ABSTRACT Studies on urban stormwater runoff quality indicate the presence of many different pollutants such as metals, toxic organics, and nutrients. These pollutants are derived from different sources, and many factors are involved in their origin and transport. Heavy metals such as cadmium, copper, lead, and zinc are among these pollutants. Because of environmental concerns over high metal levels in stormwater runoff, the regulatory agencies in many developed countries have required cities and large jurisdictions to monitor the water quality of stormwater discharges. In this study, to treat stormwater pollutants before discharge to receiving waters a management and treatment facility has been investigated. The facility consists mainly of sandy loam soil and a thin layer of mulch on the top. Some typical plants/shrubs are established in the soil. This facility is known as a bioretention system. Bioretention systems can be constructed in a close proximity to imperious surfaces such as the parking lots of shopping malls, office buildings, or institutional areas. In this research study, the performance of bioretention for the treatment of stormwater runoff was investigated. Both laboratory and field studies were conducted. In laboratory studies, a small bioretention box was constructed with dimensions of 3.5 ft L x 2.5 ft W x 2.5 ft D and a large bioretention system had dimensions of 10 ft L x 5 ft W x 3.5 ft D. The field study was performed on a facility located at Beltway Plaza Shopping Mall, Greenbelt, Maryland. In all studies, synthetic stormwater runoff was prepared in 50-gallon PVC drums and applied to the bioretention systems at the rate of 1.6 in/hr for six-hour periods. Results of investigations for treatment of stormwater runoff by bioretention indicate excellent metal retention and some nutrient uptake by the system. Very good agreement was found among results from the two laboratory scales and the field study. The removal of copper, lead, and zinc by the system was over 95%. The removal efficiency of nutrients via bioretention for phosphorus was 50 to 70%, ammonia and TKN removals were 79-92% and 52-68%, respectively. Little removal of nitrate was found (0-20%) and in several instances, nitrate in excess of input was noted. This apparently resulted from conversion of other nitrogen compounds to nitrate.

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