Probabilistic characterization of pollutant discharges from highway stormwater runoff

This paper presents the preliminary results of a project aimed at developing models that can be used by planners and highway engineers for predicting pollutant runoff from highways. A brief review of different approaches to predicting pollutant runoff loads from highways is followed by a description of the data base being assembled as a part of this project. The probabilistic data analysis methodology that is being used to characterize highway stormwater runoff is then described in some detail. Preliminary analytical results are presented in two main areas-rainfall and runoff data and water quality data. For the sites examined so far, it is shown that taking the percent imperviousness of an unmonitored site as its runoff coefficient, with an upper bound of around 0.9 to account for initial abstraction, offers a reasonable first estimate. Best estimates for pollutant concentrations for each of six pollutants are presented and compared with corresponding values for urban runoff. Lacking site specific data, they represent reasonable first estimates of highway stormwater runoff quality.