Starting in the late 1980s, efforts to address polluted storm water runoff have increased significantly, and the requirements for treating the runoff have gotten more stringent. Not long ago, most highway runoff could be treated using a few simple treatment methods such as bioswales, wet ponds, or vegetated filter strips. More recently however, the treatment requirements have been shifting to include the removal of dissolved metals. Dissolved metals in storm water are becoming more of a concern to regulatory agencies, particularly in highly urbanized areas where land values and lack of available space limit the treatment options. There are a number of currently available best management practices (BMPs) that are effective in removing dissolved metals, but the effectiveness of these treatments relies on the availability of sufficient space to accommodate them. Departments of transportation (DOTs) need effective treatments to meet the requirements of environmental regulatory agencies in highly urbanized areas. In some areas of the country where native aquatic species are very sensitive to minute levels of heavy-metal pollutants, DOTs are being required to meet even more stringent removal levels. Furthermore, there are concerns about the current methods used to determine dissolved metal content. There is evidence that the measurements obtained can vary widely from the effects of a number of factors, including the measurement method and testing protocols, the testing equipment used, methods of cleaning the test equipment, and the scheduling of sampling times during storm events. A closer scrutiny of current testing protocols would provide the scientific basis for a more informed discussion with regulatory agencies. There is a need for BMPs that are effective at removing dissolved metals that can be accommodated in highly urban areas, and for scientifically defensible test methods that can provide a reliable and repeatable measure of their effectiveness.
The objectives of this research are to (1) develop accurate and scientifically defensible testing protocols that can provide a reliable and repeatable measure of dissolved metals content in storm water and (2) develop conceptual design specifications for at least two cost-effective storm water treatment practices that could be used to effectively remove dissolved metals in highly urbanized areas. As a target performance measure, the treatments should be able to meet or surpass the removal levels required by typical current environmental regulations. The conceptual designs should be developed to address different degrees of complexity in the urban environment; for example, one to address areas near steep embankments or areas with 50-75% impervious surface, and another to address the most difficult cases with 75-100% impervious surface. Each can consist of an individual treatment or treatment train as required to meet the dissolved metals reduction objectives.