Introduction

The conversion of forested and agricultural land to urban land is one of the most prevalent forms of land alteration in the United States (Schoonover and Lockaby, 2006). Urbanization is accompanied by increases in the amount of impervious surfaces and the number of pollutant sources. Impervious surfaces and traditional storm sewer systems disrupt the natural drainage processes of the land by decreasing infiltration and eliminating vegetation that filters and slows surface runoff. Hydrology and water quality of downstream water bodies are impacted by the resulting increase in surface runoff quantity and the decreasing runoff quality leaving a site. In addition, the amount of sediment introduced to surface water is increased as a result of higher volumes and flow rates of water leaving urban areas and land disturbance due to construction. (Colosimo and Wilcock, 2007). In addition to increases in nitrogen and phosphorous levels, which can lead to increased algal growth and eutrophication (Busse et al., 2006), impervious surfaces combined with dry weather storm sewer discharges can contribute increased levels of fecal coliform and E-coli to surface waters (Tufford and Marshall, 2002; Petersen et al., 2005).
The concept of low impact development (LID) arose in the 1990s as the impacts of increasing urbanization and traditional stormwater management became more apparent. The overall goal of this relatively new approach to stormwater management is to minimize and distribute stormwater across a site, while promoting infiltration (Dietz, 2007). LID specifically promotes the use of multiple onsite best management practices (BMPs), such as bioretention, porous pavement, infiltration trenches and vegetated swales, to provide decentralized treatment of surface runoff.

The goals for this study were to assess the impact of bioretention and CU-Structural Soil BMPs on peak flow rates and runoff volumes leaving an urban site and to quantify total nitrogen, total phosphorus and bacteria (fecal coliform and E-coli) reductions due to each BMP treatment.