The transportation community is faced with a need to reduce pollutant loadings from existing facilities to achieve watershed Total Maximum Daily Loads (TMDLs) or to meet other regulatory requirements. Existing infrastructure was designed for efficient drainage and flood control, and offers several possibilities for retrofits to enhance water quality. The literature on retrofitting of storm drainage systems to improve effluent water quality is divided into two broad areas.  The first assumes the availability of land or right-of-way sufficient to place new or off-line Best Management Practices (BMPs) for treatment; the second is usually referred to as “ultra-urban,” meaning that the right-of-way is limited and there is little or no permeable surface.  The latter condition is the focus of this work.  Research was needed to develop guidelines on evaluating and selecting modifications to existing drainage infrastructure in ultra-urban areas. 

This project developed guidelines for evaluating and selecting hydraulic modifications to existing drainage infrastructure in order to reduce pollutant loads and concentrations in ultra-urban areas. 

The final report has been published and is available for purchase or download.