The Efficacy of Treating Highway Runoff to Meet Watershed TMDL Goals

A Total Maximum Daily Load (TMDL) is a calculation of the maximum amount of a pollutant (the "load") that a water body can receive while still meeting water quality standards and an allocation of that load among the various sources of that pollutant. TMDLs are developed for water quality-impaired bodies pursuant to Section 303(d) of the federal Clean Water Act. State Departments of Transportation (DOTs) are being named as Designated Management Agencies in TMDL management plans. Such a designation often requires state DOTs to commit a substantial amount of staff time, conduct compliance reporting, and construct capital facilities for stormwater treatment at a high whole-life cost. The requirements outlined in TMDL reports are applied broadly to a number of land uses, are often based on assumption--rather than actual constituent load data on DOT stormwater discharges--and consider neither the relative nor the absolute contribution to the water quality problem. Some TMDL implementation actions have been adopted as regulations, as is the case with requirements in the National Pollutant Discharge Elimination System's municipal and construction stormwater permits, increasing the risk of third-party legal challenges for DOTs through these permits. The impacts related to transportation have been considered equal to those impacts from municipal, commercial, and industrial uses in some cases. While highways are a significant source of some pollutants, for others, highways may be only a minor contributor, or the pollutant of concern may have its origins outside the highway right-of-way, unrelated to the operation or maintenance of the roadway. For example, while highway runoff may have high bacteria concentrations, water body impairments are usually associated with inadequate on-site sewage treatment systems and agricultural livestock operations. Consequently, under certain scenarios, it is likely more economical for entities other than the state DOT to control the pollutant at its source. The portion of the total pollutant load attributable to the DOT may be small compared to the total load reduction needed, resulting in only nominal improvement in the receiving water at a relatively higher cost than addressing the primary pollutant source. Treating all stakeholders equally for all pollutants does not result in the highest benefit for the environment, but does misallocate resources. As outlined in EPA's Clean Water Act 303(d) Vision and Goal Statement (2013), effective integration of responsible parties and sources increases the likelihood of successful TMDL implementation, especially for TMDLs that include nonpoint source pollution. A U.S. Government Accounting Office publication states that "experts also reported that the TMDLs that do not diagnose and aim to treat the true causes of water body impairment are unlikely to lead to attainment of designated uses." Previous research has focused on how DOTs can respond to and meet TMDLs, and substantial effort has been put into characterizing highway runoff and identifying the sources of pollutants. This project will integrate existing information and develop strategies for determining appropriate and cost-effective TMDL requirements for DOTs. Also, this research would directly support the SCOE strategic plan mission to "provide policy and technical support to the AASHTO member departments to integrate environmental stewardship goals into all transportation decisions and activities;" the goal to "develop policy alternatives for integrating environmental considerations into all transportation decisions;" and the Natural Resources Subcommittee goals to "actively participate at the federal level in implementation of the Clean Water Act" and "target…the committee's efforts to…operating activities and technologies…such as Storm Water Runoff and nonpoint source pollution." The first phase of this project will focus on conducting a general evaluation of the importance of the various highway runoff pollutant contributions in a TMDL context. This analysis will be based on the concentrations of pollutants in highway runoff, the sources of the pollutants in the runoff, and the relative and absolute contribution of the highway runoff pollutant to receiving waters (taking geographic and traffic variations into account). The objective is to provide watershed managers and regulatory agencies with guidance to determine if it is appropriate to name the DOT as a stakeholder in a TMDL, and provide factual data to assist in screening DOTs as potential TMDL stakeholders. Such guidance could ultimately result in a more clearly defined and appropriate set of requirements for highways. In the second phase, the project will reference other National Cooperative Highway Research Program (NCHRP) projects to develop a protocol for evaluating the cost effectiveness of implementing highway runoff treatment requirements to meet TMDL pollutant reduction goals. There are many excellent references available for computing a unit cost by best management practice (BMP) and by constituent. More efficient control strategies could be realized by both DOTs and regulatory agencies if unit costs by BMP and by constituent were considered when determining requirements within the highway environment. This phase two research has two intended outcomes. The first is that TMDL load allocations and implementation plans be based on appropriate information and accurately reflect DOT impacts and water quality mitigation capabilities. The second is to ensure that the responsibility placed on DOTs is commensurate with DOT contributions to the receiving water body impairments and actual watershed loads. Also, innovative compliance strategies and alternatives to TMDLs, which have been utilized by some state DOTs will be compiled and summarized. Results from this investigation can be used by both DOTs and regulatory agencies in the development of TMDL management plans and/or alternative compliance strategies. Better guidance and data-based decisions will ensure that responsibilities and resources are allocated to maximally benefit the receiving waters and that the costs of compliance for the designated management agencies do not outweigh the benefit to the watershed. It is expected that the research will include the following tasks: Task 1 - Literature Review, Compilation of Data, and Survey of State Practices and Experience: Literature review and data compilation will focus on the following areas: highway runoff characterization data selected from a broad range of geographic conditions and traffic levels; source studies for the most common TMDL pollutants, both in highway runoff and watersheds as a whole; effectiveness of stormwater BMPs at removal of the most common TMDL pollutants; costs associated with the stormwater BMPs constructed in the highway environment; a specific evaluation NCHRP Synthesis 20-05/Topic 43-06 that has information useful for this work, and NCHRP Projects 25-37 and 25-40; innovative compliance strategies (e.g., Caltrans, DelDOT, MnDOT) including alternative implementation approaches to numeric waste load allocations; and alternative approaches to TMDLs (e.g., NCDOT). Task 2 - Evaluating Highway Runoff Contribution to TMDL Pollutant Loads: Using the information collected in Task 1, the project will evaluate when and under what circumstances TMDL pollutants are in highway runoff, and, if so, is runoff a substantial or primary source of the regionally significant TMDL pollutants. This evaluation would include the geographic variables such as land use, local soils and geology; traffic volumes; relative and absolute size of receiving waters compared to highway drainage area; and ultimate sources of the pollutants. A decision tree would be developed to help the DOT practitioner and regulatory agency assess if the DOT should participate as a stakeholder in a TMDL. The information from Tasks 1 and 2 can be used to help inform the DOTs if alter


  • English


  • Status: Proposed
  • Contract Numbers:


  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway & Transportation Officials

    444 North Capitol Street, NW, Suite 225
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Sundstrom, Lori

  • Start Date: 20150805
  • Expected Completion Date: 0
  • Actual Completion Date: 0
  • Source Data: RiP Project 40230

Subject/Index Terms

Filing Info

  • Accession Number: 01572339
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: 25-53
  • Files: TRB, RiP
  • Created Date: Aug 6 2015 1:00AM