Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff

State departments of transportation (state DOTs) are increasingly subject to water quality improvement requirements derived from §303(d) of the federal Clean Water Act (CWA) related to Total Maximum Daily Loads (TMDL). A 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; the load is allocated among the various sources of that pollutant in order to reduce the amount and nature of pollutants discharged to water quality-impaired receiving water bodies pursuant to §303(d) of the CWA. Although substantial effort has been put into characterizing highway runoff and identifying the sources of pollutants, additional effort is needed to support the development of appropriate TMDL requirements and implementation plans that accurately reflect a state DOT’s water quality impacts and its water quality mitigation capabilities. TMDL requirements are often applied broadly to a number of land uses. In the absence of detailed comparative studies, the impacts on water quality from roadway stormwater runoff has been approximately equated with water quality impacts from stormwater runoff from municipal, commercial, and industrial land uses. The portion of the total pollutant load attributable to the roadway is frequently calculated in a general manner—based on assumptions about relative contributions from different land uses—and it is often the case that no distinction is made between pollutants that originate from roadway stormwater runoff and sources outside the right-of-way. As a result, state DOTs may incur unnecessary compliance costs to construct, operate and maintain, inspect and validate stormwater treatment facilities, and implement other Best Management Practices (BMPs). This project developed guidance for state DOTs to evaluate pollutant loads from stormwater runoff from roadways and other land uses to inform development of appropriate TMDL requirements, and to provide guidance for selecting potential stormwater management and TMDL compliance strategies within a watershed.


  • English


  • Status: Completed
  • Funding: $299912
  • Contract Numbers:

    Project 25-53

  • Sponsor Organizations:

    Federal Highway Administration

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

    American Association of State Highway & Transportation Officials (AASHTO)

    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:

    Hartell, Ann

  • Performing Organizations:

    Michael Baker International

    310 New Pointe Drive
    Ridgeland, MS  United States  39157
  • Principal Investigators:

    Lantin, Anna

  • Start Date: 20150608
  • Expected Completion Date: 20181209
  • Actual Completion Date: 20181209
  • Source Data: RiP Project 40230

Subject/Index Terms

Filing Info

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