Abstract

In a study for the Federal Highway Administration (FHWA) completed several years ago, my co-workers and I assembled and analyzed pollutant runoff data for highway sites (Driscoll, Shelley, and Strecker, 1990). The data were obtained in a number of independent studies at locations throughout the USA. The studies were conducted between 1978 and 1984, and the monitoring periods were generally one or two years in duration. In addition to characterizing the quantity and quality of highway stormwater, another project objective was to develop a procedure by which a highway engineer or planner could perform a screening analysis to determine whether a receiving water quality problem was likely to be created by stormwater discharges from a particular highway site. In the event a problem condition was projected, it was desired to identify the extent of runoff control that would be required to mitigate the indicated water quality problem.

We developed an analysis procedure and described it in a guidance document (Driscoll Shelley, and Strecker, 1990). The procedure was structured in the form of spreadsheet-based fill-in tables to convert raw input data into values for the parameters used in the receiving water impact computation. Tables and maps were provided to assist selection of values for raw inputs. Other tables were developed which listed separately-computed impact results for a range of input values, from which a user would "look up" the answer, interpolating as necessary. General guidance was provided on how independently-determined stormwater pollutant control effects could be incorporated into the analysis.

FHWA agreed with our suggestion that, given the intended audience and use, more effective use of the impact assessment procedure would result from the availability of a user-friendly computer program which would guide a user through the procedure. This program was organized in the form of a decision support system, the structure and operation of which is described in this chapter. The Highway Runoff Decision Support System (HWY DSS) that was developed expanded on the scope of the method manual to permit a user to examine the effect of selected stormwater control measures on the mitigation of a projected adverse water quality impact. Both the types of pollutant control measures appropriate for highway stormwater, and the performance estimates that are incorporated in the DSS, are based on a separate FHWA research study (Versar & Camp, Dresser, and McKee, 1988).

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