The U.S. Federal Highway Administrations receiving water impact methodology

This paper presents the final results of the application of a probabilistic approach for evaluating the water quality impact of highway stormwater runoff to receiving waters. A brief review of the development of the probabilistic characterization of runoff water quality data is presented along with a description of the probabilistic stream impact method. In this paper we present the interactive Decision Support program that takes the procedure user through the Federal Highway Administration's highway runoff analysis procedure. The procedure requires the input of fixed site data, rainfall and streamflow statistics, highway runoff water quality, and target concentrations. The methodology user is provided guidance in entering the required data. Output of the procedure is a return frequency of the exceedances of the target concentration. This methodology is intended for planning level analyses.