Retrofitting Existing Drainage Systems for Water Quality

The U.S. Environmental Protection Agency's (EPA) National Pollutant Discharge Elimination System (NPDES) Phase I rules require stormwater discharge permits for major urban centers. The EPA established Phase II rules that expand the impact of the original Phase I rules for meeting the Clean Water Act, Section 401 provisions. In order to comply with Phase II rules, all Texas Department of Transportation (TxDOT) districts with urbanized areas of over 50,000 in population will be required to obtain stormwater discharge permits. In addition, new regulations for reducing stormwater pollutant loads may require retrofitting existing drainage structures. Essentially, all districts will likely be required to retrofit and maintain some of the existing drainage infrastructure in order to comply with these provisions. This project's purpose was to: * investigate the water quality performance of best management practices (BMPs) suitable for retrofitting, * evaluate proprietary technologies being marketed for stormwater quality improvement, * evaluate and make recommen-dations for selection of stormwater quality BMPs, and * propose a system for prioritizing the allocation of resources for the installation of retrofit water quality structures.