Evaluation of sources and control of pollutants in urban/suburban runoff

Studies on urban storm water runoff quality indicate the presence of many different pollutants such as metals, toxic organics, and nutrients in rain water runoff. These pollutants are derived from different sources, and many factors are involved in their origin and transport. To identify sources of heavy metals (cadmium, copper, lead, and zinc) in storm water runoff a comprehensive sampling and analysis procedure employing a synthetic rainwater was performed on automobiles, buildings, engine oils, tires, and road salt. These four target metals were detected in all types of samples. However, the range of concentrations varied among various sources, as well as within each sampling category. In car sampling brake emissions were found as a major source of copper and zinc. Brick and wood buildings were determined to be significant contributing sources of zinc and lead. Zinc was found in very high concentrations in the aqueous phase of used engine oil mixtures and in high concentrations from abraded automobile tires. Also, first flush rain water was captured from roof downspouts during actual rain events. Significant amounts of lead, zinc, and especially copper were detected in the runoff from some roofs. Overall, it is noted that these sources can be significant contributors of metals to storm water runoff, and therefore to natural water systems.; To treat the heavy metals as well as other pollutants such as nutrients in the storm water runoff, a treatment system has been designed. The system consists of sandy loam soil and a thin layer of mulch on the top. Some typical wetland plants/shrubs are planted in the soil. This system is known as a bioretention system. Results of investigations for the treatment of storm water runoff by the system indicate excellent metal retention and some nutrient uptake by the system.; In the actual field application, bioretention systems are constructed in a close proximity to imperious surfaces such as parking lots of a shopping mall, office building or an institutional area. The system captures sheet flow from these imperious surfaces. Pollutant removal of the captured runoff is performed through physical and biological treatment processes occurring in the plants and soil of the system. Water exits the bioretention system by infiltration or evapotranspiration. The infiltrated water will recharge the shallow aquifer of the local groundwater system. By optimizing the bioretention process, its use for storm water treatment can be expanded, providing added protection to the water resources of the nation.