Abstract. The development of relationships for predicting the impact of highway stormwater runoff is described. The predictive relationships are regression-based equations reflecting variations in the magnitude of the constituents of interest. The objective is to identify a subset of constituents that can be used as surrogates for the remaining constituents as a means of decreasing the costs of collection and measurement of highway stormwater runoff quality data.The Minnesota highway stormwater quality database complied in the late 1970's and early 1980's is employed in identifying the set of surrogate parameters. The findings indicate that total suspended solids, total dissolved solids, total volatile solids, and total organic carbon are effective surrogate parameters for numerous metals, ionic species, and nutrients. The findings also indicated that the developed ionic species constituent relationships are portable, while the metal and nutrient constituent relationships were limited to urban sites with similar environmental conditions. The development of these relationships represents a step towards remediating and preventing the problem of nonpoint source highway pollution.

Increased concern over the contamination of surface waters by road salts and their adverse effects on the freshwater organisms led to the inclusion of “road salts” on the second Priority Substances List (PSL2) under the Canadian Environmental Protection Act The list identifies substances that must be assessed on a priority basis to characterize the nature and extent of the risk they pose to the environment or human health. This paper adds to the collection of several reports which constitute “supporting documentation” for the environmental risk assessment of the priority substance “road salts”. It reviews the physical-chemical properties of inorganic salts commonly used for road maintenance and their fate and transport in surface waters and sediments, together with the environmental concentrations of road salt constituents in the context of watershed geology and other environmental factors governing their concentrations. The paper also provides a spatial map of chloride concentrations as a basis for developing an understanding of a spatially based, ecological risk assessment for surface water systems and relates the spatial risk map to observed concentrations of chlorides. The data suggest that the surface waters most sensitive to road salts impacts are small ponds and streams draining large urbanized areas. Environment Canada is presently considering several alternatives for dealing with road salts.

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This chapter provides an overview of ongoing research towards improving the understanding of water quality characteristics of highway storm water runoff. A review of source contributors, some important water quality constituents, and the requirements of a data collection program is provided. The methodology involved and the comprehensive data base employed in the single-site analyses portion of this work is outlined. Results from an investigation into the presence of the first flush phenomenon, and the identification of surrogate water quality parameters is also included.