing research on impact methodologies and data related to bridge runoff quality and quantity. (2) Survey representative management, maintenance, and operational practices and costs as they relate to bridge runoff and receiving waters. Prior to initiating the survey, obtain panel review and approval. (3) Based on the results of Tasks 1 and 2, design the preliminary process. Identify additional data and information needs and submit an updated work plan for field work to be carried out in Task 5. (4) Prepare an interim report covering the activities in Tasks 1 through 3. Present the findings to the panel and obtain approval to proceed.
Phase II consisted of the following tasks: (5) Apply the process to selected sites where mitigation is and is not required (include at least one past case study, a new construction site, and a retrofit situation). As needed, collect additional data to support evaluation. Obtain feedback from users, resource agencies, and other stakeholders. (6) Document the lessons learned and the input received during Task 5. (7) Refine the process and recommendations for implementation within state DOTs. Present the process and an accompanying commentary in the form of a practitioner handbook. (8) Submit a final report documenting the results and findings of this research, recommendations for additional research, unresolved issues, and recommendations for implementation of the resulting process. Develop, as a stand-alone appendix to the final report, the practitioner handbook that also includes graphic materials to support communication and implementation.
Research is completed. The final report and practitioner's handbook are published as NCHRP Report 474 Volume 1
and NCHRP Report 474 Volume 2
The results of Phase I were summarized in NCHRP Research Results Digest 235,
"Assessment of Impacts of Bridge Deck Runoff Contaminants on Receiving Waters." The final report and handbook are available by clicking the link above.