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Summary -- Highway Runoff Water Quality Study, 1977-1982


A highway stormwater runoff pollutant loading model has been developed based on results from composite sampling of approximately 600 storms at nine locations in the State of Washington over five years. The model expresses total suspended solids (TSS) loading in proportion to the product of highway segment length, average runoff coefficient, and vehicles traveling during storm periods. It was demonstrated that loadings of contaminants such as chemical oxygen demand, nutrients and trace metals could be estimated from TSS loadings using ratios derived from the data. The model described was developed and validated for assessing total loadings over a time span encompassing a number of storms (monthly or annually). To predict pollutant concentrations and loadings in runoff from a given storm, cumulative distributions were plotted and analyzed to determine the probability of exceeding specific concentration and loading values in a given case. Bioassay studies using highway runoff indicated toxicity volumes (in excess of 10,000 - 20,000 vehicles per day) or high metals concentrations in rainfall caused runoff concentrations to exceed lethal levels. Draining highway runoff through grass channels 60 meters in length greatly reduced TSS and metals concentrations and the consequent toxic effects. The major product of this research is a guide to assessing and mitigating the impacts of highway runoff to receiving waters.


  • Date Published: September, 1982
  • Publication Number: WA-RD 39.16
  • Last Modified: August 5, 2007
  • Authors: Brian W. Mar, Richard R. Horner, John F. Ferguson, Dimitris E. Spyridakis, Eugene B. Welch.
  • Originator: University of Washington. Environmental Engineering and Science Program.
  • # of Pages: 139 p., 5,771 KB (PDF)
  • Subject: Aquatic life, Bioassay, Concentration (Chemistry), Contaminants, Environmental impacts, Environmental risk assessment, Grasses, Hazard mitigation, Heavy metals, Highways, Mathematical models, Petroleum solids, Pollutants, Runoff, Sampling, Storms, Toxicity, Traffic volume, Water quality, Water quality management.
  • Keywords: Highways, runoff, pollutants, loadings, concentrations, model, toxicity, mitigation, assessment, Washington State.
  • Related Publications: Water Quality Impacts Associated with Leachates from Highway Woodwastes Embankments, (WA-RD 39.1).
    Effects of Velocity and Nutrient Alterations on Stream Primary Producers and Associated Organisms, (WA-RD 39.2).
    Highway Runoff Monitoring: The Initial Year, (WA-RD 39.3).
    Composite Sampling of Highway Runoff: Year 2, (WA-RD 39.4).
    Criteria and Requirements for Statewide Highway Runoff Monitoring Sites, (WA-RD 39.5).
    Characterization of Highway Runoff in Washington State, (WA-RD 39.6).
    Year 3 - Runoff Water Quality, August 1979 - August 1980, (WA-RD 39.7).
    Views of Risk and Highway Transportation of Hazardous Materials - A Case Study in Gasoline, (WA-RD 39.8).
    A Survey of Trace Organics in Highway Runoff in Seattle, Washington, (WA-RD 39.9).
    Transport Deposition and Control of Heavy Metals in Highway Runoff, (WA-RD 39.10).
    Effects of Seattle Area Highway Stormwater Runoff on Aquatic Biota, (WA-RD 39.11).
    Highway Runoff in Washington State: Model Validation and Statistical Analysis, (WA-RD 39.12).
    Assessment of Pollutant Loadings and Concentrations in Highway Stormwater, (WA-RD 39.12.1). 
    Year 4, Runoff Water Quality, August 1980-August 1981, (WA-RD 39.13).
    Guide for Water Quality Impact Assessment of Highway Operations and Maintenance, (WA-RD 39.14).
    Impacts of Channel Reconstruction in the Pilchuck River, (WA-RD 39.15).

This abstract was last modified April 29, 2008